Ship hull form optimization by evolutionary algorithm in order to diminish the drag

This study presents a numerical method for optimizing hull form in calm water with respect to total drag which contains a viscous drag and a wave drag. The ITTC 1957 model-ship correlation line was used to predict frictional drag and the corrected linearized thin-ship theory was employed to estimate the wave drag. The evolution strategy (ES) which is a member of the evolutionary algorithms (EAs) family obtains an optimum hull form by considering some design constraints. Standard Wigley hull is considered as an initial hull in optimization procedures for two test cases and new hull forms were achieved at Froude numbers 0.24, 0.316 and 0.408. In one case the ES technique was ran for the initial hull form, where the main dimensions were fixed and the only variables were the hull offsets. In the other case in addition to hull offsets, the main dimensions were considered as variables that are optimized simultaneously. The numerical results of optimization procedure demonstrate that the optimized hull forms yield a reduction in total drag.     

基于遗传算法的带有调纵倾尾板及拦截器的滑行艇水动力性能评估及优化（英文）

Nowadays, several stern devices are attracting a great deal of attention. The control surface is an effective apparatus for improving the hydrodynamic performance of planing hulls and is considered an important element in the design of planing hulls. Control surfaces produce forces and a pitching moment due to the pressure distribution that they cause, which can be used to change the running state of high-speed marine boats. This work elaborates a new study to evaluate the hydrodynamic performance of a planing boat with a trim tab and an interceptor, and optimizes them by using an optimization algorithm. The trim tab and the interceptor have been used to optimize the running trim and motion control of semi-planing and planing boats at various speeds and sea conditions for many years. In this paper, the usage of trim tab is mathematically verified and experimental equations are utilized to optimize the performance of a planing boat at a specificd trim angle by using an optimization algorithm. The genetic algorithm(GA) is one of the most useful optimizing methods and is used in this study. The planing boat equations were programmed according to Savitsky's equations and then analyzed in the framework of the GA-based optimization for performance improvement of theplaning hull. The optimal design of trim tab and interceptor for planing boat can be considered a multiobjective problem. The input data of GA include different parameters, such as speed, longitudinal center of gravity, and deadrise angle. We can extract the best range of forecasting the planing boat longitudinal center of gravity, the angle of the trim, and the least drag force at the best trim angle of the boat.     

Determining the hydrodynamic forces on a planing hull in steady motion

A combination of methods was developed that can determine hydrodynamic forces on a planing hull in steady motion. Firstly, a potential-based boundary-element method was used to calculate the hydrodynamic pressure, induced resistance and lift. Then the frictional resistance component was determined by the viscous boundary layer theory. Finally, a particular empirical technique was applied, to determine the region of upwash geometry and determine spray resistance. Case studies involving four models of Series 62 planing craft were run. These showed that the suggested method is efficient and capable, with results that are in good agreement with experimental measurements over a wide range of volumetric Froude numbers.     

Optimization of Wigley Hull Form in order to Ensure the Objective Functions of the Seakeeping Performance

The research performed in this paper was carried out to investigate the computational procedure to design seakeeping optimized ship hull form. To reach the optimized hull form, four stages should be done, which consists of： generate alternative hull form, seakeeping calculations, objective functions and optimization techniques. There are many parameters that may be determined in ship hull form optimization. This paper deals with developed strip theory for determining the seakeeping performance, genetic algorithm （GA） as optimization method, high order equations for curve fitting of the hull form and finally reaching to the minimum bow vertical motion in regular head waves. The Wigley hull is selected as an initial hull and carried to be optimized. Two cases are considered. For the first case, the only form coefficients of the hull （CB, CM, Cw, Cp） are changed and main dimensions （L, B, 7） are fixed. In the second case both hull form and main dimensions are varied simultaneously. Finally, optimized hull form and its seakeeping performances are presented. The results of optimization procedure demonstrate that the optimized hull forms yield a reduction in vertical motion and acceleration.     

槽道型高速滑行艇船型的自动生成(英文)

The creation of geometric model of a ship to determine the characteristics of hydrostatic and hydrodynamic, and also for structural design and equipments arrangement are so important in the ship design process. Planning tunnel high speed craft is one of the crafts in which, achievement to their top speed is more important. These crafts with the use of tunnel have the aero-hydrodynamics properties to diminish the resistance, good sea-keeping behavior, reduce slamming and avoid porpoising. Because of the existence of the tunnel, the hull form generation of these crafts is more complex and difficult. In this paper, it has attempted to provide a method based on geometry creation guidelines and with an entry of the least control and hull form adjustment parameters, to generate automatically the hull form of planning tunnel craft. At first, the equations of mathematical model are described and subsequent, three different models generated based on present method are compared and analyzed. Obviously, the generated model has more application in the early stages of design.     

保证耐波性能的目标函数的Wigley船型优化(英文)

The research performed in this paper was carried out to investigate the computational procedure to design seakeeping optimized ship hull form. To reach the optimized hull form, four stages should be done, which consists of: generate alternative hull form, seakeeping calculations, objective functions and optimization techniques. There are many parameters that may be determined in ship hull form optimization. This paper deals with developed strip theory for determining the seakeeping performance, genetic algorithm(GA) as optimization method, high order equations for curve fitting of the hull form and finally reaching to the minimum bow vertical motion in regular head waves. The Wigley hull is selected as an initial hull and carried to be optimized. Two cases are considered. For the first case, the only form coefficients of the hull(C B, C M, C W, C P) are changed and main dimensions(L, B, T) are fixed. In the second case both hull form and main dimensions are varied simultaneously. Finally, optimized hull form and its seakeeping performances are presented. The results of optimization procedure demonstrate that the optimized hull forms yield a reduction in vertical motion and acceleration.     

Numerical analysis of surface piercing propeller in unsteady conditions and cupped effect on ventilation pattern of blade cross-section

The aim of this study is to calculate hydrodynamic performance and ventilation flow around wedge, 2D blade and 3D surface piercing propeller (SPP), using computational fluid dynamic based on Reynolds-averaged Navier–Stokes method. First, numerical analyses for two-phase fluid flow around the wedge and 2D blade section (cupped and non-cupped) are presented. Flow ventilation, pressure distribution and forces are determined and compared with experimental data. Then, the method is extended to predict the hydrodynamic performance of propeller SPP-841B. The propeller exhibits a cupped blade. In the simulated configuration, SPP is one-third submerged (I = h/D = 0.33) and is working at various loadings with full ventilation occurring at low advance coefficient (J). The open water performance, pressure distribution, forces/moments and ventilation pattern on the SPP-841B model are obtained and compared with experimental data. The numerical results are in good agreement with experimental measurements, especially at high advance coefficient.     

滑行艇半浸式螺旋桨的水动力学特性

Demand for high-speed marine vehicles (HSMVs) is high among both commercial and naval users. It is the duty of the marine vessel’s designer to provide a hull and propulsion system that diminishes drag, improves propulsive efficiency, increases safety and improves maneuverability. From the propulsor side, surface piercing propellers (SPPs) should improve performance. Unlike immersed propellers, behavior of the SPP is affected by depth of immersion, Weber number and shaft inclination angle. This paper uses a practical numerical method to predict the hydrodynamic characteristics of an SPP. The critical advance velocity ratio is derived using the Weber number and pitch ratio in the transition mode, then the potential based boundary element method (BEM) is used on the engaged surfaces. Two models of three and six-bladed SPPs (SPP-1 and SPP-2) were selected and some results are shown.