角度测量下双机协同standoff目标跟踪

基于最大化目标位置估计精度,针对两架无人机(UAV)仅有角度测量的情况,提出一种新的协同随机运动目标standoff跟踪控制方法.以目标位置估计均方根误差(RSME)作为性能指标,建立其与UAV观测几何构型之间的关系模型,进而确定了最优跟踪时UAV最优观测几何构型.采用扩展信息滤波实现目标状态的融合估计;考虑平台性能、碰撞规避、安全距离等约束条件,采用非线性模型预测控制(NMPC)实现UAV协同分布式在线优化控制.仿真结果表明该算法在确保最优观测构型和跟踪精度的同时有效地提高了算法实时性.

基于tau矢量场制导的多无人机协同standoff跟踪方法

针对有时间约束的多无人机(UAV)协同standoff跟踪需求,研究基于四维矢量场的多UAV协同制导方法.利用本征tau-G制导策略能够依照期望时间对各运动状态进行同步规划的特性,构建tau制导矢量场,并在此基础上提出综合性多UAV协同standoff跟踪方法.该方法用tau矢量场导引各UAV的位置在期望时间准确收敛于目标圆,利用tau-G策略调整UAV之间的相位间隔,应用序列二次规划对跟踪参数进行优化,并采用人工势场法进行协同避碰避障.仿真结果表明,基于tau矢量场制导的协同standoff跟踪方法计算负荷低,跟踪偏差小、制导策略可飞性好,飞行安全性高,能够更好地满足多UAV协同standoff跟踪的应用需求.

多无人机同时到达的standoff跟踪控制

为实现多无人机standoff目标跟踪与同时到达,提出了一种新的比例Lyapunov矢量场和基于τ耦合理论的协同速度控制器。首先,与其他的Lyapunov矢量场相比,比例Lyapunov矢量场中增加了一个可设置的参数,使得在跟踪过程中无人机能够在收敛速度和航向角速率限制之间取得平衡,最大限度的发挥无人机的性能;然后,通过进一步的理论分析得出参数越小,收敛速度越快,但是航向角速率越大。同时给出了在最大航向角速率限制下参数的选取方法,以保证获得较快的收敛速度。最后,为保证无人机能够从不同初始位置同时到达目标点,设计了基于τ耦合理论的协同速度控制律,该控制律不需要考虑实际的不规则飞行路径,只需要计算当前点到目标点的直线距离,避免了现有四维路径规划方法中路径积分复杂的问题,算法更加简单,更有利于工程实现。结果表明,通过数字仿真实例和硬件在环实验,验证了所提方法能够导引无人机同时到达目标点,并快速收敛到standoff半径,说明了该方法的有效性和优越性,且能够应用于工程实际。

Study of extrudability and standoff distance effect during nanoclay-enabled direct printing

Nanoclay-enabled self-supporting printing has been emerging as a promising filament-based extrusion fabrication approach for different biomedical and engineering applications including tissue engineering. With the addition of nanoclay powders, liquid build materials may exhibit solid-like behavior upon extrusion and can be directly printed in air into complex three-dimensional structures. The objective of this study is to investigate the effect of nanoclay on the extrudability of N-isopropylacrylamide （NIPAAm） and the effect of standoff distance on the print quality during nanoclay-enabled direct printing. It is found that the addition of nanoclay can significantly improve the NIPAAm extrudability and effectively eliminate die swelling in material extrusion. In addition, with the increase of standoff distance, deposited filaments change from over-deposited to well-defined to stretched to broken, the filament width decreases, and the print fidelity deteriorates. A mathematical model is further proposed to determine the optimal standoff distance to achieve better print fidelity during nanoclay-enabled direct printing. Based on the extrudability and standoff distance knowledge from this study, NIPAAm-Laponite nanoclay and NIPAAm-Laponite nanoclay-graphene oxide nanocomposite hydrogel precursors are successfully printed into a three-layered one-dimensional responsive pattern, demonstrating the good extrudability and print quality during nanoclay-enabled printing under optimal printing conditions.

基于改进Lyapunov矢量场法的standoff跟踪研究

针对基于Lyapunov矢量场法的目标standoff跟踪中收敛速度慢的问题展开研究,提出了一种改进的Lyapunov矢量场法。首先建立了无人机运动学模型,通过对基于速度信息主导的方法和基于位置信息主导的方法的优缺点进行对比,定义了新的速度式,先判断无人机是否收敛到跟踪圆上,然后实施机动。通过速度式实现了跟踪形成前无人机的快速收敛到跟踪圆,跟踪形成后跟踪没有延迟和滞后。最后仿真结果表明了所提出方法的有效性。

Effects of standoff distance on the supersonic flow fields in cold gas dynamic spraying

In this study,the effects of standoff distance （SOD） on the supersonic flow fields （including gas and particle flow fields） during cold gas dynamic spraying （ CGDS ） are investigated by means of computational fluid dynamics （CFD）. The variation of velocity,temperature,pressure and density with different SoD is elucidated through the analysis of the distribution properties of the flow fields. It is found that the shock waves in front of the substrate remarkably influence the gas and particle flow fields. The wave system of expansion waves and pressure waves come into being continuously. The velocity of gas reaches the super.,;onic speed at the position of the Mach disc, while it decreases sharply when the gas flow crosses the Mach disc. The optirnal SoDs are 40 mm for 1 um particles and 50 mm for both 5 um and 22 um particles.

The Doklam Standoff Crisis and the Future of Sino-Indian Relations

Doklam Standoff, a crisis of Sino-Indian bilateral relations, was a large-scale military deployment between China and India. The crisis reflects the newly forming distrust between the two countries that led to an outburst as a result of a series of conflicts over the past two years, which signifies that Sino-Indian relations are entering a new stage characterized by increasingly obvious structural conflict. On the surface, the Modi Administration designed the crisis to stop China from building border infrastructure, to pursue its own absolute security, to maintain South Asian order dominated by India, and to consolidate the basis of strategic cooperation among India, the United States and Japan. Ultimately, however, the British buffer zone theory, the Mandala theory, the Brahmin supremacy theory in traditional Indian culture and the US Monroe Doctrine have also shaped the mindset and behavioral patterns of the Modi Administration. Under the influence of seeking absolute security and its strategic culture, as well as the strong desire to be a great power, the assertive Modi Administration has obviously strengthened its precautionary measures and hostilities toward China. The relations between the two countries are becoming tense. In order to achieve the goal of ＂dragon and elephant dancing together＂, and to avoid the recurrence of crises like the Doklam Standoff, the two sides have to adhere to the two basic principles of viewing each other as opporttmities for development instead of threats to each other. The mindset of a zero-sum game should be abandoned, and efforts should be made to co-found mutual respect and win-win cooperation in areas of common interest.

面向协同standoff跟踪问题的无人机制导律

针对多无人机(UAV)协同standoff跟踪问题,提出了UAV的横侧向和纵向制导律。对参考点制导(RPG)进行改进,作为UAV的横侧向制导律。然后,采用一组非线性微分方程对UAV和目标相对距离的调节过程进行建模,在此基础上证明了改进RPG的渐近稳定性,并推导了RPG参数与系统性能的关系,为RPG参数的选取提供了依据。最后,给出了UAV的纵向制导律,并分析了其渐近稳定性。仿真结果表明,改进RPG的跟踪误差和时间乘以误差绝对值积分(ITAE)指标均优于Lyapunov向量场制导(LVFG)和模型预测控制(MPC),故改进RPG具有更快的响应速度和更高的稳态精度。

Coordinated standoff tracking of moving targets using differential geometry

This research is concerned with coordinated standoff tracking, and a guidance law against a moving target is proposed by using differential geometry. We first present the geometry between the unmanned aircraft(UA) and the target to obtain the convergent solution of standoff tracking when the speed ratio of the UA to the target is larger than one. Then, the convergent solution is used to guide the UA onto the standoff tracking geometry. We propose an improved guidance law by adding a derivative term to the relevant algorithm. To keep the phase angle difference of multiple UAs, we add a second derivative term to the relevant control law. Simulations are done to demonstrate the feasibility and performance of the proposed approach. The proposed algorithm can achieve coordinated control of multiple UAs with its simplicity and stability in terms of the standoff distance and phase angle difference.

In situ analysis of magnesium alloy using a standoff and double-pulse laser-induced breakdown spectroscopy system

To monitor the components of molten magnesium alloy during the smelting process in real time and online, we designed a standoff double-pulse laser-induced breakdown spectroscopy （LIBS） analysis system that can perform focusing, collecting and imaging of long-range samples. First, we tested the system on solid standard magnesium alloy samples in the laboratory to establish a basis for the online monitoring of the components of molten magnesium alloy in the future. The experimental results show that the diameters of the focus spots are approximately 1 mm at a range of 3 m, the ablation depth of the double-pulse mode is much deeper than that of the single-pulse mode, the optimum interpulse delay of the double pulse is inconsistent at different ranges, and the spectral intensity decays rapidly as the range increases. In addition, the enhancement effect of the double pulse at 1.89 m is greater than that at 2.97 m, the maximum enhancement is 7.1-fold for the Y（I）550.35-nm line at 1.89 m, and the calibration results at 1.89 m are better than those at 2.97 m. At 1.89 m, the determination coefficients （R2） of the calibration curves are approximately 99% for Y, Pr, and Zr; the relative standard deviations （RSDs） are less than 10% for Y, Pr, and Zr; the root mean square errors （RMSEs） are less than 0.037% for Pr and Zr; the limits of detection （LODs） are less than 1000 ppm for Y, Pr, and Zr; and the LODs of Y, Pr, and Zr at 2.97 m are higher than those at 1.89 m. Additionally, we tested the system on molten magnesium alloy in a magnesium alloy plant. The calibration results of the liquid magnesium alloy are not as favorable as those of the sampling solid magnesium alloys. In particular, the RSDs of the liquid magnesium alloy are approximately 20% for Pr and La. However, with future improvements in the experimental conditions, the developed system is promising for the in situ analysis of molten magnesium alloy.

Study on the influence of standoff distance on substrate damage under an abrasive water jet process by molecular dynamics simulation

The process of a cluster-containing water jet impinging on a monocrystalline silicon substrate was studied by molecular dynamics simulation. The results show that as the standoff distance increases, the jet will gradually diverge. As a result, the solidified water film between the cluster and the substrate becomes "thicker" and "looser". The "thicker" and "looser" water film will then consume more input energy to achieve complete solidification, resulting in the stress region and the high-pressure region of the silicon substrate under small standoff distances to be significantly larger than those under large standoff distances. Therefore, the degree of damage sustained by the substrate will first experience a small change and then decrease quickly as the standoff distance increases. In summary, the occurrence and maintenance of complete solidification of the confined water film between the cluster and the substrate plays a decisive role in the level of damage formation on the silicon substrate. These findings are helpful for exploring the mechanism of an abrasive water jet.

Target Tracking in Standoff Jammer Using Unscented Kalman Filter and Particle Fiter with Negative Information

To handle the problem of target tracking in the presence of standoff jamming(SOJ), a Gaussian sum unscented Kalman filter(GSUKF) and a Gaussian sum particle filter(GSPF) using negative information(scans or dwells with no measurements) are implemented separately in this paper. The Gaussian sum likelihood which is derived from a sensor model accounting for both the positive and the negative information is used. GSUKF is implemented by fusing the state estimate of two or three UKF filters with proper weights which are explicitly derived in this paper. Other than GSUKF, the Gaussian sum likelihood is directly used in the weight update of the GSPF. Their performances are evaluated by comparison with the Gaussian sum extended Kalman filter(GSEKF)implementation. Simulation results show that GSPF outperforms the other filters in terms of track loss and track accuracy at the cost of large computation complexity. GSUKF and GSEKF have comparable performance; the superiority of one over another is scenario dependent.

Effects of Standoff Distance on Magnetic Pulse Welded Joints Between Aluminum and Steel Elements in Automobile Body

In industrial production,the standoff distance of magnetic pulse welding(MPW)is a critical parameter as it directly affects welding quality.However,the effects of standoff distance on the physical properties of MPW joints have not been investi-gated.Therefore,in this study,aluminum alloy(AA5182)sheets and high-strength low-alloy steel(HC340LA)sheets were welded through MPW at a discharge energy of 20 kJ,under various standoff distances.Thereafter,mechanical tests were performed on the MPW joints,and the results indicate that there is a significant change in the shear strength of the AA5182/HC340LA-welded joints with respect to the standoff distance.When the standoff distance ranges from 0.8 to 1.4 mm,the strength of the joint is higher than that of the base AA5182 sheet.Microscopic observations were conducted to analyze the interfacial morphology,element diffusion behavior,and microdefects on the welding interface of the AA5182/HC340LA joints.The AA5182/HC340LA joint with a standoff distance of 1.4 mm possesses the longest welded region and the largest interfacial wave.This interfacial wave pattern is suitable for achieving MPW joints with high shear strengths.

Shock wave standoff distance of near space hypersonic vehicles

The shock wave standoff distances of near space hypersonic vehicles, which execute missions mainly at the altitude of 25 km to 55 km, are vital in aerothermodynamic analysis. The implicit finite volume schemes are derived from axisymmetric Navier-Stokes equations for chemical equilibrium flow, and programmed in FORTRAN. Taking a sphere cone for example, the effects of Much numbers （from 22 to 36） on the shock wave standoffdistance and the average density behind the shock are simulated at different altitudes from 25km to 55km. The numerical results illustrate that the turning point of the standoff distance is corresponding to that of the average density with the variation of Mach numbers. Based on the numerical results, we propose a formula for shock wave standoff distance, which is the function of the radius of the blunt body, the Mach number and the altitude in the atmosphere. Compared with previous correlations, the new formula can overcome the drawbacks of larger relative errors and complex calculations of the average density.

Observation-Driven Multiple UAV Coordinated Standoff Target Tracking Based on Model Predictive Control

An observation-driven method for coordinated standoff target tracking based on Model Predictive Control(MPC)is proposed to improve observation of multiple Unmanned Aerial Vehicles(UAVs)while approaching or loitering over a target.After acquiring a fusion estimate of the target state,each UAV locally measures the observation capability of the entire UAV system with the Fisher Information Matrix(FIM)determinant in the decentralized architecture.To facilitate observation optimization,only the FIM determinant is adopted to derive the performance function and control constraints for coordinated standoff tracking.Additionally,a modified iterative scheme is introduced to improve the iterative efficiency,and a consistent circular direction control is established to maintain long-term observation performance when the UAV approaches its target.Sufficient experiments with simulated and real trajectories validate that the proposed method can improve observation of the UAV system for target tracking and adaptively optimize UAV trajectories according to sensor performance and UAV-target geometry.

如何利用Standoff来优化磁芯设计

1引言在变压器和电感器等磁性器件中，Standoff是一个必备设计，起到稳定器件，方便洗板，散热，以及促进爬锡等作用，本文主要论述如何利用Standoff在磁芯设计中达到优化的效果。在网联科技，物联网技术迅猛发展的今天，轻薄化成为消费电子的主流，而在很多DC—DC模块中，我们可以看到，功率电感器往往是众多器件中的大个子。

Dependence of magnetic field just inside the magnetopause on subsolar standoff distance:Global MHD results

The subsolar magnetopause is the boundary between the solar wind and the Earth's magnetosphere,where reduced solar wind dynamic pressure is equal to the magnetic pressure of the Earth's outer magnetosphere.We use a global magnetohydrodynamic (MHD)model to estimate the ratio f of the compressed magnetic field just inside the subsolar magnetopause to the purely dipolar magnetic field.We also compare our numerical results to a similar work by Shue,which used Time History of Events and Macroscale Interactions during Substorms(THEMIS)data.Our results show that the ratio f is linearly proportional to the subsolar magnetopause standoff distance(r0)for both the northward and southward interplanetary magnetic field,properties consistent with Shue but with a smaller proportionality constant.However,previous theoretical studies show that f is nearly independent of the subsolar standoff distance.The global model results also show that f is smaller for the southward Interplanetary Magnetic Field(IMF)under the same r0,and that the proportionality constant for the southward IMF is larger than that for the northward IMF.Both conclusions agree with statistical results from observations by Shue.

硬质黏土淹没射流冲刷试验研究

近年来自吸式管道排沙系统以其省水、高效、廉价等优势,逐渐成为水库清淤的主要措施之一,然而在遇到土颗粒较细、淤积历时较长的硬质黏土时,它的清淤效果下降明显。为了探究硬质黏土的破土机制和起动影响因素,采用模型试验的方法,选取一种黏性泥沙,通过负压固结的方式制备硬质黏土样,然后进行了不同出口流速、喷嘴尺寸和射流靶距的直立淹没射流试验。试验结果表明,鉴于土样存在黏性,其受冲刷破土机制与无黏性土存在较大差异,冲坑发育过程存在一定的随机性和自相似性,并且射流冲刷效率与射流出口流速和喷嘴尺寸成正比、与射流靶距成反比,同时射流靶距对冲刷坑形态的影响最为明显。

HBS-LNSB Ⅲ 型旋流燃烧器回流区和着火距离的试验研究

针对某煤粉燃烧器的回流区和着火距离进行了试验研究。试验考查了中心风量、外二次风量、内二次风量以及内二次风旋流强度对回流区大小的影响规律,结果发现内二次风量的变化对回流区宽度的影响最大,中心风量对回流区与燃烧器的轴向距离影响最大。试验结果为不同煤种燃烧时的燃烧器配风选择提供依据。通过对各影响因素下煤粉着火距离的研究发现,针对着火距离短的易燃煤种,为了避免燃烧器喷口烧损,提高中心风量以及一次风速是最有效的措施。由于低负荷下炉内整体温度水平低,煤粉着火距离变长,可以适当提高易燃煤种的掺烧比例。对于着火温度较高的煤种,中心风量、内外二次风量的变化对于其着火距离均有明显的规律性,内二次风旋流强度的影响需要综合考虑旋流强度带来的风量变化的影响。不同煤种着火距离的工业试验为旋流燃烧器的配风选择提供了指导。煤种发生较大变化时应进行回流区与着火距离的工业试验,为燃烧器配风找到最优选择。

一种API长圆螺纹套管外螺纹接头虚拟紧密距算法

针对目前紧密距测量效率低、重复性和稳定性较差、易损伤螺纹等问题,提出了一种API长圆螺纹套管外螺纹接头虚拟紧密距的算法。该算法通过测量同一批次套管螺纹的顶径、锥度及少量紧密距即可预测批次内后续石油套管虚拟紧密距值。通过与2种规格的长圆螺纹套管实测结果对比,该虚拟紧密距计算结果与石油套管的实测紧密距具有较好的一致性。同时分析了定扭矩测量和人工手紧测量的情况下虚拟紧密距与实测紧密距的一致性,发现在定扭矩情况下测量的紧密距与虚拟紧密距的一致性更好。研究表明,该方法在保证测量精度的前提下提高了紧密距的检测效率和稳定性,能够作为一种预测方法为石油套管紧密距测量提供参考。