Latest Discussions - COMSOL Forums

where can I find the user guide for "Heat transfer module" and "joule heating module"?

Tue, 07 Feb 2012 23:15:53 +0000

Hi guys, just wondering where can I get the user guide of "Heat transfer module" and "joule heating module"? Electronic files will be better.

I do have it for v 3.5, but as the software upgraded to 4.2, I would like to see the explanations corresponding to conditions and equations.

Thanks for letting me know.

Boundary condition of natural convection (heat transfer)

Tue, 07 Feb 2012 23:07:25 +0000

Dear all,

I am having a general question about the boundary condition in natural convection. I am starting with a really simple 2-D model, one rectangular box set as high temperature metal, and outside is another box set as air at room temperature. I would like to see the temperature change when metal is set to 100 C and air is 20 C.

However, I find many ways to set boudary conditions in this case, for example: convective cooling, heat flux, inflow heat flux, and boundary heat source. To me, all the govening equations mentioned above are the same, because they all need to input heat flux amount or heat convection coefficient. It also works if I do not set any boundary condition between the air and metal, I guess the default setting may be heat conduction.

I am not able to set the boundary as "convective cooling" or "heat flux" when I was setting the material as air in the outside box. If I delete the air box, I am able to obtain a reasonable temperature distribution profile by choosing "air" and "external natural convection" in "convective cooling" condition.

Could anybody give me a introduction what is the difference between all these conditions I listed above, and what is the most appropriate one I should choose for a natural convection boundary condition between metal and air? Also, is there any difference between setting the air as "heat transfer in solid" and "heat transfer in liquid" if velocity is not given?

Thanks in advance!!!

Export coefficient matrix of FEM

Tue, 07 Feb 2012 22:11:45 +0000

Hello Every Body,
I would like to obtain potential distribution in my geometry that I draw in COMSOL.
Moreover, the following of my work, I need the coefficient matrix which has been obtained in FEM. I would be thankful, if you let me know how can I get this matrix?

Terminal Current

Tue, 07 Feb 2012 20:27:49 +0000

Hi

Can anybody tell me What exactly "Terminal current" means? [the one which is in Derived values-->Global evaluation
for AC/DC module]

It gives me a number as a value but I can't relate this definition to my currents in the system!

Best
Bahar

Save a log file on each iteration step with parametric sweep.

Tue, 07 Feb 2012 19:35:10 +0000

Hi,

In COMSOL 3.5a I can run parametric sweep over parameter “A” and write a global variable (“B” for instance) into a log file during calculation. With each iteration step I have an updated log file with two columns A and B.

Now I am trying to move to COMSOL 4.2a and to do the same parametric sweep with variable export into one txt file on each iteration step. I tried the following procedure:
1) Add a boundary probe of integral type. This probe value I want to export in to the log file.
2) Add a parametric sweep node under the study 1 node.
3) Add a data node under Export node and set the file name.
4) Add a Export to file node under Study->Job configurations->Parametereic and select Data 1 from Run list.
5) Deselect Clear previous and Add parameters to filename checkboxes.
And I am getting the effort massage: “Error in sweep: could not overwrite existing file.”

Is there probably an easy way to save the log file with “A” and “B” columns on each iteration step? In version 3.5a there is a very simple solution for log file export, see picture 6 in the attachments.

Thank you,
Maxim

How to calculate/record peak value of T variable?

Tue, 07 Feb 2012 18:08:20 +0000

I have a Heat Transfer in Solids model. I would like to know the peak temperature (highest T during the model time) at each (x, y, z) location. Is it possible to add an equation, something like

Tpk = (T>Tpk) * (Tpk-T) + T

?

I tried a few items under Mathematics without any luck. What's the correct method to do it?

NaN on surface integration

Tue, 07 Feb 2012 17:45:48 +0000

Hi

I get a NaNon surface integration of a cut plane but if the integration is on a boundary on the same plane the results

are good.

Cut planes are easy to define after running the model,

Is there a way to avoid the NaN result?

thanks

David

How to integrate fluxes across a line

Tue, 07 Feb 2012 15:27:04 +0000

I know that it is very easy to integrate a quantity over a boundary. My question is: it is possible to integrate a quantity over a line between two points belonging to a boundary ? I dont need to integrate the quantity over the entire boundary, but only over a part of that boundary

request for help please

Tue, 07 Feb 2012 15:09:31 +0000

Could anyone please help me to know how can i apply a temperature dependent density in my comsol.

I am model laser welding and as u may know,the density will change regarding to temperature, therefore i wanted to know how should i specify the density change in comsol please?

my material is stainless steel 316L

thanks and regards

Modifying Physics Equation

Tue, 07 Feb 2012 14:35:14 +0000

Hello ,

Basically, I am doing a simulation for a squeeze film damping in perforated srtucture based on Veijola Numerical Model (VNM). This model is based on extended reynold's equation that is the same as Reynolds equation except that a lekage term is added to count for the pressure drop through perforations
Reynlod's equation is implemented in thin film damping shell in COMSOL 4.2, but how shuld Imodify it to include this lekage term.

Should I start form the begining looking for the required mathematical equation. OR can I modify the existing Reynold's equation in Thin Film Damping?

Thanks a lot
Waiting for your reply

Regards,
Mohamed

import a bmp image into COMSOL geometry

Tue, 07 Feb 2012 14:10:48 +0000

Hey,

as stated in this webpage: http://www.comsol.com/products/formats/ Comsol can both read and write few types of images. However, when I tried to import a bmp image as my structure for flow simulation, it was not possible, because the options given include only mphtxt, dxf, etc. Does any one know how I can get a bmp or jpeg image imported? Thanks!

Chunyan

Help with 'Undefined value found in the stiffness matrix' error!

Tue, 07 Feb 2012 13:14:28 +0000

Hi,

I am trying to build a model that first constructs a temperature field, and then uses that temperature in a second study that has a temperature dependent viscoelasticity. The end result I'm hoping for is a time and temperature dependent displacement. I have been using the library model 'viscoelastic_tube' as a guide.

However, when I try and run the second study I get the following error:

Undefined value found.
- Detail: Undefined value found in the stiffness matrix.
• There are 111 equations giving NaN/inf in the matrix rows for the variable mod1.solid.qPHIPHI1
at coordinates...
• There are 111 equations giving NaN/inf in the matrix rows for the variable mod1.solid.qRR1
at coordinates...
• There are 111 equations giving NaN/inf in the matrix rows for the variable mod1.solid.qRZ1
at coordinates...
and similarly for the degrees of freedom, Nan/Inf in the matrix columns.
- Feature: Time Dependent Solver 1(sol2/t1)
- Error: Undefined value found

Any help on this matter would be greatly appreciated.

Thanks in advance,

James.

infinitely growing field from a transient dipole

Tue, 07 Feb 2012 09:41:45 +0000

Hi,
so I am still working on exciting a gold nano chain with a dipole.
For now on the Basis of this paper (Maier 2003), just to get the hang of what I am actually doing.
(Maier 2003) http://authors.library.caltech.edu/2448/1/MAIprb03.pdf

For reference also previous discussion pages
http://www.comsol.com/community/forums/general/thread/25670/
http://www.comsol.com/community/forums/general/thread/16892/

#####

So after that brief overview to the actual problem at hand:
I have been making some progress in understanding COMSOL and what I want it to do, but it is still not working the way I would expect it to.

The Problem is that the Electromagnetic field that is coupled from the dipole into/onto the gold nano chain just grows continuously. ie. after every time step the field amplitude will have grown a few orders of magnitude. This is obviously not desirable and wrong.

What I have so far been able to tell is that this behaviour is somewhat dependant on the time stepping settings for the transient solver. (Thanks again to Ivar for pointing out that I should use manual settings in order to stop erratic behaviour)
The settings that are currently set in the attached model file cover a time range of: range(0,5.0e-17,1.0e-14) with a manual set interval of 5e-17
Regarding the Ex field for the different time steps the before mentioned behaviour of amplitudes that are spiralling out of control can be seen.
decreasing the time step size by a factor 10 to 50e-17 this behaviour is not directly apparent, it is however visible again when also increasing the regarded time frame.
this leads me to assume that the problem lies at least partially somewhere else as it occurs no matter how the range and or time step for the transient solver are specifically set.

I am however at a loss as to what it might be or how I could possibly narrow the search down.

So Any pointers would be very much appreciated!

What just seriously bugs me is that the wave coupling from the dipole to the nano chain works like a charm in the frequency domain but is screwing me when trying to view the transient behaviour, it is somewhat frustrating.

Help please SOFC model

Tue, 07 Feb 2012 07:41:04 +0000

I have been working on SOFC recently and i found this model. I am looking for help in how to vary more than 1 parameter in the software. As given in the model only V_pol can is being varied. I wish to vary hydrogen concentration and the V_pol values. Please guide me how to plot that result ..

Nano_antenna simulation

Tue, 07 Feb 2012 05:49:24 +0000

Hi everybody,

I am trying to simulate a rectenna for solar energy harvesting. I am using RF module using PMLs, but do not know how to simulate solar radiation in this model. I will appreciate if anyone could help me.

Thanks,
Atid

semi infinte

Tue, 07 Feb 2012 04:38:48 +0000

Dear Ivar

I have infinte cable (3 m) and i want to study a sector (0.165 m) to get the temperture distribution

how can i define the boundary at the infinte end?

i.e how can i tell comsol that this end of cable is too long and infinte

thank you very much

materials of a surface mesh element

Mon, 06 Feb 2012 17:05:20 +0000

Hi everyone ,
I’m looking for a possibility to distinguish the different materials that belong to a single surface-mash-element (for example: a triangle) in matlab? For better understanding - my problem in a second way. Starting from a model containing a single meshed surface. Each mesh-element is now between two materials. So how do I get knowledge about the two materials/groups/… the element is between?
Thanks for help!

Problem with the meshing of a structure

Thu, 02 Feb 2012 15:52:49 +0000

I am trying to mesh a structure. I have a block and objects inside that block. The blocks gets meshed insanly coarse, while the objects inside get meshed rather fine. The block has elements that are in the size of it's diameter, this just cannot be. Where do I make a mistake.

Phase animation in COMSOL 4.1

Wed, 30 Mar 2011 11:39:19 +0000

Is it possible to get a phase animated plot of a RF solution in COMSOL 4.1?

Thanks.

Modelling of ion transit in oscillating electric field

Tue, 05 Jan 2010 08:38:08 +0000

Hi,

I've recently spent quite a bit of time using SIMION to model the trajectories of ions as they pass through fine wire meshes, upon which electric potentials are applied (such that a small DC electric field is generated). In addition, I am very interested in plotting the trajectories the ions take when a high frequency oscillating voltage is superimposed on the DC potentials which are applied to the grids.

The SIMION modelling has generated some very interesting results, and I would like to validate them by performing a similar analysis using COMSOL.

I recently attended the Intensive COMSOL course, held at Hatfield University, UK. The course only briefly covered the Particle Tracing option in the Post Processing screen, however from the little amount that we covered I was left with the impression that COMSOL will only plot the trajectory that an ion would take under steady state field conditions (after a solution to the model has been generated), and would not be able to calculate the trajectory of an ion under an oscillating electric field.

I am curious to find out whether my understanding of the particle tracing option is correct, and I would be very interested to hear from anyone who has succesfully used COMSOL to plot ion trajectories in non steady state field conditions.

Regards,

Jon Atkinson