Catalin Toderan

Least cost optimization of large passenger vessels

Abstract The LBR-5 software allows optimizing ship structures according to objectives of higher inertia, less weight and/or lower cost. This last criterion offers the choice between two approaches of calculation. The first approach is based on a simplified assessment of the cost in which the total cost is described by rather simple analytical functions which bring into play on the one hand the design variables and on the other hand empirical parameters. In the second approach, the calculation of the cost is based on data specific to the shipyard. The material cost is analyzed according to the first approach while the cost of the labor considers each relevant operation of the ship building with respect to the LBR-5 model. A survey of all the tasks was carried out at Aker Yards France, and a thorough study made it possible to develop assessment tools of the labor cost for each operation as functions of the design variables. Plate straightening operations are also considered in this analysis. This paper presents a cost-based optimization study carried out on a large passenger ship structure with more than 600 design variables, by the use of the detailed approach for the cost calculation. The structural model has been formulated on the basis of technical documentation prepared by Aker Yards France. The loads and strength criteria applied on the model are considered according to classification society rules (Bureau Veritas). Results and conclusions of the study are presented.

Floating LNG: New Rule Note for the Classification of LNG FPSO

Offshore LNG terminals are today broadly considered by the industry to respond to the world thirst of energy in a rapid and efficient manner. In order to match these technical developments, Bureau Veritas has completed, in May 2009, the first phase of a rule development project for the classification of floating offshore gas terminals. Combining BVs experience with the classification of liquefied gas carriers and FPSOs, this resulting guidance note provides requirements for structural safety and cargo containment system assessment. These requirements are applicable for offshore units including LNG FPSOs, FSRUs, gas production units or FSOs. In September 2010, BV has completed this guidance note with specific requirements for stability, electrical installations, safety and offloading of offshore LNG terminals. The paper will describe the work and conclusions of this guidance note and focus on the 2 main challenges faced during the work: On one hand culture differences between shipping, gas and offshore industries. Although modern design techniques are largely using sophisticated numerical calculation tools for both ships and offshore units, there is still a notable cultural difference between the shipping and the offshore industries in the fact that the design of offshore platforms has historically been inclined to be quite based on first principles and direct risk analyses as opposed to ships, the design of which integrates, to a large extent, the return of experience in service in a more empirical way. On the other hand, the difficulty to built standards for a new technology. Despite the long experience in gas transportation at sea and in offshore units, LNG FPSO projects need to identify the risk induced by transferring new technologies from shipping or from onshore industry to offshore floating gas project. The difficulties encountered will be illustrated with practical examples. For full text of this paper, please go to : http://www.spe.org

Ultimate Strength of Stiffened Panels Assessment Taking Into Account Model Uncertainty

This paper presents a methodology to take into account model uncertainties related to the load-end shortening curve of stiffened panels. This method is a part of a research activity carried out at University of Liege. His goal is to propose a reliability based model to assess hull girder ultimate strength using a progressive collapse algorithm. The numerical results presented here concern the load-shortening model chosen for this research, which is based on Bureau Veritas rules. Model uncertainty is quantified as a parameter considered as a random variable. Four statistical moments (mean, standard deviation, skewness and kurtosis) of this parameter are calculated and analyzed using a data-base of stiffened panels test results published in recent years. In order to increase the number of “actual” values for the statistical assessment, the data-base is completed with non-linear finite element analysis results. The paper contains also some recommendation for the implementation of the proposed method in ultimate strength reliability based analysis.Copyright