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Thermofluidic Modelling of hydrogen absorption in metal hydride bed

May 18, 2011, 12:44 am
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For learning purposes, I was trying to do the this project Thermofluidynamic Modelling of hydrogen absorption and desorption in a LaNi4.8Al0.2 Hydride Bed at www.comsol.com/papers/7311/download/Lombardo.pdf (published in Comsol conference 2009 Milan). Except instead of two subdomain, I have only one domain containing the porous media and hydrogen enters the cylender through inlet. I am using the Darcy Law's Module and Heat transfer in Porous medium module. For kinetic expression, I have defined the formula in the definition section. I am using the same values and formulas defined in this paper. When I tried to run the program, I get errors which are associated with heat source definition and hydrogen mass absorption rate definition. Furthermore, I would like to see how would you plot the temperature and internal pressure plots which are published in the paper.


I have attached the file. Thank you in advance.

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Coefficient Form PDE and periodic boundary conditions

August 2, 2011, 6:08 pm
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Hi,

I'm new to COMSOL so I would like some help regarding the following -

I'm trying to perform a phononic crystal simulation using coefficient form pde. I have a hexagon with a circular hole shape removed - this is my geometry.

I want to apply a zero flux boundary condition at the circular shape and periodic boundary conditions at opposing edges of the hexagon.

So I end up using 3 periodic boundary conditions, for the 3 pairs of opposing sides of the hexagon. Unfortunately COMSOL sets up zero flux boundary conditions by default on all the boundaries and I don't see how I can remove this boundary condition on the hexagon's edges on which I only want the periodic boundary conditions.

Any help would be greatly appreciated!

Kartiek.
I'm using COMSOL 4.0a
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Voronoi 2D network drawing in COMSOL 4.3b

October 21, 2013, 11:57 pm
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Hi All
I am just wondering whether anyone knows how to draw Voronoi 2D diagram in COMSOL. I also require the division to draw with thickness such that it becomes a boundary instead of line. Any suggestions/help would be appreciated.Thanks.
Saimoom.
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Coupling two physics

January 13, 2015, 5:03 am
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Hello
I want to simulate a heater which transfer temperature to a reservoir.which physics is needed for this simulation? also how to couple these physics?
Any suggestion, reference, tutorial, or sample, is appreciated!

Thanks
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Material Overview shows a stop sign

January 13, 2015, 8:05 am
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Hi all,

I am having a problem when setting several materiales to my model.
When I do so, there is a red stop sign. I have given a material to all of my entities, so there is no "entities needing a material" message on my model. All the domains seem to have a material assigned. There is a stop sign next to each of my materials so I do not know what is wrong.

Thanks!
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Phase change in Metals (heat of mixing alloys) !!!

January 13, 2015, 8:50 am
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Hi everybody,

I am trying to model a dissolution of Sn (or any metal) into a bath of liquid Ti (or any other metal). So far I have made very nice models of temperature profile (stationary and time-dependent). However, now I am interested in the solid/liquid interface (S/L) to see the heat transfer behavior during phase change. I am most interested in the heat of mixing (Enthalpy of mixing) of 2 different metals, I am not sure if it could be calculated by Comsol, but at least, I want to make an approach watching heat flux behavior.

I took the phase change model (Tin melting front) from model Libraries, but I changed the liquid phase from Sn to Ti and I established different conditions, in order to make my own model. However it shows me this error that I dont know how to fix it......please help !!! (see my attached file)

Repeated error test failures. May have reached a singularity.
Time : 0
Last time step is not converged.
- Feature: Time-Dependent Solver 1 (sol1/t1)

Thanks in advance
Michael

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Electric contact pair

January 13, 2015, 8:52 am
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Hi everyone,
I have a problem with my quite simple simulation. It is about a MEMS thermal actuated switch which should close and put in contact two biased electrodes.

The problem is that the simulation does not converge in the moment when the two parts (plate and electrodes) come in contact, and this seems to be due to the presence of Aluminum; in fact, in a previous version which is completely made of Silicon, things are apparently running in the right way.

I have tried many things (changes in the geometry, in the solver parameters, and in the definition of the contact and electrical pair) but I can't solve the problem, which disappears only when I return to a structure completely made of Silicon.

Can anyone help me? I really have no idea of what I'm doing wrong, but I feel like I'm missing something fundamental. Unfortunately I cannot upload the models because they are too big files (6 MB), does anyone know how to do it?

Thanks for help!
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Two step study

January 13, 2015, 1:53 pm
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I am trying to couple laminar fluid flow with mass transfer in a micro scale geometry.
I have two category of geometries :
1- Complex geometries exported from CT image based software
2- Homogeneous geometries
Regarding both them I am simplifying the model by solving the model in two step :
a- Solving a laminar fluid stationary step flow to compute velocity in each node
b- Solving Time dependent mass transfer model using constant velocity value in each node

I am not sure the way I have done this studying is correct or what ?
I appreciate any comment from all friend has been faced by the same problem .

Here is my model .
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Clash of metal ball and plate

January 13, 2015, 7:15 pm
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I want to calculate the acceleration of the collision of the ball and the plate. But Comsol simulates them individually and collision does not occur (the ball flies through the plate as if it does not exist). I tried using Multibody Dynamics and Solid Mechanics, but nothing happens. How can I simulate it?
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track contours

January 13, 2015, 9:10 pm
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Hello,

I solved a 1D transient convection diffusion equation and I have different curves shown the decay of the concentration. I would like to plot a graph that shows the point in the 1D domain where the concentration > co, where co is a threshold. This is similar to tracking contours in 2D problems. Does anyone know how to do this?

Thank you.


Best wishes,
Ean Hin
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Solidification of a binary alloy and PDE

January 13, 2015, 11:05 pm
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Hello everyone,

I am trying to build a 2D-model to simulate the cooling of a binary alloy. The tricky point of my model is that I want to take into account the transport of the species during this solidifcation. My model is a continuous model, which means that there is only one domain, where liquid and solid can coexist.

I have found an equation, based on Fick's law, to simulate the transport of species :
dC/dt - div [D*liquid_fraction*grad (Cl)] + U * grad (Cl) = 0

where C = liquid_fraction * Cl + solid_fraction * Cs
and D is the diffusion coefficient.

I have used PDE, coefficient form, to take into account this equation. Another equation, based on the lever rule (a link between C, Cl and information coming from the phase diagram, know) is needed. And here is my problem.

I have no idea on how to implement this last equation. I have used "Pointwise Constraint" and it seems to work, but it is really really slow and eventually, it crashes. I have also used "Global Constraint" but in this case, the constraint isn't satisfied by the two variables. Does someone have an idea on how to do this ? I have never tried to use and define new PDEs and I am a little bit lost here.

Thanks,

Julien
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Turn off a hotplate permanently (Permanently change a variable)

January 14, 2015, 12:15 am
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Hi
I have a hotplate that I want to turn off permanently when it reaches 230 °C, and I need some help. I have a heat input of 285 W and a Domain Point Probe ppb1 that measure temperature.
I have tried q = 285*(ppb1<=230 [degC]) …. This works fine and turn the hotplate off at 230 °C, BUT as the hotplates cools and gets a temperature below 230 °C the hotplate turns on again.

What I need is an expression saying:
a = 1
if ppb1>230[degC]
a=0
end
q = 285*(ppb1<=230 [degC])*a

Can someone help me? Point me in the right direction?

Best regards
Bjarne
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boundary condition changing with surface polygones

January 14, 2015, 12:16 am
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Hello all,

One basic question: how is it possible to impose boundary condition which is related to the spatial variability in time dependent study?

More in detail: Suppose I want to impose balck polygons which are in the word document attched here.
and if you look this black polygons are varying during time.

Looking forward to hearing your comments and answers.
Thanks for help in advance
Sepideh



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integration over parameter instead of geometry

January 14, 2015, 3:34 am
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Dear all,

I was wondering if the following integral was possible in Comsol.



where f(g) is a known function, a,b are the limits (also known) and emw.Ex would be the electric field which depends on the position and on the value of g, i.e., emw.Ex=emw.Ex(x,y,z,g). I have seen a very similar question here: www.uk.comsol.com/community/forums/general/thread/39845 , but I have no idea have to deal with my problem. Normally, the integrals are defined over a domain, but this is not the case.

I guess that one solution would be do a Parametric Sweep over g, and make the integration in matlab, but I would like to know if this is possible in Comsol

Thank you so much
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Periodic condition, symmetry, 3D, cylinder

January 14, 2015, 4:00 am
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Hi everybody,

I model a cylindrical resistance. Two physics are used.
1. Electric Currents
2. Electric circuit
The coupling of the two physics works.
The total current in this scenario is I_total = 48.69 A

I would like to take advantage of the symmetry of the body.
Now I only use 1/4 of the body to produce the same result.
The Periodic condition is now used. However, it does not work.

The total current in the second scenario is I_total = 50,003 A

I have attached model and hope someone can help me.

Best regards
Dejan
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How to generate pulsed laser in Bioheat Eq.

March 3, 2013, 4:28 pm
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For Bioheat equation, there is one parameter which I can input corresponding to laser source, Q_ext (spatial heat source)

In this part, I typed the equation of laser radiation below,

I0*a*exp(a*z-r^2/(2*sigma^2))

and this is all what I could do.

The laser of course radiated as CW(continuous wave) mode.

I need to use the laser source as a pulsed mode.

What should I do?

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Convergence plots

December 13, 2013, 6:28 am
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Does anyone know if it is possible to show a convergence plot during a livelink with Matlab? I'm using version 4.4 and matlab R2013a.

Thanks
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Parametric sweep solution is lost after non-convergence

November 27, 2014, 1:16 am
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Hi, I'm running a time-dependent simulation, using electric currents and solid heat transfer physics. I'm ramping up the current with time, which heats the material. I have included an effect, which makes the current increase with temperature. At one point, the temperature and current will have a positive feedback effect, which should increase the temperature to infinity, and thus I get non-convergence at some timestep. This is expected. I need the solution before the non-convergence.

Now, when doing regular simulations (without parametric sweep), the solution is kept, but when doing a parametric sweep (e.g. over a range of geometries), the solutions are not kept when non-convergence occurrs.

Currently I'm doing every simulation without a parametric sweep, find the timestep when it doesn't converge and, create stop-conditions for those timesteps and then run the parametric sweep to get all the data conveniently. This is inconvenient and basically means I have to simulate everything twice.

Any ideas? How to keep the non-converged solutions in parametric sweeps?
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Prestressed piezoelectric analysis in frequency domain

January 10, 2015, 12:46 am
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Hi everyone,

I'm trying to simulate the prestress effect on the resonance frequency of a piezoelectric material using the "piezoelectric devices" physics.

I'm trying to do it in two steps :
1. Apply the static force to the structure and solve the problem using a stationary study and store the solution.
2. I use the stored solution to initialize the variables of the frequency domain step. I disable the "boundary load" condition and apply voltage to the piezoelectric material.

The result seems not good. when i look at the 3D stress for different values of the prestress the result remain unchanged.

I believe i'm missing something here, in particular the transition from step 1 to step 2.

Could you please help ?

thank you
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A problem in electromagnetics.it seems to ba a bug of COMSOL

January 14, 2015, 5:05 am
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As we all know, if there is a current in conductor, there will be a static magnetic field around it.If i simulate it using a 3D numerical model， i can get the static magnetic field. However, when i simulate it by a 2D axisymmetric model to reduce the computation , the magnetic field equal 0 ! Both model use the "elecric and magnetic field"and the boundary condition is same. WISH SOMEONE CAN HELP ME .THANKS A LOT.
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