scope:

Scope and Overview of the Following Sections

This Guide provides a description of the analysis procedure to be pursued to obtain the optional classification notation 'Dynamic Loading Approach', DLA. Emphasis is given here to the determination of dynamic loads rather than the structural FE analysis procedure. This has been done mainly because structural analysis practices are well established and understood among designers, but dynamic load determination is a less familiar subject. Therefore, the procedures for FE analysis are only briefly described for the purpose of ready reference and completeness.

The Dynamic Loading Approach uses explicitly determined dynamic loads, and the results of the analysis are used as the basis to increase scantlings where indicated, but allows no decreases in scantlings form those obtained form the direct application based on FPI Guide scantling equations.

While outside the scope of this Guide, any local impact pressure and global whipping loads due to slamming are to be separately addressed for the strength assessment of the hull structure. Also, any green sea loads due to the ingress of green water on deck is to be addressed for scantlings of the forecastle deck and breakwater. For this purpose, the adequacy of the selected software may need to be demonstrated to the satisfaction of ABS.

This Guide systematically introduces the assumptions in the load formulation and the methods used in the response analysis underlying the DLA Analysis for FPSOs. These include the following topics:

i) Specification of the loading conditions

ii) Specification of the Dominant Load Parameters

iii) Response Amplitude Operators and extreme values

iv) Equivalent design waves

v) Wave-induced load components and the assembly of Load Cases

vi) Structural FE model development; and

vii) Permissible stresses used in the acceptance criteria.

These topics are presented in the following Sections 2 through 12, and Appendix 1 summarizes the DLA analysis procedure.

Refer to Section 1, Figure 1 for a schematic representation of the DLA analysis procedure.

While the DLA can, in principle, be applied to all types of floating offshore structures, the focus of this Guide is on FPSOs. In the case of other ship types, clients should consult with ABS to establish appropriate analysis procedures. This applies particularly to the choice of loading conditions and Dominant Load Parameters. For trading ship types, designers can refer to the ABS Guide for SafeHull-Dynamic Loading Approach for Vessels published in December 2006.