The Hydrodynamic Conditions On Navigation In The Bridge Waterway

Waterway transportation is important in the transportation system with the advantages of low-pollution,large volume and low-cost.With the increasing number of river-crossing bridges,the increasingly large-scale ships and the increasingly busy waterway transportation,the complex flow in the waterway bridge section increases the risk of pier collision,which causes huge loss of life and property.Based on the theory of 3D N-S equations,this paper explores the 3D characteristics of flow in bridge waterway.Combining level set method,ghost cell immersed boundary method and solving 6DOF equations,the moving ship model is constructed to analyze ship motion.The conclusions are as follows:(1)3D flow characteristics.The flow in front of pier has stratified characteristics,which is divided into ascending and descending flow.The vertical position of the maximum length of the descending flow zone is 0.48 times inflow depth.In the middle of pier,the peak value of cross current will appear,and the maximum distance between the peak value on FWS(free water surface)and pier wall is about 0.45D;the peak value of vertical velocity is about 0.25 D.Increased inflow velocity causes the disappearance of the peak points of longitudinal velocity and flow velocity at FWS,and enlarges the difference of cross current distribution between different vertical sections.The increase of pier diameter will strengthen the integration of the vertical distribution law.For the flow behind the pier,the two clusters streamlines move obliquely downward along the pier wall,and a sudden change of velocity occurs in a certain range,which makes the flow move from downward to upward.At the position where the sudden change of velocity occurs,the wake vortexs form.(2)Moving ship model.The ship is subjected to a positive yaw moment which pushed the ship away from the pier when approaching the pier.The yaw moment is negative which makes the ship attractted by pier when navigating near the middle of the pier.The yaw moment is positive which attracting the ship when the stern is away from the pier.Yaw moment increases rapidly with the decrease of pier-ship spacing and the increases of the inflow velocity,especially at the middle of pier,the negative yaw moment increases obviously.The maximum negative yaw moment changes slightly with different ship speed.Low ship speed causes a big yaw angle,but large ship speed increases drift distance.In the area behind the pier,the vortices cause flow abrupt changes,yaw moment changes obviously.(3)Distribution of cross current in front of pier.Cross current symmetrically distributes along the longitudinal coordinate axis of the pier,the cross current value is larger in the 15°~75° clockwise(anticlockwise)region of the longitudinal axis of pier,and the 45° is the max value direction.The pier turbulence width defined by the cross current 0.3m/s has a highly correlated non-linear relationship with the flow Froude number.The yaw moment curves show that the width defined by 0.3m/s is too small.Therefore,various factors of flow around pier should be taken into account in navigation of bridge waterway.The 3D numerical model can well restore the motion pattern of ship in bridge waterway.