Hello,
I am looking for advice on optimizing parameters for a viscoelastic solid with hyperelastic elastic component. I am able to get models working but my issue comes from when I change parameters every run. Sometimes the model works and about half of the time febio does not reach the end of the analysis and gives a "negative jacobian" error. I tried uncoupled vs coupled viscoelasticity, refined vs course meshes, and large vs small time steps. I have tried multiple material models: viscoelastic with ogden unconstrained, viscoelastic with EFD neohookean, uncoupled viscoelastic Veronda westmann, and uncoupled viscoelastic ogden. All of these changes and changes to parameters have given errors at seemingly random times.
I am wondering if the problem is that the stress in my data are too large? Or have I not found the correct model yet? I am optimizing my parameters in MATLAB (attached picture shows my data in orange and FEBio model output in blue - first attachment results)
ViscoEFDNeohookeanOptimization.PNG
Working viscoelastic EFD Neohookean:
bladder_visco_EFDNH_working.feb
Adding a second relaxation strength and getting negative jacobian:
bladder_visco_EFDNH_error1.feb
Increasing k and getting negative jacobian:
bladder_visco_EFDNH_error2.feb
These are just two examples of the many combinations I have tried that have stopped before finishing at 14000 seconds. Any suggestions would be very much appreciated!
Regards,
Laura
Edit: Are there bounds that I should place on the parameters and is there anywhere I can find suggested bounds for each of the different materials?
I am looking for advice on optimizing parameters for a viscoelastic solid with hyperelastic elastic component. I am able to get models working but my issue comes from when I change parameters every run. Sometimes the model works and about half of the time febio does not reach the end of the analysis and gives a "negative jacobian" error. I tried uncoupled vs coupled viscoelasticity, refined vs course meshes, and large vs small time steps. I have tried multiple material models: viscoelastic with ogden unconstrained, viscoelastic with EFD neohookean, uncoupled viscoelastic Veronda westmann, and uncoupled viscoelastic ogden. All of these changes and changes to parameters have given errors at seemingly random times.
I am wondering if the problem is that the stress in my data are too large? Or have I not found the correct model yet? I am optimizing my parameters in MATLAB (attached picture shows my data in orange and FEBio model output in blue - first attachment results)
ViscoEFDNeohookeanOptimization.PNG
Working viscoelastic EFD Neohookean:
bladder_visco_EFDNH_working.feb
Adding a second relaxation strength and getting negative jacobian:
bladder_visco_EFDNH_error1.feb
Increasing k and getting negative jacobian:
bladder_visco_EFDNH_error2.feb
These are just two examples of the many combinations I have tried that have stopped before finishing at 14000 seconds. Any suggestions would be very much appreciated!
Regards,
Laura
Edit: Are there bounds that I should place on the parameters and is there anywhere I can find suggested bounds for each of the different materials?
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