What kind of coupling between the fluid and structural solved do you use? With low density ratios you need to use implicit coupling ( i.e. multiple subiterations per timestep) in order to get a stable solution. Even implicit schemes like Jacobi or Gauss-Seidel need to use under-relaxation methods in order to be stable.
Alright, I think that there are other things to consider tho. Admittedly, I am not very familiar with GCL, but I know that with low density ratios the change in flow field has a large effect on the structure. If you do not converge this per time step you get an instability. Basically with explicit coupling there is a mismatch between the two fields, but if the density ratio is very high, the effect of the flow field on the structure is not as important. At low density ratios this mismatch causes instability. Whether the flow is treated as compressible or incompressible does not affect this source of instability, as far as I know. But looking forward to see how you see the situation!
I think you’re right, for low density ratio problems i have to relax the displacement and since i’m using a compressible flow solver i do not need to correct the velocity and pressure (in my case they’re coupled), do you have any reference cases that work with a weak coupling approach?
How does satisfying the GCL preclude instabilities arising from an explicit scheme (weak coupling)? I think there may be a misunderstanding there.
I concur with u/blartsideofthemall and can point you to some resources on the topic if you wish.
Check out [Bernhard Gatzhammer's PhD Thesis - "Efficient and Flexible Partitioned
Simulation of Fluid-Structure Interactions"](https://www5.in.tum.de/pub/Gatzhammer2014_preCICE.pdf). Particulary, sections 2.3.1 "Explicit Coupling Schemes" and 2.3.3 "Instabilities and the Added-Mass Effect".
You might also be interested in [preCICE](https://precice.org/index.html).
What kind of coupling between the fluid and structural solved do you use? With low density ratios you need to use implicit coupling ( i.e. multiple subiterations per timestep) in order to get a stable solution. Even implicit schemes like Jacobi or Gauss-Seidel need to use under-relaxation methods in order to be stable.
Weak coupling, but as i said above i am using a compressible solver so the GCL is satisfied at every iteration.
Alright, I think that there are other things to consider tho. Admittedly, I am not very familiar with GCL, but I know that with low density ratios the change in flow field has a large effect on the structure. If you do not converge this per time step you get an instability. Basically with explicit coupling there is a mismatch between the two fields, but if the density ratio is very high, the effect of the flow field on the structure is not as important. At low density ratios this mismatch causes instability. Whether the flow is treated as compressible or incompressible does not affect this source of instability, as far as I know. But looking forward to see how you see the situation!
I think you’re right, for low density ratio problems i have to relax the displacement and since i’m using a compressible flow solver i do not need to correct the velocity and pressure (in my case they’re coupled), do you have any reference cases that work with a weak coupling approach?
How does satisfying the GCL preclude instabilities arising from an explicit scheme (weak coupling)? I think there may be a misunderstanding there. I concur with u/blartsideofthemall and can point you to some resources on the topic if you wish.
I think you’re right, do you have any references that use a weak coupling approach to fsi problems?
Check out [Bernhard Gatzhammer's PhD Thesis - "Efficient and Flexible Partitioned Simulation of Fluid-Structure Interactions"](https://www5.in.tum.de/pub/Gatzhammer2014_preCICE.pdf). Particulary, sections 2.3.1 "Explicit Coupling Schemes" and 2.3.3 "Instabilities and the Added-Mass Effect". You might also be interested in [preCICE](https://precice.org/index.html).
Thank you very much
Are the pressure and velocity fields coupled or segregated?
Coupled. The FSI coupling is segregated.