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From: Iron on 25 May 2010 03:20
Hello everybody.
I am programming a .m-file that computes the temperature distribution in a cylinder that consists of 4 layers each one having different specific heat capacities / densities / thermal conductivities. The inner temperature is constant, whereas the outer wall is giving heat via conduction to the environment. However when I let the programm to give me the values for t=> infinity, I dont get the correkt values like in the steady-state-model :S any help would be appreciated. Here is the m.file:

function pdex2
m = 1;
x = linspace(0.295,0.655,40);
t = linspace(0,8e+7,40);
sol = pdepe(m,@pdex2pde,@pdex2ic,@pdex2bc,x,t);
u = sol(:,:,1);

surf(x,t,u)
title('Numerical solution computed with 40 mesh points.')
xlabel('Distance x')
ylabel('Time t')

figure
plot(x,u(end,:),'r')
title('Solution at t = oo')
xlabel('Distance x')
ylabel('u(x,oo)')

% --------------------------------------------------------------
function [c,f,s] = pdex2pde(x,t,u,DuDx)
ri=0.295; lambdai2=1.685; rocpi2=1600000;
r2=0.395; lambda23=0.176; rocp23=800000;
r3=0.520; lambda34=0.13; rocp34=400000;
r4=0.645; lambda4w=52; rocp4w=7850000;
rw=0.655;

lambda=stepfun(x,ri)*lambdai2+stepfun(x,r2)*(lambda23-lambdai2)+stepfun(x,r3)*(lambda34-lambda23)+stepfun(x,r4)*(lambda4w-lambda34);
rocp=stepfun(x,ri)*rocpi2+stepfun(x,r2)*(rocp23-rocpi2)+stepfun(x,r3)*(rocp34-rocp23)+stepfun(x,r4)*(rocp4w-rocp34);

c = rocp;
f = DuDx.*lambda;
s = 0;

% --------------------------------------------------------------
function u0 = pdex2ic(x)
u0 = 400;
% --------------------------------------------------------------

function [pl,ql,pr,qr] = pdex2bc(xl,ul,xr,ur,t)
pl = ul-400;
ql = 0;
pr = (ur-20)*10/52;
qr = 1;



THANKS ALOT FOR ANY HELP
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