FSI restart issues

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 July 21, 2020, 09:36 FSI restart issues #1 Member   Join Date: Apr 2011 Posts: 57 Rep Power: 14 Hello, I've found I have restart issues with solids4Foam FSI problems. For example, if I run the laminar HronTurekFsi3 tutorial problem from 0 to 6 seconds, it runs fine with no issues. However if I restart the problem from 5 seconds, it soon blows up and diverges (in my test case it gave a few material stability errors at 5.002, started giving a bunch more around 5.03 seconds, and crashed at 5.035 seconds). I'm using foam-extend-4.0, and the master solids4Foam branch, updated as of July 14th. Anyone else notice this issue, or have any recommendations? Thanks!

 August 3, 2020, 13:04 #2 Member   Join Date: Apr 2011 Posts: 57 Rep Power: 14 This issue is still plaguing me, and makes it rather difficult to perform large FSI problems. Here's some data from a run of the Hron & Turek FSI3 example problem (nothing in the problem setup has been changed, other than allowing it to run beyond t=6). Original run (no restarts) at time 18.241: Code: ```Time = 18.241 Setting traction on solid interfaces Interpolating face values using GGI Total force on fluid interface 0: (0.481859 -2.11122 -1.70705e-15) Total force on solid interface 0: (-0.481865 2.11122 1.70701e-15) Evolving solid solver Corr 0, relative residual = 1 Corr 382, relative residual = 9.77886e-08 FDICPCG: Solving for D, Initial residual = 0.00294397, Final residual = 2.67555e-09, No outer iterations = 382 Max relative residual = 1, Relative residual = 9.77886e-08, enforceLinear = false Interpolating point values using GGI Interpolating point values using GGI FSI relative residual1 norm for interface 0: 1 FSI residual2 norm for interface 0: 0.0361545 Time = 18.241, iteration: 1 Modes before clean-up (plate): 13, modes after clean-up (plate): 0 Current fsi under-relaxation factor (plate): 0.05 Maximal accumulated displacement of interface 0: 0.0331739 GAMG: Solving for cellMotionUx, Initial residual = 0.998813, Final residual = 5.78483e-07, No Iterations 5 GAMG: Solving for cellMotionUy, Initial residual = 0.999831, Final residual = 5.11375e-07, No Iterations 5 GAMG: Solving for cellMotionUx, Initial residual = 0.00904394, Final residual = 3.03658e-07, No Iterations 5 GAMG: Solving for cellMotionUy, Initial residual = 0.00795309, Final residual = 2.59858e-07, No Iterations 5 Evolving fluid model: icoFluid Courant Number mean: 0.0719761 max: 1.15849 velocity magnitude: 4.25753 DILUPBiCG: Solving for Ux, Initial residual = 0.00256183, Final residual = 2.02558e-07, No Iterations 3 DILUPBiCG: Solving for Uy, Initial residual = 0.0110399, Final residual = 1.06781e-07, No Iterations 4 GAMG: Solving for p, Initial residual = 0.543665, Final residual = 9.29462e-07, No Iterations 68 GAMG: Solving for p, Initial residual = 0.426793, Final residual = 7.29255e-07, No Iterations 26 time step continuity errors : sum local = 6.4016e-10, global = 1.18308e-10, cumulative = 3.74158e-07 GAMG: Solving for p, Initial residual = 0.146667, Final residual = 8.44153e-07, No Iterations 27 GAMG: Solving for p, Initial residual = 0.0458902, Final residual = 9.87122e-07, No Iterations 20 time step continuity errors : sum local = 1.11489e-09, global = 2.03898e-10, cumulative = 3.74362e-07 GAMG: Solving for p, Initial residual = 0.0254093, Final residual = 7.90576e-07, No Iterations 21 GAMG: Solving for p, Initial residual = 0.0106926, Final residual = 9.48972e-07, No Iterations 17 time step continuity errors : sum local = 1.05209e-09, global = 2.00444e-10, cumulative = 3.74562e-07 Setting traction on solid interfaces Interpolating face values using GGI Total force on fluid interface 0: (14.6646 -789.207 1.29213e-15) Total force on solid interface 0: (-14.6645 789.206 -1.29209e-15)``` Now from a restart at time=18.241: Code: ```Time = 18.241 From function fluidSolidInterface::updateCoupled() in file fluidSolidInterfaces/fluidSolidInterface/fluidSolidInterface.C at line 62 Enabling fluid-solid coupling Setting traction on solid interfaces Interpolating face values using GGI Create GGI zone-to-zone interpolator interface-to-interface face error: 0.0226088 calcMasterPointAddressing() const Extended GGI, master point distance, max: 3.14671e-06, avg: -2.0144e-06, min: -7.16238e-06 interface-to-interface point error: 7.16238e-06 Number of uncovered master faces: 0 Number of uncovered slave faces: 0 Total force on fluid interface 0: (0.591128 -2.0965 -1.70314e-15) Total force on solid interface 0: (-0.591152 2.09653 1.70321e-15) Evolving solid solver Corr 0, relative residual = 1 Corr 400, relative residual = 9.96212e-08 FDICPCG: Solving for D, Initial residual = 0.0985019, Final residual = 3.8842e-07, No outer iterations = 400 Max relative residual = 1, Relative residual = 9.96212e-08, enforceLinear = false Interpolating point values using GGI Interpolating point values using GGI FSI relative residual1 norm for interface 0: 1 FSI residual2 norm for interface 0: 7.59435 Time = 18.241, iteration: 1 Modes before clean-up (plate): 0, modes after clean-up (plate): 0 Current fsi under-relaxation factor (plate): 0.05 Maximal accumulated displacement of interface 0: 0.908185 GAMG: Solving for cellMotionUx, Initial residual = 0.99996, Final residual = 8.82619e-07, No Iterations 5 GAMG: Solving for cellMotionUy, Initial residual = 0.999994, Final residual = 3.1945e-07, No Iterations 6 GAMG: Solving for cellMotionUx, Initial residual = 0.00959629, Final residual = 4.53848e-07, No Iterations 5 GAMG: Solving for cellMotionUy, Initial residual = 0.00936811, Final residual = 7.7219e-07, No Iterations 5 Evolving fluid model: icoFluid Courant Number mean: 0.0724723 max: 0.718575 velocity magnitude: 4.25766 PISO: Operating solver in PISO mode DILUPBiCG: Solving for Ux, Initial residual = 0.00310856, Final residual = 3.53159e-07, No Iterations 2 DILUPBiCG: Solving for Uy, Initial residual = 0.0107548, Final residual = 6.75168e-07, No Iterations 3 GAMG: Solving for p, Initial residual = 0.523643, Final residual = 9.0237e-07, No Iterations 88 GAMG: Solving for p, Initial residual = 0.387484, Final residual = 7.55657e-07, No Iterations 26 time step continuity errors : sum local = 7.59467e-10, global = 1.19647e-10, cumulative = 1.19647e-10 GAMG: Solving for p, Initial residual = 0.0990405, Final residual = 9.37202e-07, No Iterations 42 GAMG: Solving for p, Initial residual = 0.0431658, Final residual = 7.1427e-07, No Iterations 22 time step continuity errors : sum local = 8.89019e-10, global = -1.37628e-10, cumulative = -1.79811e-11 GAMG: Solving for p, Initial residual = 0.0186159, Final residual = 9.35416e-07, No Iterations 23 GAMG: Solving for p, Initial residual = 0.00802076, Final residual = 7.12265e-07, No Iterations 19 time step continuity errors : sum local = 8.63516e-10, global = -1.3629e-10, cumulative = -1.54271e-10 Setting traction on solid interfaces Interpolating face values using GGI Total force on fluid interface 0: (-37.2983 -941.572 4.14577e-16) Total force on solid interface 0: (37.2977 941.579 -4.14509e-16)``` The non-restart run converged in 15 FSI iterations. The restart run began getting "material linearity enforced for stability!" warnings at iteration 4. It did however 'converge' after 20 iterations, though with a maximum fluid velocity of over 12. In the non-restarted run, the maximum fluid velocity was 4.25. Obviously something isn't working quite right here, and I'm not quite sure where the issue lies.

 October 18, 2021, 09:20 #3 New Member   Justyna Salachna Join Date: Dec 2019 Posts: 10 Rep Power: 6 Hi. I found a similar problem. I validated the Hron Turek FSI case without any problem on a single run. Now I am working now on different 3D case, and I get a strange results of a structure deformation First I restarted my case after 2,3s. Here, I report x displacement(violet) and ydispl against experiment (dotted) https://ibb.co/n1KFDP2 Here I restarted my case after around 1,5s and I see strange shift of displacement https://ibb.co/mGLdqgt I see the similar problem was reported here https://sciendo.com/pdf/10.2478/caim-2021-0002 'The restart introduces a larger error at the FSI interface with respect to the error of an uninterrupted simulation.' Have you found a fix for the issue? Let me know,

 April 22, 2022, 07:10 #4 New Member     Anas Muhamad Pauzi Join Date: Nov 2019 Posts: 16 Rep Power: 6 Hi, In the bitbucket solids4Foam, Dr Cardiff mentioned the problem with extrapolatedPressure BC, and the solution is to change to zeroGradient https://bitbucket.org/philip_cardiff...-restart-gives Last edited by anaspauzi; April 29, 2022 at 07:07. Reason: Solved problem

 June 29, 2022, 13:43 Problem during 2nd restart #5 New Member     Anas Muhamad Pauzi Join Date: Nov 2019 Posts: 16 Rep Power: 6 Dear respected FOAMers, I managed to restart for the first time but failed for the 2nd time. A large lift force was present at the start of the restart and later changed the solid deformation. In the time folder, there seems to be missing epsilon_0, and also occurs with other RANS models, omega_0 and R_0 after the first restart. I tried copying the epsilon, omega, and R from the previous time-step to the newer one, rechanged the file name, and heading in the consequence time step to epsilon_0, omega_0, and R_0, but failed to run, missing ")" at zeroGradient; Can anyone help? Thank you ANAS