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Undefined value found.

February 5, 2013, 5:27 pm
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I am using poroelasticity module to simulate soil behavior of porous materials, the error information is as follows:

Undefined value found.
- Detail: Undefined value found in the stiffness matrix.
There are 892 equations giving NaN/Inf in the matrix rows for the variable mod1.poro.pw.
at coordinates: (0,0), (0,0.00192308), (0.00125682,0.00130079), (0.00192308,0), (0,0.00384615), ...
There are 3437 equations giving NaN/Inf in the matrix rows for the variable mod1.u.
at coordinates: (0,0), (0,0.000961538), (0,0.00192308), (0.000628409,0.00161194), (0.00125682,0.00130079), ...
There are 3437 equations giving NaN/Inf in the matrix rows for the variable mod1.w.
at coordinates: (0,0), (0,0.000961538), (0,0.00192308), (0.000628409,0.00161194), (0.00125682,0.00130079), ...
and similarly for the degrees of freedom, NaN/Inf in the matrix columns.

Anyone can tell me how should I cope with this error? from what kind of aspects? thanks
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COMSOL Error Message

February 6, 2013, 5:26 am
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Hi

I've been problems with COMSOL in Plasma Module

The following feature has encountered a problem:

"The source selection for the operator intpot1 must be nonempty. Error in multiphysics compilation.
- Feature: Compile Equation : Time Dependent (Sol1/st1)
- Error: The source selection for the operator intpot1 must be nonempty"

Would you mind to help me?

Thanks you very much

Natthawut
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Setting temperature initial condition at specific location

February 6, 2013, 7:53 am
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Hello,

I'm trying to solve a porous media heat transfer problem. the geometry of the problem includes 10/200 meters rectangle, where I'm setting a linear temperature gradient by the following equation:

T=((10[m]-y)/10[m])*100 [K]+293.15[K]

which works fine, next I need to set at the middle node of the rectangle (at location x=100, y=5) a temperature perturbation different from the value imposed by the equation.

How do I do that?

I Hope I'm explaining myself well.

Best Regards
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Why COMSOL still requires the Young's modulus and Poisson ratio when defining an anisotropic material?

February 6, 2013, 8:31 am
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Hi all,

I want to play with Comsol for 3D simulations of linear elastic material. The materials are anisotropic so that I define elasticity matrices for them. But Comsol still requires me to give values for the Young's modulus and Poisson ratio (there is the little "stop" red sign in front of these properties). Why is that?

Thanks
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How to use Laminar Flow Pressure results in Solid Mechanics, help?

February 6, 2013, 10:29 am
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Hi,
I need to use as an input in the Solid Mecanic module the Pressure results from Laminar Flow calculations. Can anyone explain me how to do this?

thank you for yor answer.

Best regards,
Leonardo.
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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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Particle Data Extraction

February 6, 2013, 12:34 pm
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Hi there,

I made a simulation of an electro-kinetic flow within a 2-phase medium, and after computing the currents I wanted to see how particles would behave within the geometry and the resulting fields. I all looked all-right, but what I really need, is a way to extract the particle properties, i.e. for individual particles I want to be able to plot the velocity and the position, as I need to compute the tortuosity.

I tried a great many combinations regarding 1D-plots of individual particles, all of which failed. As a matter of fact everything which one could select from the Charged Particle list failed to result in a plot (besides the global quantities, such as mass and charge, which are steady over the entire domain/time/etc).
I also tried pulling them into Matlab, which again resulted in an errors (of the same kind as the ones in the 1D-plot attempts).

Here is how I tried to extract the data:

q=mpheval(M,{'qx'},'dataset','dset2','complexfun','off','selection','sel1','t',t_list(1:2));

Error using com.comsol.model.impl.NumericalFeatureImpl/getData
Java exception occurred:
Exception:
com.comsol.nativejni.FlNativeException: Failed to evaluate expression
(rethrown as com.comsol.util.exceptions.FlException)
Messages:
Failed to evaluate expression

Undefined post expression

Failed to evaluate variable
- Variable: mod1.qx
- Geometry: 1
- Domain: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Failed to evaluate expression
- Expression: real((999999999.99999988*mod1.qx))

Failed to evaluate expression
- Expression: real(9.999999999999999E8*mod1.qx)

Thanks,
Dan.
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How to solve the problem"Attempt to evaluate non-integral power of negative number. Function: ^"

February 6, 2013, 2:56 pm
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Hello,

I am solving a Drift diffusion model for plasma using general form PDE. However, I am facing the following error,

Failed to find consistent initial values.
Attempt to evaluate non-integral power of negative number.
Function: ^
Failed to evaluate variable.
Variable: mod1.uth, Defined as: (((mod1.Te*(k B const*8))/(pi*mod1.me))^0.5)
Failed to evaluate expression.
Expression: d((0.5*mod1.uth*mod1.u*test(mod1.u))*(dvol),{test0})
Last time step is not converged.


Here, Te= (2/3)*(n/ne)
n, ne is the dependent variables for the problem and their initial ratio is 3. So it is positive. And also k_B_const is Boltzman constant is a constant, me is the mass of electron also a positive quantity.

Can you tell me why it happens?

Thanks is advance.

Rajib
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Pressure in Reacting Flow in Porous Media

February 6, 2013, 4:49 pm
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Hello All,

I am running a model in 4.3a with the node "Reacting Flow in Porous Media," and simulating groundwater flow in a confined aquifer. When I look at the results, my average pressure gets down to -10000 Pa. Does anyone know what exactly that P is representing? The pressure of the domain material (bedrock)? Or pore pressure? Or the pressure of the water in the pore space? I set the boundary conditions by velocity of flow. Also, the pressure changes when I change the concentration of my reacting species...
Any help would be much appreciated!

Cheers,
Kelley
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Cloth or flag modeling

February 6, 2013, 8:26 pm
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Hi all,

Does anybody have a COMSOL model that simulates a cloth on a table or a flag moving under a wind flow?

Cheers,

SL
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Parallel computing MatLab Comsol

December 5, 2012, 11:24 pm
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Hi,

I am using Comsol 4.3 with Livelink for Matlab. I run an optimization code in Matlab where i call Comsol to perform frequency response simulations. Now i would like to start two parallel frequency response simulations that are independent of each other from my Matlab code.
My approach so far has been to open another Matlab worker by using matlabpool and parfor. However, only one of the Matlab workers are then connected to Comsol. Is it possible to perform parallel computing in Comsol when using the Matlab livelink?

//Anders

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Automatic remeshing depending upon the gradient of the solution

February 4, 2013, 4:00 am
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Hello, everyone,
I am solving a nonlinear equation on the plane. Its solution, u=u(x,y) is everywhere close to zero except for some region in the vicinity of the coordinate origin. This region is not necessarily small. Within this region u(x,y) is almost everywhere close to a constant, say, 1. The object of interest is the transition region, its cross-section representing a kink. The problem consists of finding its configuration and thickness.

My difficulty is that the size, L, of the whole region, where u is close to 1, is much larger that the width, d, of the kink. L/d is about few hundreds and may reach 1000 in some cases.

The problem requires, therefore, to use a mesh which is coarse away from the kink, but is at least about 100 times finer in its close vicinity.

I have no idea of how to achieve that. Please take into account that a priori the contour of the kink region is unknown. It can only be established by solving the equation. I tried to solve the equation first on the coarse mesh, and then to apply the Refine Mesh option to the region where the coarse solution exhibits the kink, but it did not work when I fixed the factor of refinement to 10 (let along 100). Besides, this approach is very time-consuming.

Is there a way to instruct Comsol to adaptively vary the mesh size in the course of solving, the variations being dependent upon the gradient of the function u?

Is it possible in to instruct it to decrease the mesh size about 100 times in such an approach? If 100 times is too much, what would be the limitation?

Thank you.
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How to determine face numbers (using matlab livelink) associated with an object

February 5, 2013, 7:39 pm
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Hello again,

I am trying to 'automatically' set my boundary conditions for a model generated in matlab with livelink. I know which objects need to have which boundary conditions based on a draw order that I specify but I don't know how to get COMSOL to tell me which boundaries (i.e. face numbers) are associated with which object. I can get a list of face numbers associated with objects by the following (which another user has kindly posted elsewhere on this forum):

upDown = model.geom('geom1').getUpDown;
domain = cell(1,max(upDown(:))+1);
for i = 1:length(upDown)
domain{upDown(1,i)+1}=[domain{upDown(1,i)+1},i];
domain{upDown(2,i)+1}=[domain{upDown(2,i)+1},i];
end

but I don't understand how to link the resulting lists of elements with their associated object since they aren't listed according to draw order.
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Parameterise the position in a text file?

February 7, 2013, 4:40 am
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Hello,

I want to use the 2D distribution of the relative permeability of a nonlinear calculation in a linear calculation of the same Model with same parameters etc.

For that I export the data of the relative Permeability, depending on my Parameter (Parametric Sweep) and the coordinates x and y (See attached file "Forum 2.png").

This text file is being imported into the linear model with an interpolation function and the source is set to "file" with 2 arguments!

It is possible to write every single "Position in File" per Hand, but since I want to use ca. 100 Parameter values, this would just take too long.

However, if I want to choose a parameter for the "Position in file" (same parameter as my Parametric Sweep parameter), COMSOL only allows positive integers (See attached File "Forum 1.png")

Do you guys have any tips?


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Continuing Modeling Issues with 2D & 3D piezoelectric SAW model

February 7, 2013, 6:22 am
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Hello all,
I’m in desperate need of help with my model. The initial model setup is a 2D cross-sectional SAW device where I have silicon, a metallic electrode as my ground, a buffer layer, a piezoelectric layer (PZT-5), and gold electrodes. The current physics I have defined is with piezoelectric devices (with COMSOL version 4.2.0) with the silicon and buffer/protective layer (SrTiO3) as my linear elastic material model, the metallic electrodes and metallic layer as my electrical material layer, and piezoelectric material model with the PZT. I have defined parameters most of the materials in terms of elastic matrix D, Young’s Modulus, Bulk modulus, permittivity, and so forth. My main issue is when I run a frequency domain analysis; I consistently get the error of:
Failed to find a solution for the initial parameter. Singular matrix. There are 3906 void equations (empty rows in matrix) for…etc.
I have looked through the discussion forum consistently to see why I continue to get the errors I received and I thought it was simply a matter of fixing my boundary conditions but I thought I had accounted for all constraints for this simplified model. I do not know at this point where I have been going wrong for the past couple of months now. I’m attaching the current model. Any suggestions or comments would be greatly appreciated. Thank you.


--
Sarah
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Problem with 3D PDE thin layer mesh

February 7, 2013, 8:46 am
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Hi everyone

I encountered a problem with meshing a thin layer(~10e-6m) with 3D PDE model. I am not sure how to mesh such thin layer. Has anyone managed to mesh a similar case?

Looking forward to your reply.
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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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"Hinge assembly" problem

February 7, 2013, 9:00 pm
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While going through the solved model 'hinge assembly' given in the COMSOL,
I came across some difficulties. Actually, I have to develop a solid model
involving hinge joint similar to what is provided in the aforementioned
example. However, I could not understand few terminologies used in the
model.

Under solid mechanics (in the model builder of the model) two global
constraints have been defined; under which in the constraint expression
it is written as "mod1.solid.b_rig2-mod1.solid.b_rig3". I did not get
any explanation of each of these terms. Because of these two I am
unable to implement similar hinge connections as well.

The model can be found in Model library> Structural mechanics> Connectors and Mechanisms> Hing Assembly.

Can anyone please help?

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How to assign a defined function to an electrode????

February 7, 2013, 9:03 pm
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Hello Friends,
Am working on AC/DC Module and new to comsol. Am trying to define a rectangular pulse of 1200v with a duration of 1ns to an electrode and i wish your kind assistance for the same.

Thanks in advance.
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Which Lithium on battery is used in Lithium ion isothermal 1D comsol model

February 7, 2013, 10:50 pm
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Who is the manufacturer? which model ? anyboby knows?
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