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Export data as .csv or .dat

May 8, 2013, 6:29 am
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Hello,

I am working on a 2D transient problem. I have the results and want to post processing them.
I can easily export data in those formats(csv or dat) and open in Matlab or Excel.
I want to select just a part of data. as my domain in big, the exported file size is big(more than 2G).
Is there any way to export just a part of domain and specific time and my variable magnitude (suppose temperature)?
So in the file I need to have the data for x,y,t(time) and my calculated variable(like temperature).

Any idea?
Thank you in advance!
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2D Arrow Surface Plot -- Arrow Length Logarithmic

May 9, 2013, 2:02 pm
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Hello,

I am plotting a 2D Surface with an arrow surface. I need to scale my arrows logarithmically, but I am unsure whether this scaling is a natural logarithm or a base 10 logarithm. Which is it? The COMSOL Multiphysics User Guide states:

"Logarithmic, so that the length of the arrows is proportional to the logarithm of the
magnitude of the quantity they represent. This makes arrows representing small
values relatively larger. The value in the Range quotient field (default: 100)
determines the ratio between the smallest and largest values in the range of values
for the logarithmic arrow length."

If this is a natural logarithm, is there any way that I can scale my arrows with a base 10 logarithm? I will have some negative values in my vectors, so taking a log10 before plotting is not an option.

Thanks,
Lauren
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find the coordinates of a point in which the magnitude of derived variable at a specific time is minimum?

May 9, 2013, 3:41 pm
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Hello,

I am working on a 2D transient problem. I have the results and want to post processing them.
I want to plot my results like this:

Detect the minimum of a derived variable all over the domain at a specific time.
then, again detect that variable in another time (and repeat it for my time period)

I could do that. Now I wanna to have the coordinates of that point in which the derived variable is minimum at that specific time.
Any idea?

Thanks
Hooman
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object in a magnetic field

May 10, 2013, 2:57 pm
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Hi,

I'm working on a similar problem as yours.
I'm currently making a model on Comsol which calculates how the angular rate of an object in a magnetic field decreases over time.
What I did, I put an object imported from CATIA on a "box" which generate the uniform magnetic field. My simulation is in 3D.
Unfortunalty, Comsol either gives me wrong results (angular rate increases infinitly) or the solution is diverging.

Did you figure out how to solve your problem ?

Here is my email: mariek@my.erau.edu, it will be easier to talk.

Thank your for your help.

Andrea
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Inlet outlet mass flux is not identical

May 13, 2013, 9:24 pm
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Hi all,

I am trying to measure the bulk temperature, but initial testing on the conservation of mass failed as it gave me different results between the inlet and the outlet mass flux. This result makes me doubt all my simulation results so I would like to know what's going on. The model is a rectangular duct flow with 1) heat transfer on one side and 2) prescribed temperature at one of the walls and the channel inlet.

I used two 'general projection' planes to measure the mass flow rate over the entire channel length. As you can see in the graph, there is a sharp rise at x=0 (not to mention the fluctuations. I would say it's a numerical uncertainty due to the meshing). I don't understand why this is happening as this happens even if I refine the mesh, which is very concerning.

Any suggestions on why there is a discrepancy in the mass flux along the channel? Please let me know if there is any mistakes in my model.

Thanks!

Best,
Tae Jin Kim

ps: I also quantified the bulk temperature based on some discussions threads and extensive trial and error. At this point, I think it's almost correct, but please let me know if there is an error.
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Countor data set does not generate plots

May 15, 2013, 5:14 am
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Hi, I´m solving a very easy Laplace equation on Comsol, I would like to extract values of some variables I´d define along the isolevels of another user define variable. I´m able to create the Contour Data Set for u (is the Laplace ecuation solution) but when I try to create this data set for ux (derivative of u) or using any of the variables I´d declared in the definition section the result plot of the isolevels is blank. The results of the problem is ok, I´m also able to Plot the iso levels of the defined variables on a Contour Plot. Any ideas?

Regards

Agustin
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Adding points and lines to 3D models with parametric surfaces

May 16, 2013, 5:35 am
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Hi all,

I was wondering if there is a way to add a point or line to a model in which I have a 3D block with the top surface replaced by a parametric surface derived from a DEM (digital elevation model).

I guess this can be done in either the geometry section so it is there for the entire model run, or in the results section under data sets.

The end result I am after is the displacements along a line that traverses the parametric surface or at a certain point on the parametric surface.

Any help in this matter would be greatly appreciated, and let me know if I haven't explained the problem sufficiently.

Thank in advance!

James.
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water hammer

May 16, 2013, 3:41 pm
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hello to everyone
well I'm a student and hydraulic master2 I presonte memory of my study is to fain ^ ^ analysis of a battering ram in a pipe under COMSOL aep ^ 10 next joure.
I have download COMSOL 4.3a with a non-valid lecense

please

if directory you can send me the following two model file:

<> Water_hammer_verification_parameters.txt (1 KB) *
<> Water_hammer_verification.mph (5.7 MB) *

Please I have really needed her ...
thank you.
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Derived values in different tables instead of in 1 table

May 16, 2013, 11:15 pm
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Sometimes the derived values are comming in 1 table when doing the clear and evaluate all.
But sometimes all the different values are comming in different tables which is not usefull to work with (copy paste becomes more difficult).
It appeared when adding calculated values after the probe values.

Somebody knows how this is triggered?

Hans
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Outliers in parametric sweep results

May 17, 2013, 5:08 am
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Hi,

I'm modelling an eddy current testing probe with the AC/DC module. So far the model basically consists of a transmitter coil, an aluminum plate test specimen, and a receiver coil. I'm using COMSOL to tell me the magnetic flux density in the receiver coil, which is then used by a program I wrote myself to calculate the induced voltage.

I'm doing a parametric sweep through different values for the distance of the aluminum plate from the coils, but I can't seem to get "nice" results. The data mostly follows a nice trend, but I keep getting outliers at various positions (see attached file). I've tried several different meshes, both free tetrahedral and physics-controlled. The mesh seems to affect the outliers, but I can't get them to go away, even with a very fine mesh.

Even though the error is small relative to the magnitude of the voltage, it becomes significant because ultimately I need to measure very small changes in voltage. Can anyone help me figure out how to get rid of the outliers?

Thanks,
Neil
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initial value for eigenvalue study

May 20, 2013, 11:04 am
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Hi everyone

I'm running an eigenvalue problem and for every "search for eigenvalue around" value that I input, I am getting totally different eigenvalues.

I was wondering how much this value affect the results, since even for a small change, I have too different eigenvalues. other words, how sensitive this value is?

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thin layers

May 21, 2013, 8:20 am
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Dear all,

I am analysing the waves induced inside a thin layer using a shaker. I apply a sine wave on one of the edges and the analysis is in the time-domain. I am using Comsol v4.0.

Altough I am using the right time step and the right maximum element size (compared to the frequency of the applied vibration), I can't see the sine wave propagating inside the medium. For example, if I apply a burst of 5 cycles, I can't see this 5 cycles. It seems that it doesn't sample the load in the right manner, even if I use a time step that corresponds to 20 samples in each period.

Could it be a problem of solver? I am using a linear time.dependent solver.

If I increase the thickness of the layer, the simulation works well with thick layer. Does it depend on the different circular frequencies? Should I calculate the time step and the maximum element size considering these frequencies and not the frequency of the applied load?


Many thanks.
Ramona
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Incorporating Lagrange Multipliers

May 21, 2013, 3:52 pm
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Hello again,

Thanks to the help of those on the forum I was able to incorporate weak constraints to get accurate flux calculations in my diffusion models. However, I am trying to understand how exactly the lagrange multipliers work in terms of the final matrix construction and there is very little documentation in the comsol manuals and guides. I tried looking up some papers but they are written at a very high level of math that I'm not able to grasp the details of.

I tried writing out a simple heat diffusion problem in 1D with 3 mesh elements and solving with direct elimination, and then incorporating the lagrange multiplier via the approach shown here: www.softeng.rl.ac.uk/st/projec...s/html/Intro/intro-node68.html

I just wrote out the weak form and calculated the matrix by hand which isn't very hard for a 3 element 1D problem.

However, when I do this, I get the same answer for flux using either method (directly elimination or lagrange multipliers) once I solve the system of equations. BUT, when I do the same thing in COMSOL with the same problem definition, same constraints, and same number of elements, same basis function order, etc., the lagrange multiplier value I get matches up perfectly with the analytical solution. I would like to know how this is implemented, so that I can understand what is going on when I choose these constraints.

If anyone is able to explain it to me or provide me with a link I would be very grateful!
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area changes when going from 2D to 3D

May 21, 2013, 10:14 pm
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When drawing a circle the are changes when going from 2D to 3D

in a 2D drawing or in a plane a circle is drawn with radius (57,61/2)[mm] resulting in a surface of 0.002602m²

when extruding this plane or drawing a cilinder with the same radius the surface changes in 0.002585m².

What is the reason of this change?

2D diameter is then 57,5584mm
3D diameter is then 57,3701mm

why are they both differing with 57,61mm initial diameter?

Hans
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Mass in not conserved even in conservative form, multiphase flow of water bubbles

May 22, 2013, 4:46 am
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Hello everybody,
I have previously posted on a problem I was trying to simulate about multiphase flows
(Multiphase Flow LS - Air Bubble in Water Cylinder - Conservative forms fails) and I have tried working out the problem, but with small results. Therefore I decided to change approach and I started from the "electrocoalescence" model from the comsol model library.
My aim is to use electric forces to actuate bubbles, without any pressure driven flow. Therefore I started making changes to the original coalescence model. First I wanted to check what happens when we shrink the dimensions to the ones I would like to use in my device. I deactivated the electrostatic module, to look only at the two phases flow, I reduced the inlet velocity and I changed from two small bubbles to only a single larger bubble.
Then I compute the surface integral of the volume fraction of the fluid in the bubble for the time dependent simulation and I realize, mass is not conserved. So I try running the conservative form of the simulation, and again mass is not conserved (see graph). The original bubble is swept away (as it should by the inlet flow) and at a certain time it should disappear through the outlet and the volume fraction should go to zero, but instead, I have bubbles of fluid 1 entering through the inlet, when I have defined the volume fraction at the inlet to be 100% fluid 2. The volume fraction of fluid 1 is increasing in time. Anyone has a guess where my mistake is?
I am using version 4.2a. Thanks a lot for any comment on the model that I attach together with the results plots. The pressure point constraint was added only, because I have seen that it stabilizes the solution giving a reference (absolute) constraint.
Ah, the property solnum mistake is just due to the wrong multiple of the time step used as a stop for the simulation.
Thanks again,
Stefano
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Eigen frequency????

May 22, 2013, 9:31 pm
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hi,
how can we determine what the eigen frequency of a designed structure is among a list of obtained frequencies..
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What's the formulation of "mechanical energy flux" in COMSOL?

August 8, 2012, 11:39 am
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There are "mechanical energy flux," "complex mechanical energy flux"
which I can derive or plot in the result.
They are cool but still I want to know the definitions of them, how it calculates, and I did not find them in the user manuals.
Could somebody tell me? Thanks.
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Two interdependent studies - but I cannot use results from frequency domain study as input for stationary study

January 21, 2013, 4:35 pm
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Dear all,

How can I use the result from a parametric (parameter 'b') sweep-frequency domain study (e.g. emw.Ez(b) ) in another function defined under Definitions (e.g. f(emw.Ez(b)) ) which is used as an input for a stationary study?

According to the results that I am getting, what is actually passed to the second study is ZERO.

Could you please send me a reference?
Or tell me how to shall I input the results from a study to another study?

Thanks a lot!

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Show parameteric value on plot

January 31, 2013, 4:05 pm
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I've made a model of a hi-pot test setup to visualize how the electric field changes at a discontinuity as the conductivity changes (fixed potential).
I'ts working great, but now I want to make an animation of the results. I can create the series of 2D plots without a problem, but I don't know how to show the value for the conductivity on the plot, making it difficult to distinguish between them.
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help required related to Gyroscope

May 8, 2013, 6:23 am
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Hello,
I wanted to know the "applications of tuning fork MEMS gyroscope" which can be easily design in comsol multiphysics.
An i also wanted to know the various applications realated to tuning fork an which can be easily design in comsol.
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