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Port propagation constant in Comsol

April 24, 2020, 1:52 pm
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Dear Friend,

Hi ,

I want to define a 6-port domain in COMSOL 5.2a. The domain contains 25 identical Rods.

I want to excite port#1 and read the powers arrive to another ports.

so , I define ports on wall of the Block domain. I also create exterior layer outside the domain and manually force the ewfd.Ex& ewfd.Ey& ewd.Ez to zero on this layer to absorb the received power on ports. I define "user defined" ports. I set x component of incident electric field of Port#1 to 1[v/m] and also the propagation constant to abs(kbz) . ( = ewfd.k0 * cos(theta) )

I attach the structure.

My question is :

  1. what is the meaning of "propagation constant" for listener ports (port#2,3,4,5,6) and in this case what should I set to ?

  2. what is the meaning of "electric mode field" for listener ports(port#2,3,4,5,6) and in this case what should I set to ?

  3. Does any body have the same experience about this issue?

Thanks !

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Mirror surrounding by PMLs overrides Boundary Conditions

April 24, 2020, 3:06 pm
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Hi,

I am new to COMSOL. I am designing a mirror inside air and then surrounded by PMLs. Before I added the PMLs , I added the PMC/PECS and Impedance boundary conditions at the mirror and I was thinking of using a SBC at the outer PML boundary for radiation to enter. However it seems now that all the boundaries but the ones that refer to outer PMLS are disabled.

What am I missing here?

Thanks!

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Contact adhesion convergence

April 24, 2020, 5:09 pm
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I’m modeling ice deformation by dislocation creep with the base of the ice frozen to the rock beneath it. The ice deforms such that the right boundary (initially almost perpendicular to the base) contacts the rock. It should then freeze onto it, so essentially there should be adhesion of the ice to the rock. I’m able to get a contact model both with (attached) and without adhesion to converge, but only up to ~200 years, and then it reaches a singularity and doesn’t converge. I think that part of the reason for this is likely the geometry, since the two sides of the contact pair are again almost perpendicular at that point. Is there any thing I can try to improve the likelihood of convergence for this sort of geometry? One idea I've had is to decrease the mesh size, but I've had some problems with decreases in mesh size making a similar model not converge for as long so I wasn't sure that would help.

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Mesh size decrease making time dependent model not converge for as long

April 24, 2020, 5:24 pm
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I’m running a time dependent model of ice deformation. Generally, I've experienced smaller mesh sizes improving results. However, I’ve recently been encountering some situations where a finer mesh is causing a time dependent model to not converge over as long a period of time. For example for the attached model, with a coarser mesh it will converge up to about 600 years, while a coarse mesh will converge to 250, and a normal mesh will converge only to 140. I'm using COMSOL's default solver settings, which have generally worked well for me, including in similar models. I'd appreciate any suggestions on what I might try to fix this problem.

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Simulataneously giving boundary load and body load

April 24, 2020, 8:42 pm
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I want to give a boundary load and then a body load. More specifically, suppose I give initially a boundary load of 8N and then gave a body load for 10 secs. For this 10 sec I want to watch the velocity in the material for the body load given. Next I want to increase my boundary load to 10N nd again give a body load for 10 sec and watch the velocity. So this will continue with the boundary load as a parameter and for each boundary load given, I will give the same body load for 10 secs and watch the velocity. I have simulated the body load for 10 sec but not sure how to vary the boundary load as a parameter. Any help?

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Tet vs quad Mesh?

April 26, 2020, 3:14 am
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I use the free tetrahedral meshing as it is the default. I read a comsol blog post basically saying that tetrahedral meshing is superior in enabling comsol to find a suitable mesh. I can't however find any specific reasons for using tetrahedral instead of ie free quad and therefore have a hard time explaining my mesh setup from an engineering standpoint.

Thank you in advance

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Particle size distribution in Li battery single particle model

April 26, 2020, 8:58 am
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Hello, I want to add a particle size distribution to a negative electrode in Li battery single particle model. In fact, the goal is to define a multi particle model instead of a single particle model. For that, a Weibull distribution should be defined within a PSD range. How could I do that? The Weibull distribution is defined by: number fraction density=(k/λ)(R/λ)^(k-1)exp(-(R/λ)^k) Thanks for your help in advance.

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Non-reciprocal transmission by spatiotemporal modulation of relative permittivity

April 27, 2020, 12:02 am
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I am trying to reproduce the paper: Complete optical isolation through indirect interband photonic transitions

The non-reciprocal transmission they have demonstrated in fdtd by their in house simulation code. I want to reproduce the same results by spatiotemporal varying the relative permittivity in comsol multiphysics.

I have simulated using the physics ewt(electromagnetics transient) and the study is time dependent. Seperately I am defining epsr(x,t) as analytic variable then using it in wave equation for the silicon choosing epsilonr (relative permittivity) as user defined. I have used for isotrpic case & diagonal case. There is no change in the FFT at the probe position with plane wave excitation. Frequency sweep has also been applied. There should have some change at the FFT probes (upshift or down shift in frequency). Is this is the correct way of modelling this dynamic permittivity modulation or there are some other ways to do it, if any.

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Ag2O-Zn Battery

April 27, 2020, 4:35 am
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Looking to purchase the batteries and fuel cell module. Can this module simulate redox reactions between Ag2O and Zn electrodes? Thanks

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Exporting data files after parametric sweep with varying mesh size

April 27, 2020, 5:22 am
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The below post is related to an archived discussion

[start here] Hi, I'm doing a parametric sweep on some of my model's geometry parameters. I would like to export the data for each parameter combination into an independent .txt file for post-processing. I followed the instructions in the above discussion, but I get the following error:

"Data can only be exported if the same mesh is used for all parameter value"

Is there any way to do this? If I run the sweep and then save the results for each solution manually it works fine, but this is very tedious when I need to run many combinations...

Thank, Ori

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lithium ion battery anode simulation

April 27, 2020, 5:56 am
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Hi everyone

I'm using comsol to simulate the anode capacity fade in lithium ion battery, now I have this model but it just does not converge. Tried many methods (such as solver congiguration and changing initial values) yet nothing worked.

Could you please help me with that? Any indication will be helpful.

Thanks in advance.

best shihao

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How to create a spiral phase plate in COMSOL?

April 27, 2020, 10:48 am
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I want to model a Spiral Phase Plate (as shown in figure SPP.png).

Here the thickness of the object varies with the azimuthal angle as in .

I have tried using a parametric surface to draw the faces of the plate and create a closed solid (as shown in figure SPP2.png) and then convert to a solid, however I keep on getting the message ´The operation resulted in an empty geometry´.

What could be the issue here? Is there a way around to create the spiral phase plate?

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Rotating Machinery field distortion for discontinuous mesh

April 27, 2020, 11:54 am
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Hello,

I am simulating a simple model of a conductor rotating in a uniform magnetic field. I am using the rotating machinery module in order to do so. I form an assembly and use a moving mesh in order to rotate the conductor, using a Continuity node between the moving and fixed domains. However, when i run the simulation, the field at the Continuity boundary is distorted, as shown in the attached figure.

I realize that the boundary is too close to the conductor and that this would probably work if the boundary was set further. However, this simulation is a precursor to another more complex model which would require the boundary to be close to the conductor.

I believe that the problem is caused by the Continuity node imposing continuity on the vector potential, whereas I am plotting the derivative of the vector potential. Is there any way to have a continuity of the derivative as opposed to a continuity of the dependent variable? I have also tried using weak constraints for the Continuity, but I still get the distortions.

Thank you

Alex!

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2D contour from x-y point data only

April 27, 2020, 4:04 pm
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Hi folks,

I have an interesting results analysis problem. I would like to be able to take extracted point data, regrid it, and then generate a contour plot within Comsol Multiphysics. Presently, we export our model point data as x, y, and model values at those points (point evaluation), and then import the data into a separate data plotting program, like Surfer, to regrid and plot the data. In this way, the plotting is blind to the FEM mesh and related computational smoothing. I would like to use Comsol Multiphysics to do the same thing Surfer does. I would like to remove this added step. Is Comsol Multiphysics capable of doing this task?

You may ask, Why would I do such a silly thing as this? Some types of data from real data acquisition systems comes from widely separated point locations, comprises a field measurement of some sort, and contains no information about the nature of the field between the point locations. This is the classical problem of imperfectly spatially sampled field data. Nevertheless, field (like potential field) measurement data acquisition systems that make spatially sparce measurements, generate this sort of data. I would like to be able to emulate this in Comsol Multiphysics, if possible.

Any ideas?

Thanks,

Allan

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Eigenfrequency change in acoustic structure interaction / radiation model

April 27, 2020, 4:34 pm
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Hello, I am interested in modelising the elasto-acoutic coupling of a thin plate surrounded by air. My model is a plate surrounded by a sphere of air. My problem is that if when I change the radius of the sphere or even when the plate changes position inside the sphere, the eigenfrequencies of the plate change quite a lot For exemple, a given eigenmode with an eigenfrequency of 1285 Hz inside a 40cm radius has an eigenfrequency of 2007 Hz in a 80 cm radius sphere. Would you have a clue on how to fix this problem ? An other information that might (or might not !) be usefull is that when I compute the eigenfrequency study, the eigenmodes of both the sphere and the plate are return. Would there be a way to compute the eigenmodes of the plate only, still taking into acount the elasto-acoustic conversion without the geometry of the volume of air being an issue ? Thank you for your help, Best wishes, Chloë

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COMSOL FSI Simulation

April 27, 2020, 9:10 pm
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Hello everyone, hope you all are safe and sound and doing well. I am new to comsol and I want to simulate the solid body like a fish moving in a water. I want to calculate the velocity, drag and lift forces and generate graphs. The fish actually has SMA wires inside for its actuation mechanism. I am wondering how to do it and provide temperature to sma wire for its actuation in simulation. Kindly help me in this. THank you.

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Modelling the Spatially Non-uniform Current Density of an Electrode

April 27, 2020, 11:31 pm
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Dear All,

I have a 3D electric current model of an electrode in a medium, where the electrode is modelled as a thin disk. I would like to model this electrode as having non-uniform current density on its surface, which is determined by the radial distance from the centre of electrode.

,where is a constant value derived from the total current, is the radial distance and is the radius of the electrode.

I think the 'Terminal' boundary condition comes close to this, but is there any way to control the distribution of the current density so it follows this equation exactly?

Asty

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The display problem of deformation results of folding structure simulation

April 28, 2020, 2:21 am
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Hi,

I am new to COMSOL. This model is a folded structure, and its simulation process is: PNIPAM folds the surrounding elastomer board through thermal contraction (the coefficient of thermal expansion is negative), the ideal effect is that it can be folded into a square box, and the surrounding four boards's thermal expansivity is 0, but l see that results → stress → surface → deformation, the surrounding plates are stretched, and it is not clear why or where the problem is.

Thanks!

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Why can I not do a periodic mesh despite identical surfaces?

April 28, 2020, 5:33 am
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I have a fairly simple structure that is visally periodic yet Comsol refuses to perform a face copy operation. I have attached the mph file and the imported .stp file. Below is my geometry. I have tried splitting my operation into parts and the surfaces that cannot be copied make no sense to be as they are clearly identical. What's the problem?

I have tried various mesh settings as well as the virtual operation of ignoring edges/vertices that intersect the boundaries to no avail.

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Multi-material Coil issue

April 28, 2020, 7:30 am
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I am having an issue simulating a coil usng magnetic fields physics. I have simplified the problem down as much as I can an find that the coil feature only seems to work when all parts of the coil circuit are made from the same material.

My simple problem consists of three blocks, initially all made from copper. I join them with a void block removed from the mf solution and surround with a sphere of air with a layer of infinite elements. I form a coil from the three copper blocks, add input/output boundaries, mesh and compute, this works with no problems. I then duplicate the copper material - to 'copper 2' and rerun the simulation. This also works just fine.

Now I change the electrical conductivity of copper 2 from the 5.998e7[S/m] value that the original copper has to 5.900e7[S/m]. A minimalchange in electrical conductivity to one section of the coil. COMSOL is unable to find a solution due to divergence.

I have (hopefully) uploaded an image to illustrate.

Does anyone have a solution or advice? Do I need to make a chain of coils linked to each other? If so, how to I link them?

Thanks in advance

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