Approximate Optimization Using Moving Least Squares Response Surface Methods: Application to FPSO Riser Support Design

J. Ocean Eng. Technol. 2010;24(1):20-33.

Song Chang-Yong,Lee Jong-Soo,Choung Joon-Mo

School of Mechanical Engineering Yonsei University,School of Mechanical Engineering Yonsei University,School of Mechanical Engineering Inha University

Keywords: Strength design, Riser support, Floating production storage and offloading (FPSO), Approximate optimization, Moving least squares method (MLSM), Constraint-feasible moving least squares method (CF-MLSM)

Abstract

The paper deals with strength design of a riser support installed on floating production storage and offloading (FPSO) vessel under various loading conditions - operation, extreme, damaged, one line failure case (OLFC) and installation. The design problem is formulated such that thickness sizing variables are determined by minimizing the weight of a riser support structure subject to stresses constraints. The initial design model is generated based on an actual FPSO riser support specification. The finite element analysis (FEA) is conducted using MSC/NASTRAN, and optimal solutions are obtained via moving least squares method (MLSM) in the context of response surface based approximate optimization. For the meta-modeling of inequality constraint functions of stresses, a constraint-feasible moving least squares method (CF-MLSM) is used in the present study. The method of CF-MLSM, compared to a conventional MLSM, has been shown to ensure the constraint feasibility in a case where the approximate optimization process is employed. The optimization results present improved design performances under various riser operating conditions.