Quantcast
Channel: Latest Discussions - COMSOL Forums
Viewing all 3761 articles
Browse latest View live
↧

limit in number of ports

November 24, 2014, 5:16 am
$
0
0
I need to define ports in 2D parallel plate waveguide (RF module). If I use standard rectangular port (TM), Port number can only go up to 10. Is there a way to increase it past this limit?

Alternatively, if I switch to user defined ports, I cannot get rid of reflections from the outgoing port. Where can I find the exact definition of mode profiles in the standard rectangular TM port?
↧
Search

need your help with comsol

November 24, 2014, 7:19 am
$
0
0
bonjour
i hope you speak french.
I'AM A NEW WITH COMSOL and i need help to draw a square spiral wiih 6 lines.

je suis nouvelle avec comsol et je cherche a dessine une spire rectangulaire.si tu parle français sa me facilitera la tache car la suite de mon problème est aussi complexe sur comsol.

merci

↧
↧

Error simulating

November 24, 2014, 9:32 am
$
0
0
I get an error simulating my model which starts out with an initial temperature and is lowered to room temperature.

The error reads:

The following feature has encountered a problem:

Failed to find a solution
In segregated group 2:
The relative tolerance (6.4e+002) is greater than the relative tolerance.
Returned solution is not converged.
- Feature: Stationary Solver 1 (sol1/s1)

I would attach the file but I get a file size error (!???). The file is 8000+ KB.

Please help me to get rid of this error. Thank you.
↧

rotating machine

September 27, 2014, 7:24 pm
$
0
0
hello guys:

I´m rocky in comsol and im trying to use the rotating machine module, I did the baffled mixer turorial , and in my understanding here the fluid is rotating and the impeller is holded. Now im trying to do it in the inverse mode, the impeller is rotating and the the fluid receiving the moment.

My reactor is a cylinder with a small impeller. I have some questions: what part of my geometry must be selected in the rotating domain section: the vessel or the impeller? is necessary to add rotating walls? I tried all the possible configurations in these task but I cant get good results, seems like the impeller is not comunicating the moment flow to the fluid. Inside the veseel there are water.


I attached images of geometry and results.


thanks for your help

↧

Confinement losses in soft glass step-index fibers. Comparison with published results

November 25, 2014, 12:04 am
$
0
0
Dear community,

I am currently looking into the confinement losses with respect to wavelength for different fiber types: SIF, PCF, ... . To check my models for the simplest type (SIF) I found a publication from Kubat et al., "Mid-infrared supercontinuum generation to 4.5 um in uniform and tapered ZBLAN step-index fibers by direct pumping at 1064 or 1550 nm ," J. Opt. Soc. Am. B (2013) who showed the confinement losses for a ZBLAN fiber accross a wavelength range from 1 to 5 micron for different core diameters. I attached an adapted graph from the paper as Confinement losses.png below.
I took the Sellmeier coefficients from another paper and used a cylindrical PML to account for confinement losses. The simulation runs fine, the dispersion curve determined from the effective refractive index is the same as determined from the eigenvalue equation, but the confinement losses in z-direction (emw.dampzdB) does not correspond to the one in the paper. My confinement loss (in the model for 4 micron diameter) sets in roughly one micron later than in the publication. As they also used COMSOL and have more experience with the software I guess I have the suspicion that I did something wrong. My first thought that sth. went wrong with the PML [does the width actually haven an influence?], but I am not sure. Does someone have an idea? As the model was too large (even without mesh) I uploaded it here: www.dropbox.com/s/yn815et2wpw04qz/SIF-ZBLAN1.mph?dl=0

Thank you very much in advance,
Bernd
↧
↧

acoustic module

November 25, 2014, 12:30 am
$
0
0
Hello
I want to model a combustion chamber that a loudspeaker installed in its bottom to stabilize thermoacoustic instability with COMSOL Acoustic module.
In the first step(without considering the flame in chamber) I want to compute frequency response in some specific points of our chamber. As you can see in the screenshot which I have attached here, I just modeled the air inside of the chamber.
I consider that our speaker is producing pressure waves with constant amplitude of 0.05 Pa
and the outlet of the system is in atmospheric condition. My problem is that I'm not sure about the boundary conditions which I have specifid to different surfaces.
For the time being, I consider pressure boundary for the point which we have speaker, sound soft boundary for the outlet and the sound hard boundary for the remaining surfaces.
But my results are not the same as experimental ones.
I would be really thankful if somebody give me an idea about what would be the problem?

↧

Conjugated heat transfer - no convergence

November 25, 2014, 12:34 am
$
0
0
Hello!

I am modelling a heat transfer problem coupled with convection in a fluid using the conjugated heat transfer module. My material properties are temperature dependent. The model is time dependent. BCs are periodic BC for fluid flow and heat, symmetry BC for fluid flow and heat, a pressure point constraint and a constant temperature at on wall. I added a volume force to account for convection.

I solved the model in 2D first and I got a reasonable solution. Now I upgraded the model to a simple 3D geometry- a block with a tube inside. The problem is, I can't get the solution to converge in 3D. I use an "extra fine" mesh and time steps of 1 sec with a relative tolerance of 1e-3.

I already tried changing the termination technique in the fully coupled mode from "constant" to"automatic highly nonlinear" but still no convergence.

Any ideas what I could try to get the model to converge?

Thank you for your input!
↧

Undefined value error with Scattering Boundary Condition

November 25, 2014, 3:38 am
$
0
0
Dear all,

I try to set up an eigenfrequency simulation for an optical nanostructure, where its eigenmodes and corresponding Q-factors should be simulated. To do so, an air cylinder with scattering boundaries is placed around the structure. This method was already used in our research group with Comsol 3.5a, where it perfectly worked. If I try this in the same way as before in Comsol 4.4 I get an error that says that some undefined values where found (I put the complete error at the end).
Even if I take an working mph-file from 3.5a and load and rerun it in 4.4 I get this error.
To demonstrate it, I created a smaller simulation in Comsol 4.4 that should just calculate the optical eigenmodes of a silicon disk. It is attached to this message.
I know that I could also use a PML around the simulation volume (which I already did and which works), but in my particular case I would like to use a scattering boundary. You find the complete error at the end of this message.

Thank you.
Hannes

Undefined value found.
- Detail: Undefined value found in the stiffness matrix.
There are 4992 equations giving NaN/Inf in the matrix rows for the variable comp1.E10.
at coordinates: (1.95739e-006,4.10639e-007,1.5e-006), (1.93312e-006,5.12863e-007,1.5e-006), (1.33784e-006,1.48666e-006,1.5e-006), (1.2579e-006,1.55489e-006,1.5e-006), (1.31557e-006,1.3701e-006,1.5e-006), ...
There are 1664 equations giving NaN/Inf in the matrix rows for the variable comp1.E20.
at coordinates: (1.23741e-006,1.44043e-006,1.5e-006), (1.27943e-006,1.26486e-006,1.5e-006), (1.52137e-006,1.29824e-006,1.40898e-006), (1.4484e-006,1.23084e-006,1.5e-006), (1.85009e-006,7.59702e-007,1.40843e-006), ...
There are 1664 equations giving NaN/Inf in the matrix rows for the variable comp1.E21.
at coordinates: (1.23741e-006,1.44043e-006,1.5e-006), (1.27943e-006,1.26486e-006,1.5e-006), (1.52137e-006,1.29824e-006,1.40898e-006), (1.4484e-006,1.23084e-006,1.5e-006), (1.85009e-006,7.59702e-007,1.40843e-006), ...
and similarly for the degrees of freedom, NaN/Inf in the matrix columns.
- Feature: Eigenvalue Solver 1 (sol1/e1)
↧
Search

About the comsol easy tutorial

November 25, 2014, 9:22 am
$
0
0
Good day to you sir,

I found the tutorial of how to create a hole in a geometry (attached), however I can't seem to start the tutorial step by step. How can I view how your built the model step by step?

Regards,
Ammar Al Armachi
↧
↧

How to generate a "Join Data" set from parametric steps?

December 3, 2012, 9:40 am
$
0
0
How to generate a "Join Data" set from two stationary and parametric steps?

Hello everybody. Does anyone know how to merge two solutions when one of them is the continuation of the other? For instance, one solution belongs to a study step with a parameter p going from 0 to 1 and the other solution is from another study step with p going from 1 to 2. Of course, I would like to use the "whole" solution (p from 0 to 2), not to compare or operate with them. I try to do an "Explicit" join and I get the message "The solutions are incompatible".

Thanks.

Jesus.
↧

Plot particle density

November 26, 2014, 4:03 am
$
0
0
Hello everyone,
As attached, it is my particle tracing result, but the color expression seems to be the particles’ velocity. Does anyone know how to plot the particle density as the color expression? I didn't find this kind of expression in “Replace Expression”.

Thank you very much in advance!
↧

Rename datasets from solver

November 26, 2014, 7:45 am
$
0
0
Hi, I have a complex model with lots of steps. I get completely confused about the naming of the datasets it generates. The only "trick" I have found is that for time-dependent sets I use slightly different temperature ranges so that I can tell them apart by trying to then plot them and looking at the "list" of temperatures to see which one is which.

Any better ideas?

Thanks, John
↧

DESIGNING A CANTILEVER BEAM

November 26, 2014, 10:23 am
$
0
0
WE ARE UNABLE TO REMOVE THE SURFACES FROM BEAM TO MAKE IT OPTIMIZED SO TELL HOW TO CUT ANY SURFACE IN RANDOM MANNER??
HOW TO PLOT A GRAPH BETWEEN THE FORCE APPLIED AT A POINT VS THE CHANGE IN DISPLACEMENT.
↧
↧

Why the solution only saves result from the last study step?

February 27, 2014, 2:29 pm
$
0
0
Hi, I have a time dependent problem to solve. Because at the start and ending stage of the simulation variables change more significantly, I decide to use several time dependent study steps, for the first and last steps the time step is smaller while in the middle I use a larger dt. In the solvers steps taken by solver is set to be strict. However, I find that at the export, only the time steps in final study step show up in the stored output times, why? In the solvers, I've set Times to Store to be specified values in Output tab. Thanks!
↧

livelink pgtag for existing plots

November 10, 2014, 7:02 am
$
0
0
Hi, I want to export my plots from comsol to matlab, to tweak and export them as eps. I am using comsol 4.4.

The plots are already made in the comsol model, and I have loaded the model up in matlab. The "mphplot" command takes an argument <pgtag>, which corresponds to a plotgroup. I understand that when you make a plotgroup through matlab, you need to give it a pgtag. But how do I check the pgtag values of the plotgroups I have already made in COMSOL desktop? Thanks.

Edit: also a second problem: when running the server with "comsol server matlab -graphics", no graphical interface opens, is this intended and I've misunderstood? I would like to open Comsol and matlab concurrently and modify/access the model through both interfaces. Is this possible?
↧
Search

Parametric sweep solution is lost after non-convergence

November 27, 2014, 1:16 am
$
0
0
Hi, I'm running a time-dependent simulation, using electric currents and solid heat transfer physics. I'm ramping up the current with time, which heats the material. I have included an effect, which makes the current increase with temperature. At one point, the temperature and current will have a positive feedback effect, which should increase the temperature to infinity, and thus I get non-convergence at some timestep. This is expected. I need the solution before the non-convergence.

Now, when doing regular simulations (without parametric sweep), the solution is kept, but when doing a parametric sweep (e.g. over a range of geometries), the solutions are not kept when non-convergence occurrs.

Currently I'm doing every simulation without a parametric sweep, find the timestep when it doesn't converge and, create stop-conditions for those timesteps and then run the parametric sweep to get all the data conveniently. This is inconvenient and basically means I have to simulate everything twice.

Any ideas? How to keep the non-converged solutions in parametric sweeps?
↧

Any tips to locally refine a swept mesh?

November 27, 2014, 11:02 am
$
0
0
Hi, I have long skinny cylinder inside a porous medium with various geometric bits and pieces. A swept mesh works pretty well and the FP module converges fine.

But I'd like to do local refinement.. I know that I can add nodes to distribution in the swept direction, but that increases mesh everywhere.

If I do a conversion to tetrahedral the FP doesn't converge because of all the nasty long thing tetrahedra....

Any thoughts how I could do a local refinement?

Regards, John
p.s. Actually related question on adaptive mesh refinement - does that work on swept grids?
↧
↧

coupling acoustic with fluid flow

November 28, 2014, 2:20 am
$
0
0
hi,
I need to use "acoustic" and "fluid flow" modules to solve my problem.the only common dependent variable in this two is pressure .i want to couple this two to reach pressure field.do you know how i can do it?
in the fluid flow i should use turbulent flow.

my next question is about boundary condition in acoustic when i want to model an sonoreactor what is the boundary condition for ultrasonic tip?is there any mathematics that i should add to my physics?

I need your help.
Thanks in advance.
Amir
↧

Extract data from comsol to matlab

November 28, 2014, 7:52 am
$
0
0
Dear All,

I am running the parameter scan simulation. After that the case is extremely so that I can't open by GUI.

I want to check the integration of loss of one domain changing with three scanned parameter.

I need to extract these data from COMSOL to Matlab by livelink

How should I write the command in matlab script?

Thanks for the help in advance.

Best regards
Yanrui
↧

COMSOL Multiphysics 4.4 is here!

November 27, 2013, 5:17 am
$
0
0
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
↧
Viewing all 3761 articles
Browse latest View live
Search
<script src="https://jsc.adskeeper.com/r/s/rssing.com.1596347.js" async> </script>