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Help for my case!

May 6, 2013, 10:03 pm
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Hi, I am new to Comsol, and I want to simulate a water droplet falling down and pass through the 2mm gap between two circle particles. (see attached file)
the important thing is that I have to consider the surface tension of the droplet and see the droplet pass through the gap.
As the level set of Comsol can consider the surface tension, can I use this model (2D->fluid Flow->multiphase Flow->
two-phase flow,level set) to simulate this process.
and I don't know how I simulate a droplet falling down? anybody can give me some idea to simulate this process thanks lot!
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Porous Monolith in a pipe

May 7, 2013, 6:19 am
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Dear All,

i'm studying heat transfer in a pipe where there is a SiC monolith surrounded by an insulating mat (see screenshot).

Up to now I have studied the system considering the monolith as pure solid using for my model only the Conjugate Heat Transfer physics.

Do I have to change physics to consider the monolith as porous?
If yes how have I to set the domain in the new physics?

Thank you in advance for your reply!
Have a nice day.
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electric field and potential distribution

May 7, 2013, 6:23 am
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Hi

I have been working on a 3D (AC/DC) model of a insulator, and I am trying to verify the uniform potential and field distribution along the insulator surface.

I apply 33Kv voltage at HV end. I got result, in this result potential along the insulator surface is uniform distribution, i want field also uniform distribution along the surface.



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calling a waveform from Definition node

May 7, 2013, 6:57 am
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Dear all,

I want to apply AC voltage to an electrode. I built my desired stimulation waveform from Definition node. How can I call this function? Do I have to enter function name in Electric Current part or Terminal name? Please let me know where is my problem since I am not sure that this waveform is considered during computing process.

Kind regards,
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Multiple user in Linux?

May 7, 2013, 11:26 am
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Hi,

since some time I use Comsol on a Linux machine. Because of some former trouble I changed the directory used for temporary files to my home directory (followwing the advice given in solution number 1083). Recently another user got an account on the machine, but he was not able to start Comsol. I gave him full access to reading, writing and executing in the directory used for the temporary files. However the following error message appears when he tries to start COMSOL:

"Locking is not possible in the directory "/home/sabine/Comsol43/comsol43data/configuration/comsol/org.eclipse.osgi". A common reason is that the file system or Runtime Environment does not support file locking for that location. Please choose a different location, or disable file locking passing "-Dosgi.locking=none" as a VM argument.
Permission denied"

Does anyone know what to do?

Thanks a lot

Sabine
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Laminar Flow +Chemical Reaction

May 7, 2013, 12:26 pm
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Hi,

Can anyone please help me with my model and guide me as to where I am going wrong. I am trying to simulate a simple chemical reaction A+B-->C in a pipe filled with water flowing at laminar velocity. I create a laminar flow profile using Laminar physics which I used as my input velocity to the Transport of Diluted Species physics. I verified that the Laminar and Transport physics are coupled.

When I plot the concentration profile, there is no change in the reactant or products concentrations. They remain the same, meaning there is no reaction.

I have defined the reactions rates in the variables section of the model. I dont know if I am plotting it wrong or what is the issue.

Please Please help. I dont know where I am going wrong. I cleared all solutions and meshes as I was not able to upload the file with them due to size limit

Thanks,
Romani
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Parametric Study making functions

May 7, 2013, 1:11 pm
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Hi there,

I am doing a parametric study with a variable T_initial for a frequency domain simulation for a fixed range of frequencies, this worked well

I need now to change the set of frequencies with a function freq_range(T_initial). In the study frequency-domain it always says failed to evaluated the function. The function was defined in the global definitions and it is plotted well in the results.


The field frequencies does not accept my function I dont know why.
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comsol 4.2a with matlab R2011a

May 8, 2013, 3:01 am
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Hi,
I saved the comsol file in matlab as told. The tutorial says open ''COMSOL with MATLAB''. What does that mean?
Also i get an error as follows when i run the m file of the comsol model.

Undefined variable "ModelUtil" or class "ModelUtil.create".

Error in ==> modelmfile at 10
model = ModelUtil.create('Model');
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2D Poiseuille flow, wrong solutions?

May 8, 2013, 5:21 am
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Hello all COMSOL users!

I was solving a simple 2D Poiseuille flow problem on a rectangle domain. I use the "creeping flow" physical model with the "incompressible" option. And I just set the boundary condition of the inlet and outlet with two different pressure values with the options "pressure, no viscous stress" and "pressure" respectively. And I just leave the other two boundaries "no slip".

But I think I got wrong answers when solving this problem, because the pressure varies with not only x but also y near the inlet. This can be seen in the contour plot of pressure. However, as is well know, pressure should be just a function of x in this situation, and so the contour plot of pressure should be a set of vertical lines all over the domain.

So I am wondering why I got the wrong answer? Did I apply wrong boundary condition at the inlet? I got confused, because there is no other options relating to pressure can be chosen in the inlet setup menu.
Any comments will be grateful.


Pai Liu
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Wedge-on-Mirror !!

May 8, 2013, 9:54 am
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Hello,,

How can we design a glass wedge layer tend a 0,5 degree angle from a thin layer in the mirror cylindrical at 3D space ?
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Need a Help!! Band diagram & extracting eigenfrequency which I solved with Comsol 4.3

May 8, 2013, 5:41 pm
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I have to plot a Band diagram in 2D Photonic Crystal.
I worked in Eigenfrequency model, which I reached via RF module > Electromagnetic waves, Frequency > Eigenfrequecy.

After using parametric sweep with wave vector k, I got a eigenfrequecy for each value of k.
As I want to plot Band diagram, I need a data such as a spreadsheet which shows eigenfrequency and k. However I cannot find a way to extract the set of eigenfrequencies which I had gotten.

If there are any one who knows the way, Plz teach me T.T


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Elasticity matrix,voigt notation of PDMS

May 9, 2013, 3:28 am
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Hi,

I am currently working on bio-compatible material based sensor, where i want to use PDMS (Polydimethylsiloxane) as a membrane.But I can not get Elasticity matrix,voigt notation(mechanical properties) of PDMS for simulation.

Do any of you know the Elasticity matrix,voigt notation of PDMS?
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Buoyancy effects for turbulence model

May 9, 2013, 7:46 am
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In nitf (non-isothermal flow), the way for setting the Buoyancy force is only can set the volume force(-rho*g)?
However in somecase it is not accuracy for compare to the experiment result (the buoyancy effect is low).

I know some CFD software has own defluat Buoyancy model in turbulence model or in laminar model , how about in comsol?

Any comparsion for comsol and experiment for buoyancy has done to know the accuracy?
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2D Arrow Surface Plot -- Arrow Length Logarithmic

May 9, 2013, 8:02 pm
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Hello,

I am plotting a 2D Surface with an arrow surface. I need to scale my arrows logarithmically, but I am unsure whether this scaling is a natural logarithm or a base 10 logarithm. Which is it? The COMSOL Multiphysics User Guide states:

"Logarithmic, so that the length of the arrows is proportional to the logarithm of the
magnitude of the quantity they represent. This makes arrows representing small
values relatively larger. The value in the Range quotient field (default: 100)
determines the ratio between the smallest and largest values in the range of values
for the logarithmic arrow length."

If this is a natural logarithm, is there any way that I can scale my arrows with a base 10 logarithm? I will have some negative values in my vectors, so taking a log10 before plotting is not an option.

Thanks,
Lauren
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simple solidmechanics

May 9, 2013, 8:50 pm
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Hi

I have a simple model that a piston presses down brain tissue.

The piston moves with a prescribed displacement.

A problem is that the piston always moved the same distance, even I have changed numbers in prescribed displacement.

Can anyone help me with this problem?

I attached the file.

Thanks,

Jay
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find the coordinates of a point in which the magnitude of derived variable at a specific time is minimum?

May 9, 2013, 9:41 pm
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Hello,

I am working on a 2D transient problem. I have the results and want to post processing them.
I want to plot my results like this:

Detect the minimum of a derived variable all over the domain at a specific time.
then, again detect that variable in another time (and repeat it for my time period)

I could do that. Now I wanna to have the coordinates of that point in which the derived variable is minimum at that specific time.
Any idea?

Thanks
Hooman
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Modelling a Lumped Capacitor in COMSOL (Frequency Domain EM simulation)

May 10, 2013, 3:30 am
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Hello,

I am trying to critically couple a resonator to a microstrip transmission line using a lumped coupling capacitor. Does anyone know how I can do this in COMSOL. I know it is possible in HFSS. Can COMSOL do the same?

Thanks you
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Oscillating electric dipole source Comsol RF module

May 10, 2013, 9:17 am
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Dear All,

I have question.

I do simulations of plasmonic gap nanoantennas, and I want to excite antenna with dipole source which is placed and oscillate in the middle of the gap.


I have questions.

First, as I know unit for electric dipole moment is Cm (coulomb * meter), and in Comsol there is electric CURRENT dipole moment and unit is Am (amper * meter). I will mark electric dipole moment as P, and electric CURRENT dipole moment as PI.

My first question is how to set up equation in of “electric point dipole”? Is that for example just 1 [mA], or cos(emw.omega*t) [mA], or something else?

My second question is what is relation between P and PI. Is that PI = P/t (time), or PI = dP/dt, or maybe PI = P*emw.omega??

My third question is about Mie scattering. I want to calculate scattering and absorption cross section and I need electric field to calculate that.

Do you maybe know relation between electric current dipole moment and electric field??


Thanks for every reply and suggestion.
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Electric Field / Potential distribution

May 10, 2013, 9:31 pm
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Dear all,

I am trying to simulate a structure which consists of different material layers. I would like to see Electric field and Electric Potential distributions of a certain potential applied to the boundaries of substrate (poly-Si). My multilayer structure includes two different metall layers. When I press compute, Comsol asks me to enter Relative Permittivity values for these metals, which is actually incorrect. I set them to 0.01 but also set all boundaries of metal layers to 0V potential. Is this approach is correct?

After computing Electric Potentials (image is attached), instead of V I type sqrt(es.Ex*es.Ex+es.Ey*es.Ey+es.Ez*es.Ez) in Expression field to get Electric Field distribution, however I am getting an error (image is attached), which says "Failed to evaluate variable ... Domain 1, 10". Material of Domain 1 and 10 is Air.
Does anyone can explain what am I doing wrong?
Thanks in advance.
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How can I define an PML in model solids mechanics ?

May 7, 2013, 10:04 am
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I need a help !

I'm using a model of a small rectangle onto a large rectangle 2D axisymmetric
to denote of wave propagation
I have to put the PML absorbed wave to not be reflects
But when i put it and i do the compute
I don't see a difference => PML like does not work !
can you help me please ? what do I do?


note:
-> Model Wizard -> 2D axisymmetric -> structural mechanics -> solid mechanics -> temporel
-> Definitions -> PML

I have searched through the documents COMSOL a model that contains a sample of the PML but I have not found.
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