Describes a study that focused on addressing the conceptual issues related to classifying and analyzing uncertainties in loads on offshore structures, and on developing a sound and practical methodology for uncertainty analysis. Uncertainties are classified with respect to source: basic uncertainty regarding physical parameters affecting the design load, model uncertainty regarding the calculations used to estimate physical parameters, and distribution uncertainty regarding probability distributions used to model random quantities. A generalized load model that incorporates all uncertainties is described and applied to wave loads on the Hibernia offshore structure. Effects of individual and combined uncertainties on calculated design loads are analyzed and the implications for design code development are discussed.

Describes a study conducted to further develop and test a previously developed methodology for characterization and modelling of uncertainties in the determination of loads on offshore structures. Tasks carried out in the study include a finalization of the methodology; an investigation of the sensitivity of the 100-year load effect with respect to the distribution types used to model uncertain parameters, the degree of non-linearity of the load effect model, and the probabilistic characterization of model uncertainty as fixed or variable in time; and development of design load factors leading to a specified target reliability level for a range of parameters. On the basis of the results, recommendations are developed regarding design code implementation for offshore structures.

Dynamic Analysis of Offshore Structures appraises offshore structures, particularly the major sources of uncertainty in the design process. The book explains the fundamentals of probabilistic processes, the theory or analysis of sea states, and the random-vibration approach to structural response. The text describes the hydrodynamics of water waves, wave forecasting, and the statistical parameters associated with sea-states. The investigator can use Morison's equation to calculate the impact of wave forces acting on slender members such as on lattice-type structures. Or he can employ the diffraction theory to calculate wave forces acting on large-diameter bodies such as concrete gravity-type structures. Other environmental forces he should be concerned with are the effects of currents and winds. The book examines the theory of vibration (including the spectral approach), the theory of vibration on multi-degree-of-freedom structures, matrix analysis of structural response, problems of fatigue, and soil-structure interaction. The book notes the importance of the method of analysis used, with emphasis on the following: dynamic analysis, frequency domain, and linearization of drag. Two types of analysis follow linearization of drag: deterministic analysis (applied in a series of design waves which uses the long-term exceedance diagram for fatigue); or probabilistic analysis (used to study the behavior of the structure during the extreme design storm and its long term behavior for a range of sea states). The book can prove useful for structural, civil, or maritime engineers, as well as for students in one-year courses in offshore structure analysis at the postgraduate or final-year undergraduate level.

and Literature Rev iew Chapter 1 1. INTRODUCTION AND LITERATURE REVIEW The exploration for oil and gas in ever increasing water depths has given an impetus to research efforts on the behaviour of offshore structures under ocean environment. These structures are continuously subjected to environmental loading because of waves, wind and current. A response analysis is required to assess the safety of offshore structure under severe storm conditions as well as for estimation of damage caused by less severe but more frequently occuring sea states. A majority of the reported failures in the life time of offshore structures are in fact fatigue failures. The offshore structures are usually built in the form of welded tubular structures. The joints of these tubular members experience the fatigue damage mainly due to small defects in welding which act as crack initiators, high stress concentrations and the variable loads. The variable loads due to the ocean waves cause cyclic stress variation in the structural members and the accumu lated effect of these stresses results in the fatigue failure.