Hi everyone,
I am doing the FSI using openfoam and calculix. Everything runs well at first, but simulation diverges after several seconds. I think it is due to that a relatively large force is exerted on the structure because simulation can run well after I increase the stiffness of material. But I am not sure about that. So I want to know how to judge the elastic limitation of the material.
I upload the .frd file and .inp file on this link GitHub - NUGUY2022/Structure_failure. Please check it. In addition, I also want to get some advice about the choice of material which can get larger displacement.
Check the strains. If they are large, you should use a different material model (see below). Linear elasticity is valid up to around 5% of strain or even less.
Hyperelastic material models are typically used for large deformations in the elastic regime. Unless there’s plasticity involved but it depends on the type of material so you would have to tell us what kind of material it is.
Thanks for your quick reply.
I use the hyperelastic Neo-Hookean model in this simulation. The MISES strain and TRESCA strain are shown in figures.
The material properties are like following:
x: -0.32 ~ 0.32
y: 0 ~ 0.32
z: -0.1 ~ 0.1
thickness: 0.02
HYPERELASTIC, NEO HOOKE, N=1
85034,7.2E-07
density: 1260
Does the material beyond the elastic limitation?
I don’t want to consider the plasticity because the material which can recovery to the original shape after removing the load is better to me.
Hyperelasticity is designed for large elastic strains, even up to a few hundred percent so it’s not an issue here. You should just make sure that you are using proper constants and possibly compare different hyperelastic models but this usually requires some test data.
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As you said, hyperelasticity is designed for large strains. Thus I think whether it is due to the dynamic mesh in openfoam, which can’t handle this mesh deformation. I need to check it. Thank you so much.
There can be various reasons for non-convergence. You don’t have contact here so you should make sure that all units (especially those in material properties) are consistent and that the values make sense. The deformation is not large and the elements are not distorted. But you can try using the explicit solver.
Thanks for your advice. I will debug all of these.
¿Why don’t you completely fix the membrane to assure convergence and get a first order of magnitude of the forces provided by Openfoam?
I have tested it by some cases. It is confirmed that it is not due to the calculix because the simulation can converge when I give the same force on membrane in calculix. So I think it is because that dynamic mesh method in openfoam can’t handle this mesh deformation, which result in carsh in openfoam. I need to adopt better mesh technology to handle this large mesh deformation.
Are you using preCICE too ? Maybe it’s a fault of this tool. Or OpenFOAM, as you said.
Yes, I am using preCICE. I output the mesh of Openfoam and find that the mesh is ditorted, which results in the divergency.
OpenFOAM has some remeshing / dynamic mesh capabilities. I wonder if you could use them for such FSI analysis with preCICE.
I plan to use the RBFMeshMotionSolver to replace the displacementLaplacian solver for mesh deformation. But there is still a problem that interFoam can’t use RBFMeshMotionSolver from my test. I need to insert RBFMeshMotionSolver into interFoam. But I have no idea about how to integrate RBFMeshMotionSolver into interFoam.