2D cylindrical boundriondition problem

function cyl3

close all;

L = 1; % total height of the coaxial cable

hr = 0.01;

hz = 0.01; % these should be the r coordinates of grid

vr = 0.8:hr:0.2;

vz = 0:hr:10; % these should be the z coordinates of grid

nr = length(vr);

nz = length(vz);

n = nr*nz;

A = zeros(n);

b = zeros(n,1);

for jz = 1:nz

for ir = 1:nr

i = (jz-1) * nr + ir; % the global index of the ir,jz vertex

r = vr(ir); % the geometrical r coordinate

z = vz(jz); % the geometrical z coordinate

if (r == 0.8) || (r == 0.2) || (z == 0) ||(z == 10)

% implement boundary condition for r_a ?

A(i,i) = 1;

b(i) = 0;

else

% implement the main equation here

A(i,i) = -2/hr^2 - 2/hz^2;

A(i,i+1) =1/hr^2 + (1/(2*r)*hr) ;

A(i,i-1) = 1/hr^2 - (1/(2*r)*hr);

A(i,i+nr) = 1/hz^2;

A(i,i-nr) = 1/hz^2;

end

end

end

% solve the problem

u = A\b;

s = reshape(u,nr,nz);

% ss = zeros(nz,nr);

% for jz = 1:nz

% for ir = 1:nr

% i = (jz-1) * nr + ir;

% ss(jz,i) = u(i);

% end

%end

surf(s)

end

[suketu vaidya]

i can not able to plot graph if any one know what is the diffect in my cord

Answer 1

[Alan Stevens]

It looks like

vr = 0.8:hr:0.2;

is the cause of the problem. This leads to vr being empty!