Study On The Hull Structural Performance Of The Ladder Tanker

Under the more and more stringent regulations about ships of International Maritime Organization,minimal ballast water ships,aiming at reducing the pollution of ship ballast water to ecological environment,are attracting more and more attention.The ladder tanker is a kind of minimal ballast water ships,for which,due to the unconventional structure form adopted,there are no corresponding specifications and real marine experience to assess its structural strength.Thus,to better assess and design it,it is necessary to study the load and structural performance of the ladder tanker.In this thesis,a comparison method between a ladder tanker and a conventional one with the same loading capacity is adopted based on available specifications.The structural performance of the ship is investigated through the specification calculation and direct calculation.The main contents of the research are as follow:(1)The wave load on a ladder tanker and a conventional one is predicted by using the Common Structure Rules(CSR)specification,and also by means of direct calculations based on the three-dimensional linear potential theory.The obtained results for regular waves and long-term statistical analysis are compared and analyzed to investigate the wave load characteristics of the ladder tanker and also the applicability of the CSR rules.(2)The overall strength of the ladder tanker is studied with chosen typical transverse sections.Both the longitudinal bending strength and the ultimate strength of the two ships are calculated and compared.Since the ladder tanker has an unconventional bottom structure,the docking strength is also investigated.(3)The yield strength and buckling strength of typical three segments of the ladder tanker and the conventional one are assessed based on the specification and also by a direct calculation method.The results are compared and analyzed to investigate the stress level of the ladder tanker.(4)The fatigue strength is assessed based on the CSR specification.Both the fatigue nominal stress calculation method and the fatigue hot spot stress calculation method are adopted to calculate the fatigue strength of longitudinals of typical cross sections and the local structure around the hot spots.The fatigue strength of the ladder tanker is discussed through a comparative analysis.(5)Based on the research of the hull structural properties of a ladder tanker,a weight analysis of typical segments is carried out and compared with a conventional tanker to analyze the economic performance of the ladder tanker on the condition of sufficient structure strength.