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Exact calculation of electrical current from current density

May 10, 2019, 3:49 am
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Hello everybody,

I am using comsol to model a bipolar probe with three surfaces : Conductive surface forced to 0V, conductive surface forced to 10V and insulation surface beetween the two conductive surfaces. The probe is put on sea water.

So when i resolve my system I have streamlines between the two condictive surfaces.

Now, I want to calculate the current on each conductive surface from the current density integration. I use the following expression ( ec.Jxnx+ec.Jyny+ec.Jz*nz ).

I have a difference between the current IN and the current OUT about 1%. So I change the mesh to have a more accurate result but I realized that the current is totaly different comparing to the first mesh. So for one kind of mesh I have different current values.

Someone can help me if he have any idea.

Thank you very much

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Applying Moving mesh (rotating domain) in microwave heating

May 10, 2019, 5:50 am
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Hello COMSOL experts!

A question about RF module configuration, applying a rotation movement to solve a microwave heating problem (using electromagnetic waves and heat transfer in solids physics): 2 files are attached.

-File “microwave_oven_FormUnion.mph” solves a time dependent problem oh heating assisted by microwaves defining just only one model mesh, using form union configuration in geometry creation. It is a model configuration similar to COMSOL library example "microwave_oven". Final result seems acceptable.

-Now, I have created a real sceneary where the part to be heated is rotating (like in a real microwave oven). It is represented in file “microwave_oven_FormAssembly_Rotating.mph”. From previous model, next configuration are added:

• Geometry are created using "form assembly" instead "form union" in order to create independent meshes.

• “Identity Boundary Pair” are indicated in definitions section.

• A “rotating domain” is applied inside “moving mesh” selection to generate a constant rotation over the part to be heated, aiming to check rotation effect over part heating.

• For each physic "electromagnetic waves" and "heat transfer in solids" is applied a continuity condition over the “Identity Boundary Pair” detected.

After that, COMSOL is not able to solve the study, and if continuity conditions are not applyed over physics, solution does not show any heating over the part. This makes sense. Questions to solve are:

  1. How to configurate properly physics conditions on last model, applying rotation movement, using different meshes, form assembly creation in geometry and the correct configuration of each required physic for microwave heating simulation.
  2. How to reproduce visually, inside results, the rotation movement of the mesh of the heated part (domain). Actually, I am not able to reproduce the visualization of the rotation of the mesh.

Additionally, this COMSOL link is very connected with my objective: https://www.comsol.com/community/exchange/581/

Thanks in advance and if somebody has any question related with microwave ovens or heating assisted by microwaves, let me know. :)

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Saving as java by default, rather than mph

May 10, 2019, 5:58 am
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Hello,

Does anyone know if there is a way to have COMSOL save the modelling currently opened in the GUI as a java file by default, rather than a mph file?

I have written a small script that reads my java everytime it changes and displays the differences with the previous saved version as a html page, but it's slowing me down to always go all the way to File > Save as ... > java

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LiveLink, using a variable and for loop to change a parameter set

May 10, 2019, 1:25 pm
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Hi all,

I would like to be able to change one parameter of my model inside of a for loop with LiveLink and then run the model. Does anyone know how to do this? My code looks something like this:

for CED=[1.0:0.01:3.0] model.param.set('C_ED', 'CED[mm]'); model.param.set('C_EP', '1[mm]'); model.param.set('C_EW', '0.5[mm]'); model.param.set('d_ci', '0.5[mm]'); model.param.set('d_nb', '0.4[mm]'); model.sol('sol1').runAll [b1,b2,b3,b4]=graphingfun(model); end

Thanks in advance!

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Electric Field Simulation

May 10, 2019, 4:05 pm
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Hi

I am trying to plot electric field between the aluminimum profiles and I got electric potential when I grounded the last one.

How can I get an electric potential plot ?

Thank you

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The magnetic insulation in RMM physics

May 11, 2019, 6:02 am
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Dear all， I am simulating a pm_motor, I have used the magnetic field(mf) to define the magnets in the model. Now I need to add more details to reach results,so I change mf into rotating magnetic machinery(rmm). Now I finished defining the magnets but the result is not the needs. I checked the difference with the two files, the magnetic insulation completely different. Have anyone met this kind of problem? How can you solve the problem?

Regards Joey

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How to consider the system time in COMSOL?

May 11, 2019, 7:33 am
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Dear Engineer： I want to know how to use the random() function to proced a random related with the systme time?Thank you.

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wire electrode simulation

May 11, 2019, 2:03 pm
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I want to know if possible to modify the wire electrode module ( electrochemical engineering application ) to work with turbulent flow hence the exist module working with laminar flow and when i tried to modify the module to work with turbulent flow ( k-e low Re ) the module did not work , could any one know about this .

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How to apply boundary conditions in a solid fulid heat transfer?

May 12, 2019, 2:06 am
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Hi ! I am currently doing a two dimensional simulation of a reactor. Chemical reaction take place in this reactor. The reactor is a cylinder reactor. I set up a two-dimensional axial symmetry model to simulate this process. In the core of the cylinder a cooling pipe run through the cylinder and water flow through the cooling pipe taking the heat away. I use heat transfer in porous media to simulate the process in the reactor, and laminar flow, heat transfer in fluid to simulate the heat transfer in the cooling water. Finally I use heat transfer in solid to simulate the heat transfer in the cooling pipe wall. However, I dont konw how to apply boundary conditions between the cooling pipe wall ,the reactor and the cooling water. The model figure is attached. Could anyone tell me how to solve this problem? Thanks in advance!!

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Calling temperature variable at specific locations to define new global variable

May 12, 2019, 2:12 am
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Hi

I have defined a matlab function for vapor pressure (arguments being temperature, salinity) of a saline solution and would like to compute vapor pressure at specific locations only. How can I target the temperatures in these locations to be used in my global definition of the new variable vapor pressure of my saline solution? My system consists of two flow channels separated by a solid (assumed to be a membrane) in 3 D simulation. I am targetting the membrane interface with these channels. Version 5.2a is used. Many thanks

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transmission coefficient of sound pressure

May 12, 2019, 2:16 am
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In the two-dimensional acoustic model, I encounter some problems to be solved.
If I set the amplitude of the incident sound pressure to 1 Pa
1. How to calculate the transmission coefficient of sound pressure?
2. Did I calculate the sound pressure through the average surface value?
3. Why is the calculated value of 2 much larger than the incident sound pressure?
4. Thank you

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How To Apply Boundary Conditions In A Solid Fulid Heat Transfer?

May 12, 2019, 3:44 am
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Hi ! I am currently doing a two dimensional simulation of a reactor. Chemical reaction take place in this reactor. The reactor is a cylinder reactor. I set up a two-dimensional axial symmetry model to simulate this process. In the core of the cylinder a cooling pipe run through the cylinder and water flow through the cooling pipe taking the heat away. I use heat transfer in porous media to simulate the process in the reactor, and laminar flow, heat transfer in fluid to simulate the heat transfer in the cooling water. Finally I use heat transfer in solid to simulate the heat transfer in the cooling pipe wall. However, I dont konw how to apply boundary conditions between the cooling pipe wall ,the reactor and the cooling water. The model figure is attached. Could anyone tell me how to solve this problem? Thanks in advance!!

I dont konw how to apply boundary conditions between the reactor and the cooling pipe wall, and boundary conditions between the cooling pipe wall and cooling water in order to make the heat transfer from the reactor to the cooling water.

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how can i make 'cylindrical wave incidence' in wave optics module?

May 12, 2019, 9:18 am
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Hi all, i'm in elemetary level using comsol, and deppressed by successive failure in computing... please give me a hand..

i want to simulate a cylindrical wave impinging on periodic metasurfaces placed on a curved surface(cylinder). so the patterns have angular periodicities.

for this situation, i placed a periodic curved port above the cylinder's surface, but comsol says like 'periodic port should be on flat surface'.

so, is there any way to make angularly periodic port with cylindrical incident wave? or should i make a flat port and then induce an 'incidence angle variation' for each position?

thanks.

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Matrix Division by 0 Error/Convergence Error

May 12, 2019, 1:50 pm
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If these errors seem familiar please tell me how I can rid of them.

I am using Comsol Multiphysics 5.4a to see how electrical conductivity in a doped semiconductor varies with mechanical stress. My goal is to be able to plot curves of stress vs current in a doped p-type material. Since this is a uni-direction problem (I want the solver to solve for stress in the block, calculate conductivity and then show me how current distribution is).. the solver is segregated.

I started by going through both Piezoresistor pressure sensor examples in the library. My first approach was to build a 3D block of p-type piezoresistive Si, apply current source and a ground on two sides and apply a stress and fixed constraint on the sides perpendicular to the direction of current flow. For some reason, the simulation does not work with an applied current source (I specify the terminal face as a current source) though it does work when I define the terminal as a Voltage source. Do you have any thoughts on this? Why would the terminal type affect the ability of the simulation to run?

My second approach was to build a rectangular block of doped Si, apply force/stress and voltage through it, and define the electrical conductivity of the doped p-Si material as a function of stress {i.e. material conductivity= f(solid.x) }, instead of using piezoresistance. But I get a solution error whenever I try to use p-type Si material under piezoresistivity. When I change the material from p-type Si to just Si I do not get matrix errors anymore but the simulation does not converge.

I don't understand why I cannot use p-type Si as a material without getting the matrix error.

I am new with Comsol and this model is a little over the top for me so any help/guidance is much appreciated.

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help

May 12, 2019, 9:34 pm
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magnetic_gear_2d_geometry_sequence version 5.3.mph

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How can avoid the model automatically selected the magnetic insulation in RMM physics

May 12, 2019, 9:53 pm
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Dear all, I am simulating a pm motor in rmm physics. I have met different in my simulation, now, after I imported the model with different parts and I successfully formed assembly. I defined the magnets with Ampere Law and I checked the magneic insulation boundaries, comsol have automatically selected and some boundaries should not be defined.I have tried defining magnetic insulation to override the boundaries, but the magnets How can I change my model and not make the magnetic insulation boundaries that i do not need.

Regards Joey

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transmission coefficient of sound pressure

May 13, 2019, 1:59 am
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When doing acoustic simulation, Is the method of calculating the sound pressure in water different from that in air? The data were always incorrect.
I set the incident sound pressure in the air to 1 Pa, which is transmitted to the water through the coupling structure, and then calculated the absolute pressure with the surface average value to get the highest sound pressure of more than ten Pa. Thank you very much.

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How to get electrical current (A) of each streamline of current density (A/m2) ?

May 13, 2019, 2:09 am
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Hello everybody,

I am using comsol to model a bipolar probe with three surfaces : Conductive surface forced to 0V, conductive surface forced to 10V and insulation surface beetween the two conductive surfaces. The probe is put on sea water.

So when i resolve my system I have streamlines between the two condictive surfaces.

Now I want to have the electrical current (A) on a cut plane by integrating the current density on each mesh surface belonging to the cut plane.

Someone can help me if he have any idea.

Thank you very much Lyes

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Importing excel data of time varying pressure in Comsol

May 13, 2019, 2:25 am
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Hi All!

I would be highly appreciate if you could help in importing the pressure data from excel in Comsol for using as Inlet boundary load in FSI problem.

One possibility is through creating analytical function by interpolation and feeding in comsol. I dont want to create analytical function due to large combination term of sin and cosine function.

Please let me know if any alternative way exists.

Warm regards, Nitish

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Statics analysis of Multi-body dynamics

May 13, 2019, 6:20 am
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Hello,

I made a mass, spring, damping system with multibody dynamics component. I already fished analysis of time depent motion with my system. but, it has a lot of errors when I solve this system with stationary solver. include symetric matrix error, singular matrix error, division by zero, etc ...

I want to know how can I do static analysis with my multibody dynamics system.

Thank you

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