Experimental Study On The Effect Of Ships On Flow Characteristics In Open Channel

In recent years,the navigation capacity of the Yangtze River has been greatly improved,and the shipping volume has also increased sharply.As a result,the ships berthing in the main line of the Yangtze River are increasing day by day,and the ship type is increasing day by day.As a result,the influence of large ships on the river flow and sediment movement is getting higher and higher,and the influence on the local riverbed and the nearby river trend is also increasing.At present,China does not pay much attention to changes in river flow motion caused by ships,and there are few relevant research results.Therefore,it is urgent to carry out experimental studies on the influence of ships on open channel flow motion,master the changes in water flow characteristics around ships(groups),and provide theoretical basis and scientific and technological support for the construction,operation and management of anchorage,wharf and port.Firstly,by collecting and sorting out the domestic and foreign research results on the influence of ships on river flow movement,and summarized them;Then,by carrying out the flume model test,the water depth and flow field along the front and back of a single ship(group)were measured by using the water level needle and PIV(Particle image velocity measurement system)under the condition of different draft depths and parallel and tandem of two ships at different distances.Finally,based on the measured data,the influences of ships on water depth,flow field,vertical velocity distribution and vorticity are analyzed.The main conclusions are as follows:(1)With a single ship:the water depth and flow field around the ship were measured without the ship and at 5 different draught depths: the presence of a ship causes a slight increase in water depth in front of the ship and a slight decrease in water depth behind the ship.The influence of a ship on water depth increases with the increase in draft depth.The maximum and minimum water depth both reach the extreme value when the draft depth is h,which can be 1.071 and 0.951 times of the water depth without a ship.Among the various working conditions,ship along the longitudinal vertical velocity distribution on the profile is: from the bow before to ship at the bottom of the "J" type "(?)" model transformation,the stern after returning to "J" type.There will be a submersible current at the bow and an upwelling at the stern.When the draft depth of a ship is 0.6h,the longitudinal and vertical velocity reaches the maximum.Vertically,the maximum velocity reaches 2.11 times of the average velocity without ship;vertically,the velocity of submerged current and ascending current reaches 0.71 and 0.29 times of the average velocity without ship.Moreover,the existence of ships changes the boundary conditions of water flow,thus affecting the direction of water flow,resulting in vortices in the bow and behind the ship.(2)When two ships are side by side:the water depth and flow field around the ship were measured when the distance between two ships was b,2b and 3b(the draught depth was 0.6 h):the variation of water depth is similar to that of a single ship.The influence of ships on water depth decreases with the increase of the distance between two ships.Both the maximum and minimum water depth reach the extreme value when the draft depth is b,which can reach 1.070 and 0.959 times of the water depth without ship.The distribution law of vertical velocity along the longitudinal profile in the middle of a ship is similar to that in the case of a single ship.The maximum velocity increases further due to the parallel of two ships.When the spacing is b,both vertical velocity and vertical velocity reach the maximum.The underwater current and the updraft current are 0.71 and0.24 times the average velocity without a boat,and whirlpool also occurs in the bow and stern.(3)When two ships are in tandem: The water depth and flow field around the ship were measured when the distance between two ships was 1/3l,2/3l and l(the draught depth was 0.6 h):The variation of water depth in front of and behind the forward ship is similar to that in front of and behind the single ship.Between the two ships,the water depth gradually recovers from below normal water depth in the forward stern to the water depth without a ship,and then it is higher than the normal water depth in front of the aft ship.The maximum and minimum water depth reach the extreme value when the distance is 1/3l,which are 1.051 and 0.967 times of the water depth without a ship,respectively.The variation of velocity along the vertical line is similar to that of two single ships,but the variation of flow field between two ships is affected by the distance between ships.Vertical flow rates were found in front of the forward ship,between the two ships,and behind the astern ship.Vertically: the maximum flow velocity is 2.48 times of the average flow velocity without a boat;vertically: the flow velocity of the submerged current and rising current is 0.73 times and 0.36 times of the average flow velocity without a boat;whirlpool will appear in the fore bow,between the two boats and after the stern.