大型转动机械碰摩故障分析的声发射检测系统

汽轮发电机、空气压缩机等采用油膜支撑的大型转动机械,由于安装或运行中的原因,在转子旋转过程中,可能和器壁发生轻微的摩擦和碰击,简称碰摩.声发射技术在碰摩发生特别是故障早期诊断上有优越性.本系统的特点是没有沿用传统的计数、幅度、能量和持续时间等声发射特性参数,而是在声发射包络信号的频率分析中进行特征提取.声发射发生的过程分析和现场试验都表明这种方法对碰摩检测很敏感,在碰摩发生的起始阶段,包络谱中与转速同步的周期性分量显著增加.根据这种新的设计思想自行研制了BUAA碰摩声发射检测仪并对此作了介绍.     

基于FPGA的高准确度数字频率信号源设计

介绍了直接数字频率合成技术的实现方法,分析了其优越的技术特性。根据其特性,利用FPGA设计了高准确度的数字频率信号源。仿真结果表明,与传统的信号源相比,使用该方法实现的信号源,其信号种类多,准确度高,满足测试设备数字化、软件化的趋势。     

利用MF雷达对耀斑期间电离层D区电子密度的观测研究

利用MF雷达观测资料对X级别耀斑爆发期间在66-80km高度之间的电子密度进行了研究，观测到了耀斑爆发期间电子密度的突然增加，在较低高度上的电子密度的时间变化趋势与耀斑的软X射线辐射通量相关．电子密度的变化强度依赖于具体的耀斑参数，有些耀斑引起的电子密度增加高达400cm^-3，有些仅为100cm^-3左右．但耀斑期间在这一高度区间增加的总电子含量增量仅占耀斑辐射引起的整个电离层总电子含量增量的千分之一左右．最后，利用恢复阶段电子密度的时间变化过程估算了1997年11月4日耀斑期间部分高度上的有效复合系数．     

Evaluation and improvement of coastal GNSS reflectometry sea level variations from existing GNSS stations in Taiwan

Global sea level rise due to an increasingly warmer climate has begun to induce hazards, adversely affecting the lives and properties of people residing in low-lying coastal regions and islands. Therefore, it is important to monitor and understand variations in coastal sea level covering offshore regions. Signal-to-noise ratio (SNR) data of Global Navigation Satellite System (GNSS) have been successfully used to robustly derive sea level heights (SLHs). In Taiwan, there are a number of continuously operating GNSS stations, not originally installed for sea level monitoring. They were established in harbors or near coastal regions for monitoring land motion. This study utilizes existing SNR data from three GNSS stations (Kaohsiung, Suao, and TaiCOAST) in Taiwan to compute SLHs with two methods, namely, Lomb–Scargle Periodogram (LSP)-only, and LSP aided with tidal harmonic analysis developed in this study. The results of both methods are compared with co-located or nearby tide gauge records. Due to the poor quality of SNR data, the worst accuracy of SLHs derived from traditional LSP-only method exceeds 1?m at the TaiCOAST station. With our procedure, the standard deviations (STDs) of difference between GNSS-derived SLHs and tide gauge records in Kaohsiung and Suao stations decreased to 10?cm and the results show excellent agreement with tide gauge derived relative sea level records, with STD of differences of 7?cm and correlation coefficient of 0.96. In addition, the absolute GNSS-R sea level trend in Kaohsiung during 2006–2011 agrees well with that derived from satellite altimetry. We conclude that the coastal GNSS stations in Taiwan have the potential of monitoring absolute coastal sea level change accurately when our proposed methodology is used.     

新一代战斗机非定常流动数值研究综述

新一代战斗机强调超机动能力和强隐身性，其中大攻角下的静态失速、动态失速及内埋弹仓绕流是与高机动和强隐身密切相关的、极具挑战的几类典型的非定常流动，它们对数值方法提出了极高的要求。为了高精度地仿真流场、清楚地揭示流动机理，有效地控制非定常流动，非常有必要发展高精度且高效率的RANS-LES混合方法体系，包含RANS-LES混合方法本身、与RANS-LES混合方法匹配的高精度自适应耗散格式、基准湍流模式、高质量计算网格、高精度时间推进方法、非定常量的统计方法等，具有极强的紧迫性。提出、发展、验证并应用该类方法数值仿真新一代战斗机（包括单独部件、组合体、甚至全机）的非定常流动，数值预测结果与风洞实验数据吻合良好；此类方法可为新型战斗机设计提供理论依据和分析手段。     

基于经纬仪的光束平差法定向方法改进

针对基于传统经纬仪工业测量系统使用光束平差法定向精度有待提高的问题，提出一种新的定向改进方法。该方法同时结合了精确互瞄法与光束平差法，简化了测量过程，提出新的约束，消减了光束平差法中定向阶段的基准点测量累积误差，实现了在非通视条件中完成多台经纬仪高精度定向的目标。试验数据表明：该方法可在10m范围内，在误差为±3″的测点交会精度下，维持0.1mm的定向精度。     

Multi-level virtual prototyping of electromechanical actuation system for more electric aircraft

Electromechanical actuators (EMAs) are becoming increasingly attractive in the field of more electric aircraft because of their outstanding benefits, which include reduced fuel burn and maintenance cost, enhanced system flexibility, and improved management of fault detection and isolation. However, electromechanical actuation raises specific issues when being used for safety-critical aerospace applications like flight controls: huge reflected inertia to load, jamming-type failure, and increase of backlash with service due to wear and local dissipation of heat losses for thermal balance. This study proposes an incremental approach for virtual prototyping of EMAs. It is driven by a model-based system engineering process in order to enable simulation-aided design. Best practices supported by Bond graph formalism are suggested to develop a model’s structure efficiently and to make the model ready for use (or extension) by addressing the above mentioned issues. Physical effects are progressively introduced, and the realism of lumped-parameter models is increased step-by-step. In particular, multi-level component models are architected to ensure continuity between engineering activities. The models are implemented in the AMESim simulation environment, and simulation responses are given to illustrate how they can be used for preliminary sizing, control design, thermal balance verification, and faults to failure analysis. The proposed best practices intend to provide engineers with fast, reusable, and efficient means to assess performance virtually and enhance maturity, performance, and robustness.     

热力学排气系统中节流效应及其冷量利用分析

为更好地理解热力学排气系统(TVS)的运行机理，优化其运行参数，针对节流装置，建立了热力学模型，讨论了节流过程中状态参数的变化规律，对比了单相气体、单相液体节流的性能特性，进一步揭示了焦汤节流效应的原理，分析了不同节流背压下节流前低温工质(液氢和液氧)压力和温度对节流性能的影响，并结合TVS实际应用，阐述了节流最大制冷量的利用效果，提出了优化的TVS工作区间。研究表明：在节流过程不发生相变情况下单相气体节流制冷效应要比单相液体节流制冷效应更加显著；而在节流过程发生相变情况下液体节流至两相后，由于空化吸热导致流体温度降低，对于液氢，0.5MPa的压降可产生接近3 K的温降。对于液体节流，节流前压力对节流过程影响可忽略，〖JP2〗而节流前温度和节流背压对节流过程起主导作用；对于液氢在在轨运行工况下，考虑到节流制冷量的充分利用，同时保证换热过程体积含气率不高于90%，推荐TVS系统中节流背压范围为75～143 kPa。     

黄渤海晴空像元下雾霾识别的机器学习算法

为实时有效地识别和监测雾霾，选取2013年10月4日与10月5日的两景MODIS遥感图像，利用不同类型像元的光谱差异，基于神经网络模型，建立海上雾霾的遥感识别机器学习算法。经检验表明，在晴空条件下，机器学习算法反演精度相对较高，已超过98%，利用算法可以实现对中国近海上空雾霾的监测。