Physics - Latest Discussions - COMSOL Forums

Stationary and Time-dependent study for Joule Heating

Mon, 21 May 2012 20:14:35 +0000

Hello,

I am working on a rather simple simulation of Joule Heating on a Pt resistor deposited on AlN substrate. Although I can perform the stationary study and have some of the results I want, I cannot perform a time-dependent study. The execution fails with error message "Failed to find consistent initial values. Last time step is not converged.".

Any ideas what might be wrong?

Cheers!

-O.

3db coupler

Mon, 21 May 2012 06:22:43 +0000

How to design 3db directional coupler.

Directional coupler

Mon, 21 May 2012 06:21:54 +0000

How to design directional coupler with 0.5 coupling coefficient using COMSOL softeare.

Define PH

Fri, 18 May 2012 16:38:10 +0000

Hi

Anyone has any idea how I can define PH of my solution in ACDC module?

Best
Bahar

analyze movement of particles in ACDC

Thu, 17 May 2012 12:22:26 +0000

Hello everyone

I have a question and I wondered if anyone can give me some info.
I am using AC/DC module right now. However I want to add movement of A charge in my model and analyze the effect of its movement on electrical field of whole system.
Do you think it is possible to do these kind of simulations by using time dependent analysis? Because I have checked different models here that use time dependent analysis but their goal was totally different from mine.
I think in order to do this I should have access to particle tracing module. Am i right?
I would be really grateful if someone can give me some information or give me a link of example related to this.

Best
Bahar

Simple convection model not converging

Tue, 15 May 2012 13:12:31 +0000

Hello all,

I have a simple beam model in which the beam is made out of silicon and it is sorrounded by air. When I apply a voltage to the beam, it creates temperature gradient along the beam due to the resistivity of the beam being dependent on the temperature at which it is at. To incorporate the convection due to the air, I went ahead and used two physics to mimic this phenomenon: electric currents (to compute the resistance of the beam and the power) and non-isothermal flow (to compute the temperature, including the effect of convection). The model itself is a one quarter model, allowing for symmetry, which I took care of with the simple boundary condition of electric and thermal insulation. The reason behind coupling these is so that I can see the effect of convection, given the fact that the heat transfer coefficient of air will change due to temperature. When I run my model with time dependent I get the following error:

"Failed to find consistent initial values.
Last time step is not converged."

When I run it with stationary I get the following error:

"Failed to find a solution.
Maximum number of segregated iterations reached.
Returned solution is not converged."

Any help is greatly appreciated.

Thanks.

Two Domains Poisson Equation

Tue, 15 May 2012 07:34:24 +0000

Dear Comsol Users
I have two cylindrically symmetric domains, O1 and O2, which are conducting and isolating, respectively, in 2D. O2 is a 2D shell around O1. I want to evaluate the potential u1 in O1. In O1, the charge density is a function of u1. O2 is charge free. At the interface, a surface charge density s12 is located.
I am wondering now how to correctly setup this problem using the Model Builder. Should I add two times the "Poisson Equation" physics to the model, one for O1 and the other for O2? Or should I add only one "Poisson Equation" physics, but add two Poisson equations to that model?

Thanks for any hints on this.
Martin

Thin film solar cell

Tue, 15 May 2012 03:41:35 +0000

I am a new user of this software
I want to build a geometry for a CIGS thin film solar cell
I don't know which physic should be added in "ADD PHYSICS" step in model wizard.
I mean it should be under AC/DC or heat transfer or conjunction heat or other categories.
could you please guide me?

boundary settings- Thin layer (surface thickness)

Fri, 11 May 2012 17:28:17 +0000

Hello everyone

I have a question about settings for boundary conditions. In most of physics, when you use 3d and you want to define a boundary condition like dielectric shielding for one surface there is one option called "Thin layer".
For this "Thine layer" you should define "Surface thickness" which is by default 1m.
My question is that what exactly this surface thickness means? because it seems it can affect my results a lot.
I know it is not thickness of my domain (if the domain is a cube with dimension of 0.1 um). So what exactly is this? I went through some tutorials and i couldn't find any explanation.

Best
Bahar

Complex Dielectric Permittivity

Fri, 11 May 2012 11:04:59 +0000

How can we insert complex dielectric permittivity as function of frequency in Comsol.
How can we plot Cole-Cole Plot in Comsol

Metal-Insulator boundary

Thu, 10 May 2012 12:39:16 +0000

Hello everyone

I have a question about boundary conditions.
I have 3 layers (Insulator-metal-insulator) and this structure is placed in a solution that i want to sense its voltage with that metal layer.
Insulators are SIO2.
The problem is that when i choose dielectric shielding for insulator boundaries, the voltage on the metal, insulator and the solution will be all the same (and i was expected that it should not be the same on insulator layer!)
So i thought may be i should choose ground for insulator (!) and then the problem is solved. I have zero on insulator, different voltages on metal, and in solution.

But i beleive there is something wrong and i shouldn't work like this. Anyone has any idea?

Best
Bahar

Divergence of gradient of a variable calculation

Thu, 10 May 2012 09:04:52 +0000

Dear Support,
I need to calculate, in the post-processing stage, the divergence of the gradient (it is the laplacian) of a known variable, in a specified volume.
May you help me, please?

Infinitely long cylinder as a simple harmonic oscillator

Sun, 06 May 2012 20:51:53 +0000

This is a very simple problem. An infinitely long rigid cylinder with a given diameter and density functions as a simple harmonic oscillator with a given spring constant (per unit length). So this is a 2D problem. How to find the eigenfrequency with Comsol? Later I intend to couple this oscillator to a fluid etc.

Trouble coupling heat transfer physics for both fluids and solids

Wed, 25 Apr 2012 03:19:20 +0000

Hey all,

So I'm getting stuck with my model where I try to couple three different physics. The three physics are: Electric Currents, Heat transfer in Solids, and Heat transfer in Fluids. Basically what I'm trying to model is a silicon microbridge which is doped, which makes it so that it has a temperature gradient accross it when heated. I am able to couple and run the electric currents and heat transfer in solids physics, where the power dissipated from the ec physics is inputed into the ht physics as the heat source, and then the temperature that is calculated is used to calculate a new resistivity value for the silicon, until the model converges to a value for the temperature at the given voltage.

The problem arises when I try to incorporate the ht2 physics to mimic the effects of natural convection from the sorrounding gases. I set a temperature boundary condition within the ht2 physics which tells the program that the temperature of the microbridge is given by T, which is calculated in the ht physics. However, when I run this, I get the following error:

"Constraing found for variables in different Segregated groups. Try to merge these groups.
-Feature: Stationary Solver 1 (sol1/s1)
-Error: Constraint found for variables in different Segragated groups. Try to merge these groups."

Any ideas? Attached you will find my model. Thanks.

Gravity modeling

Wed, 18 Jan 2012 01:28:34 +0000

Hi all,

I am trying to model the gravitation field due disturbances of density.
I am using the Poisson's equation for gravity

e.g. http://en.wikipedia.org/wiki/Poisson's_equation

Let's consider a cube with 1x1x1 meter as geometry.

Now starting comsol, I use the Poisson module, where I assign c=1,
and f=4*pi*6.67*10e-11*rho

rho defined as a toy problem
rho=1+10*(x>0.4)*(x<0.6)*(y>0.4)*(y<0.6)*(z<0.4)*(z>0.6)

Solution returns this error message:
Failed to find solution.
The relative residual is greater than the relative tolerance.

Why is that?

Dielectric B.C. in Plasma Module

Tue, 30 Aug 2011 19:35:03 +0000

Hello All,

I am trying to adapt the 2D argon_gec_icp file to have a dielectric boundary at the walls of the plasma domain. For this purpose I would like to use Surface Charge Accumulation as an Electrostatic boundary condition, but all boundaries appear as "not applicable". Does anyone know the reason for this? Better yet, does anyone have a suggestion for implementing the dielectric boundary condition properly?

Thank you,
Sonya

scripting import and interpolation of solution

Sat, 06 Aug 2011 13:40:23 +0000

Hi all,

I'm attempting to automate a series of time-dependent 3D simulations, in which the geometry changes from one simulation to the next, but the final distribution of the dependent variable from one simulation should be the initial condition for the next one.

The geometry is set by a matlab script, but due to some memory issues in COMSOL (v 4.1, I haven't rewritten the code sonce 4.2 to try whether they've been solved) the only way to convert the matlab-made geometry to COMSOL is piece by piece, exiting and entering COMSOL after each bit, so as not to encounter the memory problem. Once the geometry is assembled, it is saved as a mphbin file.

Now here's my problem: I'd like to take this saved geometry, mesh it, and interpolate the previous solution onto its mesh. I cannot find a way, however, to import the solution exported by a previous COMSOL simulation. I could perhaps simply read a solution report to a set of matlab variables (coordinates and data) and try write a function using matlab's interp3 to set the initial values from that as f(x,y,z). I'm unclear, however, as to the proper way to set the outputs up so that the they are in the right shape to be used as initial values.

Alternatively, I could try to open up the model with the solution, import the geometry and try mesh it, then interpolate the previous solution to create the initial values with mphinterp (by the way, I have the same issue as with interp3 here: I'm not sure how to reshape the mphinterp outputs so they can be used as initial values), and solve on the new mesh. I'm not sure which of these approaches, if either, works with the way COMSOL is conceived.

Does anyone know of a successful approach to this or a similar problem?

Thanks,
Martin

Extruding to 3d

Wed, 29 Jun 2011 18:00:15 +0000

Hi,
2 questions:

1) I am creating a ring in 2d, and it seems perfectly circular, but when I extrude it to 3d, it suddenly gets slightly jagged sides and becomes a sort of polygon. I tried to fillet it in 2d and then extrude, but it makes no difference, the 3d still has edges. Anyone know how to fix this?

2) Is there any way to put a 2d face on a 3d object? For example, on a cylinder, I would like to put a small circle on its top face to model a laser's heat deposition. I think this would let me impose heat transfer conditions on the boundary. Other suggestions are also welcome.
Thanks

Equation editing in Structural physics in Comsol 4.0

Sat, 08 May 2010 16:08:05 +0000

Hi Everyone,

I was exploring comsol 4.0. I found that the GUI is good but some functionalities in 3.5a are removed.

I wanted to edit the Structural physics equation system to suit my PDE. In comsol 3.5a, I could do it by going to Physics menu>Equation system. In comsol 4.0, I couldn;t find the option. Does anyone know how to do it?

One more question, how to use the unitless system in comsol 4.0?

Thanks in advance,
Rakesh

Determine Arrenhius damage integral for a solution

Wed, 12 Aug 2009 18:05:07 +0000

I am trying to apply an Arrenhius damage integral DURING the solution of an electrosurgical problem using the Bioheat Transfer Module along with the Conductive Media DC module (T and V are the dependent variables) . The integral is of the form:

Adi = int(A*exp(-E/(R*T),t)

where Adi is the Arrenhius damage integral, int stands for integral and A, E, and R are constants. T is the nodal tissue temperature and t is time.

Is there a way to apply this into the Global Equations by taking the derivative of Adi? Thus making the equation:

Adit = A*exp(-E/(R*T)

I tried this, but received an error that T could not be solved for. Do I need to do something in order for Global Equations to access my dependent variables?

Thanks for any help...I am also interested in any other way that anybody can think of!