Mihkel Kõrgesaar

An Assessment Procedure of the Crashworthiness of an LNG Tanker Side Structure

Abstract In this paper a procedure is presented for the conceptual design of a crashworthy side structure of a liquefied natural gas (LNG) tanker. The crashworthiness of an LNG tanker is assessed taking into account the deformation restrictions of the containment system. A particle swarm algorithm is used for the structure optimisation. The classification society compliance of the conceptual design is checked for a characteristic service loading condition. Collision simulations are carried out with a non-linear finite element solver in order to assess crashworthiness. An element length-dependent constant strain failure criterion is used to model possible rupture. The resulting optimised conceptual side structure is compared with the initial rules-based concept and with a minimum weight concept, demonstrating the influence of the structural concepts and the containment system restrictions on the crashworthiness.

Collision Consequence Assessment of ROPAX Vessels Operating in the Baltic Sea

A Ship collision accident represents a daily threat for vessels operating in dense traffic zones. The collision consequences may include loss of life or severe injuries if passengers are on board. The latter would be the case for ROPAX vessels, which are fairly dominant in the Baltic Sea connecting various member states. Furthermore, their routes tend to be in cross-traffic with the cargo vessels travelling through the full extent of the Baltic Sea. Therefore, it is of utmost importance to be able to assess the collision consequences for ROPAX vessels operating in the Baltic Sea with sufficient accuracy. This will result in an overview of possible damage scenarios for the actual traffic situation at a given location. As an example location the dense cross traffic between Helsinki and Tallinn will be analyzed and discussed.The analysis procedure combines three steps: (1) determination of possible accidental scenarios based on traffic statistics; (2) assessment of the structural resistance of the colliding ship and (3) the evaluation of selected accidental scenarios using a time-efficient semi-analytical approach. The level of structural resistance of the chosen ships is assessed in a quasi-static manner using finite element method. This information is the basis for the calibration of a semi-analytical collision simulation model used to simulate large number of the accidental scenarios typical to the selected location. The presented results will be limited to the initial choice between vessels and dimensions, respectively masses, but the procedure can easily be extended to cover a vast amount of colliding vessels. However, the actual collision risk can be obtained using the presented results if the traffic along the vessels route is known.Copyright