Plotting stress tensor in MATLAB, Parametric Surface

[Xaspire88]

First off, I'm not sure if MATLAB questions go here or not, or if they are even dealt with on this forum. If not more or remove I guess.

I am no MATLAB wiz so this is mind-boggling to me. I am given a state of stress at a critical point of a component and told to plot a 3D parametric surface of the normal stress, but in spherical coordinates.*see attached figure*

http://i666.photobucket.com/albums/vv22/Zzsark/Matlabproblem.jpg
http://i666.photobucket.com/albums/vv22/Zzsark/Matlabproblem2.jpg

I tried plotting the equation given for sigma_nn for the indicated values of theta(0:2pi) and phi(0:pi), and it output a surface but I was expecting to get a spherical shape, and this was no where near spherical.

Some of my MATLAB code:

>> sigma=[200 100 120;100 350 100;120 100 300];
>> theta=sym('theta');
>> phi=sym('phi');
>> n=[cos(theta)*sin(phi);sin(theta)*sin(phi);cos(phi)];
>> sigma_normal=sigma*n*n';
>> theta=0:0.2:2*pi;
>> phi=0:0.1:pi;
>> Z=eval(sigma_normal);
>> Z=abs(Z);
>> surf(Z)

any direction or advice as how to correctly plot a parametric surface in MATLAB such as this would be much appreciated.

 

[nilesh_pat]

To plot a parametric surface in MATLAB, you will need to use the surf() command. The syntax for this command is as follows: surf(X,Y,Z). X and Y represent the values of theta and phi, respectively, while Z represents the normal stress value. For example, if you wanted to plot the surface for theta = 0 to 2pi and phi = 0 to pi, you could use the following code: theta = 0:0.2:2*pi;phi = 0:0.1:pi;[X,Y] = meshgrid(theta,phi);Z = eval(sigma_normal);surf(X,Y,Z);