Company: Southwest Research Institute (Prime), Rocketdyne (Subcontractor)
Contracting Agent: NASA Lewis Research Center

Purpose: To develop probabilistic structural analysis methods and computational tools to evaluate the reliability and risk of space propulsion system structural components representative of space shuttle main engine components such as turbine blades, transfer ducts, and liquid oxygen posts.

Background: For complicated and expensive aerospace structures, the ability to perform reliability and risk assessment without using extensive hardware testing is critical to design and certification. The PSAM project has developed a state-of-the-art structural system risk assessment computer program called NESSUS (Numerical Evaluation of Stochastic Structures Under Stress), which integrates advanced reliability methods with finite element and boundary element methods. NESSUS can model uncertainties in loads, material properties, and geometries with random variables. Probabilistic performance models implemented in NESSUS include stress, strain, displacement, vibration, fatigue, fracture, creep, etc. NESSUS can perform reliability analyses for multiple components and failure modes and identify critical random variables and failure modes to support structural design, certification, and risk assessment. Rocketdyne, as a subcontractor to SwRI, has used NESSUS to analyze SSME structural components to verify the PSAM technology.

Summary: The primary product, the NESSUS code, has been delivered and documented as planned and numerous papers have been published. In addition to achieving the program objective, the PSAM technology offers general probabilistic analysis capabilities and has been widely used in various industries. Previous and on-going application areas include: aerospace propulsion system, aircraft wings and engines, underground structures, nuclear waste packaging, and biomechanics.

Key Publications:

Wu, Y.-T., and H.R. Millwater, T.A. Cruse, "Advanced Probabilistic Structural Analysis Method for Implicit Performance Functions,'' AIAA Journal, 28(9), 1990.

Thacker, B.H., and H.R. Millwater, S.V. Harren, "Computational Methods for Structural Load and Resistance Modeling," Proceedings of the 32nd AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials (SDM) Conference, Baltimore, Maryland, Paper No. AIAA-91-0918, pp. 1,227-1,235, AIAA, Washington, D.C., April 7-10, 1991

Millwater, H.R., and Y.-T. Wu, Y. Torng, B.H. Thacker, D.S. Riha, C. Leung, "Recent Developments of the NESSUS Probabilistic Structural Analysis Computer Program,'' Proceedings of the 33rd SDM Conference, Dallas Texas, 1992.

Riha, D.S., and H.R. Millwater, B.H. Thacker, "Probabilistic Structural Analysis Using a General Purpose Finite Element Program," Finite Elements in Analysis and Design, Elsevier Publishers, Vol. 11, pp. 201-211, 1992.

Wu, Y.-T., "Computational Methods for Efficient Structural Reliability and Reliability Sensitivity Analysis," AIAA Journal, 32(8), 1994.