Study On Resistance Performance Of Vessels With Notches

Working ship is a kind of specialized ship for water and underwater engineering. Owing to the special working characteristics and operation requirements, working ship always has large specific installations. In order to layout and operate these equipments, corresponding notches are set in the hull. These notches run through the hull from deck to bottom, and intersect with the water plane forming a large opening, which makes working ship's resistance performance dramatically different from the normal transport ship.At the early stage the working sites of working ships were limited to rivers and coastal waters, and most of them were not self-propelled. These days, with the continuous development of marine industry and globalization of markets, working ships are required to be of larger scale, specialization and to be able to fulfill more long-distance offshore tasks. As a consequence, more and more large self-propelled working ships are introduced into the market. Furthermore because of resource shortage, how to improve the work efficiency and reduce the energy consumption has become a common research topic in all fields. Under this background, the studies on the resistance performance of the vessel with notches begin to get more and more attentions.The researches on resistance performance of special ship were usually based on model tests before. And nowadays along with the development of computer science, CFD (Computational Fluid Dynamics) tools have been widely used in ship design and experiment. Compared with the traditional model experiment, CFD is of low-cost, free from limit of contact point and accuracy, convenient for drawing detailed flow field, etc. CFD can also simulate complex phenomenon which is difficult to actualize in towing tank. So, as an effective complement to model test CFD tools play an increasingly important role in studying on ship performance and design optimization.The resistance performance of the vessel with notches is in-depth studied using a large self-propelled cutter suction dredger by experiments and CFD calculation method in this dissertation. It mainly investigates the following contents:1. Study on the resistance performance of the vessel with notches by experiment. A series of model tests of a large self-propelled cutter suction dredger were performed in the towing tank of the Shanghai Jiao Tong University in respect to a large self-propelled cutter suction dredger, and the resistances of the ship in different speeds in normal condition, with notch in bow and with notches both in bow and stern were measured. Based on analysis to the experimental data the impact of the notches in hull on ship resistance and the change of the ship total resistance caused by the different locations of notches are obtained.2. Research on the resistance performance of the vessel with notches by computational fluid dynamics. The large self-propelled cutter suction dredger models tests are simulated based on the computational fluid dynamics tools, and the hull resistances and free wave surfaces in corresponding experimental conditions are obtained. The CFD calculated wave contours around ship hull show that the notches in bow and stern form new pressure points on the basis of the original wave system. The waves around ship hull are changed; as a result, the wave-making resistance is changed. By the comparison of the experimental data and the CFD calculation results, the reliability of the CFD tools in the study of resistance performance of the vessel with notches is proved. It provides the basis for the following research and the new idea and method for the study of resistance performance of the vessel with notches.3. Effect of the size of notches in hull on ship resistance performance. The variation of the ship resistance with the changes of notch size in bow in longitudinal and transverse direction, notch size in stern in longitudinal and transverse direction and the interaction of the notches in bow and stern is studied based on CFD method by numerically simulating the viscous flow around a series of large self-propelled cutter suction dredger models. The calculation results show that the effect of the notch in bow on ship resistance is much more obvious than the same size notch in stern and the added resistance caused by the notch in bow accounts for the main components in the total added resistance of the vessel with notches both in bow and stern. So how to reduce the resistance caused by the notch in bow is the key to improve the resistance performance of ship with notches. The resistance caused by notch in bow and notch in stern can be considered independent of each other in ship with notches both in bow and stern. Thus the resistance of the ship with notches both in bow and stern can be estimated by simple formula in engineering.4. Effect of the shape of notch in bow on ship resistance performance. Taking rectangular notch running through the hull from deck to bottom in bow with certain size in longitudinal and transverse direction as the basic model, different shapes of notches in bow are obtained by changing the forms of the notches on x-y, y-z and z-x cross sections without changing the working performance of the self-propelled cutter suction dredger. The effect of the shape of notch in bow on ship resistance performance is calculated by CFD tools, and the main factors affecting the resistance performance of ship with notch in bow are found by calculation analysis. It provides the basis for the design and optimization of this kind of ships.5. Optimization of the molded lines for an existing ship with notches. Based on the results of the study in this dissertation, an optimization proposal of the molded lines for"Tian Jing Hao"the first jumbo self-propelled cutter suction dredger in China is presented. The resistance performances of the original ship and the improved ship are calculated by CFD tools. The results of the calculation show that the improved ship has lower ship resistance and energy consumption than the original ship. It proves the practical significance of conclusions from the research in this dissertation in modern ship and ocean engineering.