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Mesh element volume

July 1, 2009, 1:07 pm
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Dear all,

I have a material property having a different value in a domain and
it is function of individual volume of deformed mesh element and undeformed mesh
element.
Could you tell me how to get the volume of the mesh element?
In 2D, this may be the area of the each element. (Am I right?)

I appreciate your reply.

Thank you.

Yoon
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Simple heat exchanger model error

November 11, 2015, 3:49 am
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Hi everyone,

I'm working on a heat transfer problem and could use some help. It concerns a large horizontal pipe containing an elongated u-shaped pipe (the 'loop'). The pipe contains air and the loop contains water. The water inside the u-shaped pipe is flowing and is laminar. The air in the larger pipe is initially at rest. There is heat being produced inside the u-shape. So heat is being transported from the loop through the pipe by convection and out of the model (using the external natural convection option inside the heat flux node). I'm interested in the steady state temperature in both pipe and u-shaped pipe.

Initially I started working on a simpler model which only contained 2 cylinders (ie. I used a cylinder instead of the loop). This model worked perfectly, but when I switched the smaller cylinder for the loop I started getting errors.

1. The direct solver gave the error of a singular matrix
2. the iterative solver returned a error message saying it ran into an undefined value.

I was wondering if these errors can be caused by poor meshing, since my boundary conditions are exactly the same for the working model and the non working model? Any help on solving my problem would be greatly appreciated!
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PN optical modulator

June 1, 2016, 8:31 am
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Hello,

I am a student in TUD and I have started to work with COMSOL. My task is to model and simulate PN silicon optical modulator.
I am using Semiconductor module. I have couple of questions I would highly appreciate if you help me with that.

My structure consists of p+, p, n and n+ regions I am using metal contacts on p+ and n+ regions and applying voltage. I have also added "Trap assisted recombination" and "Auger recombination" physics. Do I need some more physics ?


1) I am a bit confused with the doping profiles in COMSOL. Currently I am using Analytic doping profile and using "user defined" distribution for all the parts in my structure. Is this correct approach ?

2) I need also to calculate the resistance and capacitance of my structure. Is it possible with comsol ? if yes how can I do that ?

3) I need to extract carrier distribution in txt file. So I am doing it from 2D figure and I have x y and value(color). But I would like to control x and y. I mean to say I want for example 1000 x and 500 y. Is it possible ?

Thank you in advance.
Best regards,
Levon
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Element killing during laser melting

July 18, 2013, 6:40 am
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Dear friends

I am working on laser cutting with moving heat source with subsequent stress analysis. I have successfully simulated the thermal analysis . However, I dont know how to delete/kill those elements whose temperature goes beyond the melting temperature during laser heating. for example, Assume that the melting temperature is 1273 K, thus any element with a temperature of 1273 or greater must be killed to simulate melting.
comsol can do this element kill process?
Can anybody guide me in this issue?

Thanks in advance

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convergence issues in cojugate heat transfer problem

July 14, 2011, 4:20 pm
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Hi,

I am trying to solve a conjugate fluid flow and heat transfer problem. The problem has a channel with fluid flowing through it and surrounding media which has some heat sources.
I am having issues when I increase the inlet velocity. Everything is laminar as it is a microchannel. As the inlet velocity is increased the solution fails to convergence.
I have tried including the results from lower velocity as initial condition for higher velocity but that is still not helping in convergence.

Any suggestion will be highly appreciated.


Regards,
Sumeet
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halbach array 8 magnet

October 29, 2011, 5:43 am
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Hej!
I made 3D model of Halbach array 8 magnet circular used NdFeB magnetic with 0.5 tesla magnetic strength.
Moreover, choose AC/DC module static magnetic field with no current. I am getting error when ever i simulate it. Moreover, i do not know how to define north and south pole of the magnet. I have attached pdf in which i explain almost everthing and also attached comsol file of halbach array of 8 magnetic. If some one can help me to sort this problem as soon as possible.

I want to use static magnetic field anaylsis to know magnetic field in the middle of the magnets

I will be thankful

I am looking forward to your mail.


Regards,

Mehdi Khan
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Undefined value found

February 28, 2013, 6:26 pm
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I had great trouble meshing a geometry. After I refined the mesh and was finally able to mesh it, I clicked the compute button. 78 seconds later, I got this message:

Undefined value found.
- Detail: Undefined value found in the equation residual vector.
.There are 1 degrees of freedom giving NaN/Inf in the vector for the variable mod1.emw.S1x
. at coordinates: (0,0,0), ...
There are 1 degrees of freedom giving NaN/Inf in the vector for the variable mod1.emw.S2x
. at coordinates: (0,0,0), ...

There is also a warning:

Inverted mesh element near coordinates (1.08012e-007, 3.25e-008, 6.4316e-007).

Can anyone help me with this? What's the problem? What should I do?
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Thermal stresses in Al2O3 cylinder due to laser heating

April 10, 2017, 5:21 am
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Hello All,

Thank you in advance for reading this. I have an issue with a solution of a 2D axisymmetric model with coupled heat transfer and solid mechanics effects. A relatively thin cylinder (like a pie chart) is heated with a laser up to temperatures on the order of 2,000 K in a thermo-shock heating profile. COMSOL seems to resolve the heat transfer effects correctly, however I am obtaining strange results for the principal stresses. I have tried changing the mesh and the heating rate, however the issue still persists. It seems that strange structures are forming for different thicknesses. In the attached image one can see the results for thicknesses of 2.05 mm and 14 mm. My question is whether these anomalies are caused by an improper resolution of the physics, or the spatial resolution (mesh), or the temporal resolution (using smaller time steps vs. heating rate), or could it be a solver issue? In the 14 mm case, lines which go through the nodal locations of my mesh are formed, which is why i thought that I had to refine it, but after I did it did not fix the issue. All comments and ideas are welcome.
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Electrostatics + Metal Electrode

June 25, 2010, 5:11 am
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Hello

I'm completely new to comsol. I'm trying to simulate the electric field between some specifically arranged metal electrodes. Between them is some material with a certain permittivity.

Now I get an error because there is no permittivity (epsilon) defined for the metal regions. Of course the metal part should have theoretically infinite permittivity. So I tried entering a very large number there but I'm not sure that this is the proper way to handle it. Is there some other model that should be used for simulation of the metal parts?
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Transmission through periodic nano array

December 12, 2015, 4:30 am
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Hello all,

I am trying to simulate the transmission through the periodic array which is fabricated on ITO coated substrate. According to the theory, this system should give us two peaks one corresponds for plasmon and other for waveguide mode. But I am not getting any type of signal. The transmission signal is very noisy and random.

Also, my model is showing some error.

I am posting my model. Can anyone help me in this regard?

Thanks
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Symmetric meshing

April 29, 2015, 6:30 am
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Dear all,

I'd like to learn if it is possible to have symmetry axis in mesh. I'm working on a 3D model, and the geometry is symmetric in both x and y axis. I'm studying on eigenfrequency analysis and I'd like the mesh to be symmetric in x-axis only.

To be more clear, I don't expect to see symmetric results for all mode shapes of course but when the mode shape is known to be symmetric by analytical means I want to see a more realistic illustration of it.

Thanks,
Utku
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Negative transmittance in comsol

August 10, 2015, 12:47 am
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Hello everyone

I am simulating a model for periodic silver sphere for in-plane and out-plane polarization. But when i am plotting the transmittance in case of in-polarization with angle of incident 50 deg then it gives me transmittance value greater than 1 while it is giving the correct value of out-plane polarization even also it is giving correct value of transmittance for angle less than 50 deg in in plane also.

I don't know why it is happening ?
If anyone have any suggestion please help me.

Thanks
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Assigning different meshes for different physics

November 15, 2016, 5:12 pm
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I am using equation based modeling with two general form PDEs that are coupled together. The spatial derivative of the independent variables in one PDE appears in the other one. In one of the equations I have to use very fine mesh while the other one works OK with a coarser mesh. Is there anyway that I can assign different meshes for each of these equations to save the computation time?
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3D Symmetry of Model

July 1, 2013, 12:41 pm
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Good afternoon all,

I am modelling two electrodes (tips facing each other) and the electric field between them. There are two Z-axis layers to each of the electrodes, measured in nanometers, whereas the width of the electrodes are measured in the hundreds of micrometers. Further, the electrode tips are half-cylinders. As you can imagine, this leads to some mesh-compiling problems (where it only compiles when the electrode width is set to a few dozen microns, instead of the desired hundreds), and I'm looking for solutions to be able to create and render a larger mesh.

The best hope to a solution (unless there are any you can recommend) seems to be symmetry, as both electrodes and the environment around them are identical.


I don't think 2D axial symmetry, extruded into 3D, would be able to suit my needs.

How would I do 3D symmetry along an axis? I've scoured the COMSOL forums, and while they are normally very helpful (thank you to everyone who takes the time to respond, you aren't just helping the OP) all the advice on symmetry is very vague and esoteric to a beginner like myself.

Thank you for your help,
Daniel
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Rickwer Wavelet as an edge boundary load

November 21, 2017, 7:25 am
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I am analysing the wave propagation on a 2D elastic medium.

I used as imput a force dependent on time having the form of a ricker wavelet on an edge boundary. I expect no residual deformations since everything is elastic, however when I plot the deformation on time, I get a considerable residual displacement. Can anyone see if I am missing something?

The domain is a rectangle (2x16) having periodic conditions on the sides. At the bottom a boundary load and at the top absorbing conditions.

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Comsol creates more domains than that defined in mphtxt

November 22, 2017, 2:58 pm
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I am trying to select the domains using matlab code.

I create a mphtxt file which has 3 domains from external software but when I import this mphtxt file to COMSOL, I get 4 domains in the selection lists.

Or are there any other methods could select the domians in Comsol consistent with the number of domains in mphtxt?

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transfer diluted species in porous media and moving mesh combining

December 4, 2017, 7:27 am
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Hi guys, Can I combine tds and moving mesh in comsol ? I mean I wanna my specie source moves as time goes on, so my concentration profile changes will change over time. I tried to combine moving mesh and tds but as you see in the pics, unfortunately, the source position didn't change. Please look at attached files. the gif is the best thing I achieved. look at jpg... I wanna my vertical boundaries of the square grow outward. any help ?

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Mean operator requires an adjacent entity of higher dimension

December 12, 2017, 8:27 pm
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The below post is related to an archived discussion

[start here] Hi, I am modelling a 3D Coriolis flow meter about eigan frequency Everything is built but when I try to compute the same it gives the error displayed below.

Failed to evaluate operator.

  • Operator: mean

  • Geometry: geom1

  • Boundaries: 1-2, 4-6, 17, 20-21, 26-28, 33, 38-40, 42, 51, 56

Mean operator requires a meshed adjacent entity of higher dimension. Failed to evaluate expression.

  • Expression: mean(comp1.spf.Wall_spf) Error in multiphysics compilation.

my picture: https://drive.google.com/open?id=1kpC-K_R35rihVbJf8WginuMUeOTWWj3u

Can anyone please explain as under what circumstances this kind of error pops up. Thanks in advance

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Element order and mesh resolution

December 19, 2017, 3:38 am
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The default discretization of fluids (incompressible Navier-Stokes laminar flow) is P1+P1. I often read that P2+P1 should better be used instead of P1+P1 in order to get better accuracy. Instead of increasing the mesh element order one could also refine the mesh to get better accuracy of course. My question is: is there a rule of thumb on what is the preferred option; increasing the mesh element order from P1+P1 to P2+P1 or refining the mesh and keeping the mesh elements to P1+P1? Or are there any considerations to keep in mind when making such a choice?

Leon Kamp

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Error "Multiple moving frame specifications on the same selection" when trying to use Moving Mesh

December 19, 2017, 6:23 am
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Dear all, I am trying to simulate a very simple spherical indentation in material and because the difficulties to get a stable convergence I 'd like to implement a moving Mesh in my Project. Nevertheless I receive everytime the error: Multiple moving frame specifications on the same selection. - Selection: Domain 1 Has someone an idea of what does it means an d how can I get rid of it?

Thanks a lot for your help

Regards
G.M.
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