Finite-time tracking control and vibration suppression based on the concept of virtual control force for flexible two-link space robot

The dynamic modeling, finite-time trajectory tracking control and vibration suppression of a flexible two-link space robot are studied. Firstly, the dynamic model of the system is established by combining Lagrange method with assumed mode method. In order to ensure that the base attitude and the joints of space robot can reach the desired positions within a limited time, a non-singular fast terminal sliding mode (NFTSM) controller is designed, which realizes the finite-time convergence of the trajectory tracking errors. Subsequently, for the sake of suppressing the vibrations of flexible links, a hybrid tra-jectory based on the concept of the virtual control force is developed, which can reflect the flexible modes and the trajectory tracking errors simultaneously. By modifying the original control scheme, a NFTSM hybrid controller is proposed. The hybrid control scheme can not only realized attitude stabili-zation and trajectory tracking of joints in finite time, but also provide a new method of vibration sup-pression. The simulation results verify the effectiveness of the designed hybrid control strategy.     

Fabrication and analysis of TIG welding-brazing butt joints of in-situ TiB2/7050 composite and TA2

Lightweight hybrid structures of Al MMCs and titanium alloy dissimilar materials have great prospect in the defence industry application. So, it is necessary to join Al MMCs with Ti metal to achieve this structural design. In this work, in-situ TiB2/7050 composite and TA2 were firstly attempted to join by TIG welding-brazing technique. The result was that the intact welding-brazing butt joint was successfully fabricated. The joint presents dual characteristics, being a brazing on TA2 side and a welding on TiB2/7050 side. At brazing joint side, ER4043 filler metal effectively wets on TA2 under TIG heating condition, and a continuous interfacial reaction layer with 1—3μm is formed at welded metal/TA2 interface. The whole interfacial reaction layers are composed of Ti(AlSi)3 intermetallic compounds (IMCs), but their morphologies at the different regions present obvious distinguishes. The microhardness of the reaction layers is as much as 141—190 HV. At welding joints side, the fusion zone appears the equixaed crystal structure, and the grain sizes are much smaller than those of welded metal, which is attributed to the effect of TiB2 particulates from the melted TiB2/7050 on acceleration formation and inhibiting growth for the new crystal nucleus. The tensile test results show that average tensile strength of the optimal welding-brazing joint is able to achieve 138 MPa. The failure of the tensile joint occurs by quasi-cleavage pattern, and the cracks initiate from the IMCs layer at the groove surface of TA2 and propagate into the welded metal.     

试论晚清军事变革对近代社会转型之影响

晚清以来,中国社会经历了由传统封建社会向近代社会的全方位社会转型,军事变革与社会转型发生着千丝万缕的联系。解读晚清军事与近代社会转型的内在联系,有利于更好的理解那段历史。     

Web服务技术在装备管理信息系统中的应用

在研究W eb服务技术的基础上,利用.NET开发平台设计了装备管理系统中的器材库存管理系统,证明了W eb服务技术的可行性和有效性。     

水下传感器网络冗余设计

冗余设计可以有效地延长水下传感器网络寿命和提高网络可靠性,基于可靠性理论,考虑水下传感器网络环境及节点垂直移动等约束,在对冗余非共享方案研究的基础上,结合水下传感器网络特点,提出了适合于水下传感器网络特点的冗余共享设计方案,并给出了冗余共享方案的可靠性模型,通过数值计算,研究了网络可靠性变化曲线及冗余节点数与网络寿命的关系。经过MATLAB软件仿真,表明在同一网络寿命情况下,相对于冗余非共享方案,冗余共享方案所需冗余节点数更少,降低了网络部署成本,达到了冗余优化的目的。     

基于GO法的多阶段共因失效任务系统可靠性评估

为了解决部件阶段依赖性与共因失效给系统可靠性分析带来的复杂性,针对多阶段共因失效任务系统,结合GO法易于处理有时序、含共因失效系统可靠性分析的特点,首先,将前一阶段的输出信号作为后一阶段的输入信号,建模时首尾连接各阶段模型,建立整个任务系统的隐性GO模型;其次,在进行各信号流状态组合运算时,融入阶段代数处理部件的阶段依赖性;再次,用隐性共因失效分析,将共因失效对系统的影响在状态组合的定量分析中表达出来,得到所需系统可靠性指标;最后,与基于二元决策图的算法进行对比验证。结果表明:GO法可以简捷、准确地处理多阶段共因失效任务系统可靠性评估问题。     

基于统一描述框架的导弹设计知识模型研究

为了解决基于知识的导弹设计中异构知识难以共享、重用及有效支持推理的问题,提出了一种基于统一描述框架的本体化知识模型.首先研究了导弹设计中各类知识的表达形式,针对这些异构的知识提出了一种统一描述框架,而后研究了基于这种统一描述框架的本体化知识模型,在该模型中定义了知识基本建模单元,其可直接用于各类异构知识的表达和建模.最后利用导弹气动设计知识建模的应用示例说明了研究成果的有效性.     

机房漏水检测与精确定位装置研究

机房漏水是危及精密信息设备长期稳定可靠运行的重大安全隐患。为了解决传统定位装置难以实现漏水点精确定位的问题,从传感电缆的检漏原理出发,利用分压补偿原理,通过STEP7软件编程,设计了一个结合自检、漏水检测和漏水定位3种功能的机房漏水检测与定位装置。在此基础上搭建了实验系统,经测试实验,结果表明短距离定位精度可以达到1．70％,从而证实了该装置检测的有效性和定位的精确性。     

Timing of information acquisition in a competitive environment

This article investigates the impact of timing on sellers' information acquisition strategies in a duopoly setting. Market uncertainty is captured by a representative consumer who has a private taste for the product's horizontal attribute, and both sellers can acquire this information either before (ex‐ante acquisition) or after (ex‐post acquisition) observing their own product qualities. We identify several conflicting effects of information acquisition that vary significantly in its timing and market characteristics. In the monopoly scenario, information acquisition is unambiguously beneficial and ex‐ante acquisition is the dominant option, because it helps a seller not only design the proper product but also craft better pricing strategy. By contrast, when there is competition, information acquisition eliminates the buffer role of market uncertainty and leads to the fiercest production or pricing competition, which makes the subsequent effects of acquisition detrimental, and a seller's payoff is nonmonotonic in terms of its acquisition cost. Moreover, compared with the ex‐ante information acquisition, ex‐post information acquisition normally generates higher sellers' equilibrium payoffs by postponing the timing of acquisition and maintaining product differentiation. Nonetheless, ex‐post information acquisition also provides the seller with greater acquisition incentive and occasionally makes him worse off than that in the ex‐ante scenario. Thus, in a competitive environment, having the option of information acquisition and flexibility in its timing can be both detrimental and irresistible. © 2016 Wiley Periodicals, Inc. Naval Research Logistics 63: 3–22, 2016     

Nonlinear pricing with consumer satiation

In various scenarios, consumers may become satiated with products, and the degree of satiation is directly associated with their prior experiences. Confronted with consumer satiation, the seller is unable to either identify consumers who have a higher likelihood of being satiated ex ante or distinguish satiated from non‐satiated consumers ex post. Therefore, the seller should address dynamic selling, valuation uncertainty, and quantity decisions, all of which are important operational issues. We consider a two‐period problem in which consumer types are influenced by their prior consumption experiences. Faced with these consumers, the seller intends to optimize quantities and adjust the prices of the products in each period to maximize revenue. We find that the seller may reduce ex ante production quantity as some consumers become satiated. Moreover, the ex ante quantity is first decreasing and then increasing with regard to the satiation rate. Furthermore, two‐period information asymmetries may provide a rationale for upward distortion in quantity when consumer preferences are highly sensitive to first‐period consumption. © 2016 Wiley Periodicals, Inc. Naval Research Logistics 63: 386–400, 2016