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Note: This discussion is about an older version of the COMSOL Multiphysics® software. The information provided may be out of date.

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Changing order of elements in Comsol4.2a

Posted 2012年2月29日 GMT-5 15:35 Version 4.2a 8 Replies

Abid Saeed
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Hi everyone,

I am new to comsol, I just want to solve some classical PDEs on curved domains using different orders of elements particularly higher order isoparametric elements.

I solved eigenvalue problem for Laplacian over a circle for default order of elements which is quadratic.

But when I want to solve the same problem over same mesh with different higher order by changing order in Element order list it does not solve the problem for new order. it solves problem with same default quadratic element (i.e. it repeats the old problem and delivers same answer) as one can see from degree of freedom.

Can anyone please help me what I am missing here.

Thank you in advance.
8 Replies Last Post 2012年3月5日 GMT-5 19:24
Alexander Kuznetsov
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Posted: 1 decade ago 2012年2月29日 GMT-5 17:59
I just checked it and it works fine for me. I used PDE (c) and change order in PDE Settings - Discretization - Element Order. DoF increased from 1217 for quadratic to 4745 for quartic
I just checked it and it works fine for me. I used PDE (c) and change order in PDE Settings - Discretization - Element Order. DoF increased from 1217 for quadratic to 4745 for quartic
Abid Saeed
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Posted: 1 decade ago 2012年3月1日 GMT-5 13:21

Thankyou for your help.

I think you talking about comsol 3.5a. I tried in comsol 3.5a and it worked there as you said. But if I use latest version i.e. comsol 4.2 and change element order in Discretization - Element Order, it does not work. I dont know why?

Would be good if I am able to solve it using latest version of comsol as well.

Anyway thanks again.

Abid
Thankyou for your help. I think you talking about comsol 3.5a. I tried in comsol 3.5a and it worked there as you said. But if I use latest version i.e. comsol 4.2 and change element order in Discretization - Element Order, it does not work. I dont know why? Would be good if I am able to solve it using latest version of comsol as well. Anyway thanks again. Abid
Abid Saeed
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Posted: 1 decade ago 2012年3月2日 GMT-5 15:11

Hellow again,

I solved eigenvalues problem using comsol3.5a. Now I want to export all eigenvalues but i could not do it. I exported the mesh by going through File-Export-Mesh to file.....but i dont see how to export all calculated eigenvalues.

Any one help me please.

Thanks in advance.
Hellow again, I solved eigenvalues problem using comsol3.5a. Now I want to export all eigenvalues but i could not do it. I exported the mesh by going through File-Export-Mesh to file.....but i dont see how to export all calculated eigenvalues. Any one help me please. Thanks in advance.
Alexander Kuznetsov
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Posted: 1 decade ago 2012年3月2日 GMT-5 15:33
No, I was talking about 4.2a. It works for me. Probably you do something differently. Upload your model so I can have a look.
No, I was talking about 4.2a. It works for me. Probably you do something differently. Upload your model so I can have a look.
Abid Saeed
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Posted: 1 decade ago 2012年3月2日 GMT-5 15:58

Hi Alexander,

Please have a look at files I am sending you both m.file and .mph files.

And also tell me about exporting calculated eigenvalues.

Thanks.
Hi Alexander, Please have a look at files I am sending you both m.file and .mph files. And also tell me about exporting calculated eigenvalues. Thanks.
Alexander Kuznetsov
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Posted: 1 decade ago 2012年3月2日 GMT-5 16:57
Here are my results after changing discretization order:

Quadratic:
Number of degrees of freedom solved for: 93.
Solution time (Study 1): 1 s.

Quintic:
Number of degrees of freedom solved for: 531.
Solution time (Study 1): 1 s.

But I changed it in the different place. Next to the "Model Builder" on top there is "Show" button. Click it to bring the menu. There you select "Discretization". Then click on PDE (c) node and in "settings" you will see that new section called "Discretization" appeared. There you can change your element order.

And sorry, I can't help you with eigenvalues.
Here are my results after changing discretization order: Quadratic: Number of degrees of freedom solved for: 93. Solution time (Study 1): 1 s. Quintic: Number of degrees of freedom solved for: 531. Solution time (Study 1): 1 s. But I changed it in the different place. Next to the "Model Builder" on top there is "Show" button. Click it to bring the menu. There you select "Discretization". Then click on PDE (c) node and in "settings" you will see that new section called "Discretization" appeared. There you can change your element order. And sorry, I can't help you with eigenvalues.
Abid Saeed
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Posted: 1 decade ago 2012年3月5日 GMT-5 14:43


Thankyou so much Alexander it worked now.

One more thing I wanted to make sure that comsol uses the isoparametric elements of same order for domain with curved boundaries. Do you know that comsol is realy doing this what i want?


Abid
Thankyou so much Alexander it worked now. One more thing I wanted to make sure that comsol uses the isoparametric elements of same order for domain with curved boundaries. Do you know that comsol is realy doing this what i want? Abid
Alexander Kuznetsov
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Posted: 1 decade ago 2012年3月5日 GMT-5 19:24
I'm not sure what you are asking about. If it's about curvilinear elements, then I don't think COMSOL uses them.
I'm not sure what you are asking about. If it's about curvilinear elements, then I don't think COMSOL uses them.

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