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Meshing a twisted wire

December 25, 2013, 12:10 pm
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Hi,

I'm trying to model the flow of current in a twisted wire. The inner rods are of steel, the outer of Al (see attached file). The steel rods are twisted clockweise, while the Al rods are twisted counter-clockwise.
When I mesh it, it fails to generate mesh for some domains.
I would like to ask how to mesh helix structures, when they experience point contact?
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problem with boiling, evaporation and heating

April 24, 2014, 1:09 am
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Hello people.

I have problem with boiling and evaporation in comsol.

I have vertical equipment. This equipment is divided in two parts. In first part is heating and part 2 is boiling+ evaporation.

I need connect these actions and modeled. Has anyone experience with that? Could anyone advise me?

Thanks Lenka
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mass conservation

August 22, 2014, 3:01 am
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Hello,

can somebody tell me, if the continuity equations needs to be fulfilled for a background gas species (in DC discharge plasma or diluted species) if I am not interested in the distribution of this species. The background species decays in a reversible reaction to electron and ion.
When I use the real values for pressure and velocity profile of the background gas species I get a wrong solution for the ion fluxes (production rate and outgoing fluxes are not the same). This is maybe due to a discontinuity in the used real velocity field (there is entering gas in the middle of a tube and pumped out at both ends, therefore in the middle there is a step in the velocity from -v to +v). Using a simple linear profile from -v_out to +v_out for the background gas gives a better solution (rate and outgoing flux for the reactants are equal). I know, in this case mass for the background gas is not conserved, but I am not interested in that gas, I am just interested in the pressure and velocity distribution of ions/electrons.

Thanks
Laura
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ICP torh

September 1, 2014, 8:31 am
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Hello, I'm new user of Comsol .
Can i modeling atmosphere pressure ICP plasma torch using Comsol?
Typical value of pressure 1-2 atm.
Typical value of power 10-500 kW
Typical working area (geometry): 70 (horizontal)x600(vertical) mm in 2d axisymmetric case???
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Skin and Proximity Effects

September 3, 2014, 6:12 pm
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Hi all,

I am calculating ac resistance of a conductor of a cable in trefoil and flat formations. I wonder, are the Skin and Proximity Effects taken into account in Magnetic Fields Physics? Or shall I define them manually?

Regards,
Akim
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Fourth Order PDE OR minimize bending energy

September 3, 2014, 10:53 pm
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Hi everybody,
I want to minimize curvature energy of a surface:
E= Integral{ H^2 + L} dS
where H is mean curvature and L is surface tension and dS is surface element. I tried to minimize this integral over a tube surface which contains a particle(or some particles). After minimizing it over a tube containing a particle I have ended up with this nasty PDE : utttt+2uttzz+uzz+2utt+u=0 with specific boundary conditions around the particle. In the attached file you can find my problem exactly. I was wondering if I can do that by using Comsol;however I'm new in working with this software.
Does any body know how to either solve my fourth order PDE or minimize the energy functional in this software?
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Combining geometry (Union) and its new position

September 3, 2014, 10:59 pm
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Hi everyone,

I combined several shapes into one by using the Boolean (Union).

Now I want to perform a parameter sweep by changing the position of this new shape. Is it possible to assign a single position to the whole shape (and sweep that single parameter), instead of trying to control all the spatial relations between all its components?

Thanks,
Bartu
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Global evaluation of ewbe.beta_1 gives same value for all rows (solutions).

September 4, 2014, 3:29 am
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I've solved the boundary mode analysis for port 1 like in the "Directional Coupler" model but with the addition of two parametric sweeps (wavelength and dimension).

Now I want to extract the effective mode index for all solutions, so I try making a Global Evaluation but the parameter ewbe.neff (or similar) does not exist as I was hoping so I figured that I could calculate it from ewbe.beta_1/(2*pi/wl) where "wl" is the wavelength parameter. However, the values are the same for each row (or solution) part of the table is shown below:

dimension, wl, solution 1, soution 2...
1.5e-6, 1e-6, 2.21885, 2.21885
1.5e-6, 1.64286e-6, 1.92064, 1.92064
1.5e-6, 2.28571e-6, 1.49211+1.64531e-10i, 1.49211+1.64531e-10i


It seems "ewbe.beta_1" is not updated for each solution of the parametric sweep but only for the different values of dimension and wl in the parametric sweeps.

Maybe there is an even easier way of getting the neff for each solution.
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LaserWelding: avoiding Temperatures > 3500°C / Temperature break

September 4, 2014, 7:34 am
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Hello everybody

with my modell i am simulating a process comparable to laser welding.

Depending on the track energy, that i use, keyhole effects can occur. (in the real process)
Me, i am not interested in simulating keyhole effects and i just want to simulate some kind of conduction mode welding with marangoni effects.

When i simulate high track energies, it is possible that the temperatures in the centre of the melt pool reach unrealistic values. (> 10,000 K)

How can i implement some kind of temperature break, if the choosen track energy is too high to avoid temperatures above 3500 K?

I tried to implement some kind of negative source that takes the energy out of the system when the temperature reached the defined temperature threshold. if(T[1/K]>3500, 10e15[W/m³],0[W/m³]) (something like this ...)

Does anybody know a more elegant solution?

Thank you very much

Michael


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Simulating coupled acoustic resonators

September 4, 2014, 7:46 am
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Hello,

I am interested in simulating the frequency response of a cantilever beam located in an acoustic resonance structure. I am able to find the eigenfrequencies of the cantilever by itself using the structural mechanics eigenfrequency simulation. I am also able to plot the pressure response of the acoustic resonator at the point of interest using a frequency domain pressure acoustics simulation. My difficulty is in combining these two simulations, to be able to plot the deflection of the cantilever inside of the acoustic resonator as a function of the frequency of the incoming pressure field. Can somebody please give me a basic overview of the approach necessary to to this, or maybe give a link to a tutorial involving a similar kind of simulation.

Additionally, I am curious if there is an easy way to pass variables between simulation steps. For example, if step 1 is an eigenfrequency simulation, I want to use the harmonic eigenfrequency as a variable for a step 2 frequency sweep simulation. This seems like something that should be easy to do but I have been unable to find a solution.

Thank you!

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Changing Intervals on generated plots

September 4, 2014, 8:19 am
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Hi,

I am running a few suimulations and have generated a few velocity profile and presure plots. I've been running the same setup for different boundary conditions and need to export said plots with the same axes intervals so as to superimpose them. Any ideas how one might be able to manipulate the axes intervals before I snapshot them?

Regards,

Arjun
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Create bidirectional inlet

September 4, 2014, 8:57 am
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Hi,

I would like to model an elastic chamber that will fill with CO2 gas based on a chemical reaction in the center of the chamber. The gas and also expended reactant (liquid) expand into a series of chambers equipped with baffles. There are also vents allowing the gas to escape when a certain pressure is reached.

The study is to understand how varying baffle dimensions and path lengths affects the inflation of the balloon as a function of time. As a first cut, I was trying to add a boundary in the center of main domain and set that boundary as a bidirectional inlet. That does not appear to work.

It's unlikely that the chemical reaction component can be easily modeled, however, it would be helpful as a start to have a bidirectional inlet in the center of the structure. The opposing ends would be outlets.

Does anyone have any thoughts on this?

Thanks,

Art
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Heat transfer in thin metal skins

September 4, 2014, 11:07 am
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I am trying to model conduction heat transfer across a solid block that is encapsulated within a thin metal skin (Thickness - ~0.01 inch). If I use physics-controlled meshing, I end up with too many meshes and the solver runs out of memory. Is there another way to treat the thin metal skin without overwhelming the solver? Any existing example(s) will be very useful.

Thanks is advance for the help.

Kaushik
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COMSOL 4.0 - Linear Extrusion

July 21, 2010, 7:05 am
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After learning version 3.5a, I was forced to jump into version 4.0 and have not had a good experience with the "upgrade." Making a linear extrusion from a 1D geometry to a 2D geometry in 3.5a was trivial and made perfect sense. What am I missing in 4.0?

I understand how to set up the source and destination vertices just fine. However, one glaring difference in 4.0 is the lack of ability to select which variable to map from one geometry to the next! Where do I tell it to map the variable "c1?" Is the chosen "operator name" a function for which I can call with an expression as its argument for what to map? I don't think this is true because it gives me an error stating unknown function found.

So, having the source and destination vertices set up, how do I tell 4.0 which variable I want to map?

Thanks for the help,

Mark
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My first PDE

August 7, 2014, 6:16 am
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Hi , we are two undergraduates students who are trying to solve a system of five PDE's in COMSOL.
We have been able to do this in MATLAB but are unable to achieve this in COMSOL. To start of we tried to implement a simple diffusion PDE using the coefficient PDE solver. We have troubles simulating our system. Can someone explain why?
SPECIFICS
-Geometry: 100 mm^2
-Coefficients: C = 4.9*10^-6, da = -1, all other 0.
-intial value: 1*10^7
- boundary: Dirchlets r = 0 for all
- normal mesh, fine
Then we used the study tool (time dependent) and solved for time (0,1,10).
Error: "Differential-algebraic equation encountered. Use Singular mass matrix = Yes.."
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Magnetic field of magnetic bar

August 31, 2014, 10:22 pm
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I want to dosimulation of magnetic field of conical as well as pyramidal shape magnet with properties of neodymium magnet. Please help me how to do
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Postprocessing using '>'

September 4, 2014, 7:54 pm
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Hi all,

I have got a question about postprocessing when I am using '>'. For example, I want to show the von mises stress over a domain. The default expression is: fsi.mises, and I can see colour distribution over the domain. However, if I change the expression to fsi.mises>50[kPa], the legend shows 0 to 1. Could anybody tell me what does 0 to 1 mean?

Thanks for you help.


Albert
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Problem with Constraint Group and Load Cases

September 4, 2014, 10:46 pm
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Hi.

I have made a simple model with the thermal stress interface. In the setup I have a beam that has a fixed temperature on one end and two different temperatures on the opposite face at the other end of the beam.
The different temperature constraints has been assign into three different constraints groups.

Under Study Extensions in the Study node I have defined two load cases that uses the different temperature constraints.

The results show no difference in temperature between the to load cases. It seems that COMSOL is using the temperature constraint at the bottom of the list in the Heat Transfer in Solids node, for all load cases.

I have also added two different boundary loads for the same face under the Solid Mechanics node. They are assign to different load groups and applied separately in the to load cases. This is just to show that for load groups everything works well.

Why doesn't the Constraint Group work together with load cases? Seems strange as the Load Group work fine using the exact same approach. Is there maybe a workaround?

In my project i have a lot of load cases with different temperature constraints i need solutions for.


Thanks
Anders

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problem with level set and heat transfer in fluids when used together

September 5, 2014, 12:07 am
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I have simulated the merging of two glycerol drops with one drop on a surface and the other one just touching it from the top. At first i used the laminar two phase flow level set physics just to animate the merging as a function of time, which completed the task well, but now i want to find the associated temperature field for this simulation and i intend to find the heat transfer across the surface over which these drops are merging.so for this purpose i added the heat transfer in fluids node to my model and applied initial values in terms of temperature to the fluid domains and for the initial velocity field i used tpf/fp1 and then i clicked compute. there was no error and the computation finished but then when i scrolled down to the results i do not find the temperature plot, instead the computation returned the velocity field exactly similar to what i had obtained while using the level set node alone. what i mean to say is that the model behaved as if it didn't have any input from the heat transfer node. i think there is a coupling issue here. will be highly grateful if someone could tip me on whats missing in my model :)
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minimum time step

September 5, 2014, 8:51 am
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Hi all,

I am stuck at trying to choose correct solver options/properties for my model. I am working on H-formulation in Time-dependent case. I cannot find an option where I can set minimum time step because now my model would take forever to find a solution.

Any help is appreciated.

Rokas
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