Hi all,

I am having convergence issues at the first iteration of a FSI simulation. I am writing a structural solver adapter and I am trying to couple it with openFOAM.

I am performing a `serial-implicit coupling`

with `Fluid`

first and `Solid`

second solver.

The convergence on `displacements`

is set on `relative convergence measure`

.

Looking at the convergence, at each iteration the first time step, I get:

`relative two-norm diff = 1`

and of course it never converges.

While I am analyzing the code on the structural side, I’d like to be sure that the structure and the sequence of operations in the adapter are correct (I basically followed *dummySolver.cpp*). My code looks like this:

```
while (interface->isCouplingOngoing()){
if(interface->isActionRequired(actionWriteIterationCheckpoint())){
interface->markActionFulfilled(actionWriteIterationCheckpoint());
}
// read forces from interface
if (interface->isReadDataAvailable()) {
interface->readBlockVectorData(forceID,
vertexSize,
vertexIDs,
adapterForces);
}
// Send forces to solver
computeForces(adapterForces,coeff);
// Solver compute motion step
solve();
// retrieve displacements from solver
getConnDisplacements(adapterDisplacements);
// send displacewments to interface
if(interface->isWriteDataRequired(precice_dt)){
interface->writeBlockVectorData(displID,
vertexSize,
vertexIDs,
adapterDisplacements);
}
// advance
precice_dt = interface->advance(precice_dt);
if(interface->isActionRequired(actionReadIterationCheckpoint())){
interface->markActionFulfilled(actionReadIterationCheckpoint());
// tell solver that timestep didn't converge
putForces(false);
}else{
// tell solver that timestep converged
putForces(true);
}
}
```

I am also writing the values (Forces and Displacements) at the interface by using `export:vtk`

in the *precice-config* file at each iteration. Basically the forces keep being constant, while displacements seem to oscillate between two sets of values (nevertheless being extremely small). The fact that the two-norm diff is always 1 makes me think that one set of displacements is zero at the numerator, but I don’t see where. The mesh can be found here:

Any suggestion is much appreciated

Thank you

Claudio