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Mathematical Particle Tracing_Weird results

December 12, 2013, 6:35 pm
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Hi there!

I am posting this thread because I am trying to simulate the deflection of a non magnetic particle in ferrofluids, under the influence of magnetic field. I have simulated the magnetic field through the mfnc module and I am now trying to simulate the deflection through the Mathematical Particle Tracing.
I have implemented the forces and their expressions and I am now computing the solution.
First of all, it takes a huge amount of time, sorry for that. Then, my deflection is completely weird, going one way and the other. I have checked again and again the forces' expressions, and can't find any mistake. It also says that it can't evaluate the expression when I try doing the graph of the position of the particle through the microchannel. Maybe it is in the use of the module itself.
I would be really grateful if you could try and help me.

I am joining the file.

Cheers

Antoine
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How to simulation thermal expansion with a T dependent CTE

December 13, 2013, 12:17 am
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I would like to simulate the thermal expansion of an combined object from cryo temperature to room temperature.

My current conditions are:
COMSOL version 3.5a,
simulation model is smsld,
the CTE (alpha) is defined as a function of T (Temp_smsld),
reference temperature is defined as Tinit (1K),
strain temperature is defined as Tfinal (which is controlled by the simulation from 1K-300K).

Simulations I tried are parametric and time dependent.
The simulation results I obtained were the program used the alpha at Tfinal to calculate the expansion of object from Tinit to Tfinal, e.g. alpha(Tfinal)*(Tfinal-Tinit), which is not correct.
The expected calculation should be the Integration from Tinit to Tfinal of alpha(T).

Do you have any suggestion on doing such a simulation?
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Calculation of effective material loss (alpha-eff)

December 13, 2013, 6:18 am
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I was wondering while doing my undergraduate research that- if there is any way to calculate the effective material absorption loss (alpha-eff) using comsol. I know the equation, but i do not know how to calculate with it. I apologize for this silly question and I'm just an undergraduate. If it's not possible with comsol, how do i do it? What theories should I study to calculate it? It would be kind enough of anybody to help me with this!
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Convergence plots

December 13, 2013, 6:28 am
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Does anyone know if it is possible to show a convergence plot during a livelink with Matlab? I'm using version 4.4 and matlab R2013a.

Thanks
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Exporting 1D point graph data

December 13, 2013, 7:46 am
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Hi all


I did simulations for different parameter values (Radius of circle) using 'parameter sweep' and draw point 1D point graph for all the different parameters taking the center of the circle. But I am not able to able to export all the data. When I try to export using the 'export plot ' I got error which says 'Unknown property ...property spacevars'



Regards,
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Singular matrix error occurred

December 13, 2013, 2:33 pm
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I am finding eigen frequency of two helical coils for wireless electricity. every thing is goes well: geometry, materials,Electromagnetic Waves- Frequency Domain & Mesh . But when I compute, Singular matrix error occurred.
Also I can't even upload file because there is also error(File size error).
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2D Marangoni Effect due to Evaporation of Solute

December 13, 2013, 7:26 pm
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Dear Community,

I am trying to solve Marangoni effect due to evaporation of solute. I have closely followed the model example in which the Marangoni effect is due to the thermal gradients.

Here is what I would like to know.

1. How to define the weak term in my model? I have tried using "-test(u)*k*cx"
Also, I don't understand weak term properly :( and what do these test functions mean?
2. I think, one can also use boundary stress instead of weak term. I defined my boundary stress as "-k*cx". When I try to solve I have convergence problems. Any thoughts?

also, I really appreciate if some one can give me an intuitive understanding of weak term.

PS: k is the evaporation rate and cx is the gradient in c (i.e.) dc/dx

thanks
Sathish.
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Simulate a musical instrument on Comsol

December 13, 2013, 8:16 pm
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Hi, I'm new to Comsol and I'm trying to perform a simulation about a con-shaped wind musical instrument. I'd like to obtain the harmonics of it, and I have already built a geometry, but I'm not sure about how to model it. Can you quickly resume what should I do (for dummies, I am a complete newbie) or at least point me at some tutorial where the steps are described?

Thank you.
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how to solve piecewise equations with integration using comsol?

December 14, 2013, 1:14 am
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Hello everyone,
I am a new comsol user, recently I have meet a problem and don't know how to solve it.
The equation are as follow:

X=0, when V<0.5;
d(X,t)=V,when V>=0.5;
V=sin(2*pi*t);

I don't know how to solve these equations using comsol, can anyone give me some sugesstions?
Thank you for your reading my posts and I am looking forward to reply.
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Concentration profile of transport of diluted species

December 14, 2013, 5:37 am
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Hi all
I am running simulation containing a node of flow through free and porous media and a node for electrostatics and one node for transportation of dilute species but i m not getting a concentration profile it is showing the same inlet value of concentration profile how to solve this. Mine geometry is a porous present between two free medium.

Please help me out
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Segregated Group Solver different results

December 14, 2013, 9:18 am
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Hi folks,

I have been using COMSOL for a while now and, sometimes, when facing a difficult convergence problem I do mess around with the solvers a bit.

I have seen some posts here on the forum regarding the segregated vs fully coupled and my question/issue
is somewhat of the same nature, I presume.

When doing CFD for solid-liquid mixtures I tend to have some issues with the dispersed phase, with 3 different segregated groups. I can get around this by putting the dispersed phase variables in the same group as the velocity and pressure, and then the convergence is considerably smoother.

The problem here is that the results have changed by comparison when I don't mess with the segregated groups. The pressure and velocities resulting from putting the dispersed phase variables in the same group as velocity and pressure. Can anyone explain why this happens?? I would think that since the fully coupled and segregated solvers are to provide with the same solution, then altering the segregated groups to emulate a quasi-fully coupled solver wouldn't mess with the results...

I'll say that my understanding of the solvers is somewhat superficial resulting from COMSOL documentation, and if someone can point me to some papers that better clarify the difference I would be very grateful.

Hope someone has some insight on this subject.

Best Regards,

Rui Silva

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Using lower limit node

December 14, 2013, 11:57 am
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Hi,

I'm trying to use the lower limit node, but I can't select any variables because the variables window is not there. I can select variables in the segregated step nodes. See attached file for screenshot.
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Fire and Structure

December 14, 2013, 11:51 pm
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How can i determine deflection of beam under fire?
How can i determine thermal expansion of concrete & steel under fire?
How can i determine heat flow rate of concrete & steel under fire?
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Capacitance

December 15, 2013, 4:12 am
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Hi!
Where could I find explanation about how Comsol computes capacitance in 3D AC/DC modeule -> statics, electric -> electrostatics (postprocessing, C11_emes)?
I have 3.5a version, but I think it is the same in all versions.

Thanks for your reply!
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Heat transfer modelling of selective laser melting

December 15, 2013, 6:38 am
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Hello everyone,
How can I simulate melting of a powder media? To be more clear, when the temperature of a part in a powder bed exceeds melting point, it turns into molten material. After that when the temperature decreases and comes below the melting point, it solidifies but does not turn into a first state, i.e powder material. Indeed, the problem is, it turns into a solid material. Thereby, phase change module of COMSOL can't understand it, hence I was wondering if someone could assist me in this situation.
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3D Window control with Space Navigator 3D-mouse

October 6, 2010, 11:25 pm
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Hi everybody,

I use a 3dconnexion Spave Navigator for control in SolidWorks.
In COMSOL such devices are (to my disappointment) not supported.
Does anbody know about a feature request? If not and more people would be interested
in this, I'd very much like to make a feature request out of this...
What does the community think about this?

Regards,
Markus
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Using saved solution Comsol v4.1

April 1, 2011, 10:40 am
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hi,

I want to use the saved solution for the initialization of the second one. for example I solve my problem with a given boundary condition and I want to increase the boundary value for the next modeling. But for the new study I want to use the previous solved results as the initialization values of the new one. how can I do it ??

I have to press the Update Solution button ??

Thanks,
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cone-jet mode in electrostatic field

August 30, 2012, 5:13 pm
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Hi,

Here is my problem.
I want to simulate a electrohydrodynamic (EHD) phenomenone , a nozzle with full water (or electrolyte) in a electrostatic field, the the water is polarized and deformed the Taylor cone,then comes the cone-jet mode. My models include the level set -laminar flow and electrostatic,but still cann't get the cone-jet result.Is there anybody also working on a similar model like mine?Did you get the cone-jet results?

Thank you.

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Need help in output acoustic pressure in air domain

December 11, 2013, 6:40 pm
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Hello,everyone
I used Pressure acoustic, frequency domain and electromechanics Physics, 2D-axisymmetric to simulate a vibration membrane to get the output pressure in the water domain. The result is good. But when I changed the water domain into air domain, the shape of the output pressure line is very strange, the line is very flat at the beginning, but change very sharp unexpected.
The x-coordinate is frequency. I don't know why.could anyone can give me some advises please? Thank you in advanced!
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Plotting ratio of displacement

December 12, 2013, 6:10 am
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Hi,

I am using COMSOL 4.2.1.166, and am simulating a circular membrane as a Structural mechanics 'plate'. I simulate to get the mode shape of the fundamental mode for a uniform load in the normal direction and intial stress in the x-direction. I now would like to plot the ratio of the vertical defelction along the x and y axis as a function of the radius, i.e. something like
w(x=0,y,z=0)/w(x,y=0,z=0)
with vertical displacement w of the fundamental mode vibration. I can't find how to access the vertical displacement along a line (e.g. x-axis w(x,y=0,z=0) ) to be able to plot it. Does anyone know how this can be done?

Best
Martin
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