ABSTRACT

The economics of scale offered by ultra large container carriers has led to the increasing use of these ships for the marine transport of goods. Recently ABS has developed an advanced ‘Dynamic Loading Approach’ (DLA) analysis procedure for the strength assessment of ultra large container carriers based on nonlinear seakeeping analysis. This paper provides the technical background of the advanced DLA analysis procedure, and focuses on the determination of equivalent design waves and nonlinear dynamic loads for finite element (FE) structural analysis. The analysis procedure presented in this paper is validated for selected large container carriers. The ABS in-house computer program NLOAD3D, which is a nonlinear time-domain seakeeping analysis program based on 3D Rankine source panel method, is used for the calculation of nonlinear dynamic loads. Numerical results of the nonlinear global loads and FE pressures are presented and discussed.

INTRODUCTION

Fifteen years ago ABS formally introduced the ‘Dynamic Loading Approach’ (DLA) as an alternative engineering analysis method for more rigorous design review of ship hull structures beyond the prescriptive classification rule requirements (Liu, et al, 1992). The DLA is a strength assessment methodology based on first-principle direct analysis of hydrodynamic loadings and the corresponding structural responses. For ultra large container carriers with length in excess of 350 meters, ABS requires a DLA analysis to support the design review of hull structure and critical structural details (See ABS 2006 Steel Vessel Rules 5–5–1/1.3.3).

A current industry trend in container carrier designs is the increase of ship length with large bow flare and stern overhang to provide more deck area and container stowage capacity. Due to the large bow flare and stern overhang, these vessels are subject to more pronounced nonlinear ship motions and wave loads compared to full form vessels.

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