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how to excite a plane wave in comsol

May 5, 2011, 1:07 pm
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Guys:

Anybody know how to excite a plane wave excitation in COMSOL? Really appreciate it

Best
Meng
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Simulation of evaporation of water drop

August 14, 2015, 8:54 am
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A water drop is resting on a solid substrate and evaporating continuously. I want to stimulate this to know the fluid flow inside the drop while evaporating. I am a beginner.

Please help me.
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Undefined variable. - Variable: comp1.es.epsilonrmZY Failed to evaluate variable

May 15, 2016, 4:01 am
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Hello,

I am designing a MEMS actuated optical filter for WDM applications,I am designing this filter on a cantilever beam of silicon, and for actuation purpose we are using piezoelectric effect. A piezoelectric material is sandwiched in the beam. This filter is multichannel and will have a serially coupled structure of Ring Resonator arrays. When DC voltage is applied to the beam then due to the piezoelectric effect the beam will expand both in horizontal and vertical direction and due to which the refractive index of ring resonator will change. Due to which it will allow a particular signal with a certain wavelength and block the other signals. This property is used in tuning the filter. Each set of filters is located in the middle of the ring to obtain uniform stress and longitudinal uniform strain.
This beam is multilayered the beam designed below is being used for actuation purpose when DC current will be applied it will expand and due to which the upper silicon beam which consists of array of ring resonator will also expand and shape of ring resonator will change because of it and wavelength tuning will be achieved.But when I try to compute I get the below described message




Undefined variable.
- Variable: comp1.es.epsilonrmZY
- Geometry: geom1
- Domain: 45
Failed to evaluate variable.
- Variable: comp1.es.epsilonrS32
- Defined as: comp1.es.epsilonrmZY
Failed to evaluate variable.
- Variable: comp1.es.epsilonrZY
- Defined as: comp1.es.epsilonrS32
Failed to evaluate variable.
- Variable: comp1.es.chiZY
- Defined as: comp1.es.epsilonrZY
Failed to evaluate variable.
- Variable: comp1.es.PZ
- Defined as: epsilon0_const*(((comp1.es.EY*comp1.es.chiZY)+(comp1.es.EX*comp1.es.chiZX))+(comp1.es.EZ*comp1.es.chiZZ))
Failed to evaluate variable.
- Variable: comp1.es.DZ
- Defined as: comp1.es.PZ+(((comp1.spatial.detF*(comp1.es.Ey*(comp1.es.Iyy*(epsilon0_const*comp1.spatial.invF23))))+(comp1.spatial.detF*(comp1.es.Ex*(comp1.es.Ixx*(epsilon0_const*comp1.spatial.invF13)))))+(comp1.spatial.detF*(comp1.es.Ez*(comp1.es.Izz*(epsilon0_const*comp1.spatial.invF33)))))
Failed to evaluate expression.
- Expression: d(((comp1.es.DX*test(comp1.es.EX)+comp1.es.DY*test(comp1.es.EY)+comp1.es.DZ*test(comp1.es.EZ))*comp1.es.d)*(dvol),{test@12})
Failed to evaluate Jacobian of expression.
- Expression: ((comp1.es.DX*test(comp1.es.EX)+comp1.es.DY*test(comp1.es.EY)+comp1.es.DZ*test(comp1.es.EZ))*comp1.es.d)*(dvol)


I am having some problems with meshing as well.This is my final year project.Any help will be greatly appreciated.

Sincerely
Rahul Parganiha
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material library

May 15, 2016, 12:04 pm
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hello

I would really appreciate if anyone can help me how to get material in Comsol?
I want to add silver and gold material to my structure but there is no silver in the list.
Please help.

Thanks!!
Kalpana
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How to model a chemical reaction with diffusion in COMSOL?

May 15, 2016, 6:23 pm
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Hi,

I really hope someone can help me. I'm trying to simulate this problem for a little bonus in my master thesis, which is due in 3 weeks.

I simplified the geometry for the sake of simplicity, but the rest is pretty much the same. I have a rectangle filled with water. One face of this rectangle is at a constant concentration of a chemical species. The opposite face is has a constant production rate of another chemical species. These chemical species diffuse into the water.

These to species then react with eachother to form another species. I would like to simulate the concentrations of all of these species in time. I drew something to hopefully make my problem more clear:

imgur.com/9xyaZYy

I have tried to use the chemical engineering toolbox to do this but the assumptions that the different reactors make are not suited for my problem. Should I use the chemistry toolbox? I cannot seem to model my reactions in this though. Can someone please explain to me how to do this? I would be forever grateful.

Thanks,
Evan
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Please, Help. Problems with calculation of partical trajectories

May 15, 2016, 7:44 pm
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Hello Everyone!
Maybe can Someone help me? I can't find out what I do wrong in Partical Tracing modul (AC/DC) for calculation of partical trajectories.
I have model with four electrodes. One from them is cathod. Three other are anodes or regulators of electric field in dependence from set value of potencials. Cathod generate electrones through field emission.
On first step I had calculated distribution of electric field in my structure using Electrostatics modul. There are not problems. On second step in Charged Particle Tracing modul (AC/DC) I had used "Electric force" and "Inlet" ("Wall" and "Partical properties" had left the default). In "Electric force" I had set data of calculated electric field on first step. In "Inlet" I had set "Release Time" and chosen "Density" in "Initial position". Then I had input "Number of particles" and "Density proportional". After that in Time dependent study I had input simulation time. Then calculation was started.
System gave me wrong results after making those actions: trajectories of particles are straight as though they weren't reacted at electric field. When I had decreased cell of mesh or desreased step of time in "Study", calculations is not converged.
I am new in COMSOL and I can do something wrong. Please, help me to find out why particles don't react at electric field. Maybe does someone know suitable samples?
Thanks in advance to anyone who can help me.
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A closed pipe

May 15, 2016, 11:37 pm
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I want to model a pipe has only an outlet, In fact, I changed inlet to wall. How can I define boundary condition for this case?

I attached an image,

TX
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Acoustic Band Structure in 2d

September 28, 2009, 3:51 pm
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Hi Folks - Ive posted a couple of questions to some related discussion but it looks like they haven't been visited in a while so I thought I would make a new discussion group.

I am interested in finding out whether or not it is possible to calculate acoustic band structures using a reciprocal lattice simulation and periodic boundary conditions. I understand this is typically done by solving for eigan solutions to the helmholtz equation as you vary the direction of the plane wave vector. My question is... while performing an eigan value analysis and say, computing 100 eigan values in the vicinity of the stop band, how does one back out the wave vector direction related to the given eigan values

Thanks

Sean
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Mesh Quality basics

September 7, 2010, 5:02 pm
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Hi,

I've got some pretty basic questions about mesh quality, but I can't find any direct answers to these questions.

Why is it important? I found sources that say that it is important for fast convergence of iterative solvers, what about direct solvers? Are there other issues such as solution accuracy, stability and mesh inversion? What causes low-quality meshes to be problematic?

Is it necessary to enforce a minimum element quality? I've read you should keep it above 0.01 but it doesn't say what happens if you don't.

Do the same meshing rules apply for triangular and quadrilateral meshes?

If anyone could answer these questions it would be of great assistance. I haven't had much luck finding explanations aimed at the beginner to intermediate users of FEA.
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Express objective function in Optimization study of Frequency domain in Acoustics module

February 6, 2015, 10:55 pm
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Hi,

I want to run an optimization study in frequency domain. I have experimental values of the variable alpha for specific frequencies and I want to adjust my control variable R in order to match these results. If my experimental results are for frequencies 20, 30, 40 kHz ... then the objective functions to be minimised are:

abs(alpha(20kHz) - expermentvalue1)
abs(alpha(30kHz)- experimentvalue2)
abs(alpha(40kHz)- experimentvalue3)
....

My question is: How do I express in Comsol "alpha(20 kHz)"? Is there an operator to do so?

Thanks
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Geometry building differently during Batch Sweeps than in individual simulations

May 12, 2015, 4:44 pm
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COMSOL'ers:

I have a geometry of a V-antenna which builds properly as a function of angle ("del") when simulated individually; however, when run under a batch sweep (of del) the geometry does not resolve the same way.

I open a solved batched model, and instead of a V-shaped antenna with the given axis angle, I get a shape that looks like the antennae have collapsed onto themselves. I then click on "Build All" (which uses the intended batch parameter) and the geometry then reverts to the intended shape! There are no errors, but there is a grey asterisk next to one of the transformations (Rotate) in the post-run model, as well as next to Solution 1. I have not been able to pull any other warnings/errors from the simulation.

Any thoughts why it would build properly for a single simulation but not for a batch?? Is there an issue with using [deg] and [rad] units? I have the geometry and input parameters set to [deg], but the batch converts to [rad]. Nevertheless, individual simulations will resolve [rad], so I do not think this is the issue...

-Ado
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Using data from Matlab

February 29, 2016, 1:33 pm
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Dear all Comsol users,

To make the question simple, a heat transfer model is set up in 2-D, and every step, I want to calculate the heat source term in Matlab (which will be a 2-D matrix), then send this heat source term back to Comsol.

Currently, from what I found online, the most viable way seems to be setting up a interpolation function. But my concern is that, for a 2-D problem, the interpolation function in Comsol seems to require the data source to be from 'file' instead of table (for 'table' I can set it in Matlab code). This means that I need to save this heat source term matrix from Matlab to hard drive, then read it again in Comsol every step. Will this be very slow? Or is there a better way to do this?

Thanks!
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Incident pressure field, can't set frequency?

April 14, 2016, 4:35 pm
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Hi all,

I am trying to apply pressure waves to a mass contained in a closed volume in order to make it vibrate. So far I got it to vibrate, but I can't seem to find a way to set the frequency of the waves. Is there any way to set the frequency of the applied waves?

I can add my model if that can clear things up more.

Thanks in advance.
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why not the the far field calculation does not work in Frequency-Domain, Perturbation ?

May 3, 2016, 11:43 am
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Hi,

I simulate the transducer performance under pre-stressed, and I reference the template"tonpilz transducer prestress" in the library. Far field pressure works under frequency domain, but I can not calculate the far field pressure under Frequency-Domain, Perturbation, the results are all zero, why?
Thank you!
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Problems with 'Impedance boundary' and 'Cylindrical Wave Radiation'?

May 16, 2016, 4:00 am
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Hi, when I simulate radiation of sound waves with 'Pressure Acoustics, Transient', i meet some problems with the settings of boundary.
I build a small circle as the sound source in a large circular region. The small circle isn't in the center of the large circle. The sound source generates sinusoidal waves in the total calculating time. I hope there is no reflection in the boundary of the large circle, and I used 'Impedance boundary' and the impedance value is the same as the big circular region. However, the values of tested waves in the boundary of large circle are all positive, although the wave is sinusoidal. When i used the 'Cylindrical Wave Radiation' boundary, the tested wave is right.
I thought the 'Impedance' boundary equals the effect of infinite space? Why it doesn't work?
Thanks for answering.
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COMSOL server

May 16, 2016, 4:51 am
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Hello,

I m new on COMSOL . I work in an university as internship and I need to create an app on COMSOL server.
But the problem is that when I click on " try on browser" nothing happens. I don't think if the link between my COMSOL version and COMsol server is done. But I don't know if I can create it without download back COMSOl.
Can you help me ?

Tack!

melanie

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Thermal Expansion

May 16, 2016, 6:46 am
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Hello,
I am working on thermal expansion of a cantilever beam. I want to find out how much my beam has expand due to applying heat on it? its a bimorph. I am applying heat on upper layer. I want to know how much it expands in respect of lower layer. How can I calculate it?
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Induction motor 2D Identity pair problem

May 16, 2016, 6:57 am
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Hi
I'm working on simulating an induction motor in 2D...I've read all guidelines and discussions in forum about electrical machine simulation especially induction one... I tried to model my case in Comsol 5.2 and did all of points and steps carefully but I'm in serious problem about identity pair and magnetic insulation
I tried two way:
1)union rotor section and stator section separately and then assembly and finalize geometry...so generate identity pair automatically...
2)assembly all geometry directly and choose identity pair boundary manually
in first case magnetic insulation apply on identity pair and i couldn't solve this problem...
in second case comsol given an error about that identity pair
could anyone help me...?
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Stopping the flow in a pipe after a certain time

May 16, 2016, 9:22 am
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Hi, I am new to COMSOL and I am simulating the expansion of steam in a a condenser from a cylinder. They are connected by a pipe. The expansion is due to pressure difference. I need to run the simulation for about 1 s.

Is there any way I can block the flow of steam from the cylinder to the condenser after a certain time say about 0.5 s and then simulate just the condenser for the remaining 0.5 s?
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Import Table for defining inflow concentration in transport of dilute species

May 16, 2016, 12:25 pm
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Hi everyone,

I am working on a diffusion problem in COMSOL 5.1. I have problem with laminar flow in a pipe. The concentration of solute in the fluid varies over time. I have a table specifying the concentration at every time step. I need to import this table as the inflow for the problem. I was hoping someone could tell me how I could do that. Right now I can only see an option to define a single constant value for inflow.

I am a new user of COMSOL and would appreciate any help.
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