Page 262 - Practical Design Ships and Floating Structures

Practical Design of Ships and Other Floating Structures 237
You-Sheng Wu, Wei-Cheng Cui and Guo-Jun Zhou (Eds)
0 2001 Elsevier Science Ltd. A11 rights reserved

PROBABILISTIC ANALYSIS TOOLS FOR SURFACE SHIPS
UNDER SEAWAY AND EXTREME DYNAMIC LOADS

Y. J. Lua' and P. E. Hess'

'Applied Mechanics Department, Engineering & Information Technology Group, Anteon Corporation
240 Oral School Road, Mystic, CT 06355-1208, USA
'Survivability, Structures, and Materials Directorate, Naval Surface Warfare Center
Carderock Division, West Bethesda, MD 20817-5700, USA

ABSTRACT

Two analysis tools, SIMLAB and PULSTR, have been developed for probabilistic vulnerability and
reliability assessments of surface ships. These tools account for variability in material properties,
geometric configuration, failure criterion, and loading parameters. SIMLAB is a stochastic finite
element analysis system which integrates a nonlinear finite element code, DYNA3D, into a simulation-
based computational framework. SIMLAB can generate a Gaussian, non-Gaussian, stationary, or non-
stationary random loading process and assess ship vulnerability under extreme dynamic loads. The
limit state function is based on the first crossing of the critical response quantity above a safe threshold
during the loading process. PULSTR is a reliability-based analysis and design tool, which can be used
in the preliminary stages of structural design. Both the Monte Carlo Simulation (MCS) and the first
order reliability analysis (FORM) modules compute the probability of failure of a hull-girder under
longitudinal bending. A hybrid approach (MCSRORM) is developed to compute small probability of
failure with a great computational efficiency and numerical accuracy. To demonstrate these analysis
tools. SIMLAB is applied to an elastoplastic beam model subjected to a random excitation, and
PULSTR is employed for the reliability assessment of a surface ship under its single and double hull
configurations.

KEYWORDS
Hull girder, structural reliability, first excursion, random process, Monte Carlo simulation, first order
reliability method. ultimate bending strength, double hull, hybrid approach, DYNA3D, stochastic finite
element method