{"id":462869,"date":"2026-08-23T05:20:59","date_gmt":"2026-08-23T05:20:59","guid":{"rendered":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/fsi-system-coupling-element-distortion-in-rubber-tube\/"},"modified":"2026-08-23T05:20:59","modified_gmt":"2026-08-23T05:20:59","slug":"fsi-system-coupling-element-distortion-in-rubber-tube","status":"publish","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/fsi-system-coupling-element-distortion-in-rubber-tube\/","title":{"rendered":"FSI System Coupling Element distortion in rubber tube"},"content":{"rendered":"

Hii, I am trying to solve Two way fsi with system coupling for a rubber pipe of Inner dia 30 mm and length 200 mm with Young’s modulus of 10 Mpa, Poisson ratio 0.45 and even lower values but it just won’t converge and blow up the solution with giving either element distortion error in Ansys mechanical or negative cell volume in fluent. I have tried a lot of things (a lot), namely, fine hex mesh (Quadratic elements), lower timestep, autosubstepping with a wide range of substeps (min 1 — max 100), increasing number of equilibrium iterations (50) and choosing Iterative PCG solver in Ansys mechanical also direct solver doesn’t necessarily improve the solution. Also, I have sinusoidal velocity profile at inlet and 12 kPa at outlet in fluent. In System coupling I have tried lower Under relaxation factor of data transfers, more number of coupling iterations (20) and also Quasi newton Global Stabilization. Note, the failure doesn’t occur at the beginning of simulation but somewhere around midway. I think I have tried everything I could but still face the same problem as day 1. The force convergence value going to solid part stays within range 1 to 10 and after a certain timestep it just blows up to 100 or 150 or even higher and then I get highly skewed elements in structure and finally failure. The standalone case in fluent CFD without FSI converges nicely, so I am guessing whatever is the problem is occuring in the data transfer between solid and fluid part. Your help would be greatly appreciated. Here is the image of solid part with mesh and fluid part with mesh. <\/p>\n

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