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how comsol calculate pressure head as boundary condition in Richards' equation?

April 3, 2014, 5:54 am
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Hi

2D model was defined, geometry is simple rectangle which is left angle is divided to three parts in the middle of the left angle, b.c defined as pressure head=0.8 (attached the geometry)

and the other angles were defined as pressure head= 0.0
Solved model

for the middle part that defined pressure head as constant value, cross section was plotted, but why the pressure head after solving the problem is not constant:( changing from 0.4-0.8) for the ends of the special part of angle?(attached cross section)

eager to hear your comments.
Sepideh
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Polygon geometry and it's boundaries

April 3, 2014, 6:58 am
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Hello community,

I have a question about the Polygon geometry and hope some colleagues here know the answer.

Basically the question is:
I use a .txt file (contain several coordinate pairs (x,y)) written from Matlab to define my geometry. This geometry shape is irregular and contains multiple boundaries.
(1) What is COMSOL's logic to assign boundary orders, eg. which is boundary 1, 2,...

Because when I use 2 irregular shapes to define 2 domains, the boundary number seems mixed between these two domains, even in the same domain, the boundary number is not ordered in logic ways such as clockwise or anti-clockwise.

Does anyone know about the magic inside?
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Geometry finalization - Assembly model -> thermal stress analysis

April 3, 2014, 7:44 am
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Hi,

I am working on a thermal stress analysis of an assembly in 4.3b and am a bit confused. I thought all the structural mechanics analyses where parts are in overlap should have it's geometry finalization defined with Form assembly and later chosen Pairs type (I mostly use Identity pairs) and a contact boundary condition such as continuity for eigefrequency analyses (I noticed it's pretty much the same if I just use Form union though...) or contact if there is an interaction of at least two elements and if they should not penetrate into each other.

However I thought when doing thermal stress analyses I should also start working with Form assembly but I noticed that all the models in the tutorial have a Form union option. Is this reasonable from the mechanical interaction point of view?

I have checked almost evey page of the documentation, posts on this forum and tutorials but am still uncertain.

Please advise me, thank you.

--
Kind regards,

Matej
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How could i do to see the data sheet of my model?

April 3, 2014, 9:58 am
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Hi, I´m working in a 2D model of ion diffusion and I need to see a data sheet of the concentration profile.
So, what should I do to see it?
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Failed to find consistent initial values

April 3, 2014, 1:03 pm
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Hi all,

I am doing simulation of tumor tissue ablation using Radiofrequency ablation technique.
I build a 3D thermal-electrical model in COMSOL and can get the respected results.
To reduce the calculating time, I try to use a 2D thermal-electrical model to mimic the ablation process.
The boundary and initial conditions of 2D model are all set as I did in 3D model.
But there is a error showing "Failed to find consistent initial values. Last time step is not converged."
I also tried different extent of mesh method and reset the relative tolerance.
But it still doesn't work.

Does anyone happen to encounter this problem?

Thanks.
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cone-jet mode in electrostatic field

August 30, 2012, 5:13 pm
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Hi,

Here is my problem.
I want to simulate a electrohydrodynamic (EHD) phenomenone , a nozzle with full water (or electrolyte) in a electrostatic field, the the water is polarized and deformed the Taylor cone,then comes the cone-jet mode. My models include the level set -laminar flow and electrostatic,but still cann't get the cone-jet result.Is there anybody also working on a similar model like mine?Did you get the cone-jet results?

Thank you.

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Laser beam in comsol

July 17, 2013, 7:48 am
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Hi,

I want to input a laser beam in comsol and see its effects after passing through a grating, mirror etc. Is this possible to do?

Thanks
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Matlab function

February 12, 2014, 4:46 am
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Hello,
I have a problem with importing matlab-functions in comsol (version 4.3b in Linux). After I have inserted the function name, variables and the range, I get the following error-message: "Matlab function is not found: ..." (see attached file). Maybe the path to the matlab-functions is wrong, can you please help me with this?
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tissue ablation model by comsol

March 30, 2014, 5:51 am
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Concerning the tumor ablation model, can someone tell how to get the volume of tissue heated within an isothermal surface. In the model an isothermal surface of 50˚C was done after 8minutes, however, I not only want to find the volume of tissue within this isothermal surface but also want to know the value of the volume with changing time, from t=0 to t=8minutes. How can I calculate the volume at each time instant?
Thanks plenty.
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Using MATLAB code as a COMSOL physics interface

April 1, 2014, 4:31 pm
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Hi all,

I was wondering if it was possible to use a MATLAB script as a COMSOL physics interface.

I have a working two-phase flow CFD model (phase field method). Coupling additional physics has been very difficult since I need to work around the diffuse interface. I have a MATLAB code that does exactly what I need for mass transfer. Is it possible to incorporate this code into the model as a COMSOL physics interface? Basically, the goal is that the imported code does what Transport of Diluted or Concentrated Species usually does.

I couldn't find any help in the MATLAB-COMSOL LiveLink User Guide for this specific type of situation. I'm just wondering if it's even possible.

I greatly appreciate any input.

-Alex
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averaging of data

April 1, 2014, 10:50 pm
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I am a new user of comsol 3.5a . I am getting data of heat transfer coefficient from a surface plot which is non-repeatable ,can you please tell me how to averaging of this data.
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Problems with Magnetic force

April 2, 2014, 4:48 am
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Hi! I am new to COMSOL and I really need some help please.

I want to study an electromagnetic actuation system to guide magnetic microparticles in blood vessels. For that I used the AC/DC module to build some coils to generate a gradient magnetic field and then I used the Fluid Flow module to model the blood. The final goal is to use the Particle Tracing for Fluid Flow module to determine the trajectory and velocity of the particles when subjected to the magnetic force, however when I include the Magnetophoretic Force (already included in the module) nothing happens! There is no change in particle velocity.

As it can be read in COMSOL: “The Magnetophoretic Force causes motion of permeable particles toward regions where the magnetic field is stronger. The magnetophoretic force is applicable for particles which are charge neutral and have a different relative permeability than the background fluid.”

But even when I insert a high value of particle relative permeability (400000) nothing happens. I was expecting a change in particle velocity. I attach some pictures of my problem.

Maybe it's something pretty obvious, but I really need some help here. Thank you!

Best regards,
Patrícia
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Define Mirror

April 3, 2014, 10:54 pm
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Dear All,

I want to simulate a reflection type of diffraction grating. How can I define a mirror surface of steel or other type of metal?

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Define LED light source

April 3, 2014, 10:55 pm
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Dear All,

I wanna to simulate an LED as a light source for diffraction grating. How can I define it?
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how to use the "Previous solution" as initial value for new analysis

April 3, 2014, 11:09 pm
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Any idea how to use the "Previous solution" as initial value for new analysis, for the sake of solution convergence??
Preferably, step-by-step procedure!

Thanks,
Hina
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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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a few question about using COMSOL

April 4, 2014, 1:36 am
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Hello, everyone,
I have a few questions to ask for your help,thanks in advance!
1. how to view the cross section of a 3D model? I wan to cut the model into two part and see the inside.
2. For the 1D plot, in the 'Expression evaluated for' , there are Harmonic perturbation, RMS for total solution. The plots are not same. Which one should I select to draw plot?
3. in far-field pressure , how to calculate the distance in COMSOL? I didn't understand it in help...
4. I set environment as the air domain and use PML. What's the differences between the cylinder domain and sphere domain?

I beg your help sincerely !
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Voltage to temperature

April 4, 2014, 2:22 am
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is it possible to apply temperature from voltage for device??
if it is possible, share the application or function.
thank you,!
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I want to get surface wave.

April 4, 2014, 3:09 am
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Hi there.
Thank you for reading my discussion.

I try to build suface wave. I make a rectangular at first and apply a open boundary condition at the top of rectangular , then I use 'Definition->Functions->wave form' on the left side for expressing periodic velocity.
what I want to get is surface wave on the top of rectangular.

for example, it is same phenomenon that you press water-tank on the left side, so you can see the sinusoidal wave on the water.

I think I need to use 'Moving Mesh'.
I would like to know what I should put on the laminar flow and moving mesh.
If you have any good advices about it , please comment here.

Many Thanks.
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Out of memory in mesh processing

April 4, 2014, 5:11 am
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Hello everybody,

I'm trying to simulate the heat transfer on a set of CdTe detectors, which are connected to chips that are heating. I have a big geometry (I have 8 detectors with the corresponding chips...) and the physics are not symmetric, since the chips do not heat with the same intensity in all directions. Therefore I have to construct all the geometry.

I made the mesh as small as I could in order to not to have out of memory problems but I do still have (I defined different mesh for all the different domains, boundaries and edges, and I made the mesh as small as I could one by one). My computer is running at 64 bits.

It is possible to do anything more in order to not to have out of memory problems?

Thank you in advance,

David
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