Adapt mesh problems and question about MPI

General Discussion
1

Hello,

I am new in the community of FreeFem. I am trying to use a code that we haven’t used in my lab for quite a long time. As you can see in the code below after loading a base mesh we use the tool adpatmesh and split mesh but the results obtained were a little bit weird . I have tested it on a rectangular domain. I have added attached the basic mesh ( left figure) that I used and the mesh after using adaptmesh ( right figure) and as you can see the mesh is absolutly randomly refined and I wanted a simple homogeneous mesh. Maybe I am not using adaptmesh correctly? Can someone see and error in the functions parameters?

I have also a question regarding the parallelization of a little part of my code. the splitmesh sometimes crashes for huge mesh and I wanted to know if it possible to use mpi to parallelize just this function?

I really thank you in advance for your help.

basic_and_adapted_mesh
basic_and_adapted_mesh.jpg1049×365 426 KB

Code used:

include “getARGV.idp”

// read the parameters
real m = 1;
string meshname = getARGV("-mesh", “BASE/ffem-mesh.msh”);
string urname = getARGV("-ur", “BASE/ffem-ur.dat”);
string utname = getARGV("-ut", “BASE/ffem-ut.dat”);
string uxname = getARGV("-ux", “BASE/ffem-ux.dat”);
string nuname = getARGV("-nu", “BASE/ffem-nu.dat”);
string prefix = getARGV("-prefix", “BASE/ffem-”);
string suffix = getARGV("-suffix", “.dat”);
string lindir = getARGV("-lin", “LIN”);
int refine = getARGV("-refine", 0);
real cRatio = getARGV("-ratio", 1.2);
real cHmax = getARGV("-hmax", 5.0e-03);
int nol = getARGV("-nol", 1);

// import dimensionless mesh
mesh Th = readmesh(meshname);

// prepare the vector spaces
fespace Xh(Th, P2);
fespace Mh(Th, P1);

// import meanfields on P1 space
Mh ur, ut, ux, nu;
{
ifstream fid(urname);
fid >> ur[];
}
{
ifstream fid(utname);
fid >> ut[];
}
{
ifstream fid(uxname);
fid >> ux[];
}
{
ifstream fid(nuname);
fid >> nu[];
}

// interpolate implicitely on P2 space
Xh U=ur, V=ut, W=ux, Visco=nu;
Mh PrMean;

ratio = 1.1
hmax = 1e-04

// adapt mesh to velocity field
if(refine == 1) {
Th = adaptmesh(Th, nbvx=10000, ratio=1.1, hmax=1e-04);
U = U;
V = V;
W = W;
Visco = Visco;
PrMean = PrMean;
}

// re-export the connectivity and coordinates for PFS format
{ ofstream file(prefix+“coordinates”+suffix);
for (int j=0;j<Th.nv; j++) {
file << Th(j).x << " " << Th(j).y << endl;}
}

{ ofstream file(prefix+“connectivity”+suffix);
int nbtriangle = Th.nt;
for (int i=0;i<Th.nt; i++){
file << Th[i][0]+1 << " " << Th[i][1]+1 << " " << Th[i][2]+1 << endl;}
}

// split it and save it again
mesh Th2 = splitmesh(Th, 2);
{ ofstream file(prefix+“coordinates-2”+suffix);
for (int j=0;j<Th2.nv; j++) {
file << Th2(j).x << " " << Th2(j).y << endl;}
}

{ ofstream file(prefix+“connectivity-2”+suffix);
int nbtriangle = Th2.nt;
for (int i=0;i<Th2.nt; i++){
file << Th2[i][0]+1 << " " << Th2[i][1]+1 << " " << Th2[i][2]+1 << endl;}
}

2

Welcome in the FreeFEM community.

In order to refine your mesh in this way, you have to write the following instruction:

real h = 1e-4;
Th = adaptmesh(Th, h, IsMetric=true, nbvx=1e5);

For the parallelization, the best way is to use the domain decomposition method with split, see e.g
This example, but you have to parallelize the complete script.

3

Hello Simon,

Thank you for your quick reply. I tried exactly the instruction that you gave me . But as you can see in the picture below my mesh is still not homogeneous. Do you have other ideas?
45

Thanks again

4

Do you have a warning where adaptmesh function is called ?
If you have not enought vertices (limit defined with nbvx), the mesh adaptation won’t run perfectly

5

Thanks it is working now! and thank you also for the parallelized code example :wink: