Boundary condition modelling and identification for cantilever-like structures using natural frequencies

The actual boundary conditions of cantilever-like structures might be non-ideally clamped in engineering practice, and they can also vary with time due to damage or aging. Precise modelling of boundary conditions, in which both the boundary stiffness and the boundary mass should be modelled correctly, might be one of the most significant aspects in dynamic analysis and testing for such structures. However, only the boundary stiffness was considered in the most existing methods. In this paper, a boundary condition modelling and identification method for cantilever-like structures is proposed to precisely model both the boundary stiffness and the boundary mass using sensitivity analysis of natural frequencies. The boundary conditions of a cantilever-like structure can be parameterized by constant mass, constant rotational inertia,constant translational stiffness, and constant rotational stiffness. The relationship between natural frequencies and boundary parameters is deduced according to the vibration equation for the lateral vibration of a non-uniform beam. Then, an iterative identification formulation is established using the sensitivity analysis of natural frequencies with respect to the boundary parameters. The regularization technique is also used to solve the potential ill-posed problem in the identification procedure.Numerical simulations and experiments are performed to validate the feasibility and accuracy of the proposed method. Results show that the proposed method can be utilized to precisely model the boundary parameters of a cantilever-like structure.     

基于微分进化算法的二自由度PID控制器参数优化

针对二自由度PID控制器参数多、调节困难等问题,提出了一种基于微分进化算法参数调节优化方法。证明了微分进化算法能够收敛到平稳点,并具有概率全局收敛性。研究了二自由度PID控制器参数与抑制特性、跟踪特性的关系,并将微分算法与遗传算法、粒子群算法的参数优化结果进行了比较。仿真验证表明,微分算法能够更好地实现二自由度PID控制器参数的调节,具有优异的跟踪特性和抑制特性。     

基于过程方法的测量设备控制

测量设备控制是企业内部管理和外部质量管理体系审核中的一项重要内容,在现有的管理中,因缺乏对相关过程进行系统识别,某些过程要素常被疏忽或遗漏,导致测量设备失控和测量结果失准。本文采用过程方法,系统地识别了测量设备控制的相关过程和过程要素,提出了过程监控指标及其评价准则,对于提高过程效率具有一定的参考价值。     

弹射救生系统大迎角大侧滑角气动特性工程计算方法研究

对弹射救生系统的气动特性进行了分析,发展了一套快速获取其气动特性的工程计算方法,并对某战斗机弹射救生系统的大迎角大侧滑角气动力特性进行了计算.结果表明,工程计算结果与风洞试验数据一致性良好.     

类X-38升力体运载器气动布局概念设计

开展升力体运载器的气动布局概念设计研究,利用二次曲线横截面及模线设计方法,提出一种类X-38升力体运载器气动外形,进行机体的优化和控制舵的匹配设计,研究飞行器的气动特性和操纵效率问题。研究表明,该方案可以获得较高的配平升阻比及配平攻角,有较高的容积效率和机动控制效率,可以作为未来航天运载器的潜在可行方案。     

影响聚四氟乙烯材料加工表面粗糙度因素的研究

在现代航空发动机的产品中,保护圈、密封件等零件广泛使用聚四氟乙烯材料制造.在加工中多采用车削加工,粗糙度一般为Ra1.6,本文通过选用不同车床、刀具、加工参数的方法,提高该类材料加工后的表面粗糙度,为后续加工提供经验和数据.     

异形排气管的热态气动试验

在发动机活动试车台上，对全尺寸的从环形过渡到腰果形的发动机排气量，进行了热态的出口压力和温度分布测试，实验结果表明，排气管出口截面的上部存在有严重的低压区，出现气流倒流的现象，产生的原因是由于发动机排气管的上壁面的扩张角过大造成的，排气管出口夫面温度由上向下不断提高，上部因受冷气倒流的影响，温度只有９０℃左右，而对应排气管环形部分直接排出燃气，由于未受冷空气的掺混，使出口截面下半的气流最调达度４２     

基于功率裕度的某型发动机全寿命性能研究

随着使用时间不断增加,研究飞行队所有选装ARRIEL2S系列发动机全寿命性能变化趋势的必要性突显.针对SRRIEL2S系列发动机全寿命性能参数变化特点,提出使用基于可几误差舍弃理论处理发动机功率校验数据,分区间描绘该系发动机全寿命性能指标变化趋势,给出该系发动机全寿命性能特点,为机务工程人员监控该系发动机提供有利依据；提出延长功率校验间隔的假设,并在理论上做了充分论证,为节约该系发动机运行成本提供一个明确及可行的方向.     

基于随机时隙的RFID读写器防冲突方法

针对密集读写器环境下的无线射频识别(RFID,Radio Frequency Identification)多读写器冲突情况,提出了一种基于随机时隙并通过中央计算机协调的读写器防冲突方法.首先,中央计算机发送每轮起始命令和时隙指令,读写器根据当前利用率随机选择时隙.选择当前时隙的读写器若没有接收到忙信号则发送信标并侦听,若无邻近读写器发送信标则开始读写标签,否则该轮回停止工作.若时隙末存在没有接收到忙信号的读写器则在额外时隙发送二次信标.与现有的分布式防冲突方法相比,该方法具有较好的吞吐量和公平性.     

Multi-station observation of ionospheric disturbance of March 9 2012 and comparison with IRI-model

The magnetic storm of 9 March 2012 is a single step intense storm (Dst = −143 nT) whose main phase begins around 0100 UT and lasted for almost 11 h. The increases in NmF2 recorded 33% and 67% incidence respectively during the main and the recovery phase of the storm at the stations considered. The increase in hmF2 occurred concurrently with the increase in thickness parameter B0 between 0000 and 1100 UT, and a simultaneous decrease in the shape parameter B1 for the entire mid-latitude stations. Generally, B1 responded to the storm with a decrease away from the quiet day average, and decreased simultaneously with the increase in NmF2. B0 displays higher variability magnitude during daytime than the nighttime period. The occasional differences in the response of the ionospheric parameters to the storm event are attributed to longitudinal differences. Variation in hmF2 and NmF2 is projected to change in B1, but the rationale behind this effect on B1 is still not known and therefore left open. The two IRI options over-estimate the observed values with that of URSI higher than CCIR. The over-estimation was higher during the nighttime than the daytime for NmF2 response for the mid-latitude stations and the reverse for the equatorial station. A fairer fit of the model with the observed for all parameters over Jicamarca suggests that equatorial regions are better represented on the model. Extensive study of B1 and B0 is recommended to arrive at a better performance of IRI.