4.0a - Latest Discussions - COMSOL Forums

question

Wed, 16 May 2012 18:31:00 +0000

Hi,

My name is Yahya. I know you from COMSOL forum. I tried to do similar simulations calculating electric field distribution between two copper electrodes, but got problem. I was wondering if you would not mind to give some tips? If you kindly agree, I attached a pdf file with detailed steps I did. At the end it gives an error which I do not understand what (see attachment). I would be very happy to get help from you. Thank you very much in advance!

Yahya.

question

Wed, 16 May 2012 18:09:12 +0000

Hi,

My name is Yahya. I am a new user of COMSOL, I tried to simulate electric field distribution between two copper electrodes, but got some problem. Would not you be able to give a help with this? I attached a pdf file with detailed steps I did. At the end it gives an error which I do not understand what (see attachment). I would be very happy if you could take a look to see what I did wrong. Thank you very much in advance!

Yahya.

question

Wed, 16 May 2012 18:01:14 +0000

Thermal Dispersion in a Poreus Medium Module Problem

Thu, 10 May 2012 11:33:25 +0000

Hi,

I am working on simulation an Aquifer Thermal Energy Storage (ATES) [1] system. In this I am trying to use thermal dispersion, which is part of the heat transfer module. However I cant get it to work. I have tried the manual and the internet, but I cant figure out what the problem is and let alone solve it. Maybe one of you guys can see what the problem is, and how I would be able to solve it?

I've included the error log and the model, which is a 4.0a model.

Greetings Nick

[1] http://www.iftech.co.uk/index.php?option=com_content&task=view&id=21&Itemid=33

Attempt to evaluate negative power of zero.
- Function: ^
Failed to evaluate temporary symbolic derivative variable.
- Variable: mod1.ht2.k_dispxx@VDN$mod1.py
- Defined as: (((1/max(sqrt((((mod1.ht2.ux^2)+(mod1.ht2.uy^2))+(mod1.ht2.uz^2))),eps))*((mod1.ht2.rho*mod1.ht2.Cp)*(((((1/(mod1.dl.g*mod1.dl.rho))*(-mod1.dl.Kyy))))*(mod1.ht2.uy*2))))+((((((((mod1.ht2.ux^2)+(mod1.ht2.uy^2))+(mod1.ht2.uz^2))^-0.5)*0.5)*(((((1/(mod1.dl.g*mod1.dl.rho))*(-mod1.dl.Kyy))))*(mod1.ht2.uy*2)))*(sqrt((((mod1.ht2.ux^2)+(mod1.ht2.uy^2))+(mod1.ht2.uz^2)))>eps))*((-((mod1.ht2.rho*mod1.ht2.Cp)*(((mod1.ht2.ux^2)+(mod1.ht2.uy^2))+(mod1.ht2.uz^2))))/(max(sqrt((((mod1.ht2.ux^2)+(mod1.ht2.uy^2))+(mod1.ht2.uz^2))),eps)^2))))
Failed to evaluate temporary symbolic derivative variable.
- Variable: mod1.ht2.k_eqxx@VDN$mod1.py
- Defined as: ((((1/max(sqrt((((mod1.ht2.ux^2)+(mod1.ht2.uy^2))+(mod1.ht2.uz^2))),eps))*((mod1.ht2.rho*mod1.ht2.Cp)*(((((1/(mod1.dl.g*mod1.dl.rho))*(-mod1.dl.Kyy))))*(mod1.ht2.uy*2))))+((((((((mod1.ht2.ux^2)+(mod1.ht2.uy^2))+(mod1.ht2.uz^2))^-0.5)*0.5)*(((((1/(mod1.dl.g*mod1.dl.rho))*(-mod1.dl.Kyy))))*(mod1.ht2.uy*2)))*(sqrt((((mod1.ht2.ux^2)+(mod1.ht2.uy^2))+(mod1.ht2.uz^2)))>eps))*((-((mod1.ht2.rho*mod1.ht2.Cp)*(((mod1.ht2.ux^2)+(mod1.ht2.uy^2))+(mod1.ht2.uz^2))))/(max(sqrt((((mod1.ht2.ux^2)+(mod1.ht2.uy^2))+(mod1.ht2.uz^2))),eps)^2)))))
Failed to evaluate temporary symbolic derivative variable.
- Variable: mod1.ht2.k_effxx@VDN$mod1.py
- Defined as: (((((1/max(sqrt((((mod1.ht2.ux^2)+(mod1.ht2.uy^2))+(mod1.ht2.uz^2))),eps))*((mod1.ht2.rho*mod1.ht2.Cp)*(((((1/(mod1.dl.g*mod1.dl.rho))*(-mod1.dl.Kyy))))*(mod1.ht2.uy*2))))+((((((((mod1.ht2.ux^2)+(mod1.ht2.uy^2))+(mod1.ht2.uz^2))^-0.5)*0.5)*(((((1/(mod1.dl.g*mod1.dl.rho))*(-mod1.dl.Kyy))))*(mod1.ht2.uy*2)))*(sqrt((((mod1.ht2.ux^2)+(mod1.ht2.uy^2))+(mod1.ht2.uz^2)))>eps))*((-((mod1.ht2.rho*mod1.ht2.Cp)*(((mod1.ht2.ux^2)+(mod1.ht2.uy^2))+(mod1.ht2.uz^2))))/(max(sqrt((((mod1.ht2.ux^2)+(mod1.ht2.uy^2))+(mod1.ht2.uz^2))),eps)^2))))))
Failed to evaluate expression.
- Expression: d(d((-mod1.ht2.k_effxx*mod1.T2x*test(mod1.T2x)-mod1.ht2.k_effyy*mod1.T2y*test(mod1.T2y))*(dvol),{test@3}),mod1.py)

Divergence of gradient of a variable calculation

Thu, 10 May 2012 09:04:52 +0000

Dear Support,
I need to calculate, in the post-processing stage, the divergence of the gradient (it is the laplacian) of a known variable, in a specified volume.
May you help me, please?

problems with the linear buckling analysis

Tue, 08 May 2012 11:30:18 +0000

hei,
I am trying to calculate the critical loads using the linear buckling analysis. I have two problems:
1. when the model is not to include geometric nonlinearity, the critical factor computed is negative value, is it valid? What does it mean?
2. when the model is to include geometric nonliearity, do I need to select it in both study's steps? There are different values of the critical factors if I select it only one of the study's steps.

thanks!
Dazhuo

can comsol support multilayer shell?

Thu, 03 May 2012 05:31:22 +0000

Dear all,

I am trying to model a membrane using shell element because thickness is quite thin compared to length and width. But the membrane is lamated with three to five different materials and thickness at different location. It seems impossible to use 3D solid model that will lead too many mesh elements. Do anyone know how to do multilayer shell in comsol?

Integration over a filtered volume

Mon, 30 Apr 2012 15:19:58 +0000

Dear Support,
I kindly ask you to help me to solve the following problem.
I am able to plot a user-defined quantity with an element filter in a 3D domain: the logical expression I use for the filter of this quantity is :"quantity>0".
Then, my 3D domain is "restricted" to the only elements where this quantity is larger than zero.
My question is: how can I do a volume integration in this "restricted" 3D domain?
I am not able to identify this restricted 3D domain as a specific entity, but I am only able to plot it.
Please, help me to fix this problem.
With my best regards,
Alessandro

Cyclic MW Heating

Mon, 30 Apr 2012 08:48:47 +0000

Hi all,

Can we perform cyclic microwave heating in COMSOL?
By cyclic, I mean switching on the power for some time and then swittching it off for some time, the way the original microwave oven works in real life.

I think the model given for microwave oven performs a continuous heating, is it?

Thanks for any help.

problem creating a model using a Matlab function from COMSOL model

Fri, 27 Apr 2012 10:08:41 +0000

Hello Sir,
I readed you answer about loading comsol code to matlab function.
I have a question about loading model from comsol to matlab function in order to simplify my equations .
Am working with windows and the software (matlab) is not installed in my PC am working with it on line (in a laboratory).
So can't found the " COMSOL with MATLAB " in the Start Menu !!!

It's my frist time working with this software am trying to read and understand the steps but i s a diffecult language so am asking you if you can give simple instructions to help me .

Sorry fo my stupid question & hope that you will help me .

Thank you very much

converting COMSOL code to the MATLAB ???

Thu, 26 Apr 2012 12:30:30 +0000

Hi ,
Sorry for inconvenience, it's my first time working with whis software so sorry for my stupid question !!
am working with matlab on line and i didn't find anything about runing comsol with matlab only pdf documentation as you can see in attach file .

Do you speek frensh ???

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 :)

multiparameter model with comsol ???

Thu, 26 Apr 2012 11:08:13 +0000

hello,

Am trying to do a model with comsol but my problem is that whenever I enter a parameter value manually and it takes alot of time . I want to know how I can enter a range of values once and for all.
thank you for your answer

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

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.

Varying capacitance due to thickness reduction

Tue, 19 Apr 2011 09:34:55 +0000

Hello,

I am simulating a capacitor with a compliant dielectric and compliant electrodes in COMSOL 3.5a, using the Structural mechanics and electrostatics modes. I am using 2D axial symmetry
I wanted to know whether it is possible to plot the change in capacitance which occurs due to structural deformation of the capacitor, e.g. increase in surface area and consequent reduction in thickness.

Any suggestions would be helpful.

Thank you,
Aseem

how to solve ODE in comsol 4.0a

Thu, 17 Mar 2011 08:33:58 +0000

Dear all ,

I want to solve coupled following ODE for specific geometry , is comsol capable of solving this ?

dT/dt=(Qg-H-T*C*M)
dh/dt=-G*B*(Ys)

G,F,C=const
H=M*(C*T+F)
T=Temperature
Ys=Temperature dependant
B & Qg = Temperature and Height dependant
h=Height

Is there any stepwise toturial exists in this regard? I tried global equation in ODE but I do not know how could I define coupling and temperature and height dependant variables ?

material definition

Sat, 15 Jan 2011 16:41:56 +0000

Hi

Currently COMSOL is unable to define frequency dependent metals. I want to define a new material for frequency dependent effective refractive index of a metal based on Johnson, P. and R. Christy (1972) Physical Review B 6(12): 4370-4379. But being a newbie I am not sure how to do go about it. Can anyone please explain this to me?

Thanks,

Amin

PML and RF Module

Wed, 29 Sep 2010 16:17:59 +0000

Hi,

I am trying to find the eigenmodes of a grated ring waveguide. To do so I simulate a segment of the ring and use periodic boundary conditions. Since light should be radiated upwards and downwards PMLs should be added to avoid reflections. However after adding the PMLs the solver always crashes, giving the message:

-------------------------------------------------------------------------------------------------------------------------
Exception:
com.femlab.jni.FlNativeException: Undefined value found Solvermodel
Messages:
Undefined value found Solvermodel

Stack trace:
at solvermodel.cpp, row 1837, (Undefined value found in the stiffness matrix.
There are 6328 equations giving NaN/Inf in the matrix rows for the variable tExEyEz10
at coordinates: (0.000189496,-1.0796e-06,1.474e-05), (0.000189496,-9.39261e-07,1.474e-05), (0.000189696,-1.07929e-06,1.474e-05), (0.000189696,-9.37368e-07,1.474e-05), (0.000189563,-9.3969e-07,1.474e-05), ...
There are 4445 equations giving NaN/Inf in the matrix rows for the variable tExEyEz20
at coordinates: (0.000189496,-1.00943e-06,1.4809e-05), (0.000189563,-1.08003e-06,1.474e-05), (0.000189629,-9.38529e-07,1.474e-05), (0.000189746,-1.00978e-06,1.474e-05), (0.000189846,-8.70737e-07,1.474e-05), ...
There are 4445 equations giving NaN/Inf in the matrix rows for the variable tExEyEz21
at coordinates: (0.000189496,-1.00943e-06,1.4809e-05), (0.000189563,-1.08003e-06,1.474e-05), (0.000189629,-9.38529e-07,1.474e-05), (0.000189746,-1.00978e-06,1.474e-05), (0.000189846,-8.70737e-07,1.474e-05), ...
and similarly for the degrees of freedom, NaN/Inf in the matrix columns
)
at com.femlab.solver.FlSolver.femEig(Native Method)
at com.femlab.solver.FemEig.run(Unknown Source)
at com.femlab.server.FlRunner.run(Unknown Source)
at com.femlab.util.i.run(Unknown Source)
at com.femlab.util.aa.run(Unknown Source)

at com.femlab.solver.FlSolver.femEig(Native Method)
at com.femlab.solver.FemEig.run(Unknown Source)
at com.femlab.server.FlRunner.run(Unknown Source)
at com.femlab.util.i.run(Unknown Source)
at com.femlab.util.aa.run(Unknown Source)

-------------------------------------------------------------------------------------------------------------------------------------------

I dont know what to do about that, maybe someone could give me a hint

thanks in advance
tobias

Tip: Batch calculations with Matlab + Comsol 4.0a

Thu, 09 Sep 2010 11:26:48 +0000

Hi,

I just wanted to share my experience regarding batch-type (i.e., non-interactive) calculations using comsol 4.0a and the matlab livelink. I lost quite some time trying to run a comsol matlab script (.m file) on a linux cluster, and I thought some people might be interested in hearing the workaround I found.

When working with the cluster, I have two major constraints:
1. I do not have any kind of display (X) support,
2. I have to submit the calculation via a simple bash script.

In 3.5a, running a .m file in batch mode was very easy (At the very least, it was nicely documented : http://www.comsol.com/support/knowledgebase/980/), One would use:

comsol matlab -ml -nodesktop -ml -nosplash -mlr "myscript, exit"

In comsol 4.0a, using something along the lines of

comsol server matlab -nodesktop -nosplash -r myfile

does not lead to similar behavior. First, an xterm is spawned, and the 'nodesktop' matlab runs in this new terminal. The '-r myfile' option is ignored, and matlab does not run my .m file on startup.

To work around the fact that 'comsol server matlab' spawns an xterm, I was told by comsol support to do the following:

1. Start the comsol server
2. Start matlab, and connect to the server using mphstart

To be able to do this within one bash script, I basically had to launch the server in the background. However, I could not use

comsol server &
matlab -nodesktop -nosplash -r myfile

as the server process would stop before matlab could connect to it whenever it was launched as a background process. By using instead

comsol server </dev/null > /dev/null &
matlab -nodesktop -nosplash -r myfile

instead of simply "comsol server &" then the server process is not stopped and you can run matlab, connect to comsol server, and run your .m script, without any user-intervention nor need for X support. Also, the comsol server exits when running ModelUtil.disconnect in Matlab, so I don't leave any process on the compute node..

Hoping this might be useful for someone ;)
By the way, if anyone has a better (cleaner?) way of achieving the same thing, I'd be happy to hear it!

Charles