Design of damage tolerant offshore structures

Abstract

A prototype method for including damage tolerance considerations in the design of offshore structures has been developed. We start with a design which has been developed using existing techniques. A finite element analysis is performed and the implied factors of safety of various members are ascertained. Critical members are removed systematically from the structural model and the structural response for each case is determined. The factors of safety are recalculated for each of these crippled conditions. Based on this information the section modulus of each member or a group of members is increased in an optimal manner. This provides alternate load paths to take the redistributed loads and thus augment the damage tolerance of the structure. The redistribution of material in order to obtain the desired factors of safety is achieved by solving a multiple objective, non-linear optimization problem. In the past, multiple objective optimization problems have been solved in the linear domain only, using goal programming techniques. We believe that this is the first application of non-linear goal programming in this field. The method is new and makes an important contribution towards incorporating damage tolerance considerations in the design process.