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comsol multiphysics

July 31, 2014, 7:12 am
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Dear Ivar

My name is Konstantinos Karalis and I am a PhD student at the National Technical University of Athens.

I am trying to solve the operation of an electric arc furnace combining the AC/DC, Heat Transfer and Fluid Flow physics.

I am solving the AC/DC coupled with the heat transfer module in steady state analysis providing me the profile of the melt, the temperature distribution and electrical potential field. After that I want to calculate the buoyancy driven velocities using the phase field or the level set method. Unfortunately, I haven't achieve to calculate these velocities in steady state mode so I am using the steady state solution of the heat transfer model and I am performing a transient analysis. Unfortunately the velocities that I am obtaining have a big variance with the time (sove there isn't a "steady state" solution) which is very strange because the temperature distribution doesn't change.

For this reason I think that in my procedure a have some mistakes. I would be grateful if you could help me.

Thank you in advance.

Yours sincerely
Konstantinos Karalis
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How to make only selected domain (or boundary or edge) visible?

August 7, 2014, 7:47 pm
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Hello.

I'm wondering how to make one that I selected only visible while other geometric components are no longer to see.

This feature is necessary to accelerate specifying mesh quality for each object.

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Question about periodic boundary condition

August 7, 2014, 7:51 pm
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Hello.

I'm wondering what periodic boundary condition means.

I mean, I have a geometry which has clear symmetric with respect to xy plane.

I guess I really need to simulate just one of the half of the whole if I can apply symmetric condition to xy plane.

Ansys has that feature and in COMSOL, 'periodic boundary condition' has the same role to this.

Am I right?

If not, How do I apply that kind of condition to the symmetric plane?
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Hi

August 7, 2014, 8:11 pm
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I want to model a sphere in comsol, but i will give center co-ordinates and radius in matlab, is this possible
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Stiffness error

August 7, 2014, 9:32 pm
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Hi Ivar,

I am having a problem (written below) to solve my model. could you please suggest me what I should do? So far, I have defined all parameters but still having the same prob. My model is attached herewith..

Undefined value found.
- Detail: Undefined value found in the stiffness matrix.
There are 1813 equations giving NaN/Inf in the matrix rows for the variable comp1.C_c.
at coordinates: (-1), (-0.9975), (-0.995), (-0.9925), (-0.99), ...
and similarly for the degrees of freedom, NaN/Inf in the matrix columns.

Thanks in advance..

Noor
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Password cannot be entered into MATLAB LiveLink

August 8, 2014, 4:56 am
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Hi,

Whenever I try to start a MATLAB LiveLink (be it over the "COMSOL 4.4 with MATLAB" icon or manually) the command window lets me enter a username, but as soon as I want to enter a password, no entries are accepted. I can write whatever I want without it being shown in the command window. It thus becomes impossible to start a LiveLink application.

I am using COMSOL 4.4 and MATLAB 2014a. The MATLAB root is configured in COMSOL.

I would highly appreciate your help.

Thanks, Moritz
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Quick Question: Change Font Color in Graphics Window or Image Snapshot?

August 8, 2014, 7:03 am
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Is it possible to change the font color in the graphics window or for an image snapshot of the graphics window?

Many of my results plots end up with dark blue encompassing the background because dark blue represents zero on the colorbar. This makes the black text of the title and colorbar labels impossible to read. I could use a colorbar with a light color at the bottom, but I'd much rather just change all the text to white.

Or maybe there's an option to have the title and colorbar appear outside the plot on the printed image instead of within the plot?
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Patch antenna Return loss calcultion

August 8, 2014, 9:23 am
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How can i plot return loss curve in COMSOL?
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Simulate deposition onto a continuously moving substrate

August 8, 2014, 2:29 pm
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I have successfully modeled a sputtering deposition process onto a static substrate and now I would like to simulate a moving web substrate. The substrate is constantly moving and the data that I want to get off of it is the cross web uniformity (film thickness) after going past the magnetrons. Does anyone know what I can use with the molecular flow module to simulate a continuously moving wall?
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Simulate deposition onto a continuously moving substrate

August 8, 2014, 2:29 pm
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I have successfully modeled a sputtering deposition process onto a static substrate and now I would like to simulate a moving web substrate. The substrate is constantly moving and the data that I want to get off of it is the cross web uniformity (film thickness) after going past the magnetrons. Does anyone know what I can use with the molecular flow module to simulate a continuously moving wall?
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infinite integral to calculate trapping potential

August 9, 2014, 4:55 am
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hi, I am calculating trapping potential by optical trapping integral. In my model, the focused light is incident into sharp gold substrate, thus the huge enhanced electric field causes the optical trapping something. I already get the optical trapping force, however, I cannot solve the trapping potential by the optical trapping force.

In detail,

As I searched in searching engine like google, the optical trapping potential is calculated by the integral equation as attached below, however, I cannot apply the equation in COMSOL. What can I do? Somebody helps me, please.



as I mentioned before, I already have the force (Fx, Fy, Fz, respectively)

Thanks,
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Reflection Calculation in Scatterer on Substrate Example

August 9, 2014, 4:40 pm
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Hi all,

I am doing a simulation similar to the scatterer on substrate example. My substrate I Si and my scatterer is Ga in frequency range of between 480 THz and 880 THz.
I would like to calculate reflection.
When I calculate reflection with port (abs(emw.S11)^2), it gives me a constant number (~0.3) which makes sense since the first study is without substrate.
Therefore, what I do: I integrate emw2.Poavz over a surface in front of the structure to get total power (P_m), including reflected and incident. Since the reflected power in in +z direction (P_ref) and incident power is in -z direction (-P), therefore according to -P+P_ref=P_m, reflected power should be obtain as P_ref = P+P_m.
But I am getting a reflection which is not sensible for me, negative values or bigger than one.
My first question:
Is the method that I am using to calculate reflected power right?
Second:
The surface which I am integrating on it does not include PML domain, actually I just activated physical domain for solution from Data Sets. Should I include whole space including PML domain in my calculation?

I appreciate if someone helps me to solve this problem.

Thanks,
Mohammad
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Acoustics of a Plate in a Spherical Space

August 10, 2014, 9:05 am
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I want to simulate the acoustics of a rectangular plate vibrating at a given frequency in a spherical air space. I need sound pressure level in the air domain. I want the PML (perfectly matched layer) to be present at the boundary of the sphere.

The closest model available in model library is that of : Vibrating Micromirror
This model takes thermo-acoustics into account. I don't know what thermo-acoustics is and I don't want thermal simulation. I just want the acoustics structure interaction. Can somebody help?

Does someone has a model related to that?
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Failed to find a solution. There are 1 void equations

August 10, 2014, 5:38 pm
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Hello,

I'm running a flow in a pipe and I'm using the Conjugate heat transfer physics. My model converges and gives me results when the fluid in the pipe is water. As soon as I change the fluid to Carbon Dioxide, I get the following error:

Failed to find a solution.
Singular matrix.

There are 1 void equations (empty rows in matrix) for the variable comp1.nitf.Pmfinl1.
at coordinates: (0,0,0), ...
There are 28 void equations (empty rows in matrix) for the variable comp1.p.
at coordinates: (0,-1.82291,0.0448905), (0,-1.8415,-6.245e-017), (0,-1.778,0.0635), (0,-1.82291,-0.0448896), (0,-1.73308,0.0448825), ...
There was an error message from the linear solver.
The relative residual (11) is greater than the relative tolerance.
Returned solution is not converged.
- Feature: Stationary Solver 1 (sol2/s1)


Can anyone tell me why when changing fluids my model wouldn't converge even though everything else is still the same? And what is the variable comp1.nitf.Pmfinl1?

Thank you
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Heat transfer analysis in a power cable

July 30, 2014, 12:23 am
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Hi all,

I am analyzing heat transfer in a power cable as the result of current flowing through conductor of the cable. Which physics, interface should I use? In Electromagnetic heating Joule heating, Induction heating or some other ones? Also I would like to know will there be any difference if I assign current using Single Turn Coil or External Current Density? Which one do I have to use?

Regards,
Akim
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Traction does not converge

August 6, 2014, 1:40 am
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Hallo everyone,

I'm trying to model thermal stress in a glas plate caused by a solder drop with a initial temperature. The problem is that the traction does not converge with finer mesh, it gets bigger and bigger after refining the mesh.
I'm doing a time dependant, 2D axissymmetric study.

I would appreciate your help.
Thanks

Max
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heating a block of material by a moving laser

August 11, 2014, 2:39 am
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Hello everyone,

I'm a beginner at COMSOL, so probably my question is quite stupid to the frequent users of COMSOL.

I want to simulate a laser hardening process. At this time only the temperature field (not yet the phase thansformations etc.). Therefore I want to simulate a block of material (160 mm long, 40 mm wide, 8 mm high), and a laser power of 450W, with a spotsize of 2.7 mm, moving at a speed of 100 mm/min.
The laser is comming out of a fiber thus with a tophat profile (not gaussian).

I started from the laser heating tutorial (silicon wafer).

I tried to make instead of the gaussian profile as in the tutorial, a top hat distribution. I created a rectangular function, with limits -r_spot/2 and +r_spot/2. The analytic function used for the power distribution is than: p_laser*rect1(x)*rect1(y)
First problem I have: this is not a top hat profile!
www.holoor.co.il/images/image1.jpg
Left: the gaussian profile, right upper image: what I have, right lower image: what I want...
So the analytic function should be different, using a circular formula. Any idea how to do this?

For the heat transfer in solids (ht), I have added the translational motion, with v_feed in x direction.

Attached you can find the model.
I have 2 problems: to small temperature differences, and no moving laser source...
Can anyone help me out please?

Best regards,

Jan

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line graph

August 11, 2014, 4:27 am
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Hi
I am trying to plot the potential over a domain edge using the line graph option which works fine using the COMSOL interface. However, when using the MATLAB link i get the error "Selected edges are not connected" although I am using the same edge numbers.
does someone have an idea of why this could happen
Thanks
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Coupled Corrosion-Structural Analysis

August 11, 2014, 6:01 am
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Dear COMSOL users,

I'm trying to model electrochemistry coupled with linear structural analysis in Comsol 4.4.

I'm using two physics: Corrosion Deformed Geometry module and Structural Mechanics (Solid Mechanics). I'm trying to solve a transient problem. The corrosion module will provide me with the deformed boundary at the solid-electrolyte. I need to get information of the deformed boundary (real time) and use as an input into the solid mechanics module to find the stress distribution in the solid.

I appreciate your comments on how to couple these two physics meaning that deformed boundary found from solving corrosion has to be used as an input into solid mechanics module. This might be trivial to model with COMSOL, however, since I am a new user of COMSOL any comments and guideline is greatly appreciates.

Thanks a lot,
Mehdi
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Magnetodynamics - Step Response

August 11, 2014, 6:24 am
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Hi, I have successfully modeled a solenoid using magnetostatics, and have achieved results (force on the armature) that are accurate when compared to actual test data. I would now like to take that one step further, and determine the transient response to a current step - the end result that I would like would be a force/time plot and a current/time plot.

However, I am stuck in changing the successful statics model into a dynamics model. I have added a new study with step 1 being "coil current calculation" and step 2 being "time dependent". I have added a step response function named "current_step" to the global definitions, which is a step from 0A current to the final 0.1A current.

I set the coil excitation for my Multi-Turn Coil physics to "current_step(t)[A}" but I get the warning "unexpected unit of input".

Also, the current is not simply a step input as I have defined in my "current_step" function - it is affected by the magnetization of the iron. How do I link these two together? Is it done automatically, or is there some link that I must define? If I provide a step input in voltage to the Multi-Turn Coil physics rather than a step input in current, will that cause the current to then be linked to the iron magnetization automatically?
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