An Evaluation of Current NASTRAN Discrete Element Models for Monocoque and Semimonocoque Structures

The current discrete element analysis models in NASTRAN, Levels 8. 1.0 and 11. 1. 0, are evaluated for semi-rnonocoque and monocoque structures. Comparative results are presented with the FORMAT-I11 general-purpose code for a swept wing statics analysis and a Skylab substructure vibration analysis.
Good agreement between Level i I. 1.0 and FORMAT-111 is demonstrated; however, a major error in Level 8. 1.0 was discovered on the Skylab vibration problem. The computational performance of NASTRAN was superior to FORMAT, but the vibration rigid format was found to have several inefficiencies. Comparative results are also presented between Level 11. 1. 0 and STACUSS, SLADE, BOND, UNIVALVE, and another special-purpose code. Results for two of the structures analyzed, a cylindrical shell and an elliptic plate, indicate curved discrete elements are significantly more accurate than the plate elements in NASTRAN for the same number of degrees of freedom.