Design,Analysis And Optimization Of The Anti-crash And Energy Absorption Subfloor Structure Of Helicopter

The subfloor structure of a helicopter is not only a part of the helicopter fuselage structure,but also an important part of the crashworthiness structures of a helicopter.The subfloor structure,the landing gear system and the helicopter chair work together as a protection system of the crews and the airborne equipment.However,when a helicopter crashes,the landing gear may not be able to be released in time,and the chair in the cabin of a helicopter can only offer limited protection to the passengers.In this case,the subfloor structure is the most effective energy-absorption structure.An important way to improve the security of the crews and the airborne equipment is to use energy-absorption devices in the helicopter crashworthiness structures.The energy-absorption devices should be lightweight devices with high energy-absorption and buffering capacities.The folded core sandwich structure is such a kind of lightweight structure.In this dissertation,the intersection element structure of the helicopter subfloor structures is studied.The folded core sandwich structures and the waved beams are used to improve the crashworthiness of the intersection element structure.The folded core sandwich structure is one kind of sandwich structures,which has a lot of advantages such as high strength-to-weight ratio,high stiffness-to-weight ratio,good bending capacity,etc.The folded core sandwich structure is complex and has a lot of geometric parameters.Geometric and material defects of the structures are unavoidable in their forming process.In this dissertation,defects of the folded cores are divided into facet configuration defects and facet partial defects due to the causes of the defects.And the random node shaking method is proposed to model the defects.Based on the random node shaking method,the numerical simulation model is established to study the energy-absorption capacity.In the model,several factors as folded core defects,material nonlinearity due to buckling and damage,boundary nonlinearity due to self-contact of the folded core and contact of the folded core and the panels,and the geometric nonlinearity due to the big deformation of the folded core are considered.The accuracy of the simulation is validated through comparison between the numerical results and the experiment results.Based on the simulation method established in this dissertation,the energy-absorption capacity of the folded core is studied.Compared with honeycomb core,folded cores with the same material and surface denisity perform better energy-absorption capacity and buffering capacity.By replacing the skin and floor of the subfloor structure with folded core sandwich structures,a new helicopter subfloor intersection element structure is designed in this dissertations.Crash simulation of the intersection element structure is carried out.The simulation result shows that the usage of folded core sandwich structures can improve the buffering and the energy-absorption capacities of the intersection element structure.In order to minimize the structure mass of the helicopter subfloor intersection element structure with the energy-absorption and buffering capacities requirements satisfied,optimization of the geometric parameters of folded core sandwich structures should be conducted.Crush simulations of intersection element structures with different geometric parameters of folded core sandwich structures are conducted.Afterwards,the surrogate model is established based on the simulation results.The surrogate model describes the relation of the peak load and the maximum velocity of the reference point of the structure during crush and the geometric parameters of folded core sandwich structures.The optimization is then accomplished using the surrogate model while ensuring the accuracy of the surrogate model.The optimization goal is the minimization of the mass of the intersection element structure.And the optimization constraint is that the buffering and energy-absorption capacities of the intersection element structure should not be worse than the typical intersection element structure.The optimization leads to 11% decrease of the structure mass.Based on the intersection element structure with optimizated folded core sandwich structures,the crashworthiness of the intersection element structure is further improved by replacing the intersected thin-walled beam structure with the intersected waved beam structure.The application of the waved beam structure reduces the structure mass and improves the energy-absorption capacity of the structure.In this dissertation,finite element analysis software ABAQUS is used to establish all the models and carry out all the analysis of the models.Parametric modeling and post processing of the subfloor intersection element structure models are realized through a lot of ABAQUS pre-processing and post-processing programs written with Python.Thus the efficiency of the simulation and analysis are greatly improved.Besides,optimization software mode FRONTIER and ABAQUS are integrated using these programs to realize the automatic mass modeling and analysis of the subfloor intersection element.Thus the surrogate model can be established and the optimization can be conducted.