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Modeling no separation in Comsol

April 20, 2020, 3:27 am
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Hi,

I am a new user of comsol. I am trying to model sliding in Comsol with no separation. I have tried to approaches to tackle this. 1. With adhesion contact and 2. General extrusion and prescribed displacement.

However, my surface is inclined which made my general extrusion a little bit confusing. And secondly, in the adhesion stiffness I am trying to give value to the "normal to shear ratio" which can make the surfaces stick together through all the simulation. I have attached how the boundary look like. I need a little guide.

Thank you so much for your help.

Kind regards,

Robel

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Particles agglomeration

April 20, 2020, 4:54 am
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Can someone tell me how to add particles merging and bounce model into comsol? I kind of know that I need to do something by Matlab livelink but don't know how. I tried to use Distributed ODE to set the particle velocity by something like:

(fpt.vx - nojac(fpt.mpfpt.vx-dest(fpt.mp)dest(fpt.vx)/(fpt.mp + dest(fpt.mp))))

However, apparently the function dest() will not work in this node. Hence, I need some stuff to tackle the traversal of all particles and see if the collision will lead to merging or bounce away. BTW, the whole process needs to be done inside one time step and I cannot find any useful discussion talking about doing this job. Is there any practical approach to deal with it.

Thanks

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Warning exists during Form Union

April 20, 2020, 7:03 am
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Hello everyone,

I met a problem by forming an union: when I try to form a union, half of the geometry is removed (2D model, r<0 is removed, axis symmetric), what should I do for this ?

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Optical self heating?

April 20, 2020, 8:27 am
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Hello everybody,

is it possible to model optical self heating in COMSOL? Currently I'm trying to simulate a silicon photonic ring resonator/modulator using the wave optics module. The resonance of such a device is very sensitive to temperature and measurements show that optical self heating plays an important role in its characteristics. So if the ring is resonant, significant optical power couples into the ring and heats it up due to absorption. This detunes the ring. If the ring is excited slightly off the resonance, it depends on to which side you are off, because on the one side, heating the ring results in even worse resonance or to the other side in a better resonance, shifting the resonance more to the excitation wavelength, resulting in better coupling, resulting in more absorption, resulting in higher temperature, back to the beginning... Unfortunately I don't know, which physical interfaces I have to use to model this behaviour and how to put them together. Could anybody help me?

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Can you give me some advice about the simulation of biofuel cells?

April 20, 2020, 7:16 pm
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I'm a postgraduate student majoring in enzymatic biofuel cells. I wanna to construct a membraneless biofuel cells model consisting of anode, cathode and electrolyte. The fuels for anode and cathode are both injected by the electrolyte. Because the oxygen concentration is directly related with the distance between anode and cathode(the thickness of electrolyte layer ), I'm planning to simulate the relationship between the thickness of electrolyte layer and the electrolyte current density. So how can I set the model?

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Geometry causes abnormal physics settings

April 20, 2020, 9:49 pm
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Hi everyone, I made a inductive heating coil with a complex geometry composed of multi-geometric shapes. When I set physics，it shows different domains rather than one total domain. The coil geometry is continuous，how can I set these part together ? (In the physics setting, it is seen that the coil is an independent domain rather than a large number of scattered domains) Thanks Andy

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Reversing the axis plot

April 21, 2020, 6:23 am
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Hi,

I am trying to plot a graph where one of my axis value ranges from 80 to 210. I would like to reverse the numbers and start from 210, in other words reverse the axis. Does any one know how to reverse axis?

Any help would be appreciated.

Thanks, Anto

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Getting the surface from a domain programmatically inside livelink

April 21, 2020, 8:21 am
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I am trying to use a coding approach, for varying models etc, to building my simulation. When it comes to exporting results I want to export values of data on a surface.

So I have a domain and I want to select a surface for the result output. It looks like this at the moment.

model.result.create('pg1', 'PlotGroup3D'); model.result('pg1').create('surf1', 'Surface'); model.result('pg1').feature('surf1').create('sel1', 'Selection'); model.result('pg1').feature('surf1').feature('sel1').selection('geom_dsv_dom'); model.result('pg1').feature('surf1').feature('sel1').selection.set([137 138 139 140 210 211 216 217]);

The question is, I dislike using the numbers, hard coded for the boundaries, and want to know how to use a selection tag to do this. I can get a selection to the domain, that the surface I want defines as follows

dsv =model.selection('geom1_dsv_dom');

(_bnd does not work)

but how can iuse this to make the selection in my result output?

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An optical fiber coupling to a waveguide

April 21, 2020, 9:51 am
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Hello, I would like to simulate the coupling between an optical fiber and LiNbO3 waveguide. Is the Beam Envelope Method a useful tool for this problem? In particular, can it manage the discontinuity of index of refraction at the fiber/waveguide interface?

Thank You

Marco

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Convergence criteria of the segregated solver are met but not all conditions for group Heat transfer are fulfilled.

April 21, 2020, 10:19 am
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Hi,

I have constantly encounter a message like this: Convergence criteria of the segregated solver are met but not all conditions for group Heat transfer are fulfilled. or Convergence criteria of the segregated solver are met but not all conditions for group mass fraction are fulfilled. I have coupled electric, transport of species, momentum and heat transfer in my model. Can anyone give me some advice? Thank you very much.

Best regards, Xiaoqiang Zhang

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Separate Studies in 5.5 Results in Undefined Variable Error

April 21, 2020, 10:41 am
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I am running a frequency domain simulation with the wave optics module to measure the resitive losses (ewfd.Qe) for an optical absorber. I then feed that value as a heat source into a time dependent simulation for solid state heat transfer. This simulation was working perfectly on 5.4 and as soon as I updated to 5.5 I get the "Undefined variable" error when I try to run my heat transfer study. Any ideas or help that you may have is appreciated!

P.S. - The time dependent solver does not follow the specified logarithmic time steps. I have had this issue with 5.4 as well but never was able to figure it out.

Undefined variable.
- Variable: freq
- Geometry: geom1
- Domain: 2
Failed to evaluate Jacobian of expression.
- Expression: comp1.ewfd.Hy
Failed to evaluate Jacobian of expression.
- Expression: (0.5*comp1.ewfd.iomega)*(((comp1.ewfd.Bx*conj(comp1.ewfd.Hx))+(comp1.ewfd.By*conj(comp1.ewfd.Hy)))+(comp1.ewfd.Bz*conj(comp1.ewfd.Hz))) Failed to evaluate Jacobian of expression.
- Expression: dvol*(comp1.ht.hs1.Q*comp1.ht.d)
Failed to evaluate Jacobian of expression.
- Expression: (comp1.ht.hs1.Q*test(comp1.T)*comp1.ht.d)*(dvol)

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What is the difference between full field and scattered field?

April 21, 2020, 10:56 am
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As stated in the title, I was just wondering what the difference between Full Field and Scattered Field in the RF moduale is?

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how to export the time steps taken by the solver to MATLAB?

April 21, 2020, 11:44 am
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I'm using the COMSOL LiveLink with MATLAB. When I solve time dependent problems and I let the solver choose the time steps (i.e. I only specify the start and end time), I can retrieve the solution in MATLAB by using the commands 'data = mpheval(model,'u1');'. However, the returned matlab structure 'data' does not contain the time steps unless I already specify the time steps in the solver beforehand.

My question is: if I do not specify the time steps, how do I know the time steps taken by the solver?

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Area Calculation in a results graph

April 21, 2020, 12:21 pm
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Hi,

I want to calculate the ratio of blue area over the red area. How is it possible to get the surface area of this kind of plots from results.

Thanks in advance, Reza

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laser diode design by comsol

April 21, 2020, 1:10 pm
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I want to design laser diode using 3d or 2d structure. as i cant find a specific example so if anybody working share with me. using semiconductor module.

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AC purturbation on top of a DC voltage

April 21, 2020, 3:01 pm
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Please see the attached MPH file for drawing.

  1. How to excite a slab with an AC perturbation voltage on top of a DC bias voltage in COMSOL? Let's say I have a slab, I want to apply voltage on both ends as,

  2. How do I properly apply the fixed constraint? If I apply, let's say, a dc voltage to the slab on both sides, it will be squeezed from both ends.

  3. How to incorporate an infinite artificial domain around the slab so that the electric field is zero at infinity?

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Simulation Zinc-Air battery

April 21, 2020, 3:03 pm
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Hi everyone!

I'm currently working on Zinc-Air battery and I'm wondering what kind of pakage is more convinient to adopt. Is it the battery with binary electrolyte a good solution? I'm a new user so any suggestion on how to proceed will be really appreciated.

Thank you Lucia

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How to Ignore Livelink Licensing Error

April 21, 2020, 6:40 pm
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Hello,

I'm using livelink with matlab to run simulations which involve opening a model. The issue I run into is that when the CAD Import licenses are used up, which my script does not require, COMSOL will throw an exception just trying to open a saved file. Interactively, when I open COMSOL and open the file myself, I get the same error, but can click "OK" on the dialog box and it opens my model. How can I effectively ignore this error in my script and continue to opening the file?

Thanks,

Denise

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Matlab giving Comsol initial values

April 22, 2020, 12:34 am
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The below post is related to an archived discussion

Hello everybody

I have an issue that doesn't seem to be resolved, would be great if you can help me:

What I want to do:

I use ComSol with Matlab (Livelink) in Matlab I call the ComSol model and run the simulation. As output in Matlab I have the temperature distribution. THEN I multiply the temperature distribution with a scalar.

NOW I want to give ComSol this new temperature distribution as initial values for the next simulation.

How can I do that?

Thank you for your help

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The process of forming a weld pool during laser welding

April 22, 2020, 1:50 am
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Good day,

I would like to ask for your help.

I am developing a model for the formation of a weld pool and, to regret, has reached a dead end. I know that the topic is not new and there are a number of articles on this topic. But, unfortunately, a complete guide to creating a neutral model failed. It is at the very cost of trial and error to create a model from scratch. At this moment, the model implements heat distribution and fluid velocity. Problems arose with the deformation of the model; this calculation takes a lot of time or an error occurs. Could you help and point out what subtleties you need to pay attention to, the best option would be a step-by-step instruction.

Thanks in advance!

Sincerely.

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