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third order differential equation

Posted 30 juin 2017, 08:17 UTC−4 2 Replies

Sanjay Prabhakar
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Hi All,

It looks like COMSOL can not handle third order differential equation in Coefficient Form to solve Eigenvalue problem.

I would like to implement this equation:

d^3/dx^3

Any help will be appreciated.

Regards
Sanjay Prabhakar
Post-doc Fellow
Physics, Vanderbilt University
2 Replies Last Post 1 juil. 2017, 17:48 UTC−4
Mohammad Amin Kazemi
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Posted: 7 years ago 1 juil. 2017, 16:48 UTC−4
Updated: 7 years ago 1 juil. 2017, 17:28 UTC−4
Sanjay,

To calculate the higher derivatives, you may define them as a new variable and solve them coupled to the other physics in your model.

To understand how to do this, see the following example by Marc Fernandez Silva:

www.comsol.com/blogs/plotting-spatial-derivatives-magnetic-field/

Hope that they resolve this issue in the newer versions.

Amin,
Sanjay, To calculate the higher derivatives, you may define them as a new variable and solve them coupled to the other physics in your model. To understand how to do this, see the following example by Marc Fernandez Silva: https://www.comsol.com/blogs/plotting-spatial-derivatives-magnetic-field/ Hope that they resolve this issue in the newer versions. Amin,
Sanjay Prabhakar
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Posted: 7 years ago 1 juil. 2017, 17:48 UTC−4
Thanks Admin,

I think, I figure it out, how to implement third order derivative as follows:

In coefficient form, there is a term \Delta. (....+\gamma)

\Delta can be \partial_x and \gamma can be uxx (second derivative of u w.r.t. x). This gives "third derivative of u w.r.t. x.

Thanks for sending your paper and I will be reading your paper very carefully.

Thanks
Sanjay
Thanks Admin, I think, I figure it out, how to implement third order derivative as follows: In coefficient form, there is a term \Delta. (....+\gamma) \Delta can be \partial_x and \gamma can be uxx (second derivative of u w.r.t. x). This gives "third derivative of u w.r.t. x. Thanks for sending your paper and I will be reading your paper very carefully. Thanks Sanjay

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