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Collision Between Platform Deck and Service Vessel Wheelhouse
Norwegian University of Science and Technology, Faculty of Engineering Science and Technology, Department of Marine Technology.
2013 (English)MasteroppgaveStudent thesis
Abstract [en]

Collisions between ships and oshore structures are rarely occurring events, but pose a constant threat to the safety at sea. Observed trends in recent years has show that the size of both oshore structures and servicing vessels is increasing, making it possible for an oshore structure deck or module to pass above the bow and hit the superstructure and bridge of the vessel. An accident like this could have severe consequences. The superstructure of ships is typically considerably less stiened than the sub-merged part of the hull, making the resistance to deformation equally small. Passenger cabins are typically placed in the forward part of the superstructure of ships, and an impact to this part could be a direct cause of fatalities. A secondary eect, if the bridge should be partly or completely destroyed, would be the reduced ability to control the ship. If the vessel was get stuck underneath the platform, it could lead to considerable secondary damage to both the oshore-and ship structure, as well as damage to e.g. a production riser connected to the platform. The external mechanics of collisions may be analyzed by utilizing the principle of conservation of energy and momentum. A moving vessels kinetic energy is dissipated by absorption of strain energy in both the struck and striking structure, as well as viscous damping by the surrounding sea, and transfer of momentum to kinetic translational and rotational energy. The internal mechanics on the other hand are hard to determine accurately with-out detailed and time consuming nite element analyses. Principles behind non-linear nite element analysis is presented, as well as dif-ferent available solution techniques and their benets and disadvantages. In this thesis, collision scenarios for a large oshore service ship superstructure are treated by non-linear nite element analysis. The ship is set to collide with a simplied Ultra Deep-Water semi-submersible drilling rig, and an aluminium living quarter of a jacket platform. A detailed model of the superstructure of a 13 600 metric ton oshore service vessel is modeled. In addition, the hull of the ship is modeled as rigid in or-der to more easily apply global mass properties, as well as restoring forces and moments. Two oshore structure models are created. The semi-submersible is modeled with representative stiening and represented as an equivalent box-girder. The living-quarter is modeled in the likeness of that found on the Kvitebjrn jacket. The LQ is modeled as extruded aluminium proles mounted atop a sti beam lattice. Five collision scenarios are successfully tested. All runs utilize prescribed dis-placement settings. ˆ Ship vs semi-like rigid plate. ˆ Ship vs deformable semi. ˆ Ship vs deformable semi. Bridge impact. ˆ Ship vs living quarter. Vertical wave motion impact. ˆ Ship vs living quarter. Horizontal bridge impact. It was discovered that the wheelhouse has inferior crushing resistance compared to the remaining hull. Great resultant forces are observed in collisions where the semi hits near the forecastle deck due to the large contact area, whereas the upper decks are greatly reduced capacity. In all analyzed load cases, the ship strain energy dominates the energy equilibrium. Results show that strength design can be used as a slightly conservative assumption in most of the analyzed situations.

Place, publisher, year, edition, pages
Institutt for marin teknikk , 2013. , 165 p.
URN: urn:nbn:no:ntnu:diva-21989Local ID: ntnudaim:8887OAI: diva2:646727
Available from: 2013-09-09 Created: 2013-09-09 Last updated: 2013-09-09Bibliographically approved

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