Recent advances in surrogate-based optimization

The evaluation of aerospace designs is synonymous with the use of long running and computationally intensive simulations. This fuels the desire to harness the efficiency of surrogate-based methods in aerospace design optimization. Recent advances in surrogate-based design methodology bring the promise of efficient global optimization closer to reality. We review the present state of the art of constructing surrogate models and their use in optimization strategies. We make extensive use of pictorial examples and, since no method is truly universal, give guidance as to each method's strengths and weaknesses.     

Recent advances in planetary ionospheres

Recent results on the ionospheres of various planets are reviewed. In view of the large amount of data now available on Venus, much of the work relates to this planet. The outer planets received somewhat less attention partly due to lack of measurements in the post-Voyager era. Two outer planetary satellites, that of Titan and Triton present very interesting ionospheres and have been included in the review.     

Waveform fusion in sonar signal processing

In active sonar systems, proper selection of the transmitted waveform is critical for target detection and parameter estimation, especially with the existence of clutter (reverberation). Two commonly used waveforms (constant frequency (CF) and linear frequency modulated (LFM)) are studied. Their characteristics are complementary both with respect to their accuracies and their sensitivity to the blind zero-Doppler ridge. Several fusion schemes of the two kinds of waveforms are explored and fusion results are studied both analytically and from simulation. It is concluded that fusion of the information of different waveforms can be not only more robust, but in some cases outright preferable, in term of detection probability and estimation accuracy.     

卫星导航进近技术进展

全球卫星定位系统（GNSS）增强系统能提供全天候无间断的卫星导航信号,可以辅助飞机进行进近。本文介绍了全球卫星导航系统进近着陆系统的基本组成、工作原理和功能特点,并对国内外研究进展进行了阐述。针对GNSS进近研究中的热点问题,重点论述了地基增强系统（GBAS）、星基增强系统（SBAS）、用户自主完好性监测（RAIM）等技术的发展现状,指出了GNSS进近技术实际工程应用仍然存在的问题,探讨了GNSS进近技术未来的发展方向。     

Sensor systems signal processing platform

A field programmable gate array-based computing platform for high-speed sensors such as short-range radars is presented. The circuit performs necessary A/D conversions, raw data stream compression and target detection, and constructs a message structure suitable for external displays. In the prototype, USB is the connecting path to a laptop computer. An elementary pulse radar is utilized as an application example. An application interest would be in collision avoidance systems. Observed data transfer rates with real radar input signals were 36 Mbytes/s when typical target detection algorithms were applied.     

Recent advances in the aerothermodynamics of spiked hypersonic vehicles

Among a variety of design requirements, reducing the drag and aeroheating on hypersonic vehicles is the most crucial one. Unfortunately, these two objectives are often conflicting. On one hand, sharp slender forebodies design reduces the drag and ensures longer ranges and more economic flights. However, they are more vulnerable to aerodynamic heating. On the other hand, blunt forebodies produce more drag, however, they are preferred as far as aeroheating is concerned. In addition, in the context of hypersonic vehicles, blunt geometries are preferred over slender ones for practical implications such as higher volumetric efficiency, better accommodation of crew or on-board equipment.In principle, a blunt vehicle flying at hypersonic speeds generates a strong bow shock wave ahead of its nose, which is responsible for the high drag and aeroheating levels. There have been a number of efforts devoted towards reducing both the drag and the aeroheating by modifying the flowfield ahead of the vehicle's nose. Of these techniques, using spikes is the simplest and the most reliable technique. A spike is simply a slender rod attached to the stagnation point of the vehicle's nose. The spike replaces the strong bow shock with a system of weaker shocks along with creating a zone of recirculating flow ahead of the forebody thus reducing both drag and aeroheating.Since their introduction to the high-speed vehicles domain in the late 1940s, spikes have been extensively studied using both experimental facilities and numerical simulation techniques. The present paper is devoted to surveying these studies and illustrating the contributions of the authors in this field. The paper also raises some of the areas in the field that need further investigations.     

Recent advances in film cooling enhancement: A review

Film cooling is an indispensable scheme in the design of highly-efficient cooling configurations to satisfy the thermal protection requirement of turbine hot section components. During the last few decades, vast efforts have been paid on the discrete-hole film cooling enhancement. In this paper, some of the recent literatures related to the passive strategies (such as shaped film cooling holes, upstream ramps, shallow trenches, mesh-fed slots) and the active strategies (such as the use of pulsation modulating device or plasma actuator) for film cooling enhancement are surveyed, with the aim at presenting an updated overview about the state of the art in advanced film cooling. In addition, some challenging issues are also outlined to motivate further investigations in such a broad topic.     

飞机结冰的不确定性量化研究进展

为深入认识影响飞机结冰的不确定性及其研究方法,从自然条件结冰、冰风洞试验、数值模拟等方面,介绍了飞机结冰不确定性来源,以蒙特卡洛法、多项式混沌法和随机配置法等为例,系统分析了各种不确定性量化方法在计算能力、求解精度等方面的优劣。考虑飞机结冰不确定性量化处于起步时期,重点综述了数值模拟中结冰条件不确定性对冰形和气动特性的影响。从结合单步法和多步法确定最佳结冰时间步长来提升结冰计算精度和效率、对其他关键部件进行结冰不确定性量化从而为更精细化的防/除冰系统的设计提供支撑,以及通过建立高精度的代理模型来代替原本复杂的数值模拟系统以应对考虑多个不确定性因素共同作用所带来的计算挑战等多个方面,全面展望不确定性量化方法及其在飞机结冰应用中的发展方向。     

脑电信号的最新研究方法

脑电信号是脑神经细胞电生理活动在大脑皮层或头皮表面的总体反映，脑电信号的研究一直是生物医学领域难度很大且倍受人们关注的课题。在简要回顾了脑电研究的历史和现状的基础上，重点论述了混沌分析法、人工神经网络(ANN)分析法、小波变换法、Wigner分布等在脑电信号分析和处理中的应用情况。最后展望了脑电信号研究的发展应用前景。     

Advances in signal processing technology for electronic warfare

The denial of effective communications by enemy forces during hostile military operations has been a primary concern for military commanders since the inception of radio communications on the battlefield before World War II. Since then, the electromagnetic environment has been in a constant state of evolution toward more sophisticated jam-resistant and convert forms of modulation. For example, exotic modulation techniques employing spread spectrum (SS) signaling are routinely used by our adversaries to provide their communication links an advantage over US and Allied jammers. These same spread spectrum modulation techniques are being refined to provide convert, low probability-of-intercept (LPI) features to the unintended interceptor. The thrust of this paper focuses on developments in the theory and algorithms for detection, characterization, and exploitation of advanced waveforms using new mathematical signal processing tools. Specifically, quadratic time-frequency signal representations, wavelet transforms, and cyclostationary signal processing are introduced. This overview demonstrates the importance of these advanced techniques in a clear and concise manner. Applications and future research activities are described     

Model-based multifrequency array signal processing for low-angletracking

Tracking low-altitude targets over the sea is problematic because of interference between the direct and reflected signal. Standard monopulse trackers can experience large errors because of multipath maximum likelihood estimation (MLE) has been used to more accurately estimate the target height in the presence of multipath MLE is a model-fitting technique where the model parameters are chosen to maximize the likelihood function. It is shown that the type of observation model has a large effect on performance. Tracking performance is compared using three different observation models employing varying amounts of a priori information. Results are presented for different array sizes: eight and 32-element arrays and two-element subarrays typical of phase monopulse. Performance is compared with that of standard techniques such as Fourier beamforming and phase monopulse     

Numerical optimization method for array signal processing

This paper presents a novel and efficient extrema-mapping algorithm, which we call the roller-coaster algorithm. Two versions of the algorithm, the one-dimensional (1-D) and the two-dimensional (2-D) roller-coaster, are developed. Its applicability to array signal processing is demonstrated. We use it to solve a multiple source direction finding problem using multiple signal classification (MUSIC), beamformer, and minimum variance methods, and for antenna array design. The algorithm is based on heuristic assumptions and its properties are not proved. Yet, its performance was tested in many simulated experiments, yielding favorable results     

含噪信号经验模式分解虚假分量识别方法

针对含噪信号Hilbert-Huang变换存在虚假分量,提出改进的奇异值分解(SVD)方法进行降噪,改进包含两个部分:一是利用重构相空间代替传统矩阵如Hankel矩阵,以去掉信号冗余,再者提出奇异值能量熵分量差分法,更易于定出重构奇异值阶次;二是提出了频谱比值法对虚假分量进行辨识,更有效辨识出虚假分量.首先利用经验模式分解(EMD)得到本征模式分量(IMF),识别并剔除趋势项,重构信号,然后进行SVD,重构降噪后的信号,消除虚假分量,最后进行时频分析.联合方法应用于含噪仿真信号,信噪比(signal noise ratio,SNR)提高了5.5%,虚假分量辨识率提高至100%,用于双跨转子故障振动信号,得到正确的时频结果,表明了所提方法识别含噪信号虚假分量的有效性.     

Recent advances in precision measurement & pointing control of spacecraft

There exists an increasing need for precision measurement & pointing control and extreme motion stability for current and future space systems, e.g., Ultra-Performance Spacecraft (UPS). Some notable technologies of realizing Ultra-Pointing (UP) ability have been developed particularly for Ultra-accuracy Ultra-stability Ultra-agility (3U) spacecraft over recent decades. Usually, Multilevel Compound Pointing Control Techniques (MCPCTs) are deployed in aerospace engineering, especially in astronomical observation satellites and Earth observation satellites. Modern controllers and/or algorithms, which are a key factor of MCPCTs for 3U spacecraft, especially the jitter phenomena that commonly exist in a UPS Pointing Control System (PCS), have also been effectively used in some UP spacecraft for a number of years. Micro-vibration suppression approaches, however, are often proposed to deal with low-level mechanical vibration or disturbance in the microgravity environment that is common for UPS. This latter approach potentially is one of the most practical UP techniques for 3U tasks. Some emerging advanced Disturbance-Free Payload (DFP) satellites that exploit the benefits of non-contact actuators have also been reported in the literature. This represents an interesting and highly promising approach for solving some challenging problems in the area. This paper serves as a state-of-the-art review of UP technologies and/or methods which have been developed, mainly over the last decade, specifically for or potentially could be used for 3U spacecraft pointing control. The problems discussed in this paper are of reference significance to UPS and millisecond optical sensors, which are involved in Gaofeng Project, deep space exploration, manned space flight, and gravitational wave detection.     

低温液体火箭燃烧室内射流雾化研究进展

从理论、实验和数值计算方面,阐述和总结了低温推进剂射流雾化的研究现状和进展。对射流雾化机理及形态进行了分类,重点从对比常温流体与低温流体射流雾化特征参数不同的角度,梳理了射流雾化方面的数值研究方法,并介绍了低温射流雾化的相关实验研究。结果表明:空气扰动破碎机理仍是最广为接受的理论,而超临界工况下射流雾化形态不符合现有的射流雾化分类;数值计算方法逐渐由流体体积法和水平集法向直接数值模拟转变,对闪蒸现象的建模是研究重难点之一;低温流体射流喷雾实验数据匮乏,需通过丰富测量手段,提高测量精度的途径获得完整、准确的实验数据。      

民用飞机全寿命周期成本及经济性设计研究

总结了民用飞机全寿命周期成本研究方法,对民机型号研制中通常采用的成本估算方法和软件工具进行了介绍。在此基础上,一方面从民机运营经济性的角度对不同市场条件下的计算分析模型进行了对比,指出发展更可靠的直接维修成本（DMC）模型的必要性;另一方面,从民机研制的角度,通过将经济性分析模块有机融入传统飞机设计流程,提出面向经济性设计的总体思路,为实现民用飞机的多学科设计提供了基础。     

A hardware signal processing platform for sensor systems

A field programmable gate array-based computing platform for high-speed sensors such as short-range radars is presented. The circuit performs necessary A/D conversions, raw data stream compression and target detection, and constructs a message structure suitable for external displays. In the prototype, USB is the connecting path to a laptop computer. An elementary pulse radar is utilized as an application example. An application interest would be in collision avoidance systems. Observed data transfer rates with real radar input signals were 36 Mbytes/s when typical target detection algorithms were applied.     

超声速混合层转捩过程实验研究的进展

超声速湍流机理的实验研究是一件十分困难的工作.在2000年以来,本研究小组在低噪声超声速混合层风洞研究、超声速流动精细结构测量技术研究方面取得了重要进展,这给超声速混合层湍流精细结构的研究奠定了基础.为了研究超声速混合层及其气动光学问题,在研制的超声速混合层风洞中,主要以基于纳米技术的平面激光散射技术(Nano-trace Planar Laser Scattering,简称NPLS)为基础,研究了几种对流马赫数的超声速混合层从层流到湍流转捩过程K-H不稳定涡的空间结构,以及K-H不稳定涡的空间结构随着时间的发展过程.实验结果清晰地反映了湍流混合的不稳定性与转捩的精细结构,以及转捩过程的展向精细结构.