Formation flying in elliptic orbits with the J2 perturbation

Relative dynamics between the chief satellite and the deputy ones in formation flying is crucial to maintaining the formation. A good choice of the formation usually requires a lower control frequency or less control energy. For formation flying missions in highly elliptic orbits, the well-known C-W equation is not accurate enough. Instead, Lawden’s equation is often used. First, the solution to Lawden’s equation with a very simple form is deduced. Then the J2 perturbation is added. It is found that Lawden’s solution is not necessarily valid when the J2 perturbation is considered. Completely discarding Lawden’s solution and borrowing the idea of mean orbit elements, two rules to initialize the formation are proposed. The deviation speed is greatly reduced. Different from previous studies on the J2 perturbation, except for the relatively simple expression for the semi-major axis, the tedious formulae of the long period terms and the short period terms of other orbital elements are not used. In addition, the deviation speed is further reduced by compensation of the nonlinear effects. Finally, a loose control strategy of the formation is proposed. To test the robustness of this strategy, a third body perturbation is added in numerical simulations.     

A Statistical Study on the Geomagnetically Induced Current Events Driven by Earth-directed Full-Halo Coronal Mass Ejections

Solar activities can cause the anomalies of electric power transmission systems, especially, for an extra-long distance transmission system. Using the data of coronal mass ejection (CME) from SOHO/LASCO (Solar and Heliospheric Observatory/Large Angle and Spectrometric Coronagraph), and the data of the geomagnetically induced current (GIC) and geomagnetic storm from the North China Electric Power University and Finnish Meteorological Institute, respectively, we analyze some important observational features and physical properties of the earth-directed halo CMEs associated with the GIC events. After classifying the observed halo CMEs according to their symmetry, it is found that the halo CMEs associated with GIC events are mainly the 3 types: completely symmetric, brightness-asymmetric, and outline-asymmetric. The geomagnetically induced current events driven by the three different types of halo CMEs have different characteristics in the intensity, duration, and period. We ?nd that the brightness-asymmetric halo CMEs are most likely to cause the major damage to the transmission systems. And that the geomagnetically induced current has also a good correlation with the time variation of geomagnetic ?eld.     

Optimization of Low-Thrust Trajectories Using an Indirect Shooting Method without Guesses of Initial Costates

According to the optimal control theory, the optimal control problem of the low-thrust tra jectory can be converted into a solution of nonlinear two- point boundary-value problem (TPBVP). To solve the TPBVP, the repeated random guesses for the initial costate variables and iterative computations are needed. In order to enhance the convergence of the iterations, we select an appropriate performance index, and then linearize the equations of the TPBVP around a Keplerian orbit. For multi-revolution transfers, instead of the multi- revolution Lambert tra jectory, multiple segmented Keplerian arcs are used to ensure the effectiveness of the linearization. The method is totally automatic with multiple iterations. With this method, we can get the results within 3 ∼ 5 iterations, and the random guess of the initial costates is unnecessary. Finally by the iterative optimization of the performance index, a better control strategy approaching to the bang-bang control is obtained.     

基于波束控制的卫星导航接收机抗干扰算法研究

卫星导航接收机抗干扰技术是接收机设计的一项关键技术。在研究基于功率反演的空域自适应抗干扰算法基础上,提出了采用基于波束控制的抗干扰算法,并进行了仿真计算,结果表明：该算法明显提高了接收机抗干扰性能。     

Optimum design and experimental study of multiple tuned mass dampers with limited stroke

This paper develops a two‐stage optimum design procedure for multiple tuned mass dampers (MTMD) to reduce structural dynamic responses with the limitation of MTMD's stroke. A new performance index, which is a linear combination of structural response ratio and MTMD stroke ratio by a weighting factor α, is proposed; α is in the range from 0 to 1.0. The larger the α, the more important the stroke. The case of α=1.0 indicates that MTMD is locked. The analytical results show that the MTMD's stroke can be significantly suppressed with little sacrifice of structural control effectiveness when an appropriate α is selected. To verify the design algorithm, a 360 kg‐MTMD composed of five TMD units arranged in parallel was fabricated. Shaking table tests of a large‐scale three‐story building with and without the MTMD under earthquake excitations were conducted at the National Center for Research on Earthquake Engineering (NCREE) in Taiwan. The experimental results show that MTMD is not only effective in mitigating the building responses but also is successful in suppressing its stroke. Copyright © 2010 John Wiley & Sons, Ltd.     

活性污泥和颗粒污泥生物吸附废水中Pb2+的对比研究

采用序批式实验,分别以活性污泥和颗粒污泥为吸附材料,考察接触时间、pH等因素对废水中Pb2+生物吸附效果的影响.结果表明,活性污泥和颗粒污泥对低浓度Pb2+(0～20 mg/L)能在30 min内达到吸附平衡,当Pb2+浓度在20～100 mg/L时,浓度越低,达到平衡时间越快,以被动吸附为主.在Pb2+低浓度条件下(0～20 mg/L),初始pH为4～5时,Pb2+的去除率达99%以上,且初始pH值是影响活性污泥和颗粒污泥生物吸附Pb2+的重要因素.活性污泥和颗粒污泥对Pb2+的生物吸附符合朗缪尔(Langmuir)方程,在pH为4及25 ℃下,活性污泥饱和吸附量为59.88 mg/g,颗粒污泥饱和吸附量为80.65 mg/g.因此,活性污泥和颗粒污泥可作为有效的生物吸附剂处理低浓度(0～20 mg/L)含铅废水,且颗粒污泥比活性污泥的生物吸附效果好.     

陇东新近纪红粘土与第四纪黄土地球化学特征及其物源和风化指示意义

甘肃省平凉市灵台县邵寨镇剖面风尘堆积底界年龄大约为5.23 Ma B.P.,通过对该剖面新近纪红粘土与第四纪黄土-古土壤序列的常量元素、 微量元素、Nd同位素的测试,分析其在物源和风化方面的指示意义,发现新近纪红粘土与第四纪黄土具有相似的常量、 微量元素UCC标准化曲线和稀土元素球粒陨石标准化曲线,指示二者皆来自广阔的...     

高岭土容重,含水量,结构特性与声波速度及动力学参数相关性的实验研究

本文叙述了高岭土的物理力学特性与声波速度及动力学参数相关关系的室内实验研究,着重探讨了高岭土容重、含水量与纵波速度、横波速度及动弹性模量,动剪切模量之间的关系,并给出了它们的关系式。此外还分析了高岭土结构特性对声波速度及动力学参数的影响。     

Numerical study of M2 internal tide generation and propagation in the Luzon Strait

Based on the z-coordinate ocean model HAMSOM,we introduced the internal-tide viscosity term and applied the model to numerically investigate the M2 internal tide generation and propagation in the Luzon Strait (LS).The results show that (1) in the upper 250 m depth,at the thermocline,the maximum amplitude of the generated internal tides in the LS can reach 40 m;(2) the major internal tides are generated to the northwest of Itbayat Island,the southwest of Batan Island and the northwest of the Babuyan Islands;(3) during the propagation the baroclinic energy scattering and reflection is obvious,which exists under the effect of the specific topography in the South China Sea (SCS);(4) the westward-propagating internal tides are divided into two branches entering the SCS.While passing through 118 E,the major branch is divided into two branches again.The strongest internal tides in the LS are generated to the northwest of Itbayat Island and propagate northeastward to the Pacific.However,to the east of 122 E,most of the internal tides propagate southeastward to the Pacific as a beam.