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October 1, 2014, 19:25 |
Viscoelastic Model
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#1 |
New Member
Josiah Lund
Join Date: Sep 2014
Location: Norman, OK, USA
Posts: 7
Rep Power: 12 |
I am working on a simulation that I would like to use viscoelastic properties for. I have simulation data from the model before applying the viscoelastic properties and also for after. After applying, the model is failing due to a negative element. The part that is confusing me is that the negative element is being seen long before my pressure wave reaches the viscoelastic material. I have attached images of the two pressure plots, which show a pressure reading that to me, is unexplained.
The only difference between the two simulation is the addition of a Prony Shear Relaxation property. Values for the table are as follows: Temperature = 27 [C] Relative Moduli(i) = 5.5556 Relaxation Time(i) = 2.5e-5 [s] These values were chosen based on the information found on page 6 of the following document http://ansys.net/ansys/papers/nonlin...ng_viscoel.pdf I have also linked this page to a previous issue that is still unsolved with this model. I would like to resolve both issues, but achieving a successful viscoelastic simulation is my priority http://www.cfd-online.com/Forums/cfx...tructural.html |
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October 5, 2014, 08:32 |
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#2 |
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,852
Rep Power: 144 |
Have you checked your convergence when it crashes? I bet the solver is going bezerk.
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October 9, 2014, 13:33 |
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#3 |
New Member
Josiah Lund
Join Date: Sep 2014
Location: Norman, OK, USA
Posts: 7
Rep Power: 12 |
Glenn,
I do not know how to check the convergence when the simulation crashes. I tried running two separate simulations using low and high convergence criteria and the results are different from one another, but surprisingly, the one with worse convergence criteria ran longer. I have included images of these two runs. Is there any reason as to why the higher convergence model would crash earlier? |
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October 9, 2014, 19:07 |
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#4 |
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,852
Rep Power: 144 |
This sounds like your model is highly numerically unstable so anything can happen. I would not read too much into how quickly things crash other than you need to improve numerical stability.
You can do that by: * Smaller time steps * Double precision numerics * Better mesh quality (this one is the usual problem, you can always do a better mesh) * better initial condition |
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Tags |
negative elements, negative volume, negative volume element, viscoelastic |
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