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Source term in poisson equation

March 29, 2017, 2:04 pm
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Hi All,

I am using a coefficient form PDE of COMSOL and I am not sure how to determine the source term coefficient for my model. Is it generally based on boundary conditions ? any suggestions and references would be much appreciated.

Thanks
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* 5.3 Webinar * Live Demo of New Features on April 4

March 29, 2017, 6:13 pm
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Hello COMSOL Community,

You are invited to join us for a webinar showcasing the new features of COMSOL Multiphysics and COMSOL Server version 5.3.

We’re excited to have Bjorn Sjodin, VP of Product Management, demonstrate the software. At the end of the webinar, Bjorn will answer your questions in a live Q&A session.

To register, visit:

- Apr 4, 2017 | 2:00 PM CEST (UTC+02:00) (Europe)
www.comsol.com/events/webinar/...ics-and-COMSOL-Server-53-28972

- Apr 4, 2017 | 2:00 PM EDT (UTC-04:00) (US & Canada)
www.comsol.com/events/webinar/...ics-and-COMSOL-Server-53-28982

Release highlights:
- Dramatic speedup for handling large models
- New COMSOL Server administration tools for clusters and usage logs
- Interactive graphics objects in simulation apps created with the Application Builder
- New powerful and user-friendly solver for CFD
- Boundary element method for electrostatics and corrosion
- Easier structural mechanics modeling with automatic constraints of rigid body motions
- Model methods for automating modeling tasks
- Quick selection filters for plots
- New tools for modeling moisture transport in air
- Time-domain acoustics improvements

Hope to see you there,
Valerio

--
Valerio Marra, PhD
Marketing Director
COMSOL, Inc.
+1-781-273-3322
valerio@comsol.com
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Creating Random Distribution of Geometry

March 29, 2017, 7:06 pm
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Hi all! i'm new to COMSOL so please be lenient to me. i'm trying to simulate fluid flow for my fabricated membrane which has a random distribution of circular pores with given dimensions . is there any way to randomly create pores on the membrane geometry? thanks for your help.
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Shielding problem in surface-to-surface radiation

March 29, 2017, 9:27 pm
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I am modelling a cryostat where the internal cavity is cooled to 4K with thermally-isolated radiation shields to isolate from room temperature. Everything within is held under vacuum. Hence, I am using the surface-to-surface radiation module.

The only heat source is the outer surface at room temperature, and hence I would expect each layer to radiatively cool inwards, and a steady-state temperature to step down across each shield until 4 K (fixed temperature) in the inner-most cavity. The shields are also actively cooled.
However, I have found that one of my inner layers is at 50 K higher temperature than all of the surrounding shields and even the inner 4 K cavity.

Things I have tested:
1) turning off all radiation results in 4K on all layers, hence it is not accidental conduction
2) adjusting the temperature of the outer-most surface changes that layer's temperature, even though the shields' temperatures vary minimally.

Thus, I suspect somehow, radiation is transmitting through all of my shields, so I must be setting some boundary conditions incorrectly, but I cannot figure it out.

Note: I have made the model using both full 3D as well as 2D axisymmetry, but both give the same result.

Thank you for any assistance in advance.
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non-normal incidence boundary conditions

March 30, 2017, 4:57 am
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Hello,

I'm very new in COMSOL and try to calculate a Corner configuration of a slab waveguide with the RF Module.
I created a 2D model with a waveguide that has a 90 deg kink in the middle of the structure. Around the structure I defined a rectangle, the cladding of the waveguide. The incident wave reaches the waveguide on the left side and the end of the waveguide is on the top of the rectangle.
I defined two ports at the beginning and the end of the waveguide core and at the bottom and the top of the rectangle PEC.

My problem is that I am not considering normal incidence in the waveguide, so the wave reaches the waveguide under an incident angle phi.

For normal incident, phi=0, I used scattered boundary conditions for the left and right part of the rectangle, which worked fine.
But which BC do I have to use for non-normal incidence?

Can somebody please help me.
Thanks in advance.
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electric field distribution

March 30, 2017, 5:50 am
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i am using 2D drawing. i have already done a simulation using the equation es.Er is this equation correct.
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Negative prescribed acceleration on a 3D geometry part

March 30, 2017, 5:54 am
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I am trying to model an impact test on a polymer cylinder by defining the deceleration of the impact tup as it compresses the part. It is a negative acceleration but using the 'prescribed acceleration' method I cannot define the acceleration as negative. Putting a minus only defines it as being in the downwards direction on the z axis.

Does anyone know any way I could model this deceleration?

Thank you,

Remi Shah
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Material improvisation

March 30, 2017, 7:24 am
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Hello
I was curious to building my own materials. Comsol allows prescribing user defined material properties, but I want to do something different. Suppose, I want to solve for flow only (spf), and my working fluid contains 99% or air and 1% Carbon di oxide. How can I do that? How can I build a material composition based or mole/mass fraction?
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Using external file data for heat generation.

March 30, 2017, 7:44 am
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How can I import coordinate data and heat generation from a file (x(cm), y (cm), z (cm), heat generation (w / cm ^ 3))? . This file is for heat transfer on a sheet. The file looks like this:

% x y z heat generation
1 1 1 0.05
1 2 1 0.75
1 3 1 1.23
1 4 1 5.7
1 5 1 7.23
2 1 1 8
....
10 10 5 0.58
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Where do I start to make a simulation of the degradation of a syringe rubber stopper?

March 30, 2017, 9:58 am
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I am new to Comsol and barely have a week using it. I am trying to simulate the degradation of a syringe rubber stopper with liquid in the syringe. May someone give some pointer on where to start.
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change the temprature

March 30, 2017, 10:58 am
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hi all
i am working on a periodic structure and i want to check the thermal effect on my structure
so my structure is a a periodic cubic quartz/air
i can reach my bandgaps
but i need to change my structure temprature for my next studies
how can i change my structure temrature
exactly not the ambient temrature - just the structure temprature
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Boundary heat source with temperature as a dependent variable

March 30, 2017, 11:29 am
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Hi,

I'm try to solve this solid heat transfer case with a boundary heat source. The heat source Q is a function of surface temperature. Can I just use 'boundary heat source' boundary condition with the Qb=f(T) equation?
Will this result in non-linearity because of solution dependency? If so, what is the right way to do it?

Thank you very much.
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COMSOL solve by parts

March 30, 2017, 12:21 pm
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Hi,

I'm building a model that need really fine mesh. I virtual partitioned the model into several pieces and wish to let COMSOL solve it piece by piece. Is there any functionality in COMSOL that can do this?

Any suggestion would be appreciated.


Chang
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Super Critical Flow

March 30, 2017, 12:46 pm
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Does COMSOL has any physics interface that solves flow in super critical condition?
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Strain due to lattice mismatch

March 30, 2017, 1:43 pm
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Hi,
I try to simulate the strain due lattice miamatch in different semiconductor materials, But, I do not know what to do, could you please help me with that.
Thanks,
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Slip and No Slip

November 8, 2012, 3:49 am
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What is the difference between slip and no slip options in the boundary conditions of laminar flow.

which will be a suitable option to choose for blood flow in capillaries.
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Simulation of composite laminates

June 21, 2013, 5:57 am
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Hi all,

Do you have any idea of modeling (simulation) of laminates , e.g. bi-layer composites having layers with different elastic modulus avoiding the so called 'free edge effect' (a stress singularity at the free edge).

i am using Comsol 4.3b and having this problem while i try to work with modeling creep in bi-layers

thanks for your time
-Tesfaye
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2D Axisymmetric and 2D simulation of permanent magnet

January 23, 2015, 4:27 pm
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Hi,


I am trying to simulate magnetic fields from a permanent magnet in simple 2D and 2D axisymmetric configuration using magnetic field no current module but COMSOL is erroring out saying that the error is greater than tolerance. The configuration in 2D is a rectangular bar magnet and configuration in 2D axisymmetric is a rectangle offset from the axis (i.e. a ring shaped magnet in 3D). However, I have tested other configurations as well and the error stays the same

3D simulations are working out perfectly for any magnet geometry. I followed the steps for setting up the magnetic field in COMOSL tutorial for a horse-shoe magnet and got perfect results in 3D but when I apply same setup in 2D and 2D axisymmetric COMSOL is erroring out. I am attaching my 2d axisymmetric case (COMSOL V 5.0).

Can anyone please point out if there needs to be a different setup for 2D and 2D axisymmetric?
Any help is greatly appreciated

Thanks and regards,
Souvik.

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error:Failed to find a solution. Maximum number of segregated iterations reached. Returned solution is not converged.

May 22, 2015, 9:39 pm
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Hi

I'm working on my model, with 3 physics, it does work but when i change sth i receive this error:

Failed to find a solution.
Maximum number of segregated iterations reached.
Returned solution is not converged.

I don;t know what is wrong with the model and what to do!
I will appreciate if any one help me.

thanks

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Combine two solutions

February 5, 2016, 4:53 am
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Hey all,

I have two consecutive time dependent studies and two solutions sol1 and sol2. In postprocessing I would now like to "stitch" these two solutions together, so that instead of having to deal with two data sets sol1 and sol2 I just have one data set solComb that contains the combination of these consecutive two solutions.

I want to be able to access the time(1) which lies in sol1 and time(6) which lies in sol2 with just one data set.

Thanks in advance for your help

best

Paul-Remo Wagner
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