Numerical Simulation Of Vertical Water Impact Of The Fuselage Section Of Typical Civil Aircraft

In this thesis,the Arbitrary Lagrange-Euler method(ALE method)is used to establish a finite element model of the vertical water impact of a typical civil aircraft fuselage section and analyze the overload,deformation,damage,and energy absorption of the fuselage structure under the hydrodynamic forces.To provide a reference for the structural design and airworthiness certification of domestically-made large passenger aircraft for ditching.First,the cylinder vertical water entry test was carried out,and obtained the original acceleration data of the cylinder vertical water entry.And combined with the experimental results of the rigid cylinder’s water entry displacement and the dynamic change of the free liquid surface in the literature to contrast verification with the cylinder vertical water entry model established by the ALE algorithm.The results show that the ALE method,which uses null materials and the equation of state to establish a fluid model,has high accuracy in the simulation of structural water entry.Established a typical civil aircraft fuselage section vertical water impact model and the response characteristics of the fuselage section under the water entry velocity of 6.02m/s were studied.The results show that the sub-cabin of the fuselage section deforms into asymmetrical deformation under the hydrodynamic forces.The deformation on the left side of the lower part of the fuselage section is obviously greater than that on the right side,and the bending degree of the fuselage frame gradually weakens from F1 frame to F3 frame.The cabin floor beam has undergone a large downward bending,and the connection between the left side of the cargo compartment component and the fuselage frame has failed.A total of three plastic hinges are formed in the fuselage section;the skin is not damaged.The maximum peak acceleration of the fuselage section decreases from back to front,and the peak acceleration on the left side of the fuselage section is slightly larger than the right.The relationship of the total energy absorption ratio of each component from large to small is as follows: Fuselage frame,skin,cabin floor beams and guide rails,fasteners,long stringer,cargo components,others,cabin floor support columns.The proportion of energy absorption is 54.2%,22.6%,10.7%,4.8%,3.5%,2.6%,0.7%,0.8%.Comparative analysis of the response characteristics of the fuselage impacted on the water surface and the rigid surface,the results show that the vertical water impact deformation of the fuselage section is significantly smaller than the rigid surface crash;and the acceleration peak at the cabin floor guide rail is always smaller than the rigid surface crash.The fuselage frame has a great influence on the overall energy absorption capacity of the entire fuselage structure under the two crash surface conditions,the energy absorption ratio of the fuselage frame exceeds 50%.Finally,the vertical water entry response characteristics of the fuselage section were analyzed at different speeds(3.05m/s,6.02m/s,9.14m/s),different roll angles(±3°,±6°,±9°)and different pitching angles(3°,6°,9°).