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Solving a 3D heat equation with the finite elements method

Posted 10 years ago

Hi everyone,

I'm trying to solve the heat equation with the finite elements method using mathematica 10 but I got some issues:/

Here's my problem

My working space is a box 100x40x100. I got a heat source which is a finite semi cylinder: -3<x<3 and y^2+z^2 <= 1 and z => 0 this source has a temperature which varies with time the flow of the heat is 0 on the borders of my working space and my source of heat. I want to modelize the heat in my box over time.

So first I tried to solve this equation with a constant source of temperature: T=300

Thus I typed the following code:

\[CapitalOmega] = 
  ImplicitRegion[! ((z^2 + y^2 <= 1) || z <= 0), {{x, -50, 
     50}, {y, -20, 20}, {z, -50, 50}}];                                          -> creation of my working space, which the whole box except the semi cylinder

op = \!\(
\*SubscriptBox[\(\[PartialD]\), \(t\)]\(u[t, x, y, z]\)\) - 
      Inactive[Laplacian][u[t, x, y, z], {x, y, z}] ;                        -> writting of the heat equation

Subscript[\[CapitalGamma], D] = 
  DirichletCondition[u[t, x, y, z] == 300, 
   z^2 + y^2 <= 1 && -3 <= x <= 3];                                     -> I'm setting up my initial conditions: a constant temperature on my semi cylinder

Subscript[\[CapitalGamma], N] = 
  NeumannValue[
   0, (x = -50) || (x = 50) || (y = -20) || (y = 20) || (z = 
      50) || ((z^2) + (y^2) = 1 && (-3 <= x <= 3))];                 -> I want the heat flow = 0 on the borders of my box and the semi cylinder ( heat must not 

escape from my box)                                                                                                            

uifHeat = 
  NDSolveValue[{op == Subscript[\[CapitalGamma], N], 
    Subscript[\[CapitalGamma], D], u[0, x, y, z] == 0}, 
   u, {t, 0, 100}, {x, y, z} \[Element] \[CapitalOmega]];                              -> I'm solving the equation 

Animate[Plot3D[
  uifHeat[t, x, y, z], {x, y, z} \[Element] uifHeat["ElementMesh"], 
  PlotRange -> {0, 600}], {{t, 10}, 0, 40, 2}, 
 SaveDefinitions -> True]                                                                           -> plotting of the solution

But I got some error messages and I don't understand where my mistakes are

enter image description here

The first one obviously comes from my definition of neumann value with the (z^2+y^2<1) border but I don't understand what is the matter. The second one seems to be due to the fact that x, y and z are no longer variables but figures at the end of my code but I can't see where is my mistake.

Does anyone has an idea of what I should correct?

Here is a picture of my code:

enter image description here

PS: English is not my native language so I'm sorry for my grammar mistakes xp

2 Replies

Thanks for your tip, I've corrected my post :)

Dear Olivier, It is helpful if you use the the Code Formatting feature as described here: http://community.wolfram.com/groups/-/m/t/270507

If you use that feature, your responders will be able to copy your code and test it without much effort.

POSTED BY: W. Craig Carter
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