GMO _problem from rotational angle

jiko · June 27, 2011, 11:47

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

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

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

Quote:

Originally Posted by jiko

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

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...

June 27, 2011, 11:47	GMO _problem from rotational angle	#1
jiko Member jiko Join Date: Sep 2010 Posts: 31 Rep Power: 15	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.

June 29, 2011, 23:12		#4
MuxaB Senior Member michael barkhudarov Join Date: Mar 2009 Location: Sante Fe, New Mexico, USA Posts: 336 Rep Power: 18	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. spaudel and shincoast like this.

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July 1, 2011, 05:18		#5
jiko Member jiko Join Date: Sep 2010 Posts: 31 Rep Power: 15	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.

July 1, 2011, 17:52		#6
MuxaB Senior Member michael barkhudarov Join Date: Mar 2009 Location: Sante Fe, New Mexico, USA Posts: 336 Rep Power: 18	i'll check it out this weekend

July 12, 2011, 09:27		#7
jiko Member jiko Join Date: Sep 2010 Posts: 31 Rep Power: 15	Hi Michael, Just a gentle reminder that I am still waiting to hear from you. Thanks.

July 12, 2011, 14:04		#8
MuxaB Senior Member michael barkhudarov Join Date: Mar 2009 Location: Sante Fe, New Mexico, USA Posts: 336 Rep Power: 18	Yes, sorry, will check it out as soon as I can. Mike

July 18, 2011, 05:11		#10
jiko Member jiko Join Date: Sep 2010 Posts: 31 Rep Power: 15	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

August 1, 2011, 04:17		#12
jiko Member jiko Join Date: Sep 2010 Posts: 31 Rep Power: 15	thanks Mickael, so its mean that version 10 solves my problem.

August 15, 2011, 11:51		#13
MuxaB Senior Member michael barkhudarov Join Date: Mar 2009 Location: Sante Fe, New Mexico, USA Posts: 336 Rep Power: 18	I hope so...