| The vibration generated by the helicopter during normal flight and the shock received during emergency landing are important factors related to the health and life safety of the occupants.At present,most helicopter seats only consider their crashworthiness function in the design process,and use traditional passive energy absorption devices.They cannot adjust their output load for different occupant weights and collision levels,and cannot provide the most effective protection for the occupants.Magnetorheological damper(MRD),as a new type of intelligent structure,can adjust its output load by changing the current,and has fast response,low energy consumption,and continuously adjustable damping.At present,scholars have applied it to helicopter seat vibration isolation.However,there are relatively few studies,and due to the large differences in the design requirements of the MRD for vibration isolation conditions and crashworthiness conditions,there is currently no intelligent structure that can simultaneously meet the requirements for vibration isolation and crashworthiness.In response to the above problems,this paper conducts research on the integrated MRD for helicopter seat vibration isolation and crashworthiness.The main tasks include:(1)A new variable damping gap MRD structure that can meet the requirements of helicopter seat vibration isolation and crashworthiness is proposed,and its mechanical model is established.Use the change of the damping gap to adapt to different impact speeds to keep the output of the damping force stable within the full stroke range and improve work efficiency.Use the idea of micro-element method to derive the pressure drop and the shape resistance pressure drop of the long piston at different damping gaps.The flow state of the MR fluid is determined by the calculation of the Reynolds number,the shear thinning phenomenon under high shear strain rate is considered,and the precise coulomb pressure drop is derived.(2)A topological surface optimization design method to enhance the environmental adaptability of the variable damping gap MRD was proposed,and its mechanical performance analysis and structural design were completed.To adapt to different impact speeds and occupant weight,the working gap shape of the variable damping gap MR damper is preset to be parabolic and power function.Take the function coefficients of piston size,working stroke,working current and working gap curve as optimization variables,and optimize the topological shape with the efficiency under seven typical working conditions as the optimization objective,and obtain the best gap curve and optimal current value.Complete device performance numerical simulation verification,structural design and magnetic circuit analysis according to the optimization results.(3)Based on the optimization results of the topological shape,the machining and assembly of the prototype variable damping gap MRD was completed,and the basic mechanical properties of its vibration isolation unit and crashworthiness unit were tested.The variable inner diameter cylinder is processed by CNC to ensure the accuracy of the working gap curve.The mechanical characteristics of the vibration isolation unit under different amplitudes,frequencies and current conditions are analyzed.Key design indicators such as adjustable range and maximum damping force are analyzed and compared with the theoretical results.The Coulomb damping force change law of the crashworthiness unit at different strokes and different current conditions is analyzed.(4)The dynamic models of the helicopter seat crashworthiness and vibration isolation system are established respectively,corresponding control strategies are proposed for different working conditions,and the simulation analysis is completed.For the helicopter seat vibration isolation system,the simulation analysis of the seat vibration isolation performance is completed by using the skyhook control strategy.Aiming at the helicopter seat crashworthiness system,the adaptive variable gap structure determined by the topological shape optimization idea is used as the control strategy to complete the performance simulation analysis of the helicopter seat crashworthiness system,and compare it with the helicopter seat with traditional fixed damping gap MRD seat system.(5)The helicopter seat drop test platform was designed and built,and the validity of the design idea of variable damping gap structure and the optimization idea of topological shape was verified.Completed the construction of semi-active MR seat suspensions for enhanced crashworthiness and vibration isolation,including the connection and arrangement of variable damping gap MRD,pure shear dampers and springs;Completed helicopter seat drop tests under different impact environments;Analyzed the adaptability of the MRD with variable damping gap to different working conditions. |
