Hi two_out_of_two,
I can think of a number of possibilities.
What type of element are you using? If you are using brick or plate elements, your hand calculations probably do not take the 3D effects into account. That is, Poissons ratio, distortion of the cross section (which would not be a problem in linear stress). If you are using beam elements, the stresses should match.
Another related effect occurs in brick elements if the end is fully fixed: no translations allowed. The stress right at the fixed end can be abnormally high. Select some of the nodes along the length leading up to the fixed end, right-click, and choose to create a path plot. If you visually extrapolate the stress to the fixed end, does it match your hand calculation?
What type of result are you viewing? Chances are your hand calculation is not taking the shear stresses and all of the other bending components into account. So stress results such as von Mises and the principal stresses will not match the hand calculation. If this is the case, then you can only view the "Results Contours > Stresses > Tensor > NN Component", where N is the axis parallel to the length of your pipe.
Otherwise, please provide your hand calculations and an archive of your model. (See "Create, Post, or Provide an Archive of your model".)
John Holtz, P.E. Global Product Support
Autodesk, Inc. If not provided already, be sure to indicate the version of Inventor Nastran you are using!"The knowledge you seek is at knowledge.autodesk.com" - Confucius 😉
