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Modeling Moving Heating Line

February 16, 2018, 6:36 am
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Hello all,

I apologize in advance as this is likely a very simple issue but I have yet to find a forum/discussion that has helped me grasp the concept...

While I am waiting to gain access to the AC/DC module (in COMSOL 5.3), I am attempting to simulate induction heating of a steel plate (with a small skin depth) as heat being applied at the surface coupled with conductive heat transfer. Additionally, as a hairpin induction coil is being used, I am using a hairpin-shaped line heating source (please refer to the attached figure).

However, I would like to have this hairpin move at a prescribed speed in the +x direction such that I can "spread" the heating across the entire plate. Is there any easy way to do this? I have had some success with one of the COMSOL tutorials in simulating welding with a moving circular heat source using an if statement but I haven't been able to translate it to this type of geometry.

Thank you!

Matt

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Multiphase steady state flow

February 16, 2018, 4:19 pm
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I am not able to simulate "Stationary flow" for Multiphase Microfluids, the flow does not happen. I'm able to simulate this case for Time-dependent flow, but facing problem in Stationary flow. I have tried it with all solvers of Direct and Iterative methods. Though I dont get any error report, but the flow does not happen and there is an error in Physics Interface for stationary model. I have not found any references or examples for Multiphase stationary flow on Internet and Comsol tutorials. Does Comsol not support to solve multiphase stationary flow? Or is there any additional conditions to be defined for Stationary case.

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Intermediate variable

February 16, 2018, 11:18 pm
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Hi what is intermediate variable(ht.d) that is used in equation view in heat tranfer module.Should i include that if i add any extra terms to the predefined equations. Any help is highly appreciated.

thanks :)

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Transmission phase shift

February 17, 2018, 5:48 am
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Hello, How to get the transmission phase shift at plasmonic waveguide-resonator systems? The insulator is chosen to be Air. The metal is chosen to be silver whose frequency-dependent complex relative permittivity can be described by the well-known Drude model. In the section II part D presented in this paper: "Plasmonic analog of electromagnetically induced transparency in multi-nanoresonator-coupled waveguide systems", the author realize the slow-light effect using the structure they designed. They described it by the group index ng. And in order to get the group index ,they use the equation:

**ng=C/Vg=C.τg/D=(C/D)*(d(ψ(ω))/d(ω))

Here vg stands for the group velocity in the plasmonic waveguide systems. τg and ψ(ω) are the optical delay time and transmission phase shift, respectively. And they are shown in the follow picture: Since I am a beginner of the Comsol Multiphysics，I don’t know how to get these results especially the transmission phase shift (because we can get another results from the equation if we know the transmission phase shift). How can I get the transmission phase shift at plasmonic waveguide-resonator systems like this?

Thanks for your help!

Best wishes.

Rida El Haffar

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Active hydraulic boundary condition

February 17, 2018, 9:45 am
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Hello

Is it possible to apply a time series of data for a parameter in Comsol? I want to apply a series of hydraulic heads to the top of the domain.I tried to do it by making a interpolate function and recalling the function in expression of the variable.However, I do not think that it is an appropriate way.

The time series is like this: T(time=day) 0 1 2 3 4 5 6 . . . H(head=meter): 39 38.5 38 39 40 40.5 39 . . .

Best Regards

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Hert'z contact pressure

February 18, 2018, 3:04 pm
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Hello Sir/Madam,

I am trying simulate hertzian conatct pressure using time depended model. But, the contact pressure i get has a slope which is not following theoretical trend.

Please find the pictures and model attached.

can someone, please suggest me where i am doing wrong and way to get correct results.

Help is really appreciated.

Thanks,

Reagrds, Sai krishna Enabothula

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two way FSI with prescribed displacement causing gaps in mesh

February 18, 2018, 5:19 pm
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I am experimenting with a very simple two way FSI. A solid square is moved through some air. I place a prescribed displacement on the bottom of the square. What seems to happen is an actual gap in the mesh appears at the bottom of the mesh at the prescribed displacement ( dont mean a stretched mesh)

You can see the gap as a white section in the default view and it is obvious in the mesh plot (both images attached).

Is a prescribed displacement illegal in a two way FSI on the boundary of the solid/liquid interface ? If so, how does one force a movement of one section of a solid ?

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Export 1D Line Graph to spreadsheet - how to prevent sorting?

February 19, 2018, 2:39 am
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I created a 1D Line Graph along a custom selection of lines (boundaries). The plot looks as intended (see lineplot_correct--.png).

However, I can't export this plot! I do Export / Plot / Line Graph and the resulting spreadsheet is sorted by the x value (see lineplotafterexport--.png), which is a problem when the curve is going "backwards". If I check Advanced / Sort or not doesn't make any difference.

Thanks in advance for any suggestions!

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reducing comsol file size

February 19, 2018, 3:52 am
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Hi all, I am trying to reduce the size of my comsol file. I need to define several cut planes and then tell comsol only save the T distribution over these planes (x,y,z,T). is this possible? to define a explicit surface, i can only see the boudaries of the model can be selected as surface and does not allow me to add my cutplanes as surfaces of interest.

Regards, Asal

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Modelling 'Helix' Turbine- Meshing Problems

February 19, 2018, 6:43 am
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Hi All,

I'm trying to model an alternative type of turbine, which is a version of vertical axis turbine that is deployed horizontally in a micro hydro electric power setting.

I'm relatively new to COMSOL, but I think I've created an accurate geometry model for the turbine. However, when I try to mesh the geometry, I'm getting numerous errors around edges being to small to compared to the element size. I've tried to mesh on the smallest size, but I still have the issue.

I believe the issue comes from the fact that the blades slightly overlap their casing (Turbine rotates with casing, not on a central axis), however this is key for providing a flush finish. I attempted to use a union to remove the interior boundries, between the overlapping blades and the casing. This works at one end of the turbine, however, at the opposite end the interior boundries aren't removed and I believe this is causing issues???

I've also tried changing the mesh manually, but I'm still getting the same issues.

Any meshing tips would be greatly appreciated!

Also my final goal is to calculate the torque of the turbine, and my current calculate is to perform a surface intergration with the expression:

p(nyx-(y+0.2)*nx)

I'm also just using the turbulent flow physics package. If anyone can let me know if im on the right lines, or if I should be using a different physics package to find the torque from the flow please let me know!

Sorry for the questions!

Tom

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getting error for failed to find a solution: singular matrix

February 19, 2018, 6:56 am
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hii, I am getting error 1 void equations for mesh : case 0 : empty rows in matrix in COMSOL multiphysics 5.2 during computation time. Can anyone help me for resolving this error. I am using EM waves frequency domain. According to previous discussion I have changed the conductivity from default 0 to 0.1. Still I am getting same error given below.

**Failed to find a solution. Singular matrix.

For mesh-case 0 there are 1 void equations (empty rows in matrix) for the variable comp1.emw.S2x. at coordinates: (0,0,0), ... and similarly for the degrees of freedom (empty columns in matrix). Returned solution is not converged. **

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Magnetostrictive energy harvester using villari effect

February 19, 2018, 6:55 pm
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I am going to design a magnetostrictive energy harvester using villari effect. Where if we applied a compressive and tensile stress on a magnetostrictive material with the present of parmanent magnet bias field and if a coil is wound around the magnetostrictive material a e.m.f is generated across the coil. can anybody say how can i apply a continuous compressive and tensile stress on the trip of the harvester..

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undefined variable comp.2.ht.rhoref, coupling between heat transfer and laminar flow after upgrade to 5.3a

February 19, 2018, 9:31 pm
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Hi everyone,

I m modelling a coupling between heat tranfer and laminar flaw using a nitf multiphysics coupling. My model runs welll in 5.3 but when i use 5.3a an erro msg comes out as if the solver can not find the reference density though it is set to be taken from ht interface.

error: undefined variable. -variable: comp1.ht.rhoref -Geometry: 11 Failed to evaluae the Jacobian of expression : dvol(((-comp1.ht.Ceff)comp1.ht.timeDerivative )Comp1.ht.

Can anyone give me a quick hint?

Regards,

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memory management

February 20, 2018, 1:18 am
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Hello everybody, i am using comsol 5.3 and i have sumile a lot of dof ~ 1000 million and i have out of memory error is there a possibility of stoker derictly on hard desque without using RAM? thank you. N.B. I use a computer core i5 2.38 Ghz 16Gb RAM

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Infinite element domain parameters

February 20, 2018, 2:32 am
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Does anyone know the meaning of two parameters, Physical Width and Pole Distance defined for infinite element domain? Or if possible, can anyone provide a reference?

And the region for the infinite element is generated automatically or I need to create a circle myself？ I use axissymmetric 2D

Thanks!

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IntVolume Parameter in MatLab

February 20, 2018, 6:52 am
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Is it possible to add the IntVolume expression parameters with a variables outside of the model? I want to calculate the coupling coefficient using a data from two different runs. I assigned the first data to a variable and tried to use it as a parameter for IntVolume function together with a second data but I am not sure about the syntax.

Ez1=mpheval(model,'emw.Ez');

model.result.numerical.create('int2', 'IntVolume'); model.result.numerical('int2').set('expr', 'emw.Ez'*Ez1);

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Splitting into several domains

February 20, 2018, 6:46 am
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The below post is related to an archived discussion

Hello,

I have a rectangular geometry with several channels, which water is supposed to flow through. Other than the channels, the rest of the geometry should be Aluminium. The geometry is imported from SolidWorks as a STEP file.

I am trying to investigate the heat transferred and the flow of the water but I encounter the problem when the geometry is imported, it becomes one whole domain, thus creating problem when I'm trying to assign water as material inside the channels.

My question is, how can I separate the channels into a different domain? I tried 'split' operation but did not seem to work.

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3D Coil with Assembly

February 20, 2018, 7:07 am
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Hello,

I am currently working on a 3-D, time-dependent model that uses the magnetic fields interface. This model uses the Coil feature to excite a 3-D conductive structure with a specified voltage waveform. This part of the model works as expected.

I am now trying to add some additional functionality which allows part of the "coil" to move with respect to the rest of the conductive structure. I have implemented the moving mesh feature as well as some global ODEs to describe the movement. In addition, I've switched the geometry to an assembly and defined an identity boundary pair between the moving and stationary structures. I then defined a continuity boundary condition within the magnetic fields interface for this identity pair.

Now, the coil functionality is not working as before. Even with the moving mesh and ODEs removed, the coil feature appears to not function properly using an assembly with identity pairs. The model will solve, but no current flows through the "moving" portion of the coil.

Is there something simple I have missed somewhere that will allow the coil feature to function properly with an assembly? Alternatively, is there a better way to excite my "coil" aside from the coil feature? Unfortunately, I am unable to upload my .mph file due to some sensitive information within, but I would appreciate any advice you can offer.

Thanks!

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Export comsol data file to tecplot

February 20, 2018, 9:24 am
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Is there any way to export COMSOL surface and contour plot to export in tecplot?

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"Unexpected unit of input" error for material property defined by piecewise function

February 20, 2018, 1:16 pm
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Hello,

I am using Comsol 4.2. defined a temperature-dependent heat capacity using a piecwise function. The argument is T and I defined the units of the argument and function as K and J/(kg*K), respectively. I named the function Cp_eff. When I enter Cp_eff(T) under the Value column for the Heat capactiy property, the entered value turns orange with the warning "Unexpected unit of input". The function unit is correct, so I don't know what the problem could be.

Thanks.

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