compiling but segmentation fault

I think you can not access f_total_ because its a vector, there is a reason why it is protected.

A better way to access the total forces and torques of one mesh is to call compute_vector(int i) of FixMeshSurfaceStress :

FixMeshSurfaceStress *fixMeshSurfaceStress = dynamic_cast(mesh);
if (fixMeshSurfaceStress == NULL) error->all(FLERR, "Internal Error - mesh is no fixMeshSurfaceStress!");
// get all outputs
for(int i=0; i<6; i++)
{
// Force and Torque from fixMeshSurfaceStress
double tmp = fixMeshSurfaceStress->compute_vector(i);
// und an die FMU uebergeben
if (i<3)
//do something with tmp (points to forceX/Y/Z)
else
//do something with tmp (points to torqueX/Y/Z)
}

I have this in mesh_mover to react on forces, in your class you need to get mesh first (in mesh_mover it is allready present)
something like this might work:

int ifix = modify->find_fix("YOUR FIX MESH ID"); //mesh id is defined in inputskript
if(ifix == -1)
error->all(FLERR,"mesh id not found");
FixMesh *fix_mesh_ = static_cast(modify->fix[ifix]);
mesh = fix_mesh_->mesh();

(untested)
Don't forget to include fix_mesh.h and fix_surface_mesh.h in your cpp file and to define

class FixMesh *fix_mesh_;
class AbstractMesh *mesh_;

in the header of your class.

What is your intend to code this ?

Best,
Christian.

Here is my implementation to transfer forces from mesh_mover to a rigid body. To be honest I don't apply the forces to a mesh because I have the fix6dof which is (c) by DCS GmbH. But I apply the forces to a multisphere to fake mesh/mesh interaction.


void MeshMoverRigid::final_integrate(double dTAbs,double dTSetup,double dt)
{
FixMesh *mesh = fix_move_mesh_->fixMesh(); //fix_move_mesh_ is internal known by the caller class ..., get reference to mesh here ..
if (mesh == NULL) error->all(FLERR, "Internal Error mesh is NULL!");
FixMeshSurfaceStress *fixMeshSurfaceStress = dynamic_cast(mesh);
if (fixMeshSurfaceStress == NULL) error->all(FLERR, "Internal Error mesh is no fixMeshSurfaceStress!");
// get all outputs
double fx=fixMeshSurfaceStress->compute_vector(0);
double fy=fixMeshSurfaceStress->compute_vector(1);
double fz=fixMeshSurfaceStress->compute_vector(2);
double Mx=fixMeshSurfaceStress->compute_vector(3);
double My=fixMeshSurfaceStress->compute_vector(4);
double Mz=fixMeshSurfaceStress->compute_vector(5);
double F_ext[3];
double M_ext[3];
vectorConstruct3D(F_ext,fx,fy,fz);
vectorConstruct3D(M_ext,Mx,My,Mz);
ms_->add_ext_forces(F_ext,internal_body_index_); //apply forces to clump
ms_->add_ext_torque(M_ext,internal_body_index_); //apply torque to clump
}


Here is a video for all who are interested in the results: https://www.youtube.com/watch?v=6lfoAgqTIxE&feature=youtu.be