| A revolution about green ship is processed in the world as the International Maritime Organization (IMO) proposed a series of new criteria for ship energy saving. The most important case that ship energy saving concerns is the resistance, which is consisted of wave resistance and viscous resistance. For a given speed of the ship, the viscous resistance is proportional to the wetted surface area which is generally not very sensitive to the small change of ship lines and float condition, In contrast, in a certain range of Froude number, wave resistance is quite sensitive to the two factors. Some small modification of any of the two factors may lead to great improvement in ship wave resistance. Therefore, this paper attempts to propose some new ideas for the ship drag reducing and energy saving by optimizing hull lines, modifying trim condition and body designing with giving pressure distribution.The first part of the present study aimes at that calculation of node potential in flow around body always causes large errors. With inner angle of nodes taken into account, a coefficient δ is intrduced to slove the problem. Comparisons of annalitic results and numerical results of sphere nodes are presented and calculation results with consideration of inner angle show more accuracy than that without inner angle.In the second part of present study, a kind of quadratic curve is use to generate a certain hull of the minimum wetted surface. An optimization algorithm is used to modify cross section of the hull and Michell integral is applied to solve the wave resistance in the optimization procedure. Numerical calculation and comparative experiments for the modified DTMB5415hull model are conducted to access the availability of the method.Trim operation is studied as a new method for ship energy saving in the third part of the research. One of most noticeable characters of the trim operation is that the resistance of ship could get obvious improvement with out any modification to hull lines. The Dawson method and a type of direct panel method for a boundary-value problem with the free surface are proposed to predict ship wave resistance under different trim conditions based on Rankine source. The free surface boundary condition is linearized with respect to the oncoming flow, and computed by a four-point finite difference scheme. Sample computations for Wigley hull and Series60are carried out to demonstrate the effectiveness and the robustness of the methods. A hull model is taken into account at two different displacements with respect to trim conditions of lower wave resistance. It is demonstrated by calculation and experiment that the wave resistance under the trim conditions provided by the proposed methods is lower than that under the initial conditions.Body design with certain pressure distribution is researched in the forth part of the study. The wave-making theory for ship can be used to solve the problem of hydrodynamics performance prediction and wave resistance often is calculated by integration along the body surface. Researchers may do some modification to the calculated pressure distribution while the wave resistance is not so satisfactory. How to find a body surface corresponding to the modified pressure distribution is one of the major issues studied in the paper. A type of direct panel method is use to calculate Rankine source intensity, which is applied to compute the geometry modification of current body. An equation of velocity potential and geometry modification is created, and an iterative algorithm is use to solve the equation. Design sample of ellipse, circle and wing section is conducted to verify two dimensional design procedures while sphere and ellipsoid design is applied for three-dimensional verification. Finally, the method is use to design the Wigley hull with known pressure distribution along the body surface. |
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