Effect Of Water Level Fluctuation At Entrance Area Of Approach Channel On Navigation Safty Of Ships

For some large hydro-junction project,due to the flood discharge,the water flow in the downstream entrance area of approach channel is disordered and the water level fluctuates greatly,which seriously threatens the safety of ships crossing the dam.Based on Xiangjiaba hydro-junction,this paper mainly studies this problem from the following two aspects:(1)Observing and studying the navigational flow conditions dominanted by the water level fluctuation;(2)Studying the relationship between the water level fluctuation in the entrance area and the parameters of ship motion attitude.Analyzing the influence of the water level fluctuation on the navigation safety of ships.These researches have important theoretical and practical significance for ensuring the safe navigation of ships.In order to provide validation data for the mathematical model of ship motion,prototype observation is carried out on several water level measuring points in the entrance area of the downstream approach channel of Xiangjiaba Junction.The mathematical model of ship motion is established.The real ship test ship is selected as the research object of the mathematical model of ship motion.The roll angle calculated by the mathematical model is compared with the measured angle of the real ship test.The validation results show that when the ship sails up and down to the entrance area,the roll angle calculated by the numerical model is in good agreement with the original measured value,which shows that the mathematical model used in the simulation has certain rationality and accuracy.Aiming at the problem of the relationship between the water level fluctuation in the entrance area and the parameters of ship motion attitude,the ship mathematical model is used to calculate the roll angle and lateral acceleration of the ship under different waves and currents.In this paper,the effects of wave height,wave direction,flow direction and velocity on the roll angle and lateral acceleration of ship motion are summarized.The effects of water level fluctuation at the entrance of approach channel on ship navigation safety are analyzed.The main conclusions are shown as follows:(1)The roll angle and lateral acceleration of the ship increase with the increase of wave height.(2)When the wave direction is 60°,90°,120°,60°,90° and 120°,the ship is subjected to large lateral external loads,and the transverse motion of the ship is more intense.(3)Different combinations of wave direction and flow direction lead to different laws of ship motion.Generally speaking,under a certain wave direction and a certain wave height,when the flow velovity is less than a certain “velocity”,the ship's roll angle and lateral acceleration decrease with the increase of the angle between the flow direction and the wave direction.When the flow velocity is greater than this "velocity" and the flow direction and the wave direction are on the same side of the axis perpendicular to the wave direction,the roll angle and the lateral acceleration of ship decrease with the increase of the angle between the flow direction and the wave direction.When flow direction and the wave direction are on the opposite side of the “axis”,the law is not obvious.(4)When the wave direction and the flow direction are on the same side of the axis perpendicular to the wave direction,the roll angle and the lateral acceleration of the ship increase with the increase of the current velocity.When the wave direction and the flow direction are the same,the increase is the largest.When the angle is 90°,the current velocity has little effect on the roll angle and lateral acceleration of ship.When the wave direction and the flow direction are on the opposite side of the “axis”,within a certain range of the flow velocity,the ship motion attitude parameters decrease with the increase of the flow velocity.When the velocity continues increasing,the roll angle and lateral acceleration increase with the increase of the velocity.In order to analyze the influence of water level fluctuation in the entrance area of approach channel on ship navigation safety,the ship safety characteristic parameters given by the captain in the Practical Manual of Ship Design is taken as the standard.Based on the ship numerical calculation results,the influence of wave height on ship navigation safety is analysed.The results show that for the characteristic parameters of the ship navigation safety of roll angle,the maximum wave height that the ship can endure is larger when the ship is not affected by crossflow.And “the wave height” is reduced when it is affected by different degrees of cross flow.For the characteristic parameters of ship navigation safety of lateral acceleration,the influence of wave height on ship navigation safety change little.Compared with the influence of wave height on roll angle,the lateral acceleration is more sensitive to the influence of wave height.