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integral value of variable till a radius value interior to the circle radius

September 10, 2012, 2:28 am
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Hi,

I want to get integral of a variable till a point in the circle of radius r0, where this point would vary from 0 to r0. That means I want to get for all radius value till r0. With intop operator whole geometry is selected so, for interior points I tried to use if statement where for till the radius point where I intend to calculate is 1 and for the rest after that is 0. This gives the value at desired r. Now, since I want it for all r value from o to r0 what condition should I write in IF statement condition so that it takes the range from 0 to r0 with discrete step points defined by me.

Best
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functions dependent on other functions

September 13, 2012, 2:00 pm
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Hello all,

I have 2 random functions in my model- rn1 and rn2. I need rn2 to be dependent on rn1, but when I try to call rn1 into the rn2 function, comsol does not recognize it as a variable.
Does any one know if it is possible to make 1 function dependent on another function within 1 model?
Thank you so much.

Kelley
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About convergence

September 17, 2012, 7:25 am
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Now I meet an unfamiliar issue. For the solver I had set the relative tolerance as 0.001 and used the direct solution. As the simulation processed, this value was lower than 0.001, but the simulation could not stop until the Maximum number of iteration reached the setting value (50). Finally it showed that :"Failed to find a solution. Maximum number of Newton iterations reached. Returned solution is not converged.". I can't understand that since the relative tolerance was lower than the setting value why It could not converge. Who knows this answer and help me. Thank you very much!!!
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980 Boundary conditions

September 18, 2012, 11:05 pm
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Hi,

I have a so called fieldcage with 980 copper strips. Now i have to set to each strip an electrical potential as boundary condition. this potential is not arbitrary but decreasing in steps.

is there a possibility to easily set this boundary condition with for example an array?

thanks
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Inverse heat conduction problem - determination temperature-dependent thermal conductivity

September 18, 2012, 11:25 pm
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Hello,

I am interesting to solve an inverse heat conduction problem in order to determine the thermal conductivity using Comsol.

The study area is a block and I have the six boundary values and 50 temperature measurements in the area. I suppose that there is not heat generation and temperature doesn’t change (steady-state).

I would like to ask you if the above problem (the determination of thermal conductivity) can be solved using Comsol.

Where can I find more information that will help me with the above problem?

Thank you in advance,
George
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about the field in the coil

September 18, 2012, 11:37 pm
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Dear all ,
I am trying to excite the primary coil with current of 10 A , and need to test the magnetic field induced in the secondary coil , i excited the primary coil with current using single turn coil domain , i am not getting any field in secondary coil ..please let me know what is problem
Thanks in advance

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kishore Naik Mude
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Meshing problems for 3D periodic problems when using GMRES

September 19, 2012, 12:45 am
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Hello all,
I need help and I hope somebody with experience of using iterative method for large 3D problem would be willing to give me help.
I wish to calculate large 3D periodic problems in the RF module but i can not seem to get the calculation to converge properly with GMRES although i hear its the solver i should try.
As i read through the help, i see that there should be special conditions i should take care of when meshing since the solver include geometric multigrid algorithm somewhere. Can somebody tell me how to prepare a mesh suitable for geometric multigrid in large 3D problems easily?
I attach my mock comsol 4.3 mph file, is such meshing adequate for the geometric multigrid algorithm?

I may have completely misdiagnosed the bug in my calculation, i hope somebody would be willing to tell me that if its so.

Many thanks in advance
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Electromagnetic field simulation

September 19, 2012, 1:05 am
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Hello! Please help me with electromagnetic field simulation. I appriciate any help! I have two wires, the first one is active, the second one is passive. I need to reserch the influence of the active wire to the passive one.

What I do:
1. Select 3D-AC/DC mode-Magnetic and Electric Fields- Stationary
2. Create two cylinders (copper) in the block (air)
3. Select Surface Current for the active wire and Perfect Magnetic Conductor for the passive wire

The difficulties:
1. I am not sure that I have selected the necessary mode
2. I need to start up the alterning current in the active wire (sin). How can I do that?
3. There is the Magnetic Insulation property in Magnetic and Electric Fields mode. Where can I use it? For what figgure?

That you very much in advance!
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mislabeling of periodic boundary conditions with changing geometry

September 19, 2012, 4:38 am
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Hi

Problem:

I have a unit cell of a periodic lattice structure. The unit cell has Floquet periodic boundary conditions [PBC], and I am doing a parametric sweep of the geometry features of the basis (the unit cell area doesn't change). The problem is that when the geometry changes become large enough, for example when a feature cross the unit cell boundary on the left it would then appear on the right to preserve the symmetry. But this obviously changes the numbering of the PBCs, and it is not practical to manually select those boundaries for each step in the geometry sweep. Anyone encountered such a problem?

thanks,
Chris
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Can I disable or delete the boundary zero flux subnode?

September 19, 2012, 6:45 am
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I am solving for the magnetic field (g) inside a resonating microwave cavity using mathematical module physics. I use a coefficient form PDE of the Helmholtz equation inside the domain and a boundary weak contribution to specify the tangential boundary condition while letting the normal component of g be a free parameter. A default boundary zero flux subnode is constraining the normal derivative to zero which is incorrect. I can't disable or delete the subnode and I would need to specify either Dirichlet or Neumann boundary conditions for the normal component of g if I was to override the zero flux condition, which I don't know.

I have already tried the RF module with boundary weak contribution to solve for E, but a similar problem occurs where a default boundary perfect electric conductor subnode is incorrect and can't be overridden by the boundary weak contribution.
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Comsol 4.2a, RF MODULE, PML

September 19, 2012, 8:38 am
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Dear All,


I have question about this module which I uploaded.

Medium is air, substrate is glass, and I want to put some dipole on that glass. My question is about PML.

As I know, I should put always same material PML and adjoining medium becuase of the discontinuity in refractive indices.

But what to do with this configuration which I uploaded?

It is easy to set up one half of PML is medium, one half is substrate, but what will happened between two halves of the PML ? Does any of you done these simulations? Is there some strong influence of that on results??


Thank you for any answer.
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HOW TO OPTIMIZE DISPERSION OF AN ACOUSTIC HORN MODEL IN 3D

September 19, 2012, 11:00 am
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I was able perform a simulation based model 2d using as reference the file in the list of tutorials (horn shape optimization), but I can not do this on a model imported from solidoworks in 3d.
My horn is not symmetrical, so I can not use simulation in 2d.
Is there a more specific study for my need?
How should I proceed?
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Mesh Data Format

September 19, 2012, 11:59 am
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Hi,

I have a 3D object that I'm trying to mesh. I exported the mesh data file and tried to understand its contents and ran into some issues.

How are the geometric entity indices related to the mesh point coordinates? I also don't understand what the number of parameter values per element are.

Also, there are 2 listings for geometric indices, I'm assuming this is so because there are 2 types of elements in my mesh: tetrahedral and prisms. Is this assumption correct?

When the number of nodes per element is mentioned, does it refer to the the specific nodes that are interconnected?
I guess I'm having overall problems interpreting the mesh information. I'm attaching the file in case it might be useful .

Any help would be appreciated.
Thank you,
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field of maximum temperatures over all time steps

September 19, 2012, 2:11 pm
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Hello everybody,


how do I get the field of maximum temperatures over all time steps in a transient heat transfer simulation (Comsol 3.5)?

I am simulating a welding process using the heat transfer module. I can already visualize the geometry of the weld pool at any time of the process using the isosurface plot of the melting temperature. Nevertheless I am actually interested in knowing the final geometry of the weld seam, which is the sum of all points that have ever (= in any timestep) reached or exceeded melting temperature.

My best idea so far was to somehow calculate the "field of maximum temperatures over all time steps" and then again use the isosurface plot. However I couldn't find out how to get the maximum temperature at every point. Any suggestions how to do it? Is it possible at all?

In case you have another (perhaps more practical) idea how to get the geometry of the weld seam, please let me know as well.


Thanks for reading and for your help in advance!

Regards,
Johannes
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Meshing_Error

September 19, 2012, 11:00 pm
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Hello everyone,
First of all I would to great everyone who help this forum working and your incredible support. Well, I am working on heat exchanger simulation here in Comsol and since I got error concerning meshing:

Domain: Failed to generate mesh for domain

Boundary: Specified element size is too large to resolve the geometry
Face is much smaller than the specified minimum element size

Please in attached is the file I am working on, can anyone help me understanding or solve those occuring problems?
Any help is welcoming-

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A. Fopah Lele
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Variable modifications between solution iterations

May 3, 2011, 7:04 am
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I'm developing a transient model using the Livelink interface. The model first calculates an initial solution for the first time window, then I would like to modify the state variable values due to some external disturbance using MATLAB, then proceed to rerun the model for the next time window using the newly adjusted values of some of the variables, but the other variables should be retained from the previous solution iteration.

When I prescribe the use of the previous solution for subsequent iterations as:

model.sol('sol1').feature('v1').set('initmethod', 'sol');
model.sol('sol1').feature('v1').set('initsol', 'sol1');

it seems that the specification of initial conditions through either

model.variable('var15').set('X0', num2str(X0));

or

model.init('init4').set('position',num2str(X0));

are ignored completely and the unchanged values from the previous solution are retained. Is there a plausible method to effectively update some of the variables this way? Perhaps by modifying the dataset of the previous solution?

Thanks.
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Gravity effect

April 19, 2012, 9:03 am
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Hi,

Sorry for my newbie question. I'm trying to simulate 2D two-phase flow in porous media. I'm wondering whether COMSOL considers gravity effect when applying Two-Phase Darcy's Law physics.

Thank you,
Jiri
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Error message

July 2, 2012, 11:43 pm
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Hi.

When I have created my model, when I have computed it an error message has appeared.

The text was : "Failed to find consistent initial values.
Last time step is not converged."

Someone can help me to find a solution to this problem?

Thanks.
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Saving probe tables in a parametric study

August 1, 2012, 1:03 pm
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Hi,

I am using several probes to plot and also write the data to a table during solving. With the new version, since we have the option to save the table in the model and as a separate file as well, I am using that option. In this way, as the model is running, the probe data are being saved to a text file.

However, when I use parametric sweep in my analysis, as it finishes running for a parameter and switches to the next one, the former probe table file is overwritten. Is there a way to save each of these probe table data for different parameters in separate files?

Thanks.
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Tolga
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Iteration in COMSOL

September 14, 2012, 1:35 pm
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Hello,

I have a problem here. I want to use COMSOL for one of my problems. In this model, I want to find the viscosity and velocity in a geometry which I have both soil and water. So I should use Darcy's law. In this law velocity is dependent to viscosity. However, the viscosity which I need to find at the end is also dependent to Darcy's law velocity. Hence my fluid is non-Newtonian fluid.
When I add Darcy's law to my physics. It asked for fluid and matrix properties. For matrix properties I have no problems, but for fluid properties it asked for viscosity, which I should write in that spot a function of Darcy's law velocity ( f(darcy's law velocity) ). When I run this model the error is : ''circular variable dependency detected'. So I used the iterative solver instead of direct one. Still the same error. Can anyone please help me here. Can COMSOL solve this problem?

Thanks,

Negin

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