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COMSOL 4.0a : how to set maximum Java heap size??

September 9, 2010, 9:34 pm
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Hi,
I have problem to set comsol java heap.
In v3.5a, I know I can modify java heap in comsol.opts.
But in v4.0a, I can't find the comsol.opts, and I have no idea about setting the java heap.
Please give me help~~~
THX~
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Hagen–Poiseuille flow

February 8, 2012, 1:52 am
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I would like to use Comsol for a microfluidics project I'm working on. As this is my first time working with Comsol I am trying to simulate a simple problem to compare the simulation with analytical results.
The Hagen-Poiseuille flow problem is a solution to a simple fluidic problem, the flow of a liquid through a circular tube. More infor here: en.wikipedia.org/wiki/Hagen%E2%80%93Poiseuille_equation

I've set up the simulation as follows:
The geometry is 2D axisymmetric (radius is 15, length is 800)
The material is water
The physics is laminar flow (spf)
I use incompressible flow as my physical model
And define the inlet and outlet
The inlet pressure is 100 Pa, the outlet pressure is 0 Pa
The mesh is 'physics controlled' and normal

I run the simulation and to obtain the flow rate I apply a surface integration spf.U with Dataset 'solution 1'.
The result for this particular simulation is: flow rate = 5.593e-11 M3/s

The problem is that the analytical result is different. I've put it in Matlab to make sure it isn't me. The result is a factor of 22 too high.

r = 15e-6; % radius
dP = 100; % Pressure
Nu = 0.001; % viscosity
L = 800e-6; % Length
Fr = (pi*r^4*dP)/(8*Nu*L) % Hagen-Poseiulle equation for flow rate

Fr = 2.4850e-012 M3/s

I've triple checked these results but I cannot find why they don't match up. A factor 22 indicates that something's wrong, either on the theory side, or on the simulation side. Because I've just started with Comsol I would like to ask anyone to look over this model and see if something is evidently wrong. If anyone can give me suggestions why the analytical model is not correct I would like to hear it as well.

Thanks in advance



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partical tracing never works

July 24, 2012, 1:46 am
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hi i cant get particle tracing to work help pls. i have a simple 2d example with a rectangular with an electric field on it. the particle tracing modul doesnt show any interaction between the particles and the electric field even though i added the electric force in the particle tracing module.

i attached the example.
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sinusoidal voltage to time dependent solver

December 5, 2012, 12:40 pm
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I am trying to apply sinusoidal voltage to a model with time dependent solver. I apply the voltage based on a function but it doesn't show anything. the model is attached.

thanks
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Cement flowing around funky 3D shape and displacing mud

December 12, 2012, 9:22 am
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Hi, I have an interesting fluids problem. 3D object in a snug fit inside a water filled tube. Pump heavy cement in one end, will it displace all of the water as it flows around the object or leave some trapped fluid.

Any recomendations on a CFD module to use?

Regards, John
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Structural Mechanics Equation System

January 19, 2013, 4:46 pm
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I am trying to understand how my structural mechanics model is computing its solution. The model solves and gives me a reasonable solution. However, I don't understand how it is arriving at its answer. I am looking at the Subdomain Settings - Equation System panel where it shows the PDE which it is solving. I am viewing it in coefficient form, and all of the coefficients are set to zero. How am I arriving at a solution when the PDE which is being solved is zero?

Ryan
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Help solving nonlinear 1D diffusion equation

February 3, 2013, 12:43 am
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Hi All,

I need to solve the following 1D diffusion equation on domain x=[0,0.4] between time t=[0,2]:
w(u) du/dt = d^2u/dx^2
where w(u) = 1+184/u*(-1/log(u))^(4/3)
subject to the initial condition u(x,0) = 1e-4 and boundary conditions u(0,t) = 0.68 and du/dx(0.4,t) = 0.

This is how I set up the problem:
Model: coefficient PDE
Parameters: c = 1, da = w(u), all other coefficients = 0
Also set initial condition and boundary conditions accordingly.
Mesh: extremely fine

I then get the error message "error in user defined function: w" when I try to solve. However, the weird thing is if I increase the value of the initial condition to u(x,0) = 0.06 or above, the thing solves fine. It only crashes for small initial values...

Why do you think that is and what can I do to resolve this issue?

Many thanks!!
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Heat Source Expanding with time!

February 3, 2013, 5:25 am
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I have a model for EDM process in which I need to put an heat source which would be expanding with time. But it shows error if I give time dependent position of a point under boundary conditions. Laser example shows a moving heat source but how can I build a heat source expanding with time???

Thanks
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script for exporting deformed geom from livlink matlab ?

February 3, 2013, 5:47 am
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Hi all,

In GUI, I could remesh the deformed configuration from the results dataset, and from there i could export to a new geometry (xx.mphbin). But how can i do the same from matlab livelink ?

I wrote, "model.result.dataset('dset3').createDeformedConfig('deform1', 'mesh2');", but what could be the next lines in the script for exporting to a new geometry file ? Of course I tried to do it from GUI and then save model as m-file to see the script for exporting, but it didn't show anything equivalent java or matlab command for 'exporting to file' action.

Any help is appreciated ! Thanks.

/Krishna
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how to calculate the parameter values of a curve edge in mesh file

February 3, 2013, 6:53 am
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Hi guys,
I exported a mesh file from comsol. Can anyone tell me how to calculate the parameter values of a curve edge at two endpoints, respectively? Below is the mesh data of a circle:

# Major & minor version
0 1
1 # number of tags
# Tags
5 mesh1
1 # number of types
# Types
3 obj

# --------- Object 0 ----------

0 0 1
4 Mesh # class
2 # version
2 # sdim
14 # number of mesh points
0 # lowest mesh point index

# Mesh point coordinates
0.54004497593511991 -0.037779200720473034
1 0
0.70711341916808013 0.70710014314270009
0.18343216591831446 0.25870137743794869
0.24479262775166793 -0.3540242553652021
0.70710014314270009 -0.70711341916808013
-0.25920024933402869 0.33623073487269922
0 1
-0.20661414623779478 -0.28393003437540593
0 -1
-0.56571912320796292 -0.0007310878671271309
-0.70710014314270009 0.70711341916808013
-0.70711341916808013 -0.70710014314270009
-1 0

3 # number of element types

# Type #0

3 vtx # type name


1 # number of nodes per element
4 # number of elements
# Elements
1
7
9
13

1 # number of parameter values per element
0 # number of parameters
# Parameters

4 # number of geometric entity indices
# Geometric entity indices
3
2
1
0

0 # number of up/down pairs
# Up/down

# Type #1

3 edg # type name


2 # number of nodes per element
8 # number of elements
# Elements
2 1
1 5
7 2
5 9
11 7
9 12
12 13
13 11

2 # number of parameter values per element
8 # number of parameters
# Parameters
0.50000566589823847 1
0 0.50000566589823847
0 0.50000566589823847 <------ How to obtain them?
0.50000566589823847 1
0.50000566589823847 1
0 0.50000566589823847
0.50000566589823847 1
0 0.50000566589823847

Thanks!
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Problem on Analytic function

February 3, 2013, 8:32 am
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I want to define analytic function E, which is a function to time, t, but when I want to plot out E(t), there is always a error, which is attached. Who can help me figure out what is the problem? t isrange(0,0.0625,30). thanks
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Comsol 4.3a Memory problem -- not using enough RAM

February 3, 2013, 3:07 pm
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Hello everyone,

Usually the complain is that Comsol is using too much memory, but in my case its other way round.


I have a really nice machine in the lab with windows 8 server. I have Comsol version 4.3a installed. I am trying to run an RF module computation, where I am trying to create a fine mesh.

My problem is that even though the computer has 256 GB or RAM, the comsol uses only 1.2 GB or so maximum. Also, I have a 16 core x 2 processor but it uses only 3.5% of the cpu at max.

Coule anyone please explain to me if there is a way to overcome this problem. did anyone else have the same problem?

Thanks in advance.
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How to calculate curve parameter

February 3, 2013, 4:26 pm
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Hi, guys,
Given a curve and a set of points on this curve, how to calculate the curve parameter value at each point?
I am struggling on this problem for a few days. I will appreciate it if someone can help me.
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Heat Transfer Problem

February 3, 2013, 6:58 pm
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Hi everyone,

I found my heat transfer problem is taking too long to solve even in stationary.

The problem is about a pair of thin pipes embedded in soil. pipe diameter 25mm, 20m long each. There is fluid flowing through inside the pipes. One pipe is the inlet with the temperature of 40deg C and the other is the outlet 35 deg C. I would like to find out the temperatures in the soil surrounding the pipes.

I have attached two different files:

SMALL SCALE with (0.5m x 1m x 1m length of pipes) soil block, which I think is successful and provides reasonable results, without taking long to solve.

LARGE SCALE is where my issue is: (0.5m x 1m x 20m length of pipes) soil strip, which is taking too long solve and I aborted it after it ran for 2 hours. Everything is the same as SMALL SCALE, except for the length increased by 20 times.

Is it something to do with the meshing, element size, number of elements? I tried to play around with the maximum and minimum element sizes, in order to minimise the element quantity, but no luck.

I am looking forward to hearing some advice, thanking you all in advance.





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Problem with insulation...

February 3, 2013, 8:26 pm
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While using the Non-Isothermal Flow (nitf) and Heat Transfer in Solids (ht), I am facing problem with insulation being allocated to the faces that are not insulated. I suppose that I am not getting correct results because of this issue. Can anybody help me how to correct it? Actually, my model does not need any insulation.
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How to enter the temperature that varies with time??

February 3, 2013, 9:02 pm
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Due to the variation in air velocity, the external temperature varies with time. Can I know how can I input the values using an equation or an excel sheet??
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width of PML

June 14, 2012, 8:15 pm
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What will be the width of the PML( circular) to determine the confinement loss in hexagonal pcf.

Regards
Md. Samiul Habib
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Parallel computing MatLab Comsol

December 5, 2012, 11:24 pm
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Hi,

I am using Comsol 4.3 with Livelink for Matlab. I run an optimization code in Matlab where i call Comsol to perform frequency response simulations. Now i would like to start two parallel frequency response simulations that are independent of each other from my Matlab code.
My approach so far has been to open another Matlab worker by using matlabpool and parfor. However, only one of the Matlab workers are then connected to Comsol. Is it possible to perform parallel computing in Comsol when using the Matlab livelink?

//Anders

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Mie scattering in 4.3

January 7, 2013, 4:44 am
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Hello,
I have already seen some discussion about mid scattering of a gold nanosphere. But I the discussions I have consulted, no one has yet implemented a mie scattering program in Comsol 4.2 or 4.3 that works as the one in 3.5. Has this problem been solved yet? Can anyone post the correct program here?
Thank you very much for the help
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give specific values for every mesh point of a boundary as boundary condition

January 24, 2013, 5:50 am
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hey everybody,

is it possibly to give different values for all points of the mesh on the boundary, respectively?

for example, just a vector containing as many values as i have boundary mesh points, or something including the coordinates/mesh point coefficients -- specifically, i want to use a solution of another study at one boundary as new boundary condition for another study, both at the same geometry+mesh. should be possible, no? (in fact, i want to use the old solution, but add to every value a time-dependent term, but this should work then as well.)

please let me know if you know anything helpful, thanks alot.

kind regards and all best,
sabine
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