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A Swept Quad Mesh Within Free Tet - Quality Concerns

March 17, 2017, 10:00 pm
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Hi everyone,

I'm looking for some advice on a meshing problem that I have - I have a heat load imposed on a 3D rectangular beam embedded within a larger beam of the same material; the two beams form a union. The area where the heat load is applied is very finely meshed with a mapped distribution so that I can control the exact number of elements in my area of interest.

This is great but my problem is that in order to cut down on computation time/memory cost - I am converting the boundaries of this swept block (or another swept block around it) to tri's and then putting in free tetrahedral mesh for the large remainder of the geometry. This has the unfortunate effect of creating a region of poor mesh element quality around the swept block where I need my mesh to be the most accurate.

I have attached an image of what the mesh element quality looks like in one iteration of this model. It seems that every time I try a slightly different meshing scheme - my results are significantly different and I have tried many variations. If anyone can suggest a better alternative to my current meshing scheme, or point me in the right direction of increasing the mesh quality, I would greatly appreciate it.

Finally, my heat loads are asymmetric and so unfortunately I cannot exploit any symmetry to cut down on the computational cost.
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Analysis of mixed convection flows within a square cavity

March 22, 2017, 11:54 am
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Hi , I am new to the topic of solving mixed convection problems in COMSOL multiphysics.
I want to validate Fig. 8 of the paper(attached). Stream function and temperature contours for uniform bottom heating case with Pr = 10, Gr = 1000: (a) Re = 1, (b) Re = 10, and (c) Re = 100.
Which physics is to used here. Is it Laminar flow(SPF) and heat transfer(ht)?How to take care of Reynolds number in the governing equation? What is the body force or volume force to be used here? There is no Rayleigh number here but Grashoff number is the parameter of study here.
Kindly suggest for a non dimensional case.
Thanks in advance.
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charge particle tracking assigning experimental magnetic field values to a magnet model

March 22, 2017, 11:38 pm
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Dear All,

I have model of my magnet. I want to give it my own measured magnetic field and want Comsol to interpolate all missing values if it needs for the particle tracking. Can somebody tell if this is possible?

Regards,

Noaman
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Export comsol file( mph) to GDS FILE

March 23, 2017, 2:00 am
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Hi
Does anyone have idea on how to export (geometry) mph file (Comsol) to GDS file.

Need your help please.
thanks
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Longer simulation study

March 23, 2017, 4:24 am
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Hello everyone,

I'm facing an usual problem with a comsol time dependent simulation study. In the study settings, upon changing the upper limit of the time range by a decade, the simulation doesn't show any physical response. While it was completely fine when the study setting was up to a certain limit in range, considering I didn't make any further changes in resolution or meshing in my physical model, going to one more decade level in the range doesn't produce any results. Could it be related to any other setting I might be unaware of?

To give you context I'm running a time dependent study of 0-10ms with a resolution of 1e-7 and relative tolerance of 1e-6. And I'm being able to run it when this range is 1ms but after that it just doesn't produce any result.
Any help would be appreciated.
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Propagation constant using port excitation

March 23, 2017, 5:56 am
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Dear All,

I have a question regarding the usage of propagation constant parameter for port excitation in the EM frequency domain simulation.

I tried to use the port functionality to excite an EM wave in a 2d geometry. I used a very simple rectangular geometry with PEC boundary conditions on the sides parallel to the x axis (length). The input excitation port was used on one of the side parallel to the y axis, with the user defined electric field as:
Ex=0, Ey=0, Ez=1.

1) Is the propagation constant defined always in the x direction (normal to excitation side).
2) If I assume that the propagation constant is in the x direction, I expect a phase shift in the Electric field vector for varying value (real) of propagation constant at any point in the x axis. However, I observed a change in magnitude (for emw.normE field) without any expected phase shift. Could you please help me to understand this?

Thanks,
Rahul
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selective laser melting_interface heat transfer

March 23, 2017, 7:42 am
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Dear all,

I am working on the simulation of SLM. I have a question, firstly laser irradiates on the surface of the metal, and I want to use the average temperature of the surface from coupling as the initial value of the surface temperature, in order to calculate the temperature driven flow effect. So actually how to realize this? Thanks in advance.

Greetings
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Two phase Liquid Liquid extraction

March 23, 2017, 10:59 am
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Hello,
I am trying to model mass transfer through interface of two liquid in a two phase model. I believe comsol by default applies flux continuity at the interface. However I also want to an equilibrium boundary condition (governed by partition coefficient) at the interface. I used pointwise constraint to tie concentration c2-K*c1, where c1 and c2 are variables. As a results interface is not tracked properly and I get anomalous results for examples the phase fragments and no concentration value.

Can you please help me with this?
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Magnetic Fields, No Current

October 14, 2012, 5:48 am
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Hi everyone,

So I've been trying for a while now to bypass the problem of creating an external magnetic field in *other* AC/DC modules; but now I see that in the MFNC there are two options: External Magnetic Flux Density, and the same without external. The External seems to be a pointless node - it does not make any change at all in the model, does not affect anything - and you cannot provide it with any information;

so here's the first question - what does the External Magnetic Flux Density node do?

the other node, without external, seems to work if you have a stationary model, but if you have a time dependent, any field that is not 0 makes it not converge. attached a model; can anyone tell me what is wrong?

I'm working with 4.2a.

thanks,
~Shoval
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Piezoelectric transducer for liquids

October 17, 2012, 3:16 am
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Hi all,

I am using COMSOL to model a piezoelectric transducer directly coupled with liquid (oil or water) and using the tutorial provided in COMSOL website in this aspect. I am just defining one boundary of piezoelectric material as oscillating boundary (applied with voltage) and the other one grounded but am not sure about the results. Can any one answer a few queries regarding this?

- Are there any reflections of ultrasonic waves from liquid when placed in this way?
- How can I check the impedance matching characteristics of the piezoelectric especially the acoustic impedance?
- Can I change the phase or beam angle of piezoelectric transducer? If so, how?
- After having a look on the attached image, can some one explain the result and why I am getting this?

Many thanks in advance for any of your help.
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Help from Experts Please: Size-Modified Poisson-Boltzmann Equation

January 8, 2013, 12:32 pm
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Hi, I am trying to simulate a 1-D Size-Modified Poisson-Boltzmann Equation with the PDE module (attached)

10 um strip with 1 end applied voltage potential 1 end grounded.

The solution voltage doesn't have any shielding effect.

Not sure where went wrong.

Help would be greatly appreciated !
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Simple Easy Resistance

March 23, 2017, 12:10 pm
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Hi,

I am looking to find the resistance of two cylinders joined end to end.
Each cylinder is a different material.
I vary just the conductivity of one the cylinders and do a parametric sweep.
1 V is applied to the top, and GND is applied at the bottom.

The results I am getting do not make any sense at very low conductivities. My simulation severely underestimates the resistance.

Any ideas? It should just be the bulk resistance of the two material
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MicroFluidic channel with Shape Optimization

March 23, 2017, 12:23 pm
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Hi all,

I was having some problems getting my shape optimization for a microfluidic channel
working. The idea is that the channel should have constant strain rate through its center.
The strain rate equations and constraint is set up correctly, however the shape
optimization on its top and bottom walls is not working. I am trying to set it up similar
to the beam optimization problem here:

www.comsol.com/blogs/designing...tures-with-shape-optimization/

The entrance height is Wu and the exit height is Wc, I am trying to use a berstain polynomial
to model the top and bottom walls. My current iteration is really close, however the right side
sags a little for some reason. the channel itself is centered on 0 and shifted in the x so that it begins at x=0. I create a prescribed deformation and outline the rectangular channel. The equation I enter for the displacement in the y is "(Yg/(Wu)-1)*((Wu)*((A2)*Xp^1*Xn^2+(A3)*Xp^2*Xn^1))+(Yg/(Wc)-1)*(Wc*Xp^3)" with Xp=Xg/Lc and Xn=1-Xp. This is the berstain polynomial. Under optimization, I control the length, a2, a3, and the entrance height (the entrance height is coupled to the exit height through and equation) while constraining the constant strain rate through the center. Attached is a picture of the output, for some reason it sags on the right side, as mentioned previously.
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comparison between two different fields

March 23, 2017, 2:08 pm
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Dear all,

suppose you have two different fields and you want to compare them in order to obtain a numerical value that reflects their similarity. Do you know a way to do this?

My first approach was to export the two fields (A and B) as matrices in Matlab. Then use a function as xcorr2(A,B) to compare them. The problem with this approach is that I cant get to export A and B.

Other way could be to use a 'Join' dataset and then try to implement the cross-correlation function inside the comsol interface. The problem with this approach is that I cant find a way to sum over all the domain.

Any help is greatly appreciated.

Best,
Felipe Beltran-Mejia
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How to resolve warnings about relative error in comsol?

March 23, 2017, 3:09 pm
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I have a model that consists of two squares that are one on the other separated by 10 mm. The bottom square measures 60 mm, is pine wood with tangential behavior (with a poisson coefficient of 0.3) and has a fixed constraint on the lower edge. The above square is 40 mm, it is made of structural steel (material pre-configured in Comsol) and is centered on the lower square, to which a prescribed displacement is applied with the value of "-f * max" where the value of Max is 10 mm and the value of f varies between 0 and 1.5.
A contact pair is defined between the upper edge of the steel square (source) and the upper edge of the wooden square (destination).
The mesh consists of free triangles with a size defined as "finer" and it is calibrated for general physics, and the edge defined as "target" is "extra fine" in size.
In the study, an auxiliary sweep is configured with parameter f and the maximum number of iterations per segregated group is 60.
When giving the model to execute, it gives me a series of warnings which say: In the segregated group 1: There was an error message of the linear resolver. The relative error (8.9) is greater than the relative tolerance.
I do not know how to resolve these warnings would appreciate any help
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Coordinate transformation in equation based modeling

March 23, 2017, 3:19 pm
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I'm trying to follow the same procedure explained in this blog post (www.comsol.com/blogs/piezoelec...-orientation-poling-direction/) to define new coordinate system in General PDE module. But, coordinate selection tool is not available in this module. Is there any other way to define a different coordinate system in equation based modeling? I'm using Base Vector System to transform my coordinates.
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Error in parameter estimation of optimization module

March 23, 2017, 8:42 pm
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Hi everybody

I want to estimate 5 parameters of my equations with optimization module. Its initial value were defined in "parameters", however appear the error

Duplicate parameter/variable name.
- Variable: comp1.kt
Error in multiphysics compilation.
- Feature: Compile Equations: Time Dependent (sol1/st1)

Someone could help me please?
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Why do I get the warning message "Warning: Low Minimum Element Quality?"

March 24, 2017, 12:00 am
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Hi, everyone,

After meshing my geometry, I checked the minimum element quality using the statistics function and it showed that the minimum element quality is 0.01. However, when I started the calculation, I got a message "Warning: Low Minimum Element Qaulity. Minimum Element Quality: 1e-7", right before the first iteration. So, does that mean there are two different critiria to judge the minimum element quality for meshing and calculation? Moreover, does anyone know how to solve the problem?
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Is it possible to plot magnetic field wrto distance plot?

March 24, 2017, 12:09 am
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Is it possible to plot magnetic field wrto distance plot?
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3D electrostatic simulation with complex geometry

March 24, 2017, 2:25 am
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Hi,

I am currently working on some 3D electrostatic simulation. Basically, I am building a model for a high voltage environment consisting of a gate electrode (-7kV), an anode electrode (+7kV), a dielectric piece spacer (PEEK), and a grounded vessel. The final geometries, imported from STL, would be quite complex.

The main issue I have is how to use form assembly correctly in my simulation?

The geometry contains different parts. It is difficult to use "form union" without encountering "geometry decomposition". However, using "form assembly", COMSOL doesn't mesh correctly between the vessel and the electrodes.

I've tried a simple case using COMSOL's capacitor example (www.comsol.com/model/computing-capacitance-12689). Instead of using "form union", I used "form assembly" to perform the calculation. However, the simulation doesn't calculate electric field or potential between different metals. I think this results from meshing the geometry.


I've attached described result and the simplified model in the attachment.

Thanks in advance.

FT
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