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mass transfer with a rotor

August 5, 2012, 8:37 am
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HI
I have some experimental data about carbon dioxide that diffuse through a membrane and reacts in a aqueous solution of MEA.
I have successfully model the case where liquid is firm in the recipient.
Now I want to simulate the case where liquid is mixed by a rotor at low velocities.
I think to do this with a "forced" diffusive coefficient for MEA, but I imagine that there is a more sophisticated way to do this.
Could anyone suggest some ideas?
Thank you in advance.

Dario
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Plane wave propagation inside a duct (Vibroacoustic)

May 23, 2012, 4:42 am
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Hello everybody,

I me dealing with an interesting vibroacoustic problem and wanna model it WIth COMSOL.

The subject is : A duct (Air inside)of one meter length and cross sectional 0.2m*0.2m (width=1m)
Boundary conditions : unit velocity at one end
zero velocity Boundary condition is applied at the other end (rigid wall)
The 4 lateral sides are assigned rigid wall.


Frequency = 100hz.
Material (duct) = Any (wood, alu,etc...)


My questions are :
- COMSOL doesn't contain Velocity boundary ? (Drive me mad)
- How to handle that with COMSOL ?

Your help would be very appreciated .......
Thanks in advance.



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Plotting Electric Field Gradient and "Dome-shaped" Electrical Field of Microelectrodes

June 17, 2012, 4:18 am
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Hi

I am using AC/DC module to simulate the electric field distribution over a microelectrode when applying AC input voltage. I manged to get the total electric field distribution E (V/m) over the microelectrode, its expression is "ec.normE".

However, I have two problems:

1) How can I plot the electric field gradient ∇|E2|? Its unit is (V2/m3).

2) Can Comsol plot the electric field in such a way it shows the "dome-shaped" electrical field?
Please refer to the attachment to see an example of "dome-shaped" electrical field.


Could anyone please help me in either questions?

Your help is much appreciated.

Bashar
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how to define a variable in livelink with matlab which changes in a loop?

July 25, 2012, 2:10 am
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hi, I have a problem to define a loop in livelink. In the loop geometries with different shapes are created. The problem is how to define a parameter varies in loop? The .m file is attached below. Thanks!
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Help with fluid flow analysis on imported SolidWorks file.

August 6, 2012, 11:15 pm
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Hi all

I have imported a SolidWorks assembly into COMSOL 3.5a using the IGS file format.
It is a smaller section of a larger nozzle that should produce swirling flows.
I have attached a screenshot of what it looks like, both solid and wire-frame.
What I am trying to do is a fluid flow analysis of a fluid flowing through it.
(In the model navigator I selected 3D, COMSOL Multiphysics, Fluid Flow, Incompressible...).
I am now trying to set boundary conditions so that the openings of the smaller ports are inlets
and the opening of the larger section at the top is an outlet, but the edge settings option in
the Physics drop down menu is grayed out and when in the boundary settings window, I can
only select the internal walls to set the boundary conditions.

Am I going about this in the wrong way, or is there something that I don't know and am missing?

Any help would be IMMENSELY appreciated.

Thanks

Brett
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How to draw a spherical dome?

August 7, 2012, 1:52 pm
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Hello all,

I am very new to Comsol. I am trying to draw a three dimensional spherical dome and mate it with a rectangular box. I have successfully drawn the box with a circular opening on one face. I would really appreciate it if someone could point me to the right direction.

Thanks in advance

Amartya
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Model heat transfer in block but can't get the solution

August 8, 2012, 4:03 am
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I modelled the heat transfer within a block with some air gaps. In the model, heat is transferred by conduction in the solid domain, and in these air voids, convection and radiation are also involved. I have attached a picture of the block.

That problem is that the computational process is extremely slow. With very coarse mesh, it takes nearly 2 hours to get the simulation result.

I then refined the meshes for the air gaps to improve the accuracy of convection, and resolve the problem. After 4-hour computation, the solver sent this message;

Failed to find a solution.
The relative residual (0.28) is greater than the relative tolerance. Returned solution is not converged.

I don't think the heat transfer within a block will be a very complex model. It is astonishing to see COMSOL takes such a long time to solve it. My laptop is Macbook pro with Intel i7, 4GB RAM. Are there any problems in my model or is my laptop not powerful enough to run COMSOL?
Can anyone help me?
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Overlay plot of geometry and analytic function

August 8, 2012, 4:09 am
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Dear Comsol Users
I defined an analytical function depending on x and y which I would like to plot in overlay with my geometry for which it is defined (similarly to the plot on page 7 of the semiconductor diode example).
How do I do that?

I created a plot group of the analytical function, but I dont know how to "add" the geometry domains to this plot.
Thanks for hints or suggestions.
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Transmission spectrum for optical waveguide

August 8, 2012, 4:17 am
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Hello,

I am currently trying to extract a transmission spectrum from a Si waveguide on top of SiO2 substrate. There are some gold particles on top of the Si (this configuration is taken from an article in which they simulate it with FDTD). I tried several things to extract the transmission spectrum:

1) S21 parameter in dB
2) ratio of the Poynting flux at the input and output (tried both with fields Ex,Ey,Ez, emw.Hx, emw.Hy and emw.Hz and with fields from the Boundary mode electric/magnetic field)

I am however not able to get the right profile (for some wavelenghts I even get quit high gains which is unphysical).

It seems that also reflections are taken into account, but in an experiment you will only take the ratio of the actual input power (which is forward propagating) and the forward propagating output power.

Does anybody know how to extract a sensible transmission spectrum (which you would obtain in experiments).

Thanks in advance.

F. Peyskens
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How to introduce non-linear variable

August 8, 2012, 4:39 am
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I am trying to introduce a non-linear variable in my temperature-dependent superconductor model, saying alpha(T)=alpha0*T_bath/T. When i run it

Error:7248
Undefined value found

Details

Exception:
com.femlab.jni.FlNativeException: Undefined value found Solvermodel
Messages:
Undefined value found Solvermodel

Stack trace:
at solvermodel.cpp, row 1837, (Undefined value found in the stiffness matrix.
There are 201 equations giving NaN/Inf in the matrix rows for the variable H
at coordinates: (0.2), (0.200001), (0.200002), (0.200003), (0.200004), ...
and similarly for the degrees of freedom, NaN/Inf in the matrix columns
)
at com.femlab.solver.FlSolver.femTime(Native Method)
at com.femlab.solver.FemTime.run(Unknown Source)
at com.femlab.server.FlRunner.run(Unknown Source)
at com.femlab.util.i.run(Unknown Source)
at com.femlab.util.aa.run(Unknown Source)

Anyone know how to introduce non-linear in comsol 3.5a?
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Geometry units

August 8, 2012, 5:07 am
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Hi,

I want to draw my geometry in micro meters in comsol 3.5(a). Drawing it in meters gives very small view of certain portions. Does any one knows how to draw in micrometers?

Regards
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1D-plot (line graph)

August 8, 2012, 5:19 am
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Hello,
I am a new ComSol user.
I have simulated the model and got the result plotting in line graph.
I would like to have a result data in table (with xy-coordinate)
How can I do this?
Thank you very much.
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What's the formulation of "mechanical energy flux" in COMSOL?

August 8, 2012, 5:39 am
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There are "mechanical energy flux," "complex mechanical energy flux"
which I can derive or plot in the result.
They are cool but still I want to know the definitions of them, how it calculates, and I did not find them in the user manuals.
Could somebody tell me? Thanks.
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Mesh Curved Structure

August 8, 2012, 7:18 am
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Hi,
I want to mesh a simple curved structure for CFD but COMSOL gives the internal error in boundary respecting. After reading a few posts, I still cannot succeed in meshing the curved tube. I have tried manully mesh the geometry and follow the blood vessel example, but none of them worked. Could someone kindly give a detailed guide please, i.e. how to add internal boundaries?

Thank you very much!
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Fluid Structure Interaction with Piezoelectric

August 8, 2012, 7:31 am
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I was wondering if someone could help me figure out how to model the fluid structure interaction using the piezoelectric device physics model as well. I am trying to model synthetic jet actuators and I am having a hard time coupling the physics together to make the model work. I am new to the fluid structure interaction model so that is probably where my issues are. I am able to get the piezo element to deflect but im not sure how to tie it to the brass element so that deflects and then that deflection causes the fluid in the cavity to displace. If anyone could help me that would be great.

Thanks,
Aaron
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Heat Transfer in a Tanker

August 8, 2012, 8:25 am
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Hi, I am a new Comsol modeler and I am trying to model a steel tanker filled with molten bitumen. The tanker is insulated and the bitumen is heated by two propane burners ( in form of U) located at the bottom. For the bitumen I have Non-isothermal Flow-Laminar , for the propane I guess Non-isothermal Flow (flow in a pipe) and also I have Heat transfer in solids for all solid structure and convection to the exterior.
I have tried many times to do my model and always I have some kind of error message.
Someone could give some directions to do this model. I am using Comsol 4.2a.
Thanks
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Visualize time dependent solution in matlab

August 8, 2012, 8:34 am
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Hello,
I am solving a time dependent problem in matlab. I can get the final solution using mphplot but is it possible to get matlab to display the time evolving solution ?
Thanks
praveen
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HEAT TRANSFERT IN A BITUMEN TANKER

August 8, 2012, 8:43 am
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Hi, I am a new Comsol modeler and I am trying to model a steel tanker filled with molten bitumen. The tanker is insulated and the bitumen is heated by two propane burners ( in form of U) located at the bottom. For the bitumen I have Non-isothermal Flow-Laminar , for the propane I guess Non-isothermal Flow (flow in a pipe) and also I have Heat transfer in solids for all solid structure and convection to the exterior.

I have tried many times to do my model and always I have some kind of message error.
Someone could give some directions to do this model. I am using Comsol 4.2a.

Thanks
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Getting 2-D geometry from 3D object

August 8, 2012, 9:44 am
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Hello,
I am running a mode propagation analysis of a waveguide so need to run a set of 2-D mode solvers along the propagation direction. I am wondering is it possible to get 2-D gemetry of the 3-D waveguide cross-section in comsol automatically? I have gone through almost everything in the helpfile and it seems usually comsol use 2-D to build 3-D geom but not the other way around.

I would greatly appreciate your answers.
regards,
Max
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Creating high density 2D mesh in 3D model

August 8, 2012, 10:34 am
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Hi,

Firstly, sorry if this is a stupid question, I'm very new to Comsol and don't know if what I want to do is even possible.

At the moment I'm just trying to model basic permanent magnets then get contour (or streamline) plots of the magnetic field going from one pole to the other. While I can happily do this in 2D and get a good looking plot using the magnetic vector potential normal to the plane I'm viewing (attached image "2D plot"). The problem I get is when I build effectively the same configuration in 3D (a cuboid magnet), then take a 2D slice through the centre of the magnet and plot the same magnetic vector potential (attached image "3D plot").

I'm assuming my problem is that the mesh density on that plane taken from the 3D model is much less than it is for the 2D plot. Therefore, I was wondering if anyone could tell me how I would go about re-solving just on this plane at a higher mesh density. Alternatively, please tell me if there's a different issue that's causing this.

Ultimately, I'd like to be able to model more complex magnet geometries, then take slices through them and look at what the magnetic field lines are doing.

Many thanks
Stephen
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