Visual navigation in orchard based on multiple images at different shooting angles

The orchards usually have rough terrain,dense tree canopy and weeds.It is hard to use GNSS for autonomous navigation in orchard due to signal occlusion,multipath effect,and radio frequency interference.To achieve autonomous navigation in orchard,a visual navigation method based on multiple images at different shooting angles is proposed in this paper.A dynamic image capturing device is designed for camera installation and multiple images can be shot at different angles.Firstly,the obtained orchard images are classified into sky and soil detection stage.Each image is transformed to HSV space and initially segmented into sky,canopy and soil regions by median filtering and morphological processing.Secondly,the sky and soil regions are extracted by the maximum connected region algorithm,and the region edges are detected and filtered by the Canny operator.Thirdly,the navigation line in the current frame is extracted by fitting the region coordinate points.Then the dynamic weighted filtering algorithm is used to extract the navigation line for the soil and sky detection stage,respectively,and the navigation line for the sky detection stage is mirrored to the soil region.Finally,the Kalman filter algorithm is used to fuse and extract the final navigation path.The test results on 200 images show that the accuracy of visual navigation path fitting is 95.5%,and single frame image processing costs 60 ms,which meets the real-time and robustness requirements of navigation.The visual navigation experiments in Camellia oleifera orchard show that when the driving speed is 0.6 m/s,the maximum tracking offset of visual navigation in weed-free and weedy environments is 0.14 m and 0.24 m,respectively,and the RMSE is 30 mm and 55 mm,respectively.

Feasibility of replacing the 3-coach with a 1.5-coach grouping trainmodel in wind tunnel experiment at different yaw angles

The effects of different yaw angles on the aerodynamic performance of city electric multiple units(EMUs)were investigated in a wind tunnel using a 1:16.8 scaled model.Pressure scanning valve and six-component box-type aerodynamic balance were used to test the pressure distribution and aerodynamic force of the head car respectively from the 1.5-and 3-coach grouping city EMU models.Meanwhile,the effects of the yaw angles on the pressure distribution of the streamlined head as well as the aerodynamic forces of the train were analyzed.The experimental results showed that the pressure coefficient was the smallest at the maximum slope of the main shape-line.The side force coefficient and pressure coefficient along the head car cross-section were most affected by crosswind when the yaw angle was 55°,and replacing a 3-coach grouping with a 1.5-coach grouping had obvious advantages for wind tunnel testing when the yaw angle was within 24.2°.In addition,the relative errors of lift coefficient C_(L),roll moment coefficient C_(Mx),side force coefficient C_(S),and drag coefficient C_(D) between the 1.5-and 3-coach cases were below 5.95%,which all met the requirements of the experimental accuracy.

Design of 2D-Bootlace Lens with Five Focal Feed for Multiple Beam Forming

Utility of microwave bootlace lens is well established. For broadband and wide scanning network, it is required to op-timize and use features of this lens for better communication and scanning device. This report presents the design of a compact 2D bootlace lens with five focal feed for multiple beam forming. This design will help in reducing phase error and will provide power efficiency and better resolution during target tracking. This design will provide better aperture efficiency and scanning angle.

Longitudinal train dynamics of electric multiple units under rescue

Once operating trains are disabled on the railway lines,an efficient manner is to utilize the train for train rescue.Owning to the different train and coupler types,it is difficult to formulate uniform regulations for train to train rescue.In this paper,the longitudinal train dynamics of electric multiple units under rescue were analyzed by field and laboratory tests.The angling behavior of the brakinginduced coupler under compressed in-train forces was analyzed.A dynamic model for the train and draft gear system was developed considering accurate boundary limitations and braking characteristics.The safety indices and their limits for the coupled rescue train were defined.Thedynamic evaluations of different train to train rescue scenarios were analyzed.It is indicated that the coupler vertical rotation occurs during the emergency braking applied by the assisting train.The vertical force components of intrain forces lead to the carbody pitch behavior and even cause local destructions to the coupler system.The carbody pitch motion can arise the inference of in-train devices.Based on the safety evaluation of train and coupler system,the regulations for typical train to train rescue scenarios were formulated.

Passive Localization of Multiple Sources Using Joint RSS and AOA Measurements in Spectrum Sharing System

In spectrum sharing systems,locating mul-tiple radiation sources can efficiently find out the in-truders,which protects the shared spectrum from ma-licious jamming or other unauthorized usage.Com-pared to single-source localization,simultaneously lo-cating multiple sources is more challenging in prac-tice since the association between measurement pa-rameters and source nodes are not known.More-over,the number of possible measurements-source as-sociations increases exponentially with the number of sensor nodes.It is crucial to discriminate which measurements correspond to the same source before localization.In this work,we propose a central-ized localization scheme to estimate the positions of multiple sources.Firstly,we develop two computa-tionally light methods to handle the unknown RSS-AOA measurements-source association problem.One method utilizes linear coordinate conversion to com-pute the minimum spatial Euclidean distance sum-mation of measurements.Another method exploits the long-short-term memory(LSTM)network to clas-sify the measurement sequences.Then,we propose a weighted least squares(WLS)approach to obtain the closed-form estimation of the positions by linearizing the non-convex localization problem.Numerical re-sults demonstrate that the proposed scheme could gain sufficient localization accuracy under adversarial sce-narios where the sources are in close proximity and the measurement noise is strong.

Multi-target localization for bistatic MIMO radar in the presence of unknown mutual coupling

A decoupling-estimation signal parameters via rotarional invariance technique（ESPRIT） method is presented for multi-target localization with unknown mutual coupling in bistatic multiple-input multiple-output（MIMO） radar.Two steps are carried out in this method.The decoupling operation between angle and mutual coupling estimates is realized by choosing the auxiliary elements on both sides of the transmit and receive uniform linear arrays（ULAs）.Then the ESPRIT method is resilient against the unknown mutual coupling matrix（MCM） and can be directly utilized to estimate the direction of departure（DOD） and the direction of arrival（DOA）.Moreover,the mutual coupling coefficient is estimated by finding the solution of the linear constrained optimization problem.The proposed method allows an efficient DOD and DOA estimates with automatic pairing.Simulation results are presented to verify the effectiveness of the proposed method.

Influence of Helix Angle on Stability of Milling Flexible Parts

Geometry of end mill cutters plays a vital role in the stability of the flexible parts milling.The present study considers helix angle and number of flutes.Multi-frequency solution is established to draw stability Lobe diagram(SLD)for different helix angles and number of flutes.SLD for the two cases shows that the greater the value of helix angle,the more stable the milling process will be,and conversely increasing the number of flutes degrades the stability of flexible parts milling.A simple empirical methodology is adopted to employ the inclined plane workpiece geometry offering agradual increase of the axial depth of cut in the feed direction.Surface roughness is used as a measure of stability.Test results corroborate the model conclusions very well.

Retrieval of Sea Surface Wind Speed by One-Dimensional Synthetic Aperture Microwave Radiometer

One-dimensional synthetic aperture microwave radiometers have higher spatial resolution and record measurements at multiple incidence angles.In this paper,we propose a multiple linear regression method to retrieve sea surface wind speed at an incidence angle between 0°65°.We assume that a one-dimensional synthetic aperture microwave radiometer operates at frequencies of 6.9,10.65,18.7,23.8 and 36.5 GHz.Then,the microwave radiative transfer forward model is used to simulate the measured brightness temperatures.The sensitivity of the brightness temperatures at 0°65°to the sea surface wind speed is calculated.Then,vertical polarization channels(VR),horizontal polarization channels(HR)and all channels(AR)are used to retrieve the sea surface wind speed via a multiple linear regression algorithm at 0°65°,and the relationship between the retrieval error and incidence angle is obtained.The results are as follows:(1)The sensitivity of the vertical polarization brightness temperature to the sea surface wind speed is smaller than that of the horizontal polarization.(2)The retrieval error increases with Gaussian noise.The retrieval error of VR first increases and then decreases with increasing incidence angle,the retrieval error of HR gradually decreases with increasing incidence angle,and the retrieval error of AR first decreases and then increases with increasing incidence angle.(3)The retrieval error of AR is the lowest and it is necessary to retrieve the sea surface wind speed at a larger incidence angle for AR.

慢性病共病、相位角与老年人肌少症相关的肌肉质量减少的关系研究

目的·探讨慢性非传染性疾病(慢性病)共病、相位角与老年人肌少症相关的肌肉质量减少的相关性,以及慢性病共病、相位角对老年人肌肉质量减少的预测价值。方法·对2018年8月1日—2019年7月31日入住上海交通大学医学院附属仁济医院老年科,年龄≥60岁的患者进行回顾性筛查。收集患者基本情况(性别、年龄、用药数、共病数、有无骨质疏松症、有无吸烟史等),以及实验室检查指标(血红蛋白、白蛋白、血肌酐、血尿酸、铁蛋白、维生素D、三酰甘油、总胆固醇、高密度脂蛋白、低密度脂蛋白等)结果。计算年龄调整后查尔森合并症指数(age-adjusted Charlson comorbidity index,aCCI)。采用InBody S10生物电阻抗身体成分检测仪进行人体成分测试,记录身体质量指数(body mass index,BMI)、骨骼肌质量指数(skeletal muscle mass index,SMI)、相位角(phase angle,PhA)。部分患者接受握力测量。肌肉质量减少采用2019年亚洲肌肉减少症工作组(Asian Working Group for Sarcopenia,AWGS)推荐的SMI值(男性≤7.0 kg/m^(2)、女性≤5.7 kg/m^(2))进行诊断。根据测定的SMI值将患者分为肌肉质量正常组与肌肉质量减少组。采用单因素和多因素Logistic分析老年患者发生肌少症相关的肌肉质量减少的危险因素。并进一步运用受试者操作特征曲线(receiver operator characteristic curve,ROC曲线)及曲线下面积评估相关因素预测肌肉质量减少的价值。结果·共入组慢性病共病患者359例,其中男性226例,女性133例;肌肉质量正常组241例,肌肉质量减少组118例,老年人肌少症相关的肌肉质量减少发生率为32.9%。单因素Logistic回归分析提示年龄(OR=1.036,95%CI 1.013~1.060)、共病数(OR=1.117,95%CI1.025~1.217)、aCCI(OR=1.123,95%CI 1.031~1.222)、高密度脂蛋白(OR=3.688,95%CI 2.065~6.622)与老年人肌肉质量减少的风险呈正相关,BMI(OR=0.514,95%CI 0.443~0.597)、PhA(OR=0.195,95%CI 0.126~0.303)、血红蛋白(OR=0.984,95%CI 0.972~0.996)、三酰甘油(OR=0.606,95%CI 0.424~0.866)与老年人肌肉质量减少的风险呈负相关。多因素Logistic回归模型提示PhA(OR=0.338,95%CI 0.119~0.959)、BMI(OR=0.634,95%CI 0.476~0.844)与老年人肌肉质量减少的风险呈负相关。BMI、PhA预测老年人肌少症相关的肌肉质量减少的ROC曲线下面积分别为0.893(95%CI 0.855~0.931)和0.786(95%CI 0.736~0.837),敏感度分别为0.724和0.676,特异度分别为0.916和0.762;BMI联合PhA预测老年人肌肉质量减少的ROC曲线下面积为0.917(95%CI 0.883~0.951),敏感度为0.867,特异度为0.860。结论·aCCI与老年人肌少症相关的肌肉质量减少具有相关性。随着BMI、PhA的下降,老年人肌肉质量减少的风险升高。BMI联合PhA具有较高的老年人肌少症相关的肌肉质量减少的预测价值。未发现慢性病共病对其的预测价值。

汽车中控壳注塑模及其五次六元复合斜滑块设计

汽车中控壳塑件注塑模具设计中,因塑件正面和背面都需要采用斜向脱模方式脱模,特别是背面的特征组成中,特征多且构成复杂,因此为该区域特征的脱模创新设计了一种五次六元复合斜滑块机构在局部区域实施抽芯脱模,并构建了该机构的力学运动模型。该复合斜滑块机构的结构设计为:利用油缸驱动1个主体斜滑块实施主抽芯,主体斜滑块的上端设置了一个先抽芯斜滑块即上斜滑块,上斜滑块先抽芯时驱动3个斜顶、4根弹簧顶针和1个C4侧型芯镶件;主体斜滑块的下端还设置了一个先抽芯斜滑块即斜型芯,该斜型芯也先于主体斜滑块抽芯;在上斜滑块完成先抽芯后,主体斜滑块的驱动油缸先驱动斜型芯抽芯,而后再驱动主体斜滑块及其上其余5种脱模元件一起完成抽芯。为实现塑件的自动化生产,在此复合斜滑块机构设计基础上,塑件的模具结构设计成热流道两板式两次开模模具,模具中还设计了1个正面油缸斜抽芯机构和4个斜导柱滑块机构,较好地实现了塑件的自动化生产。

基于Raptor编码的多输入多输出光通信系统设计

为了提高可见光通信(Visible Light Communication,VLC)系统的复用增益,本文提出一种基于多输入多输出(Multiple Input Multiple Output,MIMO)的固定比例像素化VLC系统。系统首先执行空间角度映射,使数据的传送可在角域中进行;同时利用Raptor编码方法来跟踪由于窗口截断而引起的数据信道特性变化;然后对于使用高速相机捕捉到的一系列时变图像,利用散景效应获得所有链路距离上的固定比例图像。实验利用液晶显示器和高速相机,对所提出的VLC系统进行了验证。与传统的像素化MIMO系统相比,本文所提出的系统在未对准朝向的情境下具有更高的鲁棒性,从而在多路复用场景有着广泛的应用前景。

一个新的涉及一个多重可变上限函数和一个部分和的半离散Hilbert型不等式

应用权函数的方法,Euler-Maclaurin求和公式,Abel部分求和公式及实分析技巧,求出了一个新的涉及一个多重可变上限函数和一个部分和的半离散Hilbert型不等式.作为应用,考虑了特殊参数下不等式中最佳常数因子联系多参数的等价条件及一些特殊不等式.

考虑多重性能水准的特高压双柱悬索拉线塔风灾易损性分析

特高压双柱悬索拉线塔为典型的风敏感结构,其在不同强度风荷载作用下易遭受不同程度的损伤及破坏,针对此类结构的风致损伤评估研究亟待开展。该文提出一种考虑多重性能水准的特高压双柱悬索拉线塔风灾易损性分析方法。首先,开展结构立柱刚性模型的风洞试验,获取立柱的气动三分力系数并模拟得到相应风荷载;进而,定性划分双柱悬索拉线塔的性能水准,并基于Pushover分析给出各性能水准所对应的量化模型;最后,在求得双柱悬索拉线塔概率风灾需求模型的基础上,对其进行风灾易损性分析,并研究风向角对易损性曲线的影响。结果表明:结构主体立柱的气动升力系数CL和气动力矩系数CM在不同工况下均接近于0,气动阻力系数CD则均大于2,且从0°到45°呈递增趋势;基于立柱顶点位移可建立双柱悬索拉线塔的多重性能水准,而由风灾易损性分析可知,双柱悬索拉线塔在正常使用条件下发生各级风致损伤及破坏的概率很小,结构具有良好的抗风性能;风向角对双柱悬索拉线塔风灾易损性影响显著,结构的最不利和最有利风向角分别为90°和0°。

基于内外侧联动式抽芯的多分型面镂空式收纳桶模具设计

根据产品的使用性能和工艺特点,对镂空式收纳桶的产品结构和工艺进行了分析。基于产品镂空和桶槽分布位置的不同,设计了3层分型面的模具结构,以实现对各个成型部分的运动控制;镂空形状分布面积比较大,为提高成型质量、节省模具空间,巧妙设计了定模侧爆炸式滑块抽芯机构;由于产品底部的侧凹形状位于定模底部,空间狭窄且缺乏动力源,因此在定模底部设计了型腔侧浮动式斜顶机构,完成了底部侧凹的抽芯动作;针对产品边缘具有内外圆角的大尺寸桶槽,在动模内部设计了内外侧联动式抽芯机构。模具投产后,各个抽芯机构动作顺畅,产品脱模顺利,达到了预期目的。

计及尾流的风电场智能等效建模及偏航优化控制

大型风电场中存在的尾流干扰会降低风电场整体输出功率,因此需要对风电场建立等效模型,并通过优化尾流分布来提升风电场整体功率输出能力。在所提出的新型风电场偏航优化框架中,提出了一种利用参数监督学习和正则化技术改进的径向基函数神经网络算法,并建立了面向多自由度偏航控制的风电场功率转换智能等效模型。在该模型的基础上,定义了以风电机组偏航角为决策变量的场级最大输出功率优化问题,提出了一种改进的精英多种群遗传算法并进行优化求解,得到各机组偏航角优化值以减少机组间尾流干扰。利用实际风电场布局和风况数据进行了仿真测试。结果表明:所建立的风电场功率转换智能等效模型与其实际特性吻合良好,在特定风况下,偏航优化控制使得风电场总功率提升718.79 kW;连续风况下,所提优化控制方法在不同风况下均有明显的优化效果,风电场总功率平均提升1208 kW,验证了所提出的新型风电场偏航优化框架在提升风电场整体输出功率上的优越性。

基于5G信号异步时钟误差补偿的多无人机协同定位方法

5G信号可为多无人机(UAV)提供精确的相对测距/测角信息,进而提升其在卫星接收机故障时的协同定位精度。然而,协同网络中各节点的5G通讯时钟往往是异步的,这会对测距/测角信息的精度产生较大影响,进而降低融合性能。针对上述问题,提出了一种基于5G信号异步时钟误差补偿的多无人机协同定位方法。首先,构建了基于5G信号异步时钟误差的相对测距模型,并利用相对测距/测角信息以及高度计信息建立了从机的位置观测方程。在此基础上,通过设计迭代扩展卡尔曼滤波器(IEKF)实现了对从机惯导系统(INS)误差以及异步时钟误差的联合最优估计,提高了从机定位精度。仿真结果表明,相比于传统方法,所提方法将从机的水平定位精度提高了25.3%。

基于多综眼的纬向T型结构多筋机织物的设计与织造

为了解决传统织机织造效率低下以及异型织物织造难度大的问题,设计了一种基于多综眼的纬向T型结构多筋机织物的织造工艺。通过研究整体T型结构机织物的成形技术,采用多层角联锁结构为基础,结合多综眼织机的特性,设计经向截面图并绘制纹版图,通过机织方法织造了梁高和基座厚度相同的纬向T型结构多筋机织物。结果表明:采用五综眼织机相较于单综眼织机织造效率提升了5倍,织造基于多综眼的纬向T型结构多筋机织物是可行的。

基于条纹投影轮廓术的航空高光零件三维测量技术

针对航空工业零件高光表面结构光三维测量中强反光和多次反光问题,提出了基于高动态多步相移和单像素成像相结合的三维测量技术,有效地解决了测量复杂反光表面时的点云缺失和精度下降问题。对标准量块进行三维测量和精度评价,基于高动态多步相移的三维测量技术拟合均方根误差为0.0066 mm,基于单像素成像的三维测量技术拟合均方根误差为0.0046 mm。以台阶标准器作为测量目标,开展绝对尺寸测量精度验证试验,绝对偏差不大于0.007 mm。分别对金属表面结构件(如航空发动机叶轮、涡轮叶片)和碳纤维结构件进行测量试验。试验结果表明,三维测量结果基本无点云缺失,强反光和多次反光区域均获取了完整的点云数据,实现了航空工业高光零件的精密三维测量。

小型凹槽环件复合环轧成形数值模拟

采用一种立式复合环轧工艺制造了小型凹糟环件,用Simufact有限元软件模拟了小型凹槽环件的环轧成形过程,并在D51环轧机上进行了验证。数值模拟结果揭示了环轧成形过程中几何、应变和温度等成形因素的分布和演化规律。为研究不同主动辊形状对环轧成形的影响,采用不同夹角的主动辊进行了数值模拟研究。结果表明,25.4°的主动辊夹角能产生更大的轧制力和内部塑性应变,但是容易产生椭圆缺陷和模具填充不满,因此选取适中的角度能保证工件的环轧质量。通过对比空转轧制前后的数值模拟结果发现,空转轧制可以显著改善椭圆缺陷,提高环件尺寸的均匀性。

发动机旋转部件温度实时无线测试系统设计

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