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Error: Singular matrix

January 7, 2010, 1:34 pm
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Hi All,

I have problem i wish you can help me with it; as when i try to module the Maxwell- Stefan equations at the anode and cathode of PEM fuel cell i got this error. please a dvice

Thank you
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Mphstart does not work even the comsolserver is running (Comsol 4.4)

April 4, 2014, 12:08 am
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I installed the latest ver. 4.4 and I found the command "mphstart" did not work when I wanted to connect my Matlab to the comsolserver. I am sure the comsolserver was already running prior to the command "mphstart" was excuted in my M-file. The error shows "Error using mphstart (line 152) A connection to Comsol could not be established .... Please check that a Comsol Server is started prior to calling mphstart ". I am also sure the folder 'mli' had already been added to the Matlab path.
Even though I ran "COMSOL 4.4 with MATLAB" and managed to establish the connection, when I type "mphstart" again in the Matlab command line, the same error occured.
This did not happen to 4.3a and 4.3b at all.
So anyone could tell me how to solve this problem?
(the version was already updated to 4.4 build 195)
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Implementing a two-temperature-model (electronic/lattice) for fast laser-excitation

July 10, 2014, 10:56 pm
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Hello,

I want to model a pulsed laser that hits a solid, excites electrons which "thermalize" then transferring their energy to the lattice (solid, atoms). I think most people do not use COMSOL for this purpose, but I want to, because I started with classical heat conduction and now want to setup my model in greater detail.

The two-temperature model is basically a model where you define two temperatures for electrons and atoms in a material respectively. This is necessary if you take into account that the electrons react much faster on an external excitation (femtosecond laser pulse [1E-15 s]) than the atoms.

The question is: how to realize this in COMSOL . In principal I would expect to be able to add and couple two heat transfer physics with two different dependent variables Te (electronic) and T (atoms) and custom material parameters (thermal conductivity, source terms). But how do I couple these?

Or would it be easier to go directly for custom PDEs and without predefined physics terminals?

Please help me here.

Best regards,
Henning Hollermann
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change the numerical values for the physical quantities

April 20, 2015, 2:35 am
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Hello COMSOL community :)

I am new to COMSOL multiphysics program , i am trying to build a simulation of a cantilever in the mm length scale. I am using Magnetic fields (mf) , Electric currents (ec) and Multiphysics modules.
I found this in the User's guide book
"It is important to be careful using physical constants if the unit system is not in SI units.
For example, the default values for the permittivity of vacuum and the permeability of
vacuum require that you provide all other quantities in SI units and that you use meter
(m) for the geometry length. If you draw the geometry using another length scale, you
need to change the numerical values for the physical quantities accordingly. "

Can anyone tell me how to change the numerical values for the physical quantities according to mm length scale ?

Thanks in advance,
have a nice day,
Amal
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Time dependent laminar flow past circular cylinder

April 20, 2015, 3:10 am
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Hi,

I am trying to solve time-dependent laminar flow past a long circular cylinder at Re=100 in unconfined condition. I am using rectangle domain.
The boundary conditions employed for inlet is the inlet bc with uniform velocity and at the outlet I imposed the pressure, no viscous stress is used.
I have a question about remaining two boundaries...
What should we can use for those two boundaries?
I tried with slip boundary but I didn't get vortex shedding even at Re=100.

Can anybody guide me for this problem??
I will be really thankful for it.
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effective permittivity calculation

April 20, 2015, 3:44 am
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dear all,

i am trying to calculate the relative permittivity (frequency dependand in COMSOL 4.4) of a double shell cell, which consists of 4 different layers circulary arranged (2d). The cell is obviously between a pair of electrodes.

Now, my question is, how to i manage to calculate the effective permittivity of all the cell for each frequency.

Thanks in advice
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calculating the resistance of a wire

April 20, 2015, 3:45 am
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Hi
Can anyone help me with calculating the resistance of a wire using AC/DC Module>Electrostatics(es)?
it's totally simple using Electrical Currents(ec) physics, how about (es)?

Thanks
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Coupling Joule heating in fluid and conjugate heat transfer

April 20, 2015, 4:04 am
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Hi all,

I am having trouble using Comsol 4.4 physics setting. I have this model where a micro-channel is built inside a solid PDMS block. The micro-channel is filled with electrolyte solution, an electrical current is applied through the channel and Joule heat is created. The heat is then dissipated into PDMS block and convective heat transfer is applied at PDMS exterior surface.

I have tried using NITF module and joule heating, but the option of nitf is not showing in the joule heating module. Hence, I switched to my current model.

In current model, I have "Heat transfer in Fluids (ht)" coupled with the Joule heating module. The HT module was chosen for all domain (both micro-channel and PDMS block). Then inside the HT module, I have created a domain condition of "Heat transfer in solid" for the PDMS block domain and convective heat flux for the exterior wall. The result temperature is 20 degrees higher than I expected.

My question is, is my current setting correct for Joule heat in fluid and conjugate heat transfer into the solid?
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How can I plot 1D-line along a self defined line?

April 20, 2015, 4:40 am
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Hallo everybody,
I have modeled a concentration distribution in a cubic 3D-model and want to draw the trend along a self defined line. I tried to create a 1D-line under 1D-plot group and couldn't choose the beginning and end of the line (the line wasn't visible). A better option would be to define the coordinates of the 1D-line. Is this an option?
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How to join four solutions?

April 20, 2015, 4:57 am
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I know how to join two solutions, but I need to join four solutions. I think, firstly to join 1 and 2 solutions and secondly to join two other solutions (3,4). At the next step I need to join all of them. How to do that?
If I set "join 1" as "data 1" and "join 2" as "data 2", then Comsol sees only one solution in each of them.
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rounding heat flux

April 20, 2015, 7:11 am
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Hello,

I would like to make a heat flux turn around a circle, and I don't know how. Could you explain me please?
More precisely, I would like to make a Gaussian pulse turn around my circle, but it's just a bonus for me.

Thank you in advance :)

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bright image

April 20, 2015, 9:38 am
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hi,

maybe my problem is not too complicated, but when i export an image of my results, this image is brighter than other image i made. how can i modify the light?

thank
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Changing a curve to surface

April 20, 2015, 12:48 pm
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Hi all,

I have a design which I created in AutoCAD and imported to comsol.The design is a combination of curves which I intend converting to a 2D surface.Can someone please help

I have attached a sample of my comsol file.


Thanks.
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2D Axisymmetric model compilation error

April 20, 2015, 3:24 pm
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Hello all,

I am trying to simulate 2D Axisymmetric model of a contact between ball and a disc. My aim is get the sub surface stresses in the disc for static loading conditions. I have attached the model that I created. I am getting error message in compilation regarding cyclic dependence of variables. I have also attached snap shot for the same.
Can someone please guide me to debug this issue? Also, I would like to know the procedure that I can follow to debug such issues in the future.
Thank you in advance,

Sincerely,
Nikhil
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Isobaric compressibility

April 20, 2015, 4:57 pm
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Hi all,
I am trying to couple free and porous medium flow to heat transfer in porous medium to model ground water flow and heat diffusion/convection in the ground using subsurface flow module
I need to account for isothermal compressibility (T=cte) as well as isobaric compressibility (p=cte) .
the isothermal one (beta) is shown in the variables in equation view and in the equation it self (free and porous medium flow, fp).
the isobaric one (alpha) is shown in the variables in the equation view but not in the general heat transfer equation (heat transfer in porous medium, ht).
I was wondering if comsol is accounting for this parameter?

your help is much appreciated

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Time dependent Hinge fluid interaction

April 20, 2015, 8:06 pm
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I am modeling an artificial heart valve that utilizes hinges as seen in the file included. In the human body the valve hinges are passive which means they open and close depending on varying blood flow. In my model, I can get the hinges to move back and forth if I apply a pressure to one side of the hinge, however, as soon as I add a steady fluid flow I get the following error. "Failed to find consistent initial values.
Segregated group 2
Attempt to evaluate real square root of negative number."


Eventually I would like to add a time -dependent fluid flow that mimics blood flow through the heart but for now I am trying to get the simplest case with steady flow to provide an answer.

I would really appreciate any suggestions on how to precede with this kind of set up.

Thanks in advance!

Charlott
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Undefined value found in the equation residual vector.

May 13, 2011, 9:05 am
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I am trying to model a pem fuel cell. Although I have entered all parameters and values, i have some errors as follows;

Undefined value found.
- Detail: Undefined value found in the equation residual vector.
There are 4 degrees of freedom giving NaN/Inf in the vector for the variable mod1.wH2Oc
at coordinates: (0.0022813,0), (0.0022432,0), (0.0022813,7e-005), (0.0022432,7e-005), ...
There are 4 degrees of freedom giving NaN/Inf in the vector for the variable mod1.wO2
at coordinates: (0.0022813,0), (0.0022432,0), (0.0022813,7e-005), (0.0022432,7e-005), ...

Can you help me please?
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Java Runtime Environment error

July 28, 2011, 2:37 am
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Getting following error,

A fatal error has been detected by the Java Runtime Environment:
#
# SIGSEGV (0xb) at pc=0x0000003da3efbc6c, pid=6909, tid=46912497239488
#
# JRE version: 6.0_20-b02
# Java VM: Java HotSpot(TM) 64-Bit Server VM (16.3-b01 mixed mode linux-amd64 )
# Problematic frame:
# C [libgtk-x11-2.0.so.0+0xfbc6c] gtk_icon_set_render_icon+0x58c

Does anyone know how to resolve it...

Regards
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import a bmp image into COMSOL geometry

February 7, 2012, 6:10 am
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Hey,

as stated in this webpage: 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
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How to apply moment to a surface?

March 23, 2015, 10:29 pm
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Hi all,

I am trying to model a brake disc in terms of thermal stress during a braking procedure.
I have the thermal part of the simulation down, but I am having trouble with the Structural Mechanics part.
I want to apply a moment on the swept area of the brake pad. The moment is caused by a resulting friction force during braking. I have tried using the Rigid Connector, but as anticipated I get a high stress concentration around the edges. How do i apply a moment to a surface and avoid the stress concentrations around the swept area edges? I have attached a sample model of my problem and a snapshot of the calculated von Mises stress with my current setup.

Thanks in advance!

/Morten R. Drost
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