Research On Hull Design And Hydrodynamic Performance Of Sea Surface Unmanned Vehicle

The marine environment is complex and changeable,and USV is prone to various adverse effects such as heave,pitch,roll and add resistance in complex sea conditions.These adverse factors will directly lead to low operational efficiency and poor security of unmanned craft.Therefore,it is of great significance to design and develop a new type of USV with excellent wave resistance in complex sea conditions.In this thesis,a single ship with simple structure is selected as the research foundation.A new hull with excellent seakeeping performance is designed by the hull form.The CFD software STAR-CCM+is used to numerically study the hydrodynamic performance of the unmanned ship under different working conditions.The main contents and conclusions of this thesis are as follows:(1)Based on the Wigley hull,the numerical simulation research in still water and waves was carried out.The grid density is used for uncertainty analysis,and the influence of different grid sizes on the numerical results is discussed.Finally,a better grid setting method is obtained,which lays a good foundation for the following sea-keeping calculation.(2)The effects of different wave conditions and different speeds on the motion response and wave add resistance of X-bow unmanned boat when it sails in the sea.Rhino modeling software and Auto-CAD are used to model the hull,and DFBI is used to release heave and pitch degrees of freedom.The hydrodynamic performance of X-bow unmanned boat under different wave heights and wavelengths is mainly studied.(3)Based on the X-bow unmanned boat,the wave-piercing bow hull with different bow angles was modified,and the effects of four bow angles on the advantages and disadvantages of the unmanned boat sailing in regular waves under high sea conditions were studied.A comprehensive comparative analysis of heave,pitch motion response and wave drag enhancement of different boat types is made at wave height(H=0.12m),different wavelengths and different speeds.(4)Based on the ’XW1’ unmanned boat with better comprehensive seakeeping performance,the seakeeping performance under several typical wave direction angles is studied at zero speed.The wave resistance of the hull in oblique waves under three degrees of freedom motion is preliminarily discussed.Specifically,the motion performance of the USV under the condition of free heave,roll and sway under the condition of rolling wave is studied,and the numerical study on the motion performance of the USV under the condition of releasing heave,roll and pitch under oblique waves.It is found that the ’XW1’ unmanned boat with the first column angle of 115° has better sea-keeping under the condition of seaward navigation.At the same time,the heave,pitch and wave drag increase of X-bow unmanned boat and ’XW1’ unmanned boat under different wavelength and different speed conditions at wave height H=0.04(m),H=0.08(m)and H=0.12(m)are compared and analyzed.It is found that X-bow unmanned boat is more suitable for sea condition at wave height H=0.04(m),while ’XW1’unmanned boat is suitable for sea condition at wave height H=0.12(m).Under the condition of beam wave,when the wavelength is small,the sway distance is far.With the increase of wavelength,the swaying distance decreases gradually.In a certain wavelength range,the heave motion of the hull is greatly affected by the wavelength.When the wave angle is less than 90°,the rolling motion of the hull increases,while when the wave angle is greater than 90°,the rolling motion of the hull decreases.The rolling motion of the hull is greatly affected by the natural frequency of the rolling when it is in the sea(β=180° and β=0°).When the wave direction angles are β=0° and β=180°,the pitch motion of the hull is greatly affected by the wave.When the wave direction angles are β=45° and β=135°,the pitch motion of the hull is also greatly affected by the low-frequency component,and the low-frequency component under the condition of large wavelength decreases,especially under the condition of bow oblique wave(β=45°),the influence of low-frequency component is slightly smaller than that of wave frequency on hull pitch motion.