| With the globalization of economy and the rapid development of science and technology,accidents of aircraft crashing also began to occur,which caused considerable with damage to society,airlines and individuals.At the same time,the searching,rescuing and salvaging for aircraft cost a lot of manpower and material resources.In order to investigate and research the cause of the aircraft crashing,it is important to promptly find the wreckage and black box of the aircraft.Because the crashed airplane is influenced by factors such as water flows and so on after the crashed aircraft dropped in the sea,this adds much difficulty to the searching.Therefore,aircraft ditching and falling in water are researched through different technical methods,the falling area and distribution laws of wreckage and black box are accurately determined,which will play an important role in the follow-up search and rescue of crashed aircrafts in sea.This paper uses Computational Fluid Dynamics(CFD)methods,and uses the VOF method to deal with free surface,and combines the dynamic grid with a Six Degrees Of Freedom model,uses the open channel model to prevent the free surface from collapsing and uses wavemaking boundaries for making waves.The simulation of the aircraft falling into the water is made.First of all,this paper uses model algorithm about CFD to simulate the phenomenon of cylinder falling in water flow,and compares the result with the experiment to prove the reliability of method and related models about CFD.Then,the model of the airplane falling in the wave is established,and the relevant parameters of the aircraft and the water area are set.Finally,the simulation analysis of the aircraft under three conditions is carried out,and the state of airplane falling in water under the negative pitching angle is analyzed.The following conclusions are obtained through analysis:1.The CFD method can simulate water entry of the structure and the airplane falling in water under the wave.2.The aircraft ditched on the wave with a pitch angle of 8°,30m/s or 70m/s.In 30m/s condition,two load peaks generated when impacting the waves,the first were greater than the second.In 70m/s condition,the airplane would occur shortly the phenomenon of "jumping",and two impact load peaks generated,the second were greater than the first.Under conditionsof two velocities,the impact load on lower part of fuselage is the largest.and the velocity is greater,the impact force on fuselage in the horizontal direction is larger,but the impact force in the vertical direction is almost the same under conditions of two velocities.3.When the aircraft fallen into the water at negative pitch angles of-30° and-90°,there would be two peaks in the slamming load,the second one is greater than the first one,and the load on the wing is the largest.In the process of airplane falling in water,the tail of the airplane is just beginning to be affected by the wave and the pitching moment was generated.Then,the vertical speed will decrease first and then increase in the-30°condition,and the pitch angle will increase first and then decrease in the-90°condition.Finally,the falling trajectory of airplane was fitted to obtain the equations of trajectory. |
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