Amirouche Amrane

ASSESSMENT OF FATIGUE RELIABILITY FOR JACKET-TYPE OFFSHORE PLATFORMS CONSIDERING DYNAMIC BEHAVOIR

In order to traditionally investigate the strength of marine structures, the structure is subjected to a maximum static load. However, the marine structures are usually sufferin g environmental forces varying with time. Wave forces are the most important time dependent loading that causes f atigue in structural elements and joints. In this paper diffe rent methods base on S-N curve and linear elastic failure mechan ics are presented. The governing equations and theories tha t are used in each method are expressed and the application of ea ch method will be discussed. The two main methods of deterministic analyses are: stress- based approach (S-N curve approach) and linear elas tic fracture mechanics (LEFM) approaches. These approaches are applicable to different analyzing strategies, ie th e first approach is used for cases in which general form of fatigue is dominant, but the latter involves the calculations of reliabi lity as functions of crack geometry and its boundary conditions. The SPD12C jacket platform is also modeled as a case study and the results of fatigue reliability analys is are presented. In this paper a comprehensive method is presented t o accurately predict the reliability of offshore plat forms. This method is based on S-N curve and the results are co mpared with the fatigue life of joints. Due to nonlinear interaction of soil and piles and the other affecting parameters such as flexibility of joints, non Gaussian procedure of loading, and nonlinearity of reaction force, the precise analyzing of stress levels will be impossib le and a complex numerical analysis could only give limited information about the statistical properties of stress. In orde r to perform the fatigue analysis and predicting the cycles of stres s SACS was used which is known as a powerful software in desig ning and analyzing offshore structures. In this paper the whole structure was modeled subje cted to different forces such as wave and sea currents. The effects of parameters such as marine growth and interaction of soil and piles are also included. The latter is shown to hav e a significant effect on determination of fatigue life of the plat form.

Estimation of Welding Distortions and Straightening Workload Through a Data Mining Analysis

This paper will present a way to minimize cost in the shipbuilding industry by using the results of a data mining analysis aiming to improve the cost knowledge of the straightening process. This statistical analysis was based on production data from a shipyard and has the scope to establish an assessment formula of the straightening workload. An intermediate step of the analysis was to estimate the welding distortions appearing in stiffened panels. Those generated formulas are useful to improve the research in the following domains: production simulation, cost assessment of ship hull, structure optimization, design for production, etc.