Tagged: SOFA Soft Robots Mesh
3 February 2021 at 1 h 44 min #18477AnoushSParticipant
- University of British Columbia
I am trying to make a pneumatic actuator, and have modelled the internal cavity that will have a varying pressure during operation. When I use this model, I am able to increase the pressure to cause the actuator to bend, however, if the pressure gets to high, the mesh of the actuator explodes. I suspect this is because the internal pressure is too high and the mesh youngs modulus is too low, however, I was wondering if this could be something due to the solver or mesh?
Any help is appreciated thanks.5 February 2021 at 13 h 36 min #18541HugoKeymaster
- SOFA Consortium
Such instabilities are usually related to wrong definition of your numerical settings (time step, tolerance, mesh size etc), impacting the conditioning and resolution of your system. This is the art of numerical analysis: the key is always to understand the mathematical/matrix system you are actually building in your simulation.
In you case, it could be:
– a too quick increase of the pressure with a time step too large
– a pressure inducing large deformation of the mesh leading to ill-shaped finite elements
– the pressure constraint can not be respected as desired and your constraint system diverges
To solve such problem, more insight of a basic scene example displaying your problem is needed. Best wishes,
Hugo5 April 2021 at 7 h 40 min #19074DavacasParticipant
I had a similar problem and I fixed it by reducing the amount of mass of my mesh, but you have to tune it in order to get a realistic behavior.
Hope this helps!8 April 2021 at 23 h 25 min #19089HugoKeymaster
- SOFA Consortium
Thank you @davacas for sharing your experience.
However, changing physical parameters to make the simulation more stable is not usually the way to go. Did you analyze the convergence of your simulation while using smaller and smaller time steps? (convergence analysis = comparing the result of the simulation with smaller time steps)
Mass, stiffness are physical parameters that you should know and define once and for all. As stated earlier, numerical settings (time step, tolerance, mesh size etc) must be tuned to ensure this convergence and the stability of your simulation.
Hugo20 April 2021 at 3 h 40 min #19213DavacasParticipant
Thanks for the advice, @Hugo. I did make some sort of convergence analysis, but I wasn’t very rigorous about it. As I stated earlier, what really worked for me was turning down the mass, but you’re right: I shouldn’t mess with those parameters. I will try making a more rigorous convergence analysis next time.
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