Simulation Mechanical and Multiphysics

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Contributor
robinsmk
Posts: 15
Registered: ‎10-04-2011

negative Jacobian

516 Views, 5 Replies
12-02-2011 05:11 AM

I am trying to mesh a base frame for a car. There are couple of structural members. But whenever I start the the analysis It says negative jacobian as the error. I have turned on the allow microholes option too. But the problem persists. I am using bricks and tetrahed mesh option. 

 

Is there any way to solve the issue?

 

 

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Employee
qzhu
Posts: 11
Registered: ‎09-27-2011

Re: negative Jacobian

12-02-2011 05:30 AM in reply to: robinsmk

There are serveral places that issue Jacobian warnings/errors. If you post the specific error messge, it will help. But in general, if the error is from the solver, it is usually caused by large deformation to some elements, some of which may initially in near singular shapes.

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Contributor
robinsmk
Posts: 15
Registered: ‎10-04-2011

Re: negative Jacobian

12-02-2011 07:54 AM in reply to: qzhu

this is the error i got

 

 

"

Warning: Element no.         2303 jacobian is very small.

 

        Make sure that element node numbering is

 

        correct and that element is not distorted.

 

ERROR: Element no.         2303 jacobian is negative.

 

What is the remedy to it as i have spend hours to mesh the model. Is it a way to correct the error without re meshing?

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Member
Keith1022
Posts: 3
Registered: ‎01-03-2013

Re: negative Jacobian

01-03-2013 08:36 AM in reply to: robinsmk

I'm having the same problem. I've searched through my element numbers and find a duplicate of the element with the negative jacobian. Is there a way to delete the duplicate?

 

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*Expert Elite*
AstroJohnPE
Posts: 570
Registered: ‎08-30-2012

Re: negative Jacobian

01-05-2013 09:36 AM in reply to: robinsmk

Hi Robinsmk: If there is any good news, it is that only one part needs to have its solid mesh redone ("Mesh > Mesh > Create Solid Mesh" when you have the part selected). You do not need to surface mesh (Mesh > Mesh > Generate 3D Mesh) the model or any parts.

 

Hopefully the warning/error gives some indication about which PART element 2303 is in. Look at the lines just before the text that you provided for a clue. Once you know which part has the problem, use the proceedure on the Help page "Nonpositive Jacobian Errors or Distorted Elements" and specify a smaller length ratio.

 

Hi Keith1022: Each part in the model has an element number XXXX (at least the parts that have that many elements!). So the problem is not caused by a duplicate element. As indicated in my description above, you need to find out which part has the problematic element, and then redo the solid mesh in that part.

 

Technically, an element can be deleted from the model, but it cannot be done through the interface. (It is done by editing the element database and model database.) Furthermore, a model whose database has been edited cannot be analyzed from within the interface! You would need to run the analysis from a DOS/Command window.

John Holtz, PE
Mechanical Engineer
Pittsburgh, PA

Simulation Mechanical user since Dec 1997
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Member
Keith1022
Posts: 3
Registered: ‎01-03-2013

Re: negative Jacobian

01-07-2013 05:18 AM in reply to: AstroJohnPE

Thanks for the help.

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