Plotting an analytical function with the right Unit

May 11, 2016, 2:37 pm

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Hey,

I am new to COMSOL and am trying to rebuild a model and the graphics of the attached tutorial. The tutorial is for version 5.2 but I am using 4.2 which was not a problem so far.

I am struggling in reproducing figure 4 (see attached pdf-file). I get an offset between the analytical solution and calculated solutions. I think it is a Unit-problem.

The attached figures 1 to 3 show:
1. How I defined the analytical solution (1.png): V = 1[A]*rho0/(2*pi)*(1/abs(x-x1)-1/abs(x-x2))
Does the error lie here? Do I somehow have to tell COMSOL what the units of the arguments x, x1 and x2 are?
2. How I added the function to the data set (2.png): This should be okay.
3. How I tried to plot it in a 1D Line graph (3.png): Here I cannot choose a Unit. But strangely, if I put the Unit "dV" (as it is in the point
graph 1 for the calculated solution (dots)) and press "Plot" the line is correct but the "dV" is deleted and if I try to do this for both line graphs it doesn't work as the dV always gets deleted as a Unit...

So the question is: How do I get this correct in a way that I can choose the right Unit in step 3?

Thank you very much in advance!
Sina

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Plot can't go back in rainbow mode

May 11, 2016, 3:37 pm

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Hi everyone,

I am a new Comsol user. While trying different options for my plots (slice), I changed the rainbow color table to grayscale. Now it seems I can't go back to rainbow mode : the only option in the drop menu is grayscale. Do you know how I can bring back the nice rainbow colors ? Thanks,

Antoine

Joule heating problem

May 11, 2016, 4:26 pm

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Hi,

I have some problems while using COMSOL4.4 to simulate model. I try to build a model that place a tungsten wire (d=0.1mm) in a water sink and apply 1 volt on the wire for 10 seconds to find out the maximum temperature. I applied electric potential and ground on the wire in the joule heating module, added heat transfer in fluid for the water sink in heat transfer module. The result is 278 degC which is much higher than the experiment result. I don't know where is the problem, can anyone help me ?

Thanks!

Importing Solidworks part

May 11, 2016, 5:10 pm

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I'm trying to import a SolidWorks 2016 part (using the CAD import module) in both 5.2 and 5.1. 5.2 is crashing during the import, and 5.1 says the file version is not supported. Which version of Solidworks do these releases support?

inertial focusing in microfluidic channel

May 11, 2016, 10:34 pm

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Firstly，I want to modeling inertial focusing in straight and curved microfluidic channels（may the channel geometry seems like more complicated ）,just like
cn.comsol.com/story/download/1...85/Veryst_Mass_Gen_CN2013.pdf;
here is my model scheme:
1、sovle a CFD probelm(steady) without the particle;
2、calculate the force act on the particle induced by the “stress tensor and pressure ”,just like
www.chem.mtu.edu/~fmorriso/cm3...esonSurfacesinComsol5_2015.pdf
(I know there have “drag force” “lift force”etc.,but I CAN NOT find an explict formula of lift force suited complicated channel)
Lift Force(x)=sphint(r,spf.T_stressx); Lift Force(y)=sphint(r,spf.T_stressy);
The sphint(r, expr) operator computes the surface integral of the expression expr on the surface with radius r around the point in which it is evaluated.;r is the radius of the particle.
3、model particle tracing for fluid flow ,and "Force_x" =lift force(x),"Force_y"=lift force(y)

But the force seems like have influence to the particle, as "the particle inserted at a specific location in the straight channel remian at that location"

So， can anyone give some advises？

Cannot evaluate expression : undefined variable - Comsol 5

January 11, 2015, 2:44 pm

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Hi,
I am new to comsol, I am using Comsol 5 as apart of my project. I am trying to run simple electrolysis model and it is showing the following error

Cannot evaluate expression.
Undefined variable.
- Variable: comp1.phil
- Geometry: geom1
- Domain: 67
Failed to evaluate expression.
- Expression: comp1.phil
- Plot: slc1 (Slice)

Can you please help me?

I am attaching the model

Consumption of species

March 14, 2015, 9:47 am

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Hello everyone,

I have a question because I'm not quite sure how to model it. I have a reactor (square) which contains a chemical component A. A can react to B with the help of a catalyst. I want to simulate the consumption on the right side of the reactor (lets say A can diffuse in the whole reactor) with respect to the generation of B.

I'm not quite sure which modules to use. I tried with the diluted species (and maybe surface reaction modul?); But I don't know how I can set this up with the diluted species module.

Thanks for you help. I appreciate it.

regards Mika

Weak form pde

May 12, 2016, 1:36 am

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What is equation in weak form pde for study the eigenvalue I am unable to get idea how to get eigenvalue using weak form pde module. In module, where we have to enter the coefficient of lambda?
Thanks

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Convective heat flux

May 12, 2016, 5:25 am

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Hi,
I'm trying to see the heat conduction from the electric power conduit pipe to the soil surrounding the pipe.
The square part which I attached as model.png is the pipe and inside.
I built two point source inside.
Inside the pipe is just air, so I applied the heat transfer in fluid.
Wanted to apply convective heat flux to the pipe walls, but there was only inward heat flux in my version.
So I just applied the inward heat fluxes to the walls.
However, the result came out like result.png. Even though I applied heat transfer in solid and heat transfer fluid for the analysis, it doesn't read the heat conduction or convection inside the pipe box at all.
Anyone knows the solution? using inward heat flux to realize the convective heat flux or finding the convective heat flux.

Is it just the problem of this version?

problem about comsol can't plot an external Matlab function that Nested a equations

May 12, 2016, 8:31 am

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Hi, everyone：

I have a problem about using an external matlab function that it nested another matlab function but comsol can't plot it.
this is my function:
>> function out = rho_x(T)
out=XSteam('rhoL_T',T);
%%XSteam is another M-File that contain a series of Material properties
This function can work in matlab,but not in comsol .
I have created another example to make out what is going on . That is :
>> function out = Cp_x(T)
out=CpL_x(T);
here is a M-File(CpL_x)
>>function out = CpL_x(T)
out=2+T.^2;
and is work ,that confused me a lot . Maybe something wrong about "XSteam('rhoL_T',T)", the 'rhoL_T' is just an char ,no an
numerical value.
Anyone with experience successfully doing this?

Thanks!
babyling

Create a 2D Laser Heat Source

May 12, 2016, 8:56 am

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Hello to all of you,
i want to implement soldering by laser in a 2D environment. Therefore i use the heat transfer branch. Actually, i created a metal sheet in form of a rectangle with solder in form of a circular segment on it. Now i want to heat up the solder by a laser heat source. I tried to transform the following tutorial "Laser Heating of a Silicon Wafer" into 2D, but i failed.
www.comsol.com/model/download/...ls.mph.laser_heating_wafer.pdf

I also tried to implement the laser heat source as a boundary heat source. But in that case, you can't implement the profile of the laser beam. What i didn't get anyway, is the "general source" input. What kind of variable is this and how can i transfrom the power of the laser into this variable?

The laser i want to simulate has the following values:
P = 4000 W
Radius of the spot size = 1,4 mm
Form of the laser beam = gaussian pulse

Can somebody explain me how it works?

Thanks a lot.

Greets, Max

charge particle tracing link with matlab

May 12, 2016, 8:58 am

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In charge particle tracing, I use 'release from data file' to release particles. Now I want to use matlab to change the data file. Seem it changed from the comsol desktop. It looked same as before. But an error occur when running the study.

Failed to load file for initial particle positions.
- File
Error in multiphysics compilation.


I have tried when setting in comsol desktop. Study can run normally. It's so confusing.

How to display free surface deformation

May 12, 2016, 9:52 am

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Hello all,

I'm trying to develop a full turbulent model for a mixing batch starting from the mixer tutorial.

By now, I've imported the geometry from the tutorial and got the solution with frozen rotor study.

Adding the "Stationary free surface" physics condition and study, I thought I could display the vortex created at the free surface (just like the tutorial does) but nothing changed with or without the "Stationary free surface" study.

The vortex doesn't appear even with high rpm (100 rpm)

I attach the .mph file where I cleared mesh and results because of file dimension.

I would display the deformation in "2D Plot Group 4" and in "3D Plot Group 5"

Could anyone help me to understand what I'm doing in the wrong way?

Thank you in advance

Angelo

Steel plate falling in oil due to graivty

May 12, 2016, 10:33 am

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Im trying to simulate a thin steel plate dropping through oil due to the force of gravity.
Currently I'm using the laminar flow, solid mechanics and moving mesh module, and whilst the model solves for pressure and velocity, the steel plate doesn't seem to move.

Can anyone provide any incite into why the plate isn't moving. I have added a prescribed displacement to the steel plate, which moves the plate by a function of gravity over time.
The steel plate is initially submerged within the oil, but I would eventually like it to start outside the oil, surrounded by air.

Thanks allot,
Ben

Slight change of current density despite of dramatically changing conductivity

May 12, 2016, 11:44 am

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Hello all,

I'm working on a 2D conductive network system in which the junction area has a much smaller conductivity (Sigma) value than the wires. However, when applied voltage, the current density only changes a little when changing the conductivity value in the junction. For example, the linear integrated current density is 8.4E4 when Sigma_junction = Sigma_wire/30; and it's 8.19E4 when Sigma_junction = Sigma_wire/1800. That seems quite illogical to me, because a large drop of current density is expected due to the dramatically increase of resistance.

Could anyone tell me what's wrong in the model or how to fix it?

Thank you in advance.

Shujun

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Finite-width excitation source

May 12, 2016, 2:45 pm

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Dear users,

I would like to define a plane wave source which does not extend throughout the entire computational domain. In order to do it, I start with a square air box embedded into a larger square PML domain. Later, I define a plane wave source in the air, launch my wave and look at the E-field distribution. My wave is polarized out-of-plane.

For the plane wave, I would expect to have a wave which propagates parallel to the source and is getting absorbed by the PMLs. However, as you can see in the attached figure my field starts to expand to the left and right.

Is there a way to define it the way I want?

Best regards,
Andrzej

periodic two faces

May 12, 2016, 4:22 pm

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How to make periodic two faces in control volume , identical surface and identical mesh

Comsol Cluster Computing Problem !

May 12, 2016, 6:22 pm

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Hi,
when i am about to choose three nodes of which are at the settings of comsol cluster, it says "process status" scheduling and it stucks like that. when i am about to choose two nodes, comsol cluster works smooth. what might be the reason for me not making it with three? all authorisations were tested and done accurately.

Head-Node : Windows Server 2008 R2 HPC
A Node : Windows 7
B Node : Windows 7

Head-Node + A Node + B Node : Not Working Cluster
Head-Node + A Node : Working Cluster
A Node + B Node : Working Cluster
Head-Node + B Node : Not Working

How Can I This Problem ? where exactly i need check Node and Head-Node ? Can you pls help me ? I am working solution one month problem ? But Not Working Cluster 2 more than Node Comsol.

thankyou.

About the upside, downside of an interior boundary, and others related

February 6, 2011, 10:41 pm

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details please see the attachment, because I draw a figure to help description, thank you!

How to switch units

November 13, 2014, 5:26 am

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Hi,

in my models I use SI as standard unit system. The transport of diluted species (tds, COMSOL 5.0) uses mol/m³. How can I switch this unit into g/l, because all my inputs are g/l or kg/s and there aren't any reactions. I know I can convert the data by multiplication with the molecular weight.

But it would be easier to switch the unit in the transport of diluted species node. Is there any idea?

Thanks and best regards
Michael