poisson.h File Reference

#include "variables.h"
#include "Metric.h"

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Functions
PetscErrorCode	PoissonSolver_MG (UserMG *usermg)
	Solves the pressure-Poisson equation using a geometric multigrid method.
PetscErrorCode	PoissonLHSNew (UserCtx *user)
	Assembles the Left-Hand-Side (LHS) matrix (Laplacian operator) for the Poisson equation on a single grid level.
PetscErrorCode	PoissonRHS (UserCtx *user, Vec B)
	Computes the Right-Hand-Side (RHS) of the Poisson equation, which is the divergence of the intermediate velocity field.
PetscErrorCode	UpdatePressure (UserCtx *user)
	Updates the pressure field P with the pressure correction Phi computed by the Poisson solver.
PetscErrorCode	Projection (UserCtx *user)
	Corrects the contravariant velocity field Ucont to be divergence-free using the gradient of the pressure correction field Phi.
PetscErrorCode	PoissonNullSpaceFunction (MatNullSpace nullsp, Vec X, void *ctx)
	The callback function for PETSc's MatNullSpace object.
PetscErrorCode	MyRestriction (Mat A, Vec X, Vec F)
	The callback function for the multigrid restriction operator (MatShell).
PetscErrorCode	MyInterpolation (Mat A, Vec X, Vec F)
	The callback function for the multigrid interpolation operator (MatShell).
PetscErrorCode	VolumeFlux (UserCtx *user, PetscReal *ibm_Flux, PetscReal *ibm_Area, PetscInt flg)
	Calculates the net flux across the immersed boundary surface.
PetscErrorCode	VolumeFlux_rev (UserCtx *user, PetscReal *ibm_Flux, PetscReal *ibm_Area, PetscInt flg)
	A specialized version of VolumeFlux, likely for reversed normals.

Function Documentation

PoissonSolver_MG()

PetscErrorCode PoissonSolver_MG ( UserMG *  usermg )

extern

Solves the pressure-Poisson equation using a geometric multigrid method.

This function orchestrates the entire multigrid V-cycle for the pressure correction equation. It assembles the Laplacian matrix on all grid levels, sets up the KSP solvers, smoothers, restriction/interpolation operators, and executes the solve.

Parameters

usermg

The UserMG context containing the entire multigrid hierarchy.

Returns

PetscErrorCode 0 on success.

Definition at line 3959 of file poisson.c.

{
    // --- CONTEXT ACQUISITION BLOCK ---
    // Get the master simulation context from the first block's UserCtx on the finest level.
    // This provides access to all former global variables.
    SimCtx *simCtx = usermg->mgctx[0].user[0].simCtx;
 
    // Create local variables to mirror the legacy globals for minimal code changes.
    const PetscInt block_number = simCtx->block_number;
    const PetscInt immersed = simCtx->immersed;
    const PetscInt MHV = simCtx->MHV;
    const PetscInt LV = simCtx->LV;
    PetscMPIInt rank = simCtx->rank;
    // --- END CONTEXT ACQUISITION BLOCK ---
 
    PetscErrorCode ierr;
    PetscInt l, bi;
    MGCtx *mgctx = usermg->mgctx;
    KSP mgksp, subksp;
    PC mgpc, subpc;
    UserCtx *user;
 
    PetscFunctionBeginUser; // Moved to after variable declarations
    PROFILE_FUNCTION_BEGIN;
    LOG_ALLOW(GLOBAL, LOG_INFO, "Starting Multigrid Poisson Solve...\n");
 
    for (bi = 0; bi < block_number; bi++) {
        
        // ====================================================================
        //   SECTION: Immersed Boundary Specific Setup (Conditional)
        // ====================================================================
        if (immersed) {
            LOG_ALLOW(LOCAL, LOG_DEBUG, "Block %d: Performing IBM pre-solve setup (Nvert restriction, etc.).\n", bi);
            for (l = usermg->mglevels - 1; l > 0; l--) {
                mgctx[l].user[bi].multinullspace = PETSC_FALSE;
                MyNvertRestriction(&mgctx[l].user[bi], &mgctx[l-1].user[bi]);
            }
            // Coarsest level check for disconnected domains due to IBM
            l = 0;
            user = mgctx[l].user;
            ierr = PetscMalloc1(user[bi].info.mx * user[bi].info.my * 2, &user[bi].KSKE); CHKERRQ(ierr);
            FullyBlocked(&user[bi]);
        }
        
 
        l = usermg->mglevels - 1;
        user = mgctx[l].user;
        
        // --- 1. Compute RHS of the Poisson Equation ---
        LOG_ALLOW(LOCAL, LOG_DEBUG, "Block %d: Computing Poisson RHS...\n", bi);
        ierr = VecDuplicate(user[bi].P, &user[bi].B); CHKERRQ(ierr);
        
        PetscReal ibm_Flux, ibm_Area;
        PetscInt flg = immersed - 1;
 
        // Calculate volume flux source terms (often from IBM)
        VolumeFlux(&user[bi], &ibm_Flux, &ibm_Area, flg);
        if (MHV || LV) {
            flg = ((MHV > 1 || LV) && bi == 0) ? 1 : 0;
            VolumeFlux_rev(&user[bi], &ibm_Flux, &ibm_Area, flg);
        }
        // Calculate the main divergence term
        PoissonRHS(&user[bi], user[bi].B);
        
        // --- 2. Assemble LHS Matrix (Laplacian) on all MG levels ---
        LOG_ALLOW(LOCAL, LOG_DEBUG, "Block %d: Assembling Poisson LHS on all levels...\n", bi);
        for (l = usermg->mglevels - 1; l >= 0; l--) {
            user = mgctx[l].user;
        LOG_ALLOW(GLOBAL,LOG_DEBUG," Calculating LHS for Level %d.\n",l);
            PoissonLHSNew(&user[bi]);
        }
 
        // --- 3. Setup PETSc KSP and PCMG (Multigrid Preconditioner) ---
        LOG_ALLOW(LOCAL, LOG_DEBUG, "Block %d: Configuring KSP and PCMG...\n", bi);
 
    ierr = KSPCreate(PETSC_COMM_WORLD, &mgksp); CHKERRQ(ierr);
        ierr = KSPAppendOptionsPrefix(mgksp, "ps_"); CHKERRQ(ierr);
 
    // =======================================================================
        DualMonitorCtx *monctx;
        char           filen[128];
        PetscBool      has_monitor_option;
 
        // 1. Allocate the context and set it up.
        ierr = PetscNew(&monctx); CHKERRQ(ierr);
 
    monctx->step = simCtx->step;
    monctx->block_id = bi;
    monctx->file_handle = NULL;
 
    // Only rank 0 handles the file.
        if (!rank) {
      sprintf(filen, "%s/Poisson_Solver_Convergence_History_Block_%d.log", simCtx->log_dir,bi);
      // On the very first step of the entire simulation, TRUNCATE the file.
      if (simCtx->step == simCtx->StartStep) {
        monctx->file_handle = fopen(filen, "w");
      } else { // For all subsequent steps, APPEND to the file.
        monctx->file_handle = fopen(filen, "a");
      }
 
            if (monctx->file_handle) {
                PetscFPrintf(PETSC_COMM_SELF, monctx->file_handle, "--- Convergence for Timestep %d, Block %d ---\n", (int)simCtx->step, bi);
            } else {
                SETERRQ1(PETSC_COMM_SELF, PETSC_ERR_FILE_OPEN, "Could not open KSP monitor log file: %s", filen);
            }
        }
 
        ierr = PetscOptionsHasName(NULL, NULL, "-ps_ksp_pic_monitor_true_residual", &has_monitor_option); CHKERRQ(ierr);
        monctx->log_to_console = has_monitor_option;
 
        ierr = KSPMonitorSet(mgksp, DualKSPMonitor, monctx, DualMonitorDestroy); CHKERRQ(ierr);
        // =======================================================================
    
        ierr = KSPGetPC(mgksp, &mgpc); CHKERRQ(ierr);
        ierr = PCSetType(mgpc, PCMG); CHKERRQ(ierr);
 
    ierr = PCMGSetLevels(mgpc, usermg->mglevels, PETSC_NULL); CHKERRQ(ierr);
        ierr = PCMGSetCycleType(mgpc, PC_MG_CYCLE_V); CHKERRQ(ierr);
        ierr = PCMGSetType(mgpc, PC_MG_MULTIPLICATIVE); CHKERRQ(ierr);
 
        // --- 4. Define Restriction and Interpolation Operators for MG ---
        for (l = usermg->mglevels - 1; l > 0; l--) {
 
         // Get stable pointers directly from the main mgctx array.
         // These pointers point to memory that will persist.
      UserCtx *fine_user_ctx   = &mgctx[l].user[bi];
      UserCtx *coarse_user_ctx = &mgctx[l-1].user[bi];
 
      // --- Configure the context pointers ---
      // The coarse UserCtx needs to know about the fine grid for restriction.
      coarse_user_ctx->da_f     = &(fine_user_ctx->da);
      coarse_user_ctx->user_f   = fine_user_ctx;
 
      // The fine UserCtx needs to know about the coarse grid for interpolation.
      fine_user_ctx->da_c       = &(coarse_user_ctx->da);
      fine_user_ctx->user_c     = coarse_user_ctx;
      fine_user_ctx->lNvert_c   = &(coarse_user_ctx->lNvert);
 
      // --- Get matrix dimensions ---
      PetscInt m_c = (coarse_user_ctx->info.xm * coarse_user_ctx->info.ym * coarse_user_ctx->info.zm);
      PetscInt m_f = (fine_user_ctx->info.xm * fine_user_ctx->info.ym * fine_user_ctx->info.zm);
      PetscInt M_c = (coarse_user_ctx->info.mx * coarse_user_ctx->info.my * coarse_user_ctx->info.mz);
      PetscInt M_f = (fine_user_ctx->info.mx * fine_user_ctx->info.my * fine_user_ctx->info.mz);
 
      LOG_ALLOW(GLOBAL,LOG_DEBUG,"level = %d; m_c = %d; m_f = %d; M_c = %d; M_f = %d.\n",l,m_c,m_f,M_c,M_f);
      // --- Create the MatShell objects ---
      // Pass the STABLE pointer coarse_user_ctx as the context for restriction.
      ierr = MatCreateShell(PETSC_COMM_WORLD, m_c, m_f, M_c, M_f, (void*)coarse_user_ctx, &fine_user_ctx->MR); CHKERRQ(ierr);
    
      // Pass the STABLE pointer fine_user_ctx as the context for interpolation.
      ierr = MatCreateShell(PETSC_COMM_WORLD, m_f, m_c, M_f, M_c, (void*)fine_user_ctx, &fine_user_ctx->MP); CHKERRQ(ierr);
    
      // --- Set the operations for the MatShells ---
      ierr = MatShellSetOperation(fine_user_ctx->MR, MATOP_MULT, (void(*)(void))RestrictResidual_SolidAware); CHKERRQ(ierr);
      ierr = MatShellSetOperation(fine_user_ctx->MP, MATOP_MULT, (void(*)(void))MyInterpolation); CHKERRQ(ierr);
    
      // --- Register the operators with PCMG ---
      ierr = PCMGSetRestriction(mgpc, l, fine_user_ctx->MR); CHKERRQ(ierr);
      ierr = PCMGSetInterpolation(mgpc, l, fine_user_ctx->MP); CHKERRQ(ierr);
      
        }
        
        // --- 5. Configure Solvers on Each MG Level ---
        for (l = usermg->mglevels - 1; l >= 0; l--) {
            user = mgctx[l].user;
            if (l > 0) { // Smoother for fine levels
                ierr = PCMGGetSmoother(mgpc, l, &subksp); CHKERRQ(ierr);
            } else { // Direct or iterative solver for the coarsest level
                ierr = PCMGGetCoarseSolve(mgpc, &subksp); CHKERRQ(ierr);
                ierr = KSPSetTolerances(subksp, 1.e-8, PETSC_DEFAULT, PETSC_DEFAULT, 40); CHKERRQ(ierr);
            } 
            
            ierr = KSPSetOperators(subksp, user[bi].A, user[bi].A); CHKERRQ(ierr);
        ierr = KSPSetFromOptions(subksp); CHKERRQ(ierr); 
            ierr = KSPGetPC(subksp, &subpc); CHKERRQ(ierr);
        ierr = PCSetType(subpc, PCBJACOBI); CHKERRQ(ierr);
        
        KSP *subsubksp;
        PC subsubpc;
        PetscInt nlocal;
 
        // This logic is required for both the smoother and the coarse solve
        // since both use PCBJACOBI.
        ierr = KSPSetUp(subksp); CHKERRQ(ierr); // Set up KSP to allow access to sub-KSPs
        ierr = PCBJacobiGetSubKSP(subpc, &nlocal, NULL, &subsubksp); CHKERRQ(ierr);
 
        for (PetscInt abi = 0; abi < nlocal; abi++) {
          ierr = KSPGetPC(subsubksp[abi], &subsubpc); CHKERRQ(ierr);
          // Add the critical shift amount
          ierr = PCFactorSetShiftAmount(subsubpc, 1.e-10); CHKERRQ(ierr);
        }
        
        ierr = MatNullSpaceCreate(PETSC_COMM_WORLD, PETSC_TRUE, 0, PETSC_NULL, &user[bi].nullsp); CHKERRQ(ierr);
            ierr = MatNullSpaceSetFunction(user[bi].nullsp, PoissonNullSpaceFunction, &user[bi]); CHKERRQ(ierr);
            ierr = MatSetNullSpace(user[bi].A, user[bi].nullsp); CHKERRQ(ierr);
            
            ierr = PCMGSetResidual(mgpc, l, PCMGResidualDefault, user[bi].A); CHKERRQ(ierr);
            ierr = KSPSetUp(subksp); CHKERRQ(ierr);
 
            if (l < usermg->mglevels - 1) {
                ierr = MatCreateVecs(user[bi].A, &user[bi].R, PETSC_NULL); CHKERRQ(ierr);
                ierr = PCMGSetRhs(mgpc, l, user[bi].R); CHKERRQ(ierr);
            }
        }
 
        // --- 6. Set Final KSP Operators and Solve ---
        l = usermg->mglevels - 1;
        user = mgctx[l].user;
        
        LOG_ALLOW(LOCAL, LOG_DEBUG, "Block %d: Setting KSP operators and solving...\n", bi);
        ierr = KSPSetOperators(mgksp, user[bi].A, user[bi].A); CHKERRQ(ierr);
        ierr = MatSetNullSpace(user[bi].A, user[bi].nullsp); CHKERRQ(ierr);
        ierr = KSPSetFromOptions(mgksp); CHKERRQ(ierr);
        ierr = KSPSetUp(mgksp); CHKERRQ(ierr);
        ierr = KSPSolve(mgksp, user[bi].B, user[bi].Phi); CHKERRQ(ierr);
 
        // --- 7. Cleanup for this block ---
        for (l = usermg->mglevels - 1; l >= 0; l--) {
            user = mgctx[l].user;
            MatNullSpaceDestroy(&user[bi].nullsp);
            MatDestroy(&user[bi].A);
            user[bi].assignedA = PETSC_FALSE;
            if (l > 0) {
                MatDestroy(&user[bi].MR);
                MatDestroy(&user[bi].MP);
            } else if (l==0 && immersed) {
                PetscFree(user[bi].KSKE);
            }
            if (l < usermg->mglevels - 1) {
                VecDestroy(&user[bi].R);
            }
        }
        
        KSPDestroy(&mgksp);
        VecDestroy(&mgctx[usermg->mglevels-1].user[bi].B);
        
    } // End of loop over blocks
 
    LOG_ALLOW(GLOBAL, LOG_INFO, "Multigrid Poisson Solve complete.\n");
    PROFILE_FUNCTION_END;
    PetscFunctionReturn(0);
}

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PoissonLHSNew()

PetscErrorCode PoissonLHSNew ( UserCtx *  user )

extern

Assembles the Left-Hand-Side (LHS) matrix (Laplacian operator) for the Poisson equation on a single grid level.

Parameters

user	The UserCtx for the grid level on which to assemble the matrix.

Returns

PetscErrorCode 0 on success.

Assembles the Left-Hand-Side (LHS) matrix (Laplacian operator) for the Poisson equation on a single grid level.

This function constructs the sparse matrix A (the LHS) for the linear system Ax = B, which is the Pressure Poisson Equation (PPE). The matrix A represents a discrete version of the negative Laplacian operator (-∇²), tailored for a general curvilinear, staggered grid.

The assembly process is highly complex and follows these main steps:

1. Matrix Initialization: On the first call, it allocates a sparse PETSc matrix A pre-allocating space for a 19-point stencil per row. On subsequent calls, it simply zeroes out the existing matrix.
2. Metric Tensor Calculation: It first computes the 9 components of the metric tensor (g11, g12, ..., g33) at the cell faces. These g_ij coefficients are essential for defining the Laplacian operator in generalized curvilinear coordinates and account for grid stretching and non-orthogonality.
3. Stencil Assembly Loop: The function iterates through every grid point (i,j,k). For each point, it determines the matrix row entries based on its status:
   • Boundary/Solid Point: If the point is on a domain boundary or inside an immersed solid (nvert > 0.1), it sets an identity row (A(row,row) = 1), effectively removing it from the linear solve.
   • Fluid Point: For a fluid point, it computes the 19 coefficients of the finite volume stencil. This involves summing contributions from each of the six faces of the control volume around the point.
4. Boundary-Aware Stencils: The stencil calculation is critically dependent on the state of neighboring cells. The code contains intricate logic to check if neighbors are fluid or solid. If a standard centered-difference stencil would cross into a solid, the scheme is automatically adapted to a one-sided difference to maintain accuracy at the fluid-solid interface.
5. Matrix Finalization: After all rows corresponding to the local processor's grid points have been set, MatAssemblyBegin/End is called to finalize the global matrix, making it ready for use by a linear solver.

Parameters

[in,out]

user

Pointer to the UserCtx struct, containing all simulation context, grid data, and the matrix A.

Returns

PetscErrorCode 0 on success, or a non-zero error code on failure.

Definition at line 2207 of file poisson.c.

{
  PetscFunctionBeginUser;
  PROFILE_FUNCTION_BEGIN;
  LOG_ALLOW(GLOBAL, LOG_DEBUG, "Entering PoissonLHSNew to assemble Laplacian matrix.\n");
  PetscErrorCode ierr;
  //================================================================================
  // Section 1: Initialization and Data Acquisition
  //================================================================================
 
  
  // --- Get simulation and grid context ---
  SimCtx *simCtx = user->simCtx;
  DM da = user->da, fda = user->fda;
  DMDALocalInfo info = user->info;
  PetscInt IM = user->IM, JM = user->JM, KM = user->KM;
  PetscInt i,j,k;
 
  // --- Grid dimensions ---
  PetscInt mx = info.mx, my = info.my, mz = info.mz;
  PetscInt xs = info.xs, xe = info.xs + info.xm;
  PetscInt ys = info.ys, ye = info.ys + info.ym;
  PetscInt zs = info.zs, ze = info.zs + info.zm;
  PetscInt gxs = info.gxs, gxe = gxs + info.gxm;
  PetscInt gys = info.gys, gye = gys + info.gym;
  PetscInt gzs = info.gzs, gze = gzs + info.gzm;
 
  // --- Define constants for clarity ---
  const PetscReal IBM_FLUID_THRESHOLD = 0.1;
 
  // --- Allocate the LHS matrix A on the first call ---
  if (!user->assignedA) {
    LOG_ALLOW(GLOBAL, LOG_INFO, "First call: Creating LHS matrix 'A' with 19-point stencil preallocation.\n");
    PetscInt N = mx * my * mz; // Total size
    PetscInt M;                // Local size
    VecGetLocalSize(user->Phi, &M);
    // Create a sparse AIJ matrix, preallocating for 19 non-zeros per row (d=diagonal, o=off-diagonal)
    MatCreateAIJ(PETSC_COMM_WORLD, M, M, N, N, 19, PETSC_NULL, 19, PETSC_NULL, &(user->A));
    user->assignedA = PETSC_TRUE;
  }
 
  // Zero out matrix entries from the previous solve
  MatZeroEntries(user->A);
 
  // --- Get direct pointer access to grid metric data ---
  Cmpnts ***csi, ***eta, ***zet, ***icsi, ***ieta, ***izet, ***jcsi, ***jeta, ***jzet, ***kcsi, ***keta, ***kzet;
  PetscReal ***aj, ***iaj, ***jaj, ***kaj, ***nvert;
  DMDAVecGetArray(fda, user->lCsi, &csi); DMDAVecGetArray(fda, user->lEta, &eta); DMDAVecGetArray(fda, user->lZet, &zet);
  DMDAVecGetArray(fda, user->lICsi, &icsi); DMDAVecGetArray(fda, user->lIEta, &ieta); DMDAVecGetArray(fda, user->lIZet, &izet);
  DMDAVecGetArray(fda, user->lJCsi, &jcsi); DMDAVecGetArray(fda, user->lJEta, &jeta); DMDAVecGetArray(fda, user->lJZet, &jzet);
  DMDAVecGetArray(fda, user->lKCsi, &kcsi); DMDAVecGetArray(fda, user->lKEta, &keta); DMDAVecGetArray(fda, user->lKZet, &kzet);
  DMDAVecGetArray(da, user->lAj, &aj); DMDAVecGetArray(da, user->lIAj, &iaj); DMDAVecGetArray(da, user->lJAj, &jaj); DMDAVecGetArray(da, user->lKAj, &kaj);
  DMDAVecGetArray(da, user->lNvert, &nvert);
 
  // --- Create temporary vectors for the metric tensor components G_ij ---
  Vec G11, G12, G13, G21, G22, G23, G31, G32, G33;
  PetscReal ***g11, ***g12, ***g13, ***g21, ***g22, ***g23, ***g31, ***g32, ***g33;
  VecDuplicate(user->lAj, &G11); VecDuplicate(user->lAj, &G12); VecDuplicate(user->lAj, &G13);
  VecDuplicate(user->lAj, &G21); VecDuplicate(user->lAj, &G22); VecDuplicate(user->lAj, &G23);
  VecDuplicate(user->lAj, &G31); VecDuplicate(user->lAj, &G32); VecDuplicate(user->lAj, &G33);
  DMDAVecGetArray(da, G11, &g11); DMDAVecGetArray(da, G12, &g12); DMDAVecGetArray(da, G13, &g13);
  DMDAVecGetArray(da, G21, &g21); DMDAVecGetArray(da, G22, &g22); DMDAVecGetArray(da, G23, &g23);
  DMDAVecGetArray(da, G31, &g31); DMDAVecGetArray(da, G32, &g32); DMDAVecGetArray(da, G33, &g33);
 
  //================================================================================
  // Section 2: Pre-compute Metric Tensor Coefficients (g_ij)
  //================================================================================
  LOG_ALLOW(GLOBAL, LOG_DEBUG, "Pre-computing metric tensor components (g_ij).\n");
  for (k = gzs; k < gze; k++) {
    for (j = gys; j < gye; j++) {
      for (i = gxs; i < gxe; i++) {
        // These coefficients represent the dot products of the grid's contravariant base vectors,
        // scaled by face area. They are the core of the Laplacian operator on a curvilinear grid.
        if(i>-1 && j>-1 && k>-1 && i<IM+1 && j<JM+1 && k<KM+1){
            g11[k][j][i] = (icsi[k][j][i].x * icsi[k][j][i].x + icsi[k][j][i].y * icsi[k][j][i].y + icsi[k][j][i].z * icsi[k][j][i].z) * iaj[k][j][i];
            g12[k][j][i] = (ieta[k][j][i].x * icsi[k][j][i].x + ieta[k][j][i].y * icsi[k][j][i].y + ieta[k][j][i].z * icsi[k][j][i].z) * iaj[k][j][i];
            g13[k][j][i] = (izet[k][j][i].x * icsi[k][j][i].x + izet[k][j][i].y * icsi[k][j][i].y + izet[k][j][i].z * icsi[k][j][i].z) * iaj[k][j][i];
            g21[k][j][i] = (jcsi[k][j][i].x * jeta[k][j][i].x + jcsi[k][j][i].y * jeta[k][j][i].y + jcsi[k][j][i].z * jeta[k][j][i].z) * jaj[k][j][i];
            g22[k][j][i] = (jeta[k][j][i].x * jeta[k][j][i].x + jeta[k][j][i].y * jeta[k][j][i].y + jeta[k][j][i].z * jeta[k][j][i].z) * jaj[k][j][i];
            g23[k][j][i] = (jzet[k][j][i].x * jeta[k][j][i].x + jzet[k][j][i].y * jeta[k][j][i].y + jzet[k][j][i].z * jeta[k][j][i].z) * jaj[k][j][i];
            g31[k][j][i] = (kcsi[k][j][i].x * kzet[k][j][i].x + kcsi[k][j][i].y * kzet[k][j][i].y + kcsi[k][j][i].z * kzet[k][j][i].z) * kaj[k][j][i];
            g32[k][j][i] = (keta[k][j][i].x * kzet[k][j][i].x + keta[k][j][i].y * kzet[k][j][i].y + keta[k][j][i].z * kzet[k][j][i].z) * kaj[k][j][i];
            g33[k][j][i] = (kzet[k][j][i].x * kzet[k][j][i].x + kzet[k][j][i].y * kzet[k][j][i].y + kzet[k][j][i].z * kzet[k][j][i].z) * kaj[k][j][i];
        }
      }
    }
  }
 
  //================================================================================
  // Section 3: Assemble the LHS Matrix A
  //================================================================================
  LOG_ALLOW(GLOBAL, LOG_DEBUG, "Assembling the LHS matrix A using a 19-point stencil.\n");
 
  // --- Define domain boundaries for stencil logic, accounting for periodic BCs ---
  PetscInt x_str, x_end, y_str, y_end, z_str, z_end;
  if (user->bctype[0] == 7) { x_end = mx - 1; x_str = 0; }
  else { x_end = mx - 2; x_str = 1; }
  if (user->bctype[2] == 7) { y_end = my - 1; y_str = 0; }
  else { y_end = my - 2; y_str = 1; }
  if (user->bctype[4] == 7) { z_end = mz - 1; z_str = 0; }
  else { z_end = mz - 2; z_str = 1; }
 
  // --- Main assembly loop over all local grid points ---
  for (k = zs; k < ze; k++) {
    for (j = ys; j < ye; j++) {
      for (i = xs; i < xe; i++) {
        PetscScalar vol[19]; // Holds the 19 stencil coefficient values for the current row
        PetscInt idx[19];    // Holds the 19 global column indices for the current row
        PetscInt row = Gidx(i, j, k, user); // Global index for the current row
 
        // --- Handle Domain Boundary and Immersed Solid Points ---
        // For these points, we don't solve the Poisson equation. We set an identity
        // row (A_ii = 1) to effectively fix the pressure value (usually to 0).
        if (i == 0 || i == mx - 1 || j == 0 || j == my - 1 || k == 0 || k == mz - 1 || nvert[k][j][i] > IBM_FLUID_THRESHOLD) {
          vol[CP] = 1.0;
          idx[CP] = row;
          MatSetValues(user->A, 1, &row, 1, &idx[CP], &vol[CP], INSERT_VALUES);
        }
        // --- Handle Fluid Points ---
        else {
          for (PetscInt m = 0; m < 19; m++) {
            vol[m] = 0.0;
          }
 
          /************************************************************************
           * EAST FACE CONTRIBUTION (between i and i+1)
           ************************************************************************/
          if (nvert[k][j][i + 1] < IBM_FLUID_THRESHOLD && i != x_end) { // East neighbor is fluid
            // Primary derivative term: d/d_csi (g11 * dP/d_csi)
            vol[CP] -= g11[k][j][i];
            vol[EP] += g11[k][j][i];
 
            // Cross-derivative term: d/d_csi (g12 * dP/d_eta).
            // This requires an average of dP/d_eta. If a neighbor is solid, the stencil
            // dynamically switches to a one-sided difference to avoid using solid points.
          if ((j == my-2 && user->bctype[2]!=7) || nvert[k][j+1][i] + nvert[k][j+1][i+1] > 0.1) {
        if (nvert[k][j-1][i] + nvert[k][j-1][i+1] < 0.1 && (j!=1 || (j==1 && user->bctype[2]==7))) {
          vol[CP] += g12[k][j][i] * 0.5; vol[EP] += g12[k][j][i] * 0.5;
          vol[SP] -= g12[k][j][i] * 0.5; vol[SE] -= g12[k][j][i] * 0.5;
        }
          }
          else if ((j == my-2 || j==1) && user->bctype[2]==7 && nvert[k][j+1][i] + nvert[k][j+1][i+1] > 0.1) {
        if (nvert[k][j-1][i] + nvert[k][j-1][i+1] < 0.1) {
          vol[CP] += g12[k][j][i] * 0.5; vol[EP] += g12[k][j][i] * 0.5;
          vol[SP] -= g12[k][j][i] * 0.5; vol[SE] -= g12[k][j][i] * 0.5;
        }
          }
          else if ((j == 1 && user->bctype[2]!=7) || nvert[k][j-1][i] + nvert[k][j-1][i+1] > 0.1) {
        if (nvert[k][j+1][i] + nvert[k][j+1][i+1] < 0.1) {
          vol[NP] += g12[k][j][i] * 0.5; vol[NE] += g12[k][j][i] * 0.5;
          vol[CP] -= g12[k][j][i] * 0.5; vol[EP] -= g12[k][j][i] * 0.5;
        }
          }
          else if ((j == 1 || j==my-2) && user->bctype[2]==7 && nvert[k][j-1][i] + nvert[k][j-1][i+1] > 0.1) {
        if (nvert[k][j+1][i] + nvert[k][j+1][i+1] < 0.1) {
          vol[NP] += g12[k][j][i] * 0.5; vol[NE] += g12[k][j][i] * 0.5;
          vol[CP] -= g12[k][j][i] * 0.5; vol[EP] -= g12[k][j][i] * 0.5;
        }
          }
          else { // Centered difference
        vol[NP] += g12[k][j][i] * 0.25; vol[NE] += g12[k][j][i] * 0.25;
        vol[SP] -= g12[k][j][i] * 0.25; vol[SE] -= g12[k][j][i] * 0.25;
          }
            
            // Cross-derivative term: d/d_csi (g13 * dP/d_zet)
          if ((k == mz-2 && user->bctype[4]!=7) || nvert[k+1][j][i] + nvert[k+1][j][i+1] > 0.1) {
        if (nvert[k-1][j][i] + nvert[k-1][j][i+1] < 0.1 && (k!=1 || (k==1 && user->bctype[4]==7))) {
          vol[CP] += g13[k][j][i] * 0.5; vol[EP] += g13[k][j][i] * 0.5;
          vol[BP] -= g13[k][j][i] * 0.5; vol[BE] -= g13[k][j][i] * 0.5;
        }
          }
          else if ((k == mz-2 || k==1) && user->bctype[4]==7 && nvert[k+1][j][i] + nvert[k+1][j][i+1] > 0.1) {
        if (nvert[k-1][j][i] + nvert[k-1][j][i+1] < 0.1) {
          vol[CP] += g13[k][j][i] * 0.5; vol[EP] += g13[k][j][i] * 0.5;
          vol[BP] -= g13[k][j][i] * 0.5; vol[BE] -= g13[k][j][i] * 0.5;
        }
          }
          else if ((k == 1 && user->bctype[4]!=7) || nvert[k-1][j][i] + nvert[k-1][j][i+1] > 0.1) {
        if (nvert[k+1][j][i] + nvert[k+1][j][i+1] < 0.1) {
          vol[TP] += g13[k][j][i] * 0.5; vol[TE] += g13[k][j][i] * 0.5;
          vol[CP] -= g13[k][j][i] * 0.5; vol[EP] -= g13[k][j][i] * 0.5;
        }
          }
          else if ((k == 1 || k==mz-2) && user->bctype[4]==7 && nvert[k-1][j][i] + nvert[k-1][j][i+1] > 0.1) {
        if (nvert[k+1][j][i] + nvert[k+1][j][i+1] < 0.1) {
          vol[TP] += g13[k][j][i] * 0.5; vol[TE] += g13[k][j][i] * 0.5;
          vol[CP] -= g13[k][j][i] * 0.5; vol[EP] -= g13[k][j][i] * 0.5;
        }
          }
          else { // Centered difference
        vol[TP] += g13[k][j][i] * 0.25; vol[TE] += g13[k][j][i] * 0.25;
        vol[BP] -= g13[k][j][i] * 0.25; vol[BE] -= g13[k][j][i] * 0.25;
          }
          }
 
          /************************************************************************
           * WEST FACE CONTRIBUTION (between i-1 and i)
           ************************************************************************/
          if (nvert[k][j][i-1] < IBM_FLUID_THRESHOLD && i != x_str) {
          vol[CP] -= g11[k][j][i-1];
          vol[WP] += g11[k][j][i-1];
 
          if ((j == my-2 && user->bctype[2]!=7) || nvert[k][j+1][i] + nvert[k][j+1][i-1] > 0.1) {
        if (nvert[k][j-1][i] + nvert[k][j-1][i-1] < 0.1 && (j!=1 || (j==1 && user->bctype[2]==7))) {
          vol[CP] -= g12[k][j][i-1] * 0.5; vol[WP] -= g12[k][j][i-1] * 0.5;
          vol[SP] += g12[k][j][i-1] * 0.5; vol[SW] += g12[k][j][i-1] * 0.5;
        }
          }
          else if ((j == my-2 || j==1) && user->bctype[2]==7 && nvert[k][j+1][i] + nvert[k][j+1][i-1] > 0.1) {
        if (nvert[k][j-1][i] + nvert[k][j-1][i-1] < 0.1) {
          vol[CP] -= g12[k][j][i-1] * 0.5; vol[WP] -= g12[k][j][i-1] * 0.5;
          vol[SP] += g12[k][j][i-1] * 0.5; vol[SW] += g12[k][j][i-1] * 0.5;
        }
          }
          else if ((j == 1 && user->bctype[2]!=7)|| nvert[k][j-1][i] + nvert[k][j-1][i-1] > 0.1) {
        if (nvert[k][j+1][i] + nvert[k][j+1][i-1] < 0.1) {
          vol[NP] -= g12[k][j][i-1] * 0.5; vol[NW] -= g12[k][j][i-1] * 0.5;
          vol[CP] += g12[k][j][i-1] * 0.5; vol[WP] += g12[k][j][i-1] * 0.5;
        }
          }
          else if ((j == 1 || j==my-2) && user->bctype[2]==7 && nvert[k][j-1][i] + nvert[k][j-1][i-1] > 0.1) {
        if (nvert[k][j+1][i] + nvert[k][j+1][i-1] < 0.1) {
          vol[NP] -= g12[k][j][i-1] * 0.5; vol[NW] -= g12[k][j][i-1] * 0.5;
          vol[CP] += g12[k][j][i-1] * 0.5; vol[WP] += g12[k][j][i-1] * 0.5;
        }
          }
          else {
        vol[NP] -= g12[k][j][i-1] * 0.25; vol[NW] -= g12[k][j][i-1] * 0.25;
        vol[SP] += g12[k][j][i-1] * 0.25; vol[SW] += g12[k][j][i-1] * 0.25;
          }
 
          if ((k == mz-2 && user->bctype[4]!=7) || nvert[k+1][j][i] + nvert[k+1][j][i-1] > 0.1) {
        if (nvert[k-1][j][i] + nvert[k-1][j][i-1] < 0.1 && (k!=1 || (k==1 && user->bctype[4]==7))) {
          vol[CP] -= g13[k][j][i-1] * 0.5; vol[WP] -= g13[k][j][i-1] * 0.5;
          vol[BP] += g13[k][j][i-1] * 0.5; vol[BW] += g13[k][j][i-1] * 0.5;
        }
          }
          else if ((k == mz-2 || k==1) && user->bctype[4]==7 && nvert[k+1][j][i] + nvert[k+1][j][i-1] > 0.1) {
        if (nvert[k-1][j][i] + nvert[k-1][j][i-1] < 0.1) {
          vol[CP] -= g13[k][j][i-1] * 0.5; vol[WP] -= g13[k][j][i-1] * 0.5;
          vol[BP] += g13[k][j][i-1] * 0.5; vol[BW] += g13[k][j][i-1] * 0.5;
        }
          }
          else if ((k == 1 && user->bctype[4]!=7) || nvert[k-1][j][i] + nvert[k-1][j][i-1] > 0.1) {
        if (nvert[k+1][j][i] + nvert[k+1][j][i-1] < 0.1) {
          vol[TP] -= g13[k][j][i-1] * 0.5; vol[TW] -= g13[k][j][i-1] * 0.5;
          vol[CP] += g13[k][j][i-1] * 0.5; vol[WP] += g13[k][j][i-1] * 0.5;
        }
          }
          else if ((k == 1 || k==mz-2) && user->bctype[4]==7 && nvert[k-1][j][i] + nvert[k-1][j][i-1] > 0.1) {
        if (nvert[k+1][j][i] + nvert[k+1][j][i-1] < 0.1) {
          vol[TP] -= g13[k][j][i-1] * 0.5; vol[TW] -= g13[k][j][i-1] * 0.5;
          vol[CP] += g13[k][j][i-1] * 0.5; vol[WP] += g13[k][j][i-1] * 0.5;
        }
          }
          else {
        vol[TP] -= g13[k][j][i-1] * 0.25; vol[TW] -= g13[k][j][i-1] * 0.25;
        vol[BP] += g13[k][j][i-1] * 0.25; vol[BW] += g13[k][j][i-1] * 0.25;
          }
          }
 
          /************************************************************************
           * NORTH FACE CONTRIBUTION (between j and j+1)
           ************************************************************************/
          if (nvert[k][j+1][i] < IBM_FLUID_THRESHOLD && j != y_end) {
          if ((i == mx-2 && user->bctype[0]!=7)|| nvert[k][j][i+1] + nvert[k][j+1][i+1] > 0.1) {
        if (nvert[k][j][i-1] + nvert[k][j+1][i-1] < 0.1 && (i!=1 || (i==1 && user->bctype[0]==7))) {
          vol[CP] += g21[k][j][i] * 0.5; vol[NP] += g21[k][j][i] * 0.5;
          vol[WP] -= g21[k][j][i] * 0.5; vol[NW] -= g21[k][j][i] * 0.5;
        }
          }
          else if ((i == mx-2 || i==1) && user->bctype[0]==7 && nvert[k][j][i+1] + nvert[k][j+1][i+1] > 0.1) {
        if (nvert[k][j][i-1] + nvert[k][j+1][i-1] < 0.1) {
          vol[CP] += g21[k][j][i] * 0.5; vol[NP] += g21[k][j][i] * 0.5;
          vol[WP] -= g21[k][j][i] * 0.5; vol[NW] -= g21[k][j][i] * 0.5;
        }
          }
          else if ((i == 1 && user->bctype[0]!=7) || nvert[k][j][i-1] + nvert[k][j+1][i-1] > 0.1) {
        if (nvert[k][j][i+1] + nvert[k][j+1][i+1] < 0.1) {
          vol[EP] += g21[k][j][i] * 0.5; vol[NE] += g21[k][j][i] * 0.5;
          vol[CP] -= g21[k][j][i] * 0.5; vol[NP] -= g21[k][j][i] * 0.5;
        }
          }
          else if ((i == 1 || i==mx-2) && user->bctype[0]==7 &&  nvert[k][j][i-1] + nvert[k][j+1][i-1] > 0.1) {
        if (nvert[k][j][i+1] + nvert[k][j+1][i+1] < 0.1) {
          vol[EP] += g21[k][j][i] * 0.5; vol[NE] += g21[k][j][i] * 0.5;
          vol[CP] -= g21[k][j][i] * 0.5; vol[NP] -= g21[k][j][i] * 0.5;
        }
          }
          else {
        vol[EP] += g21[k][j][i] * 0.25; vol[NE] += g21[k][j][i] * 0.25;
        vol[WP] -= g21[k][j][i] * 0.25; vol[NW] -= g21[k][j][i] * 0.25;
          }
 
          vol[CP] -= g22[k][j][i];
          vol[NP] += g22[k][j][i];
 
          if ((k == mz-2 && user->bctype[4]!=7)|| nvert[k+1][j][i] + nvert[k+1][j+1][i] > 0.1) {
        if (nvert[k-1][j][i] + nvert[k-1][j+1][i] < 0.1 && (k!=1 || (k==1 && user->bctype[4]==7))) {
          vol[CP] += g23[k][j][i] * 0.5; vol[NP] += g23[k][j][i] * 0.5;
          vol[BP] -= g23[k][j][i] * 0.5; vol[BN] -= g23[k][j][i] * 0.5;
        }
          }
          else if ((k == mz-2 || k==1 ) && user->bctype[4]==7 && nvert[k+1][j][i] + nvert[k+1][j+1][i] > 0.1) {
        if (nvert[k-1][j][i] + nvert[k-1][j+1][i] < 0.1) {
          vol[CP] += g23[k][j][i] * 0.5; vol[NP] += g23[k][j][i] * 0.5;
          vol[BP] -= g23[k][j][i] * 0.5; vol[BN] -= g23[k][j][i] * 0.5;
        }
          }
          else if ((k == 1 && user->bctype[4]!=7)|| nvert[k-1][j][i] + nvert[k-1][j+1][i] > 0.1) {
        if (nvert[k+1][j][i] + nvert[k+1][j+1][i] < 0.1) {
          vol[TP] += g23[k][j][i] * 0.5; vol[TN] += g23[k][j][i] * 0.5;
          vol[CP] -= g23[k][j][i] * 0.5; vol[NP] -= g23[k][j][i] * 0.5;
        }
          }
          else if ((k == 1 || k==mz-2 ) && user->bctype[4]==7 && nvert[k-1][j][i] + nvert[k-1][j+1][i] > 0.1) {
        if (nvert[k+1][j][i] + nvert[k+1][j+1][i] < 0.1) {
          vol[TP] += g23[k][j][i] * 0.5; vol[TN] += g23[k][j][i] * 0.5;
          vol[CP] -= g23[k][j][i] * 0.5; vol[NP] -= g23[k][j][i] * 0.5;
        }
          }
          else {
        vol[TP] += g23[k][j][i] * 0.25; vol[TN] += g23[k][j][i] * 0.25;
        vol[BP] -= g23[k][j][i] * 0.25; vol[BN] -= g23[k][j][i] * 0.25;
          }
          }
 
          /************************************************************************
           * SOUTH FACE CONTRIBUTION (between j-1 and j)
           ************************************************************************/
          if (nvert[k][j-1][i] < IBM_FLUID_THRESHOLD && j != y_str) {
          if ((i == mx-2 && user->bctype[0]!=7) || nvert[k][j][i+1] + nvert[k][j-1][i+1] > 0.1) {
        if (nvert[k][j][i-1] + nvert[k][j-1][i-1] < 0.1 && (i!=1 || (i==1 && user->bctype[0]==7))) {
          vol[CP] -= g21[k][j-1][i] * 0.5; vol[SP] -= g21[k][j-1][i] * 0.5;
          vol[WP] += g21[k][j-1][i] * 0.5; vol[SW] += g21[k][j-1][i] * 0.5;
        }
          }
          else  if ((i == mx-2 || i==1) && user->bctype[0]==7 && nvert[k][j][i+1] + nvert[k][j-1][i+1] > 0.1) {
        if (nvert[k][j][i-1] + nvert[k][j-1][i-1] < 0.1) {
          vol[CP] -= g21[k][j-1][i] * 0.5; vol[SP] -= g21[k][j-1][i] * 0.5;
          vol[WP] += g21[k][j-1][i] * 0.5; vol[SW] += g21[k][j-1][i] * 0.5;
        }
          }
          else if ((i == 1 && user->bctype[0]!=7)|| nvert[k][j][i-1] + nvert[k][j-1][i-1] > 0.1) {
        if (nvert[k][j][i+1] + nvert[k][j-1][i+1] < 0.1) {
          vol[EP] -= g21[k][j-1][i] * 0.5; vol[SE] -= g21[k][j-1][i] * 0.5;
          vol[CP] += g21[k][j-1][i] * 0.5; vol[SP] += g21[k][j-1][i] * 0.5;
        }
          }
          else if ((i == 1 || i==mx-2) && user->bctype[0]==7 && nvert[k][j][i-1] + nvert[k][j-1][i-1] > 0.1) {
        if (nvert[k][j][i+1] + nvert[k][j-1][i+1] < 0.1) {
          vol[EP] -= g21[k][j-1][i] * 0.5; vol[SE] -= g21[k][j-1][i] * 0.5;
          vol[CP] += g21[k][j-1][i] * 0.5; vol[SP] += g21[k][j-1][i] * 0.5;
        }
          }
          else {
        vol[EP] -= g21[k][j-1][i] * 0.25; vol[SE] -= g21[k][j-1][i] * 0.25;
        vol[WP] += g21[k][j-1][i] * 0.25; vol[SW] += g21[k][j-1][i] * 0.25;
          }
 
          vol[CP] -= g22[k][j-1][i];
          vol[SP] += g22[k][j-1][i];
 
          if ((k == mz-2 && user->bctype[4]!=7)|| nvert[k+1][j][i] + nvert[k+1][j-1][i] > 0.1) {
        if (nvert[k-1][j][i] + nvert[k-1][j-1][i] < 0.1 && (k!=1 || (k==1 && user->bctype[4]==7))) {
          vol[CP] -= g23[k][j-1][i] * 0.5; vol[SP] -= g23[k][j-1][i] * 0.5;
          vol[BP] += g23[k][j-1][i] * 0.5; vol[BS] += g23[k][j-1][i] * 0.5;
        }
          }
          else if ((k == mz-2 || k==1) && user->bctype[4]==7 && nvert[k+1][j][i] + nvert[k+1][j-1][i] > 0.1) {
        if (nvert[k-1][j][i] + nvert[k-1][j-1][i] < 0.1 ) {
          vol[CP] -= g23[k][j-1][i] * 0.5; vol[SP] -= g23[k][j-1][i] * 0.5;
          vol[BP] += g23[k][j-1][i] * 0.5; vol[BS] += g23[k][j-1][i] * 0.5;
        }
          }
          else if ((k == 1 && user->bctype[4]!=7)|| nvert[k-1][j][i] + nvert[k-1][j-1][i] > 0.1) {
        if (nvert[k+1][j][i] + nvert[k+1][j-1][i] < 0.1) {
          vol[TP] -= g23[k][j-1][i] * 0.5; vol[TS] -= g23[k][j-1][i] * 0.5;
          vol[CP] += g23[k][j-1][i] * 0.5; vol[SP] += g23[k][j-1][i] * 0.5;
        }
          }
          else if ((k == 1 || k==mz-2) && user->bctype[4]==7 && nvert[k-1][j][i] + nvert[k-1][j-1][i] > 0.1) {
        if (nvert[k+1][j][i] + nvert[k+1][j-1][i] < 0.1) {
          vol[TP] -= g23[k][j-1][i] * 0.5; vol[TS] -= g23[k][j-1][i] * 0.5;
          vol[CP] += g23[k][j-1][i] * 0.5; vol[SP] += g23[k][j-1][i] * 0.5;
        }
          }
          else {
        vol[TP] -= g23[k][j-1][i] * 0.25; vol[TS] -= g23[k][j-1][i] * 0.25;
        vol[BP] += g23[k][j-1][i] * 0.25; vol[BS] += g23[k][j-1][i] * 0.25;
          }
          }
 
          /************************************************************************
           * TOP FACE CONTRIBUTION (between k and k+1)
           ************************************************************************/
          if (nvert[k+1][j][i] < IBM_FLUID_THRESHOLD && k != z_end) {
          if ((i == mx-2 && user->bctype[0]!=7)|| nvert[k][j][i+1] + nvert[k+1][j][i+1] > 0.1) {
        if (nvert[k][j][i-1] + nvert[k+1][j][i-1] < 0.1 && (i!=1 || (i==1 && user->bctype[0]==7))) {
          vol[CP] += g31[k][j][i] * 0.5; vol[TP] += g31[k][j][i] * 0.5;
          vol[WP] -= g31[k][j][i] * 0.5; vol[TW] -= g31[k][j][i] * 0.5;
        }
          }
          else if ((i == mx-2 || i==1) && user->bctype[0]==7 && nvert[k][j][i+1] + nvert[k+1][j][i+1] > 0.1) {
        if (nvert[k][j][i-1] + nvert[k+1][j][i-1] < 0.1) {
          vol[CP] += g31[k][j][i] * 0.5; vol[TP] += g31[k][j][i] * 0.5;
          vol[WP] -= g31[k][j][i] * 0.5; vol[TW] -= g31[k][j][i] * 0.5;
        }
          }
          else if ((i == 1 && user->bctype[0]!=7)|| nvert[k][j][i-1] + nvert[k+1][j][i-1] > 0.1) {
        if (nvert[k][j][i+1] + nvert[k+1][j][i+1] < 0.1) {
          vol[EP] += g31[k][j][i] * 0.5; vol[TE] += g31[k][j][i] * 0.5;
          vol[CP] -= g31[k][j][i] * 0.5; vol[TP] -= g31[k][j][i] * 0.5;
        }
          }
          else if ((i == 1 || i==mx-2) && user->bctype[0]==7 && nvert[k][j][i-1] + nvert[k+1][j][i-1] > 0.1) {
        if (nvert[k][j][i+1] + nvert[k+1][j][i+1] < 0.1) {
          vol[EP] += g31[k][j][i] * 0.5; vol[TE] += g31[k][j][i] * 0.5;
          vol[CP] -= g31[k][j][i] * 0.5; vol[TP] -= g31[k][j][i] * 0.5;
        }
          }
          else {
        vol[EP] += g31[k][j][i] * 0.25; vol[TE] += g31[k][j][i] * 0.25;
        vol[WP] -= g31[k][j][i] * 0.25; vol[TW] -= g31[k][j][i] * 0.25;
          }
 
          if ((j == my-2 && user->bctype[2]!=7)|| nvert[k][j+1][i] + nvert[k+1][j+1][i] > 0.1) {
        if (nvert[k][j-1][i] + nvert[k+1][j-1][i] < 0.1 && (j!=1 || (j==1 && user->bctype[2]==7))) {
          vol[CP] += g32[k][j][i] * 0.5; vol[TP] += g32[k][j][i] * 0.5;
          vol[SP] -= g32[k][j][i] * 0.5; vol[TS] -= g32[k][j][i] * 0.5;
        }
          }
          else if ((j == my-2 || j==1) && user->bctype[2]==7 && nvert[k][j+1][i] + nvert[k+1][j+1][i] > 0.1) {
        if (nvert[k][j-1][i] + nvert[k+1][j-1][i] < 0.1) {
          vol[CP] += g32[k][j][i] * 0.5; vol[TP] += g32[k][j][i] * 0.5;
          vol[SP] -= g32[k][j][i] * 0.5; vol[TS] -= g32[k][j][i] * 0.5;
        }
          }
          else if ((j == 1 && user->bctype[2]!=7)|| nvert[k][j-1][i] + nvert[k+1][j-1][i] > 0.1) {
        if (nvert[k][j+1][i] + nvert[k+1][j+1][i] < 0.1) {
          vol[NP] += g32[k][j][i] * 0.5; vol[TN] += g32[k][j][i] * 0.5;
          vol[CP] -= g32[k][j][i] * 0.5; vol[TP] -= g32[k][j][i] * 0.5;
        }
          }
          else if ((j == 1 || j==my-2) && user->bctype[2]==7 && nvert[k][j-1][i] + nvert[k+1][j-1][i] > 0.1) {
        if (nvert[k][j+1][i] + nvert[k+1][j+1][i] < 0.1) {
          vol[NP] += g32[k][j][i] * 0.5; vol[TN] += g32[k][j][i] * 0.5;
          vol[CP] -= g32[k][j][i] * 0.5; vol[TP] -= g32[k][j][i] * 0.5;
        }
          }
          else {
        vol[NP] += g32[k][j][i] * 0.25; vol[TN] += g32[k][j][i] * 0.25;
        vol[SP] -= g32[k][j][i] * 0.25; vol[TS] -= g32[k][j][i] * 0.25;
          }
 
          vol[CP] -= g33[k][j][i];
          vol[TP] += g33[k][j][i];
          }
 
          /************************************************************************
           * BOTTOM FACE CONTRIBUTION (between k-1 and k)
           ************************************************************************/
          if (nvert[k-1][j][i] < IBM_FLUID_THRESHOLD && k != z_str) {
          if ((i == mx-2 && user->bctype[0]!=7)|| nvert[k][j][i+1] + nvert[k-1][j][i+1] > 0.1) {
        if (nvert[k][j][i-1] + nvert[k-1][j][i-1] < 0.1 && (i!=1 || (i==1 && user->bctype[0]==7))) {
          vol[CP] -= g31[k-1][j][i] * 0.5; vol[BP] -= g31[k-1][j][i] * 0.5;
          vol[WP] += g31[k-1][j][i] * 0.5; vol[BW] += g31[k-1][j][i] * 0.5;
        }
          }
          else if ((i == mx-2 || i==1) && user->bctype[0]==7 && nvert[k][j][i+1] + nvert[k-1][j][i+1] > 0.1) {
        if (nvert[k][j][i-1] + nvert[k-1][j][i-1] < 0.1) {
          vol[CP] -= g31[k-1][j][i] * 0.5; vol[BP] -= g31[k-1][j][i] * 0.5;
          vol[WP] += g31[k-1][j][i] * 0.5; vol[BW] += g31[k-1][j][i] * 0.5;
        }
          }
          else if ((i == 1 && user->bctype[0]!=7)|| nvert[k][j][i-1] + nvert[k-1][j][i-1] > 0.1) {
        if (nvert[k][j][i+1] + nvert[k-1][j][i+1] < 0.1) {
          vol[EP] -= g31[k-1][j][i] * 0.5; vol[BE] -= g31[k-1][j][i] * 0.5;
          vol[CP] += g31[k-1][j][i] * 0.5; vol[BP] += g31[k-1][j][i] * 0.5;
        }
          }
          else if ((i == 1 || i==mx-2) && user->bctype[0]==7 && nvert[k][j][i-1] + nvert[k-1][j][i-1] > 0.1) {
        if (nvert[k][j][i+1] + nvert[k-1][j][i+1] < 0.1) {
          vol[EP] -= g31[k-1][j][i] * 0.5; vol[BE] -= g31[k-1][j][i] * 0.5;
          vol[CP] += g31[k-1][j][i] * 0.5; vol[BP] += g31[k-1][j][i] * 0.5;
        }
          }
          else {
        vol[EP] -= g31[k-1][j][i] * 0.25; vol[BE] -= g31[k-1][j][i] * 0.25;
        vol[WP] += g31[k-1][j][i] * 0.25; vol[BW] += g31[k-1][j][i] * 0.25;
          }
 
          if ((j == my-2 && user->bctype[2]!=7)|| nvert[k][j+1][i] + nvert[k-1][j+1][i] > 0.1) {
        if (nvert[k][j-1][i] + nvert[k-1][j-1][i] < 0.1 && (j!=1 || (j==1 && user->bctype[2]==7))) {
          vol[CP] -= g32[k-1][j][i] * 0.5; vol[BP] -= g32[k-1][j][i] * 0.5;
          vol[SP] += g32[k-1][j][i] * 0.5; vol[BS] += g32[k-1][j][i] * 0.5;
        }
          }
          else if ((j == my-2 || j==1) && user->bctype[2]==7 && nvert[k][j+1][i] + nvert[k-1][j+1][i] > 0.1) {
        if (nvert[k][j-1][i] + nvert[k-1][j-1][i] < 0.1) {
          vol[CP] -= g32[k-1][j][i] * 0.5; vol[BP] -= g32[k-1][j][i] * 0.5;
          vol[SP] += g32[k-1][j][i] * 0.5; vol[BS] += g32[k-1][j][i] * 0.5;
        }
          }
          else if ((j == 1 && user->bctype[2]!=7)|| nvert[k][j-1][i] + nvert[k-1][j-1][i] > 0.1) {
        if (nvert[k][j+1][i] + nvert[k-1][j+1][i] < 0.1) {
          vol[NP] -= g32[k-1][j][i] * 0.5; vol[BN] -= g32[k-1][j][i] * 0.5;
          vol[CP] += g32[k-1][j][i] * 0.5; vol[BP] += g32[k-1][j][i] * 0.5;
        }
          }
          else if ((j == 1 || j==my-2) && user->bctype[2]==7 && nvert[k][j-1][i] + nvert[k-1][j-1][i] > 0.1) {
        if (nvert[k][j+1][i] + nvert[k-1][j+1][i] < 0.1) {
          vol[NP] -= g32[k-1][j][i] * 0.5; vol[BN] -= g32[k-1][j][i] * 0.5;
          vol[CP] += g32[k-1][j][i] * 0.5; vol[BP] += g32[k-1][j][i] * 0.5;
        }
          }
          else {
        vol[NP] -= g32[k-1][j][i] * 0.25; vol[BN] -= g32[k-1][j][i] * 0.25;
        vol[SP] += g32[k-1][j][i] * 0.25; vol[BS] += g32[k-1][j][i] * 0.25;
          }
 
          vol[CP] -= g33[k-1][j][i];
          vol[BP] += g33[k-1][j][i];
          }
 
          // --- Final scaling and insertion into the matrix ---
 
          // Scale all stencil coefficients by the negative cell volume (-aj).
          for (PetscInt m = 0; m < 19; m++) {
            vol[m] *= -aj[k][j][i];
          }
 
          // Set the global column indices for the 19 stencil points, handling periodic BCs.
          idx[CP] = Gidx(i, j, k, user);
          if (user->bctype[0]==7 && i==mx-2) idx[EP] = Gidx(1, j, k, user); else idx[EP] = Gidx(i+1, j, k, user);
          if (user->bctype[0]==7 && i==1) idx[WP] = Gidx(mx-2, j, k, user); else idx[WP] = Gidx(i-1, j, k, user);
          if (user->bctype[2]==7 && j==my-2) idx[NP] = Gidx(i, 1, k, user); else idx[NP] = Gidx(i, j+1, k, user);
          if (user->bctype[2]==7 && j==1) idx[SP] = Gidx(i, my-2, k, user); else idx[SP] = Gidx(i, j-1, k, user);
          if (user->bctype[4]==7 && k==mz-2) idx[TP] = Gidx(i, j, 1, user); else idx[TP] = Gidx(i, j, k+1, user);
          if (user->bctype[4]==7 && k==1) idx[BP] = Gidx(i, j, mz-2, user); else idx[BP] = Gidx(i, j, k-1, user);
          if (user->bctype[0]==7 && user->bctype[2]==7 && i==mx-2 && j==my-2) idx[NE] = Gidx(1, 1, k, user); else if (user->bctype[0]==7 && i==mx-2) idx[NE] = Gidx(1, j+1, k, user); else if (user->bctype[2]==7 && j==my-2) idx[NE] = Gidx(i+1, 1, k, user); else idx[NE] = Gidx(i+1, j+1, k, user);
          if (user->bctype[0]==7 && user->bctype[2]==7 && i==mx-2 && j==1) idx[SE] = Gidx(1, my-2, k, user); else if (user->bctype[0]==7 && i==mx-2) idx[SE] = Gidx(1, j-1, k, user); else if (user->bctype[2]==7 && j==1) idx[SE] = Gidx(i+1, my-2, k, user); else idx[SE] = Gidx(i+1, j-1, k, user);
          if (user->bctype[0]==7 && user->bctype[2]==7 && i==1 && j==my-2) idx[NW] = Gidx(mx-2, 1, k, user); else if (user->bctype[0]==7 && i==1) idx[NW] = Gidx(mx-2, j+1, k, user); else if (user->bctype[2]==7 && j==my-2) idx[NW] = Gidx(i-1, 1, k, user); else idx[NW] = Gidx(i-1, j+1, k, user);
          if (user->bctype[0]==7 && user->bctype[2]==7 && i==1 && j==1) idx[SW] = Gidx(mx-2, my-2, k, user); else if (user->bctype[0]==7 && i==1) idx[SW] = Gidx(mx-2, j-1, k, user); else if (user->bctype[2]==7 && j==1) idx[SW] = Gidx(i-1, my-2, k, user); else idx[SW] = Gidx(i-1, j-1, k, user);
          if (user->bctype[2]==7 && user->bctype[4]==7 && j==my-2 && k==mz-2) idx[TN] = Gidx(i, 1, 1, user); else if (user->bctype[2]==7 && j==my-2) idx[TN] = Gidx(i, 1, k+1, user); else if (user->bctype[4]==7 && k==mz-2) idx[TN] = Gidx(i, j+1, 1, user); else idx[TN] = Gidx(i, j+1, k+1, user);
          if (user->bctype[2]==7 && user->bctype[4]==7 && j==my-2 && k==1) idx[BN] = Gidx(i, 1, mz-2, user); else if(user->bctype[2]==7 && j==my-2) idx[BN] = Gidx(i, 1, k-1, user); else if (user->bctype[4]==7 && k==1) idx[BN] = Gidx(i, j+1, mz-2, user); else idx[BN] = Gidx(i, j+1, k-1, user);
          if (user->bctype[2]==7 && user->bctype[4]==7 && j==1 && k==mz-2) idx[TS] = Gidx(i, my-2, 1, user); else if (user->bctype[2]==7 && j==1) idx[TS] = Gidx(i, my-2, k+1, user); else if (user->bctype[4]==7 && k==mz-2) idx[TS] = Gidx(i, j-1, 1, user); else idx[TS] = Gidx(i, j-1, k+1, user);
          if (user->bctype[2]==7 && user->bctype[4]==7 && j==1 && k==1) idx[BS] = Gidx(i, my-2, mz-2, user); else if (user->bctype[2]==7 && j==1) idx[BS] = Gidx(i, my-2, k-1, user); else if (user->bctype[4]==7 && k==1) idx[BS] = Gidx(i, j-1, mz-2, user); else idx[BS] = Gidx(i, j-1, k-1, user);
          if (user->bctype[0]==7 && user->bctype[4]==7 && i==mx-2 && k==mz-2) idx[TE] = Gidx(1, j, 1, user); else if(user->bctype[0]==7 && i==mx-2) idx[TE] = Gidx(1, j, k+1, user); else if(user->bctype[4]==7 && k==mz-2) idx[TE] = Gidx(i+1, j, 1, user); else idx[TE] = Gidx(i+1, j, k+1, user);
          if (user->bctype[0]==7 && user->bctype[4]==7 && i==mx-2 && k==1) idx[BE] = Gidx(1, j, mz-2, user); else if(user->bctype[0]==7 && i==mx-2) idx[BE] = Gidx(1, j, k-1, user); else if(user->bctype[4]==7 && k==1) idx[BE] = Gidx(i+1, j, mz-2, user); else idx[BE] = Gidx(i+1, j, k-1, user);
          if (user->bctype[0]==7 && user->bctype[4]==7 && i==1 && k==mz-2) idx[TW] = Gidx(mx-2, j, 1, user); else if(user->bctype[0]==7 && i==1) idx[TW] = Gidx(mx-2, j, k+1, user); else if (user->bctype[4]==7 && k==mz-2) idx[TW] = Gidx(i-1, j, 1, user); else idx[TW] = Gidx(i-1, j, k+1, user);
          if (user->bctype[0]==7 && user->bctype[4]==7 && i==1 && k==1) idx[BW] = Gidx(mx-2, j, mz-2, user); else if (user->bctype[0]==7 && i==1) idx[BW] = Gidx(mx-2, j, k-1, user); else if (user->bctype[4]==7 && k==1) idx[BW] = Gidx(i-1, j, mz-2, user); else idx[BW] = Gidx(i-1, j, k-1, user);
 
          // Insert the computed row into the matrix A.
          MatSetValues(user->A, 1, &row, 19, idx, vol, INSERT_VALUES);
        }
      }
    }
  }
 
  //================================================================================
  // Section 4: Finalize Matrix and Cleanup
  //================================================================================
  
  LOG_ALLOW(GLOBAL, LOG_DEBUG, "Finalizing matrix assembly.\n");
  MatAssemblyBegin(user->A, MAT_FINAL_ASSEMBLY);
  MatAssemblyEnd(user->A, MAT_FINAL_ASSEMBLY);
 
  PetscReal max_A;
 
  ierr = MatNorm(user->A,NORM_INFINITY,&max_A);CHKERRQ(ierr);
 
  LOG_ALLOW(GLOBAL,LOG_DEBUG," Max value in A matrix for level %d =  %le.\n",user->thislevel,max_A);
 
  // if (get_log_level() >= LOG_DEBUG) {
  //  ierr = MatView(user->A,PETSC_VIEWER_STDOUT_WORLD); CHKERRQ(ierr);
  // }
  
  // --- Restore access to all PETSc vectors and destroy temporary ones ---
  DMDAVecRestoreArray(da, G11, &g11); DMDAVecRestoreArray(da, G12, &g12); DMDAVecRestoreArray(da, G13, &g13);
  DMDAVecRestoreArray(da, G21, &g21); DMDAVecRestoreArray(da, G22, &g22); DMDAVecRestoreArray(da, G23, &g23);
  DMDAVecRestoreArray(da, G31, &g31); DMDAVecRestoreArray(da, G32, &g32); DMDAVecRestoreArray(da, G33, &g33);
  
  VecDestroy(&G11); VecDestroy(&G12); VecDestroy(&G13);
  VecDestroy(&G21); VecDestroy(&G22); VecDestroy(&G23);
  VecDestroy(&G31); VecDestroy(&G32); VecDestroy(&G33);
 
  DMDAVecRestoreArray(fda, user->lCsi, &csi); DMDAVecRestoreArray(fda, user->lEta, &eta); DMDAVecRestoreArray(fda, user->lZet, &zet);
  DMDAVecRestoreArray(fda, user->lICsi, &icsi); DMDAVecRestoreArray(fda, user->lIEta, &ieta); DMDAVecRestoreArray(fda, user->lIZet, &izet);
  DMDAVecRestoreArray(fda, user->lJCsi, &jcsi); DMDAVecRestoreArray(fda, user->lJEta, &jeta); DMDAVecRestoreArray(fda, user->lJZet, &jzet);
  DMDAVecRestoreArray(fda, user->lKCsi, &kcsi); DMDAVecRestoreArray(fda, user->lKEta, &keta); DMDAVecRestoreArray(fda, user->lKZet, &kzet);
  DMDAVecRestoreArray(da, user->lAj, &aj); DMDAVecRestoreArray(da, user->lIAj, &iaj); DMDAVecRestoreArray(da, user->lJAj, &jaj); DMDAVecRestoreArray(da, user->lKAj, &kaj);
  DMDAVecRestoreArray(da, user->lNvert, &nvert);
  
  LOG_ALLOW(GLOBAL, LOG_DEBUG, "Exiting PoissonLHSNew.\n");
  PROFILE_FUNCTION_END;
  PetscFunctionReturn(0);
}

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PoissonRHS()

PetscErrorCode PoissonRHS ( UserCtx *  user, Vec  B  )

extern

Computes the Right-Hand-Side (RHS) of the Poisson equation, which is the divergence of the intermediate velocity field.

Parameters

user	The UserCtx for the grid level.
B	The PETSc Vec where the RHS result will be stored.

Returns

PetscErrorCode 0 on success.

Definition at line 2810 of file poisson.c.

{
  DMDALocalInfo info = user->info;
  PetscInt  xs = info.xs, xe = info.xs + info.xm;
  PetscInt      ys = info.ys, ye = info.ys + info.ym;
  PetscInt  zs = info.zs, ze = info.zs + info.zm;
  PetscInt  mx = info.mx, my = info.my, mz = info.mz;
 
  PetscInt      i, j, k;
  PetscReal ***nvert, ***aj, ***rb, dt = user->simCtx->dt;
  struct Components{
    PetscReal x;
    PetscReal y;
    PetscReal z;
  } *** ucont;
 
  PROFILE_FUNCTION_BEGIN;
 
  LOG_ALLOW(GLOBAL, LOG_DEBUG, "Entering PoissonRHS to compute pressure equation RHS.\n");
 
  DMDAVecGetArray(user->da, B, &rb);
  DMDAVecGetArray(user->fda, user->lUcont, &ucont);
  DMDAVecGetArray(user->da, user->lNvert, &nvert);
  DMDAVecGetArray(user->da, user->lAj, &aj);
 
 
   LOG_ALLOW(GLOBAL, LOG_DEBUG, "Computing RHS values for each cell.\n");
  
  for (k=zs; k<ze; k++) { 
    for (j=ys; j<ye; j++) {
      for (i=xs; i<xe; i++) {
 
    if (i==0 || i==mx-1 || j==0 || j==my-1 ||  k==0 || k==mz-1) {
      rb[k][j][i] = 0.;
    }
    else if (nvert[k][j][i] > 0.1) {
      rb[k][j][i] = 0;
    }
    else {
      rb[k][j][i] = -(ucont[k][j][i].x - ucont[k][j][i-1].x +
              ucont[k][j][i].y - ucont[k][j-1][i].y +
              ucont[k][j][i].z - ucont[k-1][j][i].z) / dt
        * aj[k][j][i] / user->simCtx->st * COEF_TIME_ACCURACY;
     
    }
      }
    }
  }
 
 
  // --- Check the solvability condition for the Poisson equation ---
  // The global sum of the RHS (proportional to the total divergence) must be zero.
  LOG_ALLOW(GLOBAL, LOG_DEBUG, "Verifying solvability condition (sum of RHS terms).\n");
  PetscReal lsum=0., sum=0.;
 
  for (k=zs; k<ze; k++) {
    for (j=ys; j<ye; j++) {
      for (i=xs; i<xe; i++) {
    
    lsum += rb[k][j][i] / aj[k][j][i]* dt/COEF_TIME_ACCURACY;
 
      }
    }
  }
  
  MPI_Allreduce(&lsum,&sum,1,MPI_DOUBLE,MPI_SUM, PETSC_COMM_WORLD);
 
  LOG_ALLOW(GLOBAL, LOG_INFO, "Global Sum of RHS (Divergence Check): %le\n", sum);
 
  user->simCtx->summationRHS = sum;
    
  DMDAVecRestoreArray(user->fda, user->lUcont, &ucont);
  DMDAVecRestoreArray(user->da, user->lNvert, &nvert);
  DMDAVecRestoreArray(user->da, user->lAj, &aj);
  DMDAVecRestoreArray(user->da, B, &rb);
 
 
  PROFILE_FUNCTION_END;
  return 0;
}

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UpdatePressure()

PetscErrorCode UpdatePressure ( UserCtx *  user )

extern

Updates the pressure field P with the pressure correction Phi computed by the Poisson solver.

(P = P + Phi)

Parameters

user	The UserCtx containing the P and Phi vectors.

Returns

PetscErrorCode 0 on success.

Updates the pressure field P with the pressure correction Phi computed by the Poisson solver.

This function is a core part of the projection method in a CFD solver. It is called after the Pressure Poisson Equation has been solved to obtain a pressure correction field, Phi.

The function performs two main operations:

1. Core Pressure Update: It updates the main pressure field P by adding the pressure correction Phi at every grid point in the fluid domain. The operation is P_new = P_old + Phi.
2. Periodic Boundary Synchronization: If any of the domain boundaries are periodic (bctype == 7), this function manually updates the pressure values in the ghost cells. It copies values from the physical cells on one side of the domain to the corresponding ghost cells on the opposite side. This ensures that subsequent calculations involving pressure gradients are correct across periodic boundaries. The refactored version consolidates the original code's redundant updates into a single, efficient pass.

Parameters

[in,out]

user

Pointer to the UserCtx struct, containing simulation context and the pressure vectors P and Phi.

Returns

PetscErrorCode 0 on success, or a non-zero error code on failure.

Definition at line 1502 of file poisson.c.

{
  PetscFunctionBeginUser;
  PROFILE_FUNCTION_BEGIN;
  LOG_ALLOW(GLOBAL, LOG_DEBUG, "Entering UpdatePressure.\n");
 
  //================================================================================
  // Section 1: Initialization and Data Acquisition
  //================================================================================
  DM da = user->da;
  DMDALocalInfo info = user->info;
 
  // Local grid extents for the main update loop
  PetscInt xs = info.xs, xe = info.xs + info.xm;
  PetscInt ys = info.ys, ye = info.ys + info.ym;
  PetscInt zs = info.zs, ze = info.zs + info.zm;
  PetscInt mx = info.mx, my = info.my, mz = info.mz;
 
  PetscInt i,j,k;
 
  // --- Get direct pointer access to PETSc vector data for performance ---
  PetscReal ***p, ***phi;
  DMDAVecGetArray(da, user->P, &p);
  DMDAVecGetArray(da, user->Phi, &phi);
 
  //================================================================================
  // Section 2: Core Pressure Update
  //================================================================================
  LOG_ALLOW(GLOBAL, LOG_DEBUG, "Performing core pressure update (P_new = P_old + Phi).\n");
  for (PetscInt k = zs; k < ze; k++) {
    for (PetscInt j = ys; j < ye; j++) {
      for (PetscInt i = xs; i < xe; i++) {
        // This is the fundamental pressure update in a projection method.
        p[k][j][i] += phi[k][j][i];
      }
    }
  }
 
  // Restore arrays now that the core computation is done.
  DMDAVecRestoreArray(da, user->Phi, &phi);
  DMDAVecRestoreArray(da, user->P, &p);
 
  
  //================================================================================
  // Section 3: Handle Periodic Boundary Condition Synchronization
  //================================================================================
  // This block is executed only if at least one boundary is periodic.
  // The original code contained many redundant Get/Restore and update calls.
  // This refactored version performs the same effective logic but in a single,
  // efficient pass, which is numerically equivalent and much cleaner.
  if (user->bctype[0] == 7 || user->bctype[1] == 7 ||
      user->bctype[2] == 7 || user->bctype[3] == 7 ||
      user->bctype[4] == 7 || user->bctype[5] == 7)
  {
    LOG_ALLOW(GLOBAL, LOG_DEBUG, "Synchronizing ghost cells for periodic boundaries.\n");
 
    // First, update the local vectors (including ghost regions) with the new global data.
    DMGlobalToLocalBegin(da, user->P, INSERT_VALUES, user->lP);
    DMGlobalToLocalEnd(da, user->P, INSERT_VALUES, user->lP);
    DMGlobalToLocalBegin(da, user->Phi, INSERT_VALUES, user->lPhi);
    DMGlobalToLocalEnd(da, user->Phi, INSERT_VALUES, user->lPhi);
 
    // Get pointers to all necessary local and global arrays ONCE.
    PetscReal ***lp, ***lphi;
    DMDAVecGetArray(da, user->lP, &lp);
    DMDAVecGetArray(da, user->lPhi, &lphi);
    DMDAVecGetArray(da, user->P, &p);
    DMDAVecGetArray(da, user->Phi, &phi);
 
    // --- X-Direction Periodic Update ---
    if (user->bctype[0] == 7 || user->bctype[1] == 7) {
      // Update left boundary physical cells from right boundary ghost cells
      if (xs == 0) {
        PetscInt i = 0;
        for (k = zs; k < ze; k++) {
          for (j = ys; j < ye; j++) {
            // Note: Accessing lp[...][i-2] reads from the ghost cell region.
            p[k][j][i] = lp[k][j][i - 2];
            phi[k][j][i] = lphi[k][j][i - 2];
          }
        }
      }
      // Update right boundary physical cells from left boundary ghost cells
      if (xe == mx) {
        PetscInt i = mx - 1;
        for (k = zs; k < ze; k++) {
          for (j = ys; j < ye; j++) {
            p[k][j][i] = lp[k][j][i + 2];
            phi[k][j][i] = lphi[k][j][i + 2];
          }
        }
      }
    }
 
    // --- Y-Direction Periodic Update ---
    if (user->bctype[2] == 7 || user->bctype[3] == 7) {
      // Update bottom boundary
      if (ys == 0) {
        PetscInt j = 0;
        for (k = zs; k < ze; k++) {
          for (i = xs; i < xe; i++) {
            p[k][j][i] = lp[k][j - 2][i];
            phi[k][j][i] = lphi[k][j - 2][i];
          }
        }
      }
      // Update top boundary
      if (ye == my) {
        PetscInt j = my - 1;
        for (k = zs; k < ze; k++) {
          for (i = xs; i < xe; i++) {
            p[k][j][i] = lp[k][j + 2][i];
            phi[k][j][i] = lphi[k][j + 2][i];
          }
        }
      }
    }
 
    // --- Z-Direction Periodic Update ---
    if (user->bctype[4] == 7 || user->bctype[5] == 7) {
      // Update front boundary
      if (zs == 0) {
        PetscInt k = 0;
        for (j = ys; j < ye; j++) {
          for (i = xs; i < xe; i++) {
            p[k][j][i] = lp[k - 2][j][i];
            phi[k][j][i] = lphi[k - 2][j][i];
          }
        }
      }
      // Update back boundary
      if (ze == mz) {
        PetscInt k = mz - 1;
        for (j = ys; j < ye; j++) {
          for (i = xs; i < xe; i++) {
            p[k][j][i] = lp[k + 2][j][i];
            phi[k][j][i] = lphi[k + 2][j][i];
          }
        }
      }
    }
    
    // Restore all arrays ONCE.
    DMDAVecRestoreArray(da, user->lP, &lp);
    DMDAVecRestoreArray(da, user->lPhi, &lphi);
    DMDAVecRestoreArray(da, user->P, &p);
    DMDAVecRestoreArray(da, user->Phi, &phi);
 
    // After manually updating the physical boundary cells, we must call
    // DMGlobalToLocal again to ensure all processes have the updated ghost
    // values for the *next* function that needs them.
    DMGlobalToLocalBegin(da, user->P, INSERT_VALUES, user->lP);
    DMGlobalToLocalEnd(da, user->P, INSERT_VALUES, user->lP);
    DMGlobalToLocalBegin(da, user->Phi, INSERT_VALUES, user->lPhi);
    DMGlobalToLocalEnd(da, user->Phi, INSERT_VALUES, user->lPhi);
  }
  
  //================================================================================
  // Section 4: Final Cleanup (pointers already restored)
  //================================================================================
 
  UpdateLocalGhosts(user,"P");
  UpdateLocalGhosts(user,"Phi");
  
  LOG_ALLOW(GLOBAL, LOG_DEBUG, "Exiting UpdatePressure.\n");
  PROFILE_FUNCTION_END;
  PetscFunctionReturn(0);
}

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Projection()

PetscErrorCode Projection ( UserCtx *  user )

extern

Corrects the contravariant velocity field Ucont to be divergence-free using the gradient of the pressure correction field Phi.

Parameters

user	The UserCtx containing the Ucont and Phi vectors.

Returns

PetscErrorCode 0 on success.

Corrects the contravariant velocity field Ucont to be divergence-free using the gradient of the pressure correction field Phi.

This function executes the final "correction" stage of a fractional-step (projection) method for solving the incompressible Navier-Stokes equations. After solving the Pressure Poisson Equation to get a pressure correction Phi, this function uses Phi to correct the intermediate velocity field, making it divergence-free.

The main steps are:

1. Calculate Pressure Gradient: At each velocity point (on the cell faces), it computes the gradient of the pressure correction field (∇Φ). This is done using finite differences on a generalized curvilinear grid.
2. Correct Velocity Field: It updates the contravariant velocity components Ucont by subtracting the scaled pressure gradient. The update rule is: U_new = U_intermediate - Δt * G * ∇Φ, where G is the metric tensor g_ij that transforms the gradient into contravariant components.
3. Boundary-Aware Gradients: The gradient calculation is highly sensitive to boundaries. The code uses complex, dynamic stencils that switch from centered differences to one-sided differences if a standard stencil would use a point inside an immersed solid (nvert > 0.1). This preserves accuracy at the fluid-solid interface.
4. Periodic Boundary Updates: Includes dedicated loops to correctly calculate the pressure gradient at the domain edges for periodic boundary conditions.
5. Finalization: After correcting Ucont, it calls helper functions to convert the velocity back to Cartesian coordinates (Contra2Cart) and update all ghost cell values.

Parameters

[in,out]

user

Pointer to the UserCtx struct, containing simulation context, grid metrics, and the velocity/pressure fields.

Returns

PetscErrorCode 0 on success, or a non-zero error code on failure.

Definition at line 948 of file poisson.c.

{
  PetscFunctionBeginUser;
  PROFILE_FUNCTION_BEGIN;  
  LOG_ALLOW(GLOBAL, LOG_DEBUG, "Entering Projection step to correct velocity field.\n");
 
  //================================================================================
  // Section 1: Initialization and Data Acquisition
  //================================================================================
 
  // --- Get simulation and grid context ---
  SimCtx *simCtx = user->simCtx;
  DM da = user->da, fda = user->fda;
  DMDALocalInfo info = user->info;
 
  // --- Grid dimensions ---
  PetscInt mx = info.mx, my = info.my, mz = info.mz;
  PetscInt xs = info.xs, xe = info.xs + info.xm;
  PetscInt ys = info.ys, ye = info.ys + info.ym;
  PetscInt zs = info.zs, ze = info.zs + info.zm;
 
  // --- Loop bounds (excluding outer ghost layers) ---
  PetscInt lxs = (xs == 0) ? xs + 1 : xs;
  PetscInt lxe = (xe == mx) ? xe - 1 : xe;
  PetscInt lys = (ys == 0) ? ys + 1 : ys;
  PetscInt lye = (ye == my) ? ye - 1 : ye;
  PetscInt lzs = (zs == 0) ? zs + 1 : zs;
  PetscInt lze = (ze == mz) ? ze - 1 : ze;
 
  // --- Get direct pointer access to grid metric and field data ---
  Cmpnts ***icsi, ***ieta, ***izet, ***jcsi, ***jeta, ***jzet, ***kcsi, ***keta, ***kzet;
  PetscReal ***iaj, ***jaj, ***kaj, ***p, ***nvert;
  Cmpnts ***ucont;
  DMDAVecGetArray(fda, user->lICsi, &icsi); DMDAVecGetArray(fda, user->lIEta, &ieta); DMDAVecGetArray(fda, user->lIZet, &izet);
  DMDAVecGetArray(fda, user->lJCsi, &jcsi); DMDAVecGetArray(fda, user->lJEta, &jeta); DMDAVecGetArray(fda, user->lJZet, &jzet);
  DMDAVecGetArray(fda, user->lKCsi, &kcsi); DMDAVecGetArray(fda, user->lKEta, &keta); DMDAVecGetArray(fda, user->lKZet, &kzet);
  DMDAVecGetArray(da, user->lIAj, &iaj); DMDAVecGetArray(da, user->lJAj, &jaj); DMDAVecGetArray(da, user->lKAj, &kaj);
  DMDAVecGetArray(da, user->lNvert, &nvert);
  DMDAVecGetArray(da, user->lPhi, &p); // Note: using lPhi, which is the pressure correction
  //DMDAVecGetArray(da,user->lP,&p);
  DMDAVecGetArray(fda, user->Ucont, &ucont);
 
  // --- Constants for clarity ---
  const PetscReal IBM_FLUID_THRESHOLD = 0.1;
  const PetscReal scale = simCtx->dt * simCtx->st / COEF_TIME_ACCURACY;
 
  LOG_ALLOW(GLOBAL,LOG_DEBUG," Starting velocity correction: Scale = %le .\n",scale);
 
  //================================================================================
  // Section 2: Correct Velocity Components
  //================================================================================
  LOG_ALLOW(GLOBAL, LOG_DEBUG, "Calculating pressure gradients and correcting velocity components.\n");
  
  // --- Main loop over interior domain points ---
  for (PetscInt k = lzs; k < lze; k++) {
    for (PetscInt j = lys; j < lye; j++) {
      for (PetscInt i = lxs; i < lxe; i++) {
 
        // --- Correct U_contravariant (x-component of velocity) ---
        PetscInt i_end = (user->bctype[0] == 7) ? mx - 1 : mx - 2;
        if (i < i_end) {
      
          if (!(nvert[k][j][i] > IBM_FLUID_THRESHOLD || nvert[k][j][i + 1] > IBM_FLUID_THRESHOLD)) {
            // Compute pressure derivatives (dp/d_csi, dp/d_eta, dp/d_zet) at the i-face
 
        PetscReal dpdc = p[k][j][i + 1] - p[k][j][i];
            PetscReal dpde = 0.0, dpdz = 0.0;
 
            // Boundary-aware stencil for dp/d_eta
          if ((j==my-2 && user->bctype[2]!=7)|| nvert[k][j+1][i]+nvert[k][j+1][i+1] > 0.1) {
        if (nvert[k][j-1][i] + nvert[k][j-1][i+1] < 0.1 && (j!=1 || (j==1 && user->bctype[2]==7))) {
          dpde = (p[k][j][i] + p[k][j][i+1] -
              p[k][j-1][i] - p[k][j-1][i+1]) * 0.5;
        }
          }
 
          else if ((j==my-2 || j==1) && user->bctype[2]==7 && nvert[k][j+1][i]+nvert[k][j+1][i+1] > 0.1) {
        if (nvert[k][j-1][i] + nvert[k][j-1][i+1] < 0.1) { dpde = (p[k][j][i] + p[k][j][i+1] - p[k][j-1][i] - p[k][j-1][i+1]) * 0.5; }
          }
 
          else if ((j == 1 && user->bctype[2]!=7) || nvert[k][j-1][i] + nvert[k][j-1][i+1] > 0.1) {
        if (nvert[k][j+1][i] + nvert[k][j+1][i+1] < 0.1) { dpde = (p[k][j+1][i] + p[k][j+1][i+1] - p[k][j][i] - p[k][j][i+1]) * 0.5; }
          }
 
          else if ((j == 1 || j==my-2) && user->bctype[2]==7 && nvert[k][j-1][i] + nvert[k][j-1][i+1] > 0.1) {
        if (nvert[k][j+1][i] + nvert[k][j+1][i+1] < 0.1) { dpde = (p[k][j+1][i] + p[k][j+1][i+1] - p[k][j][i] - p[k][j][i+1]) * 0.5; }
          }
 
          else { dpde = (p[k][j+1][i] + p[k][j+1][i+1] - p[k][j-1][i] - p[k][j-1][i+1]) * 0.25; }
 
            // Boundary-aware stencil for dp/d_zet
          if ((k == mz-2 && user->bctype[4]!=7) || nvert[k+1][j][i] + nvert[k+1][j][i+1] > 0.1) {
        if (nvert[k-1][j][i] + nvert[k-1][j][i+1] < 0.1 && (k!=1 || (k==1 && user->bctype[4]==7))) { dpdz = (p[k][j][i] + p[k][j][i+1] - p[k-1][j][i] - p[k-1][j][i+1]) * 0.5; }
          }
 
          else  if ((k == mz-2 || k==1) && user->bctype[4]==7 && nvert[k+1][j][i] + nvert[k+1][j][i+1] > 0.1) {
        if (nvert[k-1][j][i] + nvert[k-1][j][i+1] < 0.1) { dpdz = (p[k][j][i] + p[k][j][i+1] - p[k-1][j][i] - p[k-1][j][i+1]) * 0.5; }
          }
 
          else if ((k == 1 && user->bctype[4]!=7)|| nvert[k-1][j][i] + nvert[k-1][j][i+1] > 0.1) {
        if (nvert[k+1][j][i] + nvert[k+1][j][i+1] < 0.1) { dpdz = (p[k+1][j][i] + p[k+1][j][i+1] - p[k][j][i] - p[k][j][i+1]) * 0.5; }
          }
 
          else if ((k == 1 || k==mz-2) && user->bctype[4]==7 && nvert[k-1][j][i] + nvert[k-1][j][i+1] > 0.1) {
        if (nvert[k+1][j][i] + nvert[k+1][j][i+1] < 0.1) { dpdz = (p[k+1][j][i] + p[k+1][j][i+1] - p[k][j][i] - p[k][j][i+1]) * 0.5; }
          }
 
          else { dpdz = (p[k+1][j][i] + p[k+1][j][i+1] - p[k-1][j][i] - p[k-1][j][i+1]) * 0.25; }
 
            // Apply the correction: U_new = U_old - dt * (g11*dpdc + g12*dpde + g13*dpdz)
 
            
          
            PetscReal grad_p_x = (dpdc * (icsi[k][j][i].x * icsi[k][j][i].x + icsi[k][j][i].y * icsi[k][j][i].y
                      + icsi[k][j][i].z * icsi[k][j][i].z) * iaj[k][j][i] +
                                dpde * (ieta[k][j][i].x * icsi[k][j][i].x + ieta[k][j][i].y * icsi[k][j][i].y
                    + ieta[k][j][i].z * icsi[k][j][i].z) * iaj[k][j][i] +
                                dpdz * (izet[k][j][i].x * icsi[k][j][i].x + izet[k][j][i].y * icsi[k][j][i].y
                    + izet[k][j][i].z * icsi[k][j][i].z) * iaj[k][j][i]);
 
        PetscReal correction = grad_p_x*scale;
        //LOG_LOOP_ALLOW_EXACT(GLOBAL,LOG_DEBUG,k,5," Flux correction in Csi Direction: %le.\n",correction);
        ucont[k][j][i].x -= correction;
 
          }
        }
 
        // --- Correct V_contravariant (y-component of velocity) ---
        PetscInt j_end = (user->bctype[2] == 7) ? my - 1 : my - 2;
        if (j < j_end) {
          if (!(nvert[k][j][i] > IBM_FLUID_THRESHOLD || nvert[k][j + 1][i] > IBM_FLUID_THRESHOLD)) {
            PetscReal dpdc = 0.0, dpde = 0.0, dpdz = 0.0;
            dpde = p[k][j + 1][i] - p[k][j][i];
 
            // Boundary-aware stencil for dp/d_csi
          if ((i == mx-2 && user->bctype[0]!=7) || nvert[k][j][i+1] + nvert[k][j+1][i+1] > 0.1) {
        if (nvert[k][j][i-1] + nvert[k][j+1][i-1] < 0.1 && (i!=1 || (i==1 && user->bctype[0]==7))) { dpdc = (p[k][j][i] + p[k][j+1][i] - p[k][j][i-1] - p[k][j+1][i-1]) * 0.5; }
          } else if ((i == mx-2 || i==1) && user->bctype[0]==7 && nvert[k][j][i+1] + nvert[k][j+1][i+1] > 0.1) {
        if (nvert[k][j][i-1] + nvert[k][j+1][i-1] < 0.1) { dpdc = (p[k][j][i] + p[k][j+1][i] - p[k][j][i-1] - p[k][j+1][i-1]) * 0.5; }
          } else if ((i == 1 && user->bctype[0]!=7)|| nvert[k][j][i-1] + nvert[k][j+1][i-1] > 0.1) {
        if (nvert[k][j][i+1] + nvert[k][j+1][i+1] < 0.1) { dpdc = (p[k][j][i+1] + p[k][j+1][i+1] - p[k][j][i] - p[k][j+1][i]) * 0.5; }
          } else if ((i == 1 || i==mx-2) && user->bctype[0]==7 && nvert[k][j][i-1] + nvert[k][j+1][i-1] > 0.1) {
        if (nvert[k][j][i+1] + nvert[k][j+1][i+1] < 0.1) { dpdc = (p[k][j][i+1] + p[k][j+1][i+1] - p[k][j][i] - p[k][j+1][i]) * 0.5; }
          } else { dpdc = (p[k][j][i+1] + p[k][j+1][i+1] - p[k][j][i-1] - p[k][j+1][i-1]) * 0.25; }
 
            // Boundary-aware stencil for dp/d_zet
          if ((k == mz-2 && user->bctype[4]!=7)|| nvert[k+1][j][i] + nvert[k+1][j+1][i] > 0.1) {
        if (nvert[k-1][j][i] + nvert[k-1][j+1][i] < 0.1 && (k!=1 || (k==1 && user->bctype[4]==7))) { dpdz = (p[k][j][i] + p[k][j+1][i] - p[k-1][j][i] - p[k-1][j+1][i]) * 0.5; }
          } else if ((k == mz-2 || k==1 ) && user->bctype[4]==7 && nvert[k+1][j][i] + nvert[k+1][j+1][i] > 0.1) {
        if (nvert[k-1][j][i] + nvert[k-1][j+1][i] < 0.1) { dpdz = (p[k][j][i] + p[k][j+1][i] - p[k-1][j][i] - p[k-1][j+1][i]) * 0.5; }
          } else if ((k == 1 && user->bctype[4]!=7)|| nvert[k-1][j][i] + nvert[k-1][j+1][i] > 0.1) {
        if (nvert[k+1][j][i] + nvert[k+1][j+1][i] < 0.1) { dpdz = (p[k+1][j][i] + p[k+1][j+1][i] - p[k][j][i] - p[k][j+1][i]) * 0.5; }
          } else if ((k == 1 || k==mz-2) && user->bctype[4]==7 && nvert[k-1][j][i] + nvert[k-1][j+1][i] > 0.1) {
        if (nvert[k+1][j][i] + nvert[k+1][j+1][i] < 0.1) { dpdz = (p[k+1][j][i] + p[k+1][j+1][i] - p[k][j][i] - p[k][j+1][i]) * 0.5; }
          } else { dpdz = (p[k+1][j][i] + p[k+1][j+1][i] - p[k-1][j][i] - p[k-1][j+1][i]) * 0.25; }
 
            PetscReal grad_p_y = (dpdc * (jcsi[k][j][i].x * jeta[k][j][i].x + jcsi[k][j][i].y * jeta[k][j][i].y + jcsi[k][j][i].z * jeta[k][j][i].z) * jaj[k][j][i] +
                                dpde * (jeta[k][j][i].x * jeta[k][j][i].x + jeta[k][j][i].y * jeta[k][j][i].y + jeta[k][j][i].z * jeta[k][j][i].z) * jaj[k][j][i] +
                                dpdz * (jzet[k][j][i].x * jeta[k][j][i].x + jzet[k][j][i].y * jeta[k][j][i].y + jzet[k][j][i].z * jeta[k][j][i].z) * jaj[k][j][i]);
 
        PetscReal correction = grad_p_y*scale;
        //LOG_LOOP_ALLOW_EXACT(GLOBAL,LOG_DEBUG,k,5," Flux correction in Eta Direction: %le.\n",correction);
            ucont[k][j][i].y -= correction;
          }
        }
        
        // --- Correct W_contravariant (z-component of velocity) ---
        PetscInt k_end = (user->bctype[4] == 7) ? mz - 1 : mz - 2;
        if (k < k_end) {
          if (!(nvert[k][j][i] > IBM_FLUID_THRESHOLD || nvert[k + 1][j][i] > IBM_FLUID_THRESHOLD)) {
            PetscReal dpdc = 0.0, dpde = 0.0, dpdz = 0.0;
            dpdz = p[k + 1][j][i] - p[k][j][i];
            
            // Boundary-aware stencil for dp/d_csi
          if ((i == mx-2 && user->bctype[0]!=7)|| nvert[k][j][i+1] + nvert[k+1][j][i+1] > 0.1) {
        if (nvert[k][j][i-1] + nvert[k+1][j][i-1] < 0.1 && (i!=1 || (i==1 && user->bctype[0]==7))) { dpdc = (p[k][j][i] + p[k+1][j][i] - p[k][j][i-1] - p[k+1][j][i-1]) * 0.5; }
          } else if ((i == mx-2 || i==1) && user->bctype[0]==7 && nvert[k][j][i+1] + nvert[k+1][j][i+1] > 0.1) {
        if (nvert[k][j][i-1] + nvert[k+1][j][i-1] < 0.1) { dpdc = (p[k][j][i] + p[k+1][j][i] - p[k][j][i-1] - p[k+1][j][i-1]) * 0.5; }
          } else if ((i == 1 && user->bctype[0]!=7)|| nvert[k][j][i-1] + nvert[k+1][j][i-1] > 0.1) {
        if (nvert[k][j][i+1] + nvert[k+1][j][i+1] < 0.1) { dpdc = (p[k][j][i+1] + p[k+1][j][i+1] - p[k][j][i] - p[k+1][j][i]) * 0.5; }
          } else if ((i == 1 || i==mx-2) && user->bctype[0]==7 && nvert[k][j][i-1] + nvert[k+1][j][i-1] > 0.1) {
        if (nvert[k][j][i+1] + nvert[k+1][j][i+1] < 0.1) { dpdc = (p[k][j][i+1] + p[k+1][j][i+1] - p[k][j][i] - p[k+1][j][i]) * 0.5; }
          } else { dpdc = (p[k][j][i+1] + p[k+1][j][i+1] - p[k][j][i-1] - p[k+1][j][i-1]) * 0.25; }
 
            // Boundary-aware stencil for dp/d_eta
          if ((j == my-2 && user->bctype[2]!=7)|| nvert[k][j+1][i] + nvert[k+1][j+1][i] > 0.1) {
        if (nvert[k][j-1][i] + nvert[k+1][j-1][i] < 0.1 && (j!=1 || (j==1 && user->bctype[2]==7))) { dpde = (p[k][j][i] + p[k+1][j][i] - p[k][j-1][i] - p[k+1][j-1][i]) * 0.5; }
          } else  if ((j == my-2 || j==1) && user->bctype[2]==7 && nvert[k][j+1][i] + nvert[k+1][j+1][i] > 0.1) {
        if (nvert[k][j-1][i] + nvert[k+1][j-1][i] < 0.1) { dpde = (p[k][j][i] + p[k+1][j][i] - p[k][j-1][i] - p[k+1][j-1][i]) * 0.5; }
          } else if ((j == 1 && user->bctype[2]!=7)|| nvert[k][j-1][i] + nvert[k+1][j-1][i] > 0.1) {
        if (nvert[k][j+1][i] + nvert[k+1][j+1][i] < 0.1) { dpde = (p[k][j+1][i] + p[k+1][j+1][i] - p[k][j][i] - p[k+1][j][i]) * 0.5; }
          } else if ((j == 1 || j==my-2) && user->bctype[2]==7 && nvert[k][j-1][i] + nvert[k+1][j-1][i] > 0.1) {
        if (nvert[k][j+1][i] + nvert[k+1][j+1][i] < 0.1) { dpde = (p[k][j+1][i] + p[k+1][j+1][i] - p[k][j][i] - p[k+1][j][i]) * 0.5; }
          } else { dpde = (p[k][j+1][i] + p[k+1][j+1][i] - p[k][j-1][i] - p[k+1][j-1][i]) * 0.25; }
 
            PetscReal grad_p_z = (dpdc * (kcsi[k][j][i].x * kzet[k][j][i].x + kcsi[k][j][i].y * kzet[k][j][i].y + kcsi[k][j][i].z * kzet[k][j][i].z) * kaj[k][j][i] +
                                dpde * (keta[k][j][i].x * kzet[k][j][i].x + keta[k][j][i].y * kzet[k][j][i].y + keta[k][j][i].z * kzet[k][j][i].z) * kaj[k][j][i] +
                                dpdz * (kzet[k][j][i].x * kzet[k][j][i].x + kzet[k][j][i].y * kzet[k][j][i].y + kzet[k][j][i].z * kzet[k][j][i].z) * kaj[k][j][i]);
 
        // ========================= DEBUG PRINT  =========================
        LOG_LOOP_ALLOW_EXACT(GLOBAL, LOG_DEBUG, k, 5,
                 "[k=%d, j=%d, i=%d] ---- Neighbor Pressures ----\n"
                 "  Central Z-Neighbors: p[k+1][j][i] = %g | p[k][j][i] = %g\n"
                 "  Eta-Stencil (Y-dir): p[k][j-1][i] = %g, p[k+1][j-1][i] = %g | p[k][j+1][i] = %g, p[k+1][j+1][i] = %g\n"
                 "  Csi-Stencil (X-dir): p[k][j][i-1] = %g, p[k+1][j][i-1] = %g | p[k][j][i+1] = %g, p[k+1][j][i+1] = %g\n",
                 k, j, i,
                 p[k + 1][j][i], p[k][j][i],
                 p[k][j - 1][i], p[k + 1][j - 1][i], p[k][j + 1][i], p[k + 1][j + 1][i],
                 p[k][j][i - 1], p[k + 1][j][i - 1], p[k][j][i + 1], p[k + 1][j][i + 1]);
        // ======================= END DEBUG PRINT =======================
 
        LOG_LOOP_ALLOW_EXACT(GLOBAL,LOG_DEBUG,k,5," dpdc: %le | dpde: %le | dpdz: %le.\n",dpdc,dpde,dpdz);      
        PetscReal correction = grad_p_z*scale;
        //LOG_LOOP_ALLOW_EXACT(GLOBAL,LOG_DEBUG,k,5," Flux correction in Zet Direction: %le.\n",correction);
            ucont[k][j][i].z -= correction;
          }
        }
      }
    }
  }
 
  // --- Explicit correction for periodic boundaries (if necessary) ---
  // The main loop handles the interior, but this handles the first physical layer at periodic boundaries.
  // Note: This logic is largely duplicated from the main loop and could be merged, but is preserved for fidelity.
  if (user->bctype[0] == 7 && xs == 0) {
    for (PetscInt k=lzs; k<lze; k++) {
      for (PetscInt j=lys; j<lye; j++) {
    PetscInt i=xs;
    
    PetscReal dpdc = p[k][j][i+1] - p[k][j][i];
    
    PetscReal dpde = 0.;
    PetscReal dpdz = 0.;
        
    if ((j==my-2 && user->bctype[2]!=7)|| nvert[k][j+1][i]+nvert[k][j+1][i+1] > 0.1) {
      if (nvert[k][j-1][i] + nvert[k][j-1][i+1] < 0.1 && (j!=1 || (j==1 && user->bctype[2]==7))) {
        dpde = (p[k][j  ][i] + p[k][j  ][i+1] -
            p[k][j-1][i] - p[k][j-1][i+1]) * 0.5;
      }
    }
    else if ((j==my-2 || j==1) && user->bctype[2]==7 && nvert[k][j+1][i]+nvert[k][j+1][i+1] > 0.1) {
      if (nvert[k][j-1][i] + nvert[k][j-1][i+1] < 0.1) {
        dpde = (p[k][j  ][i] + p[k][j  ][i+1] -
            p[k][j-1][i] - p[k][j-1][i+1]) * 0.5;
      }
    }
    else if ((j == 1 && user->bctype[2]!=7) || nvert[k][j-1][i] + nvert[k][j-1][i+1] > 0.1) {
      if (nvert[k][j+1][i] + nvert[k][j+1][i+1] < 0.1) {
        dpde = (p[k][j+1][i] + p[k][j+1][i+1] -
            p[k][j  ][i] - p[k][j  ][i+1]) * 0.5;
      }
    }
    else if ((j == 1 || j==my-2) && user->bctype[2]==7 && nvert[k][j-1][i] + nvert[k][j-1][i+1] > 0.1) {
      if (nvert[k][j+1][i] + nvert[k][j+1][i+1] < 0.1) {
        dpde = (p[k][j+1][i] + p[k][j+1][i+1] -
            p[k][j  ][i] - p[k][j  ][i+1]) * 0.5;
      }
    }
    else {
      dpde = (p[k][j+1][i] + p[k][j+1][i+1] -
          p[k][j-1][i] - p[k][j-1][i+1]) * 0.25;
    }
    
    if ((k == mz-2 && user->bctype[4]!=7) || nvert[k+1][j][i] + nvert[k+1][j][i+1] > 0.1) {
      if (nvert[k-1][j][i] + nvert[k-1][j][i+1] < 0.1 && (k!=1 || (k==1 && user->bctype[4]==7))) {
        dpdz = (p[k  ][j][i] + p[k  ][j][i+1] -
            p[k-1][j][i] - p[k-1][j][i+1]) * 0.5;
      }
    }
    else  if ((k == mz-2 || k==1) && user->bctype[4]==7 && nvert[k+1][j][i] + nvert[k+1][j][i+1] > 0.1) {
      if (nvert[k-1][j][i] + nvert[k-1][j][i+1] < 0.1) {
        dpdz = (p[k  ][j][i] + p[k  ][j][i+1] -
            p[k-1][j][i] - p[k-1][j][i+1]) * 0.5;
      }
    }
    else if ((k == 1 && user->bctype[4]!=7)|| nvert[k-1][j][i] + nvert[k-1][j][i+1] > 0.1) {
      if (nvert[k+1][j][i] + nvert[k+1][j][i+1] < 0.1) {
        dpdz = (p[k+1][j][i] + p[k+1][j][i+1] -
            p[k  ][j][i] - p[k  ][j][i+1]) * 0.5;
      }
    }
    else if ((k == 1 || k==mz-2) && user->bctype[4]==7 && nvert[k-1][j][i] + nvert[k-1][j][i+1] > 0.1) {
      if (nvert[k+1][j][i] + nvert[k+1][j][i+1] < 0.1) {
        dpdz = (p[k+1][j][i] + p[k+1][j][i+1] -
            p[k  ][j][i] - p[k  ][j][i+1]) * 0.5;
      }
    }
    else {
      dpdz = (p[k+1][j][i] + p[k+1][j][i+1] -
          p[k-1][j][i] - p[k-1][j][i+1]) * 0.25;
    }
    
    
    
    if (!(nvert[k][j][i] + nvert[k][j][i+1])) {
      ucont[k][j][i].x -=
        (dpdc * (icsi[k][j][i].x * icsi[k][j][i].x +
             icsi[k][j][i].y * icsi[k][j][i].y +
             icsi[k][j][i].z * icsi[k][j][i].z) * iaj[k][j][i] +
         dpde * (ieta[k][j][i].x * icsi[k][j][i].x +
             ieta[k][j][i].y * icsi[k][j][i].y +
             ieta[k][j][i].z * icsi[k][j][i].z) * iaj[k][j][i] +
         dpdz * (izet[k][j][i].x * icsi[k][j][i].x +
             izet[k][j][i].y * icsi[k][j][i].y +
             izet[k][j][i].z * icsi[k][j][i].z) * iaj[k][j][i])
        * scale;
      
    }
      }
    } 
  }
  if (user->bctype[2] == 7 && ys == 0) {
 
    for (PetscInt k=lzs; k<lze; k++) {
      for (PetscInt i=lxs; i<lxe; i++) {
    PetscInt j=ys;
    
    PetscReal dpdc = 0.;
    PetscReal dpdz = 0.;
    if ((i == mx-2 && user->bctype[0]!=7) || nvert[k][j][i+1] + nvert[k][j+1][i+1] > 0.1) {
      if (nvert[k][j][i-1] + nvert[k][j+1][i-1] < 0.1 && (i!=1 || (i==1 && user->bctype[0]==7))) {
        dpdc = (p[k][j][i  ] + p[k][j+1][i  ] -
            p[k][j][i-1] - p[k][j+1][i-1]) * 0.5;
      }
    }
    else if ((i == mx-2 || i==1) && user->bctype[0]==7 && nvert[k][j][i+1] + nvert[k][j+1][i+1] > 0.1) {
      if (nvert[k][j][i-1] + nvert[k][j+1][i-1] < 0.1) {
        dpdc = (p[k][j][i  ] + p[k][j+1][i  ] -
            p[k][j][i-1] - p[k][j+1][i-1]) * 0.5;
      }
    }
    else if ((i == 1 && user->bctype[0]!=7)|| nvert[k][j][i-1] + nvert[k][j+1][i-1] > 0.1) {
      if (nvert[k][j][i+1] + nvert[k][j+1][i+1] < 0.1) {
        dpdc = (p[k][j][i+1] + p[k][j+1][i+1] -
            p[k][j][i  ] - p[k][j+1][i  ]) * 0.5;
      }
    }
    else if ((i == 1 || i==mx-2) && user->bctype[0]==7 && nvert[k][j][i-1] + nvert[k][j+1][i-1] > 0.1) {
      if (nvert[k][j][i+1] + nvert[k][j+1][i+1] < 0.1) {
        dpdc = (p[k][j][i+1] + p[k][j+1][i+1] -
            p[k][j][i  ] - p[k][j+1][i  ]) * 0.5;
      }
    }
    else {
      dpdc = (p[k][j][i+1] + p[k][j+1][i+1] -
          p[k][j][i-1] - p[k][j+1][i-1]) * 0.25;
    }
    
    PetscReal dpde = p[k][j+1][i] - p[k][j][i];
    
    if ((k == mz-2 && user->bctype[4]!=7)|| nvert[k+1][j][i] + nvert[k+1][j+1][i] > 0.1) {
      if (nvert[k-1][j][i] + nvert[k-1][j+1][i] < 0.1 && (k!=1 || (k==1 && user->bctype[4]==7))) {
        dpdz = (p[k  ][j][i] + p[k  ][j+1][i] -
            p[k-1][j][i] - p[k-1][j+1][i]) * 0.5;
      }
    }
    else if ((k == mz-2 || k==1 ) && user->bctype[0]==7 && nvert[k+1][j][i] + nvert[k+1][j+1][i] > 0.1) {
      if (nvert[k-1][j][i] + nvert[k-1][j+1][i] < 0.1) {
        dpdz = (p[k  ][j][i] + p[k  ][j+1][i] -
            p[k-1][j][i] - p[k-1][j+1][i]) * 0.5;
      }
    }
    else if ((k == 1 && user->bctype[4]!=7)|| nvert[k-1][j][i] + nvert[k-1][j+1][i] > 0.1) {
      if (nvert[k+1][j][i] + nvert[k+1][j+1][i] < 0.1) {
        dpdz = (p[k+1][j][i] + p[k+1][j+1][i] -
            p[k  ][j][i] - p[k  ][j+1][i]) * 0.5;
      }
    }
    else if ((k == 1 || k==mz-2) && user->bctype[4]==7 && nvert[k-1][j][i] + nvert[k-1][j+1][i] > 0.1) {
      if (nvert[k+1][j][i] + nvert[k+1][j+1][i] < 0.1) {
        dpdz = (p[k+1][j][i] + p[k+1][j+1][i] -
            p[k  ][j][i] - p[k  ][j+1][i]) * 0.5;
      }
    }
    else {
      dpdz = (p[k+1][j][i] + p[k+1][j+1][i] -
          p[k-1][j][i] - p[k-1][j+1][i]) * 0.25;
    }
        
    if (!(nvert[k][j][i] + nvert[k][j+1][i])) {
      ucont[k][j][i].y -=
        (dpdc * (jcsi[k][j][i].x * jeta[k][j][i].x +
             jcsi[k][j][i].y * jeta[k][j][i].y +
             jcsi[k][j][i].z * jeta[k][j][i].z) * jaj[k][j][i] +
         dpde * (jeta[k][j][i].x * jeta[k][j][i].x +
             jeta[k][j][i].y * jeta[k][j][i].y +
             jeta[k][j][i].z * jeta[k][j][i].z) * jaj[k][j][i] +
         dpdz * (jzet[k][j][i].x * jeta[k][j][i].x +
             jzet[k][j][i].y * jeta[k][j][i].y +
             jzet[k][j][i].z * jeta[k][j][i].z) * jaj[k][j][i])
        * scale;
    }
      }
    }
  }
 
  if (user->bctype[4] == 7 && zs == 0) {
    for (PetscInt j=lys; j<lye; j++) {
      for (PetscInt i=lxs; i<lxe; i++) {
    
    PetscInt k=zs;
    PetscReal dpdc = 0.;
    PetscReal dpde = 0.;
 
    if ((i == mx-2 && user->bctype[0]!=7)|| nvert[k][j][i+1] + nvert[k+1][j][i+1] > 0.1) {
      if (nvert[k][j][i-1] + nvert[k+1][j][i-1] < 0.1 && (i!=1 || (i==1 && user->bctype[0]==7))) {
        dpdc = (p[k][j][i  ] + p[k+1][j][i  ] -
            p[k][j][i-1] - p[k+1][j][i-1]) * 0.5;
      }
    }
    else if ((i == mx-2 || i==1) && user->bctype[0]==7 && nvert[k][j][i+1] + nvert[k+1][j][i+1] > 0.1) {
      if (nvert[k][j][i-1] + nvert[k+1][j][i-1] < 0.1) {
        dpdc = (p[k][j][i  ] + p[k+1][j][i  ] -
            p[k][j][i-1] - p[k+1][j][i-1]) * 0.5;
      }
    }
    else if ((i == 1 && user->bctype[0]!=7)|| nvert[k][j][i-1] + nvert[k+1][j][i-1] > 0.1) {
      if (nvert[k][j][i+1] + nvert[k+1][j][i+1] < 0.1) {
        dpdc = (p[k][j][i+1] + p[k+1][j][i+1] -
            p[k][j][i  ] - p[k+1][j][i  ]) * 0.5;
      }
    }
    else if ((i == 1 || i==mx-2) && user->bctype[0]==7 && nvert[k][j][i-1] + nvert[k+1][j][i-1] > 0.1) {
      if (nvert[k][j][i+1] + nvert[k+1][j][i+1] < 0.1) {
        dpdc = (p[k][j][i+1] + p[k+1][j][i+1] -
            p[k][j][i  ] - p[k+1][j][i  ]) * 0.5;
      }
    }
    else {
      dpdc = (p[k][j][i+1] + p[k+1][j][i+1] -
          p[k][j][i-1] - p[k+1][j][i-1]) * 0.25;
    }
    
    if ((j == my-2 && user->bctype[2]!=7)|| nvert[k][j+1][i] + nvert[k+1][j+1][i] > 0.1) {
      if (nvert[k][j-1][i] + nvert[k+1][j-1][i] < 0.1 && (j!=1 || (j==1 && user->bctype[2]==7))) {
        dpde = (p[k][j  ][i] + p[k+1][j  ][i] -
            p[k][j-1][i] - p[k+1][j-1][i]) * 0.5;
      }
    }
    else  if ((j == my-2 || j==1) && user->bctype[2]==7 && nvert[k][j+1][i] + nvert[k+1][j+1][i] > 0.1) {
      if (nvert[k][j-1][i] + nvert[k+1][j-1][i] < 0.1) {
        dpde = (p[k][j  ][i] + p[k+1][j  ][i] -
            p[k][j-1][i] - p[k+1][j-1][i]) * 0.5;
      }
    }
    else if ((j == 1 && user->bctype[2]!=7)|| nvert[k][j-1][i] + nvert[k+1][j-1][i] > 0.1) {
      if (nvert[k][j+1][i] + nvert[k+1][j+1][i] < 0.1) {
        dpde = (p[k][j+1][i] + p[k+1][j+1][i] -
            p[k][j  ][i] - p[k+1][j  ][i]) * 0.5;
      }
    }
    else if ((j == 1 || j==my-2) && user->bctype[2]==7 && nvert[k][j-1][i] + nvert[k+1][j-1][i] > 0.1) {
      if (nvert[k][j+1][i] + nvert[k+1][j+1][i] < 0.1) {
        dpde = (p[k][j+1][i] + p[k+1][j+1][i] -
            p[k][j  ][i] - p[k+1][j  ][i]) * 0.5;
      }
    }
    else {
      dpde = (p[k][j+1][i] + p[k+1][j+1][i] -
          p[k][j-1][i] - p[k+1][j-1][i]) * 0.25;
    }
    
    PetscReal dpdz = p[k+1][j][i] - p[k][j][i];
    
    if (!(nvert[k][j][i] + nvert[k+1][j][i])) {
      
      ucont[k][j][i].z -=
       (dpdc * (kcsi[k][j][i].x * kzet[k][j][i].x +
                   kcsi[k][j][i].y * kzet[k][j][i].y +
                   kcsi[k][j][i].z * kzet[k][j][i].z) * kaj[k][j][i] +
               dpde * (keta[k][j][i].x * kzet[k][j][i].x +
                   keta[k][j][i].y * kzet[k][j][i].y +
                   keta[k][j][i].z * kzet[k][j][i].z) * kaj[k][j][i] +
               dpdz * (kzet[k][j][i].x * kzet[k][j][i].x +
                   kzet[k][j][i].y * kzet[k][j][i].y +
                   kzet[k][j][i].z * kzet[k][j][i].z) * kaj[k][j][i])
                        * scale;
      
    }
      }
    }
  }
  
  // --- Optional: Enforce specific mass flow rate for channel flow simulations ---
  if (simCtx->channelz) {
    LOG_ALLOW(GLOBAL, LOG_DEBUG, "Applying channel flow mass flux correction.\n");
    // DMDAVecGetArray(fda, user->lCsi, &csi); DMDAVecGetArray(fda, user->lEta, &eta); DMDAVecGetArray(fda, user->lZet, &zet);
    //DMDAVecGetArray(da, user->lAj, &aj);
    // This entire block was commented out in the original code. It calculates the current
    // total flux in the z-direction, compares it to a target flux (user->simCtx->FluxInSum),
    // and computes a uniform velocity correction `ratio` to enforce the target.
    // The implementation for applying the `ratio` was also commented out.
    // Preserving this as-is.
  } 
 
  //================================================================================
  // Section 3: Finalization and Cleanup
  //================================================================================
 
  // --- Restore access to all PETSc vector arrays ---
  DMDAVecRestoreArray(fda, user->Ucont, &ucont);
  // DMDAVecRestoreArray(fda, user->lCsi, &csi); DMDAVecRestoreArray(fda, user->lEta, &eta); DMDAVecRestoreArray(fda, user->lZet, &zet);
  //DMDAVecRestoreArray(da, user->lAj, &aj);
  DMDAVecRestoreArray(fda, user->lICsi, &icsi); DMDAVecRestoreArray(fda, user->lIEta, &ieta); DMDAVecRestoreArray(fda, user->lIZet, &izet);
  DMDAVecRestoreArray(fda, user->lJCsi, &jcsi); DMDAVecRestoreArray(fda, user->lJEta, &jeta); DMDAVecRestoreArray(fda, user->lJZet, &jzet);
  DMDAVecRestoreArray(fda, user->lKCsi, &kcsi); DMDAVecRestoreArray(fda, user->lKEta, &keta); DMDAVecRestoreArray(fda, user->lKZet, &kzet);
  DMDAVecRestoreArray(da, user->lIAj, &iaj); DMDAVecRestoreArray(da, user->lJAj, &jaj); DMDAVecRestoreArray(da, user->lKAj, &kaj);
  DMDAVecRestoreArray(da, user->lP, &p);
  DMDAVecRestoreArray(da, user->lNvert, &nvert);
 
  // --- Update ghost cells for the newly corrected velocity field ---
  LOG_ALLOW(GLOBAL, LOG_DEBUG, "Updating ghost cells for corrected velocity.\n");
  DMGlobalToLocalBegin(fda, user->Ucont, INSERT_VALUES, user->lUcont);
  DMGlobalToLocalEnd(fda, user->Ucont, INSERT_VALUES, user->lUcont);
 
  // --- Convert velocity to Cartesian and update ghost nodes ---
  LOG_ALLOW(GLOBAL, LOG_DEBUG, "Converting velocity to Cartesian and finalizing ghost nodes.\n");
  Contra2Cart(user);
  GhostNodeVelocity(user);
 
  LOG_ALLOW(GLOBAL, LOG_DEBUG, "Exiting Projection step.\n");
  PROFILE_FUNCTION_END;
  PetscFunctionReturn(0);
}

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PoissonNullSpaceFunction()

PetscErrorCode PoissonNullSpaceFunction ( MatNullSpace  nullsp, Vec  X, void *  ctx  )

extern

The callback function for PETSc's MatNullSpace object.

This function removes the null space from the Poisson solution vector by ensuring the average pressure is zero, which is necessary for problems with pure Neumann boundary conditions.

Parameters

nullsp	The MatNullSpace context.
X	The vector to be corrected.
ctx	A void pointer to the UserCtx.

Returns

PetscErrorCode 0 on success.

Definition at line 1686 of file poisson.c.

{
  UserCtx *user = (UserCtx*)ctx;
 
  DM da = user->da;
 
  DMDALocalInfo info = user->info;
  PetscInt  xs = info.xs, xe = info.xs + info.xm;
  PetscInt      ys = info.ys, ye = info.ys + info.ym;
  PetscInt  zs = info.zs, ze = info.zs + info.zm;
  PetscInt  mx = info.mx, my = info.my, mz = info.mz;
  PetscInt  lxs, lxe, lys, lye, lzs, lze;
 
  PetscReal ***x, ***nvert;
  PetscInt  i, j, k;
 
/*   /\* First remove a constant from the Vec field X *\/ */
 
 
  /* Then apply boundary conditions */
  DMDAVecGetArray(da, X, &x);
  DMDAVecGetArray(da, user->lNvert, &nvert);
 
  lxs = xs; lxe = xe;
  lys = ys; lye = ye;
  lzs = zs; lze = ze;
 
  if (xs==0) lxs = xs+1;
  if (ys==0) lys = ys+1;
  if (zs==0) lzs = zs+1;
 
  if (xe==mx) lxe = xe-1;
  if (ye==my) lye = ye-1;
  if (ze==mz) lze = ze-1;
 
  PetscReal lsum, sum;
  PetscReal  lnum, num;
 
  if (user->multinullspace) PetscPrintf(PETSC_COMM_WORLD, "MultiNullSpace!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!\n");
  if (!user->multinullspace) {
    lsum = 0;
    lnum = 0;
    for (k=lzs; k<lze; k++) {
      for (j=lys; j<lye; j++) {
    for (i=lxs; i<lxe; i++) {
      if (nvert[k][j][i] < 0.1) {
        lsum += x[k][j][i];
        lnum ++;
      }
    }
      }
    }
 
    MPI_Allreduce(&lsum,&sum,1,MPI_DOUBLE,MPI_SUM,PETSC_COMM_WORLD);
    MPI_Allreduce(&lnum,&num,1,MPI_DOUBLE,MPI_SUM,PETSC_COMM_WORLD);
   /*  PetscGlobalSum(&lsum, &sum, PETSC_COMM_WORLD); */
/*     PetscGlobalSum(&lnum, &num, PETSC_COMM_WORLD); */
    sum = sum / (-1.0 * num);
 
    for (k=lzs; k<lze; k++) {
      for (j=lys; j<lye; j++) {
    for (i=lxs; i<lxe; i++) {
      if (nvert[k][j][i] < 0.1) {
        x[k][j][i] +=sum;
      }
    }
      }
    }
  }
  else {
    lsum = 0;
    lnum = 0;
    for (j=lys; j<lye; j++) {
      for (i=lxs; i<lxe; i++) {
    for (k=lzs; k<lze; k++) {
      if (k<user->KSKE[2*(j*mx+i)] && nvert[k][j][i]<0.1) {
        lsum += x[k][j][i];
        lnum ++;
      }
    }
      }
    }
    MPI_Allreduce(&lsum,&sum,1,MPI_DOUBLE,MPI_SUM,PETSC_COMM_WORLD);
    MPI_Allreduce(&lnum,&num,1,MPI_DOUBLE,MPI_SUM,PETSC_COMM_WORLD);
   /*  PetscGlobalSum(&lsum, &sum, PETSC_COMM_WORLD); */
/*     PetscGlobalSum(&lnum, &num, PETSC_COMM_WORLD); */
    sum /= -num;
    for (j=lys; j<lye; j++) {
      for (i=lxs; i<lxe; i++) {
    for (k=lzs; k<lze; k++) {
      if (k<user->KSKE[2*(j*mx+i)] && nvert[k][j][i]<0.1) {
        x[k][j][i] += sum;
      }
    }
      }
    }
 
    lsum = 0;
    lnum = 0;
    for (j=lys; j<lye; j++) {
      for (i=lxs; i<lxe; i++) {
    for (k=lzs; k<lze; k++) {
      if (k>=user->KSKE[2*(j*mx+i)] && nvert[k][j][i]<0.1) {
        lsum += x[k][j][i];
        lnum ++;
      }
    }
      }
    }
    MPI_Allreduce(&lsum,&sum,1,MPI_DOUBLE,MPI_SUM,PETSC_COMM_WORLD);
    MPI_Allreduce(&lnum,&num,1,MPI_DOUBLE,MPI_SUM,PETSC_COMM_WORLD);
   /*  PetscGlobalSum(&lsum, &sum, PETSC_COMM_WORLD); */
/*     PetscGlobalSum(&lnum, &num, PETSC_COMM_WORLD); */
    sum /= -num;
    for (j=lys; j<lye; j++) {
      for (i=lxs; i<lxe; i++) {
    for (k=lzs; k<lze; k++) {
      if (k>=user->KSKE[2*(j*mx+i)] && nvert[k][j][i]<0.1) {
        x[k][j][i] += sum;
      }
    }
      }
    }
               
  } //if multinullspace
  if (zs == 0) {
    k = 0;
    for (j=ys; j<ye; j++) {
      for (i=xs; i<xe; i++) {
    x[k][j][i] = 0.;
      }
    }
  }
 
  if (ze == mz) {
    k = mz-1;
    for (j=ys; j<ye; j++) {
      for (i=xs; i<xe; i++) {
    x[k][j][i] = 0.;
      }
    }
  }
 
  if (ys == 0) {
    j = 0;
    for (k=zs; k<ze; k++) {
      for (i=xs; i<xe; i++) {
    x[k][j][i] = 0.;
      }
    }
  }
 
  if (ye == my) {
    j = my-1;
    for (k=zs; k<ze; k++) {
      for (i=xs; i<xe; i++) {
    x[k][j][i] = 0.;
      }
    }
  }
 
  if (xs == 0) {
    i = 0;
    for (k=zs; k<ze; k++) {
      for (j=ys; j<ye; j++) {
    x[k][j][i] = 0.;
      }
    }
  }
 
  if (xe == mx) {
    i = mx-1;
    for (k=zs; k<ze; k++) {
      for (j=ys; j<ye; j++) {
    x[k][j][i] = 0.;
      }
    }
  }
 
  for (k=zs; k<ze; k++) {
    for (j=ys; j<ye; j++) {
      for (i=xs; i<xe; i++) {
    if (nvert[k][j][i] > 0.1)
      x[k][j][i] = 0.;
      }
    }
  }
  DMDAVecRestoreArray(da, X, &x);
  DMDAVecRestoreArray(da, user->lNvert, &nvert);
 
  return 0;
}

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MyRestriction()

PetscErrorCode MyRestriction ( Mat  A, Vec  X, Vec  F  )

extern

The callback function for the multigrid restriction operator (MatShell).

Defines the fine-to-coarse grid transfer for the Poisson residual.

Parameters

A	The shell matrix context.
X	The fine-grid source vector.
F	The coarse-grid destination vector.

Returns

PetscErrorCode 0 on success.

Definition at line 2061 of file poisson.c.

{
  UserCtx *user;
 
  MatShellGetContext(A, (void**)&user);
 
  
  DM    da = user->da;
 
  DM    da_f = *user->da_f;
 
  DMDALocalInfo info;
  DMDAGetLocalInfo(da, &info);
  PetscInt  xs = info.xs, xe = info.xs + info.xm;
  PetscInt      ys = info.ys, ye = info.ys + info.ym;
  PetscInt  zs = info.zs, ze = info.zs + info.zm;
  PetscInt  mx = info.mx, my = info.my, mz = info.mz;
  //  PetscInt  lxs, lxe, lys, lye, lzs, lze;
  
  PetscReal ***f, ***x, ***nvert;
  PetscInt i, j, k, ih, jh, kh, ia, ja, ka;
 
  DMDAVecGetArray(da,   F, &f);
 
  Vec lX;
 
  DMCreateLocalVector(da_f, &lX);
  DMGlobalToLocalBegin(da_f, X, INSERT_VALUES, lX);
  DMGlobalToLocalEnd(da_f, X, INSERT_VALUES, lX);  
  DMDAVecGetArray(da_f, lX, &x);
 
  DMDAVecGetArray(da, user->lNvert, &nvert);
 
  PetscReal ***nvert_f;
  DMDAVecGetArray(da_f, user->user_f->lNvert, &nvert_f);
 
  if ((user->isc)) ia = 0;
  else ia = 1;
 
  if ((user->jsc)) ja = 0;
  else ja = 1;
 
  if ((user->ksc)) ka = 0;
  else ka = 1;
 
  for (k=zs; k<ze; k++) {
    for (j=ys; j<ye; j++) {
      for (i=xs; i<xe; i++) {
    if (k==0) {
      f[k][j][i] = 0.;
    }
    else if (k==mz-1) {
      f[k][j][i] = 0.;
    }
    else if (j==0) {
      f[k][j][i] = 0.;
    }
    else if (j==my-1) {
      f[k][j][i] = 0.;
    }
    else if (i==0) {
      f[k][j][i] = 0.;
    }
    else if (i==mx-1) {
      f[k][j][i] = 0.;
    }
    else {
      GridRestriction(i, j, k, &ih, &jh, &kh, user);
      f[k][j][i] = 0.125 *
        (x[kh   ][jh   ][ih   ] * PetscMax(0., 1 - nvert_f[kh   ][jh   ][ih   ]) +
         x[kh   ][jh   ][ih-ia] * PetscMax(0., 1 - nvert_f[kh   ][jh   ][ih-ia]) +
         x[kh   ][jh-ja][ih   ] * PetscMax(0., 1 - nvert_f[kh   ][jh-ja][ih   ]) +
         x[kh-ka][jh   ][ih   ] * PetscMax(0., 1 - nvert_f[kh-ka][jh   ][ih   ]) +
         x[kh   ][jh-ja][ih-ia] * PetscMax(0., 1 - nvert_f[kh   ][jh-ja][ih-ia]) +
         x[kh-ka][jh-ja][ih   ] * PetscMax(0., 1 - nvert_f[kh-ka][jh-ja][ih   ]) +
         x[kh-ka][jh   ][ih-ia] * PetscMax(0., 1 - nvert_f[kh-ka][jh   ][ih-ia]) +
         x[kh-ka][jh-ja][ih-ia] * PetscMax(0., 1 - nvert_f[kh-ka][jh-ja][ih-ia]));
 
 
 
      if (nvert[k][j][i] > 0.1) f[k][j][i] = 0.;
    }
      }
    }
  }
 
 
  DMDAVecRestoreArray(da_f, user->user_f->lNvert, &nvert_f);
 
  DMDAVecRestoreArray(da_f, lX, &x);
  VecDestroy(&lX);
 
  DMDAVecRestoreArray(da,   F,  &f);
  DMDAVecRestoreArray(da, user->lNvert, &nvert);
 
 
  return 0;
}

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MyInterpolation()

PetscErrorCode MyInterpolation ( Mat  A, Vec  X, Vec  F  )

extern

The callback function for the multigrid interpolation operator (MatShell).

Defines the coarse-to-fine grid transfer for the pressure correction.

Parameters

A	The shell matrix context.
X	The coarse-grid source vector.
F	The fine-grid destination vector.

Returns

PetscErrorCode 0 on success.

Definition at line 1879 of file poisson.c.

{
  UserCtx *user;
 
  MatShellGetContext(A, (void**)&user);
 
  
  
  DM    da = user->da;
 
  DM    da_c = *user->da_c;
 
  DMDALocalInfo info = user->info;
  PetscInt  xs = info.xs, xe = info.xs + info.xm;
  PetscInt      ys = info.ys, ye = info.ys + info.ym;
  PetscInt  zs = info.zs, ze = info.zs + info.zm;
  PetscInt  mx = info.mx, my = info.my, mz = info.mz;
  PetscInt  lxs, lxe, lys, lye, lzs, lze;
  
  PetscReal ***f, ***x, ***nvert, ***nvert_c;
  PetscInt i, j, k, ic, jc, kc, ia, ja, ka;
 
  lxs = xs; lxe = xe;
  lys = ys; lye = ye;
  lzs = zs; lze = ze;
 
  if (xs==0) lxs = xs+1;
  if (ys==0) lys = ys+1;
  if (zs==0) lzs = zs+1;
 
  if (xe==mx) lxe = xe-1;
  if (ye==my) lye = ye-1;
  if (ze==mz) lze = ze-1;
 
 
  DMDAVecGetArray(da,   F, &f);
 
 
  Vec lX;
  DMCreateLocalVector(da_c, &lX);
 
  DMGlobalToLocalBegin(da_c, X, INSERT_VALUES, lX);
  DMGlobalToLocalEnd(da_c, X, INSERT_VALUES, lX);  
  DMDAVecGetArray(da_c, lX, &x);
 
  DMDAVecGetArray(da, user->lNvert, &nvert);
  DMDAVecGetArray(da_c, *(user->lNvert_c), &nvert_c);
  for (k=lzs; k<lze; k++) {
    for (j=lys; j<lye; j++) {
      for (i=lxs; i<lxe; i++) {
 
    GridInterpolation(i, j, k, ic, jc, kc, ia, ja, ka, user);
 
      f[k][j][i] = (x[kc   ][jc   ][ic   ] * 9 +
            x[kc   ][jc+ja][ic   ] * 3 +
            x[kc   ][jc   ][ic+ia] * 3 +
            x[kc   ][jc+ja][ic+ia]) * 3./64. +
        (x[kc+ka][jc   ][ic   ] * 9 +
         x[kc+ka][jc+ja][ic   ] * 3 +
         x[kc+ka][jc   ][ic+ia] * 3 +
         x[kc+ka][jc+ja][ic+ia]) /64.;
      }
    }
  }
 
  for (k=zs; k<ze; k++) {
    for (j=ys; j<ye; j++) {
      for (i=xs; i<xe; i++) {
 
    if (i==0) {
      f[k][j][i] = 0.;//-f[k][j][i+1];
    }
    else if (i==mx-1) {
      f[k][j][i] = 0.;//-f[k][j][i-1];
    }
    else if (j==0) {
      f[k][j][i] = 0.;//-f[k][j+1][i];
    }
    else if (j==my-1) {
      f[k][j][i] = 0.;//-f[k][j-1][i];
    }
    else if (k==0) {
      f[k][j][i] = 0.;//-f[k+1][j][i];
    }
    else if (k==mz-1) {
      f[k][j][i] = 0.;//-f[k-1][j][i];
    }
    if (nvert[k][j][i] > 0.1) f[k][j][i] = 0.;
 
      }
    }
  }
 
  DMDAVecRestoreArray(da, user->lNvert, &nvert);
  DMDAVecRestoreArray(da_c, *(user->lNvert_c), &nvert_c);
 
  DMDAVecRestoreArray(da_c, lX, &x);
 
  VecDestroy(&lX);
  DMDAVecRestoreArray(da,   F,  &f);
 
 
 
  return 0;
 
}

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VolumeFlux()

PetscErrorCode VolumeFlux ( UserCtx *  user, PetscReal *  ibm_Flux, PetscReal *  ibm_Area, PetscInt  flg  )

extern

Calculates the net flux across the immersed boundary surface.

Parameters

user	The UserCtx for the grid level.
ibm_Flux	(Output) The calculated net flux.
ibm_Area	(Output) The total surface area of the IB.
flg	A flag controlling the correction behavior.

Returns

PetscErrorCode 0 on success.

Definition at line 3133 of file poisson.c.

{
  // --- CONTEXT ACQUISITION BLOCK ---
  // Get the master simulation context from the UserCtx.
  SimCtx *simCtx = user->simCtx;
 
  // Create local variables to mirror the legacy globals for minimal code changes.
  const PetscInt NumberOfBodies = simCtx->NumberOfBodies;
  const PetscInt channelz = simCtx->channelz;
  const PetscInt fish = simCtx->fish;
  // --- END CONTEXT ACQUISITION BLOCK ---
 
  DM    da = user->da, fda = user->fda;
 
  DMDALocalInfo info = user->info;
 
  PetscInt  xs = info.xs, xe = info.xs + info.xm;
  PetscInt      ys = info.ys, ye = info.ys + info.ym;
  PetscInt  zs = info.zs, ze = info.zs + info.zm;
  PetscInt  mx = info.mx, my = info.my, mz = info.mz;
 
  PetscInt i, j, k,ibi;
  PetscInt  lxs, lys, lzs, lxe, lye, lze;
 
  PetscInt  gxs, gxe, gys, gye, gzs, gze;
  
  gxs = info.gxs; gxe = gxs + info.gxm;
  gys = info.gys; gye = gys + info.gym;
  gzs = info.gzs; gze = gzs + info.gzm;
 
  lxs = xs; lxe = xe;
  lys = ys; lye = ye;
  lzs = zs; lze = ze;
 
  if (xs==0) lxs = xs+1;
  if (ys==0) lys = ys+1;
  if (zs==0) lzs = zs+1;
 
  if (xe==mx) lxe = xe-1;
  if (ye==my) lye = ye-1;
  if (ze==mz) lze = ze-1;
  
  PetscReal epsilon=1.e-8;
  PetscReal ***nvert, ibmval=1.9999;
  
  struct Components {
    PetscReal x;
    PetscReal y;
    PetscReal z;
  }***ucor, ***lucor,***csi, ***eta, ***zet;
 
 
  PetscInt xend=mx-2 ,yend=my-2,zend=mz-2;
 
  if (user->bctype[0]==7) xend=mx-1;
  if (user->bctype[2]==7) yend=my-1;
  if (user->bctype[4]==7) zend=mz-1;
 
  DMDAVecGetArray(fda, user->Ucont, &ucor);
  DMDAVecGetArray(fda, user->lCsi, &csi);
  DMDAVecGetArray(fda, user->lEta, &eta);
  DMDAVecGetArray(fda, user->lZet, &zet);
  DMDAVecGetArray(da, user->lNvert, &nvert);
 
  PetscReal libm_Flux, libm_area, libm_Flux_abs=0., ibm_Flux_abs;
  libm_Flux = 0;
  libm_area = 0;
 
  LOG_ALLOW(GLOBAL, LOG_DEBUG, "Entering VolumeFlux to enforce no-penetration condition.\n");
 
  //Mohsen March 2017
  PetscReal *lIB_Flux, *lIB_area,*IB_Flux,*IB_Area;
  if (NumberOfBodies > 1) { 
  
    lIB_Flux=(PetscReal *)calloc(NumberOfBodies,sizeof(PetscReal));
    lIB_area=(PetscReal *)calloc(NumberOfBodies,sizeof(PetscReal));
    IB_Flux=(PetscReal *)calloc(NumberOfBodies,sizeof(PetscReal));
    IB_Area=(PetscReal *)calloc(NumberOfBodies,sizeof(PetscReal));
  
 
    for (ibi=0; ibi<NumberOfBodies; ibi++) {
      lIB_Flux[ibi]=0.0;
      lIB_area[ibi]=0.0;
      IB_Flux[ibi]=0.0;
      IB_Area[ibi]=0.0;
    }
  }
 
 
  //================================================================================
  // PASS 1: Calculate Uncorrected Flux and Area
  // This pass measures the total fluid "leakage" across the immersed boundary.
  //================================================================================
  LOG_ALLOW(GLOBAL, LOG_DEBUG, "Pass 1: Measuring uncorrected flux and area.\n");
  
  for (k=lzs; k<lze; k++) {
    for (j=lys; j<lye; j++) {
      for (i=lxs; i<lxe; i++) {
    if (nvert[k][j][i] < 0.1) {
      if (nvert[k][j][i+1] > 0.1 && nvert[k][j][i+1] < ibmval && i < xend) {
        
        if (fabs(ucor[k][j][i].x)>epsilon) {
          libm_Flux += ucor[k][j][i].x;
          if (flg==3)
        libm_Flux_abs += fabs(ucor[k][j][i].x)/sqrt(csi[k][j][i].x * csi[k][j][i].x +
                                csi[k][j][i].y * csi[k][j][i].y +
                                csi[k][j][i].z * csi[k][j][i].z);
          else
        libm_Flux_abs += fabs(ucor[k][j][i].x);
          
          libm_area += sqrt(csi[k][j][i].x * csi[k][j][i].x +
                csi[k][j][i].y * csi[k][j][i].y +
                csi[k][j][i].z * csi[k][j][i].z);
          
          if (NumberOfBodies > 1) {
        
        ibi=(int)((nvert[k][j][i+1]-1.0)*1001);
        lIB_Flux[ibi] += ucor[k][j][i].x;
        lIB_area[ibi] += sqrt(csi[k][j][i].x * csi[k][j][i].x +
                      csi[k][j][i].y * csi[k][j][i].y +
                      csi[k][j][i].z * csi[k][j][i].z);
          }
        } else
          ucor[k][j][i].x=0.;
        
      }
      if (nvert[k][j+1][i] > 0.1 && nvert[k][j+1][i] < ibmval && j < yend) {
        
        if (fabs(ucor[k][j][i].y)>epsilon) {
          libm_Flux += ucor[k][j][i].y;
          if (flg==3)
        libm_Flux_abs += fabs(ucor[k][j][i].y)/sqrt(eta[k][j][i].x * eta[k][j][i].x +
                                eta[k][j][i].y * eta[k][j][i].y +
                                eta[k][j][i].z * eta[k][j][i].z);
          else
        libm_Flux_abs += fabs(ucor[k][j][i].y);
          libm_area += sqrt(eta[k][j][i].x * eta[k][j][i].x +
                eta[k][j][i].y * eta[k][j][i].y +
                eta[k][j][i].z * eta[k][j][i].z);
          if (NumberOfBodies > 1) {
        
        ibi=(int)((nvert[k][j+1][i]-1.0)*1001); 
 
        lIB_Flux[ibi] += ucor[k][j][i].y;
        lIB_area[ibi] += sqrt(eta[k][j][i].x * eta[k][j][i].x +
                      eta[k][j][i].y * eta[k][j][i].y +
                      eta[k][j][i].z * eta[k][j][i].z);
          }
        } else
          ucor[k][j][i].y=0.;
      }
      if (nvert[k+1][j][i] > 0.1 && nvert[k+1][j][i] < ibmval && k < zend) {
        
        if (fabs(ucor[k][j][i].z)>epsilon) {
          libm_Flux += ucor[k][j][i].z;
          if (flg==3)
        libm_Flux_abs += fabs(ucor[k][j][i].z)/sqrt(zet[k][j][i].x * zet[k][j][i].x +
                                zet[k][j][i].y * zet[k][j][i].y +
                                zet[k][j][i].z * zet[k][j][i].z);
          else
        libm_Flux_abs += fabs(ucor[k][j][i].z);
          libm_area += sqrt(zet[k][j][i].x * zet[k][j][i].x +
                zet[k][j][i].y * zet[k][j][i].y +
                zet[k][j][i].z * zet[k][j][i].z);
          
          if (NumberOfBodies > 1) {
        
        ibi=(int)((nvert[k+1][j][i]-1.0)*1001);
        lIB_Flux[ibi] += ucor[k][j][i].z;
        lIB_area[ibi] += sqrt(zet[k][j][i].x * zet[k][j][i].x +
                      zet[k][j][i].y * zet[k][j][i].y +
                      zet[k][j][i].z * zet[k][j][i].z);
          }
        }else
          ucor[k][j][i].z=0.;
      }
    }
 
    if (nvert[k][j][i] > 0.1 && nvert[k][j][i] < ibmval) {
      
      if (nvert[k][j][i+1] < 0.1 && i < xend) {
        if (fabs(ucor[k][j][i].x)>epsilon) {
          libm_Flux -= ucor[k][j][i].x;
          if (flg==3)
        libm_Flux_abs += fabs(ucor[k][j][i].x)/sqrt(csi[k][j][i].x * csi[k][j][i].x +
                                csi[k][j][i].y * csi[k][j][i].y +
                                csi[k][j][i].z * csi[k][j][i].z);
          else
        libm_Flux_abs += fabs(ucor[k][j][i].x);
          libm_area += sqrt(csi[k][j][i].x * csi[k][j][i].x +
                csi[k][j][i].y * csi[k][j][i].y +
                csi[k][j][i].z * csi[k][j][i].z);
          if (NumberOfBodies > 1) {
        
        ibi=(int)((nvert[k][j][i]-1.0)*1001);
        lIB_Flux[ibi] -= ucor[k][j][i].x;
        lIB_area[ibi] += sqrt(csi[k][j][i].x * csi[k][j][i].x +
                      csi[k][j][i].y * csi[k][j][i].y +
                      csi[k][j][i].z * csi[k][j][i].z);
          }
              
        }else
          ucor[k][j][i].x=0.;
      }
      if (nvert[k][j+1][i] < 0.1 && j < yend) {
        if (fabs(ucor[k][j][i].y)>epsilon) {
          libm_Flux -= ucor[k][j][i].y;
          if (flg==3)
        libm_Flux_abs += fabs(ucor[k][j][i].y)/ sqrt(eta[k][j][i].x * eta[k][j][i].x +
                                 eta[k][j][i].y * eta[k][j][i].y +
                                 eta[k][j][i].z * eta[k][j][i].z);
          else
        libm_Flux_abs += fabs(ucor[k][j][i].y);
          libm_area += sqrt(eta[k][j][i].x * eta[k][j][i].x +
                eta[k][j][i].y * eta[k][j][i].y +
                eta[k][j][i].z * eta[k][j][i].z);
          if (NumberOfBodies > 1) {
 
        ibi=(int)((nvert[k][j][i]-1.0)*1001);
        lIB_Flux[ibi] -= ucor[k][j][i].y;
        lIB_area[ibi] += sqrt(eta[k][j][i].x * eta[k][j][i].x +
                      eta[k][j][i].y * eta[k][j][i].y +
                      eta[k][j][i].z * eta[k][j][i].z);
          }
        }else
          ucor[k][j][i].y=0.;
      }
      if (nvert[k+1][j][i] < 0.1 && k < zend) {
        if (fabs(ucor[k][j][i].z)>epsilon) {
          libm_Flux -= ucor[k][j][i].z;
          if (flg==3)
        libm_Flux_abs += fabs(ucor[k][j][i].z)/sqrt(zet[k][j][i].x * zet[k][j][i].x +
                                zet[k][j][i].y * zet[k][j][i].y +
                                zet[k][j][i].z * zet[k][j][i].z);
          else
        libm_Flux_abs += fabs(ucor[k][j][i].z);
          libm_area += sqrt(zet[k][j][i].x * zet[k][j][i].x +
                zet[k][j][i].y * zet[k][j][i].y +
                zet[k][j][i].z * zet[k][j][i].z);
          if (NumberOfBodies > 1) {
        
        ibi=(int)((nvert[k][j][i]-1.0)*1001);
        lIB_Flux[ibi] -= ucor[k][j][i].z;
        lIB_area[ibi] += sqrt(zet[k][j][i].x * zet[k][j][i].x +
                      zet[k][j][i].y * zet[k][j][i].y +
                      zet[k][j][i].z * zet[k][j][i].z);
          }
        }else
          ucor[k][j][i].z=0.;
      }
    }
    
      }
    }
  }
  
  MPI_Allreduce(&libm_Flux, ibm_Flux,1,MPI_DOUBLE,MPI_SUM, PETSC_COMM_WORLD);
  MPI_Allreduce(&libm_Flux_abs, &ibm_Flux_abs,1,MPI_DOUBLE,MPI_SUM, PETSC_COMM_WORLD);
  MPI_Allreduce(&libm_area, ibm_Area,1,MPI_DOUBLE,MPI_SUM, PETSC_COMM_WORLD);
 
  if (NumberOfBodies > 1) { 
    MPI_Allreduce(lIB_Flux,IB_Flux,NumberOfBodies,MPI_DOUBLE,MPI_SUM,PETSC_COMM_WORLD);
    MPI_Allreduce(lIB_area,IB_Area,NumberOfBodies,MPI_DOUBLE,MPI_SUM,PETSC_COMM_WORLD);
  }
 
  PetscReal correction;
 
  PetscReal *Correction;
  if (NumberOfBodies > 1) {
      Correction=(PetscReal *)calloc(NumberOfBodies,sizeof(PetscReal));
      for (ibi=0; ibi<NumberOfBodies; ibi++) Correction[ibi]=0.0;
  }
 
  if (*ibm_Area > 1.e-15) {
    if (flg>1) 
      correction = (*ibm_Flux + user->FluxIntpSum)/ ibm_Flux_abs;
    else if (flg)
      correction = (*ibm_Flux + user->FluxIntpSum) / *ibm_Area;
    else
      correction = *ibm_Flux / *ibm_Area;
    if (NumberOfBodies > 1) 
      for (ibi=0; ibi<NumberOfBodies; ibi++) if (IB_Area[ibi]>1.e-15) Correction[ibi] = IB_Flux[ibi] / IB_Area[ibi];
  }
  else {
    correction = 0;
  }
  // --- Log the uncorrected results and calculated correction ---
  LOG_ALLOW(GLOBAL, LOG_INFO, "IBM Uncorrected Flux: %g, Area: %g, Correction: %g\n", *ibm_Flux, *ibm_Area, correction);
  if  (NumberOfBodies>1){
    for (ibi=0; ibi<NumberOfBodies; ibi++)   LOG_ALLOW(GLOBAL, LOG_INFO, "  [Body %d] Uncorrected Flux: %g, Area: %g, Correction: %g\n", ibi, IB_Flux[ibi], IB_Area[ibi], Correction[ibi]);
  }
 
  //================================================================================
  // PASS 2: Apply Correction to Velocity Field
  // This pass modifies the velocity at the boundary to enforce zero net flux.
  //================================================================================
  LOG_ALLOW(GLOBAL, LOG_DEBUG, "Pass 2: Applying velocity corrections at the boundary.\n");
  
  for (k=lzs; k<lze; k++) {
    for (j=lys; j<lye; j++) {
      for (i=lxs; i<lxe; i++) {
    if (nvert[k][j][i] < 0.1) {
      if (nvert[k][j][i+1] > 0.1 && nvert[k][j][i+1] <ibmval && i < xend) {
        if (fabs(ucor[k][j][i].x)>epsilon){
          if (flg==3) 
        ucor[k][j][i].x -=correction*fabs(ucor[k][j][i].x)/
          sqrt(csi[k][j][i].x * csi[k][j][i].x +
               csi[k][j][i].y * csi[k][j][i].y +
               csi[k][j][i].z * csi[k][j][i].z);
          else if (flg==2) 
        ucor[k][j][i].x -=correction*fabs(ucor[k][j][i].x);
          else if (NumberOfBodies > 1) {
        ibi=(int)((nvert[k][j][i+1]-1.0)*1001);
        ucor[k][j][i].x -= sqrt(csi[k][j][i].x * csi[k][j][i].x +
                    csi[k][j][i].y * csi[k][j][i].y +
                    csi[k][j][i].z * csi[k][j][i].z) *
          Correction[ibi];
          }
          else
        ucor[k][j][i].x -= sqrt(csi[k][j][i].x * csi[k][j][i].x +
                    csi[k][j][i].y * csi[k][j][i].y +
                    csi[k][j][i].z * csi[k][j][i].z) *
          correction;
        }
      }
      if (nvert[k][j+1][i] > 0.1 && nvert[k][j+1][i] < ibmval && j < yend) {
        if (fabs(ucor[k][j][i].y)>epsilon) {
          if (flg==3) 
        ucor[k][j][i].y -=correction*fabs(ucor[k][j][i].y)/
          sqrt(eta[k][j][i].x * eta[k][j][i].x + 
               eta[k][j][i].y * eta[k][j][i].y +
               eta[k][j][i].z * eta[k][j][i].z);
          else if (flg==2) 
        ucor[k][j][i].y -=correction*fabs(ucor[k][j][i].y);
          else if (NumberOfBodies > 1) {
        ibi=(int)((nvert[k][j+1][i]-1.0)*1001);
        ucor[k][j][i].y -= sqrt(eta[k][j][i].x * eta[k][j][i].x +
                    eta[k][j][i].y * eta[k][j][i].y +
                    eta[k][j][i].z * eta[k][j][i].z) *
          Correction[ibi];
          }
          else
        ucor[k][j][i].y -= sqrt(eta[k][j][i].x * eta[k][j][i].x + 
                    eta[k][j][i].y * eta[k][j][i].y +
                    eta[k][j][i].z * eta[k][j][i].z) *
          correction;
        }
      }
      if (nvert[k+1][j][i] > 0.1 && nvert[k+1][j][i] < ibmval && k < zend) {
        if (fabs(ucor[k][j][i].z)>epsilon) {
          if (flg==3) 
        ucor[k][j][i].z -= correction*fabs(ucor[k][j][i].z)/
          sqrt(zet[k][j][i].x * zet[k][j][i].x +
               zet[k][j][i].y * zet[k][j][i].y +
               zet[k][j][i].z * zet[k][j][i].z);
          else if (flg==2) 
        ucor[k][j][i].z -= correction*fabs(ucor[k][j][i].z);
          else if (NumberOfBodies > 1) {
        ibi=(int)((nvert[k+1][j][i]-1.0)*1001);
        ucor[k][j][i].z -= sqrt(zet[k][j][i].x * zet[k][j][i].x +
                    zet[k][j][i].y * zet[k][j][i].y +
                    zet[k][j][i].z * zet[k][j][i].z) *
          Correction[ibi];
          }
          else
        ucor[k][j][i].z -= sqrt(zet[k][j][i].x * zet[k][j][i].x +
                    zet[k][j][i].y * zet[k][j][i].y +
                    zet[k][j][i].z * zet[k][j][i].z) *
          correction;
        }
      }
    }
 
    if (nvert[k][j][i] > 0.1 && nvert[k][j][i] < ibmval) {
      if (nvert[k][j][i+1] < 0.1 && i < xend) {
        if (fabs(ucor[k][j][i].x)>epsilon) {
          if (flg==3) 
        ucor[k][j][i].x += correction*fabs(ucor[k][j][i].x)/
          sqrt(csi[k][j][i].x * csi[k][j][i].x +
               csi[k][j][i].y * csi[k][j][i].y +
               csi[k][j][i].z * csi[k][j][i].z);
          else if (flg==2) 
        ucor[k][j][i].x += correction*fabs(ucor[k][j][i].x);
          else if (NumberOfBodies > 1) {
        ibi=(int)((nvert[k][j][i]-1.0)*1001);
        ucor[k][j][i].x += sqrt(csi[k][j][i].x * csi[k][j][i].x +
                    csi[k][j][i].y * csi[k][j][i].y +
                    csi[k][j][i].z * csi[k][j][i].z) *
          Correction[ibi];
          }
          else
        ucor[k][j][i].x += sqrt(csi[k][j][i].x * csi[k][j][i].x +
                    csi[k][j][i].y * csi[k][j][i].y +
                    csi[k][j][i].z * csi[k][j][i].z) *
          correction;
        }
      }
      if (nvert[k][j+1][i] < 0.1 && j < yend) {
        if (fabs(ucor[k][j][i].y)>epsilon) {
        if (flg==3) 
          ucor[k][j][i].y +=correction*fabs(ucor[k][j][i].y)/
        sqrt(eta[k][j][i].x * eta[k][j][i].x +
             eta[k][j][i].y * eta[k][j][i].y +
             eta[k][j][i].z * eta[k][j][i].z);
        else if (flg==2) 
          ucor[k][j][i].y +=correction*fabs(ucor[k][j][i].y);
        else if (NumberOfBodies > 1) {
          ibi=(int)((nvert[k][j][i]-1.0)*1001);
          ucor[k][j][i].y += sqrt(eta[k][j][i].x * eta[k][j][i].x +
                      eta[k][j][i].y * eta[k][j][i].y +
                      eta[k][j][i].z * eta[k][j][i].z) *
        Correction[ibi];
        }
        else
        ucor[k][j][i].y += sqrt(eta[k][j][i].x * eta[k][j][i].x +
                    eta[k][j][i].y * eta[k][j][i].y +
                    eta[k][j][i].z * eta[k][j][i].z) *
                    correction;
        }
      }
      if (nvert[k+1][j][i] < 0.1 && k < zend) {
        if (fabs(ucor[k][j][i].z)>epsilon) {
        if (flg==3) 
          ucor[k][j][i].z += correction*fabs(ucor[k][j][i].z)/
        sqrt(zet[k][j][i].x * zet[k][j][i].x +
             zet[k][j][i].y * zet[k][j][i].y +
             zet[k][j][i].z * zet[k][j][i].z);
        else if (flg==2) 
          ucor[k][j][i].z += correction*fabs(ucor[k][j][i].z);
        else if (NumberOfBodies > 1) {
          ibi=(int)((nvert[k][j][i]-1.0)*1001);
          ucor[k][j][i].z += sqrt(zet[k][j][i].x * zet[k][j][i].x +
                      zet[k][j][i].y * zet[k][j][i].y +
                      zet[k][j][i].z * zet[k][j][i].z) *
        Correction[ibi];
        }
        else
          ucor[k][j][i].z += sqrt(zet[k][j][i].x * zet[k][j][i].x +
                      zet[k][j][i].y * zet[k][j][i].y +
                      zet[k][j][i].z * zet[k][j][i].z) *
        correction;
        }
      }
    }
    
      }
    }
  }
  
  //================================================================================
  // PASS 3: Verification
  // This optional pass recalculates the flux to confirm the correction was successful.
  //================================================================================
  LOG_ALLOW(GLOBAL, LOG_DEBUG, "Pass 3: Verifying corrected flux.\n");
  
  libm_Flux = 0;
  libm_area = 0;
  for (k=lzs; k<lze; k++) {
    for (j=lys; j<lye; j++) {
      for (i=lxs; i<lxe; i++) {
    if (nvert[k][j][i] < 0.1) {
      if (nvert[k][j][i+1] > 0.1 && nvert[k][j][i+1] < ibmval && i < xend) {
        libm_Flux += ucor[k][j][i].x;
        libm_area += sqrt(csi[k][j][i].x * csi[k][j][i].x +
              csi[k][j][i].y * csi[k][j][i].y +
              csi[k][j][i].z * csi[k][j][i].z);
              
      }
      if (nvert[k][j+1][i] > 0.1 && nvert[k][j+1][i] < ibmval && j < yend) {
        libm_Flux += ucor[k][j][i].y;
        libm_area += sqrt(eta[k][j][i].x * eta[k][j][i].x +
              eta[k][j][i].y * eta[k][j][i].y +
              eta[k][j][i].z * eta[k][j][i].z);
      }
      if (nvert[k+1][j][i] > 0.1 && nvert[k+1][j][i] < ibmval && k < zend) {
        libm_Flux += ucor[k][j][i].z;
        libm_area += sqrt(zet[k][j][i].x * zet[k][j][i].x +
              zet[k][j][i].y * zet[k][j][i].y +
              zet[k][j][i].z * zet[k][j][i].z);
      }
    }
 
    if (nvert[k][j][i] > 0.1 && nvert[k][j][i] < ibmval) {
      if (nvert[k][j][i+1] < 0.1 && i < xend) {
        libm_Flux -= ucor[k][j][i].x;
        libm_area += sqrt(csi[k][j][i].x * csi[k][j][i].x +
              csi[k][j][i].y * csi[k][j][i].y +
              csi[k][j][i].z * csi[k][j][i].z);
              
      }
      if (nvert[k][j+1][i] < 0.1 && j < yend) {
        libm_Flux -= ucor[k][j][i].y;
        libm_area += sqrt(eta[k][j][i].x * eta[k][j][i].x +
              eta[k][j][i].y * eta[k][j][i].y +
              eta[k][j][i].z * eta[k][j][i].z);
      }
      if (nvert[k+1][j][i] < 0.1 && k < zend) {
        libm_Flux -= ucor[k][j][i].z;
        libm_area += sqrt(zet[k][j][i].x * zet[k][j][i].x +
              zet[k][j][i].y * zet[k][j][i].y +
              zet[k][j][i].z * zet[k][j][i].z);
      }
    }
 
      }
    }
  }
 
  MPI_Allreduce(&libm_Flux, ibm_Flux,1,MPI_DOUBLE,MPI_SUM, PETSC_COMM_WORLD);
  MPI_Allreduce(&libm_area, ibm_Area,1,MPI_DOUBLE,MPI_SUM, PETSC_COMM_WORLD);
 
 /*  PetscGlobalSum(&libm_Flux, ibm_Flux, PETSC_COMM_WORLD); */
/*   PetscGlobalSum(&libm_area, ibm_Area, PETSC_COMM_WORLD); */
    LOG_ALLOW(GLOBAL, LOG_INFO, "IBM Corrected (Verified) Flux: %g, Area: %g\n", *ibm_Flux, *ibm_Area);
 
 
  if (user->bctype[0]==7 || user->bctype[1]==7){
    if (xe==mx){
      i=mx-2;
      for (k=lzs; k<lze; k++) {
    for (j=lys; j<lye; j++) {
      // if(j>0 && k>0 && j<user->JM && k<user->KM){
        if ((nvert[k][j][i]>ibmval && nvert[k][j][i+1]<0.1) || (nvert[k][j][i]<0.1 && nvert[k][j][i+1]>ibmval)) ucor[k][j][i].x=0.0;
        
        // }
    }
      }
    }
  }
 
  if (user->bctype[2]==7 || user->bctype[3]==7){
    if (ye==my){
      j=my-2;
      for (k=lzs; k<lze; k++) {
    for (i=lxs; i<lxe; i++) {
      // if(i>0 && k>0 && i<user->IM && k<user->KM){
        if ((nvert[k][j][i]>ibmval && nvert[k][j+1][i]<0.1) || (nvert[k][j][i]<0.1 && nvert[k][j+1][i]>ibmval)) ucor[k][j][i].y=0.0;
        // }
    }
      }
    }
  }
 
  if (user->bctype[4]==7 || user->bctype[5]==7){
    if (ze==mz){
      k=mz-2;
      for (j=lys; j<lye; j++) {
    for (i=lxs; i<lxe; i++) {
      // if(i>0 && j>0 && i<user->IM && j<user->JM){
        if ((nvert[k][j][i]>ibmval && nvert[k+1][j][i]<0.1) || (nvert[k][j][i]<0.1 && nvert[k+1][j][i]>ibmval)) ucor[k][j][i].z=0.0;
        // }
    }
      }
    }
  }
 
 
  DMDAVecRestoreArray(da, user->lNvert, &nvert);
  DMDAVecRestoreArray(fda, user->lCsi, &csi);
  DMDAVecRestoreArray(fda, user->lEta, &eta);
  DMDAVecRestoreArray(fda, user->lZet, &zet);
  DMDAVecRestoreArray(fda, user->Ucont, &ucor);
 
  DMGlobalToLocalBegin(fda, user->Ucont, INSERT_VALUES, user->lUcont);
  DMGlobalToLocalEnd(fda, user->Ucont, INSERT_VALUES, user->lUcont);
 
  /* periodci boundary condition update corrected flux */
  //Mohsen Dec 2015
  DMDAVecGetArray(fda, user->lUcont, &lucor);
  DMDAVecGetArray(fda, user->Ucont, &ucor);
  
  if (user->bctype[0]==7 || user->bctype[1]==7){
    if (xs==0){
      i=xs;
      for (k=zs; k<ze; k++) {
    for (j=ys; j<ye; j++) {
      if(j>0 && k>0 && j<user->JM && k<user->KM){
        ucor[k][j][i].x=lucor[k][j][i-2].x;  
      }
    }
      }
    }
  }
  if (user->bctype[2]==7 || user->bctype[3]==7){
    if (ys==0){
      j=ys;
      for (k=zs; k<ze; k++) {
    for (i=xs; i<xe; i++) {
      if(i>0 && k>0 && i<user->IM && k<user->KM){
        ucor[k][j][i].y=lucor[k][j-2][i].y;
      }
    }
      }
    }
  }
  if (user->bctype[4]==7 || user->bctype[5]==7){
    if (zs==0){
      k=zs;
      for (j=ys; j<ye; j++) {
    for (i=xs; i<xe; i++) {
      if(i>0 && j>0 && i<user->IM && j<user->JM){
        ucor[k][j][i].z=lucor[k-2][j][i].z;
      }
    }
      }
    }
  }
  DMDAVecRestoreArray(fda, user->lUcont, &lucor);
  DMDAVecRestoreArray(fda, user->Ucont, &ucor);
 
 /*  DMLocalToGlobalBegin(user->fda, user->lUcont, INSERT_VALUES, user->Ucont); */
/*   DMLocalToGlobalEnd(user->fda, user->lUcont, INSERT_VALUES, user->Ucont); */
  DMGlobalToLocalBegin(user->fda, user->Ucont, INSERT_VALUES, user->lUcont);
  DMGlobalToLocalEnd(user->fda, user->Ucont, INSERT_VALUES, user->lUcont);
 
  if (NumberOfBodies > 1) {
    free(lIB_Flux);
    free(lIB_area);
    free(IB_Flux);
    free(IB_Area);
    free(Correction);
  }
 
 LOG_ALLOW(GLOBAL, LOG_DEBUG, "Exiting VolumeFlux.\n");
  
  return 0;
}

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VolumeFlux_rev()

PetscErrorCode VolumeFlux_rev ( UserCtx *  user, PetscReal *  ibm_Flux, PetscReal *  ibm_Area, PetscInt  flg  )

extern

A specialized version of VolumeFlux, likely for reversed normals.

Parameters

user	The UserCtx for the grid level.
ibm_Flux	(Output) The calculated net flux.
ibm_Area	(Output) The total surface area of the IB.
flg	A flag controlling the correction behavior.

Returns

PetscErrorCode 0 on success.

Definition at line 2891 of file poisson.c.

{
 
  // --- CONTEXT ACQUISITION BLOCK ---
  // Get the master simulation context from the UserCtx.
  SimCtx *simCtx = user->simCtx;
 
  // Create a local variable to mirror the legacy global for minimal code changes.
  const PetscInt NumberOfBodies = simCtx->NumberOfBodies;
  // --- END CONTEXT ACQUISITION BLOCK ---
  
  DM    da = user->da, fda = user->fda;
 
  DMDALocalInfo info = user->info;
 
  PetscInt  xs = info.xs, xe = info.xs + info.xm;
  PetscInt      ys = info.ys, ye = info.ys + info.ym;
  PetscInt  zs = info.zs, ze = info.zs + info.zm;
  PetscInt  mx = info.mx, my = info.my, mz = info.mz;
 
  PetscInt i, j, k;
  PetscInt  lxs, lys, lzs, lxe, lye, lze;
 
  lxs = xs; lxe = xe;
  lys = ys; lye = ye;
  lzs = zs; lze = ze;
 
  if (xs==0) lxs = xs+1;
  if (ys==0) lys = ys+1;
  if (zs==0) lzs = zs+1;
 
  if (xe==mx) lxe = xe-1;
  if (ye==my) lye = ye-1;
  if (ze==mz) lze = ze-1;
 
  PetscReal ***nvert, ibmval=1.5;
  Cmpnts ***ucor, ***csi, ***eta, ***zet;
  DMDAVecGetArray(fda, user->Ucont, &ucor);
  DMDAVecGetArray(fda, user->lCsi, &csi);
  DMDAVecGetArray(fda, user->lEta, &eta);
  DMDAVecGetArray(fda, user->lZet, &zet);
  DMDAVecGetArray(da, user->lNvert, &nvert);
 
  PetscReal libm_Flux, libm_area;
  libm_Flux = 0;
  libm_area = 0;
  for (k=lzs; k<lze; k++) {
    for (j=lys; j<lye; j++) {
      for (i=lxs; i<lxe; i++) {
    if (nvert[k][j][i] < 0.1) {
      if (nvert[k][j][i+1] > ibmval-0.4 && nvert[k][j][i+1] < ibmval && i < mx-2) {
        libm_Flux += ucor[k][j][i].x;
        libm_area += sqrt(csi[k][j][i].x * csi[k][j][i].x +
              csi[k][j][i].y * csi[k][j][i].y +
              csi[k][j][i].z * csi[k][j][i].z);
              
      }
      if (nvert[k][j+1][i] > ibmval-0.4 && nvert[k][j+1][i] < ibmval && j < my-2) {
        libm_Flux += ucor[k][j][i].y;
        libm_area += sqrt(eta[k][j][i].x * eta[k][j][i].x +
              eta[k][j][i].y * eta[k][j][i].y +
              eta[k][j][i].z * eta[k][j][i].z);
      }
      if (nvert[k+1][j][i] > ibmval-0.4 && nvert[k+1][j][i] < ibmval && k < mz-2) {
        libm_Flux += ucor[k][j][i].z;
        libm_area += sqrt(zet[k][j][i].x * zet[k][j][i].x +
              zet[k][j][i].y * zet[k][j][i].y +
              zet[k][j][i].z * zet[k][j][i].z);
      }
    }
 
    if (nvert[k][j][i] > ibmval-0.4 && nvert[k][j][i] < ibmval) {
      if (nvert[k][j][i+1] < 0.1 && i < mx-2) {
        libm_Flux -= ucor[k][j][i].x;
        libm_area += sqrt(csi[k][j][i].x * csi[k][j][i].x +
              csi[k][j][i].y * csi[k][j][i].y +
              csi[k][j][i].z * csi[k][j][i].z);
              
      }
      if (nvert[k][j+1][i] < 0.1 && j < my-2) {
        libm_Flux -= ucor[k][j][i].y;
        libm_area += sqrt(eta[k][j][i].x * eta[k][j][i].x +
              eta[k][j][i].y * eta[k][j][i].y +
              eta[k][j][i].z * eta[k][j][i].z);
      }
      if (nvert[k+1][j][i] < 0.1 && k < mz-2) {
        libm_Flux -= ucor[k][j][i].z;
        libm_area += sqrt(zet[k][j][i].x * zet[k][j][i].x +
              zet[k][j][i].y * zet[k][j][i].y +
              zet[k][j][i].z * zet[k][j][i].z);
      }
    }
 
      }
    }
  }
 
  MPI_Allreduce(&libm_Flux, ibm_Flux,1,MPI_DOUBLE,MPI_SUM, PETSC_COMM_WORLD);
  MPI_Allreduce(&libm_area, ibm_Area,1,MPI_DOUBLE,MPI_SUM, PETSC_COMM_WORLD);
 
 /*  PetscGlobalSum(&libm_Flux, ibm_Flux, PETSC_COMM_WORLD); */
/*   PetscGlobalSum(&libm_area, ibm_Area, PETSC_COMM_WORLD); */
  PetscPrintf(PETSC_COMM_WORLD, "IBMFlux REV %le %le\n", *ibm_Flux, *ibm_Area);
 
  PetscReal correction;
 
  if (*ibm_Area > 1.e-15) {
    if (flg)
      correction = (*ibm_Flux + user->FluxIntpSum) / *ibm_Area;
    else
      correction = *ibm_Flux / *ibm_Area;
  }
  else {
    correction = 0;
  }
 
  for (k=lzs; k<lze; k++) {
    for (j=lys; j<lye; j++) {
      for (i=lxs; i<lxe; i++) {
    if (nvert[k][j][i] < 0.1) {
      if (nvert[k][j][i+1] > ibmval-0.4 && nvert[k][j][i+1] < ibmval && i < mx-2) {
        ucor[k][j][i].x -= sqrt(csi[k][j][i].x * csi[k][j][i].x +
                    csi[k][j][i].y * csi[k][j][i].y +
                    csi[k][j][i].z * csi[k][j][i].z) *
                    correction;
              
      }
      if (nvert[k][j+1][i] > ibmval-0.4 && nvert[k][j+1][i] < ibmval && j < my-2) {
        ucor[k][j][i].y -= sqrt(eta[k][j][i].x * eta[k][j][i].x + 
                    eta[k][j][i].y * eta[k][j][i].y +
                    eta[k][j][i].z * eta[k][j][i].z) *
                    correction;
      }
      if (nvert[k+1][j][i] > ibmval-0.4 && nvert[k+1][j][i] < ibmval && k < mz-2) {
        ucor[k][j][i].z -= sqrt(zet[k][j][i].x * zet[k][j][i].x +
                    zet[k][j][i].y * zet[k][j][i].y +
                    zet[k][j][i].z * zet[k][j][i].z) *
                    correction;
      }
    }
 
    if (nvert[k][j][i] > ibmval-0.4 && nvert[k][j][i] < ibmval) {
      if (nvert[k][j][i+1] < 0.1 && i < mx-2) {
        ucor[k][j][i].x += sqrt(csi[k][j][i].x * csi[k][j][i].x +
                    csi[k][j][i].y * csi[k][j][i].y +
                    csi[k][j][i].z * csi[k][j][i].z) *
                    correction;
              
      }
      if (nvert[k][j+1][i] < 0.1 && j < my-2) {
        ucor[k][j][i].y += sqrt(eta[k][j][i].x * eta[k][j][i].x +
                    eta[k][j][i].y * eta[k][j][i].y +
                    eta[k][j][i].z * eta[k][j][i].z) *
                    correction;
      }
      if (nvert[k+1][j][i] < 0.1 && k < mz-2) {
        ucor[k][j][i].z += sqrt(zet[k][j][i].x * zet[k][j][i].x +
                    zet[k][j][i].y * zet[k][j][i].y +
                    zet[k][j][i].z * zet[k][j][i].z) *
                    correction;
      }
    }
 
      }
    }
  }
  
 
 
  libm_Flux = 0;
  libm_area = 0;
  for (k=lzs; k<lze; k++) {
    for (j=lys; j<lye; j++) {
      for (i=lxs; i<lxe; i++) {
    if (nvert[k][j][i] < 0.1) {
      if (nvert[k][j][i+1] > ibmval-0.4 && nvert[k][j][i+1] < ibmval && i < mx-2) {
        libm_Flux += ucor[k][j][i].x;
        libm_area += sqrt(csi[k][j][i].x * csi[k][j][i].x +
              csi[k][j][i].y * csi[k][j][i].y +
              csi[k][j][i].z * csi[k][j][i].z);
              
      }
      if (nvert[k][j+1][i] > ibmval-0.4 && nvert[k][j+1][i] < ibmval && j < my-2) {
        libm_Flux += ucor[k][j][i].y;
        libm_area += sqrt(eta[k][j][i].x * eta[k][j][i].x +
              eta[k][j][i].y * eta[k][j][i].y +
              eta[k][j][i].z * eta[k][j][i].z);
      }
      if (nvert[k+1][j][i] > ibmval-0.4 && nvert[k+1][j][i] < ibmval && k < mz-2) {
        libm_Flux += ucor[k][j][i].z;
        libm_area += sqrt(zet[k][j][i].x * zet[k][j][i].x +
              zet[k][j][i].y * zet[k][j][i].y +
              zet[k][j][i].z * zet[k][j][i].z);
      }
    }
 
    if (nvert[k][j][i] > ibmval-0.4 && nvert[k][j][i] < ibmval) {
      if (nvert[k][j][i+1] < 0.1 && i < mx-2) {
        libm_Flux -= ucor[k][j][i].x;
        libm_area += sqrt(csi[k][j][i].x * csi[k][j][i].x +
              csi[k][j][i].y * csi[k][j][i].y +
              csi[k][j][i].z * csi[k][j][i].z);
              
      }
      if (nvert[k][j+1][i] < 0.1 && j < my-2) {
        libm_Flux -= ucor[k][j][i].y;
        libm_area += sqrt(eta[k][j][i].x * eta[k][j][i].x +
              eta[k][j][i].y * eta[k][j][i].y +
              eta[k][j][i].z * eta[k][j][i].z);
      }
      if (nvert[k+1][j][i] < 0.1 && k < mz-2) {
        libm_Flux -= ucor[k][j][i].z;
        libm_area += sqrt(zet[k][j][i].x * zet[k][j][i].x +
              zet[k][j][i].y * zet[k][j][i].y +
              zet[k][j][i].z * zet[k][j][i].z);
      }
    }
 
      }
    }
  }
 
  MPI_Allreduce(&libm_Flux, ibm_Flux,1,MPI_DOUBLE,MPI_SUM, PETSC_COMM_WORLD);
  MPI_Allreduce(&libm_area, ibm_Area,1,MPI_DOUBLE,MPI_SUM, PETSC_COMM_WORLD);
 
 /*  PetscGlobalSum(&libm_Flux, ibm_Flux, PETSC_COMM_WORLD); */
/*   PetscGlobalSum(&libm_area, ibm_Area, PETSC_COMM_WORLD); */
  PetscPrintf(PETSC_COMM_WORLD, "IBMFlux22 REV %le %le\n", *ibm_Flux, *ibm_Area);
 
  DMDAVecRestoreArray(da, user->lNvert, &nvert);
  DMDAVecRestoreArray(fda, user->lCsi, &csi);
  DMDAVecRestoreArray(fda, user->lEta, &eta);
  DMDAVecRestoreArray(fda, user->lZet, &zet);
  DMDAVecRestoreArray(fda, user->Ucont, &ucor);
 
  DMGlobalToLocalBegin(fda, user->Ucont, INSERT_VALUES, user->lUcont);
  DMGlobalToLocalEnd(fda, user->Ucont, INSERT_VALUES, user->lUcont);
  return 0;
}

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