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Assessment of structural requirements related to LNG fuel tanks
Norwegian University of Science and Technology, Faculty of Engineering Science and Technology, Department of Marine Technology.
2013 (English)MasteroppgaveStudent thesis
Abstract [en]

This thesis considers collision between ships, and the structural resistance of the struck ship with the aim to minimize the indentation into the ship side. First it gives a background in ship collision analysis, different techniques are discussed, and emphasis is given to the decoupling of the ship collision problem. Secondly it assesses the rules that come into account when introducing LNG fuel tanks in a cargo ship, rules regarding modelling of ship structures as well as expected rule development. An introduction to the existing methods for estimation of energy involved in ship collisions is given. The different structural components of a ship section are discussed, and applicable analytical formulae as well as an analytical method for determining the force indentation curves for a full ship section are reviewed. Special structural elements of core type are briefly discussed. A parametrical model of a ship side section capable of modelling different configurations for the structural layout is developed. This model is used for collision analysis by means of LS-DYNA, where displacement controlled impact with a rigid and simple cone shape indenter is driven into the side section at a right angle. The simulations are uncoupled. They are verified by means of convergence and sensitivity testing. Variables which should be given close attention enclose failure strain of the material and the static friction coefficient. The model is compared to analytical solutions, showing agreement to a certain degree. For comparative studies the model is given confidence. The model is used for a comparative study where the aim is to assess the reduction in safe distance for a gas tank, by taking into account the effect of ice strengthening. In this case study it is concluded that the fuel tanks could be moved 1.37 metres or 1.45 metres closer to the ship side for two different implementations of ice class. Structural parameters are studied. The main conclusions are that an increase of the outer skin thickness or the introduction of an extra stringer gives good results. For concurrent increase the thicknesses in webframes, stringers and outer skin give good results. A comparison table is developed, and a comparison ratio is presented for each parametrical variation. It is noted that the ice strengthened design gives promising comparison ratios. This study has been carried out by variation over the whole height of the section and ?individualization? of the variables over the height might lead to improved results.

Place, publisher, year, edition, pages
Institutt for marin teknikk , 2013. , 142 p.
URN: urn:nbn:no:ntnu:diva-22343Local ID: ntnudaim:8782OAI: diva2:649586
Available from: 2013-09-19 Created: 2013-09-19 Last updated: 2013-09-19Bibliographically approved

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