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While running my simulation i am getting the error "Negative Jacobian was detected at element", What is the meaning of this error? How can we avoid this error to get a converged solution?
This error means that at least one element in your mesh has turned inside out due to the large deformation. At this point the FEBio cannot continue since the solution has become nonphysical. There are many reasons why this could happen. I would suggest to take a look at Chapter 7 of the online manual. If you can't find the answer in there, you may send me your model and I'd be happy to take a closer look.
Cheers,
Steve
Department of Bioengineering, University of Utah
Scientific Computing and Imaging institute, University of Utah
Thanks for the reply, I am attaching the preview file that is having the convergence issue.
I want to implement gait cycle in openKnee model, for that i provide rotation curve and load curve for 1 second. I have given rotation in initial step using curve editor with maximum extension angle of 22 degree. I want to give a load curve with 1000 N of maximum load, First i tried with 10 N in step-1 and the simulation run successfully, after i increased the load to 100 or 1000 N, error termination is coming. It would be very helpful if u can figure out the isssue and with a valuable feedback.
Thanks
Vaishakh
Last edited by Vaishakhraju; 07-12-2019, 11:29 PM.
I think the problem is that you are applying the force too quickly. At the first iteration of the first time step, contact is not yet established, so there is nothing to stop the femur from moving down. Since the force is already big at this point, the femur moves quite a bit and inverts elements. This is causing your negative jacobians. I suggest that you ramp up the force more slowly, so that contact can be established and the femur "settle in", before the loading begins. You could setup a two-step analysis, where you do this initial slow loading in the first step, and then your desired loading pattern in the second step.
Cheers,
Steve
Department of Bioengineering, University of Utah
Scientific Computing and Imaging institute, University of Utah
I am facing the negative jacobian problem. First I ran the simulation with the following material
"Elastic
Solid Mixture
Neo Hookean
Fiber EXP Pow
Fiber EXP Pow"
It worked
But as I changed the material from elastic to uncoulped it gave me negative jacobian error
"Uncoupled
Uncoupled Solid Mixture
Mooney Rivlin
Fiber EXP Pow uncoupled
Fiber EXP Pow uncoupled"
I also went through the FEbio user manual but I did not understand what exact problem I have. I changed the time step but it did not help me.
any kind of help would be greatly appreciated.
Here is the error I am getting while running in preview.
When you use an uncoupled solid mixture, you have to set the bulk modulus (parameter k) to a suitable value. First, ensure that this parameter is there and then try changing the value. You have to set it high enough so that the material behaves nearly-incompressible, but if you set it too high you could introduce ill-conditioning, which could lead to negative jacobians.
If that's not the problem, check your boundary conditions and loads. Since the error is happening in the first time step you might be applying the load to quickly. Check if the loads and prescribed boundary conditions have a load curve associated.
If none of this helps, feel free to send me the feb file and I will take a closer look.
Best,
Steve
Department of Bioengineering, University of Utah
Scientific Computing and Imaging institute, University of Utah
Thank you so much for your kind response. I followed the steps you mentioned but still it is not working. Is that possible can I send my .feb file to your email.
Hi, I have taken Negative jacobian was detected. error. How can this error be solved in a soft tissue extension test model?
I have sent my .feb file to the steve.maas@utah.edu . I would highly appreciate it if you let me know how can I solve the error.
Best,
Shah
Dear Steve,
I hope you are doing well.
Many thanks in advance for your reply. when I am running my simulation the error " negative Jacobian was detected" will appear. I checked everything based on the Febio manual but unfortunately, I didn't find the solution for it. I will be happy and so appreciative if you could help me in this regard. I shared my file in the link below:
In this model you assigned the neo-Hookean material, which appears to be for the soft tissues, to the tibia. Was that your intention? I assume you intended to assign a rigid body to the tibia as well?
Best,
Steve
Department of Bioengineering, University of Utah
Scientific Computing and Imaging institute, University of Utah
Dear Steve,
Thank you so much. I have sent an email to steve.maas@utah.edu to explain this issue—many thanks for your consideration.
Kind Regards
Pooyan
Dear Steve,
I hope you are doing well.
I modified my model and the loading condition, but unfortunately, I am still getting the “ negative Jacobian error was detected”. Please see the shared model below:
In rigid section, I applied rigid force, rigid fix, rigid, rigid moment, and rigid rotation. The problem is that when I put a value for the rigid rotation (0.785), the error “ negative Jacobian error was detected” will appear. To resolve this issue, I did the following steps:
Model modification
The rigid rotation was applied in different steps up to 4 (slowly ramped up)
The tied contact between the graft and the hole
Modifying the loading curve so that the load applies in step form.
I didn't apply the rigid rotation value (0.785) in the attached model, and it is working. I will be happy and so appreciative if you could help me in this regard—many thanks for your consideration.
Kind Regards
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