Modeling and Optimal Design of 3 Degrees of Freedom Helmholtz Resonator in Hydraulic System

Three degrees of freedom (3-DOF) Helmholtz resonator which consists of three cylindrical necks and cavities connected in series (neck-cavity-neck-cavity-neck-cavity) is suitable to reduce flow pulsation in hydraulic system. A novel lumped parameter model (LPM) of 3-DOF Helmholtz resonator in hydraulic system is developed which considers the viscous friction loss of hydraulic fluid in the necks. Applying the Newton’s second law of motion to the equivalent mechanical model of the resonator, closed-form expression of transmission loss and resonance frequency is presented. Based on the LPM, an optimal design method which employs rotate vector optimization method (RVOM) is proposed. The purpose of the optimal design is to search the resonator’s unknown parameters so that its resonance frequencies can coincide with the pump-induced flow pulsation harmonics respectively. The optimal design method is realized to design 3-DOF Helmholtz resonator for a certain type of aviation piston pump hydraulic system. The optimization result shows the feasibility of this method, and the simulation under optimum parameters reveals that the LPM can get the same precision as transfer matrix method (TMM).     

Large-scale Vacuum Vessel Design and Finite Element Analysis

The vacuum plume effects experimental system (PES) is the first experimental system designed to study the effects of vacuum plume in China. The main equipment, a vacuum chamber of 5.5 m in diameter and 12.8 m in length, and structure design of hinged door are described. The finite element method (FEM) is adopted to analyze the static strength and stability of the PES vacuum chamber. It is demonstrated that the static strength and stability are qualified. For the 5.5 m diameter vacuum chamber door, three design schemes are put forward. After comparisons are made, the single-axis-double-pin hinged door is selected. The FEM is applied to checking its static strength as well as distortions. The results show that the door’s distortion and displacement change mainly due to the gravity of the door which leads to its sinking. The calculated displacement is less than 7.8 mm, while the actual measurement is 5 mm. The single-axis-double-pin hinged door mechanism completely satisfies the design requirements. This innovative structure can be introduced as a reference for the design of large-scale hinged doors.     

亚轨道飞行器返回轨迹快速优化

快速、准确、鲁棒的轨迹生成方法可以增加任务的安全性与可靠性,极大地降低成本。针对亚轨道飞行器返回段特点,引入"伪控制量"、"末端进场走廊"等概念,分别采用高斯伪谱法和向前拉道伪谱法进行了返回轨迹快速优化研究,比较了两种伪谱法在处理复杂问题时的能力。仿真结果表明,向前拉道伪谱法不适合处理含控制量约束的问题,而高斯伪谱法在满足各种约束条件下,能够快速准确地生成亚轨道飞行器返回轨迹,同时验证了结果的可行性与最优性。     

空间相机支撑结构选型动力学分析

在航天遥感领域,离轴三反射镜消像散光学系统(TMA)以大视场、无遮拦等特点被广泛运用。由于离轴TMA系统的特点以及空间相机在发射过程中经历的恶劣的力学环境,相机支撑结构的力学特性对于相机成像品质的保证具有至关重要的意义。文章用Solidworks建立了支撑结构的实体模型,并在此基础上建立了有限元模型。通过对4种结构构型方案的力学特性的分析比较,为相机光机结构设计打下了基础,对三反离轴相机支撑结构的工程设计具有一定的指导作用。     

基于ANSYS概率分析的导弹结构可靠度计算

针对导弹结构的材料性能、载荷环境、几何尺寸等参数不确定性的影响,基于ANSYS概率设计系统,提出了利用ANSYS概率分析功能对导弹进行结构可靠性分析的方法。通过建立某型导弹同体发动机推进剂药柱的极限状态方程,采用蒙特卡洛模拟随机载荷和固体推进剂药柱初始强度来获取推进剂药柱的可靠度。该方法能有效地计算贮存、飞行等环境条件下的导弹结构可靠性。     

Aerodynamic Modeling and Parameter Estimation from QAR Data of an Airplane Approaching a High-altitude Airport

Aerodynamic modeling and parameter estimation from quick accesses recorder (QAR) data is an important technical way to analyze the effects of highland weather conditions upon aerodynamic characteristics of airplane. It is also an essential content of flight accident analysis. The related techniques are developed in the present paper, including the geometric method for angle of attack and sideslip angle estimation, the extended Kalman filter associated with modified Bryson-Frazier smoother (EKF-MBF) method for aerodynamic coefficient identification, the radial basis function (RBF) neural network method for aerodynamic modeling, and the Delta method for stability/control derivative estimation. As an application example, the QAR data of a civil airplane approaching a high-altitude airport are processed and the aerodynamic coefficient and derivative estimates are obtained. The estimation results are reasonable, which shows that the developed techniques are feasible. The causes for the distribution of aerodynamic derivative estimates are analyzed. Accordingly, several measures to improve estimation accuracy are put forward.     

压气机叶片气动阻尼的改善设计

针对气动阻尼在强迫响应分析中的应用现状,提出了一种在叶型基本确定的条件下进一步设计气动阻尼的方法.该方法只对叶片基元级的积叠轴做微小的调整,这种调整对叶栅流场气动特性和固有频率的影响很小,可以忽略不计.研究了积叠轴调整对叶片气动阻尼的影响,得出在不需要大量流场计算的条件下,即可判断如何调整叶片积叠轴以达到增加气动阻尼目的的结论.在分析中用振型相似度衡量叶片模态振型与气动阻尼比的关系,相似度越小气动阻尼比越大.      

基于可靠性的飞机风挡抗鸟撞优化设计

传统的飞机风挡设计通常在确定的工况下进行,未能充分考虑实际鸟撞风挡过程中不确定性因素的影响,导致飞机鸟撞风挡的故障多发。综合考虑鸟撞飞机风挡过程中鸟体材料参数、质量、撞击速度等不确定因素的影响,以飞机风挡抗鸟撞的可靠度为约束,风挡质量为目标,基于双循环方法和近似技术建立了风挡抗鸟撞可靠性优化设计系统,利用一阶矩法进行可靠性分析,对某飞机风挡进行了基于可靠性的优化设计。实例分析证明所建风挡抗鸟撞可靠性优化设计系统可行有效。     

超声波喷水穿透法在先进复合材料检测中的应用

介绍了超声波喷水穿透法的检测原理及自行研制的四轴自动超声波喷水穿透C扫描检测系统.利用该检测系统对包括平板试样件,大厚度模压件,以及筒形结构件等先进复合材料进行超声波喷水穿透法检测,结果表明该方法对先进复合材料中存在的孔隙、裂纹、脱粘和分层等缺陷能有效检出.     

灰色聚类法在航空装备维修保障能力评估中的应用

通过对航空装备维修保障系统的分析,用灰色聚类法给出了航空装备维修保障能力评估指标体系综合评估模型,并进行了实例分析.