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mass participation factors for rotational degrees of freedom

March 24, 2017, 4:13 am
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Hi all,
Please may someone confirm to me whether it is possible to calculate the mass participation factors for rotational degrees of freedom? As I believe this is currently not possible ( COMSOL version 5.2a). And please can someone explain why this is not possible? I would presume that if the linear mass participation factors can be calculated then it is possible to calculate the rotational mass participation factors.
Thank you
Henry
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Quadrifilar Helix Antenna

March 24, 2017, 7:45 am
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Hi!

I'm looking to simulate a Quadrifilar Helix Antenna with infinite balun and was hoping that some one either: Done it before or knows how to do it.

I have built a model in comsol as seen in the picture. I've put the arms, inner conductor and the outer conductor as "Perfect electric conductor" boundary. in the bottom of the center coax cable i've put the boundary between the inner and outer conductor as a "lumped port". I have a far field boundary as seen in the pictures. The outer boundary of the Far field sphere is put to a "Scattering boundary condition"

All domains ar set to air and the the arms and conductors are in copper, the dielectric in the coax is PTFE with epsilon_r = 2.1.

The mesh is set to minimum wavelength of 0.2*wavelength.

When I simulate it, it never seem to converge and ran for a hour on one freq. Thats when i gave up and started thinking that I have done something wrong. I've only done RF simulations for a week and will take any help/lesson I can get and will appreciate it immensely.


Thanks,

Sebastian
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I need to perform displacement transmissibilty in magnetic suspension. Is it possible to couple mbd with magnetic analysis. Any reference tutorial available.?

March 24, 2017, 10:52 am
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My analysis consists of two permanent magnets and need to find stiffness contributed by magnets to the system.
Now is it possible to give road motion as input to one magnet and fix another magnet and find the stiffness of the system.
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helix with rectangular cross section.

October 27, 2011, 6:07 pm
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hello

I need to know how to make a helical ribbon with rectangular cross-section.

thanks
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modeling of Diffusion

May 14, 2013, 1:24 pm
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Hi,
I want to model a simple mass diffusion process, but with a concentration dependent diffusion coefficient.
In variable I defined a function for diffusion coefficient. but when I want to solve the problem it end with error ("Failed to find consistent initial values. Last time step is not converged.").

Is there any solution for this problem?
Thanks.
Saeed.
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Basic Question: How to add modules

October 1, 2013, 3:38 am
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Hello,

I am following a number of tutorials as I need to learn COMSOL. I need to use the RF Module but it does not appear in the "add physics" window when I am creating a model. I have AC/DC, Acoustics etc. but my model concerns Electromagnetics so I need the RF Module.

Please advise me on how to add modules to COMSOL.

Many thanks
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phononic crystal band gap

April 22, 2015, 1:09 pm
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Hi,

I would like to know how to obtain the band gap diagram of a phononic crystal in Comsol. I was trying to use photonic crystal model presented to model one unit cell, but I don't know how to use it to for phononic crystals.
Could you please help me to choose the proper study and solver?
I really appreciate it,

Thanks,
Minoo
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Far field of dipole antenna on substrate

December 8, 2016, 6:46 am
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Dear COMSOL community

I try to model a nanodipole antenna on glass substrate , first I create a model for a nanodipole in air and the far field seems good to me ( the tours shape typical for dipole antenna ) , where the far field calculation is made by a surface surround the dipole and placed lamb/2 far away from the dipole.

Now I placed the dipole on the top of a glass substrate , while the far field domain this time will be half air and half substrate , unfortunately the shape of the far field seems to me incorrect , I read on the thread that the far field domain has to be homogeneous, but how to calculate the far field in the case of antenna placed on substrate

Thanks in advance

M.H.Elshorbagy

UCM , Spain
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HELP

March 25, 2017, 2:53 pm
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hello good afternoon
someone can help me, i need a Earth science Module to create a model, but i don't have it in the library, if someone can tell me where i can found it i will thank you
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Time Dependent of intake manifold

March 26, 2017, 5:30 pm
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Hello,

I am having an issue trying to simulate an intake manifold of 4 cylinders. I want to do it as transient flow. But in real life the each cylinder is not open at the same time. How do i tell COMSOL to open an outlet and close another one at a certain time,

Regards,
Thank you
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2D, in form of dimensionless .

March 26, 2017, 8:55 pm
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Hello,
I am Omar Saaed, now I am working on simulation of CO2-absorption by membrane contractor.
I have problem with illustration of the concentration distribution in (tube, membrane and shell)-site, in form of dimensionless as well dimensionless boundaries.
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How to define a Dependent variable as zero in specific area？

March 27, 2017, 12:13 am
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I want to solve a PDE equation, and I want control the Dependent variable as zero in a specific area when another variable is small than a value. How to do that?
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level set without body forece

March 27, 2017, 2:51 am
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Hello,everyone!
Could anyone give me a case of level set without body force?
I have already seen "the rising bubble" case, and I want to simulate a oil bubble in water flow without gravity.
The inlet is at "2700 pa" and the outlet is at "0 pa".
However, it doesn't converge.
Thanks a lot!

Sandy Wang
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How to calculate force in comsol dc discharge?

March 27, 2017, 3:20 am
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Hi

I have successfully modeled a simple 2d dc discharge between two electrodes in comsol 5.2 and now I want to calculate the force applied by the discharge in the domain.

I chose "Force Calculation" from the domains and set a name for it but didn't change "torque axis" and "torque rotation point".

after computing, I tried to plot the force on a surface with the expression: DC Discharge(Electrostatics) >Mechanical >Electromagnetic force>z component

and i received the following errors:

Undefined variable.
- Variable: comp1.dc.unTz
- Geometry: geom1
- Boundaries: 1, 3-4
Failed to evaluate variable.
- Variable: comp1.dc.nTz_force
- Defined as: comp1.dc.unTz
Failed to evaluate expression.
- Expression: r*(pi*(2*comp1.dc.nTz_force))
Failed to evaluate expression.
- Expression: comp1.dc.intfcal1(r*(pi*(2*comp1.dc.nTz_force)))
Failed to evaluate variable.
- Variable: comp1.dc.Forcez_force
- Defined as: comp1.dc.intfcal1(r*(pi*(2*comp1.dc.nTz_force)))
Failed to evaluate expression.
- Expression: comp1.dc.Forcez_force
- Plot: surf1 (Surface)

======================

Can anyone please help me?

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Import image contour plot (polylines) from Matlab

March 27, 2017, 3:24 am
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Dear COMSOL users

I wrote a script in Matlab to generate a special contour plot of a binary image in Matlab. In a next step I would like to import these polylines into COMSOL.

How can I import the geometry generated by Matlab ?

Thank you in advance.

Bram Mast
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Distributed ode with convection and diffusion equation

March 27, 2017, 5:06 am
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Hi Guys,
I have added a distributed ode to one of my boundaries to be solved with my convection and diffusion equation. I am trying to use the difference of the average of outflow and inflow concentrations in this equation. How can I define these terms? When I use Average operators I donot get any thing. It seems my equations solve seperately.

Ode ( Ct): dct /dt = Q ( c at outflow - c at inflow)
C will be solved in convection and diffusion equation.
I will appriate if you answer my question.

Regards
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how to build an ultrasound examination model in 4.4 version

March 27, 2017, 5:09 am
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Hello, all
I'm definitely new to comsol. I want to build a 3D model which could be tested if there existe a fissure or not under ultrasound effet.But the tutorials i found in comsol blog all use 5.1 or 5.2 version, they've used a physic called" convected wave equation"(cwe), which is not existed in 4.4 version. so could anyone tells me how to build this kind of model in 4.4 version?
Best Regards
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Why the COMSOL results can not give infinity values at resonance?

March 27, 2017, 5:13 am
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Dear all,

I am now stuck in a problem about the acoustic pressure distribution inside a long duct with a monopole source in the cubic center.

Considering one-dimension wave propagation problems, when all of the surfaces were set as 'sound hard boundary', why can't the acoustic pressure reach the infinite value at resonance?

The COMSOL document gives the following discussion: when the sound waves propagate in a lossless medium, attenuation frequently occurs by interaction with the surrounding at the boundaries of the system.

There might be some assumptions in the software when dealing with the calculation, but for the influence on the maximum values at resonance, I wonder how and to what extent the boundary condition or assumption affect the final pressure results, in detail?

Thank you very much in advance.
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Photonic crystal In COMSOL

March 27, 2017, 8:29 am
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How can i give the refractive index or dielectric constant of a sample on the line defect ( Where I will delete rods , it will be the plain path for light) which we are creating on the photonic crystal rod in air configuration in comsol. I believe that rod in air configuration rod having one refractive index and then to air.But when i want to give a refractive index of sample.. I m in doubt how can i give this value in comsol ?

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Boundary Conditions not being read

March 27, 2017, 8:48 am
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Hello,

I am trying to model a high frequency horn for my senior design project. I am importing a .STEP file into COMSOL since I built the model in SOLIDWORKS. When I run the simulation, the velocity does not recognize the sound hard boundaries and radiates outward. Is there a way I can fix this?

Thank you in advance, any advice will help.
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