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please help me to measure Voltage,!

March 28, 2014, 5:32 am
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HI, I am very new to use COMSOL,
so I wanna ask some problem to proficient person who could use COMSOL,

I'am measuring Voltage from piezo with some stress,
when I measured Voltage from piezo by using probe , applying load,
there is some problem.


Failed to find a solution.
The relative residual (4.3) is greater than the relative tolerance.
Returned solution is not converged.

how to solve this error?
there are some my solutions which I referred some idea from discussion forum

more fine mesh, increasing tolerance, etc,,,
it does not work.

I do not know what I have to do,,,
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Can Dirichlet B.C. affect the eigenvalues?

March 29, 2014, 4:52 pm
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Hi everyone

I'm dealing with an eigenvalue problem that is supposed to study the effect of the Boundary condition on the eigenvalues.
Apparently, in an Eigenvalue study in COMSOL, any prescribed values of the dependent variable (no matter the magnitude) are taken to be zero.
Anyone has any idea if there is any trick to affect the eigenvalues through the Dirichlet Boundary conditions?

Thank you
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Identify the effective mode for Photonic Crystal Fiber based SPR design

March 29, 2014, 6:35 pm
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Hi, I have designed a Photonic Crystal Fiber for Surface Plasmonic sensor. When, I run the COMSOL than I found several mode confine the light in the core....Now, my question is how can I understand which mode I should to take? Please help me.
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Mixture of sweep mesh+Tetrahedral mesh in a 3D model

March 29, 2014, 7:28 pm
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I have a helical coil embedded in solid cylinder and was trying to figure out best way to mesh it since helix always creates problems.

1)I did a mapped mesh on one end of coil cross section.
2)Swept it along the coil, till the destination face.
3)I meshed the cylinder with tetrahedral mesh.

I am always getting errors. The model is just not meshing. I tried meshing complete model with tets and it did mesh after a looong time, but it gave error while solving.

Would really appreciate if someone could give some guidance.

Thanks
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Boundary conditions on 2D axis-symmteric model in Thermal stressProblem

March 30, 2014, 4:58 pm
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I am imposing the very high temperature field i.e. T(r,z) on 2D axis-symmetric (cylinder) model in order to calculate stresses/strains. As temperature is high enough to yield the material , so I am expecting plastic strain.

Surprisingly, If I use only symmetry boundary conditions (on center and bottom edge) there is no plastic strains!

If, I try to constrain the bottom edge, it causes a large error and convergence issues.

Any suggestion please. I wondering why symmetry boundary conditions are causing no plastic strains!

Thanks,
Hina
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Couple strain with ion concentration?

July 22, 2010, 4:59 pm
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I've been modelling ion transport in a porous material using the chemical engineering module. I would like to also model an induced strain in the material that is linearly proportional to the local ion concentration (swelling/dilation, similar to a thermal expansion but dependant on concentration not temperature). How do I modify a standard Hooke's law stress-strain relationship to include this additional term? I also have access to the solid mechanics and MEMs application modules.
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Help needed for intercalation stress at COMSOL

March 31, 2014, 6:15 pm
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Hi C.Lim,
I am, working on same problem i.e. intercalation stress. I followed your suggestion like putting partial molar volume as expansion coefficient and concentration as temperature. However, my stress value is not exceeding yield point so as a result I am not getting any plastic strain. Can you help me to answer:

1- Did you use the "normalized concentration as temperature" i.e. the C/Cmax (value range 0 ~ 1 within material? OR you used actual concentration?

2- How about reference temperature? Did you use zero reference temperature?

3- Lastly, which mechanical boundary conditions did you use and any solver settings are needed?

Please help me.

regards,
Hina
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Errors with conjugate heat transfer...

April 1, 2014, 1:48 am
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Hello

I am new to COMSOL and I am doing simple test model of natural convection of air around hot metal cylinder. I think, that I set everything properly (like volume force etc), physics is quite easy but after 2 or 3 iterations i get errors like this:

Failed to find consistent initial values.
Undefined value found.
NaN or Inf found when solving linear system using SOR.

or similar. When i change to dierct solver it keeps increasing memory allocation factor and nothing happends.

I tried to change mesh to courser or finer, tried different solvers and options and nothing helped.

I cannot attach my model in comsol, its too big, but I can send it on email if someone would like to help.

Please help me I really run out of ideas....
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Use the result of 2D simulation into 3D simulation

April 1, 2014, 5:48 am
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hi everyone!

i want to increease the speed of my 3D simulation, so i have a idea: the result of a 2D simulation is used as the initial value of a 3D simulation, then maybe the 3D simulation can find a suitable result quickly. Does my idea work? how can i use the result of 2D into the 3D simulation?

thank you very much!
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Parametric sweep through time

April 1, 2014, 6:27 am
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Hi Ivar,

In this thread:
www.comsol.com/community/forums/general/thread/31432/
you mention that for a stationary solver, you can sweep on "t" using "t" to point into a time series solution. I am attempting to do exactly this (I have a time series solution from PDE physics, and I want to use those results in EC physics to find stationary solutions at each time point).

I have success manual stepping through each time point, but when I try to automatically generate the results, e.g., with a parametric sweep, only one time point from the time series solution is used.

Can you help, maybe describing how you set up your sweep?

Thank you very much,
~Vanessa Tidwell
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Accessing solution of one study into another one ?

May 14, 2012, 6:29 am
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Hi,

I been modeling hyperelastic material models in comsol which revolves around three different studies on the same geometry, with different boundary conditions. I would like to access results from the second study to give input to some of the variables in the third study. Well, i could use the second solution as initialization to third study, but i want to access, for example, shear stress at every point in the material domain, which in turn affects inelastic deformation gradient matrix in third study.

Any one has any idea how to do this ? Any help is greatly appreciated !!

Thanks !

/Krishna
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File import/export procedure: Not reading whole data

April 1, 2014, 9:39 pm
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I am importing a notepad .txt file that contains the temperature values with respect to position i.e. T(x,y,z) in 3D geometry.

I am using:
1- Global Definitions --- Interpolation --- import file
2- Structural module ---- Thermal expansion--- int1(x,y,z) as Temperature load ---- Reference Temperature= 0

However, after solving the Time-Dependent problem, when I plot the Temperature in" Results": It shows only first entry / value of temperature of the imported file i.e. no gradient at all or not matching with interpolated values plot.. When I plot the interpolation: it shows the right plotting of T(x,y,z)

Can someone tell me why it is not being imposing as gradient? Because, I am not getting the expected stresses. The result of stress value is very low than expected.
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time dependent study for sinusoidal wave

April 2, 2014, 10:34 pm
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Dear all,

I'm trying to simulate my module in 2D axis of COMSOL version 4.3 in joule heating physics with sinusoidal input voltage of { V0*sin(2*pi*50*t)} and for the frequency of 50 Hz it will takes 0.02 second for full wave . so i must use small time step of around 0.0001sec. . i have problem when i increase the time to more than 5 second with step of 0.0001 sec .

I need to simulate my module for time between 0 sec until 300 second with time step of 0.0001. as times: range(0,0.0001,300)s
So it needs around 3 million step to get the full result and i think it's difficult to that .

is ther are any way to get it in the transient study so i can check the time that need to arrive the steady state temperature .

best regards ,




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Frequency domain using two pi/4 phaseshifted Piezos

April 2, 2014, 10:52 pm
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Hello,

I want to analyse the mechanical behaviour of a spring, that is being piezoelectrically activated. With one piezo this wasnt any problem, as i would just use 5V as electrical potential, and run a simple FrequencyDomain analysis.
But in my case the Piezos need to be phaseshifted like:
U1=U0*sin(2pi*f*t)
U2=U0*sin(2pi*f*t+pi/4)
I tried to use waveforms as global definitions and used them for my electrical potential like "wv1(t[1/s])" (found that hint on another thread), which seems to work in the first place, as the entry wont turn red/yellow.
Trying to simulate, i get this error:
--------------------------
Failed to evaluate variable.
- Variable: t
- Geometry: 1
- Boundary: 52 67
Failed to evaluate variable.
- Variable: comp1.pzd.V0
- Defined as: wv2((t/unit_s_cf))
Failed to evaluate expression.
- Expression: comp1.pzd.V0-comp1.V
-------------------------

I tried looking for solutions on the forum, but couldnt find any useable (or im just searching for the wrong topics, as im very new on comsol). I mean this is a very basic problem:
Two phaseshifted oscillations on something... it probably hardly matters in that case if its voltage, force or whatever..

Thanks Andreas
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Automatic time step increase in generalized-alpha solver

April 3, 2014, 5:32 am
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Particle tracing is conducted by a generalized-alpha solver.
For many cases, when the particle motion is finished, the time step is increased drastically.
However, in current case, time step is oscillating.
In some case, when I turn off the Brownian force (which is a monte carlo modelling), this problem is solved.
However, this is not a solution for the current problem.
What should I do for avoiding this problem?
This problem causes the longer solution time.
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how to use the "Previous solution" as initial value for new analysis

April 3, 2014, 11:09 pm
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Any idea how to use the "Previous solution" as initial value for new analysis, for the sake of solution convergence??
Preferably, step-by-step procedure!

Thanks,
Hina
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I want to get surface wave.

April 4, 2014, 3:09 am
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Hi there.
Thank you for reading my discussion.

I try to build suface wave. I make a rectangular at first and apply a open boundary condition at the top of rectangular , then I use 'Definition->Functions->wave form' on the left side for expressing periodic velocity.
what I want to get is surface wave on the top of rectangular.

for example, it is same phenomenon that you press water-tank on the left side, so you can see the sinusoidal wave on the water.

I think I need to use 'Moving Mesh'.
I would like to know what I should put on the laminar flow and moving mesh.
If you have any good advices about it , please comment here.

Many Thanks.
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Electric field just above an interface

April 4, 2014, 7:13 am
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I apply a static electric field across a 2D air gap.

Somewhere in the air gal I place a square dielectric. I notice the solved E field is discontinuous at the air-dielectric interface. So it's a different value just inside and just outside the dielectric.

Now I want to plot the E field along one of the edges of the dielectric, just inside or just outside it. I could draw another slightly larger or smaller box around it, and plot E along the edge of this new box, but that tends to mess up my meshing, and I won't get the true boundary values that way. Is there a better way?
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meshing long and thin wire

April 5, 2014, 3:33 am
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Dear all,

I need to create long and thin wire with different length of (500,700,1000)m, and radius of (0.315mm) and layer of insulator of (0.135 mm) in (2D) axi-symmetrical. But when I add the insulator layer and trying to mesh it using mapped mesh I got error of ‘’Can’t create mapped mesh for this geometry’’ .

but when I mesh it without the insulator it will be fine and no problem , except for longer wire more that 700 m.

Is there are any way to mesh the geometry with two layer? And can I create wires with length of 1000 m and radius of 0.315 mm?
I attache a simple geometry using painter.

Best Regards,
Hazlee
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convective heat transfer on a sphere

April 5, 2014, 10:08 am
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Hey guys,

I'm writing a simulation of freeze drying for my bachelor thesis.

In my bachelor-thesis, i’m looking at a system with a particle of pure ice (T=230 K), which is exposed to a ingoing water vapor mass flow (T=240 K, mass flow=const.) under reduced pressure (10 Pa). I’m studying the change of the outgoing mass flow, which is caused by the presence of the particle, and I’m also looking at the time dependent temperature distribution inside the particle. The steam shall heat the particle, the supplied energy of the steam leads to sublimation of the ice.

I orientated myself on the simulation from the model library:
www.comsol.com/model/a-transie...analysis-of-freeze-drying-3924

I use the physics "conjugate heat transfer" for the heat transfer in the particle and the mass flow, "transport of diluted species" for the concentration distribution inside the system, and "deformed geometry" for the moving of the sublimation front of the particle. The simulation works, but the whole particle stays at a constant temperature and won't shrink. I use the ideal gas equation for defining the BC of temperature on the particle surface. I think something is wrong with my combination of the physics. If somebody could help me, I would be very thankful. I already tried everyting... I uploaded the simulation:

www.file-upload.net/download-8...-heat-transfer-sphere.rar.html


Best regards,

Andreas Schäfer
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