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3D MOSFET model

September 16, 2014, 10:35 pm
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I am trying to simulate 3d mosfet model. I have applied all boundary and initial conditions to the 3D model. I have used a swept mesh for domain 2.

But in the solver i am getting an error

Undefined value found.
- Detail: Undefined value found in the equation residual vector.
There are 727 degrees of freedom giving NaN/Inf in the vector for the variable comp1.Ne.
at coordinates: (2.20179e-008,5.25e-007,7.70846e-007), (6.63152e-008,5.25e-007,8.12566e-007), (2.21487e-008,3.75e-007,8.12527e-007), (6.61844e-008,3.75e-007,7.70885e-007), (4.41665e-008,4.5e-007,7.91706e-007), ...
There are 728 degrees of freedom giving NaN/Inf in the vector for the variable comp1.Ph.
at coordinates: (2.22271e-008,5.25e-007,9.37527e-007), (2.22271e-008,5.25e-007,8.95861e-007), (6.6233e-008,5.25e-007,9.79194e-007), (2.20029e-008,3.75e-007,9.79167e-007), (6.64571e-008,3.75e-007,9.37554e-007), ...
There are 2 degrees of freedom giving NaN/Inf in the vector for the variable comp1.V.
at coordinates: (3.63886e-007,7.80064e-007,4.80733e-007), (3.85843e-007,7.05064e-007,4.80733e-007), ...

Please, can someone help me out? I have attached my file below.

Thank You.
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Meshing Tiny Thermal Vias

September 18, 2014, 3:53 am
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Hi everyone,

By using the Joule Heating Modul, I am trying to get the max. temperature around an electronic component. I have studied similar models before; but this time addionally placed several tiny (in radial direction) and long thermal vias across the PCB.

You can imagine those as really narrow and relatively long cylindrical tunnels connecting both sides of the PCB.

I figured that the "build all" takes forever and meshing gives memory errors. Even if I use an extra coarse mesh the simulation seems like it would take ages.

What would be an ideal (meshing or some other type of) approach to those structures?

Thanks,
Bartu
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Thermocapillary recirculation

September 18, 2014, 9:37 pm
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Hello,

I am a beginning user of COMSOL.
Currently, I am trying to create a preliminary model of Marangoni convection, like this one available on the COMSOL site: www.comsol.com/model/marangoni-convection-110

The main difference is that mine is axisymmetric, rather than two-dimenional, and instead of a temperature difference, the fluid is heated with a point heat source on the upper, free surface.
I was planning on doing both a stationary and time dependent study, but both are running into errors.

The stationary study yields results, but for some reason, the heated spot is colder than the rest of the fluid, rather than hotter.
I can only take from this something is wrong.

The time dependent study always encounter errors. the most recent one was the following.

Repeated error test failures. May have reached a singularity.
Time : 5.445849929194077e-006
Undefined value found.
Undefined value found in the stiffness matrix.
There are 2 equations giving NaN/Inf in the matrix rows for the variable comp1.w. at coordinates: (0,0), (0.00512513,0), ...
and similarly for the degrees of freedom, NaN/Inf in the matrix columns.
Last time step is not converged.


Could someone help me get this right?
I've attached my model to this post.

With regards,
Aaron Ayal
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time steps in time dependent study

September 21, 2014, 12:59 am
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hi!
im simulating fluid flow in a pipe with transport of diluted species.

when i run a time dependent study i noticed that comsol does not keep the time steps constant and skips over large periods of time without providing any data.

it starts with small steps but very soon they turn into very large steps.

how can i keep the time steps constant for the entire run ?

thanks a-lot!

tal.
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Step by Step debugging

September 21, 2014, 3:58 pm
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I am try to solve around 300 non linear partial differential equations which should take around 320 seconds but the simulations breaks after 20 seconds. I really can't find the error in my equations. I need to know to which equation has the error. So is there a way the simulation can be run step by step.

Thanks a lot!!
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Filling of a capillary channel

September 22, 2014, 9:02 pm
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Remco, hi!

Have you ever tried to simulate filling of a capillary channel in 3D? I've been trying to do that for some time, but still with no success. Maybe you know how to do that correctly?

Regards,
Kirill
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Catching errors in parametric sweeps

September 22, 2014, 9:12 pm
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Dear all

Is there an elegant way to catch errors in large parametric sweeps?
E.g.: When varying values of parameters one might well reach a point when convergence (or other) problems are encountered.
It would be a very nice feature if COMSOL would log this error and continue the sweep with the next parameter value(s) instead of stopping the whole sweep.
Is this possible even when not running COMSOL via the Matlab interface?
Or would something like the "try catch" method in Matlab be the only way to achieve this?

How do you treat this issues?

Thanks for interesting hints on this and best regards,
Juergen

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"Update scaled absolute tolerance"

September 22, 2014, 9:56 pm
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About the "Update scaled absolute tolerance" check box.
This feature of the Time-dependent solver has been on by default in the last few versions of Comsol.

In some models in the Model Library, the instruction is to uncheck it, but it's given without comment. For example, in these models:
• Capacity Fade in a Lithium-Ion Battery
• Peristaltic Pump
• Nonlinear Acoustics: Modeling of the 1D Westervelt Equation

I can't find a single theme in them (but I haven't looked in-depth).

From the documentation, when the check box is checked, the behaviour is described essentially as an interpolation in time, between the absolute tolerance value as entered into the "Absolute tolerance" field, and the same thing multiplied by the maximum value of the dependent variable taken over the entire field, where it is smaller than 1. (Plus, the L2 norm of it is added, which will always be smaller than the L-infinity norm, so that must be for the case where L-infinity norm is greater than 1.)

So it seems reasonable (and, in fact, better) to adaptively adjust the absolute tolerance to be relative to the max value or the L2 norm of the dep. variable, like that.

My questions are:
• When should this *not* be used?
• In particular for the above sample models, why has this feature been disabled?
• Is there a way to access the value of the absolute tolerance as it's being adapted throughout the time-dependent simulation?
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problems with linear projection

September 23, 2014, 3:07 am
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Hi all,

I developed a model for calculation of AC losses and I am using Linear projection operator to ensure sufficient current flow (Point-wise constraint later). The problem is that my linear projection operator fluctuates a lot. You can see that in attached graph. What could be the reasons?
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Convergence problem in RF module

April 1, 2013, 2:16 am
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I am doing some plasmonics simulation using silver nano particles in comsol. For silver particle convergence is either very very slow or there is no convergence in most cases for some specific wavelengths. The same model works fine for gold nano particles. Kindly help.
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Simulating capacitive device operating at collapse voltage

September 23, 2014, 8:29 pm
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Hi,

I'm trying to simulate an capacitive ultrasound transducer operating at collapse voltage. The model, made of two parallel capacitor plates, are expected to collapse into each other during simulation, then its eigenfrequencies are to be calculated. Is this possible with COMSOL? If not, would it work if I start the simulation using an already collapsed model?

Thanks,

Sergei
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Simulation in Finned Tubes

September 24, 2014, 12:02 am
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How to do heat transfer and flow simulation in Finned Tubes

I tried a lot ; but i could not able to give correct boundary conditions.

Please help me to solve this problem.
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Difference between optimization and parametric sweep?!

September 24, 2014, 3:28 am
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Hi Comsolers,

Could you kindly tell me that what is the difference between optimization module and parametric sweep in comsol, please?
I know that maybe it is simple question, But I want to need when a user choose optimization or parametric sweep for his/her model?

Thanks in advance for your help.
Sepideh
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Piezoelectric inkjet printhead (unknown physics and boundary conditions)

September 24, 2014, 7:33 am
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Hello everyone! I'm a newbie to COMSOL. Unfortunately, I'm experiencing some difficulty in trying to model a relatively simple problem in COMSOL, and I'd be really really thankful if anyone could help me out. Let me cut to the chase. I was tasked with modelling a cuboidal container with a diaphragm on top. The diaphragm is the ceiling of the container (with a finite thickness of course). Now, a Piezoelectric material (a cuboidal strip of finite thickness) is supposed to be attached to the top of the diaphragm (ceiling). In theory, when a voltage is applied to the surface of a piezoelectric material, it deforms. My task was to make it such that the diaphragm deflected downwards. So through trial and error, I found that the voltage must be applied at the top surface of the Piezoelectric material. Moving on, the container is filled with a fluid (say water or ink). (This is supposed to be a really primitive version of a Piezoelectric inkjet printhead WITHOUT THE NOZZLE :p). There is no inlet or outlet. The deflection of the diaphragm, theoretically, causes a change in pressure of the fluid which I am supposed to measure. This is the part where I'm stuck. How do I fill fluid in the container? Which physics should I use for this problem? I tried modelling a solid cuboid and assigned it to "water" and made the diaphragm and piezo material on top? But then what boundary conditions should I give for the fluid physics that I use? (say laminar flow) Should I couple a fluid physics at all? If I don't use a fluid physics, it asks me for the coupling matrix and elasticity matrix for water, both of which I couldn't find out. If I couple a fluid physics with piezoelectric physics then, I do not know what boundary conditions to give for the fluid. I'd really appreciate it if someone could help me out with this. I'll post an image file for reference. I can't upload the model though (my university net restricts me from uploading files of sizes larger than 1MB :( ) Downloads are allowed though, so if you can make a similar model with the necessary changes and upload it, that'd be great! But general instructions and advice are also really welcome and would be highly appreciated. Also keep in mind that I'm a newbie to COMSOL. Thanks in advance!
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Solving Self - Consistent Schrodinger and Poisson with MATLAB and COMSOL LiveLink.

September 5, 2012, 6:44 pm
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I'm a COMSOL 4.2a user. I need to solve 2D self-consistent Schrodinger and Poisson equation. Thus, I need to feed the potential values and the wavefunctions to the Schrodinger and Poisson equations as argument and solve iteratively.

The thing I need to know, how can I feed the updated the wavefunction and potential values as argument iteratively in my model? I have livelink with MATLAB and I intend to solve the problem inside a loop (i.e. Calling one models while passing the result of another as argument). I have solved the models with PDE solver but cant do it iteratively with LiveLink.

One more thing, is it possible to access the results directly from MATLAB and thus use them as variable ( though a class of course) from MATLAB for post-processing, like we get the solution matrix in MATLAB?

--
Thanks
Mehedi
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Smoothing battery current changes

September 24, 2014, 12:28 pm
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I've been having issues with the capacity fade model and I think I may have narrowed down the problem.

See the model in question here: www.comsol.com/model/capacity-fade-of-a-li-ion-battery-12667


I am trying to increase the number of cycles, and I usually encounter errors in the transition between constant voltage discharge and constant current charge. The abrupt change in current density from ~+0.1 A/m^2 to 10 A/m^2 usually results in a lot of error and a large voltage spike which completely interrupts the charging-discharging cycle determined using the events interface.

As I understand it, the discontinuity of the current input is not something COMSOL likes.

I see that there are smoothing functions available, but I am not sure how to use them in concert with the events system used to determine the current load in this model. Any help would be appreciated.
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resistance measurement

September 24, 2014, 7:18 pm
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Hi,
I am working on joule heating and thermal expansion module.
I want to measure resistance between two terminals. No voltage is applied to the terminals, no current flow initially. Later through induction or channel formation current will flow and it will change the resistance.
How do i measure the resistance initially and after current flows.
Thanks
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Modeling closed circuits with pipe flow module (linking inlet and outlet)

September 25, 2014, 7:07 am
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Hi Comsol experts,

I an trying to model a closed pipe circuit consisting of a network of pipes, bends, valves, junctions and heat transfer areas. A pump is inserted to create the force (dP) to move the water inside the pipes.
Is it possible to model this with a closed pipe circuit or do I need to have an inlet and an outlet?
If inlet and outlet is necessary, how do I link the boundary conditions of the inlet and inlet (mainly velocity and pressure and temp) to model my closed circuit?

Any help is very much appreciated :-)

Regards
"A novice cfd/pipe flow dude" / Morten
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Problem with max field calculation

September 25, 2014, 7:41 am
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Hi.
I have a resonator inside background media. I use PML around. I am looking at a particular mode. Then I can find the maximum of normE field which is inside the resonator. Now if I change the size of background media normE max is changed!! Although the resonator shouldnt be affected by the size of background media.

Is it possible that comsol normalizes modes to the computational volume?
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Fluid Piezoelectric coupling problem

September 26, 2014, 9:40 am
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Hello everyone! I'm a newbie to COMSOL. Unfortunately, I'm experiencing some difficulty in trying to model a relatively simple problem in COMSOL, and I'd be really really thankful if anyone could help me out. Let me cut to the chase. I was tasked with modelling a cuboidal container with a diaphragm on top. The diaphragm is the ceiling of the container (with a finite thickness of course). Now, a Piezoelectric material (a cuboidal strip of finite thickness) is supposed to be attached to the top of the diaphragm (ceiling). In theory, when a voltage is applied to the surface of a piezoelectric material, it deforms. My task was to make it such that the diaphragm deflected downwards. So through trial and error, I found that the voltage must be applied at the top surface of the Piezoelectric material. Moving on, the container is filled with a fluid (say water or ink). (This is supposed to be a really primitive version of a Piezoelectric inkjet printhead WITHOUT THE NOZZLE :p). There is no inlet or outlet. The deflection of the diaphragm, theoretically, causes a change in pressure of the fluid which I am supposed to measure. This is the part where I'm stuck. How do I fill fluid in the container? Which physics should I use for this problem? I tried modelling a solid cuboid and assigned it to "water" and made the diaphragm and piezo material on top? But then what boundary conditions should I give for the fluid physics that I use? (say laminar flow) Should I couple a fluid physics at all? If I don't use a fluid physics, it asks me for the coupling matrix and elasticity matrix for water, both of which I couldn't find out. If I couple a fluid physics with piezoelectric physics then, I do not know what boundary conditions to give for the fluid. I'd really appreciate it if someone could help me out with this. I'll post an image file for reference. I can't upload the model though (my university net restricts me from uploading files of sizes larger than 1MB :( ) Downloads are allowed though, so if you can make a similar model with the necessary changes and upload it, that'd be great! But general instructions and advice are also really welcome and would be highly appreciated. Also keep in mind that I'm a newbie to COMSOL. Thanks in advance!
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