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coupling model, extrusion 2D-axy towards 3D

February 18, 2013, 4:13 am
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Hello,

Is it possible to re-use temperature boundary results of a 2D-axy simulation towards a boundary destination of a 3D model (4.3a version)?

Which operator could I use if it's possible?

Thank you

Julien
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Segregated Solver, Segregated group

February 19, 2013, 9:14 pm
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What is the meaning of "Segregated Solver" and "Segregated Group"?

While computing for the results, I am getting a line like follows... "Segregated Solver 17% Step 3" .
And the value beside Step in that line is varying between 1, 2 & 3.

Does the step in that line mean "time step"?
As i have a time step of 300 sec spanning from 0 sec to 86400 sec, total 288 step.
So, will need to go through 288 steps??
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Adapting transport of diluted species interface using mathematical PDE

February 19, 2013, 10:46 pm
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Hello!

I'm trying to adapt the transport of diluted species interface using custom PDE:s in order to open up for further modification later on. I have been trying to copy the functionality of the interface using coefficient form PDE or the specialized classical Convection-Diffusion equation. The purpose is to model the concentration of a dilute species in a laminar flow of a carrier gas. No electric field.

Using the PDE interfaces to implement Fick’s second law proved no problem, but the diluted species transport interface also uses Fick's first law, it seems. I wasn't able to implement it with any of the PDE interfaces (I don't know how to use weak form equations). The interface gives almost no indication to which part it plays a role. Why isn’t it a part of the classical Convection-Diffusion equation if it is needed? It doesn’t seem to work without it. Is it only important for boundary conditions?

Another thing I haven’t been able to implement is the outflow boundary condition of the diluted species transport. The diluted species should disappear with the carrier fluid. If I try to implement it with the flux/source boundary condition in the Convection-Diffusion interface with the flux set to zero, it is identical to the outflow condition, apart from a minus sign. But it turns out this is the same as the zero flux condition. The question is, how do I implement an outflow boundary condition in the Convection-Diffusion equation?

Thanks!
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E or E1 or E2 in my plasma model

February 20, 2013, 12:02 am
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Hello,

I am trying since some days now to "copy" the microwave heated 2D model to a different geometry.
My geometry is axial-symmetric in real.
But I first started it in 2D only, but since I am not able to handle the EM fields right on 2D (I want a coaxial Power input of microwave) , I gave up this 2D to go to the 2D axial-symmetry. At least there I can have the coax input right away.
(But there I have a problem with the S-parameters.. it plots me Fourrier Coefficients?) (2Daxisym-EM)

Now implementing the plasma is not that easy.. in my model I may have deleted and put back the EM node..
So I have a E2 field variable..
But it does not look consistent with the port equation descriptions?
(2Daxisym-Argon)

Where do I do my errors?

If someone has an expert eye on it, that would be very helpful.

Thanks
Lukas
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How to define Function in Definitions / Variables.

February 20, 2013, 1:15 am
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I'm currently working on electrical simulation using AC/DC module. I define nonlinear electric conductivity for zinc oxide material using following function(ZnO) in subdomain settings, but it shown syntax error while defining the function.

sigma0_FDM*exp(ec.normE/Eb_FDM)

where
FDM- Field Dependent Material.


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domain deformation while doing moving mesh

February 20, 2013, 1:47 am
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Right now i am solving a moving mesh problem where the particle is moving in the domain. i have used moving wall and prescribed mesh velocity for the problem. It is doing fine for sometimes , however the geometry of the domain is changing with the moving mesh after sometime. I have attached the picture of mesh for two different times.


I need some suggestions so that the domain won't change with the moving mesh deformation. Please respond as soon as possible.
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Peak-to-peak amplitude in Comsol 4.3a ?

February 20, 2013, 2:24 am
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Hi

I need to evaluate the peak-to-peak (pk-pk) amplitude of a voltage, which means the difference between the maximum positive and the maximum negative of a waveform. Are there any predefined function to do so in Comsol 4.3a, please?

Or are there, at least, any predefined functions to calculate max postive (highest amplitude value) and max negative (lowest amplitude value, which can be negative) of a waveform ? That would be a help too.

I searched the docs and the forums but to no avail.

Thanks very much
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How to set displacement from study 1 as prescribed displacement in study 2?

February 20, 2013, 4:31 am
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Hey,

I have a trouble with defining a prescribed displacement.

Let's say that i received displacement of the edge caused by heating of sample. But displacement of this edge is different in every point of its length.

I want to keep this displacement as prescibed displacement condition in next study. So i can't just add condition prescibed diplacement in y=a, becouse it's more like ax*bx^2.

I tried to use mod1.u as prescribed in y, but it's not working or I doing something wrong.

How can I solve this problem?

Kind Regards

Robert
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Compressible Flow

February 20, 2013, 6:15 am
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Hello , I have a simple question. What module should I use to simulate a gas flow in a tube.Something like the Pipeline Insulation in the Model Library but with a gas.

Thanks,
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There's pressure gradient, but no velocity, anyone can help me out? thanks

February 20, 2013, 7:39 am
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Hi, I'm using the Free and Porous Media Flow module to simulate the fluid flow on the particle level. I used it for 2D condition and it worked. When I switched to 3D case, something weird happened. I can get the proper pressure gradient, but all the velocity is zero....

Any help would be greatly appreciated!
Attached is the model.
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Out of memory during LU factorization!! ( please help!!! )( muffler simulate )

February 20, 2013, 9:09 am
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Hey guys!
I have a muffler that i will simulate by acpr interface. I used this pdf for do this job:

www.mediafire.com/?zzvc170c23s3zvt

I have a problem when i solve this projcet.
i take a picture of the error:

www.mediafire.com/?a68qyp2pwpk6vr8

the error:

"Failed to find a solution for the initial parameter.
Out of memory during LU factorization.
Returned solution is not converged."


and this is my project:

www.mediafire.com/?45134a1swjep353

how to solve this problem?
can you solve this problem for me?
please help me, because i'm very necessary to this project!
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Spatially graded index / graded material properties

January 13, 2011, 6:12 pm
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Hi,

can anyone of you tell me if it is possible to define a graded index in comsol?
It seems as if sth. like this has been done in www.comsol.se/academic/papers/2871/
But how? Is it simply possible to use the coordinates as variables in the definition of global parameters for the dielectric properties?

This would mean, is just something like
parameter n
definition: factor * x
possible to achieve (simplified) a linear gradient of n over the geometric x dimension?
I would be happy about help.

Best regards

Arian
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Geometric nonlinearity

February 1, 2012, 12:39 am
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Hi,

I have used structural mechanics to simulate an indenting sphere on a half space polymer film. I am changing the elastic modulus of the polymer film to go from hard material to soft material.
I am trying to reach a certain force using weak constraints. When I use the elastic moduli from some GPa to around 80 MPa for indentation of 100- 400 nm, very well I can use linear elastic physics without selecting the box "consider geometry nonlinearity".

However, as long as I choose the elastic modulus 60 MPa or less with indention between 500 nm to 600 nm (I want to reach to a certain force and as the material is soft indentation is high), the simulation fails. It does not stop but a big triangular max pick appears at around 500 nm. However if I turn on "consider nonlinear geometry " and change the poission ratios, it works. but then I reach to a force at much lower indentation that I cannot compare the results with the previous calculations.

I would like to know why do that happens? and how can I fix it?


Yours,
Marjan
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Modeling Jet flow of Water in Air Atmosphere

July 5, 2012, 7:11 am
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Dear All
I am modeling the flow of jet (say water or similar liquid) in an atmosphere of air. The problem is very similar to the one in the model library (the inkjet example). However, my domain dimensions should be in cm instead of mm as in the example. When I change to the cm in the geometry and keep everything the same, the model does not solve. Does anyone have an idea what should be adjusted when growing in size on the domain? I was thinking of Reynlods number getting into the turbulent regime while I am using N-S, but I found it around ~ 100 so, I should be on the safe side in this regard.
Any advice would be highly appreciated.
Thanks
Ahmed
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Movement of air due to thermal expansion

December 16, 2012, 8:13 am
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Hi everybody!

I'm trying to simulate the movement of the air in 2D and I only get errors. I use two physics: laminar flow with heat transfer. I've created a square full of air and I put easy boundary conditions:
-Left edge: 120 ºK
-Right edge: 300 ºK
-Top side and down side have thermal insulation and don't have any loss of heat.
The square is closed and it hasn't got inflows or outflows.
I have used a lot of different volume forces: Boussinesq approximation, a reference density...However I think the best idea is to put F=g_const*spf.rho.

I saw Buoyancy Flow in Free Fluids in Model Gallery and followed every step though it uses adimensional parameters and I want to draw on the material library using air properties. I've noticed that when I use a liquid instead of the air all works properly, I think it is due to the viscosity. I use a parametric sweep starting on a value of viscosity which doesn't give any error and decreasing it until the real air's viscosity.

I get a solution with this parametric sweep but I'm sure it's erroneous because I get the values of total heat flux according to each value of viscosity and they aren't the same on the right edge than on the left edge and they must be. However when the viscosity have high values, the total heat flux are the same.

The mesh I use is finer and the study is stationary.

I'm so frustrated because it should be really simple.
Sorry for my English level and thank you for your time.
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Postprocessing in cyclindrical coordinates

February 6, 2013, 11:50 am
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I am doing a plane strain analysis of a pipe with a crack in it.

I would like to get the stress components in the cyclindridcal coordinate system (radial, hoop stress) rather than in the cartesian coordinate system (x & y stress components).

There seems to be do obvcious way of doing this.

Is there anyone who can suggest something?

Thanks,
--
Arthur Rupel
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Eigenfrequency seems right, but displacement units are totally wrong.

February 7, 2013, 7:18 pm
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Dear Comsol Community,

in the model attached I have a 20 micron long beam using the Solid Mechanics module to get the Eigenfrequencies. I calculated them manually using Euler-Beam theory and the first Eigenfrequency should be around 5 MHz.. Comsol calculates 4.8 MHz. I thought great result, but if you look carefully at the screenshot, you will notice that Comsol claims the displacement is on the order of meters, which is totally wrong (it is rather pico meters). I feel I am missing something fundamentally, but I cannot get Comsol to spit out the correct displacement as well. (Scaling or anything of that sort is disabled).

Thanks for advices!

Erik
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Problems with sweep mesh

February 17, 2013, 7:28 pm
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Hi,

I have been trying to sweep mesh a domain (3-D). It will be like a small straight tube of rectangular cross section and having turns at right angles (like a serpentine). I tried to mesh the source and destination faces using 'edge' and 'mapped' option and subsequently tried to sweep mesh the entire domain. All I can get is, "invalid topology at the vertex". I found a pdf (lnf.umich.edu/nnin-at-michigan...loads/2012/11/comsol-guide.pdf), in which a domain similar to mine has been sweep meshed in page number 356 using comsol 3.5a. I am not able to find options like that in comsol 4.2, which I am using.

I kindly ask the experts in this area to comment on this and advice me. Thanks in advance.
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Basic issue with plotting derivative

February 21, 2013, 1:40 am
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Hi everybody,

I am using the 2d structural mechanics for static simulations of a cantilever undergoing a point force. I want to plot the derivative of the deflection u by respect to the position x along a boundary. But plotting d(u,x) gives me a zeroed value function.
By digging in the forum, I thought first that this may be due to the order of the shape function, but it should not be an issue in my case as I just want to know a first order derivative. It looks like a basic issue but I do not find the solution.

Thanks
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Stresses built up in a rotating disk

February 21, 2013, 2:28 am
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I am trying to analyze the stresses built up in in rotating disk. This disk is not subjected to any external loading. Only forces applied is centrifugal forces due to rotation.

When I try to model the problem using Structural Mechanics>Solid Mechanics (solid) from COMSOL 4.2 it allows me to enter a linear velocity as a Prescribed Velocity. But I cant enter the rotational or angular speed.

Can I implement this problem in COMSOL using this Prescribed Velocity functionality?or Is there any other way to analyze the stresses in this rotating disk.?

Thank You Very Much.

Shehan
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