A high-fidelity design methodology using LES-based simulation and POD-based emulation: A case study of swirl injectors

Engineering design is undergoing a paradigm shift from design for performance to design for affordability, operability, and durability, seeking multi-objective optimization. To facilitate this transformation, significantly extended design freedom and knowledge must be available in the early design stages. This paper presents a high-fidelity framework for design and optimization of the liquid swirl injectors that are widely used in aerospace propulsion and power-generation systems. The framework assembles a set of techniques, including Design Of Experiment (DOE), high-fidelity Large Eddy Simulations (LES), machine learning, Proper Orthogonal Decomposition (POD)-based Kriging surrogate modeling (emulation), inverse problem optimization, and uncertainty quantification. LES-based simulations can reveal detailed spatiotemporal evolution of flow structures and flame dynamics in a high-fidelity manner, and identify important injector design parameters according to their effects on propellant mixing, flame stabilization, and thermal protection. For a given a space of design parameters, DOE determines the number of design points to perform LES-based simulations. POD-based emulations, trained by the LES database, can effectively explore the design space and deduce an optimal group of design parameters in a turn-around time that is reduced by three orders of magnitude. The accuracy of the emulated results is validated, and the uncertainty of prediction is quantified. The proposed design methodology is expected to profoundly extend the knowledge base and reduce the cost for initial design stages.     

大角度斜置激光惯组与里程计组合导航方法

针对激光惯组斜置条件下惯组坐标系相对里程计坐标系是大角度的情况,建立了两坐标系之间的转换关系,推导了里程计输出转换的安装误差补偿模型,在补偿模型基础上给出了安装误差计算公式.以惯组位移与里程计位移之差作为量测值,建立了状态和量测方程,运用Kalman滤波技术实现惯组/里程计组合导航,最后通过跑车试验对提出的惯性/里程计组合导航方法进行了验证,结果表明了该方法的有效性.     

大弯角开槽叶栅槽道位置与结构研究

为拓宽大弯角扩压叶栅可用攻角范围,优化叶片吸力面流动分离结构,本文以一大弯角叶栅为研究对象,对叶片采用压力面到吸力面打通的双“C”型槽道结构处理,在保持槽道长度及其他参数不变的条件下,设置85%、80%、75%、70%轴向弦长四个出口位置研究槽道出口位置对叶栅性能的影响。研究发现,特定攻角下,槽道出口位于吸力面角区分离线起始点之后、尾缘分离线之前,对吸力面流动分离的控制效果较佳;在全攻角范围,槽道出口则取在0o攻角对应较佳出口位置为好。为减小槽道内总压损失,本文提出了一种“SC”型槽道改进结构,在80%轴向弦长槽道出口位置处与双“C”型槽道以及原型叶栅进行对比。结果表明,“SC”型槽道结构相比于双“C”型槽道结构,叶栅尾迹损失及槽道内总压损失减少,槽道出口射流速度提高,叶片尾缘处静压升高;相比于原型叶栅则能有效降低其在全攻角范围内的总压损失,基本消除叶片吸力面附面层分离,削弱角区分离,提高叶栅的扩压能力。     

面向大型承载结构强度性能的试验系统高精度装配调控方法

以直径0.6 m开口筒壳为例,分析了装配误差对仿真结果产生的影响,表明高精度量化试验系统装配方法研究的必要性。传统装配方法采用直尺等机械工具开展试验系统装配,导致实际装配误差较大且难以精准定量。因此提出一种试验系统装配误差精准测量与调控方法,该方法通过测量标识点获取装配件实际位置,并计算实际与理论位置的装配误差,结合机械推动以及位移测量等设备实现位置精确调控。为验证方法的可行性与精度,基于自研的强度试验高精度装配软件,分别开展了直径0.6 m和1.6 m圆柱筒壳装配调控试验。相比传统方法,最大位移误差从15.00 mm降至0.75 mm,最大角度误差从0.93°降至0.04°,数值分析承载力误差从1.67%降到了0.04%,降低了装配误差对承载力的影响,提高了试验系统装配精度。     

电磁混响室高强度辐射场下机载电台敏感度研究

机载电台作为飞机典型用频机载设备,对其进行高强度辐射场(HIRF)辐照效应试验研究具有重要意 义。为了解决混响室高强度辐射场环境的快速构建、快速调控及机载设备敏感度有效测试问题,依托混响室高 强度辐射场辐射敏感度测试系统,以某型直升机机载电台为试验对象,在400 MHz~2GHz频段内,通过改变 混响室内部场强,分别确定混响室连续与步进两种工作模式下机载电台的典型故障类型和敏感度阈值。结果 表明:在试验环境场强相同的条件下,相比步进工作模式,连续工作模式更容易测试出机载电台的敏感度阈值; 搅拌器连续工作模式下,搅拌速度越快测试得到的机载电台敏感度阈值越低,随脉冲波脉宽的增加其敏感度阈 值的测试结果呈下降趋势。     

Difficulties in the study of cosmic radio noise absorption at 30 MHz using riometer at low latitude station,Kolhapur (Lat-16.8°N,Long-74.25°E)

A dual dipole antenna has been installed at low latitude station Kolhapur (Geographic 16.8°N, 74.25°E), Maharashtra, India for the study of cosmic radio noise absorption using Solid State Riometer (which operates at 30 MHz) during pre phase of 24th solar maxima. The aim for this type of study over Kolhapur was to know the response of lower (D region) ionosphere over low latitude by cosmic radio noise absorption using riometer technique during quite period as well as sudden ionospheric disturbances (SID). The observations are being taken for 3 years. Two different sites (∼40 km away from each other) were used for the installation of riometer equipment assuming minimum local noise. It is found that solar noise to cosmic radio noise hence resulting in signal saturation. The night time signal is relatively free of interference but sometimes local noise is responsible for spike-like signatures. Hence it is concluded that Kolhapur (a low latitude station) is not suitable for the study of cosmic radio noise absorption on 30 MHz with riometer and dual dipole antenna. Proper choice for operating frequency of riometer and antenna gain is suggested for low latitude use of this technique for ionospheric deviative and nondeviative absorption studies.     

The beginning of cosmic ray astrophysics

A short history of the beginning of cosmic ray (CR) astrophysics is considered: from the hypothesis on CR origin as a result of Supernova explosions in the Metagalaxy, to a model of solar origin of CR, galactic origin based on the stochastic mechanism of charged particle acceleration in interstellar space, to extragalactic and hierarchical models of CR origin, as well as galactic CR origin taking into account radio-astronomical data. We consider also the first balloon results on the chemical contents of primary CR (especially of the contents Li, Be, B), important for any model of CR origin. Investigations of the injection problem, CR drift and diffusion acceleration by shock waves, and CR generation in Supernova remnants were also important steps in the beginning of CR astrophysics.     

Decentralized formation pose estimation for spacecraft swarms

For spacecraft swarms, the multi-agent localization algorithm must scale well with the number of spacecraft and adapt to time-varying communication and relative sensing networks. In this paper, we present a decentralized, scalable algorithm for swarm localization, called the Decentralized Pose Estimation (DPE) algorithm. The DPE considers both communication and relative sensing graphs and defines an observable local formation. Each spacecraft jointly localizes its local subset of spacecraft using direct and communicated measurements. Since the algorithm is local, the algorithm complexity does not grow with the number of spacecraft in the swarm. As part of the DPE, we present the Swarm Reference Frame Estimation (SRFE) algorithm, a distributed consensus algorithm to co-estimate a common Local-Vertical, Local-Horizontal (LVLH) frame. The DPE combined with the SRFE provides a scalable, fully-decentralized navigation solution that can be used for swarm control and motion planning. Numerical simulations and experiments using Caltech’s robotic spacecraft simulators are presented to validate the effectiveness and scalability of the DPE algorithm.     

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.     

First millimetric detections of AE Aquarii

We report the first millimetric detections of the magnetic cataclysmic variable AE Aquarii, accompanied by contemporaneous microwave observations. These data show that the time-averaged spectrum is well fit by a power-law which extends to mm wavelengths. We suggest that the spectrum is consistent with that expected from a superposition of flare-like events.