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-   -   Cylinder moving in fluid,Solution diverging (http://www.cfd-online.com/Forums/star-ccm/113817-cylinder-moving-fluid-solution-diverging.html)

arun7328 February 27, 2013 07:16

Cylinder moving in fluid,Solution diverging
 
3 Attachment(s)
Dear All,

I had posted a thread yesterday regarding some help on problem of oscillating cylinder. Since i did not get any reply i thought of making the problem a little more simpler,before i could go on with the oscillating cylinder.I have considered a translating cylinder in +X dir and fluid flow towards -X. The velocity of cylinder is 5m/s and that of fluid is 20m/s. I have attached the meshing snap shot.

I am using polyhedral and prism layer meshing. The motion is defined using DFBI morphing. Inlet and outlet,top and bottom regions are fixed in physics condition, Cylinder is as six DOf body and symmetry defined using grid velocity.

The grid velocity is same as the velocity of the cylinder. I have tried various time steps. At first the solution was not even starting but after a couple of hours of reading and working i have got it running and the cylinder is also moving but the residuals are continuously increasing. It runs for sometime and then an error message is displayed which is attached.

Can any one please guide me with the problem?

Once i can establish this i can move on to the problem of an oscillating cylinder.

Again if anyone can give me some idea of how to define the oscillations, it will be of great help.

Please advice

Regards
Arun

arun7328 February 27, 2013 09:39

Atleast can some one tell me if i am using the right methods. Can i use morpher for this problem or should i use overset meshes? Please advice.

thanks
Arun

grad@itu February 27, 2013 14:17

Hi,

This is a mesh quality error but still you can perform your simulation. You have to check Cell Quality Remediation option in Physics Continuum. Lets you try that and We talk again about your problem.

By the way, Cell Quality Remediaton process will come extra calculations and then your analysis will be more slower but you will not think about your bad cell (for now!).

arun7328 February 27, 2013 14:54

Can you please tell me if i can use a morpher for this? because i have been reading the manuals and i feel now an overset mesh is a better option. It will help me have relative motion between the background and the overset mesh/body? For even the prob of oscillating cylinder isn't the overset mesh to be used?

grad@itu February 27, 2013 15:13

I do not use mesh morpher before and i used many times overset mesh but espsecially in variable angle of attack solutions on a wing.

I think both methods suitable for your problem, overset mesh using more easy than mesh morphing technique and then i prefer that.

But, you can try both methods..
There is an very good example in tutorials related to aerodynamics/wing and then you can easily apply to your problem i think..

Plus, in my opinion you should transient analysis. You gave an error message image i explained that previous message besides with this method you can remove bad cells but be careful you can remove a part of the cylinder or something related any body in any projects.

arun7328 February 27, 2013 15:28

Thanks a lot..if i have any trouble will post..I also think overset mesh will be easier. I have gone thru the life boat example and will also check the airfoil before i proceed to my real problem.

Thanks again for your advice..
Cheers
Arun


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