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-   -   GMO _problem from rotational angle (http://www.cfd-online.com/Forums/flow-3d/89959-gmo-_problem-rotational-angle.html)

jiko June 27, 2011 11:47

GMO _problem from rotational angle
 
I have a GMO rocking around fixed(Y) axis. It is observed that when the rotational angle is all positive or all negative then the oscillating x force is in reasonable range. but when this rotational angle oscillates from -M to +M value the resulting x-force is nearly zero . why? Please suggest something to fix this issue. thanks
Here the GMO is moving under prescribed sinusoidal velocity.

MuxaB June 27, 2011 20:05

Quote:

Originally Posted by jiko (Post 313753)
I have a GMO rocking around fixed(Y) axis. It is observed that when the rotational angle is all positive or all negative then the oscillating x force is in reasonable range. but when this rotational angle oscillates from -M to +M value the resulting x-force is nearly zero . why? Please suggest something to fix this issue. thanks
Here the GMO is moving under prescribed sinusoidal velocity.

Jiko,

I am not sure I grasp the geometry of the motion. Do you have an prepin please?

jiko June 29, 2011 06:04

1 Attachment(s)
Thanks M,
Here is the prepin file attached. the phase of 270degree is to rock the GMO evenly on both sides of the initial position. observe the x-force for 0 phase and for 270phase.

thanks.
waiting for your reply.
J

MuxaB June 29, 2011 23:12

Thanks for the file. The first thing I'd suggest is not using the GMRES implicit viscous solver. It does not produce reliable solution and needs further work. In fact, I don't think you need an implicit viscous solver at all. An explicit solver is always better if it does not limit the time step too much. In your case the fluid is water, so I am sure the time step stability is controlled by convection rather than viscous dissipation.

Let me know if it behaves differently with the explicit sovler.

jiko July 1, 2011 05:18

Thanks Michael,

Under Numerics--> the allowed option for
pressure solver is only Implicit but for viscous stress I did switched it to the suggested Explicit. But unfortunately the problem is still there.

Could you suggest another remedy Please?

even if you try x-translation (of any GMO) and put the initial phase as 270degree. the unrealistic x-force can be observed.



MuxaB July 1, 2011 17:52

i'll check it out this weekend

jiko July 12, 2011 09:27

Hi Michael, Just a gentle reminder that I am still waiting to hear from you.
Thanks.



MuxaB July 12, 2011 14:04

Yes, sorry, will check it out as soon as I can.

Mike

MuxaB July 12, 2011 19:59

1 Attachment(s)
Quote:

Originally Posted by jiko (Post 315830)
Hi Michael, Just a gentle reminder that I am still waiting to hear from you.
Thanks.



Jiko, I ran it as you sent me and get a pretty substantial force in the x-direction. So far it is just short of 5 seconds. See the plot

jiko July 18, 2011 05:11

Thanks for your time Michael, I wonder why on my PC it turns out to be much different. I would be grateful if you could send me the prepin used for these results from your end.
thanks

MuxaB July 29, 2011 15:59

Quote:

Originally Posted by jiko (Post 316434)
Thanks for your time Michael, I wonder why on my PC it turns out to be much different. I would be grateful if you could send me the prepin used for these results from your end.
thanks

Jiko, it is the same file you sent me. I ran it with version 10.0 of FLOW-3D. Version 9.4 should give the same results.

jiko August 1, 2011 04:17

thanks Mickael, so its mean that version 10 solves my problem.

MuxaB August 15, 2011 11:51

I hope so...


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