PDEPE boundary condition outputting odd results.
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Scott Lines
le 22 Mar 2019
Réponse apportée : Scott Lines
le 22 Mar 2019
For the boundary condition I've set the left (pl) to a constant value of 280 with the idea being that this value will always be 280, however when i output the results the value is instead 4e10 and appears to be changing. What am I doing incorrectly so that my boundary condition is a) not constant and b) way above the value I've stated.
I've gone over the pdepe page a few times trying to figure it out but unfortauntely haven't made much progress.
Thank you for any help provided.
m = 0;
tspan = linspace(0,365*20*86400,21);
xmesh = linspace(0,20,201);
sol = pdepe(m,@pdefun,@icfun,@bcfun,xmesh,tspan);
u = sol(:,:,1);
figure, plot(u(2,:),xmesh)
ylabel('Depth (m)')
xlabel('Oxygen Concentration (g/m3)');
set(gca, 'XAxisLocation', 'top')
set(gca, 'YDir','reverse')
function[c,f,s]=pdefun(x,t,u,DuDx)
c = 0.18;
f = 1e-8*DuDx;
s = -1e-9*u;
end
function u=icfun(x)
u = 0;
end
function[pl,ql,pr,qr]=bcfun(xl,ul,xr,ur,t)
pl = 280;
ql = 1;
pr = ur;
qr = 0;
end
4 commentaires
Réponse acceptée
Torsten
le 22 Mar 2019
Modifié(e) : Torsten
le 22 Mar 2019
function main
m = 0;
tspan = linspace(0,365*20*86400,21);
xmesh = linspace(0,20,201);
sol = pdepe(m,@pdefun,@icfun,@bcfun,xmesh,tspan);
u = sol(:,:,1);
figure, plot(u(2,:),xmesh)
ylabel('Depth (m)')
xlabel('Oxygen Concentration (g/m3)');
set(gca, 'XAxisLocation', 'top')
set(gca, 'YDir','reverse')
end
function[c,f,s]=pdefun(x,t,u,DuDx)
c = 0.18;
f = 1e-8*DuDx;
s = -1e-9*u;
end
function u=icfun(x)
u = 0;
end
function[pl,ql,pr,qr]=bcfun(xl,ul,xr,ur,t)
u0 = 280;
pl = ul - u0;
ql = 0;
pr = ur;
qr = 0;
end
2 commentaires
Torsten
le 22 Mar 2019
Yes, call pdepe twice: first from t=0 to t=t_switch, then from t=t_switch to t=tend. And use the solution obtained at the end of the first time interval as initial profile for the second time interval.
Plus de réponses (2)
Scott Lines
le 22 Mar 2019
1 commentaire
Torsten
le 22 Mar 2019
Modifié(e) : Torsten
le 22 Mar 2019
function main
m = 0;
xmesh = linspace(0,20,101);
tspan = linspace(0,365*5*86400,201);
u0 = 280.0;
icarg = @(x) 0.01*ones(size(x));
sol = pdepe(m,@pdefun,@(x)icfun(x,icarg),@(xl,ul,xr,ur,t)bcfun(xl,ul,xr,ur,t,u0),xmesh,tspan);
w = sol(end,:);
plot(xmesh,w)
tspan2 = linspace(tspan(end),365*20*86400,201);
u0 = 0.0;
icarg = @(x)interp1(xmesh,w,x);
sol2 = pdepe(m,@pdefun,@(x)icfun(x,icarg),@(xl,ul,xr,ur,t)bcfun(xl,ul,xr,ur,t,u0),xmesh,tspan2);
w2 = sol2(1,:);
hold on
plot(xmesh,w2)
end
function [c,f,s] = pdefun(xmesh,tspan,u,DuDx)
c = 2;
f = 1e-8*DuDx;
s = -1e-7*u;
end
function u = icfun(x,icarg)
u = icarg(x);
end
function [pl,ql,pr,qr] = bcfun(xl,ul,xr,ur,t,u0)
pl = ul - u0;
ql = 0;
pr = ur;
qr = 0;
end
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