Analysis Model Improvement And Application Research Of Aircraft Impact Load

With the occurrence of major disasters in the world,the relevant safety protectionstandards for nuclear power structures against large aircraft impacts have been significantly improved,and safety analysis against large aircraft impacts has become an essential part of nuclear power structure design.At present,the results of refined numerical simulation of aircraft impact containment are accurate,but due to the defects of complex model establishment and long calculation time,the aircraft impact load curve is often used in engineering for structural design and safety assessment.In aircraft impact studies,the Riera impact load curve model is commonly used.The Riera formula is proposed based on momentum,which is more accurate when evaluating the impact of small aircraft.However,due to the short impact duration and constant velocity assumption of the momentum theorem,it will greatly overestimate the impact load in the impact analysis of commercial large aircraft.Based on the refined models of Boeing 767-200 ER and Airbus A340-300,the detailed non-linear impact simulations of two commercial large aircraft impacting rigid walls were simulated with the classic explicit nonlinear finite element analysis software ANSYS /LS-DYNA.The following researches have been carried out in this thesis:First,in terms of numerical models,the impact force results of the finite element analysis are compared with the results of the classic Riera method.The results show that the two are in good agreement,which proves the applicability and effectiveness of the constitutive model and analysis method of aircraft materials.The influence of the failure strain of the aircraft model on the impact load curve is also discussed.By comparing the results of different failure strains,it is found that the failure strain of the material has little effect on the peak value of the impact force of the aircraft,but has a greater influence on the impact impulse of the aircraft.Secondly,the importance and necessity of studying the velocity term in the Riera model to the impact load curve are discussed.Through detailed non-linear impact simulation of the aircraft impact process,the load time-history curve is extracted,and the comparative studies with the Riera formula are made.The Riera impact load model in velocity decay mode is discussed.It is pointed out that it is of great significance to study the law of velocity change in the Riera impact load model.At the same time,the influence of the number of aircraftengines on the impact curve of the aircraft is also discussed.The results show that the number of aircraft engines has little effect on the trend of impact loads.Thirdly,based on the principle of energy conservation,the energy change during the impact of the aircraft is analyzed,and the relationship between total energy,kinetic energy and internal energy is given.According to the law of energy change,three impact phases in an aircraft impact process are proposed,and the energy distribution in each impact phase is discussed in detail.The energy change formula in each impact phase is given quantitatively.Based on the energy conservation theory,a Riera bilinear velocity model is proposed.Finally,a detailed implementation algorithm based on the proposed improved Riera bilinear attenuation model is given.The rationality is verified from two aspects: finite element refinement simulation and energy theory derivation.The results show that the improved Riera bilinear attenuation model and the corresponding complete implementation algorithm provided in this thesis can provide a more reasonable technical basis for the safety assessment of nuclear reactors against the large commercial aircraft impact.At the same time,the influence of the initial impact speed of the aircraft on the impact load is also discussed.The results show that the larger the initial impact velocity,the shorter the moment when the maximum impact force appears,and the larger the maximum impact force,the shorter the impact duration.