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Christophe Geuzaine authored
new mesh::clear() Rationale: setNodes/setElements were intrinsically a bad design choice, as these functions had to delete nodes and/or elements before storing the new ones. Using these functions in the wrong way could lead to an invalid mesh, with elements pointing to nodes that were deleted (in an adjacent entity). The only viable workflow is to delete the mesh (with the new clear() function), before adding nodes/elements.
Christophe Geuzaine authorednew mesh::clear() Rationale: setNodes/setElements were intrinsically a bad design choice, as these functions had to delete nodes and/or elements before storing the new ones. Using these functions in the wrong way could lead to an invalid mesh, with elements pointing to nodes that were deleted (in an adjacent entity). The only viable workflow is to delete the mesh (with the new clear() function), before adding nodes/elements.
t18.cpp 5.76 KiB
// -----------------------------------------------------------------------------
//
// Gmsh C++ tutorial 18
//
// Periodic meshes
//
// -----------------------------------------------------------------------------
// Periodic meshing constraints can be imposed on surfaces and curves.
#include <set>
#include <algorithm>
#include <gmsh.h>
int main(int argc, char **argv)
{
gmsh::initialize(argc, argv);
gmsh::model::add("t18");
// Let's use the OpenCASCADE geometry kernel to build two geometries.
// The first geometry is very simple: a unit cube with a non-uniform mesh size
// constraint (set on purpose to be able to verify visually that the
// periodicity constraint works!):
gmsh::model::occ::addBox(0, 0, 0, 1, 1, 1, 1);
gmsh::model::occ::synchronize();
std::vector<std::pair<int, int> > out;
gmsh::model::getEntities(out, 0);
gmsh::model::mesh::setSize(out, 0.1);
gmsh::model::mesh::setSize({{0, 1}}, 0.02);
// To impose that the mesh on surface 2 (the right side of the cube) should
// match the mesh from surface 1 (the left side), the following periodicity
// constraint is set:
std::vector<double> translation(
{1, 0, 0, 1, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1});
gmsh::model::mesh::setPeriodic(2, {2}, {1}, translation);
// The periodicity transform is provided as a 4x4 affine transformation
// matrix, given by row.
// During mesh generation, the mesh on surface 2 will be created by copying
// the mesh from surface 1.
// Multiple periodicities can be imposed in the same way:
gmsh::model::mesh::setPeriodic(
2, {6}, {5}, {1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 1, 0, 0, 0, 1});
gmsh::model::mesh::setPeriodic(
2, {4}, {3}, {1, 0, 0, 0, 0, 1, 0, 1, 0, 0, 1, 0, 0, 0, 0, 1});
// For more complicated cases, finding the corresponding surfaces by hand can
// be tedious, especially when geometries are created through solid
// modelling. Let's construct a slightly more complicated geometry.
// We start with a cube and some spheres:
gmsh::model::occ::addBox(2, 0, 0, 1, 1, 1, 10);
double x = 2 - 0.3, y = 0, z = 0;
gmsh::model::occ::addSphere(x, y, z, 0.35, 11);
gmsh::model::occ::addSphere(x + 1, y, z, 0.35, 12);
gmsh::model::occ::addSphere(x, y + 1, z, 0.35, 13);
gmsh::model::occ::addSphere(x, y, z + 1, 0.35, 14);
gmsh::model::occ::addSphere(x + 1, y + 1, z, 0.35, 15);
gmsh::model::occ::addSphere(x, y + 1, z + 1, 0.35, 16);
gmsh::model::occ::addSphere(x + 1, y, z + 1, 0.35, 17);
gmsh::model::occ::addSphere(x + 1, y + 1, z + 1, 0.35, 18);
// We first fragment all the volumes, which will leave parts of spheres
// protruding outside the cube:
std::vector<std::vector<std::pair<int, int> > > out_map;
std::vector<std::pair<int, int> > sph;
for(int i = 11; i <= 18; i++) sph.push_back(std::pair<int, int>(3, i));
gmsh::model::occ::fragment({{3, 10}}, sph, out, out_map);
gmsh::model::occ::synchronize();
// Ask OpenCASCADE to compute more accurate bounding boxes of entities using
// the STL mesh:
gmsh::option::setNumber("Geometry.OCCBoundsUseStl", 1);
// We then retrieve all the volumes in the bounding box of the original cube,
// and delete all the parts outside it:
double eps = 1e-3;
std::vector<std::pair<int, int> > in;
gmsh::model::getEntitiesInBoundingBox(2 - eps, -eps, -eps, 2 + 1 + eps,
1 + eps, 1 + eps, in, 3);
for(auto i : in) {
auto it = std::find(out.begin(), out.end(), i);
if(it != out.end()) out.erase(it);
}
gmsh::model::removeEntities(out, true); // Delete outside parts recursively
// We now set a non-uniform mesh size constraint (again to check results
// visually):
std::vector<std::pair<int, int> > p;
gmsh::model::getBoundary(in, p, false, false, true); // Get all points
gmsh::model::mesh::setSize(p, 0.1);
gmsh::model::getEntitiesInBoundingBox(2 - eps, -eps, -eps, 2 + eps, eps, eps,
p, 0);
gmsh::model::mesh::setSize(p, 0.001);
// We now identify corresponding surfaces on the left and right sides of the
// geometry automatically.
// First we get all surfaces on the left:
std::vector<std::pair<int, int> > sxmin;
gmsh::model::getEntitiesInBoundingBox(2 - eps, -eps, -eps, 2 + eps, 1 + eps,
1 + eps, sxmin, 2);
for(auto i : sxmin) {
// Then we get the bounding box of each left surface
double xmin, ymin, zmin, xmax, ymax, zmax;
gmsh::model::getBoundingBox(i.first, i.second, xmin, ymin, zmin, xmax, ymax,
zmax);
// We translate the bounding box to the right and look for surfaces inside
// it:
std::vector<std::pair<int, int> > sxmax;
gmsh::model::getEntitiesInBoundingBox(xmin - eps + 1, ymin - eps,
zmin - eps, xmax + eps + 1,
ymax + eps, zmax + eps, sxmax, 2);
// For all the matches, we compare the corresponding bounding boxes...
for(auto j : sxmax) {
double xmin2, ymin2, zmin2, xmax2, ymax2, zmax2;
gmsh::model::getBoundingBox(j.first, j.second, xmin2, ymin2, zmin2, xmax2,
ymax2, zmax2);
xmin2 -= 1;
xmax2 -= 1;
// ...and if they match, we apply the periodicity constraint
if(std::abs(xmin2 - xmin) < eps && std::abs(xmax2 - xmax) < eps &&
std::abs(ymin2 - ymin) < eps && std::abs(ymax2 - ymax) < eps &&
std::abs(zmin2 - zmin) < eps && std::abs(zmax2 - zmax) < eps) {
gmsh::model::mesh::setPeriodic(2, {j.second}, {i.second}, translation);
}
}
}
gmsh::model::mesh::generate(3);
gmsh::write("t18.msh");
// Launch the GUI to see the results:
std::set<std::string> args(argv, argv + argc);
if(!args.count("-nopopup")) gmsh::fltk::run();
gmsh::finalize();
return 0;
}