Latest Discussions - COMSOL Forums

Cap faces feature without CAD

Wed, 22 May 2019 22:39:07 +0000

The below post is related to an archived discussion

[start here] I've made parts directly in COMSOL (not CAD) but I need to identify the volume inside an enclosed space a domain. It appears that the "Cap faces" feature would accomplish this but since I built it directly in COMSOL it doesn't appear available. How can I accomplish creating this domain without CAD?

Thank you Osa

Calculate R squared in Comsol

Wed, 22 May 2019 20:57:26 +0000

Hi,

If I have the measured and the computed curves in the same plot (see attached file), how can I calculate R^2 in Comsol? Thanks.

Best regards, Zhidong

Pulsed RF ICP

Wed, 22 May 2019 14:50:34 +0000

Hello. I am wondering about COMSOL Multiphysics can solve Pulsed ICP problem. I know there is Pulsed CCP example in application library. But, I couldn't find any information about Pulsed ICP. Who has some ideas about Pulsed ICP ?

Contraction of a cell on a gel

Wed, 22 May 2019 14:25:05 +0000

Hi!

I created a 2D axisymmetrical model to examine the deformation of a (stem) cell on a (polyacrylamide) gel after contraction.

In order to do so, I should define a prestress over a part of the cell (the cytoplasm). However, since the cytoplasm is made up of a hyperelastic Neo-Hookean material, it is not possible to define a prestress -I used "Initial stress"- in a way it is possible for a linear elastic material (also, when applying linear elastic materials, the model does only converge for a positive prestress, so radially outward, instead of radially inward as in a contraction).

What could cause the model to not converge for a radially inward prestress?

And is there any other way to define a prestress for a Hyperelastic Material, to imitate contraction?

Thank you in advance!

Different S11 values for the same frequency

Wed, 22 May 2019 09:50:48 +0000

Hi all,

I simulate a pin-fed patch antenna at 3.5 GHz. When I set Frequency to 3.5[GHz], The S11 value is -28.474 dB. But if I enter range(3.3[GHz],0.1[GHz],3.7[GHz]) phrase into the frequencies text box. I get the following results, which is -23.569 dB at 3.5 GHz.

3.3000  -3.9214
3.4000  -8.0754
3.5000  -23.569
3.6000  -10.408
3.7000  -5.3938

Why are two S11 values different at the same frequency (3.5 GHz) even I don't change anything else?

Thanks.

Computing transmittance and reflectance of glass for different wavelengths

Wed, 22 May 2019 08:50:15 +0000

Hello everyone, I'm a beginner user of COMSOL, and I'm stuck on a little problem. I'm using the "Electromagnetic Waves, Frequency Domain" interface to model an incident wave on a smooth surface, in order to calculate the transmittance and the reflectance of an N-BK7 glass. I followed the instructions of the "Plasmonic Wire Grating" tutorial, but my purpose is to compute the aforementioned quantities for different wavelengths. For this reason, I don't want the refractive index of my material to be constant: it must vary with the wavelength. Therefore, I created an analytic expression for the real part of the refractive index (which I named "n_NBK7"), as well as an interpolation function for the imaginary one (which I named "k_NBK7"). As concerns the air above my sample, I did the same thing with the real component (naming the function "n_air"), while I set the extinction coefficient to 0. I took all these relations from this link. My questions are the following: 1) In the study settings, I can make the wavelength sweep within the range of interest: how can I tell the software that the wavelength must be the input variable for my interpolation/analytic functions (i.e.: n_NBK7, k_NBK7 and n_air)? 2) In the Port boundary conditions, the ewfd interface needs to know the refractive index of the air (Port 1) and of the N-BK7 glass (Port 2), in order to compute the diffraction orders. Provided that I don't have a constant value for them (they depend on the wavelength), I want to call here the functions n_air and n_NBK7, respectively: is this feasible? Which is the correct syntax to do it? 3) If I understood correctly, the software computes the number of diffraction orders as a function of three parameters: the angle of incidence, the refractive index of the material (in my case, the N-BK7 glass) and the wavelength itself. This means that, during the sweep study that I'd like to run, the software should be able to adjust the number of Ports in order to compute the different diffraction orders: I mean, without requiring me to click manually on the "Compute Diffraction Orders" button (provided that it is disabled while the solver is running!). Am I reasoning right? Is there a way to automate the computation of diffraction orders?

Any help is very much appreciated! Thank you

PS: I'm going to attach the .mph file of my model, it could be useful to better understand my problem

How to Define Poisson Boltzmann equation in Cylindrical coordinates

Tue, 21 May 2019 16:18:50 +0000

Hi, I want to define poisson Boltzmann equation in cylindrical coordinates in comsol, can some one please help me. The equation is dsqrU/dRsqr + (1/R)*dU/dR + dsqr U/dZsqr = (kh)^2 * sinh(U)

Maximum concentration in the domain (transport of diluted species in Pouros Media)

Tue, 21 May 2019 13:46:16 +0000

I'm working on simulating a mass transfer in porous media. I am having difficulty setting the maximum concentration in the domain. The stream has a higher concentration that my domain can adsorb.

Any help will be welcome!

Att. Mirian

Deformation of an agar surface

Tue, 21 May 2019 11:59:55 +0000

Hello alll,

I'm new to comsol and i am wanting to use it to model the deformation of a disk of agar by a small force being applied to the underside of the disk by a piece of plastic. The plastic is a square in shape and is smaller in diameter than the disk of agar.

So far i've identified that i can set the material parameters for both the plastic and the agar and also that i can place them in space so that they are initally directly touching, with the plastic being below the agar and they are boith centered around x,y,z=0. I've also read about making the two structures into an assembly with contact regions (but i'm not sure exactly if this is needed for my simulation).

I was wondering if anyone can help me with any advice about how to progress next with this simulation. I now need to input that 1. the square of plastic is moved in the postive z direction by 3mm as so the impose a force on the agar and deform it and 2. i need to put in boundary conditions so that the sides of the agar remain fixed at z=0 so that only the middle regions of the agar is moved by the square of plastic.

Sorry if this all sounds a bit confusing and hopefully someone can help!

Cheers

Paul

Simulate voids in soil

Tue, 21 May 2019 10:41:51 +0000

Hi, I want to know if someone have already built a model of propagation of EM waves in soil. If yes how? Thanks for your answers!

2D FSI Failed to evaluate reaction forces

Tue, 21 May 2019 09:45:34 +0000

Hi I'm performing a microfluidic FSI: 4us analysis

Error: Failed to evaluate reaction forces

COMSOL version 5.3

(See attached geometry and input)

This is what comes out from my time dependent analysis of a layered vibrating membrane, with prescribed displacement of 0.5um, over a fluid chamber, following a rectangle wave. I'm using Generalized alpha solver, 0.001 relative tollerace +0.1 tolerance factor, fully coupled + Automatic Newton, strict time stepping:

range(0,1e-7,7e-7)range(7.4e-7,1e-9,3.4e-6)range(3.5e-6,1e-8,4e-6)

The error comes out after the first ramp, around 1.7 us ( i tried a lot of configurations, at most I reached 1.9 us).

Any suggestions? Thanks in advance.

crash test for batteries

Tue, 21 May 2019 08:57:20 +0000

What is the equation to be used for solid mechanics module for crash test of batteries?

Element's Data

Tue, 21 May 2019 07:40:22 +0000

There are a simple duct and just laminar flow, Is it possible to extract the velocity of each element at outlet boundary in Time-dependent study at output times without using "excel", I mean using internal COMSOL's functions?

triboelectric pressure sensor. electrical fluid solid mechanic

Tue, 21 May 2019 07:23:04 +0000

Hi, I am currently working on the development of triboelectric pressure sensor. I am now facing with the simulation of the flowing of the fluid driviive by pressure, interaction of PDMS and my fluid, and lastly the physics that i had to applied on each boundaries. i had working on this for three month plus already and feeling quite exhausted. Anyone here can help me to solve my problem?

Effective thermal conductivity of alloy

Tue, 21 May 2019 07:09:41 +0000

Hi all,

I am trying to model a thermal crystal made up of Si-Ge alloy and airholes in comsol 5.4, for which i am using linear elastic materials in solid mechanics module. I have already modeled the band structure of unit cell by applying floquet boundary conditions and eigen solver analysis. Now i want to find effective thermal conductivity v/s eigen frequency graph of alloy used in same geometry. As COMSOL solves the heat equation in each part of the geometry using its own thermal properties. How can i extract the effective properties?

Thanks in advance

Selection of physics

Tue, 21 May 2019 01:40:22 +0000

What physics needs to be used to analyse the stress/strain experienced by a pipe due to fluid flow?

convective heat flux boundary condition

Tue, 21 May 2019 01:31:58 +0000

Hi,

I'm confused by the result I got by using convective heat flux boundary condition. Hope I can find the answer here. Thanks a lot.

I'm working on a time dependent heat transfer model, one of the boundaries is defined as convective heat flux, q0=h(Text-T). Based on the definition of heat flux, q0=-k(dT/dx), I checked my result after running a few time steps. I plotted ht.q0 line graph along the boundary, as well as -material.k_isoTx along the boundary, they are not the same.

I also plot integration(q0) and integration(-k*Tx) along the boundary with respect to time, they are getting closer as time, but I'm still confused about this, is it because my mesh is not good enough? I'm checking all these because I didn't get a good result for my model and trying to find out the reason.

Really appreciate your help. Thanks a lot.

Jing

How to use the result of each time-step as input to next time-step?

Mon, 20 May 2019 20:06:26 +0000

Basically this is how I would do it in hand calculation:

T_out_0 = 22 [degC] %% Guessed initial value.

%% at t=1:

COP(1) = 5[1/K] * T_out_0

T_out(1) = T_avg_Domain(1) - COP(1)/7[1/K]

%% at t=2:

COP(2) = 5[1/K] * T_out(1)

T_out(2) = T_avg_Domain(2) - COP(2)/7[1/K]

and so on ..

My problem is how to calculate COP from the previous T_out? When I define this in Variables node (As shown below), I got this warning: "circular variable dependencies".

COP : 5[1/K] * T_out

T_out : T_avg_Domain - COP/7[1/K]

How to simulate AC Multi-turn coil numeric

Mon, 20 May 2019 17:09:33 +0000

Hi,

I want to simulate the result as changing inductace of coil in an active eddy current sensor with different material target. The Multi-turn coil numeric fuction is selected to simulate regtangular coil geometry. I use two steps in simulaiton; step1 Coil Geometry Analysis and step2 Frequency Domain. However, I cannot find the coil inductance parameter in results. There are only coil current and coil resistance DC.

Can anyone guide me to solve this problem?

Note that I follow the example of using Multi-turn coil numeric with Alternative Current in https://www.comsol.de/forum/thread/attachment/214261/3D_Coils_43a-45831.pdf. However, there is only DC simulation case in that example.

Thank

How to set user defined Boundary Conditions in poisson equation

Mon, 20 May 2019 16:26:01 +0000

Hi, I want to define n ˙∇U = (e2/εε0kBT)σsh as my boundary condition in the Poisson boltzman equation, can some please guide me how to do this. Thank you.