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-   -   how to solve negative volume? (http://www.cfd-online.com/Forums/fluent/93184-how-solve-negative-volume.html)

colopolo October 7, 2011 07:12

how to solve negative volume?
 
1 Attachment(s)
Dear All,

I am trying to simulate 2d vortex vibration of cylinder.

I just made simple 2d domain which have inlet, symmetry (top and bottom), outlet and just wall ( large domain subtracts cylinder).

Then, I imposed an udf file on cylinder to move vertical motion in dynamic option.

I have searched all of google sites about same problems but I cannot solve my problem.

In dynamic mesh, cylinder has rigid body with udf file.
1 turn on smoothing with spring constant factor 0 and boundary node relaxation 1.
2. turn on remeshing option with sizing funtion and use defaults of parameters.

I know I have something wrong in my steps but I have no idea what is wrong with.

I appreciate your guys leave any comments or any ideas.

Regards,

Amir October 7, 2011 10:22

Hi,

Increase spring constant.
Additionally, check it in display->grid; I think in newer versions, there is an option to view motion of specific parts not all of them if you faced this in solve->grid motion.

Bests,

colopolo October 9, 2011 20:42

1 Attachment(s)
Quote:

Originally Posted by Amir (Post 327064)
Hi,

Increase spring constant.
Additionally, check it in display->grid; I think in newer versions, there is an option to view motion of specific parts not all of them if you faced this in solve->grid motion.

Bests,

Thanks for your comments.

I have a weird moving mesh (attached file)

I assigned osc to cylinder and osc_inert to the entire fluid region (this part is in udf file)
I assigned the top and bottom walls as stationary.

But, the mesh wend out beyond top /bottom walls.
Do you have any idea for this problem?

Best Regards
JY

Amir October 10, 2011 03:28

Quote:

Originally Posted by colopolo (Post 327236)
Thanks for your comments.

I have a weird moving mesh (attached file)

I assigned osc to cylinder and osc_inert to the entire fluid region (this part is in udf file)
I assigned the top and bottom walls as stationary.

But, the mesh wend out beyond top /bottom walls.
Do you have any idea for this problem?

Best Regards
JY

Hi,

I'm not sure that understand your problem clearly, but there are few comments on such dynamic mesh issues:
- your elements are quadratic, so you have to enable moving them in smoothing method in TUI. (refer to manual)
- your cylinder oscillate in y-direction, so the only thing you need is to hook DEFINE_CG_MOTION on cylinder boundary and let fluent to change other cells with smoothing method; (fluid zone doesn't need any UDF).

Bests,

colopolo October 10, 2011 03:31

Quote:

Originally Posted by Amir (Post 327264)
Hi,

I'm not sure that understand your problem clearly, but there are few comments on such dynamic mesh issues:
- your elements are quadratic, so you have to enable moving them in smoothing method in TUI. (refer to manual)
- your cylinder oscillate in y-direction, so the only thing you need is to hook DEFINE_CG_MOTION on cylinder boundary and let fluent to change other cells with smoothing method; (fluid zone doesn't need any UDF).

Bests,


Thanks, My problem looks like solved.
Very Thanks!!


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