IBNearestFacetNormal.c File Reference

Find the nearest facet for immersed boundary points. More...

#include <stdio.h>
#include <basic.h>
#include <mathfunctions.h>
#include <mpivars.h>
#include <immersedboundaries.h>

Go to the source code of this file.

Functions
int	IBNearestFacetNormal (void *ib, void *m, double *X, double large_distance, int *dim_l, int ghosts)

Detailed Description

Find the nearest facet for immersed boundary points.

Author

Debojyoti Ghosh

Definition in file IBNearestFacetNormal.c.

Function Documentation

int IBNearestFacetNormal	(	void *	ib,
		void *	m,
		double *	X,
		double	large_distance,
		int *	dim_l,
		int	ghosts
	)

For each immersed boundary point, find the nearest facet (Facet3D) of the immersed body (ImmersedBoundary::body). The "nearest" facet is the one which is closest to the boundary point in terms of the distance along the normal defined for that facet.

• The function will first try to find the nearest facet for which a line starting from the boundary point along the direction defind by the facet normal passes through that facet.
• Failing the above criterion, the function will find the nearest facet.

Note: This function is sensitive to the fact that the normals defined for the immersed body are the outward normals, i.e., pointing away from the body. If this function returns an error, make sure this is true in the STL file the body is defined in.

Parameters

ib	Immersed boundary object of type ImmersedBoundary
m	MPI object of type MPIVariables
X	Array of (local) spatial coordinates
large_distance	A large distance
dim_l	Integer array of local grid size in each spatial dimension
ghosts	Number of ghost points

Definition at line 25 of file IBNearestFacetNormal.c.

{
  ImmersedBoundary  *IB       = (ImmersedBoundary*) ib;
  MPIVariables      *mpi      = (MPIVariables*) m;
  Body3D            *body     = IB->body;
  Facet3D           *surface  = body->surface;
  IBNode            *boundary = IB->boundary;

  double  eps = IB->tolerance;
  int     nb  = IB->n_boundary_nodes,
          nf  = body->nfacets;

    int i, j, k, dg, n;
    for (dg = 0; dg < nb; dg++) {
        i = boundary[dg].i;
        j = boundary[dg].j;
        k = boundary[dg].k;

    double xp, yp, zp;
    _GetCoordinate_(0,i,dim_l,ghosts,X,xp);
    _GetCoordinate_(1,j,dim_l,ghosts,X,yp);
    _GetCoordinate_(2,k,dim_l,ghosts,X,zp);
    boundary[dg].x = xp;
    boundary[dg].y = yp;
    boundary[dg].z = zp;

        double  dist_min = large_distance;
        int     n_min    = -1;

        for (n = 0; n < nf; n++) {
            double x1, x2, x3;
            double y1, y2, y3;
            double z1, z2, z3;
            x1 = surface[n].x1; x2 = surface[n].x2; x3 = surface[n].x3;
            y1 = surface[n].y1; y2 = surface[n].y2; y3 = surface[n].y3;
            z1 = surface[n].z1; z2 = surface[n].z2; z3 = surface[n].z3;
            double dist =   surface[n].nx*(xp-surface[n].x1) 
                    + surface[n].ny*(yp-surface[n].y1) 
                    + surface[n].nz*(zp-surface[n].z1);
            if (dist > 0)   continue;
            if (absolute(dist) < dist_min) {
                short   is_it_in = 0;
                double  x_int, y_int, z_int;
                x_int = xp - dist * surface[n].nx;
                y_int = yp - dist * surface[n].ny;
                z_int = zp - dist * surface[n].nz;
                if (absolute(surface[n].nx) > eps) {
                    double den = (z2-z3)*(y1-y3)-(y2-y3)*(z1-z3);
                    double l1, l2, l3;
                    l1 = ((y2-y3)*(z3-z_int)-(z2-z3)*(y3-y_int)) / den;
                    l2 = ((z1-z3)*(y3-y_int)-(y1-y3)*(z3-z_int)) / den;
                    l3 = 1 - l1 - l2;
                    if ((l1 > -eps) && (l2 > -eps) && (l3 > -eps))  is_it_in = 1;
                } else if (absolute(surface[n].ny) > eps) {
                    double den = (x2-x3)*(z1-z3)-(z2-z3)*(x1-x3);
                    double l1, l2, l3;
                    l1 = ((z2-z3)*(x3-x_int)-(x2-x3)*(z3-z_int)) / den;
                    l2 = ((x1-x3)*(z3-z_int)-(z1-z3)*(x3-x_int)) / den;
                    l3 = 1 - l1 - l2;
                    if ((l1 > -eps) && (l2 > -eps) && (l3 > -eps))  is_it_in = 1;
                } else {
                    double den = (y2-y3)*(x1-x3)-(x2-x3)*(y1-y3);
                    double l1, l2, l3;
                    l1 = ((x2-x3)*(y3-y_int)-(y2-y3)*(x3-x_int)) / den;
                    l2 = ((y1-y3)*(x3-x_int)-(x1-x3)*(y3-y_int)) / den;
                    l3 = 1 - l1 - l2;
                    if ((l1 > -eps) && (l2 > -eps) && (l3 > -eps))  is_it_in = 1;
                }
                if (is_it_in) {
                    dist_min = absolute(dist);
                    n_min = n; 
                }
            }
        }
        if (n_min == -1) {
            for (n = 0; n < nf; n++) {
                double dist =   surface[n].nx*(xp-surface[n].x1) 
                      + surface[n].ny*(yp-surface[n].y1) 
                      + surface[n].nz*(zp-surface[n].z1);
                if (dist > eps) continue;
                else {
                    if (absolute(dist) < dist_min) {
                        dist_min = absolute(dist);
                        n_min = n;
                    }
                }
            }
        }

        if (n_min == -1)    {
      fprintf(stderr,"Error in IBNearestFacetNormal(): no nearest normal found for boundary node (%d,%d,%d) ",i,j,k);
      fprintf(stderr,"on rank %d.\n",mpi->rank);
      return(1);
    } else boundary[dg].face = &surface[n_min];
    }

  return(0);
}