Latest Discussions - COMSOL Forums

complex relative permittivity and permeability

Thu, 28 Jan 2021 12:04:25 +0000

Hello, Do you know how to consider the complex part of relative permittivity and permeability?

I am using Comsol Multiphysics, Eletromagnetic waves/frequency domain. I would like to put also the complex part of these two parameters when I specify the characteristics of the material. Any idea?

Thank you in advance, Giulia

Can someone help with a comsol error?

Thu, 28 Jan 2021 11:46:44 +0000

I tried to build a model of free surface problems by using the coefficient PDE.BUT Until I finished the model and dad this error: There are 163 void equations (empty rows in matrix) for the variable comp1.phi. at coordinates: (0,-25), (2.5,-25), (5,-25), (1.6044,-23.2926), (0,-22.5), ...

(The dependent variable is Phi) I want to know what's wrong with the error? Thanks!

Not getting erosion plot

Thu, 28 Jan 2021 09:41:03 +0000

I am not able to get erosion plot while using erosion term with particle tracing? can any one guide me pls....

how to set a conditions if an error happens in livelink matlab?

Thu, 28 Jan 2021 06:44:39 +0000

Hi, i am running a wear analysis of a pin-on-plate case. According as the pin worn, the contact area change, then the initial selection of the contact have to change for avoiding numerical errors related to an insuficient or exesive contact area. So i want to know if there is an option or function in livelink matlab where i could set a conditional like: if comsol has an error, then change the size of the contact region and run. It is possible?

Many Errors in File

Wed, 27 Jan 2021 22:04:45 +0000

I am trying to model Water absorbing CO2 using the Phase transport in porous media physics. I am getting constant errors so I thought I would post my file.

I get many errors including: " Failed to find a solution. Maximum number of Newton iterations reached. Returned solution is not converged. Not all parameter steps returned. "

Missing Specular Reflection Functionality in the Ray Acoustics Module

Wed, 27 Jan 2021 19:38:56 +0000

Hello,

I am trying to set up my own Ray Acoustics study, very similar to the "small concert hall" file from the application libraries. I want to perform almost the exact same study, but with my own geometry. I have set up my geometry by building it inside COMSOL 5.5, rather than importing it from an outside file. I'm interesting in computing the impulse response from a 3D receiver, the ray trajectories and the reverberation times (T60).

So far, I believe I have set everything up correctly, but there are some key differences in my wall boundary condition tab. I will attach screenshots to show the differences. I wish to carrry out the study in the same way, by using the Specular Reflection option for the wall conditions.

In the original tutorial file, selecting "Specular Reflection" as the wall condition opens up the "Reflection Coefficient Model" box that allows you to specifiy the absorption coefficient. In my version, this does not happen. You can also see that the equations specified for use in the tutorial and my own file are not the same.

Any ideas on how to get this to work?

Many thanks,

Tom Walker Student at the University of Glasgow

Triangular fixed-fixed nano-beam

Wed, 27 Jan 2021 13:56:04 +0000

Hi all,

I am trying to evaluate the quality factor of the vibration of a nano-beam. The beam is etched in a diamond substrate so I model it as large pads on the sides of the beam (see attached image). When I use this model, even the eigenfrequencies cannot be simulated and the results are absured.

If I just use fixed-fixed boundary conditions the eigenfrequencis and mode shapes make sense but the quality factor is infinitly large because there are no support losses.

Would like to hear your suggestions how to evaluate the quality factor taking into account the support losses.

Cheers, Itamar

Model Numerical Aperture Optical Fiber

Wed, 27 Jan 2021 13:50:21 +0000

Hi all,

I am performing a Ray Tracing study of light passing several different optical fibers with 50um distance between them. Each of these fibers has a different acceptance angle. How can I determine the incidence angle for each individual ray when it crosses a boundary and freeze it if it is outside the acceptance angle range? Can I use the variables gop.nix, gop.niy and gop.niz for that?

Best regards, Paul

How to calculate cooling rate and temperature gradient

Wed, 27 Jan 2021 08:18:46 +0000

Hello everyone,

I am simulating a 1D solid heat transfer. However, I want inquire about how to deduce the cooling rate and temperature gradient.

I have been able to deduce the temperature vs time (temperature at every minute in the material) but I am confused on how to get the cooling rate and temperature.

I would be glad to receive a response..

Thanks.

How to couple equations

Wed, 27 Jan 2021 07:48:35 +0000

Equations: ∂n/∂t=∇⋅(D∇n−μn·∇ψ) (1)
∇⋅σ∇ψ=0 (2)
−∇⋅k∇T=σ|∇ψ|^2 (3)

I know (2) and (3) equations are current continuity equation and transient heat transfer equation. So I choose Solid electric Current module and heat transfer module. Can anyone help me how to couple (1) and (2) equations. Which mathematical equation should I choose and How to set boundary conditions. I'd be grateful if someone can help me.

Plateau–Rayleigh instability on Comsol

Tue, 26 Jan 2021 23:59:23 +0000

Hello all This may seem like a standard problem. I am interested in simulating the P-R instability on COMSOL using the level set method. I am aware of an existing sample "Jet instability" provided by comsol. However, I want to introduce a small pertubation to the initial liquid interface and then see how the long jet becomes unstable with time.

Does anyone have any idea how could I introduce an pertubation (which would a sine function) to the initial cylinfrical (rectangular) geometry and analyze the breakup?

Thanks

Reversible Reaction Group - Third Body Effect - Chemkin

Tue, 26 Jan 2021 12:37:00 +0000

How can I define the Third Body and Pressure-dependant effects from a imported Chemkin mechanism?

Postprocess thin layer

Tue, 26 Jan 2021 11:53:03 +0000

I'm trying to visualise the trend in some variables very close to a boundary that has rounded corners. Ideally I'd like either: A) a series of 2D data slices normal to the boundary of interest; or B) a series of curves that run parallel to the boundary at a definable distance.

I note that the 2D cut line allows you to define additional parallel lines, but these are obviously parallel to the original defined cut vector, so won't follow the boundary around a corner.

I guess I could define a series of parameterised curves that run adjacent to the boundary using piece-wise type functions but trying to write this makes my head hurt.

Using the contour data set on a wall-distance result gives me approximately what I want, but of course contour data cannot be plotted on 1D line plots.

Attached is an image showing the types of 2D slices I want, albeit the actual contours will be orders of magnitude closer to the wall. Is there an easier way than defined multiple parameterised curves, or lots of different 2D slices?

Many Thanks

Reference temperature in Marangoni model

Mon, 25 Jan 2021 20:51:34 +0000

I am modeling a transient laser heating process in which a laser beam heats a solid metal from room temperature to values higher than the melting point. The surface tension gradient drives the liquid motion in the melt pool until the metal solidifies. I am using the Phase Change Material model for the metal, thus it is a "fluid" with very high viscosity from room temperature to the melting point.

For modeling liquid metals the reference temperature is normally the melting temperature for the Marangoni model. It is not clear if Comsol automatically uses the melting temperature as the reference temperature, or if it uses the initial room temperature as the reference temperature since the metal is a "fluid" for the entire simulation. Does anyone know the answer to this?

Current flow due to surface charge density

Mon, 25 Jan 2021 12:13:55 +0000

Hi, I am trying to model the current flow due a surface charge density. For that i have a conductor material on top of a dielectric material. Then using electrostatic module a surface charge density is added to the bottom surface of the dielectric. This charge induces a potential on the conductor, which can be calculated using stationary solver. But I need to find the current flow if that conductor is connected to ground through a resistor. For that I have added electrostatic, electric current and electric circuit (for connecting resitor and ground) modules. Then the model was meshed and computed a time dependent study, however, I couldont get any output, different errors pop up each time. What is the correct way to do this, any help is appreciated.

how randomize circle sizes ?

Mon, 25 Jan 2021 11:39:50 +0000

Hi there, please I need help with the application builder to run the following tasks I am trying to test the effect of small features changes in flow paths I would like to randomize the circles sizes of with 500 random realizations and run the simulation and export a png capture to a folder I would appreciate your help .

Calculate phase delay and amplitude with s-parameters

Mon, 25 Jan 2021 10:13:51 +0000

Good morning everybody,

my problem consists in a electromagnetic 3D model with 2 ports that are two opposite faces of an air parallelopiped. One of the two port is excited and the electric field travel throught the other port. I obtained ewfd.S21 and ewfd.S11. Now I'd like to plot group delay and amplitude of the field at the second port. How can I compute these two elements?

Thank you!

The current changes but the voltage does not change

Mon, 25 Jan 2021 03:18:12 +0000

In the process of lithium-ion battery simulation, the battery voltage does not change with the electrode input current, as shown in the figure below.

Triboelectric dynamic emulation

Mon, 25 Jan 2021 01:49:40 +0000

if there are any cases about triboelectric dynamic emulation like follow, I hope you can share your experience with me. Thx!!!! http://muchong.com/t-13639652-1

Does COMSOL work with a Nvidia Quadro 4000 graphics card?

Sun, 24 Jan 2021 21:32:37 +0000

It doesn't explicitly say it will in the hardware guide, however I was curious if anyone had experience with it.