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Mikic elastic correlation error in thermal contact node

January 7, 2015, 11:12 am
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I keep getting an error when trying to model thermal contact.

Division by zero.
- Function: /
Failed to evaluate variable.
- Variable: comp1.ht.tc1.Econtact
- Defined as: ((down(comp1.ht.tc1.Eequ)*up(comp1.ht.tc1.Eequ))/(((1-(up(comp1.ht.tc1.nuequ)^2))*down(comp1.ht.tc1.Eequ))+(up(comp1.ht.tc1.Eequ)*(1-(down(comp1.ht.tc1.nuequ)^2)))))
Failed to evaluate expression.
- Expression: if(((comp1.ht.tc1.Tn==0)||(comp1.ht.tc1.Econtact==0)),0,((comp1.ht.tc1.Tn*1.4142135623730951)/(comp1.ht.tc1.m_asp*comp1.ht.tc1.Econtact)))
Failed to evaluate variable.
- Variable: comp1.ht.tc1.TnRel
- Defined as: if(((comp1.ht.tc1.Tn==0)||(comp1.ht.tc1.Econtact==0)),0,((comp1.ht.tc1.Tn*1.4142135623730951)/(comp1.ht.tc1.m_asp*comp1.ht.tc1.Econtact)))
Failed to evaluate operator Jacobian.
- Operator: if
- Geometry: geom1
- Boundary: 93
- Feature: Stationary Solver 1 (sol1/s1)

I don't see anything wrong with my inputs, though. I put in values for E and the Possion ratio for the Weighted Harmonic Mean, but it treats Eup and Edown as 0? I have no idea where to input those values. I would think it pulls the values from the material properties. In any case, what exactly is it that I am filling in when I put in the value for E and the Poisson ratio in that node?

The boundaries I'm defining are simple -- just a rectangle against another rectangle.
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limiting the maximum value of concentration

January 7, 2015, 3:23 pm
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Hello,

I am solving a 1D convection-diffusion equation using the Classical PDE set up. My equation has a source term. The left BC has a zero flux, while the right BC has a dirichlet condition of u = 0. Since the left BC has zero flux, the concentration u will increase with time due to the source term. How can I limit the concentration on the left boundary to a specified value so that as time increases, the concentration there is capped at the threshold?

Thanks.


Best wishes,

EH
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Ultrasonic Non Destructive Testing

January 7, 2015, 3:27 pm
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Hello Everyone,

It's about my graduate thesis, I ve been trying to make an analysis which is NDT. There is a specimen, transducer, and cylinder( for showing to cracks-voids)

I can't send a sound from transducer to specimen. That's why I can't see the result as a [db] and [f]

I'm so pleased whether anyone help me

thanks
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How to add a continuous pulse with a frequence from 25THz to 100THz?

January 7, 2015, 5:47 pm
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How to add a continuous pulse with a frequence from 25THz to 100THz in RF moudle? I want to let the pulse be a source to irradiate a structure,but i don't how to do it .I hope you can give me a hand.Thank you very much.
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Phase Change + Flow

May 8, 2011, 6:48 am
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Dear All,

I need to simulate a tank filled with Phase Change Material that is heated by circulating hot water through a pipe inside it.
I am using COMSOL 4.1. What kind of physics would you recommend me to use?

Thank you!
Paul
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Parallel Computing with MATLAB Livelink and COMSOL

July 20, 2013, 8:37 am
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Hi everyone,
I am currently trying to use Matlab's Global Optimization tool (specifically using genetic algorithms) with my function. Every time my function evaluates, it loads a model file, modifies some parameters in it, does the calculation and sends it back to the Matlab program. In order to speed up this process, I intend to parallelize my code. The Matlab part of this is easy, as I simply have to start a pool of MATLAB workers and turn the parallelization option in the optimization tool. However, for the COMSOL part, I think that I need an independent COMSOL server for every worker/core. How does one go about doing this?

I have tried the solution outlined in this thread (www.comsol.com/community/forums/general/thread/33446/). Specifically what I tried to do was write the following code to initialize multiple COMSOL servers:

matlabpool open 3
comsolPort = 2036;
system( ['comsol -np 1 server -silent -port ' num2str(comsolPort) ' &'] );
pause( 6 )

comsolPort = 2037;
system( ['comsol -np 1 server -silent -port ' num2str(comsolPort) ' &'] );
pause( 6 )

comsolPort = 2038;
system( ['comsol -np 1 server -silent -port ' num2str(comsolPort) ' &'] );
pause( 6 )

Then after this I start the Matlab genetic algorithm, which calls upon my function.

Within my function, I add an mphstart(portno), with the portno depending on the MATLAB worker ID.

What happens when I run this code is that at first three COMSOL servers seem to come up (with three splash screens etc.). Initially each worker seems to be able to start accessing the model. However after a few seconds (while the workers are modifying the model) the COMSOL servers shut down and only one worker is left doing its job. What is the cause of this? Is it that COMSOL doesn't allow more than one server operating?

On the other hand, when I tried to make all workers simply connect to the same COMSOL server, a "java.lang.NullPointerException" occurs, which led me to believe that I need three independent servers.

If anyone has any pointers on how to execute this task (running a parallel operation on MATLAB livelink where each worker has access to a COMSOL server, or perhaps do this without needing multiple COMSOL servers), that would be great!

Thanks in advance for any help given.
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compilation error

March 19, 2014, 8:49 am
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Hi,

I ran a conjugate gradient model for determine temperature distribution (time domain). Then I added a structural analysis model (steady state) with last solution from conjugate gradient as input (with deselecting fluid from the analysis). However, I get the following error:

"No sequence specified
Error in multiphysis compilation."

I would appreciate if any one can point me to a potential solution.

Regards,
Susant
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Modeling Fsi physics with viscoelastic material and low-Re-K-epsilon turbulence model

January 4, 2015, 11:04 am
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I am trying to model fsi physics. For fluid part, "low-Re K-epsilon" turbulence model is proper in this case and for solid mechanic part linear viscoelastic model must be chosen.
unfortunately, I encounter an error message "duplicate parameter/variable name"! it refers to auxiliary wall distance and instantaneous shear modulus which is "fsi.G0".
is there any way to solve this problem?

Thank You,
--
SY
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From modal participation factor to modal mass

January 8, 2015, 12:57 am
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Hi everyone,

I read all the posts about Modal Participation Factor. I understood that for one direction the sum of all the MPF will give us the total mass thanks Ivar.
The fact is that I'd like to get the modal mass for one mode and can't manage to do it. I mean, how from the 3 MPF (MPF_u, MPF_v & MPF_w) for one mode I can get the effective (modal) mass for this mode?
I don't know if it's really clear, I can precise my question if necessary.

Thank you to everyone who could help me,

Jean
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A contact model with exceptional force related to the distance

January 8, 2015, 2:54 am
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Hello, everyone. I'm a new user of COMSOL. I want to bulid a contact model with Structural Mechanics Module that the hemisphere contacts a flat plane. The contact pair is used between the spherical surface and the plane. However, I want to add another exceptional force between two surfaces. This force is a kind of surface force existing on the non-contact area next to the contact area. The interactional surface force is proportional to the distance between the calculated point on the spherical surface and the corresponding point on the plane with same values in X and Y axis. The force exists when the distance is close enough. The value of this force on the spherical surface is different due to the different distance to the plane. On the other hand, the flat plane is going to deform elastically so that the distance is a variation in the calculation. I sincerely want to ask how could I exert this force on my model. This would be great helpful to my work.
Thank you!!
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Charge accumulation

January 8, 2015, 3:13 am
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Hello,

We want to simulate charge accumulation on a surface. The surface has a penetrating electric field on in and there is a non trivial charge density outside the surface. As the charges accumulate on the surface they will change the electric field until the field becomes parallel to the surface at which point charge accumulation should stop.

But how to do this?

We would be grateful for any hits how to proceed. Also if there is a existing COMSOL model that can do this or something similar.

Thank you in advance.
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resume parametric sweep from crash

January 8, 2015, 10:40 am
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I'm running some big simulation with parametric sweep. Before the crash, a portion of the sweep is completed, how do i resume the parametric sweep instead of restarting it after the crash? If i press f8, the sweep just start over...
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Magnetic Flux Function

January 8, 2015, 11:27 am
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Hello,

I'm working with the magnetic fields, no currents module to create an axially symmetric model. I'm verifying past work done by a colleague. He used another program to plot the flux function of the model (see attached image).

Does Comsol have similar functionality? I have modelled the same item, but I only seem able to plot the flux density, not the flux function (see second attached). Ideally I would like the two attached images to match fairly closely.

My understanding is that the flux function, Phi, is a function of the flux density, B:
Phi = Integral( B dA)

Any help is greatly appreciated!

Thanks,
Chris
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COMSOL error

January 8, 2015, 1:42 pm
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Hi,

When I do the coupling calculation for laminar flow module and transport and diluted species module (concentration), it always shows an error:

Undefined value found.
- Detail: Undefined value found in the stiffness matrix.
There are 11 equations giving NaN/Inf in the matrix rows for the variable comp1.c.
at coordinates: (-0.00124375,0.00168601), (-0.00124375,0.00168501), (-0.00124375,0.00168401), (-0.00124375,0.00168301), (-0.00124375,0.00168201), ...
and similarly for the degrees of freedom, NaN/Inf in the matrix columns.

Do you know what it is? How to avoid this happen?

Thanks,

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random function

January 8, 2015, 8:11 pm
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I want to disperse 300 ellipses randomly oriented in a rectangle. Is it possible to do this in comsol?
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Particle tracing module for 1D problem

January 8, 2015, 8:16 pm
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Hi everyone,
I am trying to use the particle tracing for 1D problem, but the manual of particle tracing says that the module is applicable for 2D and 3D problem.

Is it possible to deal with 1D problem in comsol? thanks!
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Cut point 3D

January 8, 2015, 10:47 pm
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Hi,

Simple question: my model is 3D, and I defined 5 points inside the results-Data Sets sections in order to evaluate them.
But how can I be sure that the points that I defined are located inside my geometry?
with visualization is not possible to understand for me.
Attached my model

Any answers will be appreciated, and many thanks in advance.
Best
Sepideh
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comsol 4.0 how to have unequal scaling on different axes

June 9, 2010, 1:52 am
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In comsol 3.5a, i could selected under
options->axes/grid settings the option that the axes not be equal.

I have problems where dimension along one of the axis are microns while along the other axes they are cm.
in 3.5a after unticking axes equal, I could use the zoom extents tool to display my results so that the short dimension could be expanded to fill the screen.

I am struggling with 4.0 now. In geometry (model builder) such a possibility exists.
I have not been able to find this possibility once I have results.
When I extrude a 2D object 5 microns in the z direction to get a 3D object from a 2D drawing made in a working plane, I do not know how to view that.
It is also a necessity to be able to define correctly some of my boundaries.

It is also necessary to be able to view the results!!!

I do not understand where this possibility is hidden. I am not sure it even exists.
if not, please include this ASAP.

Can someone help??
Thanks


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Coefficient Form PDE and periodic boundary conditions

August 2, 2011, 6:08 pm
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Hi,

I'm new to COMSOL so I would like some help regarding the following -

I'm trying to perform a phononic crystal simulation using coefficient form pde. I have a hexagon with a circular hole shape removed - this is my geometry.

I want to apply a zero flux boundary condition at the circular shape and periodic boundary conditions at opposing edges of the hexagon.

So I end up using 3 periodic boundary conditions, for the 3 pairs of opposing sides of the hexagon. Unfortunately COMSOL sets up zero flux boundary conditions by default on all the boundaries and I don't see how I can remove this boundary condition on the hexagon's edges on which I only want the periodic boundary conditions.

Any help would be greatly appreciated!

Kartiek.
I'm using COMSOL 4.0a
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Variable defining/refering

August 28, 2011, 5:24 am
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I am going through some of available examples of models and and I have some difficulty understanding syntax of certain variables' references such as tpf.G0i, chds.ndflux_c, chns.G0i, nitf.rho or chns.Vf2. The bit before dot is obvious (physics ID), but how do you identify the part after it?
I went through the part of manual on variables (from COMSOL Multi. User Guide) but somehow it did not clarify it. For instance in one place I found what ndflux is (Normal conductive heat flux), but what does it mean with _c at the end? Or where does rho come from (no such variable appears in the model, only symbolic). Same for G0i or Vf2.

I know what some of you may think right now (RTFM), but I kindly ask for a more specific answer. Actually the relevant part of manual would be nice, but one that actually DOES mention such construction and variables above.

Thank you,
Mike
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