A procedure to assess the crashworthiness of a LNG tanker side structure
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School of Engineering |
Master's thesis
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Date
2010
Department
Major/Subject
Laivanrakennusoppi
Mcode
Kul-24
Degree programme
Language
en
Pages
67 s. + liitt.
Series
Abstract
Ship collisions and groundings are one of the greatest operational risks in maritime transportation. Yet, accidental loading due to the collision and grounding is still superficially treated by the classification societies as they have enforced little generally accepted collision and grounding design standards. These standards are currently based on design objectives, for example, oil outflow standards or survivability standards and none of them are universally accepted. However, approval procedure presented by Germanischer Lloyd (GL) aims to improve ship side structures through novel crashworthy structural arrangements. Therefore, this thesis outlines a procedure to obtain an optimized crashworthy conceptual side structure and as a case study this procedure is applied to a liquefied natural gas (LNG) tanker. Furthermore, the widely unknown crashworthiness of the LNG tanker is assessed considering the deformation restrictions of the containment system. A particle swarm optimization algorithm is utilized for the optimization of LNG tanker side structure. The classification society compliance of the conceptual design is checked through one characteristic service loading condition that is applied to the ship's hull girder. The collision simulations to assess the crashworthiness are carried out with the non-linear finite element solver LS-DYNA. An element length-dependent constant strain failure criterion is chosen to simulate possible rupture. As a result, one optimized conceptual side structure is compared with the initial rule-based concept and with the minimum weight concept. Thereby the influence of the structural concepts and the containment system restrictions on the crashworthiness is assessed and presented. It is shown that mass of the structure can be decreased while increasing the E/M ratio. Furthermore, modest increase in mass will result in considerable increase in collision energy. Therefore, this procedure considers accidental loading in the conceptual design stage and results with novel lighter structure absorbing more collision energy.Description
Supervisor
Varsta, PetriThesis advisor
Ehlers, SörenTabri, Kristjan
Naar, Hendrik
Keywords
accidental loading, LNG tanker, collision simulations, crashworthiness, optimization, strain and stress relation