rectangular heated composite

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rectangular heated composite

Postby k123456 on Mon Jul 17, 2017 4:01 am

Dear PDE Solutions,

i read similiar problems but i have nevertheless a problem with defining a pulsating (rectangular) heat supply as boundary condition. A two layered composite with different conductivities should be heated periodically at one edge (see script). The initial surface temperature is 300 K. As result i want to see the time-dependent signal, the temperature history respectively pulse-heating.

It would be nice if anyone could give me some tips :)
heat transfer throug composite.pde
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Re: rectangular heated composite

Postby moderator on Mon Jul 17, 2017 1:13 pm

I don't understand what you are trying to do here.
In the first place, you can't have both a value and a natural BC in the same place.
You have an insulated box, containing an interior box whose boundary temperature is somehow magically held at 300. Onto this you try to impose an additional magical interior flux, while still holding the temperature at 300.
I'm very confused. Perhaps you meant to set 300 as the initial value and not as a value BC? As for the interior flux, by what mechanism would the energy appear at the interior boundary without crossing the surrounding material?

As far as creating a pulsed flux, there are several ways to do this. One is simply to add together a group of upulse terms like the one you have already, but with the times changed. Another is to use a USTEP with a SIN(a*t)-offset argument, so that the value flips from zero to 1 whenever the sin passes through "offset". An IF..THEN..ELSE would work the same way with the SIN-Offset, or you could use a SWAGE to smooth the transition (see Samples|Usage|Functions|Swage_Pulse.pde). You should define the switch points as plot or monitor times or as critical times, so that the time steps don't jump over the transitions.
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Re: rectangular heated composite

Postby k123456 on Tue Jul 18, 2017 1:05 am

Thanks for the answer :)

Apologize for the inaccurate expression. The plate should have an initial temperatur of 300 K. This inital temperature will be increased gradually (400 K, 500 K up to 1000 K) in further simulations and is realized by an heater (placed in a well insulated chamber which is cooled to 300 K- region 1). Then i supply energy in form of a (laser-)pulse on the left edge (material 1). The aim is to simulate the thermal diffusivity through the composite dependent on the energy of the pulse and the pulse duration. On the surface of the plate there will be no convection losses, only radiation losses. (which is not yet implemented).

I thought it`s better to neglect the radiation term in the first step to see if the result is useful. Or do you think it is better to implement the radiation term already at the beginnung as natural(u) on the four edges?

If this description is still unclear i can post a little sketch :)

Transfering the boundary conditions/initial conditions into the right syntax is a little unclear for me.

I will try out to generate a chain of pulses.

Many Thanks.
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Joined: Thu Jun 08, 2017 4:42 am

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