Study On The Influence Of Backflow In The Approach Channel Area Of Lock On Ship Navigation

With the accelerated construction of "One Belt and One Road" and "Yangtze River Economic Belt",the role of inland river shipping in China’s economic construction has become increasingly prominent,and the safety of shipping has attracted more and more attention.Complex flow patterns,such as backflow,swirl,dropflow and jumpflow,inevitably exist in the entrance area and connection section of the water conservancy projects built in the sections with complicated channel conditions,which affect the navigation of ships.The existence of complex flow patterns and the relatively narrow space at the approach channel entrance undoubtedly put forward higher requirements for ship maneuverability,which is easy to cause accidents.At present,there are a lot of researches on navigable flow conditions in approach channel entrance area,most of which focus on longitudinal flow,transverse flow and backflow,etc.,and the industry standard also provides the limit of velocity at the entrance area.However,from the perspective of engineering practice,the velocity in some approach channel entrance areas of locks exceeds the limit,but ships can still be navigable smoothly.To backflow,for example,in the standard only gives the velocity limit,for a relevant factors such as flow length and no further description,so that use the method of physical model test and numerical simulation research,explore the entrance area effect of backflow of the ship sailing,to ensure the good development of shipping industry,reduce the ship navigation risk,reduce accidents has important theoretical and practical significance.First,to establish a two-dimensional mathematical model of lock approach backflow characteristics,simulation analysis is discussed,the upstream or downstream is discussed different approaches to broadening ratio and the depth of the water to flow length and the influence of flow velocity,and the results show that with the increase of the broadening backflow intensity has a tendency to increase,and the same conditions,the downstream area flow condition at the entrance of the approach channel flood-discharge are superior to the upstream.And the backflow of the generalized model test,provide support for selfpropelled ship model test.Then,design and implementation of the ship through the backflow zone since the ship model test,analysis of different ship speed,the length of backflux and backflux area on the influence of the maximum velocity of the ship sailing,the experimental results showed that the ship speed is high,the smaller the influence of backfolw,and the maximum drift angle and with the flow length and maximum flow velocity increases.In the paper test conditions,the maximum velocity of recirculation region is less than 2m/s,flow length within about 45 m,ship sailing safer.Tthrough the sensitivity test analysis of ship tonnage,it is concluded that ships with smaller tonnage are more affected by.backflux.Finally,using the overset technology,a two-dimensional numerical simulation was carried out to investigate the flow field distribution before,when and after the ship passed through the backflow area.The simulation results show that when the ship is in the backflow area,the bow and stern of the ship are subject to the transverse velocity of different directions,and the ship is subject to a certain rotational moment.When the ship is just out of the backflow area,the stern of the ship is subject to the current,so it is easy to produce "tail flapping" behavior,which poses a certain threat to the navigation safety of the ship.