Elmer7 Transient Heat Equation

Numerical methods and mathematical models of Elmer
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VVS
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Joined: 30 Aug 2013, 17:43
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Elmer7 Transient Heat Equation

Post by VVS »

Hi,

I want to simulate the transient behaviour of a cone-cell geometry.
I have already done steady state analysis by setting the Temperature at the top and fixing the heat flux along the edges of the structure.
Now I would like to simulate the transient behaviour.
I tried by changing the simulation by setting from steady state to transient, but I get a really weird result.

I think the initial condition of the problem is crashing with the boundary condition.

One way of fixing this I think is to change the boundary condition to a body force, but I just want the force to act on the top boundary.

could you please help me resolve my problem.

Thank you
VVS
mzenker
Posts: 1999
Joined: 07 Dec 2009, 11:49
Location: Germany

Re: Elmer7 Transient Heat Equation

Post by mzenker »

Hi,

I assume that you have defined an initial condition for the transient analysis?
If you post your sif file, someone can have a look at it...

Matthias
VVS
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Re: Elmer7 Transient Heat Equation

Post by VVS »

Hi,

Yes I have defined initial conditions.

Here is the Sif file
case.sif
Sif file
(3.15 KiB) Downloaded 437 times
thank you
mzenker
Posts: 1999
Joined: 07 Dec 2009, 11:49
Location: Germany

Re: Elmer7 Transient Heat Equation

Post by mzenker »

Hi,

I don't see the cause of your problem at first glance.
What does your geometry look like?
You have a large temperature range: 0 as initial condition, 270 as boundary condition (°C, I assume?)

Matthias
VVS
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Re: Elmer7 Transient Heat Equation

Post by VVS »

Hi,

The Geometry os a cone with a sphere at the bottom of the cone.
The temperature is in Kelvin I think. 0 is of course unrealistic, but I just wanted to test whether it works.

The problem I think is that "Boundary Condition 1" is not compatible with the Initial Condition, because I am setting the boundary condition to be 270 and the Initial Condition to 0.

thanks
mzenker
Posts: 1999
Joined: 07 Dec 2009, 11:49
Location: Germany

Re: Elmer7 Transient Heat Equation

Post by mzenker »

Hi,

I don't think that the initial condition is the problem here.
Since you don't use phase change or any temperature dependent properties, the absolute temperature value shouldn't be important.
What happens if you remove the Heat Flux BC? And if you use a very simple geometry (say, a cube)?

Matthias
VVS
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Re: Elmer7 Transient Heat Equation

Post by VVS »

Hi Matthias!

Thanks for you help.
I figured out the problem. Actually there was no problem. It was just the first frame which looks really messed up.
But the rest of frames converged nicely and the distribution looks smooth even when playing.

But I now have a different problem.
I want to plot the heat distribution for certain points inside my geometry.
I found out that the way to do this is to first create a selection of points and then using "Plot Selection Over Time".
But I have trouble selectin the points. Online I read that there is a Selection Inspector. But I can only find a Selection Display Inspector.
I am using version 4.1.

Could you please help me find out how to select points which are the intersection of a slice of the geometry with a sphere?

Thank you
VVS
mzenker
Posts: 1999
Joined: 07 Dec 2009, 11:49
Location: Germany

Re: Elmer7 Transient Heat Equation

Post by mzenker »

Hi,

there have been some changes in ParaView in this area recently. I didn't test the new ParaView yet, as I am busy with another project that keeps me away from simulations at the moment. :(
The best thing is to go to the ParaView mailing list archive and read the recent posts on the selection related topics there.
Here is an extract from the ParaView 4.1.0 announcement:
Find Data dialog, introduced several versions ago, has quickly become of the main mechanisms for creating new selections. However, until now, if the user created selection using some other mechanism, such as selecting cells in the 3D view, the Find Data dialog could not be used to inspect that selection. One had to use what was called the Selection Inspector. That has now been changed. Find Data dialog has been updated to always show the active selection, no matter how it was created.

Selection Inspector panel has been removed. Selection Inspector was primarily used to control how selections are labelled, their font properties, etc. One can affect these directly from the Find Data dialog or the new Selection Display Inspector which is dockable panel specially designed for picking selection labels, label properties, or showing the selection frustum for frustum based selections.
HTH,

Matthias
VVS
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Re: Elmer7 Transient Heat Equation

Post by VVS »

Thanks for your help. I figured it out.

My project is slowly coming to an end.

The final step I have to do now is to plug in realistic parameters, by converting parameters of heat flux to parameters of mass diffusion.
I have a question regarding this. How exactly is the heat flux boundary condition defined? Is it in W/m^2? And what exactly is the heat transfer coefficient?

thanks
VVS
mzenker
Posts: 1999
Joined: 07 Dec 2009, 11:49
Location: Germany

Re: Elmer7 Transient Heat Equation

Post by mzenker »

VVS wrote: How exactly is the heat flux boundary condition defined? Is it in W/m^2?
Yes.
VVS wrote: And what exactly is the heat transfer coefficient?
It is the heat flux per unit area and Temperature difference. It is in W/(K*m^2).
See Models manual, equation 1.14.

HTH,

Matthias
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