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Magnetic Brake example fails at higher rotation rates- Detail: NaN or Inf found when solving linear system using SOR.

September 5, 2014, 2:38 pm
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I'm currently modeling a situation quite like COMSOLs example of the magnetic brake as expressed in the magnetic_brake.mph file in the example forums. I've gotten my model to work at low angular rates, but whenever I attempt to increase to higher velocities, the model issues an :" - Detail: NaN or Inf found when solving linear system using SOR" error. If I increase the angular rate by small increments from where it works to the speeds where this error is issued, at some point the model simply fails to converge.

To try to understand what was going on, I decided just explore higher angular rates using the actual magnetic_brake.mph model, and to my surprise it behaves just the same way: The model is distributed with an initial angular rate of 1000 rpm (as set by the dV0 term in the Global Definitions: Parameters list), but try bumping it up to 10,000 and it fails to converge and by 100,000 it also issuses "NaN or Inf found when solving linear system using SOR".

As everyone has access to the online magnetic_brake.mph example, could someone help me understand what I have to do to get such mef models to converge when using higher velocities?

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Fill Geometric gap

July 14, 2011, 3:32 pm
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Hi, probably a trivial question but it is an annoying problem for me.

I have a model essentailly made up of a number beams connected together and then 'union'ed together to form the whole and extruded into 3D.

The problem i have is that sometimes a smal,..sliver of a gap remainswhere some beams look to join which then leads to COMSOL throwing a fit in a number of places :).

Anyone happen to know of a way to get Comsol to fill the gap so to speak. I thought repair might work but it does not seem to do anything high or low value.

I attatched a small example pic.

Any help is appreciated.

Regards Mike F
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deformed geometry for Electromagnets

September 6, 2014, 2:52 pm
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hi every one ,
i defined a moving armature by using deformed geometry in AD\DC module .also auto Remeshing defined .when the distortion exceed from 1 ,comsol remesh geometry again .
but after three remeshing ,comsol give an error(A problem occurred when building mesh feature 'Reference 1')also inverted mesh element can be seen .
does any one know how can i solve this problem ?
thanks with regards
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Two phase laminar flow and FSI

September 6, 2014, 9:54 pm
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Hi Everybody,

I would like to simulate an AFM cantilever, halfly immersed in water in FSI using two phase fluid flow.

So far I have simulated a small spherical cylinder (tip) in a larger spherical cylinder (reservoir) and and I have used 2 phase flow - level set model together with solid mechanics to obtain meniscus height around the tip. Now I want to move my cantilever vertically and see the effect of damping on cantilever motion. How should I implement two phase flow- level set in FSI?
Marjan
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COMSOL Multiphysics 4.4 is here!

November 27, 2013, 5:17 am
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Hello COMSOL Community,

The most powerful multiphysics software just got more powerful: We are excited to announce that the latest release of COMSOL Multiphysics, version 4.4, is now available for download. Learn about the new multiphysics coupling functionality, the enhanced user interface, and more at www.comsol.com/release/4.4

News in COMSOL Multiphysics
- New COMSOL Desktop interface for Windows with a ribbon design that provides easier navigation
- A completely new Multiphysics node in the model tree for setting up multiphysics models
* Combine physics interfaces to define your own multiphysics
* Choose from built-in multiphysics couplings
* View each physics interface as a separate node in the tree
- One-click select: hover-and-click selection method speeds up the modeling process
- Auto-complete search to quickly find variables to use in results in the Windows version
- Geometry subsequences for user-defined geometric primitives
- If/else statements in the model tree for conditional geometry creation
- Export mesh to NASTRAN file formats
- Time-unit handling in the solvers

News in add-on products
- Structural Mechanics Module: easy access to rotordynamic forces, updated shell-solid couplings, and fast method for contact
- Heat Transfer Module: fast methods for radiation in participating media, thermoelectric effect, and heating of biological tissue
- Acoustics Module: Linearized Euler equations for aeroacoustics simulations
- CFD Module: dramatically increased conservation of mass and energy for laminar flow
- AC/DC Module: now includes 167 nonlinear magnetic materials
- RF Module: ports on interior boundaries (reintroduced from version 3.5a)
- Particle Tracing Module: efficient method for particle-field and fluid-particle interactions
- Optimization Module: additional gradient-free method (BOBYQA) for dimensional optimization and additional gradient-based method (MMA) for topology optimization

New product
- Mixer Module: analysis of stirred mixers and reactors with tools for free surface modeling and non-Newtonian fluids

COMSOL Multiphysics 4.4 can be downloaded at www.comsol.com/support/download

Enjoy version 4.4!

Valerio

--
Valerio Marra, Ph.D.
Technical Marketing Manager
COMSOL, Inc.
+1-781-273-3322
valerio@comsol.com
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2D Hexagonal Periodic Array

April 9, 2014, 12:13 am
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Hi All,
I am trying to built a model on 2D Hexagonal Periodic Array with periodicity in the xy-plane. For that I have defined a 3D hexagonal unit cell with the top and bottom hexagonal faces as the excitation and destination ports respectively. For the remaining 6 rectangular faces I define 3 (2 faces each) periodic conditions on the opposite faces. A plane wave is incident along the z direction( presently normal to the xy plane but later would like to change for different incident angles) with E polarized along the x-direction.

First of all is the unit cell definition along with the periodic condition application sides are correct?
Secondly how do I use Floquet Periodicity with correct Kf definitions? Will it be similar to plasmonic wire grating case where array periodicity and Floquet kf are parallel which is not in my case ?

A pdf showing the model geomerty along with the periodic Boundary conditions is attached.

I would be really grateful if you guys help me out.
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Import CATPRoduct file

September 7, 2014, 4:13 am
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Hi
i want to import a "stl" file (AMIRA-a porous structure) directly into COMSOL but it doesnt work.
"Err: the file cannt be parameterized"
even though i tried to import the stl file first in CATIA and then import the new CATproduct file into COMSOL
but anyway it doesnt work::
error : "Not a valid ENTITY type for this operation"
Detail: Output_file_could_not_be_saved
I have tried the igs and stp format too but the result is the same!
:(
really stuck in!!!
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phased array transducer in frequency domain

September 7, 2014, 5:16 am
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Hello

I am trying to do a ring piezo transducer phased array simulation. it has 8 rings. i successfully have done the design. I am doing a harmonic analysis.

I am facing problem with one thing. For the drive signal I want to introduce different driving phase for different rings. There is no option for doing that in the frequency domain. It was possible for transient analysis.

Can anyone help me please?

Thanks
Rupak
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electrical actuation of droplet on hydrophobic substarte.

September 7, 2014, 10:21 am
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hey did someone perform the simulation of water droplet motion on substrate?plz share the file here,I face a lot of problems including the vanishing of the droplet volume to zero.
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Coupling variables

September 7, 2014, 2:12 pm
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Hello,

I am attempting to model a complex physical processes in batteries where there is a domain representing the electrode that contains active materials. The governing equations in the active materials are different from the governing equations on the domain. Moreover, the length scales are very different (microns compared to meters).
My goal is to couple the equations without building a new domain. I am guessing this may be achieved by building two distinct geometries and coupling the variables through extrusion but I am not quite sure.
Any help with this issue would be greatly appreciated.

Adib Samin
The Department of Aerospace and Mechanical Engineering
The Ohio State University
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"Undefined value found in the equation residual vector" error in "bipolar_transistor.mph" model (Semiconductor Modul)

September 7, 2014, 6:31 pm
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Hi everyone,

I try to calculate bipolar_transistor.mph example from COMSOL library models.
After sucsesful finishing study "V_B sweep, V_CE=0.5 V, V_E=0 V" I run Compute command for study "V_CE sweep, V_E=0 V, I_B=1 uA" and recieve Error message "Undefined value found in the equation residual vector".

I have the same errors on both Windows 8, x64 and Fedora 20, x64 computers.
Can somebody explaine me, what's wrong?

The log see below:

COMSOL 4.4.0.195

Opened file: bipolar_transistor.mph
Complete mesh consists of 8047 domain elements and 519 boundary elements.
Solution time (Solver 1): 3 s.
Number of degrees of freedom solved for: 24141.
Solution time (V_B sweep, V_CE=0.5 V, V_E=0 V): 78 s. (1 minute, 18 seconds)
Number of degrees of freedom solved for: 24142.

Error:
Undefined value found.
- Detail: Undefined value found in the equation residual vector.
There are 438 degrees of freedom giving NaN/Inf in the vector for the variable comp1.Ne.
at coordinates: (6.46671e-008,-1.47054e-007), (7.47439e-008,-1.47035e-007), (6.9664e-008,-1.44089e-007), (7.47295e-008,-1.52949e-007), (6.97037e-008,-1.5588e-007), ...
There are 363 degrees of freedom giving NaN/Inf in the vector for the variable comp1.Ph.
at coordinates: (5.46959e-008,-1.47084e-007), (4.99044e-008,-1.44442e-007), (5.9625e-008,-1.44138e-007), (8.96945e-008,-1.43933e-007), (9.46986e-008,-1.46974e-007), ...
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Hexagonal periodic array...

September 7, 2014, 7:07 pm
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I need to apply Floquet periodicity to a Hexagonal array of dielectric rods in an another dielectric matrix and calculate mode field distribution at a particular k-point of Brillouin zone for a particular frequency. Can you tell me how should I apply that boundary condition so that I can use my desired k-point at ease.

Thanking you...
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Editing Parametric Sweeps

September 7, 2014, 7:23 pm
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Hi all,

I created this model to test the effectiveness of AntiReflective Coatings. I wanted to modify this so that it can check results over a wide variety of wavelengths as well as angles. Can anyone help me fix this (creating two parametric sweeps does not seem to create the correct data).
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BAW Resonator Mesh

September 7, 2014, 9:04 pm
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Hai

I am designing a AlN BAW resonator operating at 3GHz. It is being observed that the frequency response changes widely with the mesh density.

The mesh criteria of the mesh size being between lambda/4 and lambda/6 seems kind of very difficult as the lambda values at 3Ghz is very low and my resonator active area is large.So the computational time is really too long to serve as a good solution.

Please do help me with suggestions as to how to build a reliable mesh for such devices at GHz range.

Regards

Gayathri Pillai
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Eigenfrequency with change in temperature

September 8, 2014, 12:41 am
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I have a gold beam fixed at both the ends. I would like to know the eigenfrequency(resonance frequency) of the beam with change in temperature(cooling the surroundings), please help me how to do that, how do I change the material properties(Young's modulus, density, Possion ratio) as function of temperature.
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Nitrogen plasma simulation: cross section file?

December 15, 2010, 7:33 am
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Hello,

I followed the webinar about plasma simulation, and they told something about
a french institut in Toulouse who was supposed to provide the cross sections
data for different gases.like the argon.txt.. but for nitrogen..

Anyone that took more attention than me?

Can somebody help on that? any file that would help getting away from Argon?

Thank you

Lukas
Germany
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Modeling electrical conductivity of CFRP..

February 8, 2013, 4:42 am
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Hello everyone,

I am trying to set up electric current model for carbon fiber reinforced polymer in COMSOL to investigate electrical conductivity variation with respect to loading fraction of fibers. Can anybody tell me how i can proceed? which module to be used?

Thanks and regards
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USE of Ambient Temperature in AC/DC module

September 3, 2014, 8:21 am
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Hello everyone,
I am new in this forum. I have built a AC/DC module model. Now I want to analyze the changes in different parameters for a certain ambient temperature range. Do I need to add any more physics. If yes, then which physics?
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How to compute time-averaged power in a frequency domain solution?

September 3, 2014, 9:29 am
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I am attempting to compute the time-averaged power delivered to a resistive load domain but cannot figure out a reliable way to do so. Any help would be appreciated.

I am modeling inductive coupling between two coils of wire in the Magnetic & Electric Fields interface. The bottom coil is driven by a voltage source imposed by terminals. The top coil is connected to a resistor, where that resistor is simply modeled as a domain with lower conductivity. I'm solving my model in the frequency domain and would like to compute the time-averaged power delivered to that load resistor. I cannot attach my full model, but a toy model is attached to illustrate the situation.

I've tried multiple tactics to compute the power delivered to the load, but none quite work. Here are a few of my attempts:

1) Compute the voltage across the load by averaging the voltage on each boundary and computing the difference. Compute the current through the load by integrating the surface current through a boundary. Compute power delivered to the load as (1/2)*real(conj(V)*I). This gives an okay estimate sometimes, but often has significant error due to varying voltage and current distributions on the load boundaries. In many cases, this can even report more power going into the load than is being provided by the source.

2) Integrate the resistive losses (mef.Qrh) within the load domain. This gives a much more accurate estimate of power delivered to the load, but only at a specific instant in time (i.e., at phase = 0 degrees). If there is a way to compute the time average of these resistive losses, then that'd be perfect, but I cannot find a way to compute the time average for a frequency domain solution.

3) Utilize the time-averaged power flow variables (mef.Pox). Unfortunately, these essentially average to zero on any given boundary and thus appear useless to me.

So how does one go about computing the average power delivered to a resistive load domain? I've been struggling with this question and would appreciate any advice.

Thank you.
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problem with Finite Element Model for The Axon of Nervous Cell

September 8, 2014, 12:36 pm
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Hi all,

I am implementing a Hodgkin-Huxley model for cell membrane activity based on a COMSOL article named "A Finite Element Model for The Axon of Nervous Cells" in version 4.4. Basically I have a minor problem as well as a major problem as follows:

minor one: I was doing all of my implementation in 4.3b but because of license expiration I had to change my version to 4.4 however I am facing an error regarding Jacobian variable. the model was working in 4.3b but now in 4.4 it does not!!

major problem: the response that the model usually gave me was not correct according to the literature and the article I mentioned. I need to know what is wrong with my model.

the file made by 4.4 version is attached

thanks a lot in advance,

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