mesh grid and mesh ploting

R = 0.003/2;
y=linspace(-1,1,30);
x=linspace(-1,1,30);
r.^2==x.^2+y.^2;
y=r./R;
a0=-6536;
z=a0*R^2*(1-y.^2)/0.016;
[X1,Y1]=meshgrid(x,y);
%zz=griddata(x,y,z,X1,Y1,'cubic');
figure
mesh(X1,Y1,z)

This is a simple poiseuelle flow in a pipe, my goal is to plot the velocity of flow(z) in 3D. R is the redius of pipe, x and y are inplane and z is the velocity along the pipe length. I get the error ' Error using mesh Z must be a matrix, not a scalar or vector.' How can I get the z as a matrix to resolve the error?

[David Hill]

R = 0.003/2;
y=linspace(-1,1,30);
x=linspace(-1,1,30);
r=sqrt(x.^2+y.^2);%is this what you mean?
y=r./R;
[X1,Y1]=meshgrid(x,y);
z=(f1.a0)*R^2*(1-Y1.^2)/0.016;%if z only depends on y, move after the meshgrid to get z as matrix
figure
mesh(X1,Y1,z)

[H-M]

David,

Since the geometry is circle (pipe) and x and y are set in the cicle cross section, I think I need to relate the distance from center of pipe (r) to x and y that is why I wrote r=sqrt(x.^2+y.^2).On the other hand y=r/R.I mean I need to impose to code that the shape is circle or pipe.I do not know how to relate x,y,r together to work properly in code.

Also I put z after the meshgrid but I get z as a vector yet.

I am not sure about what I am doing. If you have any idea please lead me. Thank you

[David Hill]

Do you have the equations you are trying to model? Or are you creating the model yourself?

Answer 1

[H-M]

I just have the poiseuille velocity equation(z equation in my code) in a circular pipe and I am supposed to plot the velocity profile in 3D with meshgrid.

[H-M]

x and y are 30*30 matrix but z is 1*30 matrix. z should be a 30*30 matrix