The Characteristics and Related Problems of the Orbits Around the Earth-Moon Libration Points

Due to the specific dynamics, the probes located at the halo orbits or Lissajous orbits around the Earth-Moon collinear libration point L₁ or L₂ are always studied in the synodic system to understand their trajectories. In fact, they are also orbiting the Earth in a distant Keplerian ellipse. Because of their intrinsic orbital instability, in the orbit prediction the initial errors propagate more prominently than those of the normal orbiting satellites, this requires special attention in the orbit design, maneuver, and control. Despite of all this, they are similar to the normal orbiting satellites in orbit determination and hardly require other special attentions. In this paper, the quantitative results of error propagation under the unstable dynamics, together with the theoretical analysis are presented. The results of precise orbit determination and short-arc orbit predictions are also shown, and compared with the results from the Beijing Aerospace Control Center.     

A new method to determine the gravity field of small bodies from line-of-sight acceleration data

We present a new method to derive line-of-sight acceleration observables from spacecraft radio tracking data. The observables can be used to estimate the mass and gravity of a natural satellite as a spacecraft flyby. The corresponding observation model adapts to one-way and two/three-way tracking modes. As a test case for method validation and application, we estimated the mass and degree two gravity field for the Martian moon Phobos using simulated tracking data when the spacecraft Mars Express flew by Phobos on 2013 December 29. We have a few real tracking data during flyby and they will be used to confirm raw data simulation. The main purpose of this paper is to demonstrate the method of line-of-sight acceleration reduction from raw tracking data and the feasibility to estimate mass and gravity of a natural satellite using this type of observable. This novel method is potentially applicable to planet and asteroid gravity field studies combined with Doppler tracking data.     

提高机采水平的配套技术及应用

随着濮城油田的持续性高速开发,油田综合含水逐渐上升,油水井井况进一步恶化,作为油田生产主体的机械采油井躺井频繁、管杆泵使用寿命缩短。近几年中原油田采油二厂濮城油田年平均躺井数达560井次之多,导致机械采油井维护费用增加,管杆泵投入增大,严重制约着油田的生产和经营。通过加缓蚀剂在油管内壁形成保护油膜,起到润滑作用;应用特殊抽油杆防腐止磨;应用尼龙扶正器对抽油杆体扶正,避免了钢体与钢体的硬磨;应用旋转井口通过地面人力转动改变油管与抽油杆的偏磨面;配合合理生产参数;各种配套技术的合理应用,使濮城油田躺井减少,避免了频繁作业,增加长寿井,管杆泵投入节约了19.3%。     

黑潮在吕宋海峡的形变及动力机制

根据１９９０年以来对吕宋海峡和中国南海（ＳＣＳ）北部的ＷＯＣＥ水文资料和其它海洋调查资料的分析，以及对同一海区的卫星遥测海表温度（ＳＳＴ）的资料处理，推断在吕宋海峡常年存在黑潮路径弯曲，西折进入ＳＣＳ并又流出ＳＣＳ的现象，作者将黑潮的这种变形称为“黑潮流套”。黑潮变形进入ＳＣＳ的位置在冬季位于海峡中部、南部附近，范围较大；在夏季略向北移，较集中于海峡中部，范围较小。作者认为，黑潮流套现象可用位涡守恒理论作定性的解释：当黑潮在吕宋海峡失去西边界支持后，其流轴以西贴近西边界的一部分流体，因具有较大的相对正涡度，会脱离黑潮主体在南海东北部形成反时针旋转或顺时针旋转的环流，而黑潮主体会以顺时针旋转的形式在海峡以西的海域出现。整个黑潮以弯曲、扩展的形式在海峡处产生形变，在海峡东侧出现反气旋涡旋的倾向。吕宋海峡黑潮流套及南海北部的诱生环流之流型，会因黑潮本身以及副热带环流整体的变化而变化，也与海峡的宽度有关。总之，吕宋海峡黑潮流套的形成是由当地特殊的地形条件和地转β效应这些内部机制决定的，它的常年存在有其必然性     

南海前新生代基底与东特提斯构造域

综合分析了地质、地球物理、地球化学、古生物学等多方面资料,将南海海域控制新生代主要沉积盆地的基底划分为6个区：北部湾古生界断堑基底区、莺歌海古生界走滑拉分基底区、琼东古生界断陷基底区、西沙北古生界裂谷基底区、西沙南古生界走滑伸展基底区和南沙古-中生界伸展基底区。通过区域地质分析．初步重建了该海域的大地构造演化历史。该海域新生代沉积基底在前新生代时期与其北面陆上云开地区同处于特提斯构造域中,形成于古特提斯构造域背景之中,为东特提斯多岛洋体系的重要组成部分。古特提斯的东延段在研究区有3个分支,即云开北、琼北、琼南3个海盆,分别表现为现存的云开北、琼北、琼南等缝合断裂带,使该区新生代沉积基底表现出明显的分区性。自晚古生代以来,伴随古、中特提斯的成生、消亡,该区新生代沉积基底经历了5个阶段的演化,其动力机制是一个复杂的研究课题,拆沉-去根-释压熔融是其主要动力机制,造成了特提斯构造演化上的序列性和叠置性。     

Low-energy Lunar Trajectories with Lunar Flybystwo

The low-energy lunar trajectories with lunar flybys are investigated based on the Sun-Earth-Moon bicircular problem (BCP). The characteristics of the distribution of trajectories in the phase space are summarized. Using the invariant manifolds in the BCP system, the low-energy lunar trajectories with lunar flybys are sought. Then, take time as an augmented dimension in the phase space of a nonautonomous system, we present the state space map and reveal the distribution of these lunar trajectories in the phase space. Consequently, we find that the low-energy lunar trajectories exist as families, and that the every moment in the Sun-Earth-Moon synodic period can be the departure date. Finally, we analyse the velocity increment, transfer duration, and system energy for the different trajectory families, and obtain the velocity-impulse optimal family and the transfer-duration optimal family, respectively.     

库车坳陷下侏罗统岩石古应力场与砂岩储层性质

对库车坳陷下侏罗统野外定向岩石样品的岩石力学性质的测试结果表明,下侏罗统以压扁变形明显、拉伸变形较弱为特点。自侏罗纪以来,该区经历了至少4期古构造变形作用,其变形方式主要为近EW向的以脆性变形为主的褶皱变形作用。在平面上,该区明显地表现为东弱西强的构造挤压变形特征,并对砂岩的储层性质产生重要影响。东区平均古构造应力值为19．8～28．3MPa,对应的平均砂岩孔隙度为17．1％;西区平均古构造应力值为62．6～80．1MPa,对应的平均砂岩孔隙度为6．4％～4．6％。     

Ring foundation on elastic subgrade: an analytical solution for computer modelling using the Lagrangian multiplier method

In the practice of geotechnical engineering, the case of a ring footing carrying a set of concentrated point loads is a common problem. At times, the induced vertical and angular displacements for the ring footing need to be evaluated at a relatively precise level. By making use of the governing set of equations derived for the case of a general curved beam, expressions that can be easily implemented in modern computing software are derived for the vertical and angular displacements of a ring footing of rectangular cross section as functions of the radial position. The loading case considered is a vertical point load, and the soil is modelled as elastic. Estimates of the displacements have been shown for a common range of practical applications. The behaviour for a set of concentrated loads may be evaluated using the derived equations through direct superposition. Nonlinear finite element analysis is used to evaluate the vertical deflection and angular twist of the ring foundation. Numerical analysis performed for three ring foundations with different radii and cross sections is reported to validate the accuracy of the derived analytical solution. Copyright © 2016 John Wiley & Sons, Ltd.     

Particle manifold method (PMM): A new continuum‐discontinuum numerical model for geomechanics

Particle manifold method (PMM) is a new extension of the numerical manifold method (NMM). PMM uses a mathematical cover system to describe the motion and deformation of a particle‐based physical domain. By introducing the concept of particle into NMM, PMM takes the advantages of easy topological and contact operations with particles. In this article, the methodology, formulations and implementation of the method are presented, together with modelling examples for validation. It is found that good solutions for both continuous and discontinuous problems are obtained by the new developed PMM. Due to the underlying coupled continuum‐discontinuum property of PMM, it has great potential for modelling of geomechanical problems. Copyright © 2012 John Wiley & Sons, Ltd.