A novel architecture of electro-hydrostatic actuator with digital distribution

To address the flow imbalance rapidly of the asymmetric Electro-Hydrostatic Actuator (EHA), this paper presents a novel architecture of asymmetric EHA with the Digital Distribution (EHA-DD). It also improves the flow nonlinearity and control accuracy of the pump, especially in the low-speed condition. The digital distribution with two High-Speed on–off Valves (HSVs) not only balances flow instead of the check valves, but also replaces the pump at the low-speed to control output flow by adjusting the PWM signal. The pump and HSVs are the crucial components to control flow output. Firstly, the flow calculation models of the pump and the duty ratio inversed model of the HSV are obtained through experimental tests and the identification method. To get the control input signal for the required flow, the pump speed and PWM duty ratio for the HSVs are inversed to compensate for flow output. Further, a multimode digital flow distribution control method based on pump speed, mainly including the pump-controlled mode for large flow demand and valve-controlled mode for little flow demand, is proposed to control the accurate flow output actively. The step extension experiments based on the flow calculation models are conducted on the EHA-DD prototype under elastic, opposite varying load. The results demonstrate that the EHA-DD realizes little position error by accurate flow control, and it is also beneficial to improve the service life of the pump.     

火星表面热环境对航天器热控影响分析

火星大气对太阳辐射产生吸收和散射作用，同时还将与火星表面航天器发生对流换热。热设计时难以直接评估对流、辐射和导热三种换热对航天器的影响，从而确定主要的控温途径。在调研火星表面辐射、大气等热环境的基础上，从线性化传热系数和对流辐射比的角度对比分析了辐射、对流和导热对航天器的影响。器表辐射传热系数随光学属性和温度的变化范围为0.3～1.4W/(m2·℃)，对流传热系数随风速变化为0.2～1.5W/(m2·℃)，器内导热传热系数可控制在0.25W/(m2·℃)以下。结果表明，太阳辐射较火星表面和天空辐射而言是主要外热源，航天器表面的辐射和对流换热为两条并联换热途径，两者均可成为主要换热途径，器内导热传热是控制航天器内外隔热的主要可控因素。     

航天器运输包装箱仿真验证平台技术研究

针对数量有限的物理跑车试验无法满足减振与保温性能测试需求的问题，提出一套航天器运输包装箱动力学与热学仿真验证方法，包括：建立适用于包装箱系统的刚柔耦合多体动力学系统，通过结合线路条件测试生成的动力学系统外部激励，实现减振性能虚拟跑车测试；建立基于计算流体力学的包装箱热学模型，通过模拟自然对流和空调控制，实现包装箱保温性能虚拟跑车测试；基于C/S架构和导航式流程设计思想，建立航天器运输包装箱仿真验证平台，通过实际案例证明该平台仿真结果与实际跑车测试数据具有较高的一致性。     

Evaluation of SARAL/AltiKa performance using GNSS/IMU equipped buoy in Sajafi,Imam Hassan and Kangan Ports

Performance of SARAL/AltiKa mission has been evaluated within 2016 altimeter calibration/validation framework in Persian Gulf through three campaigns conducted in the offshore waters of Sajafi, Imam Hassan and Kangan Ports, while the altimeter overflew the passes 470, 111 and 25 on 13 Feb, 7 March and 17 June 2016, respectively. As the preparation, a lightweight buoy was equipped with a GNSS receiver/choke-ring antenna and a MEMS-based IMU to measure independent datasets in the field operations. To obtain accurate sea surface height (SSH) time series, the offset of the onboard antenna from the equilibrium sea level was predetermined through surveying operations as the buoy was deploying in the onshore waters of Kangan Port. Accordingly, the double-difference carrier phase observations have been processed via the Bernese GPS Software v. 5.0 so as to provide the GNSS-derived time series at the comparison points of the calibration campaigns, once the disturbing effects due to the platform tilt and heave have been eliminated. Owing to comparing of the SSH time series and the associating altimetry 1?Hz GDR-T datasets, the calibration/validation of the SARAL/AltiKa has been performed in the both cases of radiometer and ECMWF wet troposphere corrections so as to identify potential land contamination. An agreement of the present findings in comparison with those attained in other international calibrations sites confirms the promising feasibility of Persian Gulf as a new dedicated site for calibration/validation of ongoing and future altimetry missions.     

Assessment of between-floor structural and topological properties on cognitive map development in multilevel built environments

The present study investigated cognitive map development in multilevel built environments. Three experiments were conducted in complex virtual buildings to examine the effects of five between-floor structural factors that may impede the accuracy of humans’ ability to build multilevel cognitive maps. Results from Experiments 1 and 2 (of three experiments) revealed that difficulties in developing multilevel cognitive maps are not solely caused by the z-axis offset, as is suggested in the literature, but are due to the factorial combination of a between-floor overlap and a z-axis offset. Results from Experiment 2 showed that this process becomes substantially more difficult when the reference directions between different floors have an angular offset from each other. Finally, results from Experiment 3 demonstrated that confusing between-floor heading shifts in aligned buildings did not make it reliably harder to build multilevel cognitive maps. The implications of these findings are discussed in terms of theories of mental representations in multilayered three-dimensional spaces, as well as for architectural design.     

Simulating planetary wave propagation to the upper atmosphere during stratospheric warming events at different mountain wave scenarios

Parameterization schemes of atmospheric normal modes (NMs) and orographic gravity waves (OGWs) have been implemented into the mechanistic Middle and Upper Atmosphere Model (MUAM) simulating atmospheric general circulation. Based on the 12-members ensemble of runs with the MUAM, a composite of the stratospheric warming (SW) has been constructed using the UK Met Office data as the lower boundary conditions. The simulation results show that OGW amplitudes increase at altitudes above 30 km in the Northern Hemisphere after the SW event. At altitudes of about 50 km, OGWs have largest amplitudes over North American and European mountain systems before and during the composite SW, and over Himalayas after the SW. Simulations demonstrate substantial (up to 50–70%) variations of amplitudes of stationary planetary waves (PWs) during and after the SW in the mesosphere-lower thermosphere of the Northern Hemisphere. Westward travelling NMs have amplitude maxima not only in the Northern, but also in the Southern Hemisphere, where these modes have waveguides in the middle and upper atmosphere. Simulated variations of PW and NM amplitudes correspond to changes in the mean zonal wind, EP-fluxes and wave refractive index at different phases of the composite SW events. Inclusion of the parameterization of OGW effects leads to decreases in amplitudes (up to 15%) of almost all SPWs before and after the SW event and their increase (up to 40–60%) after the SW in the stratosphere and mesosphere at middle and high northern latitudes. It is suggested that observed changes in NM amplitudes in the Southern Hemisphere during SW could be caused by divergence of increased southward EP-flux. This EP-flux increases due to OGW drag before SW and extends into the Southern Hemisphere.     

ORB-SLAM系统优化框架分析概述

首先阐述了ORB-SLAM系统的核心思想和基本框架,介绍了SLAM系统中光束平差法的应用实现,然后针对视觉里程计部分不同的关键帧位姿优化过程分别进行了详细阐述,并利用KITTI数据集的不同序列的实验结果进行比较研究,给出了核心的光束平差法在ORB-SLAM中的具体工作方式及性能分析,最后讨论和分析了ORB-SLAM的优势和不足。     

Alfvén gravity waves in viscous solar plasma: Effect of the background flow

We study the Propagation and damping properties of Alfvén gravity waves in the presence of the vertical magnetic field in the viscous solar plasma under influence of the background flow by deriving a fourth order dispersion relation in terms of the Doppler shifted frequency. We derive the dispersion relation under WKB and Boussinesq approximation. We study the damping of Alfvén gravity waves for the wave frequencies less than and greater than the Brunt-Väisälä frequency. We find that the Brunt-Väisälä frequency divides the frequency ranges where the weakly or strongly damped oscillations occur. The background flow exhibits a strong effect on weakly damped oscillations and a weak effect on the strongly damped oscillations. We also notice that the damping of both the strong and weakly damped oscillations depend on the Brunt-Väisälä frequency and wave number. The effect of the background flow is also being governed by the Brunt-Väisälä frequency and wave number. We also study the properties of gravity wave mode after filtering the Alfvén wave mode by minimizing the magnetic field and noticed that the background flow shows a very strong effect on the gravity wave mode.     

偏心撞击对撞击式喷嘴雾化特性的影响

为研究偏心撞击对撞击式喷嘴雾化特性的影响,建立了求解自燃推进剂冷态射流撞击雾化过程的数值模拟方案,计算了不同偏心度条件下的射流撞击雾化过程。采用树形自适应加密算法直接求解不可压Navier-Stokes方程组,由分段线性的流体体积(VOF)方法对流体界面进行捕捉。结果表明偏心撞击会导致雾场发生偏转,当无量纲偏心度E为1/8时,雾场偏转角度约为9.2°,应控制加工偏差小于该值。随着偏心度的增大,液膜的偏转角度增大,理论推导得到的液膜偏转角度要小于数值计算得到的液膜偏转角度。正心撞击时燃料与氧化剂流强峰值接近,雾场的流强分布呈单峰分布。当发生偏心撞击时,由于燃料与氧化剂部分射流未参与撞击导致流强峰值出现交错,雾场的流强分布呈双峰分布,混合比的空间分布发生较大改变。正心撞击时撞击点下游液滴的速度分布近似呈轴对称分布,而偏心撞击之后的速度分布则呈中心对称分布。偏心撞击导致的射流动量损失使得雾化性能变差,当无量纲偏心度E为1/8时,一甲基肼(MMH)的Sauter平均直径增大约4.8%,四氧化二氮(NTO)的Sauter平均直径增大约5.8%。      

面向下一代运载火箭的综合电子系统集成技术

介绍了面向下一代运载火箭分布式模块化电子系统(DIMA)的集成技术及系统架构。针对下一代运载火箭复杂电子系统的特点，按照系统集成的路线，对系统设计目标、系统功能需求分析、系统抽象机制、系统综合技术等多方面进行论述。首先，根据电气系统功能获得系统需求，采用功能抽象和层次抽象定义系统抽象模型，提取出高内聚低耦合的原子功能模块，并对模块的属性、交换关系、时序约束关系等进行定义；然后采用可视化表征方法对系统进行深入分析，利用系统综合技术实现了从系统功能到硬件资源的映射，从而给出了集成控制单元和模块的种类；随后采用分时分区的设计理念对系统节点分区划分方案及容错架构进行了定义，并对分区操作系统的调度模型和交换式的数据交互网络进行了论述，最终给出了系统软硬件架构。