scope:

Scope and Overview

Structural direct analysis is a strength assessment methodology based on first principles approach. In this regard, acceptance criteria are applied to verify that predicted stress levels do not exceed a specified percentage of yield strength and do not exceed buckling and ultimate strength. This analysis satisfies the requirements of Required Analyses specified in 1-1-4/5.1 of the ABS Rules for Conditions of Classification - Light and High-Speed Craft (Part 1). The Guides also note that Supplementary Analyses may be required. The most likely such requirements are fatigue and vibration analyses. While outside the scope of these Guidance Notes, they are, nevertheless, discussed in general terms. However, these Guidance Notes do not provide specific guidance for assessing these failure modes.

1/7 FIGURE 1 shows an overview of the SDA procedures for high-speed craft, wherein the strength analysis is highlighted and the supplementary analyses are shown shaded. In these Guidance Notes, special consideration is provided to include the slamming and whipping load effects in the strength analysis.

These Guidance Notes systematically introduce the analysis procedures in the load formulation, and the methodology underlying the analysis procedures used in applying direct analysis to high-speed craft. These include the following topics:

● Specification of the loading conditions and load cases

● Environmental and service conditions

● Formulation of equivalent design waves

● Calculation of nonlinear wave loads

● Structural finite element (FE) model development

● Strength analysis

● Application of the acceptance criteria

These topics are presented in the following Sections 2 through 14. Refer to 1/7 FIGURE 2 for a schematic representation of the steps involved in the direct structural analysis procedure.

A report detailing the analysis should be submitted for review and approval along with finite element models used in the analysis. As a minimum the report should include the following information:

i) Craft's loading conditions and weight distribution

ii) Craft's operational profile or Wave Scatter data for the area of operation

iii) A brief description of all software used in the analysis

iv) A detailed description of the analysis procedure and steps

v) All results of the hydrodynamic analysis and results of the Extreme Values analysis

vi) Model test data, with a comparison with analysis results (if applicable)

vii) Material properties and the allowable stresses applicable to the craft

viii) A brief description of the Finite Element model and the mesh size used

ix) Details of the Finite Element Analysis results

x) Graphs for all areas of non-compliance

xi) Detailed discussion of non-compliance areas and proposed fixes

xii) Description of the buckling analysis and a sample calculation

xiii) Any other available information related to the analysis