Results and visualization - Latest Discussions - COMSOL Forums

Fluid Shear Stress in Thin Film Fluid Module

Thu, 17 May 2012 13:49:04 +0000

Hello,

I'm currently working with the journal bearing model (Comsol 4.2) from the model library and I'm trying to calculate the shear stress within the fluid film with is an essential for the torque calculation. Unfortunatly the shear stress is not one of the output values of this module.

I tried the surface integration and using the simple formula:
tau = eta*du/dh
with dh = tffs.dh
and eta = constant value

I used du = d(tffs.uy,y)+d(tffs.ux,x)

Unfortunately the results don't seem logical. I believe my expression for du or my usage of the integration (under results, derived values) is wrong.

Please help!

Thanks,
Toan

Mesh

Wed, 16 May 2012 06:26:13 +0000

Hi. I have a problem with moving mesh too. Please help me with materials. Where I can find something about it?

finding a specified flow rate in a '3D cut plane'

Tue, 15 May 2012 20:08:55 +0000

Hello,

I'm trying to do some postprocessing in a 3D fluid channel flow over a fractured hole.
The channel is filled with water and is laminar.
Here's what I'm trying to do:

1. cut the surface at an arbitrary channel location (i used the 'cut plane')
2. within that surface, I would like to start from one edge and integrate the velocity profile in a prescribed area.
eg) if the surface slice is a 2mmx2mm rectangle, i want to make another rectangle that is 1mmx1mm within that original 'cut plane' and measure the surface integrated velocity value (flow rate).

I was able to cut the surface where I wanted it, but I cannot find a way to resolve what I said in 2.

Any ideas?

Thanks!

TJ

Parametric sweep results

Tue, 15 May 2012 13:51:54 +0000

Hi,

I am launching a parametric sweep over one single parameter P. For each paremeter P, I am launching a modal analysis and get two eigenmodes. Then, I integrate my solution over four subsets of boundaries and get four scalar per eigenmode: int1_mode_i,int1_mode_i,int2_mode_i,int3_mode_i,int4_mode_i with i = 1 or 2 indexes the modes.

Therefore, if P is varying from p1 to p3, I would like to store in a table:

P1 EigenValue_1_P1 int1_mode_1_P1 int2_mode_1_P1 int2_mode_1_P1 int2_mode_1_P1
P1 EigenValue_2_P1 int1_mode_2_P1 int2_mode_2_P1 int2_mode_2_P1 int2_mode_2_P1
P2 EigenValue_1_P2 int1_mode_1_P2 int2_mode_1_P2 int2_mode_1_P2 int2_mode_1_P2
P2 EigenValue_2_P2 int1_mode_2_P2 int2_mode_2_P2 int2_mode_2_P2 int2_mode_2_P2
P3 EigenValue_1_P3 int1_mode_1_P3 int2_mode_1_P3 int2_mode_1_P3 int2_mode_1_P3
P3 EigenValue_2_P3 int1_mode_2_P3 int2_mode_2_P3 int2_mode_2_P3 int2_mode_2_P3

Is there simple way to do that without using the livelink MATLAB? Maybe with accumulated probe table. I am very struggling with this basic request. Any tutorial or example will be very helpful.

For your informations, I usually end up with error messages like: "Tabe input type 'None' does not match data input type 'Eigenfrequency'. Try evaluating in another table."

Thank you all for your answers,

Best Regards,

Denis

Metal-Insulator boundary

Thu, 10 May 2012 12:39:16 +0000

Hello everyone

I have a question about boundary conditions.
I have 3 layers (Insulator-metal-insulator) and this structure is placed in a solution that i want to sense its voltage with that metal layer.
Insulators are SIO2.
The problem is that when i choose dielectric shielding for insulator boundaries, the voltage on the metal, insulator and the solution will be all the same (and i was expected that it should not be the same on insulator layer!)
So i thought may be i should choose ground for insulator (!) and then the problem is solved. I have zero on insulator, different voltages on metal, and in solution.

But i beleive there is something wrong and i shouldn't work like this. Anyone has any idea?

Best
Bahar

Solving model with several ModelNodes

Thu, 10 May 2012 10:19:23 +0000

Hi,
I'm trying to build a model that contains several ModelNodes (sub-models). Each Node should have different properties (same geometry but I want to alter the mesh). The the Model should be solved at once.

My questions are:
How to set dependent variables (since the sub-models should not be coupled)?
How to access the solution for each ModelNode?
Are there some examples available (couldn't find anything about this in the Comsol 4.2a documentation)?

Best regards,
CS

Divergence of gradient of a variable calculation

Thu, 10 May 2012 09:04:52 +0000

Dear Support,
I need to calculate, in the post-processing stage, the divergence of the gradient (it is the laplacian) of a known variable, in a specified volume.
May you help me, please?

Hiding geometry boundaries in graphics window?

Tue, 08 May 2012 12:46:42 +0000

Hi,

I have a model geometry that includes some sub-domains. I want to show the results from these domains, but I don't want their boundaries to be visible in the graphics window, so visually the model looks like only one domian. Does anyone know if and how this can be done?

shear stress in microchannel

Tue, 08 May 2012 02:50:24 +0000

Hello,

I am clueless as to how to start the post-process data analysis to get the spatial distribution of shear stress of a micro channel. I have read the few discussion threads but it involves exporting the slice 3D plot of the velocity and then do the calculation of shear stress in Matlab. I would appreciated it if someone can either tell me (a) what Matlab code or equation you used to solve for shear stress from the velocity profile slice or (b) a way to get Comsol to compute shear stress for me and graph it (a much easier way for a newbie like me).

Thank you so much!

Enquiry on Livelinks for Matlab

Mon, 07 May 2012 11:26:32 +0000

Dear Mr Lars,

I'm using COMSOL 4.2a in my lab, and I have no problem with simple examples in extracting data from COMSOL to matlab.
The thing is, when I try to use a more complicated model, I just cannot get any values of any variable!!!
I posted it on this page: http://www.comsol.dk/community/forums/general/thread/28413/#p77051
The mph and m file is also attached there.
Could you please spend some time to help me out？
I'm looking forward to your reply.
Thank you very much!

Best regards,
Di Kai

No previous solutions after an error - parametric solver

Mon, 07 May 2012 06:20:04 +0000

Hi,

I am doing a quasi-static simulation with displacement BCs using solid mechanics module. I use the extension option in the stationary solver and use the parametric node to control my displacement steps. My model is in 3D and is big.

The problem is when there is an error-for whatever be the reason-the simulation exits and there are no previous solution steps available in the results section. The recovery file is not useful or not present at all in some cases. (I have the option for writing recovery files enabled.)

Irrespective of whether I choose to store solution at the "steps given" or "steps taken by the solver" in the "output" field of the "parametric" node and use the option "store solution out-of-core", I get no previous parametric solutions stored. I do not plot the results on the fly.

What is the way to keep the solutions of the previous parameters?

Regards,
Kodanda

electro-thermal analysis of micro-heeater

Mon, 07 May 2012 04:07:32 +0000

sir,when i tried to simulate it it is showing some errror, and i could not find the error .can u please help me to solve this structre..

How to use multiple parameter to generate the desire probe plots

Sun, 06 May 2012 14:36:58 +0000

Hello everyone,

Does anyone know how to get the desired graphs axis from the table when using a continuation parameter and auxiliary sweep, study 1 and 2 respectively?

Initially the probe plots (9total) is a 3 spikes (acceleration vs. number of values computed consecutively for each corresponding user-defined internal pressures). I've chosen 0 300 600 psi, respectively.
When running the Pre-stress (study1) and then Frequency Domain (study2) the Result tab shows a generated tables values with accelerations (i#) for the 9 probes mounted onto the shell, evaluated over a frequency 16905-16920 Hz, step size 0.25. When the calculations are re-run the 3spikes now has a different x axis replaced with ExtPressure, not 0-123 steps (41 for each pressure defined), which is the consecutive sum of the frequency range/step size for each pressure evaluated. The issue may be a Parameter problem. Both desire 3-peaks and the generated plots w/ x-axis EXTPressure have the same Table values, just different representation.

How can I get Comsol to generate the initial 3 spikes with the # of evaluated steps on the x-axis for different external pressure say: 0 100 600 psi every time we compute study 1 & 2 is re-computed from initial file state?
I ignore the irrelevant study 3 (eigenvalues) .
See attached problem file and Pictures of the two desired probe plots with the right x-axis.

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Arts, crafts and sciences uplift the world of being and are conducive to its exaltation.
~Baha'u'llah

Will COMSOL solve the PDE defined in the domain at the boundary also?

Sun, 06 May 2012 08:27:08 +0000

Hi

Will COMSOL solve the PDE defined in the domain at the boundary also?

If I plot the variable at the boundary from domain plot parameters dialogue box, then it is showing the correct boundary conditions.
But if I plot the same from from the cross-section plot parameters dialogue box, then I am getting different values than the specified boundary values. Why is this happening? Can anybody please help?

Regards,
Seetha

Far field plotting needs a very long time

Fri, 04 May 2012 15:40:25 +0000

Hello,

I'm trying to simulate a antenna over a ground plane with far field condition around, like it is in the examples.

The attached model works fine. But when I try to show the emw.normEfar on a surface, my computer utilize all cores with 100% (HP xw6600, 2xXeonE5450, 16GB). This is fine for some time. But after half an hour I canceled the process, because there is no cancel button at the GUI.

So I have two question:
First: Is there a mistake in my model or preferences?

And second: I lost some models on this way, because the emw.normEfar plot was the last active view when I saved. And COMSOL tries to recalculate, when I open it. Is there a way to prevent the recalculating, when COMSOL gets opened?

Thanks in advance

--
stefan

Case distinctive periodic boundary condition

Fri, 04 May 2012 13:49:46 +0000

Hello,

I need a case distinctive periodic boundary condition (magnetic vector potential), depending on atan2(y,x).

I thought about using a simple piecewise function for the magnetic vector potential on the wanted boundary. But I have no idea, how to tell COMSOL that I want the magnetic vector potential from another specific boundary as source (except using the COMSOL- given periodic boundary conditions).

magnetic vector potential on destination boundary should be the piecewise function:

argument __________________ expression
0 - pi/2 ____________________ Az (on source boundary)
pi/2 - pi ___________________ -Az (on source boundary)
etc.

The physical problem behind this is a simulation of a fourth electrical rotating machine.
When the rotor rotates out of the stator, the continuity condition changes to anti.
So the destination boundary is rotating all the time with the rotor and the source boundary stays still.

It would be useful if there was a way to use Parameterized curves from the Post Processor as input funtions.

Any help?

Thanks in advance

How to divide a solution by another solution

Wed, 02 May 2012 18:11:13 +0000

Greetings all, I am solving Darcy's Law and Solute Transport in a 2D rectangular model domain (using Comsol 4.2). I would like to normalize the solution by a known solution. This would basically entail dividing my solution by another solution.

More detailed explanation:

I am calculating groundwater solute concentrations using the solute transport model for 2 scenarios: one is an isotropic hydraulic conductivity (Darcy's Law), and the second is an anisotropic hydraulic conductivity. I would like to divide the anisotropic results by the isotropic results for visualization on a surface plot. Can anybody provide an explanation for how to divide a solution by another solution?

Thanks for your help!

E.J.E.H.

Calculating of torque

Tue, 01 May 2012 20:29:47 +0000

Hi

I have COMSOL 4.2a and I'm new in COMSOL. I'm simulating in AC/DC module Switched Reluctance Motor and I need to calculate torque of rotor and build plot of torque depending on angle of rotation. In user guide I found only equations how to calculate torque using Maxwell’s stress tensor and any example how to do it. Does someone have an example or user guide how to calculate torque.

Thank you in advance,
Artem

voltage induction due to changing magnetic field

Tue, 24 May 2011 12:14:58 +0000

hello,

I'm a relative newbie to comsol. what I'm trying to do is (I think) relatively easy, but I have no idea how to tackle it. what I need to do is model voltage induction in a coil due to a changing magnetic field. I know how to how to create a coil in a fixed magnetic field, but I don't know how to set up time varying field. but, more importantly, I don't know how to measure the induced voltage. should the coil be open and then specify two points where the voltage would be measured? thanks for any suggestions.

r.

How to delete unwanted stored solutions?

Thu, 30 Sep 2010 11:50:35 +0000

Hello,
I am simulating large 3D RF problem in time domain in version3.5a. And I found my whole stored file is as large as 40GB, since I stored around 600 time steps. And I want to delete the last 100 time steps to save some memory of the server without recalculate the whole process.

I would be very happy if someone knows how to do it.

Best wishes,