LiveLinks - Latest Discussions - COMSOL Forums

How to apply diffusion coefficient of PDE at node point

Tue, 22 May 2012 01:46:59 +0000

I am working on an inverse problem solving.

1)I used coefficient form PDE for forward solving
2)Obtained the solution in matlab and calculated new updated diffusion coefficient at each nodes
3)Now I want to apply this value of diffusion coefficient the nodes and solve the PDE again.

Please help me in solving this problem

importer les codes comsol sur matlab et les executer !!!

Wed, 16 May 2012 06:05:44 +0000

Bonjour,

Merci pour votre attention de repondre a mon message.
Enfait j'ai pas encore resolu le probleme.meme avecle guide de LiveLink for Matlab.
Apres sauvegarder le ficher sous m.file et ouvrir COMSOL with matlab j'arrive pas a executer mon programme.
Est ce que vous pouvez me guider SVP(démonstration détailler).je suis débutante avec ces logiciel.
Je vous envoie le ficher m.file .

Merci d'avance
Cordialement
Mariem

Problem with revolve object and matlab

Fri, 11 May 2012 07:22:27 +0000

Hi,

I'm trying to make a basic horn by revolving a 2D exponential curve around an axis. If i make it in Comsol, the revolving operation works fine. But if I use Matlab, it doesn't want to set the right revolving axis, no matter what I do.

I used "Save as model M-file" to generate the matlab file. So, it should do exactly the same as in Comsol. I don't understand why it gives this result. I attached the Comsol file and the Matlab file generated from it.

Do I need to set an additional parameter in Matlab ? Is there a trick to make it work ?

Thanks,

Ugo

Enquiry on Livelinks for Matlab

Mon, 07 May 2012 11:26:32 +0000

Dear Mr Lars,

I'm using COMSOL 4.2a in my lab, and I have no problem with simple examples in extracting data from COMSOL to matlab.
The thing is, when I try to use a more complicated model, I just cannot get any values of any variable!!!
I posted it on this page: http://www.comsol.dk/community/forums/general/thread/28413/#p77051
The mph and m file is also attached there.
Could you please spend some time to help me out？
I'm looking forward to your reply.
Thank you very much!

Best regards,
Di Kai

License error using livelink matlab

Mon, 07 May 2012 10:07:02 +0000

Hello community!

I would like to share a problem with you.. because you might have a suggestion.

I am running comsol with matlab. I have a for loop in matlab and for each iteration it runs the following command to solve the comsol model.

model.study('std1').run;

The problem comes that every time it runs the the line, it opens a new license. Since I am student and I am running with the server of the university, it opens so many files that crashes the server...

My question is: Is there any command to free this license? or something like saving the model to stop this problem?

thanks.

Matias

How to form Jacobian

Thu, 03 May 2012 18:34:50 +0000

I have measurement nodes in my geometry,I want to form a Jacobian matrix which has change in measurement value with respect to change in coefficient of pde at individual node position.

Please help me solving the problem.

MATLAB functions in comsol

Thu, 03 May 2012 10:33:25 +0000

Hello...

I defined a MATLAB function in global definitions with argument T
i created function.m file in matlab and saved both .mph and .m file in the same folder..
and i set the matlab path to point the same folder..

when i am trying to execute ..gives the error ' Function is not found'..

Is there any steps i am missing..

i follwed in comsol 4.1.. 1.define MATLAB function and arguments in comsol
2. create .m file in matlab
3. set the matalb working path to the folder where .mph and .m files are saved.

can any one suggest how to make comsol to find the matlab function..

thanks
pavan

Insulation problem when importing model from Inventor Autodesk

Fri, 27 Apr 2012 04:44:59 +0000

Hello,

I have made a 3D model in Inventor Autodesk, as an assembly consisting of three parts. I use LiveLink to import the model to Comsol V4.2. Everything seems to be ok, I get no errors or warnings and I can simulate the model. The problem is that the boundary condition "Insulation" is placed upon all my interior boundaries and I cannot remove them. Why is that, and can I remove them somehow?

Thanks in advance!
Marie

converting COMSOL code to the MATLAB ???

Thu, 26 Apr 2012 11:21:43 +0000

Hello,

I'm working with COMSOL to simulate a chemical experience, but it takes too much time to display the results.
So i want to find a link between comsol and matlab if i can convert the code of comsol to matlab that will be faster than using comsol alone !!!
So am asking if i can do this and how ????

watting your answer
thank you very much :)

Saving plot from mphplot() to disk

Sun, 22 Apr 2012 20:05:49 +0000

Hi,
I'm having a hard time trying to save a plot which comes from mphplot(). What I'm trying is:

figure;
mphplot(model,'pg3');
saveas(gcf,'result_plot.tiff');

But it just produces an error 'Warning: RGB color data not yet supported in Painter's mode'. So I guess it's an issue with the renderer Matlab uses. Changing the renderer with set(gcf,'Renderer','zbuffer'); does seems not to work.

Is there an easy way to save a Comsol Plot to disk?

Livelink for Matlab and COMSOL v4.2a Meshing and Solution not synchronized...

Tue, 17 Apr 2012 18:40:34 +0000

I have not found any discussion on this topic yet and I am having difficulty finding anyone in COMSOL support in North America that can help with this problem today.

Basically, I simply want to take a solution from COMSOL, import it into MATLAB and plot the solution on the mesh within MATLAB.

For an example problem:

1) I solve the 1D Helmholtz equation on a line segment from x=0...1, with Dirichlet boundary conditions at both ends.
*** I use the PDE Coefficient form setting the source term to zero (c=1,d_a=1,f=0). On a side note, I have tried to use the Helmholtz Equ "classic PDE" and it doesn't work (setting f=0) as it claims the "mass matrix is zero" - which is true, however, unnecessary when solving a sourceless problem (COMSOL please fix this).
*** I have also solved this for 2D and 3D as well, the problem I am describing still exists, but is harder to track down, read on....
2) Either export the solution to comsolserver or save the model as an mph file.
3) In Matlab (started from COMSOL with LiveLink for Matlab), load in the 1d Helmholtz solution:
either use:

fem1 = mphload('filename')

or use

fem1 = ModelUtil.model('Model');

4) load the solution vector (eigenvector) using either:

soltranspose = fem1.sol('sol1').getU(1);

or

soltranspose2 = mphgetu(fem1,'solnum',1)

5) load in the mesh using:

mesh1 = mphxmeshinfo(fem1,'solname', 'sol1');

6) set some variables for the x and y coordinates of the mesh (if you have a 2D mesh), if you have a 1D mesh, then only use the x coordinate:

xxx = mesh1.nodes.coords(1,:);
yyy = mesh1.nodes.coords(2,:);

it is good at this point to look at the mesh to verify that it is the same as in COMSOL:

plot(xxx,yyy,'.')

It looks good!

7) **** It is interesting to note that the solution vector coming from mphgetu is a column vector, but the mesh vector is a row vector. For this reason, I take the transpose of the solution vector to make it the same dimensions as the mesh vector.

8) Now, try to plot the solution for the 1D case:

solu = soltranspose';
plot(solu)

It looks good, like the correct answer should look, a half-wavelength eigenmode (the lowest mode).

9) Now try to plot the solution for the 1D case at the positions of the mesh:

plot(xxx,solu)

PROBLEM! The positions of the mesh are NOT ALIGNED with the solution vector. Although they both have the same size, the ordering of the mesh vector is not aligned to the ordering of the solution vector.

This is obvious when looking at the 1D solution to the Helmholtz equation, but is harder to trace when looking at a 2D or 3D solution.

So, WHY would you want to do this? In other words, why would I like to have total control over a solution from COMSOL? Simple, what if I wanted to perform my own ortho-normalization calculation. In this case, I would need to know the area around each point in the solution so that I could properly weight the integration (quadrature). There are many other reasons why I need to have the solution vector properly coordinated with the mesh, but that is the most obvious reason.

Any thoughts? Is there a property to the "mphxmeshinfo" structure that gives me the correct order for the mesh vector?

Help me Obiwan....

-KLM

The current on a section of a 3D model

Sun, 11 Mar 2012 14:48:20 +0000

hello,
i have a problem with the calculation of current in one section of a 3D model (v.4.2).
My model is imported with LiveLinks SolidWorks.
I have a three-dimensional model on which inject current from two electrodes. I would like to calculate how to distribute the current in the model and, in particular, how much current is distributed over a section given.
How do I calculate it?
Thank you so much.

Chiara

Creating geometry features with LiveLink for Matlab

Tue, 21 Feb 2012 13:53:10 +0000

What is the most efficient way of cutting a large number (>1000) circles out of a rectangle using LiveLink for Matlab?
I do it in a simple "for"-loop, but the program slows down with an increasing number of circles.
Is there a more efficient way?
Thanks!

How to choose the MATLAB version that ran by "COMSOL 4.2 with MATLAB"?

Mon, 13 Feb 2012 19:31:28 +0000

Hello all,

I have two versions of MATLAB on my computer, R2010a and R2011b. When I launch the COMSOL 4.2 with MATLAB shortcut (C:\COMSOL42\bin\win64\comsolserver.exe matlab), R2010a is launched. I am wondering if there is a way to let this shortcut and LiveLink run R2011b instead of R2010a.

Thanks.

Best,
Kan

Comsol Matlab script invoking Matlab external function

Sun, 22 Jan 2012 18:01:04 +0000

Hi everyone,

I hope someone will be able to help me with this. So basically what I am doing is I am using comsol to solve a pde with an external matlab function. When I run my model through the comsol gui, I can invoke this function without any problem and I obtain a fine solution.
The problems comes when I save my model as a .m file and then try to run the matlab generated script through matlab.

Basically, I get the error:
can not start Matlab ()
- Library: /somepath/flmatlab.so

Note that I am running linux, but this shouldn't be a problem. So I think the problem comes because in the matlab generated script, an external matlab function is defined through something similar to: model.func.create('extm1', 'MATLAB');
and when it comes time to call this function, the script tries for some reasons to run another instance of matlab and fails.

I have been able to run Comsol matlab model script through matlab without any problem when I wasn't using any "external matlab" function.

So does anyone know a way to circumvent this problem? I need the matlab generated script because I need more control on what's going in Comsol, namely, I would like to deal with matlab global variables between my matlab function and the matlab workspace.

So how do I tell my script not to try to run another instance of matlab or how do I tell it that it doesn't need to do so in order to call this function?

Thanks for the help.

Out of Memory while creating mesh!!

Wed, 11 Jan 2012 02:37:36 +0000

Hi,
I am trying to create a 2D model, wherein I import geometry from AutoCad.
The Problem is that the geometry is so huge, that I cannot form mesh on it, even with a very high element size.

Now, I cannot use symmetry BC, because it isnt symmetric bout any axis and I cannot scale it or redesign it.

So is there any way, I can solve this?

Is there a way to increase the memory allotment of comsol?

Will running the program on a supercomputer cluster help solve the problem?

Thank you,

-Rohan.

COMSOL embedded in solidworks

Sat, 31 Dec 2011 03:47:25 +0000

HI,

recently, my Solidworks2012 was installed. COMSOL has a livelink with it.

a good feature is could embedded COMSOL in the solidworks interface.

for my situation is, COMSOL could import 3D model from solidworks, but cannot embeded it inside solidworks.

the instruciton shows open the COMSOL tab in the commond manager, but I didn't see it at all.

the livelink add-in was actived in solidworks.

is there anyone could help me ?
thanks

--
learn COMSOL, like COMSOL

accessing MATLAB global variables when running models in MATLAB

Thu, 22 Dec 2011 16:59:41 +0000

I have defined an external function in matlab that I use in my Comsol/Matlab livelink model to set a volume heat source, let's call this function my_heat(x,y,z), where x,y,z are comsol spatial variables.
Everything works fine with this (comsol passes x,y,z vectors and matlab returns heat source values based on this, and the model is set up and solved)

Now, I tried to use some global MATLAB variables within the 'my_heat' function. When I run function in MATLAB the variables and their values are accessible in 'my_heat'. However, when the same function is called by COMSOL as part of setting the physics, it seems 'my_heat' does not recognize these variables.

I think I know what the problem is, but don't know the solution to it:

When the model is run from Matlab, Comsol seem to open another instance of MATLAB (as manifested by a second command window). This seems like the place where all the Comsol/Matlab interfacing happens. No wonder that in this new instance of Matlab, the information about any global variables in the main Matlab window is missing.
Any ideas on how to 'pass' all the info from the main Matlab window to this auxiliary one?

Thanks,

Robert

P.S.: On an unrelated note, I discovered that by typing 'clear functions' in this new matlab window, I can have comsol get the updated version of any edits to my matlab fuinctions. Without this, comsol only has the first version of external functions. Typing 'clear functrions' in the main matlab window doesn't maker any difference.

import complex 3D geometry internal error code 900 / boolean operation failed

Mon, 06 Jun 2011 13:10:25 +0000

Hi everyone,

I am trying to import a complex 3D geometry into COMSOL 4.0a. I've created it using CATIA (R19). The file format to be imported is .stp. Also, I do have access to the CAD import tool. The model consists of four domains that, once united, have a cylindrical shape. The interfaces between the domains, however, are very complex and irregular. I can import each domain separately (and form a union for each domain individually). However, once i try to form a union between all four domains I obtain the following error message: "Boolean operation failed". In a different thread I read that this might be due to the repair tolerance. Hence, I played with the import tolerances. Now, however, I obtain another error message: "Internal error in geometry processing internal error code: 900".

My questions:
===========

1. I am dealing with a coupled fluid structure problem (using "acsl" toolbox), is it 100% necessary to form a union or will an assembly do the trick as well?

2. If I need to form a union, why do I get the outlined error messages and what can I do to fix the problem (I am almost 100% sure that my geometry is correct and that the domain interfaces are error free)

Thanks you very much in advance

Martin

Comsol 4.2

Wed, 18 May 2011 14:34:09 +0000

For your informations,

I just received an email for a free workshop on COMSOL Multiphysics Version 4.2 at montreal in one week. We should receive the cd soon!