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Contact model

March 22, 2016, 1:28 pm
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Hi,

I'm new to COMSOL and would like to model a sphere in elastic material surrounding by a layer in viscoelastic material, that is pushed inside a deformable cavity. To link my sphere with the layer, what is the best to do ? A rigid connector ? What is the difference with an attachment ?
Another question is to model the contact between the sphere and the cavity. Do I have to create a contact pair ?
Thanks in advance,
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Internal error in geometry decomposition.

March 22, 2016, 2:20 pm
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Dear all,

I recently experienced quite some trouble building my geometries when they involved structures build from parametric curves. I saw a quite a bunch of related posts here and wanted to ask whether there is now some solution to it.

The error usually happens when a structure from a parametric curve (converted to solid and then extruded) is going to be combined with another object by any kind of boolean or partition operation.

The error messages that are produced look like: "Detail: Could not trace curve"
or: "Detail: Error in parameter domain topological analysis."

I attached an example file for the latter one.

So, any hints are welcome. Thank you.

Best wishes,
Hannes
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Acoustic Band Structure in 2d

September 28, 2009, 3:51 pm
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Hi Folks - Ive posted a couple of questions to some related discussion but it looks like they haven't been visited in a while so I thought I would make a new discussion group.

I am interested in finding out whether or not it is possible to calculate acoustic band structures using a reciprocal lattice simulation and periodic boundary conditions. I understand this is typically done by solving for eigan solutions to the helmholtz equation as you vary the direction of the plane wave vector. My question is... while performing an eigan value analysis and say, computing 100 eigan values in the vicinity of the stop band, how does one back out the wave vector direction related to the given eigan values

Thanks

Sean
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Interpolation Function Help

July 18, 2011, 10:33 am
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Good Morning,

I'm having trouble using COMSOL's interpolation function, and I was hoping someone might be able to help. I'm trying to load data from a tab-delimited text file. I've followed the instructions in the COMSOL user guide on interpolation functions, however I get the following error when I click "plot":

"Internal error in mesh initialization.
-Plot: previewplot1 (Surface)
-Function: int1"

Additionally, when I try to solve the model I get the following error message:

"-Feature: Compile Equations: Stationary (sol1/st1)
-Error: Internal error in mesh initialization."

When I disable the interpolation function, COMSOL successfully solves the model.

The input data used for the interpolation function was a velocity distribution exported from a previous solution surface. It has the following structure:

% x y z myfun1
0.005164328 0.094835672 0.2 0.098519135
0.015894103 0.087647192 0.2 0.511590803
0.015569986 0.095339275 0.2 0.22689919
0.006197193 0.083275657 0.2 0.312314232
0.005469283 0.016082383 0.2 0.2672031
0.004733427 0.004733427 0.2 0.081290304
0.012546053 0.01240331 0.2 0.43510989
0.015707096 0.004896326 0.2 0.232560416
0.027164381 0.094602393 0.2 0.368319369
etc.

A very simple flow model demonstrating the problem is attached, along with an excel version of the data I'm using. I'm a new COMSOL user, and any advice would be greatly appreciated.

Thank You!
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Urgent research problem: How to solve PDE systems( 2 PDEs 2 unknown u1,u2 coupled in 2 PDEs) in Comsol 4.0????

March 14, 2012, 8:45 pm
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1.Each PDE is composed of u1,u2.
How to set up the coupling process?

2. The spatial dependence for this problem can be reduced to 1D. du/dx
But it is a 2D rectangle.
The laplcian operator will also consider another dimension(du/dx+du/dy).
We want y dependency vanished.
How to deal with this issue?

THANK YOU VERY MUCH to get a little help.

Best Regards
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reservoir modelling with two phase linear poroelasticity

March 2, 2016, 5:48 am
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Hi everyone,
I have a question: is it possible to create a two-phase reservoir model in Comsol by using Subsurface flow Module (Poroelasticity)?

Thank you all

Giulia
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Moment diagram along a 3D beam

March 19, 2016, 4:11 pm
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Hi,
I am new to COMSOL and having problem with extracting moment diagram from a 3D cantilever beam under various loads. I have applied loads and moments at the free end of the beam and defined the plastic properties of the material used in the model. Accordingly, I do not want to calculate the resultant moments by using the structural analysis formula ( F*d=M), but I was hoping COMSOL could calculate the resultant moment at each section of the beam and present the moment diagram along the beam length as a result.
I have used the "probe" feature for this matter and been unsuccessful (Probe gives the reaction moment of just one section).
Any help is appreciated.
Thank you
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How can I modify equations of a built-in physics model ?

March 21, 2016, 11:31 am
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Hello,

I am working on a piezoelectric device and I would like COMSOL to take into account the electrostrictive effect.
I know that it's possible to build your own physics but here I just need to add a single term to one equation.
So I'm looking for an option in a menu, or a .mphphb file that I could modify; but so far I haven't found it.

Do I need to rebuild the Solid mechanics physics? Can I add an equation that override the one COMSOL currently using ?

I really appreciate any help you can provide.

Thank you,

Pierre
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Self-consistent Schrödinger-Poisson - Comsol

March 23, 2016, 8:04 am
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Hello,
my question is how I can coupled two equations PDEs (schrodinger-poisson) such as the 1st equation depends on two variable ( u1 and V) or V is a variable in the 2nd equation (poisson).
thank you
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Constraint force -Aeroacoustics Structure Boundary-

March 23, 2016, 1:11 pm
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I'm trying to calculate the fluid-structure coupling analysis.


The question:

The constraint of Aeroacoustics-Structure Boundary is i*omega*u-v, where u is the displacement in solid and v is the velocity in fluid.
But, the constraint force is test(u+v).

Why the constraint force is not test(i*omega*u-v)?
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Integrate an Isosurface

March 23, 2016, 1:54 pm
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Hello,

I am wondering if there is any way to find the area of an isosurface, or integrate a function over such a surface.

For example, if I am working with electrostatics, is there a way to check the area of the surface where es.V is equal to 100 V?

One technique I can think of would be to actually perform a volume integral of the divergence of a vector field over the volume enclosed by the surface. I can integrate over the right domain using boolean functions, and if the vector field were chosen to be orthogonal to the surface of interest, the desired area would follow by Stoke's Theorem. However, I suspect the divergence calculation would be very noisy and not yield a nice result.

I've done similar things in MATLAB, and there I found that a much more accurate technique was to export the graphics data from a plotted isosurface and sum up the areas of the tiny triangles composing the surface individually. I know I can plot and color isosurfaces in COMSOL, so could I get the area this way somehow?
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Problems with High Mach Number laminar flow

August 9, 2012, 12:52 pm
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Hi,

My case is not so common for an application of hmnf that I have not been able to make it work. The main idea consists on modeling the flow physics of an electric arc by considering the arc channel heat as the main energy source for the surrounding gas, using a 2D-axisymmetry model. This gas at the same time will start moving inside an enclosed volume creating shockwaves that will reach the container walls several microsec. after the energy stimulus has been already applied to the one of the solid electrodes in less than 1us.

The problem I've facing is that the simulation does not start and I get the following error message:

Attempt to evaluate real square root of negative number.
- Function: sqrt

I've tried to simplify my model so the initial condition of temperature and pressure (6kK and 0.6MPa at the geometry axis, decreasing to 293K and 0.1MPa within the 0.5mm from the axis) IS the ONLY energy input to the model, on the gas volume (cylinder of r=4mm height=6mm). The materials properties used (copper-electrodes, nitrogen-gas) are mainly constant, avoiding problems with those that might not function for temperatures >1.5kK.

I would really appreciate any comment or suggestion.

Thanks.
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parametric sweep

April 5, 2013, 5:22 am
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hi,
can we use geometry parameter like (length, width, height) in parametric sweep, i want to see how the output changes with variation in geometry
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Using matlab function in comsol model

December 14, 2015, 7:05 am
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Hi. I do need help with using m-function in comsol 5.1. after all procedures decribed in tutorials(define function, adding path to m-function i need) comsol cant open matlab even to plot function. comsol shows error:
Can not start Matlab
- Library: csmatlab.dll
Error in multiphysics compilation.
I do sth wrong?
Could sbd who has expirience in such a problems explain where mistake is and what sequence of actions should i execute to succeed.
P.S. I dont need Comsol_with_matlab to use external m-function just to transform some results from comsol, do i?
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Custom Linear Solver

March 17, 2016, 5:24 am
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Hi,
I'm wondering whether it is possible to use custom linear solver for my model on comsol.
For example, can I use my original solver implementation instead of MUMPS or PARDISO at Study ->Solver configuration -> Solution -> Direct Solver -> Solver?
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Relative tolerance vs Relative Error

March 18, 2016, 12:19 am
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Hi all,

having read many relevant threads and also searched in the comsol manual , i still dont understand the difference (if there is indeed some) between relative error and relative tolerance.

for example:
1)in this thread (also in manual)
www.comsol.com/community/forums/general/thread/13157

''The Relative tolerance value is the relative error tolerance that the ODE solver uses.''
''Use the Relative tolerance edit field to enter a positive number. This number controls how accurately the nonlinear system of equations is solved in each time step. In general, the desired relative error in the solution should be entered here.''

2)in comsol manual
''The software stops the iterations when the relative tolerance exceeds the relative error computed as the weighted Euclidean norm''
suggesting a difference

i need some clarification
V4.4

Thanks in advance
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AC current simulation

March 23, 2016, 8:28 pm
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Dear COMSOL community,
I am kind of new to COMSOL and I am building a Lorentz force based MEMS sensor. Basically the current passing through an Aluminum wire on top of the cantilever will interact with the magnetic field from the permanent magnet thus causing the cantilever to deflect accordingly. I manged to simulate it but currently i am using DC current (using single turn coil and terminals) and didn't got any deflection so i think that i should use AC current with a frequency equals to the resonance frequency of the cantilever, could anyone please tell me how i can simulate this ? I already got the eigenfrequencies from another study so i know the resonance frequency. I just need to simulate the AC current now. By the way , i am using stationary study now, should i use frequency domain ?

Looking forward to your answers and discussions,
Best Regards,
Amal
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How can I implement an incremental constitutive model with external material

March 23, 2016, 9:22 pm
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Hi, I want to implement an incremental constitutive model such as dσ=E(σ,α)dε, σ,ε,α are vectors and E is tensor with external material. dε can be calculated by increment of independent variable u. So, how can I get the increment of independent variable in iteration step and how can I build the incremental constitutive model? Thank you very much.
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Level set/Phase field with mass addition

March 23, 2016, 9:35 pm
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Hello all,

I am trying to combine the level set/phase field method with mass addition, but I couldn't find a way to implement it. I saw that the level set/phase field examples in gallery basically follow mass conservation, but I wonder how could I apply boundary shape change at the same time? I've tried to add a moving mesh or deformed geometry module, but failed to evaluate. Anyone could share your experience?

Thanks a lot in advance!
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Global equation expected unit

March 23, 2016, 9:57 pm
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Hi guys,

I'm using a global equation to drive a prescribed mesh rotation.

The equation I'm using is for angular velocity. It has the form

ut = x (a long expression, with units of rad/s, as ut. all variables/parameters are correct, I've triple checked)

In global equations I have the following:

name: u (plane angle)

f(u,ut,utt): ut - x

initial value (u_0): rot_0 (parameter defining initial rotation

initial value (ut_0): 0

Dependent variable quantity: plane angle (rad)

Source term quantity: plane angle (rad)

The equation is in orange and the mouse-over tool-tip says "deduced unit is [1/s], expected is [1]"

Given that the equation is for the angular velocity, was does it not expect [1/s]? I can't see any syntax errors, and it seems logical to me that if the units of 'u' are [rad], then COMSOL knows that the units of 'ut' are [rad/s].

I've tried changing the dependent variable and source term units to angular velocity, but this doesn't help.

I feel like the solution is probably simple but I can't figure out how to fix it and the manual is no help at all. Any guidance welcome.
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