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rf mems switch design (comsol 4.2a)

April 14, 2013, 12:09 am
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HeLLO,
i'm working on designing a switch that should work on rf range. I'm able to draw 2d structure in work plane but still not able to fix one side of the cantilver beam. i hve following questions,

1) When i drawn a random structure i was able to get domains and boundaries, but when i restricted dimensions at micron scale, i didnt found domains, only i was able to get 11 boundaries, plz help me in knowing how to fix one side of the beam on anchor...

2) moreover when i chose xy plane in workplane how to add dimension of device in z plane? i had worked on quick plane section in workplane but i'm fiding extremely difficult to draw structure at micron scale. i'm working on coplanar waveguide .

kindly help

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Eigen frequency analysis

April 24, 2013, 1:52 am
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hi,
i am dealing with a nanotube sensor...can i use eigen frequency study step to find frequency at which displacement is maximum or should i use some other study step..
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Using a Gaussian Pulse

April 25, 2013, 11:47 pm
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Hi everyone,

I'm actuallay working on a modeling of a laser pulse which is heating a front of a material in order to determinate the diffusivity, my current issue is that i would like to model my heat source by a pulsian gauss but i don't really know how to integrate the fact that the heat source is a gaussian pulse type.
Thank you for reading this topic and i hope some of you could answer to my question.
Have a nice day !

Cordially,
Samy
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State Space Export

April 26, 2013, 2:16 am
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Hi ,
i have build a simple cantilever beam model using time depented model.
after defining the points of forces and parameters, i want to export the model to matlb (State Space Matrices) so i could "play" with the paramters and their location.
for example applying force at the tip = 100sin(theta(t)) and applying more forces to restrain the system.
i have searched the forum and found the mphstate function but i wasn't able to use it.

would like to get some help and tipps :)
(sorry for my poor english)

Regards, Eyal
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[SOLVED] Comsol v4.3.0.233 crashes

April 26, 2013, 4:55 am
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Hi,

Today, after restarting my machine I opened several applications and I was logged out from my desktop session.

After checking one by one, I get to see it was comsol that was giving problems.
I've tested other Java based applications such as Matlab or Mathematica and don't had a problem.

Right now I have lots of applications opened without any problem, but I cannot open comsol v4.3.0.233 or I'll get logged out instantaneously.

Running scripts with Livelink v4.3.0.233 also crashes my session.
Creating, logging in and running comsol with a new user does not resolve the problem.

Comsol v4.2.0.150 seems to run fine.

Is it just me or there is somebody else who is getting logged out from session after running comsol v4.3.0.233?

Using:
Debian GNU/Linux 6.0
Kernel 2.6.32-5-amd64
gcc 4.4


Please find the last log files from my .comsol/v43a/logs directory at these links:
www.ifi.unicamp.br/~febeme/comsol_logs/comsol6.log
www.ifi.unicamp.br/~febeme/comsol_logs/server6.log
(sorry for the external links, I'm not able to upload any .log files trough the forum web interface)

cheers,
Felipe BM
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How to plot the relative error?

April 28, 2013, 10:42 pm
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I've just spent more than a whole day troubleshooting my model.
However, if I could plot the relative error over the geometry, I believe it would have been solved in minutes.
There was a problem localised to a particular junction between domains.

So, is there any way to visualise the relative error in a domain? Maybe via Livelink for Matlab? I couldn't find anything about that.
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Integral Constraint

April 30, 2013, 8:44 am
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Hi, I am using the Nernst Planck Module (chnp) on Comsol 4.3 and I want to create a constraint so the total current in a boundary it's equal to 0, but I have no idea how to do it.
Can any body help me?

Thanks in regard

PS: Sorry if my english isn't the best, it's not my first language.
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Initial values error using mapped mesh

April 30, 2013, 10:37 am
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Hello,

Every time I try to use a mapped mesh for a time dependent simulation I have the following error :
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The following feature has encountered a problem :
failed to find consistent initial values.
System matrix is zero.
Last time step is not converged...
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It is weird because when I run the same simulation with a mesh generated by default, everything works fine.
My geometry is more or less a rectangle (3D).

Is there anything special to do with the initial condition when a mapped mesh is used ? I don't find anything on the web.

Thank you for your help.
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gas mixture

April 30, 2013, 11:50 am
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Hi

I am trying to model an ejector with 2 inlets and one outlet. In the first inlet I have hydrogen with low pressure, in the second inlet I have (hydrogen 30% + steam 70%) with a higher pressure. The material from the second inlet is sucked to the ejector due to pressure gradient. There is no chemical reaction. Two inlets just mix together.
The outlet will be (hydrogen + steam), however I don't know the mass fraction of the species.
The flow is turbulence.

I don't know how to define the compositions of the second inlet as well as the outlet. should I use multiphase flow or...?
I almost tried every thing. I appreciate your help.

Elham
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Override not-applicable boundary

April 30, 2013, 1:42 pm
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Hi,

This may be easy but I don't see how to do it in V4.3a. In V3.5a it was not hard. I would like to apply convective cooling at an interior boundary in my model.

Currently, all the interior boundaries are listed as not-applicable.

How do I override the not-applicable boundary in order to apply a convective film there?

Thanks,

Art
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acceleration due to gravity Laminar flow

April 30, 2013, 6:47 pm
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I want to give acceleration due to gravity effects to fluid in Laminar pipe flow, any one know how to give,?????

I have tried by applying domain volume force like 9.81*density of fluid but i am not sure it is right ???


any suggestions??
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Simulating an expanding plasma plume

April 30, 2013, 9:29 pm
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Hello,

There are two ways (at best of my knowledge) we can simulate the expanding plasma plume due to the irradiation from a laser on a target.
1. Particle tracing module
2. Fluid model.

We are working on the particle tracing module. In which we wish to release the particle with a half maxwellian velocity distribution profile. So we need to enter the velocity parameters vx, vy and vz.

I know the formulae for maxwellian velocity which is in the form:
f(vx) = (m / 2*pi*K*T)^(3/2) * exp(-m*vx^2 / 2*K*T),. Similarly f(vy), f(vz). T which we are using is 1ev = (approx.) 10^4 K.

To make it half maxwellian we need to use vx > vb,
So how do we do this?
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How to set boundaries as continuity ?

April 30, 2013, 10:10 pm
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I want set the boundary as a continuity but I don't know how?
I know that in Comsol by default the boundaries are define as continuity and it follow this equation: n.j=0
but I want change it to n(j1- j2)=0 (i want the boundary between two domain will be as continuity like n(j1-j2)=0)
how I can do this?

Any help would be appreciated.
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Fluid structure interaction with Turbulence k omega model

April 30, 2013, 10:51 pm
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Hi,

I want to study he effect of blood(fluid )on arteries wall layers(structure ). so i have been trying to model it with FSI and turbulence K omega.

There is in inlet velocity waveform that is developed turbulent waveform having equation 1.22*Um(t)*((1-((2*r)/d))^(1/7)) and I have defined Um(t) as interpolation function.

But when i run the simulation it gives an error "Attempt to evaluate negative power of zero Function: ^
Failed to evaluate temporary symbolic derivative variable. Variable: Uz@VDN$r".

I have tried to change solvers and adding terms like eps (which got known in comsol community ) but it does not works.

Firstly i solved it by using turbulent flow and structural mechanics separately and imported parameters of flow in structure module. this equation worked in this, but FSI module is not working with it ..??

Suggestions needed!!!!!!!!! I have attached COMSOL file
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Plasma electron impact reaction

May 1, 2013, 12:49 am
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In plasma simulation
If i have the reaction Metastable –metastable associative ionization
Hes+Hes=>He2++e with rate constant, k and threshold energy -18.2
where Hes is metastable Helium and He2+ ion of molecular helium and e the electron
i will use the Dc.Discharge=>Heavy species Transport=>Electron impact reaction?
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Export Image through script

May 19, 2010, 6:20 am
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I would like to be able to save an image of my plot using a script. I thought opening my script and going to export image in the GUI would add the steps to my m file but that didn't work...

Thanks
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microfluidics

June 13, 2011, 4:50 am
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hai all

my geometry is a rectangular having 10mm in x direction and 1mm in y-direction.

the first half ( up to x=5mm) consists of one fluid and second half consists of other fluid having same properties.

top and bottom walls are moving walls with 0.05m/s velocity . the left and right boundaries are stationary.

at x=5 mm i have two edges.

I want to equate the shear stresses on these bounadires. is it possible in COMSOL?



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Waveguide Dispersion Curve

January 11, 2013, 7:00 am
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The MATLAB coding for solving second order differential equation(D(λ)=- (λ /c)*(d^2n/d λ^2)) of wave guide dispersion is heavily needed. I have values of effective index n, c is constant and variable lambda is varied from 1.34-1.70 um . I have already completed the MATLAB coding of material dispersion, confinement loss. But i am failing to do coding of wave guide dispersion. I can use diff command if n is not given . But here both n and lambda is known. Thats why i face problem as there is no equation of effective index,n. So please anyone help me.It is urgently needed.......
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Convergence of time dependent and linear solver

April 30, 2013, 2:46 am
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Hello All,

I am trying a model in which electrodes can electrically stimulate certain layers having different conductivity (input being a biphasic pulse train). Using time dependent study, the model is running without any error. The electric current physics seems to be properly set up. But the convergence plots (both nonlinear and time dependent BDF) look peculiar and doesn't seem to converge. Changing the relative and absolute tolerance didn't help. Can anyone suggest where to find the error in the model?

I have attached the convergence plots. Also can anybody let me know what will be the range of convergence upto which I can consider the results reliable?

Thanking you
With regards
Satarupa
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transmission spectrum for beam focusing in plasmonics

May 1, 2013, 1:39 am
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Hi everyone


Iam trying to simulate using the RF Module beam focusing through subwavelength slit using grating but unable to get transmission spectrum i hv defined two port one side it is small in width equal to slit width while other port is equal to width of the device TM mode is propagating dont know what to do does unequal width is the problem



does anyone have any idea about this
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