Ultimate strength

Concern for the ductile behaviour of ships and offshore structures and their structural components under ultimate conditions. Attention shall be given to the influence of fabrication imperfections and in-service damage and degradation on reserve strength

Effect of combined shear stresses on the ultimate axial response of the double bottom of a containership

Ultimate strength of the hull girder of containerships became a significant issue in the last years in view of recent accidents and related investigations. Actually, larger and larger ships were put into service and still are designed and built. Recognizing such an issue, investigations were carried out and led to the issuance of a specific longitudinal strength standard for containerships by the International Association of Classification Societies [1]. Loading conditions become more and more challenging and especially combinations of various actions were found to impair the hull girder ultimate strength. In the attempt to better understand the influence of load combinations onto the ultimate strength of the hull girder, investigations were carried out. In this paper, the effects of the shear is considered using rather refined and accurate finite element models of a typical containership double bottom

Effect of shear stresses onto the hull girder ultimate strength of a containership

When using large models, building a comprehensive finite element (FE) numerical model able to simulate the portion of a containership whose extension in length is sufficient to properly evaluate combined loading effects is rather time consuming, and assigning proper boundary conditions representing the distribution of actual forces and moments on the hull girder is a challenging task. In this paper, the effect of shear stress distribution on the structural components of the hull girder is analyzed. At first, finite element (FE) models simulating a suitable length of the hull girder are considered. Later, smaller models of stiffened panels are extracted from the hull girder models and analyzed. The aim of this work is to investigate the shear stress distribution originating in the entire cross section and to build a smaller model extracted from a selected portion of the ship where hull girder collapse is supposed to initiate

Technical Investigation on Drill Pipe Failure

Scientific drilling vessel Chikyu faced drill pipe failure during offshore commissioning of drilling control and instrumentation system upgrade work. The failure occurred with cyclic bending stress which was enough low to prevent fatigue failure according to S-N curve obtained from full-scale fatigue tests. Material tests and observation of a remaining part of the failed drill pipe, investigation of onboard data observed and measured during the operation, and fatigue analysis based on the material tests data and stress amplitude determined by both the onboard observation and the simulation of drill pipe motion are examined to investigate the cause of the failure. All three examinations provide that the number of cycles of bending stress to fail is in the order of 104. The examinations also provide an evidence of cause of initiating cracks. This study presents the results of examinations and discusses the cause of drill pipe failure by verifying and complementing the results. It finally concludes that micro cracks were initiated owing to heat and stress, then cracks grew with cyclic stress, and it consequently reached to failure owing to the drill pipe motion including Magnus effect

Very large floating structures

Very Large Floating Structure (VLFS) is a unique concept of ocean structures primary because of their unprecedented length, displacement cost and associated hydroelastic response. International Ship and Offshore Structures Congress (ISSC) had paid attention to the emerging novel technology and launched Special Task Committee to investigate the state of the art in the technology. This paper summarizes the activities of the committee. A brief overview of VLFS is given first for readers new to the subject. History, application and uniqueness with regard to engineering implication are presented. The Mobile Offshore Base (MOB) and Mega-Float, which are typical VLFS projects that have been investigated in detail and are aimed to be realized in the near future, are introduced. Uniqueness of VLFS, such as differences in behavior of VLFS from conventional ships and offshore structures, are described. The engineering challenges associated with behavior, design procedure, environment, and the structural analysis of VLFS are introduced. A comparative study of hydroelastic analysis tools that were independently developed for MOB and Mega-Float is made in terms of accuracy of global behavior. The effect of structural modeling on the accuracy of stress analysis is also discussed. VLFS entails innovative design methods and procedure. Development of design criteria and design procedures are described and application of reliability-based approaches are documented and discussed