Dear All, I have a structure for which i have carried out frequency response analysis using Hypermesh as preprocessor and NASTRAN as solver. I have the following queries: 1) In the .f06 output file, the principal stresses are not printed. 2) I have used hex hedral meshing for the entire structure. After carrying out the meshing and frequency response analysis only Normal shear stress are printed. When i use the formula(see attachment) to calculate 3d principal stresses, at some points, i am unable to calculate the angle due to incorrect value? Is this due to inaccurate meshing? Please advise.