Turbulent Structures And Resistance Characteristics Of Ship In Shallow Water Based On PIV Technology

When the ship sails in the shallow waterway,the movement characteristics of the ship will change greatly with the decrease of the water depth and the draft ratio of the ship.If the resistance increases,the ship velocity drops,the hull sags and the trim,etc.,these phenomena are shallow effect.When the shallow water effect occurs,the process of water flow on the ship is quite complex,is the classic shipping problem,but has not been clear its impact mechanism.At present,the fine study of the flow structure has achieved some results,but the progress is relatively slow,few studies involving shallow water navigation.And the southwest water transport mainly rely on the upper reaches of the mountain river section,there are shallow water,upstream difficulties,often caused by the resulting water traffic accidents,shallow water effects become one of the obstacles to the vigorous development of shipping.It is of great practical and theoretical significance to study the structure and resistance characteristics of shallow water bottom.Based on the high frequency PIV velocity measurement system,the flow field of the shallow bottom of the ship is sampled.The velocity of the flow field is obtained by image processing.The time and transient analysis of the flow field are carried out.The characteristics of the shallow water flow structure are obtained,and the theoretical analysis is deduced Out of the resistance level formula,calculate the impact of the flow structure on the resistance characteristics,the main results are:1)The time-averaged treatment of the test data is obtained,and the vertical flow velocity and the Reynolds stress distribution of the shallow water bottom are in accordance with the trend of uniform turbulence in the open channel,but deviated from the flow velocity gradient in the ship model boundary,which constitutes the main resistance contribution The bottom of the tank and the boundary of the ship and the turbulence of the stern flow are extremely high.2)Based on the instantaneous flow field analysis,the pulsating flow velocity in the shallow waters of the shallow waters is fluctuating at all times.According to the quadratic zoning of pulsating velocity,Q2 and Q4 structures,especially Q4,are obtained,which play a dominant role in shallow water flow field.Q4 structure from thefree surface of the open channel into the bottom of the ship to return to the open channel the whole process,experienced extrusion extrusion and then rise in the process of dramatic changes in the stern.3)shallow waters of the bottom of the water flow in different forms of vortex structure.According to the shape of a circular vortex,oval vortex,ribbon vortex and irregular vortex;by location in the ship to the bottom of the tank are distributed in the upper and lower;according to the direction of rotation clockwise rotation vortex and counterclockwise rotation vortex;According to the direction of inclination of the horizontal vortex,a three-quadrant vortex and four quadrant vortex.4)Hairpin vortex is prevalent in the flow field,the main reason is the formation of different isokinetic fluid mass between the movement,the formation of a strong flow velocity shear surface to form a vortex;water depth mainly affects the width of the vortex,draft more Small,the greater the vortex probability of the whole field,and the flow rate mainly affects the position distribution of the vortex belt,Fu Ruode number is too small,the small probability area is lower.5)On the basis of the theory of plate boundary layer,the formula of the tank flow rate is introduced,and the formula of resistance level for local transient is deduced:After calculating the formula,the resistance is pulsating characteristic in time series,high level resistance and low level resistance Alternately appear,draft than the small and deep water Ru Rude large number of high-level resistance to the majority of the bad voyage.