Consequence analysis for Air cavity design A comparable structural and hydrostatic study between a conventional hull and an Air cavity hull

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Examensarbete för masterexamen
Master Thesis
Program
Publicerad
2015
Författare
Lindbäck, Mathias
Molander, Patrik
Modellbyggare
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This thesis is a comparable study between a conventional tanker hull design and a tanker hull design when introducing the ”Air cavity” bottom structure. The study is initiated by Stena Teknik to investigate the structural and hydrostatic effects. The concept "Air Cavity", were air pockets are introduced in the bottom structure, holds air kept under the hull so the vessel “floats” on cushions of air. The interface between the water and the air provides a lower viscous friction than the interface between water and the hull. Investigating this alternative hull design is an important step for the continuous work to reduce fuel consumption and environmental impact. The objective is to identify and evaluate how the two designs relate to each other with respect to cargo loading properties, steel weight, critical structural areas and intact stability. The hydrodynamic data, from were the resistance reduction is taken, is a separate study and will not be covered in this thesis. The conventional tanker hull have been be modelled to serve as a reference, while the new Air cavity hull design have been modelled from scratch, using the conventional hull as a design platform. The structure of the two designs was evaluated with respect to CSR (Common Structural Rules) as well as with the general stability requirements. A financial indication is done for the two concepts to further understand the impact of an Air cavity design. The Air cavity design complies with the general stability requirements. Structural results indicate an increased steel weight of 6% and reduced cargo volume of 7% for the midship section. A shift in the stress distribution between the two designs is clearly seen and critical areas around the cavities are identified. Based on these indicators the efficiency of the Air cavity system could be estimated. This was done with 15% friction reduction including loss for the air compressors/fans and systems for maintaining the air pressure in the cavity. Air cavity related systems and equipment is roughly estimated and included in the cost breakdown. The bunker savings need to meet the added financial cost, "break-even" is met at bunker reduction of 19%, which equals the frictional reduction 26%.
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Materialvetenskap, Konstruktionsteknik, Materials Science, Construction engineering
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