Research On Influence Of New Bow On Ship Hydrodynamic Characteristics And Motion Response

As an important platform for marine operations,warships must have excellent rapidity,maneuverability and seakeeping,which are directly related to the vitality and combat effectiveness of ships.It is a very important combat technical index of modern ships.As the most important comprehensive navigation performance of the ship in waves,rapidity and seakeeping should be paid enough attention in the ship design process.Therefore,how to improve the rapidity and seakeeping of ships in the current ship design segment is an urgent technical problem.Due to the influence of waves,sea breeze and ocean current and so on,ships will inevitably produce various adverse effects such as roll,pitch,heave and added resistance of ship in waves when sailing on the sea.Violent swaying has a great influence on the navigability,safety,normal operation of the equipment and the comfort of the crew.The mechanism of resistance reduction and anti rolling of ships in waves is urgently needed.In this paper,based on the RANS equation of viscous flow theory,coupled with the equation of ship motion,the numerical prediction of resistance performance of different ship models in sill water and the environmental load and motion response characteristics of different ship models under the high speed in regular waves are carried out.The resistance performance and seakeeping performance of three types of bows(inverted type V bow,KCS type bow and raked bow)are discussed,and the advantages and disadvantages of the three kinds of bows are analyzed respectively,then choose the bow type with better resistance performance and better seakeeping performance as the parent ship.In order to further improve the ship’s resistance reduction and anti roll ability in waves,based on computational fluid dynamics theory,the remodel design of three different ship bows,including water cutter bow,erect bow and deep V bow,is completed,and the comparison and analysis of the hydrodynamic performance and the motion performance of the modified ship models and the parent ship models are completed,the guiding plan for the ship’s resistance reduction and roll reduction design is given.The main research content are as follows:In this paper,DDG1000 is used as the mother ship.In the premise of changing the shape of the bow only,Solidworks software is used to design the KCS-DDG ship model with the bulb bow and the YZ-DDG ship model with the raked bow.Based on computational fluid dynamics software Fine/Marine,the calculation models of three ship models under different working conditions are established respectively,namely,under the six speed of 0.9m/s,1.2m/s,1.8m/s,2.39m/s,2.99m/s and 3.29m/s,the numerical simulation of the moving process of three different ship models in calm water is carried out,which completed the hull resistance and seakeeping calculation.Through the comparison and analysis of the calculation results,it is found that the inverted V bow is superior to the other two kinds of bows in calm water resistance performance and pitch motion characteristics,which shows that the inverted V bow of DDG1000 has a certain effect of resistance reduction and anti rolling.However,the amplitude of heave is larger than that of the other two kinds of bows,while the heave amplitude of YZ-DDG ship model is the smallest.This paper also focuses on the hydrodynamic performance of three different bow shapes in regular waves.The wave height is 8cm(the actual wave height corresponding to the 5 level sea condition),the wavelength and the ship length ratio are 0.75,1,1.5,2,3,4 and 5,and the speed includs 1.8m/s and 2.99m/s.Based on Fine/Marine,the hydrodynamic calculation under the above calculation conditions is completed.Using Matlab self programming software to process and analyze the calculated data,it is found that under the high speed long wave condition,the resistance at the equilibrium position of DDG1000 is smaller,but the amplitude of the resistance fluctuation is large,as a result the peak resistance is less than KCS-DDG ship model but greater than that of YZ-DDG ship model.Moreover,the heave motion response of DDG1000 is larger than that of the other two,which indicates that the inverted V bow has adverse effect on the heave motion of ship.However,when moving in high speed short wave condition,the bow of DDG1000 ship has an effect of pitching stabilization.While in the case of long wave,this advantage is replaced by the YZ-DDG ship model.Therefore,in summary,the comprehensive performance of the YZ-DDG ship model is the best,and it can make up the disadvantage of the DDG1000 bow.Moreover,the pitch motion response of it is minimal at low and medium speed.On this basis,this paper provides three modification schemes for the parent ship DDG1000.Scheme I makes the front part of the bow extend from the stem directly to the bilge keel below the waterline.In scheme Ⅱ,the front bow is changed to a vertical bow and a ellipsoid appendage is added to the bow area below the waterline.On the basis of scheme Ⅱ,the front end of the bow is changed to the forward leaning bow,which is taken as scheme Ⅲ.The relative calculations of three schemes in calm water and regular waves are completed respectively with the software Fine/Marine.Then the results of the numerical simulation are analyzed and the conclusions are drawn.Under the same calculation condition,resistance in calm water,as well as in regular waves,of scheme Ⅱ is the smallest of all the modification schemes,indicating that the hull resistance performance of scheme Ⅱ is the best.Moreover,heave and pitch amplitude of scheme Ⅱ in regular waves turns out to be less than that of the prototype and the other two modification schemes.It shows that the resistance and seakeeping performance of the scheme Ⅱ is optimal.