Hi everybody,
I’ve recently started working on modal superposition in an FSI setting, so I tried switching CalculiX in the breaking-dam-2d tutorial (OpenFOAM + CalculiX) from direct time integration to modal dynamics. The coupled simulation crashes. To make sure the problem isn’t in my own setup, I reproduced it on the unmodified tutorial, changing only the analysis step.
System and versions:
OS: Ubuntu 24.04.4 LTS
preCICE: 3.4.1
OpenFOAM: v2512
OpenFOAM adapter: 1.3.1
CalculiX: 2.20
CalculiX adapter: 2.20.2-1
What I changed: In the CalculiX input file, I replaced
*DYNAMIC, ALPHA=0.0, DIRECT
with
*MODAL DYNAMIC DIRECT
Everything else is the same as in the tutorial: mesh, material (E = 40 MPa, ν = 0, ρ = 3000), boundary conditions, *CLOAD, and the 2e-3 s coupling window.
Because the adapter rejects any input file containing *FREQUENCY, I computed the first 10 eigenmodes in a separate, uncoupled CalculiX run with
*FREQUENCY, STORAGE=YES
10
and copied the resulting .eig file to the modal dynamic job name so CalculiX picks it up.
The unmodified tutorial with *DYNAMIC runs without problems using the same preCICE configuration, so the problem seems to be on the structural side or at the interface.
What happens: Before the water reaches the flap at about t = 0.3 s, the loads are small and the watch-point displacement in x rises smoothly to about 1 mm. After impact, the x displacement reverses and swings to -2.32 mm at t = 0.362 s and then to +3.40 mm at t = 0.386 s. The y component of the coupling force has a small high/low alternation between neighbouring time windows from the start of the simulation. After impact this alternation slowly gets larger, and at t = 0.368 s both force components start changing sign every window. Within three windows the y force reaches about ±6 and the x force about ±0.25. The displacement stays smooth the whole time, even while the force changes sign. At t = 0.386 s, IQN-ILS fails to converge within 30 iterations (relative displacement residual 2.37, limit 1e-3). Two iterations into the next window, the simulation crashes.
The Fluid participant crashes first. alpha.water, which should stay between 0 and 1, jumps from about 1.01 to Min = -926.9, Max = 25.85 in a single MULES correction, followed by a floating-point exception in Foam::GAMGSolver::scale. This is the last time step before the crash (t = 0.39):
---[precice] Mapping "Force" for t=0.39 from "Fluid-Mesh" to "Solid-Mesh"
---[precice] Mapping "Displacement" for t=0.39 from "Solid-Mesh" to "Fluid-Mesh"
---[precice] it 2 (min: 1, max: 30), time-window 195, t 0.388 (max: 1), Dt 0.002, max-dt 0.002
Courant Number mean: 0.049499 max: 0.718678
Interface Courant Number mean: 0.00211176 max: 0.52678
Time = 0.39
PIMPLE: iteration 1
smoothSolver: Solving for cellDisplacementx, Initial residual = 0.997277, Final residual = 1.25549e-17, No Iterations 3
smoothSolver: Solving for cellDisplacementy, Initial residual = 0.998763, Final residual = 1.67704e-18, No Iterations 3
GAMGPCG: Solving for pcorr, Initial residual = 1, Final residual = 2.83574e-06, No Iterations 8
GAMGPCG: Solving for pcorr, Initial residual = 0.192751, Final residual = 5.85416e-06, No Iterations 5
time step continuity errors : sum local = 0.000100864, global = 1.27581e-05, cumulative = 4.31089e-05
smoothSolver: Solving for alpha.water, Initial residual = 0.0463995, Final residual = 6.47399e-09, No Iterations 25
Phase-1 volume fraction = 0.195618 Min(alpha.water) = 5.60407e-39 Max(alpha.water) = 1.00992
MULES: Correcting alpha.water
Phase-1 volume fraction = 0.212111 Min(alpha.water) = -926.892 Max(alpha.water) = 25.8514
[stack trace]
=============
#1 Foam::sigFpe::sigHandler(int) in /usr/lib/openfoam/openfoam2512/platforms/linux64GccDPInt32Opt/lib/libOpenFOAM.so
#2 ? in /lib/x86_64-linux-gnu/libc.so.6
#3 Foam::GAMGSolver::scale(Foam::Field<double>&, Foam::Field<double>&, Foam::lduMatrix const&, Foam::FieldField<Foam::Field, double> const&, Foam::UPtrList<Foam::lduInterfaceField const> const&, Foam::Field<double> const&, unsigned char) const in /usr/lib/openfoam/openfoam2512/platforms/linux64GccDPInt32Opt/lib/libOpenFOAM.so
#4 Foam::GAMGSolver::Vcycle(Foam::PtrList<Foam::lduMatrix::smoother> const&, Foam::Field<double>&, Foam::Field<double> const&, Foam::Field<double>&, Foam::Field<double>&, Foam::Field<double>&, Foam::Field<double>&, Foam::Field<double>&, Foam::PtrList<Foam::Field<double> >&, Foam::PtrList<Foam::Field<double> >&, unsigned char) const in /usr/lib/openfoam/openfoam2512/platforms/linux64GccDPInt32Opt/lib/libOpenFOAM.so
#5 Foam::GAMGSolver::solve(Foam::Field<double>&, Foam::Field<double> const&, unsigned char) const in /usr/lib/openfoam/openfoam2512/platforms/linux64GccDPInt32Opt/lib/libOpenFOAM.so
#6 Foam::fvMatrix<double>::solveSegregated(Foam::dictionary const&) in /usr/lib/openfoam/openfoam2512/platforms/linux64GccDPInt32Opt/lib/libfiniteVolume.so
#7 ? in /usr/lib/openfoam/openfoam2512/platforms/linux64GccDPInt32Opt/lib/libfiniteVolume.so
#8 Foam::fvMesh::solve(Foam::fvMatrix<double>&, Foam::dictionary const&) const in /usr/lib/openfoam/openfoam2512/platforms/linux64GccDPInt32Opt/lib/libfiniteVolume.so
#9 ? in /usr/lib/openfoam/openfoam2512/platforms/linux64GccDPInt32Opt/bin/interFoam
#10 ? in /lib/x86_64-linux-gnu/libc.so.6
#11 __libc_start_main in /lib/x86_64-linux-gnu/libc.so.6
#12 ? in /usr/lib/openfoam/openfoam2512/platforms/linux64GccDPInt32Opt/bin/interFoam
=============
Floating point exception (core dumped)
What I have already tried: I first suspected an added-mass instability, but the added mass is not large enough to explain the divergence. I also tried using more eigenmodes, different time step sizes, and adding Rayleigh damping. None of these fixed the problem; the damping only slightly delayed the crash.
Attached files:
precice-config.xml (2.5 KB)
precice-Solid-convergence.log (46.0 KB)
precice-Solid-iterations.log (10.5 KB)
precice-Solid-watchpoint-Tip.log (22.5 KB)
fluid-openfoam.log (3.3 MB)
precice-Fluid-iterations.log (5.9 KB)
My questions:
- Has *MODAL DYNAMIC been tested with the CalculiX adapter?
- Is there a known problem with using it with implicit coupling?
- Is there anything else I should try?
Thanks in advance for any help 
Bianca