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Heat transfer in solids boundary conditions

May 1, 2020, 3:00 am
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Hi, I am trying to model the time dependent thermal diffusion in a solid with the Heat Transer in Solids physics. It works well, except for the boundary conditions. The heat source is only active initially, and I would expect the model to reach thermal equilibrium with the surroundings/boundary conditions.

I want the boundary to simulate the material being continuous outside of the model. I have tried the open boundary as well as symmetry conditions but in both cases there seems to be no conduction outside of the model. Whilst the heat source is active the model heats, then it holds at the max temperature instead of dissipating the heat. I think I am mis-using a boundary condition but I am not sure.

Thanks

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Importing STL file made in SOLIDWORKS

May 1, 2020, 8:16 am
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I have imported a file in Solidworks and saved it as a STL to be used in Comsol 5.4 however when importing the geometry changed as shown below.

The COMSOL I use doesn't have a CAD import module which left me with no option other than use a STL file. I don't know why the geometry changed and Im hoping someone can give me an answer to why this occurs.

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Water flow in a canal

May 1, 2020, 9:04 am
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Hello to all the community. I am new to using this Software, and I need to simulate the flow of water in a canal. The water must cool the channel (it absorbs heat). I was thinking of using a conjugate heat transfer, and thus define all the characteristics of the solid (channel) and the fluid (water). Could someone give me some advice to make this problem better or some example, please. Thank you.

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Resuming a simulation from a previous run at a time the solver could not converge

May 1, 2020, 3:09 pm
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I was running a simulation a 2D axisymmetric plasma DC discharge. Unfortunately, after 2 days of ruuning, at one of the time intervals, the simulation stopped with the following error:

"Nonlinear solver did not converge. Maximum number of Newton iterations reached. Time: 2.4364424006683502e-06 s. Last time step is not converged."

Is there any way I can resume my simulation from the aforementioned time interval (2.43E-6s) onwards?

N.B. I tried creating a new study starting from 2.43E-6 s by taking initial conditions from the previous study (that crashed out) at that particular time but it did not seem to give dependable results.

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Running COMSOL on cluster

May 1, 2020, 3:12 pm
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Is there any tutorial for running COMSOL on high performance clusters via command line interface?

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weak expression

May 1, 2020, 10:36 pm
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i want to know about the weak form used by comsol. Can anyone tell mw from where can I get the details.

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natrual convection - heat flux calculation - pls help

May 2, 2020, 12:37 am
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Hi there I’m exploring natural convection and still new in it, I solved a simple problem and it works as attached My issue is why heat flux from natural convection are huge as can be seen in dervided 664.6 w/m2 ? its laminar floiw, How COMSOL estimate that? why so high I calculated average surface value , i attached my model (its 10 mb so I ahd to zip it) , its v 5.5 thanks for your help Abraham

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Mirror Surrounding By PMLs Overrides Boundary Conditions?

May 2, 2020, 1:35 am
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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?

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Modelling The Deflection Of Magnetic Elastomers?

May 2, 2020, 1:43 am
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Hi,

I am trying to model the deflection of cantilever-shaped magnetic elastomers in the presence of a magnetic field. I've selected the magnetic fields and solid mechanics modules to model the physics and I've also created the geometry (a rectangular beam in a rectangular box of air). But I am not too sure how to proceed. Any help would be greatly appreciated.

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Choosing a specific batch recovery instance

May 2, 2020, 4:26 am
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The below post is related to an archived discussion

Hello, I made a mistake on my batch script while trying to restart a comsol simulation in batchmode. I'm running a large scale simulation in a cluster and it needs to be restarted several times because of the time limitation of the cluster. I used -continue instead of -recovery -continue and COMSOL started a fresh new simulation so I cancelled it. Is it possible to choose which recovery instance to restart from? It seems that restarting the simulation always tries to recover the last instance (which makes sense), but I would like to choose a previous one.

Thank you, R

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Open COMSOL 5.4 files in 5.3a?

May 2, 2020, 10:44 am
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Hi,

I came across many great models in COMSOL version 5.4. However, my COMSOL is version 5.3a and I cannot open them.

May I know if there's a way to open newer version file?

Thanks, Stacey

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electric mode field for listener ports in wave optics module

May 2, 2020, 11:25 am
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Hi ,

In wave optics module(COMSOL 5.2a.) I want to define a 6-port domain . (lambda = 500[nm])

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. so, I define "user defined" ports. I set x component of incident electric field to 1 and also propagation constant to abs(kbz) . ( = ewfd.k0 * cos(theta) )

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 ?

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

Thanks !

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Implement MATLAB Command onto COMSOL 5.5

May 2, 2020, 4:25 pm
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Hi All, I had everything ready in COMSOL(the boundary condtions, external forces and the geometries are all finished and assigned), while I would like to implement some commands used in MATLAB onto COMSOL, I think LiveLink for MATLAB might be one option, since I am using a Classkit license for COMSOL, what are the best solutions, are there any ways that I do not need the aid from MATLAB, I could still achieve the same MATLAB commands with COMSOL alone?

Thanks

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Boundary conditions for triangular lattice

May 2, 2020, 8:51 pm
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I am trying to simulate an infinite 2D triangular lattice in Comsol for phononic band structure but I am confused that how should I use periodic floquet boundary conditions on the unit-cell.

A unit cell that I am using is given below.

Image

It has 6 sides, L1,L2,...,L6. In the case of a square lattice, we simply just select floquet boundary conditions on both pairs of opposite sides because k_x and k_y are parallel to those sides.

Now, the pair of opposite sides (i.e. L1 and L4, L2 and L5, and L3 and L6) are not parallel to the k vectors. How do we define boundary conditions now?

(I am trying to calculate the band structure on \Gamma, K and M points which are defined on this orthogonal k_x, k_y axis.)

Is there any other way to define k axis and simualte triangular lattice?

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undefined variable comp1.D

May 3, 2020, 8:16 am
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The below post is related to an archived discussion

[start here] "Undefined variable. - Variable: comp1.D" The default name for the diffusivity in the tds interface would be tds.D_cxx (or you could use comp1.tds.D_cxx) ; the name would not be "comp1.D"

-DW

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Diffusion model

May 3, 2020, 9:06 am
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Hi I am trying to model a simple diffusion equation using Fick's law in a square. The left BC is conc = 0 and the right BC is dc/dx =0. Can you please help me with the boundary condition. I need help with how can I incorporate dc/dx = 0 as a boundary condition on COMSOL?

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Example on a piezo sphere excited by an acoustic wav e

May 3, 2020, 11:18 am
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Hello, Is there an example of a piezo sphere (or any shape) excited by an acoustic wave?.

I have seen examples of piezo generating acoustic wave after having a potential difference applied (e.g. tonpilz transducer). I am looking for the other way around.

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- Couple Studies from Different Components

May 3, 2020, 11:46 am
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Hi!

I want to use the output from one study to compute the phyiscs in my second study. The two physics I am using are 'semiconductor physics' and 'solid mechanics'. These two physics are being run on different components in the model.

What I want to do is the use the solution of the first study (and component) to solve the second study (belonging to another comp). The material properties in my second comp. are a function of the output that is supposed to be generated by study 1.

Screenshots attached show a rough example of how I am defining my property as a function of result from comp2, and the error I receive when I run my second study.

Can I do this given that I am working with separate components? If so, how do I work around the undefined var error?

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Problem in updating probe value in time dependent study

May 3, 2020, 1:59 pm
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Hi I'm trying to simulate a disk which has two parts, a rotator and stator. there are two electrodes on stator, and voltage between these electrodes changes when rotator moves. I rotate the rotator using parametric sweep and get the correct voltage, but I want to rotate the rotator with specific velocity so I used moving mesh rotating domain and time dependent study, after computing, I can see the rotator, rotates with time but the probes value doesn't change. I'm using electrostatic physiscs and I defined surface charge density for rotator and stator, and it causes voltage induction on stator electrodes. Is there anyone who can help?

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Way to input power to single turn coil

May 3, 2020, 7:39 pm
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Hello, guys. Maybe, my English is poor. If so, I'm sorry.

I have a problem regarding the simulation of flat spiral coil. And I want to measure the voltage from induction at two ends of coil. The physics that I use is mef. And the study I use is Frequency domain. At the attached file, I used 3D single turn coil and gap feed. But, my comsol said error "Can't find a solution. Divergence of linear iterations. The return solution has not converged. ". Strangely, when I change the study steady, comsol don't say error. However, what I'd like to know is the coil inductance , so I can't tell by steady-state analysis.

And I only have comsol 4.4. I can't open the new version files.

Thank you for any help.

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