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predescribed displacement equals displacement value at certain point

Posted 29.10.2012, 08:24 GMT-4 5 Replies

Jan Kaul
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hi guys,

I'm pretty new to Comsol and i'm trying to implement a certain kind of boundary condition. Perhaps there is an easy solution to this, but i can't figure it out. My Problem is that i want to use a constraint like u(1,1,1)-u = 0 for an edge setting. In words, the displacement on an edge is supposed to be the same as the displacement at a certain point.
No matter how i try this I get an error.

I really appreciate your help.

kind regards

Jan Kaul
5 Replies Last Post 24.02.2014, 07:02 GMT-5
Jesus Lucio
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Posted: 1 decade ago 29.10.2012, 12:07 GMT-4
Hello, Jan,

There are several ways of doing what you want. Perhaps the simplest one is to define a "Domain Point Probe" in "Model/Definitions", and give there the coordinates of your point (1, 1, 1); in the "Point Probe Expression" set the variable or expression you want to measure (in your case simply u). Finally, in the boundary where you want to se t the (Dirichlet) boundary condition set the value to that of the Point Probe (something like "ppb1", see your Probe variable name).

That's all.

Jesus.
Hello, Jan, There are several ways of doing what you want. Perhaps the simplest one is to define a "Domain Point Probe" in "Model/Definitions", and give there the coordinates of your point (1, 1, 1); in the "Point Probe Expression" set the variable or expression you want to measure (in your case simply u). Finally, in the boundary where you want to se t the (Dirichlet) boundary condition set the value to that of the Point Probe (something like "ppb1", see your Probe variable name). That's all. Jesus.
Jan Kaul
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Posted: 1 decade ago 13.11.2012, 07:06 GMT-5
Thank you very much, that helped a lot!

kind regards

Jan
Thank you very much, that helped a lot! kind regards Jan
Wenqi Deng
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Posted: 1 decade ago 21.02.2014, 13:31 GMT-5

Hello, Jan,

There are several ways of doing what you want. Perhaps the simplest one is to define a "Domain Point Probe" in "Model/Definitions", and give there the coordinates of your point (1, 1, 1); in the "Point Probe Expression" set the variable or expression you want to measure (in your case simply u). Finally, in the boundary where you want to se t the (Dirichlet) boundary condition set the value to that of the Point Probe (something like "ppb1", see your Probe variable name).

That's all.

Jesus.


Hi Jesus,
I just run into a problem. For example, I defined a domain point probe as ( 1,1,1), then set it as 'w', vertical displacement. However, when I want to use the point probe variable 'ppb1', Comsol show this is unknown variable. Did I use it in a wrong way? I just want to apply a boundary load in terms of k*ppb1 (k is the spring constant).

Anyway, look forward to your reply. Hope you are still using forum.

Thanks a lot.

Wenqi
[QUOTE] Hello, Jan, There are several ways of doing what you want. Perhaps the simplest one is to define a "Domain Point Probe" in "Model/Definitions", and give there the coordinates of your point (1, 1, 1); in the "Point Probe Expression" set the variable or expression you want to measure (in your case simply u). Finally, in the boundary where you want to se t the (Dirichlet) boundary condition set the value to that of the Point Probe (something like "ppb1", see your Probe variable name). That's all. Jesus. [/QUOTE] Hi Jesus, I just run into a problem. For example, I defined a domain point probe as ( 1,1,1), then set it as 'w', vertical displacement. However, when I want to use the point probe variable 'ppb1', Comsol show this is unknown variable. Did I use it in a wrong way? I just want to apply a boundary load in terms of k*ppb1 (k is the spring constant). Anyway, look forward to your reply. Hope you are still using forum. Thanks a lot. Wenqi
Jesus Lucio
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Posted: 1 decade ago 22.02.2014, 05:41 GMT-5
Hi Wenqi,

It seems that you are doing well. If you create a 'Domain Point Probe' it should be accessible from any point/edge/boundary/domain in the model, as it really is a global domain variable (it has a global scope). If you write a correct expression for it ('w' seems good for vertical displacement, but check that this variable name is correct) and you also use the right name of the variable ('ppb1' and so, by default), you should get the correct result. For some reason, COMSOL is not seeing your variable. Please, check the above steps. If you still cannot make it work, you can upload your model (or a simplified version of it, without solution, if your model is large).

Regards,
Jesus.
Hi Wenqi, It seems that you are doing well. If you create a 'Domain Point Probe' it should be accessible from any point/edge/boundary/domain in the model, as it really is a global domain variable (it has a global scope). If you write a correct expression for it ('w' seems good for vertical displacement, but check that this variable name is correct) and you also use the right name of the variable ('ppb1' and so, by default), you should get the correct result. For some reason, COMSOL is not seeing your variable. Please, check the above steps. If you still cannot make it work, you can upload your model (or a simplified version of it, without solution, if your model is large). Regards, Jesus.
Wenqi Deng
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Posted: 1 decade ago 24.02.2014, 07:02 GMT-5
Hi Jesus,

Thanks for your help. I make it now, maybe there was something wrong with the software.

Regards,
Wenqi
Hi Jesus, Thanks for your help. I make it now, maybe there was something wrong with the software. Regards, Wenqi

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