Learning Forum

[Bijoy Prasad]

Hello,

I am trying to simulate steady flow around a hull model with 3 DoF (surging, heaving and pitching) in calm water. I used tetrahedral grid only around the hull and hexahedral grid rest of the domain. So I used Smoothing and Remeshing method with Six DOF option in dynamic mesh setting. I faced Update-Dynamic-Mesh failed. Negative cell volume detected after some time steps. Please help me to solve the problem, if possible please also check the attached case and udf file.

Bijoy

[Max4]

Hi,

have you decrease the time step yet?

[Rob]

Thanks Max. Also check how the mesh is set up: missing a surface/volume in the MDM panel can also turn the mesh inside out. 

[Bijoy Prasad]

Thanks for the comments. Actually I already tried almost everything after reading lots of comments in ANSYS student community and CFD online forum but still no improvements. So could you please check my case and udf file to solve the problem?

Here I upload udf file but I can not upload case file. Could you please also help me to upload the case file in any other way? 

[Keyur Kanade]

as ansys employees we can not download attachments. also as support, we do not debug udfs. 

you may need to insert some images. other forum members can pitch in. 

with that said, please check quality before you start the run. the starting mesh   quality should be good to proceed. 

[Bijoy Prasad]

Thanks for the response. Here I add the image of udf 3 DoF (surging, heaving and pitching), please check it.

 

 

 

[Bijoy Prasad]

[Keyur Kanade]

can you please reduce mass and check it. this may give less displacement and may avoid negative cells.

if you still get negative elements, then we will have to see smoth and remeshing controls. 

[Bijoy Prasad]

I previously tried to reduce the mass but no improvement.

Here I add the images of smoothing and remeshing settings, please check.

 

[Bijoy Prasad]

[Keyur Kanade]

can you please use spring method for smoothing. 

use no. of iterations   = 100

under remeshing, please use length scales given in 'mesh scale info'. 

[Bijoy Prasad]

Thanks for the comments. I tried spring method but still it shows error after 2 seconds. Do you have any idea how can I get the results for at least 5-6 seconds?
I also used mesh scale info for length scales previously.
 
 
 

[Keyur Kanade]

you need to reduce your mesh movement so that it does not move too much to give negative cells. you may want to do it in your udf. 

[esgiraldop]

Hi Bijoy. I am trying to simulate exactly the same thing as you. I tried using dynamic mesh during months with no positive results. Now I am triying with overset mesh instead of moving deforming mesh but I am still coping with the negative volume cells. Did you find any solution already?

[George Mathew]

I am trying to simulate the 2-d model of an IC engine using the dynamic meshing method. I enabled smoothing, layering, and remeshing options for the mesh methods and the in-cylinder options for the piston motion. I am facing the negative volume detected error even after reducing the time step size

 

[Cláudio Corrêa]

 

Hello,

I’m trying to reproduce the flow around a mechanically controlled door tutorial ((846) Ansys Fluent: Flow Around A Mechanically Controlled Door. - YouTube)  and my simulation crashed after a few seconds with the error message “Update-Dynamic-Mesh failed. Negative cell volume detected”.

Analysing the results in CFD-Post, the problem occurs in the valve movement because it literally enters the mesh.

How do I fix the error?

Attached is a picture of the movement of the valve.