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3D contact Problem

March 24, 2016, 12:28 am
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Hi everyone,

I confronted with a tough problem about contact pairs. I attached my model below. The upside is a structure, the downside is the other structure. Both has semi-sphere roughness, At the beginning, the two semi-sphere just contact, no penetrate. With a downward pressure on the upside structure, the upside has great vertical displacement, resulting the large penetration. However, the software didn't alarm any warning or error. I used the identity pair for this contact. What's the reason for that?
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ALE technique to large deformation about mold blowing

March 24, 2016, 12:42 am
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Hi I am planning to use COMSOL for modeling MOLDBLOWING. This model has been described in the paper of Demonstration of 1 Million Q-Factor on Micro-glassblown Wineglass Resonators With Out-of-Plane Electrostatic Transduction . I want to know which physics do I select, and how to parameters do I set up. I am a new for COMSOL and I REALLY NEED YOU HELP , THANK YOU.
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Boundary conditions for electromagnetic waves

March 24, 2016, 6:35 am
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Dear comminity,

Can you help me with the following:

What should be the boundary conditions if my wave changes its polarisation during the propagation from linear to elyptically - polarised? I suppose ports will not work, because we should define the polarisation of the wave, but in my case it can vary.

I tried PML, but it doesn`t work properly.

So I have a linear - polarised plane wave that is propagating through anisotrpic medium and changes its polarisation to elyptic.

Thanks for help!


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How can I build a elasto-plastic constitutive model with external material model

March 24, 2016, 11:14 am
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Hi, I want to build a elasto-plastic model with external material model. However, there is no strain increment input within external material model. How can I carry out?
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3D vs. Axial 2D Symmetry

February 20, 2010, 10:24 pm
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Hello,

I want to find the magnetic field from a magnet that has the shape of a cylinder. Can I do this using 2D Axial Symmetry instead of 3D? If so, how? Does the Axial Symmetry just mean I only need to draw half of the cylinder, or can it be used to represent a 3D figure with ony 2 dimensions?

Thank you,
Kevin
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How to extract the stiffness Matrix for a certain element?

August 30, 2011, 5:21 pm
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Dear all,

Hi. I need to extract the stiffness Matrix for a certain element or node before assembling. The "mphmatrix" command gives me the results for whole geometry (After assembly). I wonder if there is any way for getting the matrix for certain elements? For example say that element number 2 or ... .

I appreciate your help,

Regards,
Masoud
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Time-Dependent initial solution violates specified initial conditions

March 24, 2016, 3:19 pm
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I am trying to build a dye-washout model (using Reacting Flow in Porous Media physics to predict the time-dependent concentration of a dilute species). I'm able to run simulations for varying lengths of time, but I'm having issues with my initial conditions.

I specify what the initial concentration of the dilute species should be with an Initial Values node, but when I run the time-dependent study the t0 concentration does not match what I specify. For example, I specify concentration should uniformly be 0.1 mol/m^3 at t=0, but instead the solution will show a non-uniform concentration distribution with an average ~5-50% lower than the Initial Values node indicates. The discrepancy from the specified initial concentration also changes with study length (i.e. ~5% error for study from t=0-0.1sec, ~50% error for study from t=0-10sec).

Am I specifying initial conditions incorrectly? Is there a way to strictly enforce initial conditions?
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no convergence

March 24, 2016, 6:33 pm
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Hello
I have problem, I am trying to simulate natural convection in air enclosure with hot pipes emended. I've tried many things to get convergence, but I failed. Can anyone help me in this issue???

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Torsion of a beam

March 25, 2016, 12:01 am
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Hi,

I would like to understand stress distribution of a twisted beam. One side boundary of a beam will be twisted by 360 deg (image is attached to better understand sample geometry).

My approach was very simple: made a box geometry, put materials properties, set fixed constraint (one side of the beam), applied boundary load (on the other side of the beam), created mesh, and computed. However, I encountered an error message (image attached).

Could you help me what I need to do more to do the simulation?

Thank you for your help.
Yoon
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Refining mesh leads to non-physical results

March 25, 2016, 12:16 am
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Hi, I'm new to COMSOL and am trying to do a relatively simple analysis of a sphere indenting into a cylindrical plane. I tweaked this model (www.comsol.com/model/cylinder-roller-contact-1431) and made it 2D axisymmetrical so it suited my model. I'm applying a point load to the top of the sphere and am trying to measure the maximum indentation depth. It runs with a coarse mesh (max element size ~10 nm) but any attempt to refine the mesh results in a non-physical result where the solver solves immediately on the first iteration and the sphere buries itself halfway through the plane.

I've attached the model I'm using if that helps.

I would just use the coarser mesh but I need a finer mesh if I am to publish the results because I need the highest accuracy possible. Any help is greatly appreciated! Thanks
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Filling a fluid

March 25, 2016, 5:24 am
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Hi, i'm a newer of COMSOL multiphysics.
I imported model from PRO/ENGINEER and i'd like to do Fluid-structure Interaction.
Because I made the model which have complicated shell, want to fill fluid in that model.
Fluid is sealed with the model, so I can't use cap face function.
Please explain me by stages.

Thank you very much.

Ji young

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calling variables by using tags

March 25, 2016, 7:09 am
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Hi everyone,
I'm trying to reproduce the COMSOL tutorial "Two phase flow in column" by using Richards' law physic interface instead of Darcy's law. I'm having problems in calling the variable kr (relative permeability). This variable is calculated by the physic interface. When I write dl.kr, the program gives me this error:

Undefined variable.
- Variable: kr
- Geometry: geom1
- Domain: 2
Failed to evaluate Jacobian of expression.
- Expression: dvol*(comp1.dl.v*comp1.dl.rho)
Failed to evaluate Jacobian of expression.
- Expression: (comp1.dl.rho*(comp1.dl.u*test(comp1.p_wx)+comp1.dl.v*test(comp1.p_wy)))*(dvol)

I've tried to write this variable in different ways, such as:
root.comp1.dl.kr
comp1.dl.kr

From the Subsurface flow module user guide it seems that these are correct. Anyway, it doesn't work.
Any idea of the problem?

Thank you
Giulia
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Would anyone else here like to see 3DConnexion support?

February 11, 2010, 12:03 am
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I for one would love it if Comsol would work with my Space Explorer, am I the only one? If you would like Comsol to support these 3D control devices please post here. I'm hoping they will act if there is a strong response.

Gary
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Using data from Matlab

February 29, 2016, 1:33 pm
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Dear all Comsol users,

To make the question simple, a heat transfer model is set up in 2-D, and every step, I want to calculate the heat source term in Matlab (which will be a 2-D matrix), then send this heat source term back to Comsol.

Currently, from what I found online, the most viable way seems to be setting up a interpolation function. But my concern is that, for a 2-D problem, the interpolation function in Comsol seems to require the data source to be from 'file' instead of table (for 'table' I can set it in Matlab code). This means that I need to save this heat source term matrix from Matlab to hard drive, then read it again in Comsol every step. Will this be very slow? Or is there a better way to do this?

Thanks!
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How to get the polarization state of the reflected light?

March 21, 2016, 9:55 am
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Dear all,

I have been working on the magneto-optical effect. A linearly polarized light is reflected by a magnetized film, Cobalt film for example. The reflected light is supposed to be ellipcitally polarized. Then is it possible to get the polarization state of this ellipcitally polarized, i.e., the polarization rotation and ellipticity?

All ideas will be appreciated. Thanks in advance!

Best regards,
Xiaokun

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Optical Ray Tracing Module: How to plot an OPD plot ?

March 21, 2016, 7:19 pm
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Dear All

Have you found out how to trace an Optical Path Difference plot ?
I want to load the Optical Path Length "gop.L" of my on-axis ray (starting at Point N from tag rpt1) into a Definition Variable "AxisOPL", such that I can plot the other rays as OPD (differences) as a ray Trajectory with a formula of the type "gop.L - AxisOPL"

Or whatever other way to plot the OPD that I have missed out ;)

--
Thanks in advance
Ivar

PS: webmaster, by the way Optical Ray Module, as well as Wave Optics Module, are both missing from the "Recommended Topics" list below ...
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Importing data in 3 dimensions to COMSOL

March 25, 2016, 3:31 pm
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Hello everyone, I have a question about importing data into COMSOL which I would then like to impose on my model. I have an excel spreadsheet that contains Width(x) and Length(y) and then x*y amount of data points for Power Density(z). I'm not quite sure how I can important this amount of data in to COMSOL. Do I need to come up with a function for the power density z and then apply this separately to my model? Any help or hints in the right direction are greatly appreciated; thanks in advance. I should include that I have been trying to use the interpolation function without much success.

Nick
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(Scaterring Nanosphere) Built in Application Model Explanation for Far Field Calculation

March 25, 2016, 4:23 pm
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I am following the Built in Model in Comsol 5.2 "Scaterring (Gold) Nanosphere" to create a similar model.
The only difference I'm aiming for is insted of modeling a quarter of the sphere I'm going for the whole sphere. For this I have avoided including the PEC and PMC conditions.

Now, after the "Results" portion in the accompanying PDF guide of the model, I am facing several problems.

Firstly:
In page 18 of the PDF under "Results" title, I am told to click the "Selection". But for some reason it's greyed out in my results toolbar.

Secondly:
After that, in the PDF under "Polar Plot Group 2", it tells me to select "Edges 5 and 15". After selecting these two edges it calculates the "Far Field Norm".
This Basically selects the Air-PML edge in the XZ plane.
Can anyone please elaborate the criteria for Far-Field Calculations. Which edges do I need to select for calculating a similar Polar Plot Group. Thanks a lot.
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How to model proton conducting SOEC

March 25, 2016, 5:06 pm
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I am just the beginner of the COMSOL and want to model proton conducting SOEC. Can any one help in this regard?
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Elasticity matrix in solid mechanics eigenfrequencies

March 25, 2016, 5:34 pm
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Dear all,
I am trying to study the vibrational eigenfrequency of a silicon nanostructure. I have built the geometry and when I try to define the materials, I used single crystalline Si with anisotropic properties in which I could define the elasticity matrix that I obtained through other calculations. However I noticed that the elasticity matrix doesn't have a check mark in front of it, so this information is not required in this case. I know there must be something that I did wrong, but I am kinda new to COMSOL and any suggestions would be greatly appreciated! Thank you very much!

Best wishes,

Vincent
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