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plot a single contour line in a temperature field

March 28, 2017, 10:08 am
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Hi!

This might be a trivial question, but wonder if it is possible to plot a single contour line in a temperature field for instance?

I have a model at a simple stationary 2D pipe flow of a hot fluid flowing through i cold pipe. I would like to find the contour line where the fluid hits a "critical" temperature.

Any tips and tricks?

Thank you
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how to simulate lamb wave in plate in comsol??

March 8, 2011, 8:18 am
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Hi,
How to simulate lamb wave in comsol??how i will get symmetry mode & antisymmetry mode.??
pls help


Regards!!

Deepak
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Adding a second y-axis to a plot

June 22, 2011, 6:10 pm
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Perhaps I've over looked something, but I can't figure out how add a second y-axis to a plot. I'm specifically interested in adding a right hand axis.

I've got a plot of two variables and would like to show their ratio on the same plot. It makes no sense to have the same y-axis for the variables as their ratio because the units are different and the scale is completely inappropriate.

Export the data and then plot in Matlab is the best solution I've found. Is there a better one?


Thanks.

O
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parametric sweep study depending on a parametric sweep study

June 25, 2015, 1:30 am
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Hello,

I am having a big issue here in my simulation.

I have two studies:

Study 1:
I did a parametric sweep stationary study with a first physics model (laminar flow) for different geometries with only one parameter variable (channel height). The aim is to compute the flow. Seems to give me good results.

Study 2:
Then I would like to do a second dependent stationary study with a second physics model (transport of diluted species) where I use the flow computed in the first study for convection of only one species. But again, I need to do it for different geometries by varying the very same parameter (channel height) with the same values as in my previous study.

How can I do it?
Defining a second parametric sweep in study 2 and using all dependent variables not solved for from the parametric solution of study 1, using "current" parameter does not give me good results. For instance It computed the pressure again and gave this time wrong results with negative pressures.

Thanks a lot
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Introduction of BEM solver for Acoustics

February 17, 2016, 8:16 am
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Hello,

I see from the recent presentation by Mads J. Herring Jensen at the COMSOL conference in Boston in October (uk.comsol.com/paper/download/257851/jensen_presentation.pdf) that there is an intention to add a Boundary Element Method solver to the Acoustics Module. We use COMSOL to teach numerical simulation methods for acoustics, but presently we are using in-house BEM code; having this functionality integrated into the same modelling environment would therefore be of great interest to us. I was wondering if you have any idea about the time-scale over which this might be released?

Best regards, Jonathan Hargreaves
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Tthe material properties transition from power-to-liquid-to-solid in SLM process

January 23, 2017, 9:44 pm
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Dear all,

I'm studying the process and detail phenomenon of Selective Laser Melting (SLM) of metals.
In SLM process, there should be couple layers of meshes which stands for single layer of metal powders. A moving heat source is applied, and the temperature of metal powders rise and exceed the material melting point. The material properties switch to liquid metal. Once the heat source removed, the temperature cools down and once again the material properties changes. In this time, it will changes from liquid metal to solid metal.

Briefly, the material properties transition is:
metal powder->liquid metal->solid metal

I'm now evaluating some CAE software. Can COMSOL model the changes of material properties (ig. k, cp, rho...) in the Selective Laser Melting (SLM) process?
If the answer is yes, can anyone shortly illustrate how to do that?

Thank you in advance,
Po-Shen
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How to plot vorticity

March 21, 2017, 4:12 am
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I can visualize only pressure and velocity.

Do you have any ideas about how to get the vorticity for a 3D problem?
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How to calculate force in comsol dc discharge?

March 27, 2017, 3:20 am
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Hi

I have successfully modeled a simple 2d dc discharge between two electrodes in comsol 5.2 and now I want to calculate the force applied by the discharge in the domain.

I chose "Force Calculation" from the domains and set a name for it but didn't change "torque axis" and "torque rotation point".

after computing, I tried to plot the force on a surface with the expression: DC Discharge(Electrostatics) >Mechanical >Electromagnetic force>z component

and i received the following errors:

Undefined variable.
- Variable: comp1.dc.unTz
- Geometry: geom1
- Boundaries: 1, 3-4
Failed to evaluate variable.
- Variable: comp1.dc.nTz_force
- Defined as: comp1.dc.unTz
Failed to evaluate expression.
- Expression: r*(pi*(2*comp1.dc.nTz_force))
Failed to evaluate expression.
- Expression: comp1.dc.intfcal1(r*(pi*(2*comp1.dc.nTz_force)))
Failed to evaluate variable.
- Variable: comp1.dc.Forcez_force
- Defined as: comp1.dc.intfcal1(r*(pi*(2*comp1.dc.nTz_force)))
Failed to evaluate expression.
- Expression: comp1.dc.Forcez_force
- Plot: surf1 (Surface)

======================

Can anyone please help me?

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Why the COMSOL results can not give infinity values at resonance?

March 27, 2017, 5:13 am
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Dear all,

I am now stuck in a problem about the acoustic pressure distribution inside a long duct with a monopole source in the cubic center.

Considering one-dimension wave propagation problems, when all of the surfaces were set as 'sound hard boundary', why can't the acoustic pressure reach the infinite value at resonance?

The COMSOL document gives the following discussion: when the sound waves propagate in a lossless medium, attenuation frequently occurs by interaction with the surrounding at the boundaries of the system.

There might be some assumptions in the software when dealing with the calculation, but for the influence on the maximum values at resonance, I wonder how and to what extent the boundary condition or assumption affect the final pressure results, in detail?

Thank you very much in advance.
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Implementing Periodic Boundary Conditions in Coefficient Form Boundary PDEs

March 27, 2017, 7:08 pm
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I'm attempting to model a Coefficient Form Boundary PDE on the surface of a 3D model. I would like to impose periodic boundary conditions on the two edges of the boundary; however, it does not appear that COMSOL supports periodic boundary conditions for Boundary PDE's by default. I have attempted to fix this by creating a linear extrusion from edge #1 to edge #2, and then setting Dirichlet boundary conditions on edge #2 equal to the value at edge #1, but this only sets the values, and not the derivatives, equal to each other. I don't see any clear way to set the derivatives equal to each other - attempting a similar approach with a flux/source boundary condition at edge #2 with dtang won't work, as the value on the edge consistently evaluates to some value on the order of 10^-13. Is there any way to do this, or a simpler way in general to impose periodic boundary conditions on coefficient form boundary PDEs?
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Negative Decibel Levels in Results

March 28, 2017, 1:31 pm
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Hello,

I am running an acoustic analysis on a high frequency horn for a school project but my results are strange. It shows that as the air moves through the horn, the decibel levels quickly drop and once it is completely out of the mouth, the values become negative. Is there something wrong with my program? Any advice will help.

Thank you,
Cam
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How to implement Discrete Elastic Viscous Split Stress (DEVSS) method for simulating viscoelastic fluids

March 28, 2017, 5:12 pm
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Hi there,

I am trying to simulate FENE-CR viscoelastic fluid in COMSOL. It seems from the literature that the DEVSS technique gives stability to the simulation of viscoelastic fluids. Anybody can please help me out how to implement this method in COMSOL ?

Regards,
Chandi
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analysis of water layer displacement due to electric dipole induced due to external electric field

March 28, 2017, 10:19 pm
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Hi ..

My name is Tausif and I am trying to do the analysis of displacement of plate attached to the water layer. And this water layer is subjected to the electric field (voltage) between the two copper plate. I want to see the maximum displacement of of the water layer due to the dipole moment effect under the electric field.

Can anybody help me please....
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Coupling of concentration with Electric current to get voltage

March 28, 2017, 11:07 pm
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Hi Comsol Users.
Hope You all will be fine and doing well in Comsol. I am doing battery modelling in comsol 5.2a. I have made a model of 2 electrodes consisting spherical particles and electrolyte. I am using transport of diluted species interface (tds), Nernst Planck equation interface (npe) and electric current interface.

I am working like that the concentration should increase in one electrode particles while it will decrease in other electrode and at the same time i will get voltage. the concentration profile works well but when i apply the electric current interface to get the voltage my model does not work. the main problem is the over potential equation for me now.

overpotential is (electric potential-electrolyte potential-equilibrium potential)

Can any one help me how to use overpotential equation and how to couple electric current interface with tds and npe interfaces.

I want to produce the results of teh mentioned below paper
jes.ecsdl.org/content/161/5/A803/F6.expansion.html
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Modeling the air temperature inside an enclosure

March 29, 2017, 12:00 am
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Good evening everyone,

I need to model the air temperature inside an enclosure heated up by an ambient temperature. To do this I made a CAD model of my enclosure with a fitted block inside of the enclosure to act as air, this is the object that I want to see the temperature distribution of along with the enclosure walls. The first image shows my model in COMSOL. At the center of the block representing air is another solid (representing a controller) made of polycarbonate, which I would also like to know the temperature distribution of. My goal was to generate the temperature distribution of these objects when starting at room temperature (65F) and being exposed to a hotter ambient temperature (80, 90, and 100F) for 1 hour.

I'm new to COMSOL and I can't figure out how to make this simulation happen. I have my model imported and all the materials set. I'm not too sure what Physics settings and boundary conditions I need to use in order to accomplish this simulation. I've attached a link showing my COMSOL model to help visualize my design.

Link: imgur.com/a/R0B9B
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import a geometry

March 29, 2017, 1:34 am
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Dear all,

I drew my geometry with autocad but I have the Linux version of Comsol which doesn't read .dwg . Therefore I converted it into a .stl file, which in theory has to be accepted by Comsol.

I also converted the file with the highest stl resulution available with autocad.

Unfortunatelly the result is very bad: strange surfaces and random holes, which I have never drown, appear.
I also tried to untick the "semplified mesh" options but the geometry is still corrupted.

Do You have any idea about how to solve this issue?
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set Br value space related

March 29, 2017, 6:42 am
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Hi,

I'm trying to set up an inhomogeneous magnetic filed in COMSOL AC/DC module. Is there a way to set Br Z component as sin(5*z) T in the Magnetic Filed Ampere's Law settings?

Thank you
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Lamb waves and dipersion curves in plates

March 29, 2017, 7:11 am
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Hi,

i'm trying to solve the paper of pablo Gomez about Lamb Waves and Dispersion Curves in Plates. I made the first part of this work, but i didn't know how can i do the rest. Especially how could i make a fourier transform (FFT) of the displacement to get the frequency - k(wave number) or frequency - group_velocity representations?
I read in many papers that the lonly way to do this, is to write a matlab code .. but i really dont have no idea how it works.
In Comsol version 5.2 there already a study step : time to frequency fft , i try it but still i dont know how can i plot the dispersions curves of lamb waves!
it would be very nice if someone had an expereince with the same subject and can help me to solve this paper.

Best Regards
Mahir
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mass loading on quartz resonator

March 29, 2017, 9:54 am
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hi
i am working on the modelling of sensor for detection of fuel adulteration based on the shift in the eigen frequency for that i am trying to employ TSM based quartz resonator, the main problem i am having is that the fuel sample should be having interaction with the resonator with density of the sample acting on the resonator as mass on it. but i amnot getting how to add the mass in the model. i will be grateful if anyone tell me how to add mass on the resonator model
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Particle Tracing Release Time Bug

March 29, 2017, 10:48 am
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Hello,

I am using the mathematical particle tracing module to release particles with the Release from Grid node. I want to model those particles with a linear elastic particle-particle interaction and have used the appropriate node.

If I release 2 particles with the above setup, the particles behave as expected. This can be seen in the v1.mph file I have included.

Now, I actually want to release more particles into the domain at a later time point in the study. So, I added another time to the Release Times field in the Release from Grid subnode. So I should release 2 particles first, then 2 more later. This is shown in the v2.mph file I have included.

However, when the second release time is added, the behavior of the first 2 particles is changed and incorrect. It is almost as if the 2 non-existant particles which haven't been released yet are affecting the interaction forces between the 2 particles that have already been released.

I'm not sure what to do about this, any help is greatly appreciated!
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