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Spring foundation unconstrained domain

December 9, 2019, 5:47 pm
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Hi,

I am modelling an time dependent FSI problem; wave interaction with discrete floating sheets. Laminar flow with phase field is used to model the air-water fluid domain. Multibody dynamics with FSI pair is used for the structural elements. The freely floating sheets can collide with each other, UNION ASSEMBLY is used with CONTACT PAIRS defined for the colliding boundaries. An offset from the geometric destination surface is provided for not breaking the fluid domain during collision, still the structure fails when the offset value is obtained. In the COMSOL blog it is mentioned that for unconstrained domains a spring foundation need to be provided, how to define that for the present scenario?

Dharma

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the initial potential V_init cannot be read

December 9, 2019, 7:01 pm
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Semiconductor simulation, the initial potential V_init cannot be read

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Ambient thermal properties defined as variables

December 10, 2019, 12:41 am
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Hi users,

I'm studying a rather simple case (1d) where I have defined some heat and moisture transport with the use of PDEs. The reason I'm not using the predefined heat transfer modules is due to an additional source/sink term defined as an ODE.

What I need is to define the moisture content as a dirichlet boundary condition. Here, I would like to define it as a function of the ambient moisture content. So I need to extract the ambient moisture content (or relative humidity) from the weather file as a variable. Is this even possible?

Best, Mes

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need to know how to customise the equations

December 10, 2019, 12:44 am
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Dear members , can anyone please kindly let me know, how to customise equations in heat transfer

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Using Mode Analysis as base for Frequency Domain, Modal Study

December 10, 2019, 3:46 am
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Dear All,

I'm trying to simulate guided waves using the SAFE approach, which is basically a 2D solid mechanics simulation with out-of-plane harmonic extension. Using mode analysis for a specific frequency, I obtain the out-of-plane wavenumbers leading to eigenmodes of the guided wave.

Then, at this particular frequency, I want to enforce a specific displacement at out-of-plane coordinate 0 and consider the resulting displacement at another out-of-plane coordinate z. This can be done by writing the solution as a linear combination of the eigenmodes obtained before. Unfortunately, so far I am not able to do so using Comsol.

What I so far tried was using a modal solver as follow up to the mode analysis and using all eigenpairs of the previous mode analysis solution. However, this resulted in comsol giving an error, noting that the variable lambda is undefined.

Thank you for any information on how to reach this.

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Dielectric Materials in Capacitor

December 10, 2019, 6:43 am
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Hi everyone! I have created a capacitor using Comsol 4.3b. I've set as dielectric material silicon and air. I need also to test the field by using also other materials such as teflon etc. However, when I select the domain, a X pic appears on the material and when I run the compute it shows there is an error. There is also a STOP sign at the "Relative Permittivity" on the "Material Contents" section. Why is that? Can somebody explain it to me?

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How to describe a function for current circulating in a coil?

December 10, 2019, 11:30 am
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In my model (Induction Heating) I want to represent the current that circulates in a coil through a time dependent function. I chose a function generated through value interpolation (figure). However, it is giving the following error:

  - Feature: Stationary Solver 2 (sol1 / s2) Undefined variable.   - Variable: t   - Global scope Failed to evaluate variable.   - Variable: comp1.Currentfunction   - Defined as: comp1.Currentfunction (t / unit_s_cf) Failed to evaluate variable.   - Variable: comp1.mf.coil1.ICoil   - Defined as: (comp1.Currentfunction * unit_A_cf) * exp (i * phase) Failed to evaluate variable.   - Variable: comp1.mf.ICoil_1   - Defined as: comp1.mf.coil1.ICoil Failed to evaluate expression.   - Expression: d ((comp1.mf.ICoil_1-comp1.mf.coil1.Iint) * test (comp1.mf.coil1.VCoil_ode), {test @ 1}) Failed to evaluate Jacobian of expression.   - Expression: (comp1.mf.ICoil_1-comp1.mf.coil1.Iint) * test (comp1.mf.coil1.VCoil_ode)

Could someone help me solve this?

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Simulation breaks when adding more than two numeric ports

December 10, 2019, 12:55 pm
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Hello, I am trying to simulate a straight rectangular waveguide with a half ring very close to it. As long as the simulation has two ports it works fine. But as soon as I attach an 3rd numeric port to see how much light is being coupled in the ring, the siulation gives weird results. Can anyone shed any light on what might be the case ?

I am using the wave optics module for the simulation. (Electromagnetics, Frequency Domain)

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Schrodinger-Poisson Parametric Sweep

December 10, 2019, 5:49 pm
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Hello,

I would like to determine the wave functions for multiple quantum well models with varying well/barrier dimension; i.e. one model with one set of parameters repeated (2/5/2/5/2), and another with a second repeated parameter set (3/5/3/5/3).

When adding a Parametric Sweep to the Study, the only useful results I can get with the Parametric Solutions Data Set is the voltage [V] and potential energy schr.V [eV]. If I try to use the Parametric Solutions Data Set to plot the wave functions using the equation

schr.Psi*0.05[eV]/schr.plot_fac +schr.Ei

I get the error:

Cannot evaluate expression. Undefined variable. - Variable: lambda - Geometry: geom1 - Domain: 15 Failed to evaluate variable. - Variable: comp1.schr.Ei - Defined as: comp1.schr.lambda_scalelambda Failed to evaluate expression. - Expression: 6.2415091258832579E18(8.010883104E-21*comp1.schr.Psi/comp1.schr.plot_fac+comp1.schr.Ei) - Plot: lngr2 (Line graph)

The results associated with the Study 1/Solution Store: Store Wave Function are only for one parameter, rather than a sweep.

If I try to do my sweep using the Study Extensions- Auxiliary Sweep node under Schrodinger-Poisson/Settings a warning pops up under the Eigenvalue Solver 1: Solve for Wave Function- "Parametric Solver does not support varying parameters in geometry or mesh. Use Parametric Sweep for this."

Can anyone help me with this issue?

Thank you!

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Geometry with repeating Units

December 11, 2019, 12:22 am
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Hi, I would like to do the 3D analysisi of an FSI problem. The structure consist of many repeating units, say it looks like a honeycomb structure. The edges of one hexagonal unit are the contact pairs for the adjacent units.

Is there a way in COMSOl to multiply a single unit to n number of hexagonal units, with a final boundary for the structure define by certain end boundary conditions?

Thanks in advance. Dharma

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Change the voltage type from AC to DC

December 11, 2019, 9:25 am
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hi, I have insilator geometry in COMSOL. Earlier I simulated it using AC voltage. How can I change the voltage to DC from AC?

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Contact modelling in a flexion test

December 11, 2019, 12:39 pm
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Hi, trying to learn a bit more about contact modelling.

I'm trying to model a simple three point flexion test, with a piece of metal between three rollers, the one on top moves down with a given force, the two on the bottom do not move. However, since a Stationary model did not converge, I decided to do a Time Dependent model to see how the assembly was reacting to the force.

To my surprise, what happens is that the roller that exerts the force bounces of the metal piece, even though the force is not too big and is always acting downward (and if I make it bigger the model will also not converge).

I would appreciate any feedback as to why this happens, since I can't explain it. I'm using Penalty factor method for the contact analysis since the Lagrangian causes the top roller to penetrate the metal piece and I'm still not sure of which adjustments to make to avoid this.

Have a good day.

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Temperature distribution in the focal plane of a solar dish receiver

December 11, 2019, 5:01 pm
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I have a question regarding the solar dish model: is it possible to evaluate the temperature distribution in the focal plane? I noticed that in the “Results” section, by adding “2D plot group”, a temperature map ("Temperature distribution") of the focal plane can obtained, but it is necessary to insert a specific formula in the form “gop.wall1.bsrc1……”. Do you know the exact expression that should be written?

Thanks for your help

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Color range

December 11, 2019, 7:52 pm
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hi, i have a simple question. how can i change the range of colors in the beam that you can see in the picture? like having a range of all colors such as red and yellow. thank you

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Pass a vector calculated by Matlab to Comsol

December 12, 2019, 7:27 am
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Does anyone know how to pass a vector calculated by Matlab to a variable or material property in Comsol？ (except using the interpolation function or external matlab function). Just like using a simple API syntax "model.variable('var1').set('E', num2str(E0))" to pass a Matlab integer or double variable to a Comsol variable.

All the best, Songcai

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Wrong Electric Field Results

December 12, 2019, 12:22 pm
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I have assigned electric potential of 600000 V to the boundries of square box shown in the attached picture. I do not know why it is showing zero electric field in the corners of the box. Please help me to correct this.

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icloud verification failed

December 12, 2019, 8:35 pm
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Determining the definitions of all variables that were used in my simulation

December 12, 2019, 9:10 pm
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Hello, COMSOL Users.

I am trying to prepare a thesis of work that I did using COMSOL Multiphysics 5.4. In that thesis, I would like to mention all of the equations that were used in the simulations, particularly because the work that I did is theoretical.

At present, I am trying to determine the definition of each variable. I have found the definitions of some of the variables. However, there are more variables that I do not yet know the definitions of.

May you help me in defining all of the remaining variables?Please see the Microsoft Word document attached. The grey highlighting of text indicates what I already know. The blue highlighting of text indicates what I yet have to determine/confirm. The "unit lenses" are the Geometry I used.

The COMSOL products that I used were COMSOL Multiphysics with the Heat Transfer and Ray Optics modules. The Multiphysics that was used was the Ray Heat Source Multiphysics.

Sincerely, Kyrollos

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Compile issues related to External material model

December 8, 2019, 2:33 pm
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Dear all:

I programed an external material model in which the utility functions provided by COMSOL are used. However, I encoutered some issues related to these utility functions when I was trying to compile the code. Could you please give me some ideas to solve these issues? Thanks for your help.

The error messages are as follows:

Code 1 line 155: int csext_from_voigt(double sTrial[6], int 1, double sTmatrix[3][3]);

Errors: EFM_new.c(155): error C2143: syntax error: missing ')' before 'constant' EFM_new.c(155): warning C4030: first formal parameter list longer than the second list EFM_new.c(155): error C2143: syntax error: missing ';' before 'constant' EFM_new.c(155): error C2059: syntax error: 'type' EFM_new.c(155): error C2059: syntax error: ')'

Code 2 int csext_eig(double sTmatrix[3][3], double vals[3], double vecs[3][3]);

Errors: EFM_new.c(175): error C2065: 'vecs': undeclared identifier EFM_new.c(175): error C2109: subscript requires array or pointer type

CODE 3 int csext_inv(double C[3][3], double 1e-5, double C_in[3][3]);

Errors: EFM_new.c(332): error C2143: syntax error: missing ')' before 'constant' EFM_new.c(332): warning C4030: first formal parameter list longer than the second list EFM_new.c(332): error C2143: syntax error: missing ';' before 'constant' EFM_new.c(332): error C2059: syntax error: 'type' EFM_new.c(332): error C2059: syntax error: ')'

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Multiphysics about electromagnetic heating

December 13, 2019, 3:38 am
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Dear all

I need to know the temperature after the inductive heating. The definitionof materials as the pic I upload. I am simulating a inductive heating in comsol. I feel confused after I define the magnetic field (mf) and Heat Transfer in Solids (ht), the boundaries in multiphysics 'electromagnetic heating' all became 'not applicable'. Have I defined mistaken? How can I define my model in a correct way? If you do the similar demo, hope you can share your idea to me.

Best regards

Joey

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