Study On The Influence Of Large Steel Cofferdam On Navigation In Construction Bridge Area

The safety of waterway transportation affects People’s Daily life and economic development.In addition to the influence of human factors,natural water flow conditions bring the most complicated safety problems to waterway transportation.The complicated flow pattern in the bridge section of waterway construction area increases the risk of ship navigation and may cause huge loss of life and property.The analysis of the flow characteristics of the large steel cofferdam and the study of the ship’s stress and navigation deviation under the complex flow environment can provide theoretical suggestions for the navigation safety of the ship in the construction bridge area.In this thesis,taking a bridge in Chongqing as an engineering case,combined with the layout of large steel cofferdam during construction,and based on the fluid mass conservation equation and Reynolds time-mean equation as the theoretical basis,the Fluent finite element software is used to conduct numerical simulation on the cross section velocity of steel cofferdam in the bridge axis direction and vertical bridge axis direction.The influence of steel cofferdam on channel flow condition is analyzed by comparing the variation of velocity of each section before and after the installation of steel cofferdam.The influence of the installation of large steel cofferdam on ship navigation is analyzed from ship navigation resistance and ship track deviation through moving ship model simulation.The main conclusions of the study are as follows:1)Influence of steel cofferdam on channel flow condition.Change of flow velocity after steel cofferdam is installed in construction bridge area.In the direction of vertical bridge axis,the closer it is to the arc surface of the upstream steel cofferdam,the more the velocity decreases.The flow velocity begins to increase near the bridge axis and reaches the maximum increase at 0.6Bs from the arc surface of steel cofferdam tail(Bs is the width of steel cofferdam).In the direction of the bridge axis,the velocity changes significantly at 1.8Bs ～ 3.2Bs away from the center of the steel cofferdam.Flow characteristics of steel cofferdam in construction bridge area.The variation of flow velocity on both sides of steel cofferdam is close,and the distribution of flow velocity is almost symmetrical.The water level at the top of steel cofferdam increases obviously,and the water surface forms backwater curve.Vortex stripping occurs at about 0.3Bs ～ 1.8Bs away from the arc surface of steel cofferdam tail.2)Influence of steel cofferdam installation on ship navigation.On the axis of the vertical channel.When the transverse distance exceeds 3.0Bs,the change of ship speed has very little influence on navigation resistance and track deviation.Therefore,3.0BS transverse distance is regarded as the safe sailing distance in this case.This method can be used to determine the safe sailing distance in related projects.On the axis of the channel.At the position about 1.2Bs from the head of the steel cofferdam,the navigation resistance reaches the peak and the phenomenon of backwater occurs at the top of the steel cofferdam.When the steel cofferdam is in the middle position,the ship will deviate to the direction close to the steel cofferdam.There is a large eddy in the area about 1.6bs away from the tail of the steel cofferdam,so keep a large transverse distance and sail at a stable speed,and try to avoid sailing in the area where the eddy is generated.