Latest Discussions - COMSOL Forums

Evaluating Objective function from only part of a parametric sweep

Mon, 24 Jun 2019 20:59:30 +0000

Dear all,

I am sweeping an electromagnetic problem in frequency domain. If I am investigating for example frequencies 1, 2, and 3, is there a way to create an objective function that is only evaluated for frequency 1, and another for frequency 2 and so on? I'm thinking something like the at() function but for general parametric sweep.

Why do Comsol and Ansys have different mode shapes?

Mon, 24 Jun 2019 18:57:30 +0000

Hi,

I am doing coupling anaysis for structural vibration and acousitc pressure. I have compared the result from Comsol to that from Ansys, but they have different mode shapes. Since I do not use Acoustic-structure interactions, I totally understand eigenfrequencies should be slightly different, but the mode shapes should be same.

Every condition such as bounday conditions, contact, or material properties is same in Ansys and Comsol, but they show some different mode shapes. Why do they result in that differece?

Electric field - electric potential - AC/DC Module

Mon, 24 Jun 2019 18:08:44 +0000

Hello,

I'm trying to simulate a photonic crystal with the AC/DC module. Does someone know why i'm having no variaton on electric potential or electric field when i changed the currently work frequency ?

Thank you in advance,

Saúl

Plotting Coordinates for Specific Condition (Heat Transfer)

Mon, 24 Jun 2019 15:30:48 +0000

Is it possible to plot a graph of x,y coordinates for a specific temperature condition in COMSOL?

I am taking a slice, similar to the one attached, out of a 3D model and looking to create a graph of the position coordinates for one tempearature. From the picture, the goal would to have the graph look like a parabola.

I found that exporting the data and using python to get the coordinates wasn't sufficient since there wasn't enough data points in the temperature range I wanted.

Thanks

Delete user defined material

Mon, 24 Jun 2019 14:37:05 +0000

Hello fellow COMSOLers,

is there a way to remove materials from the user defined materials library. I already checked the forum and manual but cannot find anything.

Any advice is greatly appreciated.

Best regards, André

SAW Device with IDTs

Mon, 24 Jun 2019 14:09:54 +0000

I'm trying to create a finite-sized surface acoustic wave device (file attached) with gold electrodes for the IDTs.

Essentially, I'm creating an IDT similar to https://www.comsol.com/paper/download/213121/dixit_paper.pdf but looking at what happens to the wave as it penetrates the piezoelectric substrate without the periodic boundary conditions (since the IDT I fabricate will be finite sized). There are a few simulations I wish to run:

(1) Finite-sized (i.e. no periodic boundary conditions) surface acoustic wave device (2) 3D version of IDT -- i.e. extrude the entire setup along an axis (3) IDT with input and output ports, as in the paper linked.

I cannot seem to get any of these three to work; I've attached files from (1), could someone take a look and see if I'm doing anything in my setup wrong? How would I set up an output port and get the resonance plot?

Deposited Ray Power

Mon, 24 Jun 2019 13:49:38 +0000

Hi all,

I am modelling a Winston cone by using geometric optic engine. I'm sucessfull getting the ray trajectories but however when I computed the deposited ray power at the entrace aperture and the exit apeture of the cone, they are always zero. Attached is the screenshot from my simulation. Please help me to compute the power enterinng and exiting the cone.

Thank you,

In the acoustic module, how to set the parameters of anisotropic materials

Mon, 24 Jun 2019 13:39:06 +0000

In the acoustic module, how to set the parameters of a material when the density of mass or the bulk modulus of elasticity is anistropic i.e. the density of mass or the bulk modulus of elasticity of the material is a martrix?

Difference between available Hydrogen gas models

Mon, 24 Jun 2019 10:48:32 +0000

What is the difference between the following?

Liquids and Gases > Gases > Hydrogen
Material Library > Elements > Hydrogen > Hydrogen [gas] > Hydrogen [gas, H2]

Specifically with respect to equations for density (the second one has density independent of pressure).

Training courses

Mon, 24 Jun 2019 07:14:46 +0000

Hello, I was interested in learning how to use comsol for simulation of penetration of drugs in spheroids in peritoneal cavity tumors Is there any training courses given by comsol or textbook that can help me in this issue

Ground Temperature Profile

Mon, 24 Jun 2019 06:11:47 +0000

I need to set boundary condition as Ground Temperature profile given by Kasuda function however i am not getting desired plot, is the cos function in Redian or in degree ? Tmean 18.5 mean surface temperature Tamp 21 apmlitude of surface temeprature depth 1 1 Depth of the Ground a 0.1728 Thermal Diffusivity tshift 35 minimum surface temp O 3.14/365 omega

Sin function in COMSOL

Mon, 24 Jun 2019 06:04:53 +0000

Dear , how to put sin function at boundary condition.

modeling heat transfer in LiNb at 10-2 K and with a heat source, power of heat source 10-3 W

Sun, 23 Jun 2019 08:29:36 +0000

Hi,

I am traying to model heat transfer in a lithium noibate resonator at E-2 K tempreture. So I defined heat conductivity k=4T3 and heat capacity 0.000234T3 at E -2 K with a heating source which has a power of E-3 W (a laser source 1550 nm wavelenght). The problem is when my power is less than E-8 It gives me a solution which I attached here but when I put my actuall power E-3 W it gives me this error:

Feature: Time-Dependent Solver 1 (sol1/t1) Failed to find consistent initial values. Error in user-defined function. Function: comp1.mat9.def.K Failed to evaluate variable. Variable: comp1.mat9.def.k33, Defined as: (comp1.mat9.def.K(comp1.T/unit K cf)unit W cf)/(unit K cfunit m cf) Failed to evaluate variable. Variable: comp1.ht.kzz, Defined as: comp1.mat9.def.k33 Failed to evaluate variable. Variable: comp1.ht.k effzz, Defined as: comp1.ht.kzz Failed to evaluate variable. Variable: comp1.ht.dfluxz, Defined as: (-comp1.ht.k effzz)comp1.Tz Failed to evaluate expression. Expression: d((2(comp1.ht.dfluxrtest(comp1.Tr)+comp1.ht.dfluxztest(comp1.Tz))comp1.ht.dpir)(dvol spatial),{test1}) Failed to evaluate Jacobian of expression. Expression: (2(comp1.ht.dfluxrtest(comp1.Tr)+comp1.ht.dfluxztest(comp1.Tz))comp1.ht.dpir)*(dvol spatial) Last time step is not converged.

Angled Waveguide 2D

Sat, 22 Jun 2019 17:16:52 +0000

Dear All

I have problem in Geometry. I am trying to Draw an angled waveguide with 60 degrees bend. Help will be appreciated

Thanks in Advance

electrokinetic flow in nano channel

Sat, 22 Jun 2019 13:53:40 +0000

I made a nano channel where I took electrostatics, transport of diluted species. i took K+ and Cl- as ions to move by controling potential. how can i get the ionic current vs potential graph.

Liquid medium surrounding BAW resonator

Sat, 22 Jun 2019 08:52:12 +0000

I’m trying to model viscous damping effects on an in-plane BAW resonator immersed in a liquid. How do I set up my resonator as a body in an infinite stationary liquid medium (only flows in the liquid are due to motion induced by contact with the resonator)? And how do I simulate viscous effects on the body?

Any help will be much appreciated!

Plot Number of Mesh Elements versus Parametric Sweep

Fri, 21 Jun 2019 18:12:18 +0000

I use a parametric sweep to define increases in size of the geometry. How can I plot the total number of mesh elements over the parametric sweep?

I.e., I have a square domain that doubles in size a few times. The side legnth of the square goes from 2, to 4, 8, 16, 32, 64. The elements are fixed at size 1, so the number of elements goes 4, 16, 64, 256, 1024, 4096. How can I get comsol to plot the number of elements vs. the interation of the sweep?

S parameter analysis for optics

Fri, 21 Jun 2019 16:18:49 +0000

Hi, I am trying to figure out the S-matrix for an optical ring resonator. Can I use COMSOL for this?

Validity of Fick's Law of Diffusion

Fri, 21 Jun 2019 16:08:34 +0000

I am working on the diffusion induced stress and deformation. The deformation is large of the order 300%. I recently read that for large deformation, Fick's second law is not valid in the spatial framework. This would mean that I have to use (dC/dt)+grad(J)=0 in the material framework. But in material framework, is J = -D grad(C)?

Non-zero stress and strain values for zero displacement with no preloading

Fri, 21 Jun 2019 10:46:07 +0000

Hi, I am trying to validate a compression test of hyperelastic material silicone. So I have taken a single cubical element of 1mm dimension and I have applied a prescribed displacement upto 0.5mm in compression. Now I am facing the following difficulties:

The cube is bowing inwards rather than bulging outwards for the compressive loading. (Image attached) The response does not improve by meshing with multiple elements.
There is non-zero stress (too high) and strin values for zero displacement of the element. (I am using auxiliary sweep) (See the probe table in the image)

I am using Ogden Model with N=2 for compressive test data.

I have been facing these high strain and stress values even for 2D simple models containg hyperelastic materials. One peculiarity is that the stretch value was correct but the strain was too high violating their relationship.

Can anyone please help me out with this?

Thanks.

compression.png