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Meshing Error

February 11, 2013, 8:09 pm
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Hello everyone,
i want to attach the electrodes to the boundary of my model , but when i am try to mesh or add the sub domains, it shows me error
"Could not resolve subdomain relations"
could you please tell why it is coming?
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Failed to find the consistent initial values

February 11, 2013, 8:20 pm
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Dear sir,

I am getting an error after solving as follows

"Failed to find the consistent initial values
Last time step is not converged.
- Feature : Time - Dependent Solver1 (sol1/t1)
- Error : Failed to find consistent initial values"

We suppose that the error is because of the fact that I am unable take back the results from 1440th time step to 0th time step (with an interval of 5 min each). Is that correct and how can I use the results of the 1440th minute back in oth minute for accurate values??

If not, what are the probable corrections for this error??

And, we have a prolonged query about the varying temperature of the fluid as it flows through the pipes. As the fluid flows through the pipe, the initial values of fluid temperature my vary from position to position. So, Can you let me know about how to incorporate this condition in the model of ours??

Thanking You sir.

Nithin
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Averaged flux

February 12, 2013, 5:06 am
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Hi,

how to average the time-dependent diffusive flux for pre-defined time intervals at a domain boundary and allocate those (averaged) values to the arithmetic mean of the time intervals? The evaluation of the averages is part of the computational (not post processing) phase.

Hence, I would like to evaluate the following expression at a given boundary:

Integral flux from t(i) until t(i+1) devided by the length of the time interval ( t(i+1) - t(i) ); that averaged flux value should be allocated to time point ( t(i+1) + t(i) ) /2, i.e. the middle of the time interval.

Many thanks for your appreciated help.

Best regards,

Andreas
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Comsol 4.2a Produce an report

February 12, 2013, 5:15 am
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Hi All,

I have been trying to produce a report from the Comsol 4.2a I am using.

However everytime I try to do so, it says :

Unknown Property
Property: funcname

In my model, I have an matlab function as input, however it is not causing any problem when I run the simulation, just not sure whether it is causing the problem when it is producing an report

I attached my model and matlab function in case anyone is interested in looking at it.

Thank you very much.
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Induced current in a power cable sheath

February 12, 2013, 7:05 am
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Dear all,

I'm probably missing something obvious, but I am having trouble creating a good model of a single-phase power cable. Herein I want to calculate the induced current in a (copper) cable sheath due to the current flowing through the conductor.

I am using Comsol V4.3a, with the magnetic field interface (2D planar) and a time-harmonic study (it's a 50 Hz power cable).
I specify the conductor current using a single-turn coil domain and get an induced current in both the conductor and the cable sheath (so far so good, I think).
The strange thing is that the induced currents depend strongly on the size of my domain. If I increase the outer radius of my domain, the induced currents increase, and vice versa.
I have tried using an external current density instead of the single-turn coil domain, but get the same dependence on the domain size.
What am I doing wrong here? Any help would be greatly appreciated.

I have attached the model.

With regards,

Frank
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Editing Weak Form within RF Module in 4.3a

February 12, 2013, 8:53 am
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Hi all,

In 3.5a, within the RF module you can edit the weak form yourself by going to Equation System -> (Subdomain or Boundary or Point) Settings (see screenshot). Is this functionality still available somewhere in Comsol 4.3a?

Thanks
--Will
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Phase Field Method - define parameters

July 8, 2010, 11:46 am
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Hi everyone,

I'm using the phase field model in Comsol, but I'm not really sure how to define the required parameters, such as: surface tension coefficient,
interface thickness,
mobility tuning parameter,
phi-derivative of external free energy,
etc.

Anyone any idea how to define these parameters and what are good values to at least start with?

Thanks,
Tara
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convergence issues in cojugate heat transfer problem

July 14, 2011, 3:20 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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Conjugate heat transfer Interface boundary condition

October 2, 2012, 2:25 am
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Hello All,

I am new to COMSOL. I am trying to solve a 3-D conjugate heat transfer problem with volumetric heat generation in the solid domain. The problem is more like solving for a temperature profile in a heat exchanger. how and what should be the boundary condition applied for the fluid-solid interface?





rgds

Anup
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PCF, PML

November 17, 2012, 9:44 pm
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Hi,

I am designing a PCF with hexagonal pattern having five air hole rings.
pitch = 1 um.
air filling fraction = 0.90
i have used circular PML to get the imaginary part of refractive index.
what should be thickness of PML ?
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Axial flux permanent magnet generator

December 5, 2012, 8:59 am
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Hi Dr. Ivar/All,

Iam trying to simulate the axial flux permanent magnet generator with two rotor and a coreless stator sandwiched between two rotor.

Permanent Magnets are attached on inner surface of the rotor in such a way that magnets on two rotor are in N-S orientation.

I used the following boundary condition for the different domain under rotating machinary physics(rmm)
- For PM i used the constitutive relation remnant flux density from the Amperes Law
- For two rotor i used the BH realtionship
- I used the multi turn coil domain to model the coil
-used the prescribed rotational velocity for the rotation fo the rotor
-used continuity

Apart this i used the free tetrahedral meshing .

I tried to simulate taking reference from the generator model in Comsol model library but still not getting the desired flux and the voltage.

I really need your suggestion regarding this matter.I tried to find out the discussion regarding the axial flux permanent magnet generator in the discussion forum but none of them are answered. I am stucked at this point please help me out .

I have attached the model by clearing all the mesh and solution for making it appropriate for uploading.

Thank you
Aruna

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Electron Cloud Confinement

January 7, 2013, 9:08 am
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Hi,

I am trying to model the confinement of a cloud of electrons in the center of a spherical axisymetric system. The electrons are confined by an electric potential. I was wondering if anyone had recommendations for how to best approach this. I'm new to COMSOL, so I'm not too familiar with the limitations of the different modules.

I initially attempted to use the Drift Diffusion module, but I have been running into problems with it. Since I am modeling electrons without ions, would this module be appropriate? In this simulation, I am trying to find the steady state electron density distribution starting with virtually no electrons, and a constant electron production rate in the center. I want all electrons hitting the outer boundary to leave the system, but when I run this the electron density continues increasing indefinitely. I tried using the wall, electron outlet, and flux boundary conditions, but none of them seem to be working.

I am now attempting to use the Charged Particle Tracing module. Without using an electric force, this simulation takes < 30 seconds to run to 0.1 ms. I ran the simulation for 3 days with this force enabled, and it only got to 2.7e-4 seconds. I will probably need to run this simulation to 1 ms, which would obviously take longer. Should the computation be taking this long? Also, I want to consider the interactions between the electrons. Would it make sense to multiply the particle mass and charge number by a constant, since I want to consider many more electrons than the number of particles that can be simulated?

Any insight for which of these approaches sounds more appropriate would be appreciated.

Thanks
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cluster computing mpi

February 13, 2013, 8:27 am
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Hello,

I am trying to run my models from comsol on our University's super computer, and having difficulty with the $PBS_NODEFILE command. Can the PBS_NODEFILE also be used to run generic MPI programs?

Thank you,
Kelley
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COMSOL 4.3 with MATLAB error 2

February 13, 2013, 9:20 pm
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I have the code that have for loop.
Before the first loop is finished, we met several error messages




??? Error using ==> mphinterp at 317
mphinterp (292): Java exception occurred:
Exception:
java.lang.RuntimeException: Error in reInitializeModel
(rethrown as com.comsol.util.exceptions.FlException)
Messages:
Error in reInitializeModel






??? Error using ==> mphinterp at 317
mphinterp (292): Java exception occurred:
Exception:
java.lang.NullPointerException
(rethrown as com.comsol.util.exceptions.FlException)
Messages:





??? Error using ==> mphinterp at 317
mphinterp (292): Java exception occurred:
Exception:
org.eclipse.emf.cdo.common.util.TransportException: java.util.concurrent.TimeoutException
(rethrown as com.comsol.util.exceptions.FlException)
Messages:
java.util.concurrent.TimeoutException



Is it a memory problem?
We have a 16GB RAM.
I increased the java memory to 7GB.
But, I have that problem continually.
May I get the solution?

Kyungnam Kang
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Meshing and Simulation of a Sphere partially covered with gold

February 14, 2013, 9:22 am
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Dears

i am trying to perform an eigenfrequency simulation of the sphere i show in the file. The sphere is anchored by the circle in the bottom. And is covered, partially of a thin layers of Gold (electrodes). Before to start with the electromechanics simulation i want to do the solid mechanics simulations to see the effect of gold electrode on the structure (i have previously simulated the sphere without the gold electrodes and it worked).

when i do the simulation the following message appears

The mass matrix is Zero
Feature: Eigenvalue Solver 1 (Sol/e1)

I guess that the key is how i define the structure but i would appreciate a bit of light over this issue. Thanks!


Joan
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Automating plot exporting in Comsol on a Linux Red Hat system

February 14, 2013, 11:44 am
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Hello, first time posting

Our group recently set up a Linux based server node for Comsol work. As it stands, we need to define our models on a workstation or personal PC, do the meshing, then copy the file over to the server, ssh in and run comsol via commands (using putty in our case). Once it's done we copy the files back to a workstation and can then extract any data we need.

I have two issues with this arrangement:

1) My meshes tend to be quite large. Meshing is slow, then file transfer is slow. It would be nice if the meshing could be handled on the server, but leaving the model unmeshed simply causes errors. Does anyone know of a way to handle remote meshing?

2) The complete file after solving is large (slow to transfer) and slow to open on a workstation. However, I really only need to see the data from a 1D plot of a port S variable to know if it needs a closer look or not. Normally I get this data via export. Does anyone know of a way to automatically export plots or variable data remotely? My ideal case would be a command that creates a .txt file in the containing folder with my data.

Background: version 4.2a, electromagnetic wave simulations, using the -batch command on the server, looking to extract the values of emw.S11 vs frequency (~300 values)

Thanks,
Bryan
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Question about eddy current model

February 14, 2013, 4:22 pm
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Dear friends,

what if I want to know the temperature distribution in the plate in the eddy currents tutorial (www.comsol.com/showroom/gallery/970/)?

The only result I get in this model is the resistive loss in the plate surface, but there is no information about temperature distribution. I tried to perform such improvement using "heat transfer in solids" and even "induction heating" physics, but did not reach something meaningful.

Anyone has a suggestion about how it could be simulated?


Regards,

Natan
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Difference between "Electron outlet" and "Insulation" in the drift diffusion physics/ plasma module

February 14, 2013, 4:26 pm
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Hi all

I have a fairly easy question about "drift-diffusion" physics in Plasma module. There are two types of settings for boundaries: "Electron outlet" and "Insulation". In the "Equation" for both of these settings there are exactly similar equations.

Can anyone explain to me the difference between these two?

Any help with this issue is much appreciated.

Peyman.
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Plotting the gap distance variable

February 14, 2013, 4:53 pm
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I am trying to do something very simple, but it doesn't seem to be intuitive. I have a contact pair in the structural mechanics module and I want to plot the gap distance variable as a function of time. I know this is should be simple, but I am stuck!

Ryan
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Modeling a Dielectric as a Real Capacitor

February 14, 2013, 8:26 pm
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Hello everyone,

I am having trouble modeling something. I would like to look at the conduction/conductance/resistivity of a insulating/conductive composite. It could be thought to be like a polymer/insulating fiber system. Electrically, the polymer itself is referenced in literature to look like a capacitor and resistor in parallel. The capacitor illustrates the ideal dielectric capacitor that one might expect and the resistor illustrates the leakage that actually flows through the capacitor when placed in a potential. The illustration is on Tony Blythe's 2nd edition "Electrical Properties of Polymers" book on page 156. I've attached an image of the equivalent circuit I am talking about(not exactly the image from the book though).

I would like to know the DC electric conduction through the entire composite, so both in the low conductivity areas (the polymer/semi-insulator) and the in the high conductivity areas (which is a fiber/metal). Is there any way I can use components of both the Electostatics and Electric Currents Modules? I want it to take into account both the electrical conductivity and also the relative permittivity of the polymer. If so how can I do this? I've attached a 2D model of the geometry of what I'm talking about.

When I do this geometry in the EC interface, the electric field is not what is expected and when I do this geometry in the ES interface, I do get the correct e-field. I would like for the model to look like the ES does (which is what is expected) but actually have some current go through it.

Thanks in advance for any help you can shed for me!

John
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