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-   -   Dynamic mesh problem (http://www.cfd-online.com/Forums/fluent/40688-dynamic-mesh-problem.html)

jojo April 21, 2006 13:26

Dynamic mesh problem
 
According to documentation, Fluent determines by itself whether a dynamic mesh procedure, let us say dynamic layering, has to be enforced or not.

I have prepared a very simple case. A rectangle with a regular mesh. The bottom of the rectangle moves upward according to the prescribed movement. However, when it passes the neighbouring cell layer, this latter is not deactivated as it should be. The consequence is the crash of the computation due to creation of negative volumes.

Has anyone an explanation?

Thanks in advance.

Yogesh April 22, 2006 00:43

Re: Dynamic mesh problem
 
Please check with meshing option tab for the cell height value. Try to keep this value equal to your initial mesh size.

jojo April 25, 2006 11:45

Re: Dynamic mesh problem
 
Hi, Yogesh.

Thanks a lot for your answer.

In the layering parameters, I have only split and collapse factors. I do not see how I can prescribe an absolute mesh size.

Looking forward to read you.

Yogesh April 25, 2006 23:15

Re: Dynamic mesh problem
 
Hi, Once you define the dynamic mesh options parameters next step is to define dynamic mesh zones Define-->Dynamic Mesh-->Zones.. in this we define various zone types as Stationary, Deforming, rigid body etc.. During this definition we have to define cell height(m) for appropriate zone type. This is third tab. Hope this will help.

jojo April 26, 2006 10:34

Re: Dynamic mesh problem
 
Hi, Yogesh.

Thanks a lot.

It works now. I shall look into details the value for the cell height. For now, Fluent seems to add sub-layers and then remove them instead of squeezing the parent layer before suppressing it.

jojo April 27, 2006 12:08

Re: Dynamic mesh problem
 
Hi Yogesh.

Everything works very fine for a simple regular mesh. Thank you a lot.

When I try to apply the same method to an hybrid mesh, I experience failures again.

I have a configuration of a diesel engine with a bowl-in piston. Given the complex shape of the piston, it is fully unstructured. However, I want it to not be subject to any mesh operation (dynamic layering, smooting, remeshing).

The above-piston cylinder part is simply layered. Thus, I would expect it to work properly as I did with my previous configuration with dynamic layering. I must say that the cylinder part is layered along the axis but unstructured on the plane perpendicular to the axis, such that it easily matches with the piston volume mesh.

I think the solution would be to specify that the whole piston bowl moves up and that the dynamic layering operates on the first layer above the piston but I have seen nothing on the user-guide on how to do that.

Thanks in advance.


Yogesh April 28, 2006 01:42

Re: Dynamic mesh problem
 
Hi Jojo, You can get the similar case in the fluent user services. Hope you are registered user for the same.

In your case domain is containing the piston top face including bowl, cylinder side faces and the top face. During definition of dynamic mesh, I think you have to select all three option i.e. layering, remeshing, smoothing. In this case you have to select the piston top face as a rigid zone and the cylinder side walls as deforming zone and define respetive parameters.


roukaia November 18, 2011 05:22

hi
i am working on diesel motor i simulate a combustion chamber with a bowl piston i am facing the same problem with the layering the cells tend to be more bigger withoit spliting
plz have you got an idea how to solve this


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