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Time derivative only allowed with respect to mesh time

Posted 14 mar 2016, 14:59 GMT-4 Porous Media Flow Version 5.2 10 Replies

Nhan Nguyen
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Hi everyone,

My model contains Darcy's Law under Porous Media and it runs well.
But if I add " Deformed Geometry" Physic under mathematics to compute Time-dependent study, it occurs "Time derivative only allowed with respect to mesh time, expression d(comp1.p,t) "

How can I solve my problem ? Any suggestion ?

Best regards,
N. N

10 Replies Last Post 27 apr 2017, 18:57 GMT-4
Edgar J. Kaiser Certified Consultant
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Posted: 9 years ago 14 mar 2016, 15:42 GMT-4
Hi,

just replace d(comp1.p,t) by d(comp1.p,TIME).

Cheers
Edgar

--
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
Hi, just replace d(comp1.p,t) by d(comp1.p,TIME). Cheers Edgar -- Edgar J. Kaiser emPhys Physical Technology http://www.emphys.com
Nhan Nguyen
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Posted: 9 years ago 15 mar 2016, 01:06 GMT-4
Hi Edgar,

Thanks a lot for your help !

But I can not find d(comp1.t)!
For example, I use Darcy's Law under porous media. Where can I replace d(comp1.p,t) by d(comp1.p,Time) ?

Best regards,
N. N
Hi Edgar, Thanks a lot for your help ! But I can not find d(comp1.t)! For example, I use Darcy's Law under porous media. Where can I replace d(comp1.p,t) by d(comp1.p,Time) ? Best regards, N. N
Edgar J. Kaiser Certified Consultant
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Posted: 9 years ago 15 mar 2016, 04:42 GMT-4
Sorry, I can't tell you. I observed this error in one of my time dependent models when I used the d() operator for post processing. You may consider to submit the case to COMSOL support or upload it to the forum.
However, I don't do CFD, so I can't check your model but other may be willing to do so.

Take care about the spelling, the specifier in the expression has to be TIME, not Time. Case matters!

Cheers
Edgar

--
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
Sorry, I can't tell you. I observed this error in one of my time dependent models when I used the d() operator for post processing. You may consider to submit the case to COMSOL support or upload it to the forum. However, I don't do CFD, so I can't check your model but other may be willing to do so. Take care about the spelling, the specifier in the expression has to be TIME, not Time. Case matters! Cheers Edgar -- Edgar J. Kaiser emPhys Physical Technology http://www.emphys.com
Nhan Nguyen
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Posted: 9 years ago 15 mar 2016, 06:36 GMT-4
Hi Edgar,

Thanks a lot for your help !

Thank you very much !

Best regards,
N.N
Hi Edgar, Thanks a lot for your help ! Thank you very much ! Best regards, N.N
Nhan Nguyen
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Posted: 9 years ago 15 mar 2016, 14:00 GMT-4
Hi everyone,

Can you help me run CFD module and Deformed Mesh under Mathematics together ?

Replacing d(comp1.p,t) by d(comp1.p,TIME) is a very good solution but I can not find where to do that !

Best regards,
N.N
Hi everyone, Can you help me run CFD module and Deformed Mesh under Mathematics together ? Replacing d(comp1.p,t) by d(comp1.p,TIME) is a very good solution but I can not find where to do that ! Best regards, N.N
Mingji Zhang
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Posted: 9 years ago 19 mar 2016, 02:19 GMT-4
You need to check the week form under Darcy Module, replace all d(XXX, t) term to d(XXX, TIME).

Good luck.
You need to check the week form under Darcy Module, replace all d(XXX, t) term to d(XXX, TIME). Good luck.
Nhan Nguyen
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Posted: 9 years ago 19 mar 2016, 04:32 GMT-4
Hi Mingji,

Thanks a lot for your help ! It's such a amazing idea. It gave me a lot of creative ideas.

But I can not still find weak form under Darcy Module where I can replace d(XXX, t) term to d(XXX, TIME).
Can you help me a little bit more by showing more detail how to do that because I'm a beginner?

Best regards,
N.N
Hi Mingji, Thanks a lot for your help ! It's such a amazing idea. It gave me a lot of creative ideas. But I can not still find weak form under Darcy Module where I can replace d(XXX, t) term to d(XXX, TIME). Can you help me a little bit more by showing more detail how to do that because I'm a beginner? Best regards, N.N
Nhan Nguyen
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Posted: 9 years ago 19 mar 2016, 04:45 GMT-4
Hi Mingji,

I found where to replace what I want!
Thank you very much one more time !

Best regards,
N.N
Hi Mingji, I found where to replace what I want! Thank you very much one more time ! Best regards, N.N
Peter Purple
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Posted: 8 years ago 16 ago 2016, 14:25 GMT-4


just replace d(comp1.p,t) by d(comp1.p,TIME).




Hi Edgar,

In my case, comp1.p is an explicit function of time, and I have it written as comp1.p = t^(-0.5)

I did change d(comp1.p,t) to d(comp1.p,TIME), but I'm getting the error "cannot evaluate negative power of zero". Does this mean that I need to substitute 't' with 'TIME' in the expression for comp1.p as well?

Thanks!
[QUOTE] just replace d(comp1.p,t) by d(comp1.p,TIME). [/QUOTE] Hi Edgar, In my case, comp1.p is an explicit function of time, and I have it written as comp1.p = t^(-0.5) I did change d(comp1.p,t) to d(comp1.p,TIME), but I'm getting the error "cannot evaluate negative power of zero". Does this mean that I need to substitute 't' with 'TIME' in the expression for comp1.p as well? Thanks!
Yanxiang Yu
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Posted: 8 years ago 27 apr 2017, 18:57 GMT-4
Hi Nhan,

Could you please specify where to modify this equation?
Is it under Analytical Solution settings or PDE settings?

Thank you,
Hi Nhan, Could you please specify where to modify this equation? Is it under Analytical Solution settings or PDE settings? Thank you,

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