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How can i generated DEP force and electric field between two electrode using comsol 4.4??

August 20, 2015, 2:07 am
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hi,

How can i generated DEP force and electric field between two electrode using comsol 4.4?? i already done my design (electrode desing) in 2D...which module should i use electrostatic(es) or electric current(ec)??what's the difference?
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Slug flow of Two immsible liquids

August 20, 2015, 3:45 am
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Hello,
I would like to generate a slug flow in a micro-channel (as shown in the attached image). I have started my model by using the Droplet Breakup Model but I noticed that the droplets started to dissolve as the move downstream! How can I overcome this problem please. Also, is there a method to generate slug flow without mixing two fluids? I mean depending on the boundary conditions of a single channel?

Thank you in advance
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Very Urgent: Piezoelectric Filter Lumped Port Problem

August 20, 2015, 11:28 am
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Hi
I am trying to find the s parameters of a mechanically coupled piezoelectric filter with lumped port. But even though I have defined the perfect conductor, I get this error:
Errors during multiphysics.
Uniform lumped port should be placed between two conductive boundaries.
- Feature: Type: Lumped Port
Tag: lport1
Operation: LumpedPort (lport1)
Uniform lumped port should be placed between two conductive boundaries.
- Feature: Type: Lumped Port
Tag: lport2
Operation: LumpedPort (lport2)
Can someone help me please? I attached the file as well.
Thanks
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Very Urgent: Piezoelectric Filter Lumped Port Problem

August 20, 2015, 11:29 am
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Hi
I am trying to find the s parameters of a mechanically coupled piezoelectric filter with lumped port. But even though I have defined the perfect conductor, I get this error:
Errors during multiphysics.
Uniform lumped port should be placed between two conductive boundaries.
- Feature: Type: Lumped Port
Tag: lport1
Operation: LumpedPort (lport1)
Uniform lumped port should be placed between two conductive boundaries.
- Feature: Type: Lumped Port
Tag: lport2
Operation: LumpedPort (lport2)
Can someone help me please? I attached the file as well.
Thanks
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How to couple multiple physics

August 21, 2015, 12:08 pm
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Hello,
I have a big issue when I try to model harmonic generation in plasmonic nanoantennas with the RF module. But this can be a general issue when you must couple multiple physics.
I am simulating the nonlinear phenomena of Second-Harmonic Generation and Third-Harmonic Generation, therefore 3 frequencies are involved: f1, f2 and f3.
I wrote my script as it was a coupled-physics problem:
- I set Study 1 to solve the problem at the frequency f1, which is independent from the others, no problem.
- I set Study 2 to solve the problem at the frequency f2, where the field is dependent only on a variable evaluated during Study 1. No problem, I set "Values of variables not solved for" in order to get the required value from the solution calculated during Study 1.
- Finally, I set Study 3 to solve the problem at the frequency f3, which must be dependent both on the fields at f1 and f2. But in this case one "variable not solved for" should be taken from Study 1, and the other one from Study 2.
Is it possible to perform this action in some way in my script? Or maybe there is a simpler way to couple studies at different frequencies?

Thanks!
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Change boundary conditions during a heating process

August 24, 2015, 4:51 am
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Hello,

In an heating simulation, I would like to change a boundary condition during the simulation. I would to impose on this boundary:

1. a heating condition during 600 min
2. an tempering condition (no heating, but there is conduction in the material) every 20 min for 5 min.
So,
0-20 min: heating
20-25 min: tempering
25-40 min: heating
40-45 min: tempering
...

Is it possible? With the solver sequence? How to do it?
Thank you. Howard
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Problem with periodic boundary condition

August 24, 2015, 9:50 am
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Hi,
i have a problem that i don't really understand.
I made some simulation of a square impedance tube to compute sound absorption coefficient.
The mode works very well.
when i apply a periodic condition for the lateral faces of the tube, the model failed (Failed to find a solution for the initial parameter). The relative error (1e+004) is greater than the relative tolerance).
It can be possible to solve this problem by increasing the mesh resolution bu it work only for some frequencies and the problem get back.
Does someone can explain to me what's wrong?
Thanks a lot.

Jean-Philippe
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Resolve error; MUMPS allocation factor increased

June 11, 2015, 7:27 am
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Hello everyone

On running a time dependent study I get an error that "MUMPS allocation factor increased to 2.0736." I know that this error can results due to incorrect boundary conditions but I am feel that my boundary conditions are correct. Is there any other reason why the solver MUMPS, gives such an error.

Appreciate the help.

Thank you

Best regards
Zaid
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RAM using

August 25, 2015, 7:34 am
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Hello everyone!
I couldn't find the answer on the forum.
I have 32 Gb RAM memory (Win8 x64). The Mesh of 3D model consists of ~300 000 cells. When calculation of a task is performed, memory consumption increases. When memory consumption > RAM = computer freezes/crashes/hangs and calculation stops...
Tell me Plz, what are the ways to solve this problem?
Whether it is possible to change something in the Solver (I have a default settings of Solver) that less memory was consumed? Whether it is possible to keep the intermediate stage of calculation on the hard drive to release the necessary memory size for the subsequent calculation?
How to limit memory consumption in the calculation, so that it does not exceed the available RAM? (I am ready to increase the time of calculation... the main thing is that the calculation is not interrupted).

P.S.
-Doesn't allow to set less cells of model, otherwise errors will occur.
-I can't increase RAM memory size of PC.
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Out of memory during assembly BUT the mesh number is just 3608

April 24, 2011, 12:38 pm
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My model is 3D using Heat transfer in porous media, and the total mesh number is only 3608, but the error "out of memory during assembly" still occurred, why? Model file was attached.
My operation system is windows 32bit, and the internal memory is 2GB
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solution can not be converged

August 26, 2015, 4:15 am
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Dear Everyone,

I built 2d axisymmetric model, which consist two iron cores(Cobalt steel vacoflux 50) and two coils(with 5A, 5000turns), I applied HB curve to iron cores. I want to see the magnetic field.
I used stationary solver , it is shown that "Failed to find a solution.Maximum number of Newton iterations reached. Returned solution is not converged."
I tried to refine the mesh, the results were still not converged.

what should do to make the model computational?

Thank you very much!
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How to give maximum and minimum limit to a variable in user defind function as comsol takes maximum and minimum values for shear rate in power law model

August 27, 2015, 9:32 am
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I am trying to give an user defined function for viscosity which is a function of pressure and shear rate. I want to take the value of pressure to be the pressure calculated by comsol but then i do not want that pressure value below a certain limit so i want to give the minimum value of p for it. Is there any way i can do it in comsol5.1?
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Boundary Stress

August 28, 2015, 12:19 pm
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Dear all,

i have a problem. I try to simulate a fluid flow effected by a boundary stress on a key hole. See attached mph-file.
With a very big mesh, comsol solve the problem. But with a smaller mesh, comsol does not solve the problem any more.
Have someone an idea why? Or what i can change to get a better convergence with this problem?
Thanks to all.
Best regards
Johannes
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Electrical Asynchronous Machine, rotor short -circuit in 2D?, rotation via equation?

July 11, 2011, 8:24 pm
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Hello,

I am trying to simulate an 4pole (q=3) asynchronous machine with the .rmm physics module in 2D with COMSOL 4.1.
So far I am able to excitate the coils with a Voltage through the "Electric Circuits"- Physics interface to create the rotating field in the stator.

Now I want to let the rotor rotate. Doing this with the prescribed velocity works fine. Composed parts and the identity pairs are being considered.
The problem is, that the rotor slots are not connected to each other in 2D, so no current is able to flow through the rotor and no torque is being excited.

I tried to create that short-circuit via a "multi coil domain" and chose the excitaion as "circuit".
Put a very big resistor between the upper node of the "External I vs U" and the voltage source, which is set to 0V.

Simulating this, brings no error. BUT the electric conductivity within the coil domain is 0. So no current can flow in the rotor. The "multi coil domain" seems to be responsible for this, because it overwrites the materials electrical conductivity.

After that I tried to use a "Single coil domain" for the rotor slots, because it doesn't overwrite the conductivity.
Simulating brings the following error:

Circular variable dependency detected.
- Variable: mod1.cir.UvsI1_v
- Geometry: 1
- Domain: 90

What does this error mean exactly and how can I solve it?


At the moment I have no other idea to tell COMSOL that the rotor slots are connected to each other... Do you?

I want to let the rotor rotate through an equation and read that would be possible with "ODE and DEAs"-physics. Do you have any advices for this?

I would be really happy about some help.


Thanks in advance.




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Acoustics - Large models convergence

August 26, 2015, 3:32 pm
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Hi,

I'm driving crazy about this subject. I think don't know many things about this model, but regardless how mesh, solver configuration (multigrid, iterative, direct, etc.) or any other thing I change doesn't matters, it can't reach the convergence.

I'm trying to simulate the noise generated by a solid source that emits noise in all frequencies, like a power transformer, in an electrical distribution substation. I'm using the acoustics module in the frequency domain.

I don't know very well how to set the sources pressure (or the pressure level) with the boundary conditions. I'm using the "pressure" boundary condition setting an arbitrary pressure in order to perform a test.

I'm using an iterative solver with multigrid method (2 or 3 levels), with Krylov preconditioning. Then I use SOR or Jacobi methods.

No matter if set or not a parametric sweep (for frequencies), the solver not converge.

There's any "trick" or something that guides me to reach the convergence in these type of models?

Please, see the attached images in order to understand the described above.

Thanks in advance.
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Isolating components in study steps (and solutions)

August 30, 2015, 10:41 pm
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Can someone help me understand why even though I tell all my study steps under one study to use only a single physics interface the solver still tries to find dependent values for variables under the other unselected physics interfaces?

Specifically I have a model with two components. These components are actually not meant to be linked in any way, they are simply included in the same model so that I can export their results together into a single report. I understand this makes things confusing for COMSOL since it likes to couple everything but it's much easier for me to do this as long as I understand how the solvers and solutions work. And it looks like I don't.

My first component only uses the "magnetic fields (mf)" interface. My second component uses "Pressure Acoustics, Frequency Domain (acpr)" and "Electrical Circuit (cir)". In my first study step I only do a small signal analysis (stationary and freq-domain, perturbation). For both steps I only select the "mf" physics interface, but for some reason when I expand down to "Solution 1" and it's "Dependent Variables 1" I am seeing variables for "acpr" and "cir". This ends up giving me unexpected, unwanted, and empty solutions in the results.

Any idea if I'm doing something wrong, and if so, what I could be doing wrong? Is there any way I can better isolate the components from each other in the study steps, solvers, and solutions?

Also, one more question. I want to do a parametric sweep on the geometry for the stationary step only. I want to run a frequency domain, perturbation biased around the stationary solver, but only at the original resting position of the geometry. Is there a "best" why to do this? Right now I just run the stationary and parametric sweep with the freq-domain, perturbation disabled then disable the parametric sweep and run the freq-domain, perturbation.

Thanks in advance for any help.
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Mass flow rate vs temperature.

August 31, 2015, 12:47 am
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Hi, I used Comsol to model a really simple problem. A pipe with 50mm diameter and 25m long with an inlet temperature of 20°C and 0.5kg/s of mass flow rate. Also, the pipe´s wall temperature was 150°C. I used a parametric sweep to increase the mass flow rate with a step of 0.15 until 2kg/s. The fluid was engine oil and in laminar flow.

When I made the plot of temperature vs mass flow rate, it behaves as a parable in which at a point near 1.4 kg/s the temperature begins to increase instead of decrease as it´s expected.

Do you know what is the explanation for this?

Thanks
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Optimisation of processing parameters in laser sintering of metal/alloy powders

December 16, 2013, 5:30 am
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Hi everyone,
I am new to COMSOL Multiphysics..
Can anyone help me in simulating selective laser melting(SLM)/direct metal laser sintering(DMLS) of metal/alloy powder media in layer-by-layer fashion?
IN SLM process a high power laser beam falls on a thin layer(say 30 micron) of metal powder bed and scans according to CAD model given to the computer. This process is repeated till the CAD part is completed layer-by-layer fashion.

thank you in advance.
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Limiting the Parametric Sweep study step to a specific step(s) in the study.

August 31, 2015, 9:58 pm
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I'm doing a small signal analysis (stationary, freq-perturbation) and I want to run a parametric sweep (on geometry) for the stationary step only. I can't seem to figure out how to isolate this within the study. No matter what I do in the solver and job configs every time I run the study it always wants to run the sweep on the stationary and freq steps. This means it wants to do a parametric sweep for each frequency in my freq step, which obviously will take a long time.

Right now I've created two different studies to separate these, essentially running the stationary step twice. But is there anyway I can do this without having to solve the stationary step twice?
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Rotation of 3D geometry taking too long time to compute

September 1, 2015, 8:26 pm
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I am using the rotating machinery laminar flow physics. I am trying to solve with time dependent study.
Every time after computing 7% or 4% it hangs up and continues doing iterations upto 2000 and never converges.

Another time i used frozen rotor then i got solution in 2 mins.

Can anyone look at the model and rectify the flaw.

Thank You
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