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negative element volume (CFX-10.0)

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Old   December 8, 2005, 11:50
Default negative element volume (CFX-10.0)
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CFDworker
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Hi,

I get the following error message during the initialization of a frozen rotor computation:

+--------------------------------------------------------------------+ | ERROR #002100011 has occurred in subroutine cVolSec. | | Message: | | A negative sector volume has been detected. Execution will proceed | | but this is a possible cause of robustness problems. | | The location of the first negative volume is reported below. | | Volume : -0.1548E-14 | | Location : ( -0.53471E-01, -0.11722E+01, -0.45800E+02) | | This warning may be made fatal by setting the expert parameter | | 'negative volume option = 1'. | +--------------------------------------------------------------------+

+--------------------------------------------------------------------+ | ERROR #002100012 has occurred in subroutine cVolSec. | | Message: | | A negative element volume has been detected. This is a fatal | | error and execution will be terminated. The location of the first | | negative volume is reported below. | | Volume : -0.6014E-19 | | Location : ( -0.50752E-01, -0.11741E+01, -0.45800E+02) | +--------------------------------------------------------------------+

I have checked in ICEM, and I am pretty sure there is no negative elements in the mesh. So I am wondering what could be wrong. Has anyone experienced the same? I am thinking that the error might origin from the import in CFX-Pre, but I am not sure.

Reards, CFDworker
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Old   December 8, 2005, 23:57
Default Re: negative element volume (CFX-10.0)
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rajit
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Are you doin a moving mesh.this error generally occurs when the applied load is more and distance moved crosses the computational domain. It has got nothing to do with the mesh import.

Thanks Rajit
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Old   December 9, 2005, 08:26
Default Re: negative element volume (CFX-10.0)
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CFDworker
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Hi rajit, Thank you for your response. I am doing a frozen rotor computation. I am not quite sure what you mean by:

this error generally occurs when the applied load is more and distance moved crosses the computational domain.

Can you be more specific?

Best regards CFDWorker
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Old   December 11, 2005, 19:53
Default Re: negative element volume (CFX-10.0)
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rajit
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Alright my first question is are you doing a moving mesh.

Is it a transient Rotary frame reference problem.iam pretty sure this error occurs

when lets say you have a cylinder.the dimensions of the cylinder in 100 mm-length and 25 radius.

now assume you are moving the left hand side of the cylinder based on the time.the maximum distance u can move will be 99.99mm not more than that.if you still move it based on time then the elements crosses the boundary on the rightside.this is negative element formation.

assume the case of moving based on the pressure of the fluid.if the timestep is more then this might occur or even at times if the massflow is more it might occur.

It has got nothing to do with meshin.

Check your boundary conditions carefully.

Thanks Rajit
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Old   December 20, 2005, 05:11
Default Re: negative element volume (CFX-10.0)
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Chirag Jayswal
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While meshing in ICEM, after creating prisms, do not smooth "Penta" elements. Smoothing "Penta" sometimes creates this problem of negative volume element creation. You can smooth all other elements. Create a new mesh & try this trick. Hope this works. Good Luck.
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Old   November 16, 2009, 06:43
Post '-ve' element volume
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pari
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Hi all,
I am working on FSI analysis of shock absorber using ANSYS 12.0, but rit now struck up due to negative element volume error.... can any bdy know y it occurs...my one end of fluid domain is moving with respect to time.

Is it because of element size? or any specific reason is responsible for this ?

can any one explain me y it is so..it will be very much helpful for me....

Thanks

Mallya.
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Old   September 26, 2011, 13:05
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Hi!

Have you solved your negative sector volume and negative element volume problem? I have been having similar issues.

If I have a negative sector the model runs. If the negative sector is upstream, it causes problems; if it is downstream (close to and outlet) the error it causes does not cause too much headache.

If I have a negative element volume then the model crashes.

what is the difference between a negative sector volume and a negative element volume? I noticed that it happens in the boundary layer mesh. Sometimes playing with the first layer thickness or the growth rate solves the problem.

Is it a meshing issue or anysys cfx or fluent screws something up when transferring/importing the mesh to the solver?

Also, if it is a meshing issue why cant this company build a mesh generator that produces a proper mesh? This software is not "free"! The company I am working for probably pays hundreds of thousands of dollars to Ansys for licensing. Why cant Ansys or Icem come up with a mesh generator that may spend a little more time on meshing but gives you a clean mesh which does not cause any problems? Unfortunately in my current position I am stuck with this software. I have used a few other cfd / fea software in the market and never had this issue before.
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Old   September 27, 2011, 06:02
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Before you get on your soap box about software quality I recommend you do a search on the forum about negative volume elements. There are dozens of threads on this topic and some of them explain what can be done to fix the issue.
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Old   September 27, 2011, 18:16
Default Negative volume error
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Ugly Kid Joe
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Hello All,

I have been doing FSI (Fluid structure interaction) for some time in CFX. I also came across this error long time back. The main reason is because the displacements were quite high and also sudden. What is recommended is to use low values of time-steps for your simulation.
The problem that I faced was that my forces generated and also the values of certain parameters like spring constant were unrealistic. Once I realized that my values in the CEL were unrealistic, I changed and my error was solved.
If all your values that you use are correct then check if all values that govern your domain motion are properly converged.

Hope that helps.
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