Research On Resistance Performance And Hull Form Optimization Of CNG Carrier

Considering that the International Maritime Organization has launched the Energy Efficiency Design Index(EEDI)and the Energy Efficiency Operating Indicator(EEOI),it limits the energy efficiency of the ship in legal form.However,the average energy consumption of China's ships is generally higher,how to effectively improve the energy efficiency of ships has become an urgent problem.The purpose of this paper is to improve the speed and seakeep performance of the ship.It is mainly combined with hull geometric deformation technique,high-precision CFD(Computational Fluid Dynamics)numerical prediction technique,approximate model technique and optimization technique,the multi-objective optimization design of CNG(Compressed Natural Gas)carrier is carried out.A new technical approach to energy saving and emission reduction of ships is explored.The main works of this paper is as follows:1.This paper focuses on the hull geometric deformation technique,fundamental principles and deformation rules of free-from deformation technique is elaborated,the NFFD(NURBS-Based Free-From Deformation)deformation technique is established based on the non-uniform rational B-spline basis function,which is suitable for the hull geometric and combined with the non-uniform control mesh.Finally,taking CNG carrier as an example,automatically geometric deformation of bulbous bow,ship bow and stern is achieved.2.The viscous flow CFD technique was used to study the numerical prediction methods of hydrostatic resistance and wake field.The influence of meshing,prismatic layer mesh and turbulence model on resistance prediction is discussed.The related model tests were carried out,the reliability of the numerical calculation method is verified by comparing the calculated results with the experimental data.3.The numerical prediction method of the added resistance and motion of the ship in regular waves is studied.A numerical wave-generating method is used to simulate wave velocity in the tank entrance,wave-forcing technique is applied to dissipating waves,the wave generation and propagation is successfully simulated in 3D numerical wave tank.The motion response of ship in waves are calculated based on overset mesh method,finally,the numerical simulation of CNG carrier sailing in waves is carried out.4.In this paper,a multi-objective optimization design is adopted for a CNG carrier.The design of experiment,Kriging approximate model and NFFD method are used to construct a hull optimization design framework based on the high-precision CFD technique.Taking the five indicators of ship's propulsion performance and sea-keeping performance as the objective functions,and a better Pareto solution is obtained by using multi-objective genetic algorithm NSGA-II.Finally,a reasonable sequence is provided by using AHP method and TOPSIS method,and the ship with the best comprehensive performance is obtained.