DYNAMIC LOAD APPROACH IN TANKER DESIGN

This paper begins by describing the Dynamic Loading Approach (DLA) concept. The basic difference between the more traditional direct engineering analysis approach and DLA is discussed. Primarily a DLA based design uses the results of the direct engineering analysis to indicate where increased scantlings should be provided. Corresponding reduction of scantlings is not permitted. Hence there is a bias introduced to the design process toward safer scantlings; the magnitude and extent of such increases is determined in a rational manner. These fundamental issues are explored from the classification standpoint as well as from that of a ship owner, and a designer/shipbuilder. Unlike the traditional rule formula based design, the loads considered in DLA reflect what are realistically and uniquely experienced by the specific vessel. Technical issues addressed in this paper encompass the aspects of dynamic loading and strength. For the topic of loading, detailed discussions in the areas of wave induced loading, ship motions, internal structural and cargo inertial loadings, etc., and, most importantly, the issue of load combinations, are discussed. The methods of determination of the characteristic strength in the realm of the limit states of yielding, buckling, and fatigue are detailed. The consideration of these aspects effectively extends the coverage in strength evaluation to both global and local strength. Finally, acceptance criteria are addressed. The valuable lessons learned throughout the process of designing the first tanker to be classed with the DLA notation are also discussed in this paper.