# objects oscillate at high speed causing collapse in Dynamic mesh and overset mesh ca

 Register Blogs Members List Search Today's Posts Mark Forums Read May 17, 2020, 23:35 objects oscillate at high speed causing collapse in Dynamic mesh and overset mesh ca #1 New Member   Ian Join Date: Aug 2018 Posts: 15 Rep Power: 6 Hi, everyone Recently I am doing a two degree of freedom objects floating in waves. Firstly, I used the dynamic grid, but only to find the calculating divergence in 0.2 s, the speed and the force of the objects on the Z direction is increased sharply. I have encountered this kind of problem before, because of deforming of the mesh is too large, but the current motion of the object can be ignored and the mesh deformation could be neglected. I changed the case to overset case, but there are similar errors, the speed increase sharply, and the oscillation amplitude of the force is particularly large. The gravity and buoyancy are about 140 initially , even completely submerged is no more than 200, but from the log file it can be seen there are some changes of force lager than thousands on a time step. Here are some timestep results of the log file both in dynamic and overset cases. Any advice would be appreciated. For the dynamic mesh, the force on the z-direction is 252 and 1572 in two timesteps. Code: ```deltaT = 0.00101181857516 Time = 0.220738 PIMPLE: iteration 1 forces forces: Not including porosity effects Rigid-body motion of the floatingObject Centre of rotation: (0 0 0.00108368499676) Orientation: (1 0 3.3789845961e-07 0 1 0 -3.3789845961e-07 0 1) Linear velocity: (0 0 0.0612626535315) Angular velocity: (0 3.62258814109e-05 0) Execution time for mesh.update() = 0.5 s smoothSolver: Solving for alpha.water, Initial residual = 8.23816903596e-06, Final residual = 7.16032233336e-10, No Iterations 1 Phase-1 volume fraction = 0.500312200358 Min(alpha.water) = -6.36232220187e-30 Max(alpha.water) = 1.00866542511 MULES: Correcting alpha.water MULES: Correcting alpha.water Phase-1 volume fraction = 0.500312200358 Min(alpha.water) = -6.3458477003e-30 Max(alpha.water) = 1.00866542511 Relaxing time: 0.01 s GAMG: Solving for p_rgh, Initial residual = 8.64298692691e-05, Final residual = 9.8169399241e-06, No Iterations 9 GAMG: Solving for p_rgh, Initial residual = 0.00010348168853, Final residual = 9.24900730207e-06, No Iterations 7 time step continuity errors : sum local = 6.61490084731e-08, global = -7.14845366174e-10, cumulative = 2.01813122868e-07 GAMG: Solving for p_rgh, Initial residual = 1.16441732373e-05, Final residual = 3.42047154349e-06, No Iterations 1 GAMG: Solving for p_rgh, Initial residual = 3.4197011599e-06, Final residual = 3.4197011599e-06, No Iterations 0 time step continuity errors : sum local = 2.69615713834e-08, global = -9.20554877097e-10, cumulative = 2.00892567991e-07 ExecutionTime = 51.32 s ClockTime = 51 s forces forces1 write: Sum of forces Total : (-0.18127711571 -1.88236463748e-23 252.403179473) Pressure : (-0.18127697457 -1.88237660153e-23 252.415146697) Viscous : (-1.41140473911e-07 1.19640498385e-28 -0.0119672240877) Sum of moments Total : (-1.90023955902e-24 -0.0845601499345 3.06605212083e-26) Pressure : (-1.90025359991e-24 -0.0845600163142 3.06618198123e-26) Viscous : (1.40408941158e-29 -1.33620321663e-07 -1.29860396598e-30) Courant Number mean: 0.00254798035261 max: 0.18775947338 Interface Courant Number mean: 2.3084939728e-05 max: 0.0564074055803 deltaT = 0.00107823137739 Time = 0.221816 PIMPLE: iteration 1 forces forces: Not including porosity effects Rigid-body motion of the floatingObject Centre of rotation: (0 0 0.00113322650212) Orientation: (1 0 3.68934121974e-07 0 1 0 -3.68934121974e-07 0 1) Linear velocity: (0 0 0.0306313617895) Angular velocity: (0 -9.37936039134e-05 0) Execution time for mesh.update() = 0.5 s smoothSolver: Solving for alpha.water, Initial residual = 1.12888430008e-05, Final residual = 8.47616724924e-10, No Iterations 1 Phase-1 volume fraction = 0.500310401852 Min(alpha.water) = -6.30568122573e-30 Max(alpha.water) = 1.00798849325 MULES: Correcting alpha.water MULES: Correcting alpha.water Phase-1 volume fraction = 0.500310401852 Min(alpha.water) = -6.28823415663e-30 Max(alpha.water) = 1.00798849325 Relaxing time: 0.01 s GAMG: Solving for p_rgh, Initial residual = 0.000826027305677, Final residual = 9.345892666e-06, No Iterations 19 GAMG: Solving for p_rgh, Initial residual = 7.55055385995e-07, Final residual = 7.55055385995e-07, No Iterations 0 time step continuity errors : sum local = 9.73939319788e-08, global = -8.90956534845e-10, cumulative = 2.00001611456e-07 GAMG: Solving for p_rgh, Initial residual = 2.61538748518e-06, Final residual = 2.61538748518e-06, No Iterations 0 GAMG: Solving for p_rgh, Initial residual = 2.61538748518e-06, Final residual = 2.61538748518e-06, No Iterations 0 time step continuity errors : sum local = 3.3735638182e-07, global = -1.86581070005e-09, cumulative = 1.98135800756e-07 ExecutionTime = 52.1 s ClockTime = 52 s forces forces1 write: Sum of forces Total : (0.000986698924306 2.13856484196e-23 1572.88591645) Pressure : (0.000986998775467 2.13856973379e-23 1572.89201928) Viscous : (-2.99851160528e-07 -4.89182974308e-29 -0.00610283104064) Sum of moments Total : (2.22842317366e-24 0.0084773625331 8.87541932908e-25) Pressure : (2.22842813704e-24 0.00847733423395 8.87542806285e-25) Viscous : (-4.96338833053e-30 2.82991556891e-08 -8.73376717721e-31)``` For the overset case, the force on the Z-direction is 146 -636 in several timesteps. Code: ```deltaT = 0.00243433879711 Time = 0.216152 PIMPLE: iteration 1 motion_.dropFlag: 0 时间 db().time().value():0.216152429581在算了 forces forces: rho: rho Not including porosity effects 6-DoF rigid body motion Centre of rotation: (0 0 -0.0213300442367) Centre of mass: (8.76359257368e-09 0 -0.00093004423675) Orientation: (1 0 4.29587871259e-07 0 1 0 -4.29587871259e-07 0 1) Linear velocity: (0 0 -0.031497857265) Angular velocity: (-0 -1.27419889364e-05 0) cellVolumeWeight : detected 2 mesh regions zone:0 nCells:400000 zone:1 nCells:17900 Marking patch-cells on zone 0 Marking patch-cells on zone 1 After patch analysis : nCells : 417900 other : 412560 patch : 4744 overset: 596 Creating mesh-to-mesh addressing for region0 and region0 regions using cellVolumeWeight meshToMesh: Using AABBTree method Overlap volume: 0.134053289585 cellVolumeWeight : detected 6 mesh regions after overset Front : fraction:1 size:1160 Overset analysis : nCells : 417900 calculated : 411602 interpolated : 946 hole : 5352 Updating StokesII wave model for patch inlet Updating shallowWaterAbsorption wave model for patch outlet Execution time for mesh.update() = 5.19 s Updating StokesII wave model for patch inlet smoothSolver: Solving for alpha.water, Initial residual = 6.75648006434e-06, Final residual = 3.47092057926e-11, No Iterations 2 Phase-1 volume fraction = 0.405001375012 Min(alpha.water) = -6.44107925227e-19 Max(alpha.water) = 1.00018322668 MULES: Correcting alpha.water MULES: Correcting alpha.water MULES: Correcting alpha.water Phase-1 volume fraction = 0.405001377548 Min(alpha.water) = -1.52464097061e-17 Max(alpha.water) = 1.00018322668 Updating StokesII wave model for patch inlet smoothSolver: Solving for alpha.water, Initial residual = 6.75808827335e-06, Final residual = 3.46761931325e-11, No Iterations 2 Phase-1 volume fraction = 0.405008116411 Min(alpha.water) = -4.2632907881e-19 Max(alpha.water) = 1.0001801161 MULES: Correcting alpha.water MULES: Correcting alpha.water MULES: Correcting alpha.water Phase-1 volume fraction = 0.405008119026 Min(alpha.water) = -1.47698402771e-17 Max(alpha.water) = 1.0001801161 Updating StokesII wave model for patch inlet DILUPBiCGStab: Solving for p_rgh, Initial residual = 7.73918900558e-05, Final residual = 7.70896010266e-07, No Iterations 179 time step continuity errors : sum local = 1.39938130275e-07, global = 6.49571398554e-08, cumulative = 4.25418012787e-06 DILUPBiCGStab: Solving for p_rgh, Initial residual = 0.000258484674878, Final residual = 8.84289053292e-10, No Iterations 402 time step continuity errors : sum local = 3.55495897207e-12, global = -1.37045513846e-12, cumulative = 4.25417875741e-06 smoothSolver: Solving for epsilon, Initial residual = 0.00248482816424, Final residual = 6.85528578613e-09, No Iterations 15 smoothSolver: Solving for k, Initial residual = 0.031742998684, Final residual = 9.07836013528e-09, No Iterations 29 PIMPLE: iteration 2 Updating StokesII wave model for patch inlet smoothSolver: Solving for alpha.water, Initial residual = 9.70110690882e-06, Final residual = 3.98515135285e-11, No Iterations 2 Phase-1 volume fraction = 0.405001348864 Min(alpha.water) = -1.03030772084e-18 Max(alpha.water) = 1.00018324609 MULES: Correcting alpha.water MULES: Correcting alpha.water MULES: Correcting alpha.water Phase-1 volume fraction = 0.405001351346 Min(alpha.water) = -1.36436906282e-17 Max(alpha.water) = 1.00018324609 Updating StokesII wave model for patch inlet smoothSolver: Solving for alpha.water, Initial residual = 6.73423582573e-06, Final residual = 3.1136314758e-11, No Iterations 2 Phase-1 volume fraction = 0.405008063893 Min(alpha.water) = -4.26329047505e-19 Max(alpha.water) = 1.00018015426 MULES: Correcting alpha.water MULES: Correcting alpha.water MULES: Correcting alpha.water Phase-1 volume fraction = 0.405008066489 Min(alpha.water) = -1.30693638106e-17 Max(alpha.water) = 1.00018015426 Updating StokesII wave model for patch inlet DILUPBiCGStab: Solving for p_rgh, Initial residual = 0.000118616893935, Final residual = 9.3012114721e-07, No Iterations 152 time step continuity errors : sum local = 3.13276633314e-09, global = 2.56566848953e-12, cumulative = 4.25418132308e-06 DILUPBiCGStab: Solving for p_rgh, Initial residual = 0.00011827675578, Final residual = 9.41783544077e-10, No Iterations 305 time step continuity errors : sum local = 5.45493528694e-13, global = -5.65974338958e-14, cumulative = 4.25418126648e-06 smoothSolver: Solving for epsilon, Initial residual = 0.000163531317999, Final residual = 7.97099529407e-09, No Iterations 8 smoothSolver: Solving for k, Initial residual = 0.00062846546524, Final residual = 7.07149761854e-09, No Iterations 21 ExecutionTime = 179.75 s ClockTime = 185 s forces forces1 write: Sum of forces Total : (-0.000835011808457 -5.45382368796e-24 146.54637577) Pressure : (-0.000835029384371 -5.45374863573e-24 146.526422965) Viscous : (1.75759144188e-08 -7.50522339763e-29 0.019952805856) Sum of moments Total : (-5.21201731689e-25 0.00027807004677 -4.71054295058e-26) Pressure : (-5.21194290964e-25 0.00027789856482 -4.71023222581e-26) Viscous : (-7.44072488661e-30 1.71481949812e-07 -3.10724768134e-30) Courant Number mean: 0.00312599378064 max: 0.293259735409 Interface Courant Number mean: 2.05386331858e-05 max: 0.114626092226 deltaT = 0.00249028949752 Time = 0.218643 PIMPLE: iteration 1 motion_.dropFlag: 0 时间 db().time().value():0.218642711639在算了 forces forces: rho: rho Not including porosity effects 6-DoF rigid body motion Centre of rotation: (0 0 -0.0213682344606) Centre of mass: (8.20449051472e-09 0 -0.000968234460565) Orientation: (1 0 4.02180907584e-07 0 1 0 -4.02180907584e-07 0 1) Linear velocity: (0 0 0.000826544670072) Angular velocity: (-0 -9.26907740871e-06 0) cellVolumeWeight : detected 2 mesh regions zone:0 nCells:400000 zone:1 nCells:17900 Marking patch-cells on zone 0 Marking patch-cells on zone 1 After patch analysis : nCells : 417900 other : 412560 patch : 4744 overset: 596 Creating mesh-to-mesh addressing for region0 and region0 regions using cellVolumeWeight meshToMesh: Using AABBTree method Overlap volume: 0.134045212245 cellVolumeWeight : detected 6 mesh regions after overset Front : fraction:1 size:1162 Overset analysis : nCells : 417900 calculated : 411600 interpolated : 946 hole : 5354 Updating StokesII wave model for patch inlet Updating shallowWaterAbsorption wave model for patch outlet Execution time for mesh.update() = 5.42 s Updating StokesII wave model for patch inlet smoothSolver: Solving for alpha.water, Initial residual = 6.09338592432e-06, Final residual = 2.40627946583e-11, No Iterations 2 Phase-1 volume fraction = 0.405014125102 Min(alpha.water) = -4.26328384992e-19 Max(alpha.water) = 1.00017701078 MULES: Correcting alpha.water MULES: Correcting alpha.water MULES: Correcting alpha.water Phase-1 volume fraction = 0.405014127847 Min(alpha.water) = -1.04461042326e-17 Max(alpha.water) = 1.00017701078 Updating StokesII wave model for patch inlet smoothSolver: Solving for alpha.water, Initial residual = 6.09441137905e-06, Final residual = 2.40259634767e-11, No Iterations 2 Phase-1 volume fraction = 0.405020187051 Min(alpha.water) = -4.26327722332e-19 Max(alpha.water) = 1.00017392216 MULES: Correcting alpha.water MULES: Correcting alpha.water MULES: Correcting alpha.water Phase-1 volume fraction = 0.405020189807 Min(alpha.water) = -9.5120499276e-18 Max(alpha.water) = 1.00017392216 Updating StokesII wave model for patch inlet DILUPBiCGStab: Solving for p_rgh, Initial residual = 0.0574319353605, Final residual = 0.000481714923153, No Iterations 252 time step continuity errors : sum local = 1.52454599301e-07, global = 4.71011922379e-08, cumulative = 4.30128245872e-06 DILUPBiCGStab: Solving for p_rgh, Initial residual = 1.25353035601e-05, Final residual = 5.41520666851e-10, No Iterations 308 time step continuity errors : sum local = 6.27030222368e-10, global = 2.53603809451e-10, cumulative = 4.30153606253e-06 smoothSolver: Solving for epsilon, Initial residual = 0.0012437548912, Final residual = 7.78688153486e-09, No Iterations 15 smoothSolver: Solving for k, Initial residual = 0.0115461348311, Final residual = 6.65057162803e-09, No Iterations 30 PIMPLE: iteration 2 Updating StokesII wave model for patch inlet smoothSolver: Solving for alpha.water, Initial residual = 1.02524778268e-05, Final residual = 1.47321270306e-11, No Iterations 2 Phase-1 volume fraction = 0.405011011353 Min(alpha.water) = -4.25540370391e-19 Max(alpha.water) = 1.00017702627 MULES: Correcting alpha.water MULES: Correcting alpha.water MULES: Correcting alpha.water Phase-1 volume fraction = 0.405011013529 Min(alpha.water) = -9.64123997826e-18 Max(alpha.water) = 1.00017702627 Updating StokesII wave model for patch inlet smoothSolver: Solving for alpha.water, Initial residual = 2.9666532562e-06, Final residual = 4.89153378505e-12, No Iterations 2 Phase-1 volume fraction = 0.405013958567 Min(alpha.water) = -4.24733396239e-19 Max(alpha.water) = 1.0001739526 MULES: Correcting alpha.water MULES: Correcting alpha.water MULES: Correcting alpha.water Phase-1 volume fraction = 0.405013960729 Min(alpha.water) = -8.74233411734e-18 Max(alpha.water) = 1.0001739526 Updating StokesII wave model for patch inlet DILUPBiCGStab: Solving for p_rgh, Initial residual = 1.52984166079e-05, Final residual = 1.1946067314e-07, No Iterations 165 time step continuity errors : sum local = 5.571216882e-08, global = -2.13063622342e-08, cumulative = 4.2802297003e-06 DILUPBiCGStab: Solving for p_rgh, Initial residual = 3.63683899449e-06, Final residual = 9.07496366273e-10, No Iterations 265 time step continuity errors : sum local = 3.97777309263e-10, global = -1.12705790442e-11, cumulative = 4.28021842972e-06 smoothSolver: Solving for epsilon, Initial residual = 0.000332863393295, Final residual = 9.72253472451e-09, No Iterations 8 smoothSolver: Solving for k, Initial residual = 0.00373997689702, Final residual = 7.30870966919e-09, No Iterations 22 ExecutionTime = 186.5 s ClockTime = 192 s forces forces1 write: Sum of forces Total : (-0.000928906233233 -1.80429377211e-23 -636.496207569) Pressure : (-0.00092895466669 -1.8042996157e-23 -636.505199892) Viscous : (4.84334573672e-08 5.84358832828e-29 0.00899232345785) Sum of moments Total : (-1.87852470623e-24 -0.000321059082781 5.79075401727e-25) Pressure : (-1.87853074491e-24 -0.000321189856886 5.79065804127e-25) Viscous : (6.03867806002e-30 1.30774104865e-07 9.5975999502e-30) Courant Number mean: 0.00142003472523 max: 0.161714928462 Interface Courant Number mean: 1.28565593805e-05 max: 0.0762584687927```  Thread Tools Search this Thread Show Printable Version Email this Page Search this Thread: Advanced Search Display Modes Linear Mode Switch to Hybrid Mode Switch to Threaded Mode Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is 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