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71.
本文提出一种新的制作环形全息光栅的方法--即利用圆锥面镜反射波干涉获得等间距环形干涉条纹,并给出了圆锥面镜反射光干涉场的强度分布及环形全息光栅记录方法,这种环形全息光栅制作方法在光学测试、光通信器件等方面有潜在的应用前景。 相似文献
72.
《中国航空学报》2016,(6):1795-1805
This paper focuses on the type synthesis of two degree-of-freedom (2-DoF) rotational parallel mechanisms (RPMs) that would be applied as mechanisms actuating the inter-satellite link antenna. Based upon Lie group theory, two steps are necessary to synthesize 2-DoF RPMs except describing the continuous desired motions of the moving platform. They are respectively generation of required open-loop limbs between the fixed base and the moving platform and definition of assembly principles for these limbs. Firstly, all available displacement subgroups or submanifolds are obtained readily according to that the continuous motion of the moving platform is the inter-section of those of all open-loop limbs. These subgroups or submanifolds are used to generate all the topology structures of limbs. By describing the characteristics of the displacement subgroups and submanifolds intuitively through employing simple geometrical symbols, their intersection and union operations can be carried out easily. Based on this, the assembly principles of two types are defined to synthesize all 2-DoF RPMs using obtained limbs. Finally, two novel categories of 2-DoF RPMs are provided by introducing a circular track and an articulated rotating platform, respectively. This work can lay the foundations for analysis and optimal design of 2-DoF RPMs that actuate the inter-satellite link antenna. 相似文献
73.
74.
《中国航空学报》2022,35(9):71-80
With the development of Unmanned Aerial Vehicles (UAVs), the applications of UAVs have been extensively explored. In the field of wireless communications, the relay nodes are often used to extend network coverage. However, traditional fixed ground relays cannot be flexibly deployed due to their low heights and fixed locations. Hence, deploying UAV as relay node is a promising solution and has become a research hotspot. In this paper, we consider an UAV-enabled relaying network in which a fixed-wing UAV is deployed between the Base Station (BS) and Ground Users (GUs). We study the energy-efficiency gap between the link “BS-UAV-GUs” and the link “BS-GUs”, and jointly optimize UAV relay transmission power and flight radius to achieve the highest energy-efficiency. Firstly, the UAV/BS-GUs channels models and the UAV energy consumption model are built. Secondly, the optimization objective function is formulated to maximize the energy-efficiency gap. Then, the solution of the optimization problem is divided into a two-step iteration process, in which the UAV relay transmission power and flight radius are adjusted to maximize the energy-efficiency gap. Finally, the experimental results under different simulation scenarios (such as cities, forests, deserts, oceans, etc.) are shown to illustrate the effectiveness of the proposed algorithm. The results show that the proposed algorithm can always find the optimal UAV relay transmission power and flight radius settings, and achieve the largest energy-efficiency gap. The convergency speed of the proposed algorithm is fast, and can obtain the optimal solution within only a few iterations. 相似文献
75.
《中国航空学报》2016,(6):1575-1581
This paper experimentally investigates the effect of surface roughness on flow and heat transfer characteristics in circular microchannels. All test pieces include 44 identical, parallel circu-lar microchannels with diameters of 0.4 mm and 10 mm in length. The surface roughness of the microchannels is Ra=0.86, 0.92, 1.02 lm, and the Reynolds number ranges from 150 to 2800. Results show that the surface roughness of the circular microchannels has remarkable effects on the performance of flow behavior and heat transfer. It is found that the Poiseuille and Nusselt num-bers are higher when the relative surface roughness is larger. For flow behavior, the friction factor increases consistently with the increasing Reynolds number, and it is larger than the constant the-oretical value for macrochannels. The Reynolds number for the transition from laminar to turbu-lent flow is about 1500, which is lower than the value for macrochannels. For the heat transfer property, Nusselt number also increases with increasing Reynolds number, and larger roughness contributes to higher Nusselt number. 相似文献
76.
一种实用的归一化互相关景象匹配算法 总被引:20,自引:6,他引:20
相关匹配算法是景象匹配定位系统的核心。本文提出一种用于景象匹配定位系统的相关匹配算法,称之为归一化互相关景象匹配算法,并进行了理论分析和用真实的景象数字地图进行了大量的计算机仿真试验。试验结果表明,该算法在信噪比不小于1并且实时图大小不小于10×10个网格的条件下,其正确匹配概率大于97%,圆概率误差在一个景象数字地图的网格以内,满足景象匹配定位系统的要求 相似文献
77.
根据Bertrand定理关于轨道闭合的条件,我们知道当中心引力的形式为径向距离的幂次型函数时,并不总能导致闭合轨道,即运动的质点不一定能返回到它自己的轨迹上去。这个定理指出:一切运动质点其初始条件稍微偏离圆轨道的要求条件时,只有当引力满足平方反比律(即牛顿万有引力定律)或线性定律(即虎克定律)时,轨道才是闭合的。 本文试图采用分析力学中作用角变量的方法,对一般情形下的轨道闭合条件进行讨论。这里我们看到使初始轨道接近于圆轨道的假设是不必要的,而且力的类型可推广到包括平方反比和其它幂次型的力。我们证明了轨道闭合的判别公式,并得到在上述情形下轨道非闭合的结论。 最后,如果中心引力包括有r~(-2)项和r~(-3)项时,象相对论性改正后所得到的那样,轨道就不再是闭合的,而是一旋进椭圆形轨道,椭圆的旋进角速度可以容易地计算出来。 相似文献
78.
在文献「1」的基础上,进一步应用广义阶梯函数对承受边缘弯矩,局部均布荷载和线性分布荷载的简支圆板进行塑性极限分析,给出了简支圆板在Tresca屈服条件下,边缘弯矩,局部均布荷载和线性分布荷载所满足的关系式。 相似文献
79.
80.
F.J.T. Salazar J.J. Masdemont G. Gómez E.E. Macau O.C. Winter 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
Assume a constellation of satellites is flying near a given nominal trajectory around L4 or L5 in the Earth–Moon system in such a way that there is some freedom in the selection of the geometry of the constellation. We are interested in avoiding large variations of the mutual distances between spacecraft. In this case, the existence of regions of zero and minimum relative radial acceleration with respect to the nominal trajectory will prevent from the expansion or contraction of the constellation. In the other case, the existence of regions of maximum relative radial acceleration with respect to the nominal trajectory will produce a larger expansion and contraction of the constellation. The goal of this paper is to study these regions in the scenario of the Circular Restricted Three Body Problem by means of a linearization of the equations of motion relative to the periodic orbits around L4 or L5. This study corresponds to a preliminar planar formation flight dynamics about triangular libration points in the Earth–Moon system. Additionally, the cost estimate to maintain the constellation in the regions of zero and minimum relative radial acceleration or keeping a rigid configuration is computed with the use of the residual acceleration concept. At the end, the results are compared with the dynamical behavior of the deviation of the constellation from a periodic orbit. 相似文献