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Microwave oven waveguide configuration

January 16, 2013, 9:05 pm
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Hi everybody,

I am trying to simulate a microwave oven using COMSOL, but I'm still a bit confused about configuring the waveguide. What is the difference between Transverse Electric (TE) and Transverse Magnetic (TM) mode? I know that when using Transverse Electric, the magnetic field is perpendicular to the direction of propagation, and the opposite happens when using the Transverse Magnetic mode. But what is practically happening inside the oven when using TE or TM mode? I mean how does TE or TM mode affecting the heated product?
Thank you so much in advance
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Error in compile Equation: Frequency Domain

January 18, 2013, 4:38 pm
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Hello everybody,

I am simulating a microwave devise in optical frequencies but I see this error:
Feature: Compile Equations: Frequency Domain (sol1/st1)
Error: error in multiphysics compilation
I would be truly grateful if you tell me what I need to do.

Thanks in advance,
Zahra
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INCRE

January 18, 2013, 7:28 pm
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How to use interpolation function in parameters?

January 19, 2013, 5:09 am
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Dear users,

I have defined a piecewise function from a file with function name 'functionName' in Global Variables.

I would like to define a parameter that uses this function in Global Definitions -> Parameters. For example:

newFunction = functionName(parameter1)*parameter2

where parameter1 and parameter2 are also defined in Global Definitions -> Parameters. Moreover parameter2 is used in a parametric sweep study. At the end of the study I would like to plot newFunction vs parameter2.

The problem is with the definition of 'newFunction'. Because of 'functionName(parameter1)' it is highlighted in red.

DO YOU KNOW HOW TO USE A PIECEWISE FUNCTION defined in Parameters for the definition of another parameter?

Thanks
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Compressible laminar flow & Transport of diluited species: why there is no outflow of moles from the domain?

January 19, 2013, 9:30 am
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Hi everyone,

I have to model the transport of a chemical species dissolved in a gas mixture during an expansion of the gas.

I simulated a time-dependent gas expansion due to a reduction of pressure in a rectangular 2D domain with the Laminar Flow module.
I set:
- compressible flow (Ma<0.3),
-one boundary as the outlet ("Pressure, no viscous stress", with the pressure equal to a smooth ramp going from 800 torr to 760 torr in 3 sec);
- the other 3 boundaries as walls.

To model the transport of the chemical species I used the "Transport of diluited species module", with the "Outflow" boundary condition on the same outlet boundary of the laminar flow, and the others as No flux). The velocity field (u,v) is taken from the laminar flow.

The expansion of the gas is well simulated: there is an outward flow during the decreasing of the pressure.
Instead, there is no an outflow of the chemical species: the total content of moles in the domain is the same all over the time of the simulation. This is clearly unphysical.

Why is that?
Someone can help me?

Thank you so much.

J.
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Convergence issue with nano pore electrodeposition model

April 18, 2012, 5:17 pm
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I am trying to model electrodeposition into a nanopores but am having troubles with convergence. My solution only converges to 1e3 fairly consistently even if I refine the mesh and then it starts to rise to 1e10 and then quits. I am new to comsol and electrodeposition and am doing this as a class project. I did copy a model from the library of models that was copper deposition in a trech, used all its values and then scaled it down and it wouldnt solve. I then made it axisymetric and used the same values and it still wont solve. Now I am running out of ideas. I have refined the mesh, changed the time step smaller, decreased some initial values(i0 and V) and no luck yet. I tried to attach my model but it seems i cant. If there is a way and someone knows how i would be glad to attach it. Instead I have attached a copy of my model and this is the link to the copper deposition model www.comsol.com/showroom/documentation/model/2112/
Thanks
Matt
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CFD - Surface roughness

December 11, 2012, 3:15 am
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Hey guys

I really need your help on this one!

I was wondering if any of you could tell me about the default settings of surface roughness's in COMSOL?
All I've found about it in the documentation is Materials 3D Model Default Appearance Settings but I can't find anything about the use of surface roughness in the calculation of the pressure loss.
But the surface roughness does have an impact on the pressure loss however, I don't know where to find it nor do I know how to change it? Does COMSOL even use the material surface roughness or is it like Blasius --> surface roughness = 0?

Best Regards

Mikael

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When I have to use 2d or 3d modeling?

January 17, 2013, 1:06 am
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Hi Everybody!

I´m Wagner, from Brazil and I have a question, a simple question I think!
How I decide if my modeling will be in 2d or in 3d?
I have Heat Transfer and AC/DC model and I work calculating and projecting Electrical Equipament, like Transformers, Reactor, Harmonic Filters and more...
Someone here have this knowledge?

Thank you for your time.

Best Regards,

Wagner.
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Variable change with time

January 17, 2013, 9:47 pm
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I have a question about variable change with time.
I try to make a mass transfer model. The inflow concentration change with time.

If t <= 1000s then C=1mol/m^3
else C=0

I upload the data and make a Interpolation Function. Function name: int1

Then I set the Inlet Concentration as int1. It shows int1 is not variable.

How can I make this kind of variable?

Thanks in advance

Dylan
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Structural Mechanics Equation System

January 19, 2013, 4:46 pm
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I am trying to understand how my structural mechanics model is computing its solution. The model solves and gives me a reasonable solution. However, I don't understand how it is arriving at its answer. I am looking at the Subdomain Settings - Equation System panel where it shows the PDE which it is solving. I am viewing it in coefficient form, and all of the coefficients are set to zero. How am I arriving at a solution when the PDE which is being solved is zero?

Ryan
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Electromagnetic Induction Tomography simple model

January 20, 2013, 2:33 am
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Hi,

I am trying to make a very simple 2D model where I have 2 coils in which in between is a medium (air). One of these coils will be excited and have a magnetic field in the direction of the second coil. I would like to measure the voltage induced in this second coil.

I am having trouble with creating a 2D coil sensor. I'm not sure how to create the coil.

Thanks,
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Heat Transfer in Fins- Help needed

January 20, 2013, 5:26 am
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I am trying to simulate a heat sink, very similar to the one shown in the tutorials... In spite of building a coarse mesh, the solution does'nt converge even after 2 hours of solving. I have an i5 processor and a 4 gb ram. I would like to know which solver and which configuration are best to solve my steady state heat transfer problem.

Thanking you,
N.Sathyanarayanan
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How can I define nonlinear electric conductivity ?

January 20, 2013, 7:08 am
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Hi,

I'm currently working on electrical simulation using AC/DC module. How can I define nonlinear electric conductivity of zinc oxide (ZnO) in subdomain settings?
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Problems with multicore time calculation

January 20, 2013, 7:39 am
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Hello everyone,

I am working with the attached file and there is a very unusual behavior with the second study. It is a frequency response study with a parametric sweep: I need to know the frequency response of the beam with 5000 different values of the parameters. The program is very fast for the first 10 per cent of the parameter values then it slows down and  becomes very slow as long as I must stop it (around 10 %) and restart it where the final points of the previous calculation become the first of the new one.
It does not depends on the different parametric values because of the difficult for different values is always the same, indeed when I restart the program it is again fast.
I have given a look to the CPU usage and what I observed is that as the program proceeds the  usage  percentage of the various cores  decreases, furthermore it does not use the virtual CPU.
The memory store indicated down right is 4|8 (almost).
I have this system:

MAC OS X 10.8.2
Processor: 2 x 2.4 GHz 6-Core Intel Xeon
Memory: 12 GB 1333 MHz DDR

Thank you for your help.



Kind regards


Fabio
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for NdFeB magnet, which constitutive relation is closer to reality

July 29, 2010, 1:11 pm
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I'm modeling two NdFeB magnets placed very close to each other in a repulsive manner. I need to compute the repelling force between them.

There are two options for the constitutive relation. One is

B = mu0*(H+M)

where I specify the magnetization M vector based on the demagnetization curve of the magnet.

The other is

B = mu0*mur*H+Br

where Br is the remanent flux density of the magnet and mur can be calculated from the demagnetization curve.

The problem is that two methods seem to give different force results, with that of the first one bigger than the second. Which constitutive relation is closer to reality?

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Sector symmetry on a 1/5 3D electro motor

January 2, 2013, 5:57 am
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Hi All,

i have a 3D model that shows only 1/5 of whole motor. It has 3 phase and 5 pool pairs. i'm using rotary machinery modul 3D.

if i disabled all continuity BC on the outer slice surface, it converge. but it cant be right.

if continuity BC are used, it wont be converged.

there is also sector symmetry. on the documentation there only some sentences about it. if i'm not mistaken, i need to define "sector" = 5 because i have only 1/5 of it.
has any body deal with this BC?

thx and happy new year!
akmal

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Variable exchange between Matlab and Comsol

January 18, 2013, 7:35 am
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Hello everyone,

I am running Comsol using the LiveLink with Matlab and am trying to do the following:

I have a value, dt, which is 0 everywhere in the beginning.
(I can either use dt=0, make an interpolation file x,y,dt(x,y), maybe make a Matlab fct.,...)
I run Comsol the first time.

Now, I use results ct calculated from the Matlab run to compute new dt values:

ct = mpheval(model, ct) // this also gives me access to the coordinates of the mesh points...
dt_new = f(ct.d1) // any function really

But how do I get Comsol to take dt_new at each meash point for the next run?!?
I've tried:

a) Using a simple variable dt.
Reassigning dt values by setIndex and using same indices as mpheval gives me.
--> Doesn't work.
b) Using an interpolation function reading dt.txt which contains: x y dt, initially: 0:1:x_max, 0:1:y_max, 0
Rewrite dt.txt to read: ct.p(1,:), ct.p(2,:), f(ct.d1)=dt_new (obtained by mpheval & Matlab calculation)
Now I have tried to: importData for the interpolation again, remove the interpolation & create a new one etc.
None of this works. It either gives weird errors (remove & create, importData) or doesn't do anything
(use solely setIndex)

What am I doing wrong in b)?
Or do I want to use a Matlab function under global definitions in Comsol?
(But how do I make that access values from a previous Matlab run?!?)

The problem to me seems to be simple:

Assign value dt=0 to mesh points. Run Comsol.
Get value ct at each mesh point. Calculate dt based on ct. Assign value dt to each mesh point. Run Comsol again.

It is straightforward to access the results at each mesh point.
Why is it so hard to assign values to mesh points for the next run?

Thanks in advance for any help.
Greets,
Thorsten
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Combination of Fluid Flow and Heat Transfer

January 20, 2013, 5:12 pm
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Hello everyone, I am a new member of this forum and also a fresh user of COMSOL. I hope I will be able to learn from and discuss problems with all of you. My first enquiry to the forum follows:

My scenario:
An embedded pipe with hot fluid flowing inside

Aim:
To find out how the heat is transferred from the pipe to the surrounding over time. hence to determine the positional temperatures in the surrounding, such as 1m or 2m away from the pipe.

I know how to model it easily only with a heated pipe being embedded, but I do not know how to model it with the hot fluid flowing inside the pipe.

I am looking forward to hearing your advice on how to model this scenario correctly.

Thanking you in advance.

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How to use user defined functions as physics's input? Thanks!

January 20, 2013, 9:42 pm
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Hello, every one!
I am learnging to use COMSOL4.2 and want to add AC signal as my device's input.

Just as Eric told me to write an equation as the input.

(www.comsol.com/community/forums/general/thread/34060/#p94106)

I want to try another way.

Because there is a way to define a function( Model bulider--> Global Definition-->Function),

I can define a funciton (name wv1) as wv1= 5 *sin( 50*pi* t ).


My question is, how can I use this function as an AC input to a capacitor's input?

Thanks!

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Importing a file from AutoCAD to COMSOL

January 20, 2013, 11:35 pm
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I have created a 3D building model on AutoCAD and wish to import it to COMSOL for CFD analysis. Can I know the process for importing?
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