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Homework Help: Plotting stress tensor in MATLAB, Parametric Surface

  1. Feb 16, 2010 #1
    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 [Broken]
    http://i666.photobucket.com/albums/vv22/Zzsark/Matlabproblem2.jpg [Broken]

    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.
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
    Last edited by a moderator: May 4, 2017
  2. jcsd
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