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Modeling closed circuits with pipe flow module (linking inlet and outlet)

September 25, 2014, 1:07 pm
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Hi Comsol experts,

I an trying to model a closed pipe circuit consisting of a network of pipes, bends, valves, junctions and heat transfer areas. A pump is inserted to create the force (dP) to move the water inside the pipes.
Is it possible to model this with a closed pipe circuit or do I need to have an inlet and an outlet?
If inlet and outlet is necessary, how do I link the boundary conditions of the inlet and inlet (mainly velocity and pressure and temp) to model my closed circuit?

Any help is very much appreciated :-)

Regards
"A novice cfd/pipe flow dude" / Morten
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Problem with max field calculation

September 25, 2014, 1:41 pm
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Hi.
I have a resonator inside background media. I use PML around. I am looking at a particular mode. Then I can find the maximum of normE field which is inside the resonator. Now if I change the size of background media normE max is changed!! Although the resonator shouldnt be affected by the size of background media.

Is it possible that comsol normalizes modes to the computational volume?
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Fluid Piezoelectric coupling problem

September 26, 2014, 3:40 pm
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Hello everyone! I'm a newbie to COMSOL. Unfortunately, I'm experiencing some difficulty in trying to model a relatively simple problem in COMSOL, and I'd be really really thankful if anyone could help me out. Let me cut to the chase. I was tasked with modelling a cuboidal container with a diaphragm on top. The diaphragm is the ceiling of the container (with a finite thickness of course). Now, a Piezoelectric material (a cuboidal strip of finite thickness) is supposed to be attached to the top of the diaphragm (ceiling). In theory, when a voltage is applied to the surface of a piezoelectric material, it deforms. My task was to make it such that the diaphragm deflected downwards. So through trial and error, I found that the voltage must be applied at the top surface of the Piezoelectric material. Moving on, the container is filled with a fluid (say water or ink). (This is supposed to be a really primitive version of a Piezoelectric inkjet printhead WITHOUT THE NOZZLE :p). There is no inlet or outlet. The deflection of the diaphragm, theoretically, causes a change in pressure of the fluid which I am supposed to measure. This is the part where I'm stuck. How do I fill fluid in the container? Which physics should I use for this problem? I tried modelling a solid cuboid and assigned it to "water" and made the diaphragm and piezo material on top? But then what boundary conditions should I give for the fluid physics that I use? (say laminar flow) Should I couple a fluid physics at all? If I don't use a fluid physics, it asks me for the coupling matrix and elasticity matrix for water, both of which I couldn't find out. If I couple a fluid physics with piezoelectric physics then, I do not know what boundary conditions to give for the fluid. I'd really appreciate it if someone could help me out with this. I'll post an image file for reference. I can't upload the model though (my university net restricts me from uploading files of sizes larger than 1MB :( ) Downloads are allowed though, so if you can make a similar model with the necessary changes and upload it, that'd be great! But general instructions and advice are also really welcome and would be highly appreciated. Also keep in mind that I'm a newbie to COMSOL. Thanks in advance!
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Boundary Variable not being Recognized

September 26, 2014, 4:17 pm
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I am having a bit of a problem with defining a boundary variable that has a counterpart defined on the model domain but with a different value.

For a simple spherical particle, I am modeling the classical diffusion equation dc/dt + div(J) = 0 Where J is the flux defined as J = -D*grad(c) using a general form PDE. For the domain I am defining a domain variable D as a function of concentration c (i.e. D(Domain) = f(c)) and for the boundary that completely encloses the domain I define a boundary variable D as a constant value.

For additional information, I define a boundary flux "Jo" on the boundary as well.

When I solve this problem and plot intermediate "D" values, I find that D changes on the boundary which I did not expect to happen.

Can someone please give me some insight on what might be going on or what I am possibly doing wrong?
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error message

September 29, 2014, 1:31 am
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I got a message in equation complaint like the picture show, what 's the problem it is?
how can I solve it?
"Interpolation grid axis values must be sorted in ascending order in each dimension.
Error in multiphysics compilation"
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Two Phase Fluid Flow Convergence Error half-way into solution

September 29, 2014, 1:59 pm
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Hi All,

Time dependent solver for Laminar Two-Phase Flow, Level Set crashes half-way through the solution with error message "last time step didn't converge". Do you know what could cause this? The geometry is a simple y-junction. The mesh is user controlled and done by creating distributions (rectangular) and sweeping them.

Thanks
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v4.1 RF How to use two or more variables in parametric sweep

February 19, 2011, 2:06 pm
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Hi

I want to do parametric sweep that effects the geometry too.
The first variable is the incident field wave length and second is angle of incidence.
How to run these parametrics or how to run nested parametric

Thanks

Irfan
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Solving Self - Consistent Schrodinger and Poisson with MATLAB and COMSOL LiveLink.

September 5, 2012, 6:44 pm
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I'm a COMSOL 4.2a user. I need to solve 2D self-consistent Schrodinger and Poisson equation. Thus, I need to feed the potential values and the wavefunctions to the Schrodinger and Poisson equations as argument and solve iteratively.

The thing I need to know, how can I feed the updated the wavefunction and potential values as argument iteratively in my model? I have livelink with MATLAB and I intend to solve the problem inside a loop (i.e. Calling one models while passing the result of another as argument). I have solved the models with PDE solver but cant do it iteratively with LiveLink.

One more thing, is it possible to access the results directly from MATLAB and thus use them as variable ( though a class of course) from MATLAB for post-processing, like we get the solution matrix in MATLAB?

--
Thanks
Mehedi
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Convergence problem in RF module

April 1, 2013, 2:16 am
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I am doing some plasmonics simulation using silver nano particles in comsol. For silver particle convergence is either very very slow or there is no convergence in most cases for some specific wavelengths. The same model works fine for gold nano particles. Kindly help.
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To demonstrate a "sieve" at the particle tracing module

February 26, 2014, 7:14 pm
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Hi all, now I'm trying to demonstrate a particle sieve using the particle tracing module.
I expected that the particles bigger than the pore size of the sieve could be filtered and stuck on the sieve surface.
But it seems that the particle tracing module cannot demonstrate such effect because every particle can pass through the pores even which are much smaller than those particles!

Do you think that I have to set up a sort of force equation or "if-condition" which can describe the sieve effect by the size difference??

Thanks!!

Dukwoo
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Eigenvalues from different study steps

July 25, 2014, 5:36 am
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Hi everyone,

I am trying to calculate an overlap integral between two modes of different origin -- a common problem of electrooptics or optomechanics. So I have two physics interfaces (say electromagnetic and structural mechanics) and I need to solve them and compute overlap integrals between all modes.

If I use two distinct studies (one for electric eigenvalues and other for mechanic eigenvalues) I get two different solutions (data sets) that cannot be brought together.
If I use two study steps in one study I again get two data sets. Though the first one has one of the modes of first problem, it looks like there is only one of them. I tried to use the with() operator but I still can't address to other modes.

Is there any way to do the thing?
Thanks.
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Piezoelectric Transducers

August 25, 2014, 7:03 am
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Hi
I am analyzing the signals in piezoelectric transducers. Can somebody help me in finding some of the difficulties I am facing.

1) How could I measure electric potential of the container on which an piezoelectric is placed.

2) How could I calculate the vibrations being observed by the piezoelectric when one piezoelectric is used to emit the vibrations and other is used to receive the vibrations.

Kindly suggest me an answer to the above questions, which would be a great help to my project.
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Convergence versus meshing granularity

September 12, 2014, 12:47 pm
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I have noticed interesting behaviour in my models.

If the model will solve using a coarser mesh, it may not solve well using a finer mesh.

And although use of the boundary layer tool can reduce the wall lift-off, it does not necessarily reduce convergence time, and often can lead to convergence instabilities. Sometimes I can only add 2 boundary layers.

Also, if I use an initial field from a coarsely meshed solution, the convergence behaviour for the finer mesh will only begin to act erratically earlier.

I have noticed these effects using the k-epsilon and k-omega turbulence models.
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Catching errors in parametric sweeps

September 22, 2014, 9:12 pm
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Dear all

Is there an elegant way to catch errors in large parametric sweeps?
E.g.: When varying values of parameters one might well reach a point when convergence (or other) problems are encountered.
It would be a very nice feature if COMSOL would log this error and continue the sweep with the next parameter value(s) instead of stopping the whole sweep.
Is this possible even when not running COMSOL via the Matlab interface?
Or would something like the "try catch" method in Matlab be the only way to achieve this?

How do you treat this issues?

Thanks for interesting hints on this and best regards,
Juergen

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problems with linear projection

September 23, 2014, 3:07 am
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Hi all,

I developed a model for calculation of AC losses and I am using Linear projection operator to ensure sufficient current flow (Point-wise constraint later). The problem is that my linear projection operator fluctuates a lot. You can see that in attached graph. What could be the reasons?
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Simulating capacitive device operating at collapse voltage

September 23, 2014, 8:29 pm
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Hi,

I'm trying to simulate an capacitive ultrasound transducer operating at collapse voltage. The model, made of two parallel capacitor plates, are expected to collapse into each other during simulation, then its eigenfrequencies are to be calculated. Is this possible with COMSOL? If not, would it work if I start the simulation using an already collapsed model?

Thanks,

Sergei
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Simulation in Finned Tubes

September 24, 2014, 12:02 am
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How to do heat transfer and flow simulation in Finned Tubes

I tried a lot ; but i could not able to give correct boundary conditions.

Please help me to solve this problem.
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Difference between optimization and parametric sweep?!

September 24, 2014, 3:28 am
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Hi Comsolers,

Could you kindly tell me that what is the difference between optimization module and parametric sweep in comsol, please?
I know that maybe it is simple question, But I want to need when a user choose optimization or parametric sweep for his/her model?

Thanks in advance for your help.
Sepideh
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Smoothing battery current changes

September 24, 2014, 12:28 pm
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I've been having issues with the capacity fade model and I think I may have narrowed down the problem.

See the model in question here: www.comsol.com/model/capacity-fade-of-a-li-ion-battery-12667


I am trying to increase the number of cycles, and I usually encounter errors in the transition between constant voltage discharge and constant current charge. The abrupt change in current density from ~+0.1 A/m^2 to 10 A/m^2 usually results in a lot of error and a large voltage spike which completely interrupts the charging-discharging cycle determined using the events interface.

As I understand it, the discontinuity of the current input is not something COMSOL likes.

I see that there are smoothing functions available, but I am not sure how to use them in concert with the events system used to determine the current load in this model. Any help would be appreciated.
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resistance measurement

September 24, 2014, 7:18 pm
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Hi,
I am working on joule heating and thermal expansion module.
I want to measure resistance between two terminals. No voltage is applied to the terminals, no current flow initially. Later through induction or channel formation current will flow and it will change the resistance.
How do i measure the resistance initially and after current flows.
Thanks
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