# Discussion Forum

## Moving Mesh problem/ Electromagnetism / Induction heating of rod

 Topics: 4.3a, 4.3, AC/DC Module, Heat Transfer, Mesh
RSS feed   |   Turn on email notifications   |   8 Replies   Last post: March 22, 2013 10:24pm UTC

February 7, 2013 11:24am UTC

Moving Mesh problem/ Electromagnetism / Induction heating of rod

Dear Ivar,

I am working over a problem, induction heating of a rod moving inside the furnace with a certain velocity, required to relieve stress from the surface.

The furnace is stationary, means the coil while the rod is moving inside the coils. So, I have given the boundary condition accordingly with transitional speed to the rod. However, I am unable to understand, the concept of moving mesh and it feature, the significance of using assembly and pairs feature etc.

All these, I want, to see the result like; the change in thermal profile over the cross section plane at d= 0 ( i.e. From the point it enters into the coil ) while its travel each cm inside the coils till it finally comes out of the coil.

Please send me some reference, example model to understand this further.

--
Ishant Jain

Ivar Kjelberg

February 7, 2013 12:44pm UTC in response to

Re: Moving Mesh problem/ Electromagnetism / Induction heating of rod

Hi

well I'm off site so it's difficult for me to search my chunk of old models, now I believe there are a few on the Forum already (perhaps a linear actuator in 2D-axi), and you have the rotary models of the model library (they were perhaps easier to understand in 3.5 as then you needed to add all physics manually, now you have pre-cooked models, eqasier to use, but less evident to adapt, as here, to change from rotation to linear motion.

Strange enough I cannot remember that COMSOL has proposed a simple linear motor motor with velocity displacement.

In your case your rod is continuosly traveling along one direction, then you should be able to use the velocity BC that virtualises the translation at a given velocity (for a fixed geometry) or you need to tweak the geometry and physically displace the rod, then you either need to rebuild your geoemtry mesh per parameter step, or you can use the Assembly mode and have your rod rectangle slide along common boundaries, for which you need to manaully define the "continuity" condition.
--
Good luck
Ivar

February 9, 2013 6:15am UTC in response to Ivar Kjelberg

Re: Moving Mesh problem/ Electromagnetism / Induction heating of rod

Dear Ivar,

Thanks for your response, but this is completely our of my understanding.

I request you to please explain step by step, as you mentioned , many things, to use Velocity Boundary condition, physical displacement of Rod, Rebuild geometry mesh per parameter step and Use of assembly step. I tried to search in your database but could find any of these, that can help to solve my problem.

We also use a different product like ANSYS etc where they have a large number of tutorials and manuals available for better understanding and this is the reason we are happy to pay the subscription fees, However , In COMSOL case we are supposed to pay the 20% of the software fees for support,and which is actually not helpful.

I sincerely request you to please help us, to take this forward and, to gain more confidence into your software.

Hi

well I'm off site so it's difficult for me to search my chunk of old models, now I believe there are a few on the Forum already (perhaps a linear actuator in 2D-axi), and you have the rotary models of the model library (they were perhaps easier to understand in 3.5 as then you needed to add all physics manually, now you have pre-cooked models, eqasier to use, but less evident to adapt, as here, to change from rotation to linear motion.

Strange enough I cannot remember that COMSOL has proposed a simple linear motor motor with velocity displacement.

In your case your rod is continuosly traveling along one direction, then you should be able to use the velocity BC that virtualises the translation at a given velocity (for a fixed geometry) or you need to tweak the geometry and physically displace the rod, then you either need to rebuild your geoemtry mesh per parameter step, or you can use the Assembly mode and have your rod rectangle slide along common boundaries, for which you need to manaully define the "continuity" condition.
--
Good luck
Ivar

--

Ivar Kjelberg

February 9, 2013 3:15pm UTC in response to

Re: Moving Mesh problem/ Electromagnetism / Induction heating of rod

Hi

first of all, to make it clear, here on the FORUM we are only users as you (except for some from COMSOL, flagged as such;) So we are all in the same sitaution w.r.t. learning and using the tool. Now also, my experience is that I have a far better interaction with the COMSOL team, that what I had previously with the two other larger (older) FEM tools I have used of ayme A & N)
I must say too that I have managed to get to 3-4 of the COMSOL training courses (after 2 years all alone) that did make a large difference, and then on the Conference, you get a lot of useful info, hands on introductions, direct chat etc.

Back to your problem, 1) I'm out of office and far from my COMSOl WS so I'm limited in possibiity to check things myself but we can try to discuss it, in between, when I find a working Wifi.

my first question is then are you in 2D-axi or in full 3D (often its easier to start in 2D or 2D-axi, at least to set up the model and to check it, then one can go to 3D (and often I notice that I do not get much more) main exception ,when the 2D-axi symmetry is spoiled by one or more dependent variable, as a horizontal pipe in CFD with gravity, it 2D-axi it becomes a rdial gravity i.e. a rotating pipe, that not what is wanted.

So your model: can you use 2D-axi, with the rod to be heated in the middle (and the heating coil around) ?
If so, I believe you can get around by using the domain Translational velocity BC for your rod. Then can you say which physics you though of, and confirm it's a transient solver or a frequency domain stationary combination ...

Another possibility: check the webinars, there was one 2 days ago on IEEE about transformes and induction, its stored somewhere (check the COMSOl main site under webinar), they show a model that hears like yours here.

--
Good luck
Ivar

February 13, 2013 5:32am UTC in response to Ivar Kjelberg

Re: Moving Mesh problem/ Electromagnetism / Induction heating of rod

Indeed, I have modelled the same in 2D axi, with the rod to be heated in the middle surrounded by the coil. There are 54 numbers of turns with different cross sectional area and I have used coil group domain for the same, applied to the voltage available.

The problem lies in the discontinuous temperature profile I am getting for the center line and surface lline of the wire rod. Please see the graph.

Hi

my first question is then are you in 2D-axi or in full 3D (often its easier to start in 2D or 2D-axi, at least to set up the model and to check it, then one can go to 3D (and often I notice that I do not get much more) main exception ,when the 2D-axi symmetry is spoiled by one or more dependent variable, as a horizontal pipe in CFD with gravity, it 2D-axi it becomes a rdial gravity i.e. a rotating pipe, that not what is wanted.

So your model: can you use 2D-axi, with the rod to be heated in the middle (and the heating coil around) ?
If so, I believe you can get around by using the domain Translational velocity BC for your rod. Then can you say which physics you though of, and confirm it's a transient solver or a frequency domain stationary combination ...

Another possibility: check the webinars, there was one 2 days ago on IEEE about transformes and induction, its stored somewhere (check the COMSOl main site under webinar), they show a model that hears like yours here.

--
Good luck
Ivar

--
Ishant Jain

Ivar Kjelberg

February 13, 2013 1:22pm UTC in response to

Re: Moving Mesh problem/ Electromagnetism / Induction heating of rod

Hi

indeed difficult to interprete, but are you even sure the directions are the same ?
You use "arc length" as horizontal axis, the direction of the build in arc length is not known, and deepnds on how COMSOL analyses the geoemtry,
I can only suggest to use true coordinates, you can change the expression of the plot to "z" to get the height coordinate for the horizontal axis.
And to use a data set cut line, with perhaps 2-3 parallel lines to catch the T value in the rod, and radially across at different hights. This might help your analysis

--
Good luck
Ivar

February 14, 2013 6:22am UTC in response to Ivar Kjelberg

Re: Moving Mesh problem/ Electromagnetism / Induction heating of rod

Hi

Which direction you are mentioning ?

And I have tried the Z coordinate also but this will not make any change. Please see the graph and suggest "How the temperature is falling below the initial level".

Hi

indeed difficult to interprete, but are you even sure the directions are the same ?
You use "arc length" as horizontal axis, the direction of the build in arc length is not known, and deepnds on how COMSOL analyses the geoemtry,
I can only suggest to use true coordinates, you can change the expression of the plot to "z" to get the height coordinate for the horizontal axis.
And to use a data set cut line, with perhaps 2-3 parallel lines to catch the T value in the rod, and radially across at different hights. This might help your analysis

--
Good luck
Ivar

--
ishant.jain@tatasteel.com

Ivar Kjelberg

February 14, 2013 3:44pm UTC in response to

Re: Moving Mesh problem/ Electromagnetism / Induction heating of rod

Hi

normally your temp shuld not fall "below" initial, but if you do not respect mesh density, heat diffusivity and mesh density criteria, you might have numerical issues, that can get swinging and unreasonable T values out. This is then because the "sampling" of the mesh does not allow to resolve correctly the heat gradient that is driving the heat equation.

There are several threads about this, perhaps about a year or two old. Nagi made several crucial comments therearound. HT is a dissusion equation, and there are here too links between the material properties, time stepping (for transient cases) and mesh density, linked in by physics

--
Good luck
Ivar

Cinzia Iacovelli
COMSOL Employee
USA

March 22, 2013 10:24pm UTC in response to Ivar Kjelberg

Re: Moving Mesh problem/ Electromagnetism / Induction heating of rod

Dear Ivar and Ishant, the archived version of the 02/07 IEEE webinar "Transformer and Inductor Modeling with COMSOL Multiphysics" can we watched here

spectrum.ieee.org/webinar/2193320

--
Best regards,

Cinzia Iacovelli
COMSOL, Inc.
Marketing - Webinars
cinzia@comsol.com

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