# solids4foam_strange solid behaviour

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October 18, 2022, 11:28
solids4foam_strange solid behaviour
#1
New Member

Tommaso
Join Date: Jan 2020
Posts: 16
Rep Power: 6
Hi all, I am modelling a solitary wave impacting a flexible plate with solids4foam. The plate shows a strange beahviour, such as the horizontal displacement is constant over certain times (as in the attached Fig. 1). The force acting on the plate due to the wave is shown in Fig. 2.

It seems that the solid is not updated over those time steps.

Any idea about why this is happening?

Thanks,
Tommaso
Attached Images
 Fig. 1.png (15.8 KB, 12 views) Fig. 2.png (15.6 KB, 10 views)

Last edited by evxta3; October 26, 2022 at 04:18.

 November 25, 2022, 12:04 #2 Super Moderator     Philip Cardiff Join Date: Mar 2009 Location: Dublin, Ireland Posts: 1,089 Rep Power: 34 Hi Tommaso, Can you give more details of your case? For example, the geometry, materials and loading conditions. Philip

 December 13, 2022, 10:48 #3 New Member   Tommaso Join Date: Jan 2020 Posts: 16 Rep Power: 6 Hi Philip, thanks for your reply. This was a 2d wave flume with a rectangular plate. The plate material was stainless steel (density: 8000 kg/m^3 and Young's modulus 200 GPa). The plate, partially submerged, was impacted by a solitary wave resulting in the total force shown in the figure in my previous post. Thanks, Tommaso

 December 14, 2022, 10:11 #4 Super Moderator     Philip Cardiff Join Date: Mar 2009 Location: Dublin, Ireland Posts: 1,089 Rep Power: 34 What are the boundary conditions on the plate? And what does the log file look like for the time steps where the displacement stays constant?

 December 14, 2022, 10:36 #5 New Member   Tommaso Join Date: Jan 2020 Posts: 16 Rep Power: 6 The plate is fixed at the bottom { type fixedDisplacement; value uniform (0 0 0); } and the remaining boundaries are treated as interface with { type solidTraction; traction uniform ( 0 0 0 ); pressure uniform 0; value uniform (0 0 0); } From the log file it looks like that the plate is not updated at all since the resisuals converged during the time steps where the displacement is constant. Something like that: PIMPLE: converged in 2 iterations Setting traction on solid patch Interpolating from fluid to solid using GGI/AMI interpolation Total force (fluid) = (-1.30659 -0.787151 -0.926353) Total force (solid) = (1.30662 0.78712 0.926346) Evolving solid solver Solving the momentum equation for D Corr, res, relRes, matRes, iters The relative residual has converged 2, 9.99787e-07, 0, 0, 0 If I use a much thicker plate (more cells through the plate thickness) this strange behaviour is not observed anymore. Thanks, Tommaso

 December 21, 2022, 10:58 #6 Super Moderator     Philip Cardiff Join Date: Mar 2009 Location: Dublin, Ireland Posts: 1,089 Rep Power: 34 For the thinner plate, I suspect that the solid solver prematurely converges in some time steps, which means the displacement stays constant in these steps. You could check if tightening the solution tolerances in constant/solidProperties helps. evxta3 likes this.

December 21, 2022, 11:19
#7
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Tommaso
Join Date: Jan 2020
Posts: 16
Rep Power: 6
Quote:
 Originally Posted by bigphil For the thinner plate, I suspect that the solid solver prematurely converges in some time steps, which means the displacement stays constant in these steps. You could check if tightening the solution tolerances in constant/solidProperties helps.
Yes, that helps in some cases (not always though). Thanks Philip!