Kaikki Masterit
Mihkel Kõrgesaar | Applied Mechanics | Marine Technology Extended

A Procedure to Assess the Crashworthiness of an LNG Tanker Side Structure

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 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 simple 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. 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 energy per mass 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.
Mihkel Kõrgesaar

Marine Technology

1986, Estonia

+358 46 640 1948