数据不确定性与背景应力场差应力的可靠约束——以1992年Landers地震为例

以1992年美国南加州Landers MW7.3地震为例,通过利用主震前后应力场和主震位错引起的应力变化来约束背景应力场差应力的方法,系统研究了数据不确定性与差应力约束可靠性的关系.通过实际地震数据结合数据模拟研究,发现由于数据的不确定性(主要是震源机制解不确定性和发震节面的难确定性),该方法得到的原始约束结果与真实差应力存在系统偏差,原始约束值不能反映真实的差应力水平.数据模拟统计曲线表明,原始约束值和真实差应力存在两段线性关系:上升段和水平段,上升段对差应力有约束能力,水平段对差应力没有约束能力.利用上升段的线性关系对原始差应力约束值调整,得到的调整约束值在一定区间消除了与真实差应力的系统偏差.在不同的分析地点(分析点),本质上是主震位错引起的不同应力变化,数据不确定性对差应力约束结果影响也不同,不同分析点在差应力约束上有优劣性.本文采用Rv、Tv、λ等三个客观评价参数来挑选分析点,在Rv≤9,|Tv|≥17.5,λ<1的条件下挑选出24个分析点,得到Landers地震背景应力场差应力的最佳约束结果是-12.2±2.6 MPa.通过对评价参数的不同取值来检验约束结果的稳定性,以及通过数据模拟的综合分析来检验约束结果的可靠性,发现该最佳约束结果是稳定和可靠的.

Task-Oriented Topology System Synthesis of Reconfigurable Legged Mobile Lander Integrating Active and Passive Metamorphoses

To explore hostile extraterrestrial landforms and construct an engineering prototype,this paper presents the task-oriented topology system synthesis of reconfigurable legged mobile lander(ReLML)with three operation modes from adjusting,landing,to roving.Compared with our preceding works,the adjusting mode with three rotations(3R)provides a totally novel exploration approach to geometrically matching and securely arriving at complex terrains dangerous to visit currently;the landing mode is redefined by two rotations one translation(2R1T),identical with the tried-and-tested Apollo and Chang'E landers to enhance survivability via reasonable touchdown buffering motion;roving mode also utilizes 2R1T motion for good motion and force properties.The reconfigurable mechanism theory is first brought into synthesizing legged mobile lander integrating active and passive metamorphoses,composed of two types of metamorphic joints and metamorphic execution and transmission mechanisms.To reveal metamorphic principles with multiple finite motions,the finite screw theory is developed to present the procedure from unified mathematical representation,modes and source phase derivations,metamorphic joint and limb design,to final structure assembly.To identify the prototype topology,the 3D optimal selection matrix method is proposed considering three operation modes,five evaluation criteria,and two topological subsystems.Finally,simulation verifies the whole task implementation process to ensure the reasonability of design.

A Footpad Structure with Reusable Energy Absorption Capability for Deep Space Exploration Lander:Design and Analysis

The footpad structure of a deep space exploration lander is a critical system that makes the initial contact with the ground,and thereby plays a crucial role in determining the stability and energy absorption characteristics during the impact process.The conventional footpad is typically designed with an aluminum honeycomb structure that dissipates energy through plastic deformation.Nevertheless,its effectiveness in providing cushioning and energy absorption becomes significantly compromised when the structure is crushed,rendering it unusable for reusable landers in the future.This study presents a methodology for designing and evaluating structural energy absorption systems incorporating recoverable strain constraints of shape memory alloys(SMA).The topological configuration of the energy absorbing structure is derived using an equivalent static load method(ESL),and three lightweight footpad designs featuring honeycomb-like Ni-Ti shape memory alloys structures and having variable stiffness skins are proposed.To verify the accuracy of the numerical modelling,a honeycomb-like structure subjected to compression load is modeled and then compared with experimental results.Moreover,the influence of the configurations and thickness distribution of the proposed structures on their energy absorption performance is comprehensively evaluated using finite element simulations.The results demonstrate that the proposed design approach effectively regulates the strain threshold to maintain the SMA within the constraint of maximum recoverable strain,resulting in a structural energy absorption capacity of 362 J/kg with a crushing force efficiency greater than 63%.

美国Landers地震和Hector Mine地震前震源机制与主震机制一致现象的研究

用美国南加州地区的震源机制资料,研究了以1992年Landers Mw7.3和1999年Hector Mine Mw7.1地震矩心为圆心,分别以300、250、200、150、100和50km为半径的圆形区域内10年内地震震源机制相对主震震源机制平均空间旋转角的变化。结果表明,两个地震前均有小震震源机制趋于主震机制的现象。震前小震震源机制与主震震源机制的平均空间旋转角约在大震前半年开始减小,搜索平均空间旋转角降低的最优半径分别为250km和100km。震前所出现的平均空间旋转角最小值均低于其2倍标准差。该标准似乎可以作为大地震危险性增加的判据。

基因组装配中存在重复序列叠加时重叠群计数的推广的Lander-Waterman定理

针对基因组组装算法理论进行了改进,该研究对于经典的Lander-Waterman定理在repeatcollapse存在的情况下进行了推广,对于判断基因组组装的contig的个数是否合理,组装质量是否可靠有重要的参考价值。

BMW X3 VS BMW X5 VS BMW 330i VS LAND ROVER Free Lander 2.5原形毕露

比 X5小一号、比330i 还高大,X3究竟有啥能耐?空间小于 X5、也比不上330i 的俊俏,X3还有什么?这些问号,是我们试车组试驾 X3之前,必要提出的强烈质疑。除此之外,我们也对 X3的越野能力感到好奇,因此,找来了具备远亲血统的LAND ROVER Free Lender 2.5...在试车组的照妖镜之前,这部宝蓝色 X3逐渐显出原形。

Chang'e 3 Lunar Lander Cameras Underwent Extended Tests

Chang’e 3 lunar lander conducted extended tests on the surface of the moon after awakening from its dormancy.It was announced in the late of January that the pointing mechanism of the cameras onboard Chang’e 3 underwent extended tests to confirm the moving performance and limit switch triggering of the pointing mechanism under various status while pitching,moving forward and backward.According to the analysis derived from the

Chang'e 3 Lander Completed Mechanical Test

Aground firing test of the Chang'e 3 lander was conducted recently to check the mechanical performance of the spacecraft. The test was vital before the propulsion system test of the Chang'e 3 lander and was also a very important precondition to verify whether the propulsion system design could meet the requirements for in-orbit operation.

Dynamic model building and simulation for mechanical main body of lunar lander

Focused on the dynamics problems of a lunar lander during landing process, the whole process was analysed in detail, and the linear elastic model of the moon soil was established by means of experiments-analogic method. Combining the way of elastic impact with the way of velocity replacement, the dynamics model of damping free vibration dynamics model with 3-degree of freedom(DOF) for lunar lander is obtained according to the vibration mechanics elementary theory. Based on Lagrange equations and the energy principle, the damping free vibration differential equations for the lunar lander with 3-DOF are derived and the equations are solved in simulation ways by means of ADAMS software. The conclusions obtained can be used for the design and manufacture of lunar lander.

Preface: The Chang'e-3 lander and rover mission to the Moon

The Chang'e-3(CE-3) lander and rover mission to the Moon was an intermediate step in China's lunar exploration program, which will be followed by a sample return mission. The lander was equipped with a number of remote-sensing instruments including a pair of cameras(Landing Camera and Terrain Camera) for recording the landing process and surveying terrain, an extreme ultraviolet camera for monitoring activities in the Earth's plasmasphere, and a first-ever Moon-based ultraviolet telescope for astronomical observations. The Yutu rover successfully carried out close-up observations with the Panoramic Camera, mineralogical investigations with the VIS-NIR Imaging Spectrometer, study of elemental abundances with the Active Particle-induced X-ray Spectrometer, and pioneering measurements of the lunar subsurface with Lunar Penetrating Radar. This special issue provides a collection of key information on the instrumental designs, calibration methods and data processing procedures used by these experiments with a perspective of facilitating further analyses of scientific data from CE-3 in preparation for future missions.

Optimum design of lander structure based on finite element method

Three kinds of possible structures of legged lander including monocoqe, semi-monocoqe and space frame are compared, and the lightest space frame structure is selected as the lander's structure. Then, a new lander with four-legged truss structure is proposed. In the premise of ensuring that the main and assistant structures of landing legs are not changed, six possible lander body structures of the new lander are put forward. Taking the section size of each component of lander as design variables, and taking the total mass of the structure as the objective function, the six structures are analyzed by using the software Altair. OptiStruct and the results show that the mass of the basic structure is the lightest, and it is selected as the final design scheme of lander due to its simple structure and convenient manufacture. The optimization on the selected lander structure is conducted, and the detailed results are presented.

Study on displacement field generated by aftershocks in Landers earthquake fault zone and its adjacent areas

The displacement field generated by aftershocks in Landers earthquake fault zone and its adjacent areas is calcu- lated in this study. The result is compared with the displacement field of the main shock calculated by co-seismic slip model of Wald and Heaton (1994). The result shows that the direction of displacement generated by after- shocks in Landers seismic fault plane and its adjacent areas is consistent with that generated by main shock. The rupture of aftershock is generally inherited from main shock. The displacement generated by aftershocks is up to an order of centimeter and can be measured by GPS sites nearby. So when we use geodetic data measured after earthquake to study the geophysical problems such as crustal viscosity structure, afterslip distribution, etc., only the displacement field generated by aftershocks considered, can uncertainty be reduced to minimum and realistic result be obtained.

Conceptual design and analysis of legged landers with orientation capability

The lander with orientation capability is of fundamental importance for the“Returning”mission because its body can be the base with a suitable launching angle for the ascender lifting off.This paper proposes the conceptual design and verification of Landers with Orientation Capability(LOCs).Firstly,the topological composition of the lander is analyzed and expressed in the form of Lie group,which provides the fundamental principle for the type synthesis of LOCs.Then,the type synthesis approach for designing LOCs is proposed,which includes designing the Equivalent Parallel Mechanism(EPM)and the auxiliary limbs.Numerous mechanisms of LOCs with twodimensional rotational motions are obtained based on the type synthesis approach by developing and combining the EPMs and auxiliary limbs.Afterward,kinematics and Jacobian matrix of a typical legged lander are developed,the workspace is analyzed,singularity configurations are analyzed based on the wrench graph method,and finally,the orientation capability is analyzed.The pitch and yaw angle reach 17.5°,considering the permissible range of joints.The proposed types of LOCs offer potential candidate for the“Returning”mission of the exploration mission.

月球探测器鲁棒环形山检测及光学导航方法

针对月球探测器环形山检测方法受光照影响、鲁棒性差的问题,本文提出一种基于极大熵阈值三值化的鲁棒环形山检测算法。采用不同滤波核对图像进行去噪平滑,然后对处理后的图像进行极大熵阈值分割、将图像信息三值化,去除图像对光源的敏感性,同时最大程度保留图像信息;提出一种归一化多指标约束环形山匹配和拟合方法完成环形山提取,将环形山提取算法应用于光学导航中进行打靶实验验证算法实时性表现。仿真结果表明:与传统基于形态学或自适应边缘检测的方法相比,本文方法在较大尺度条件下提取出连续、光滑的环形山边缘,有效环形山数量提升35%以上,同时实时性更好、计算消耗降低40%;基于鲁棒环形山提取的光学导航算法实时性更好。

小天体柔性着陆任务规划的动态时间约束推理方法

针对小天体柔性着陆任务规划中的复杂耦合时间约束一致性推理效率问题,建立任务规划时间约束网络,通过划分时间约束类型,设计约束动态添加策略,提出动态弧一致时间约束推理方法,限制新添加约束的传播范围,局部求解时间网络一致性,实现规划过程中时间约束网络一致性的高效维护。最后,构建小天体着陆规划场景,生成着陆任务规划活动及时间约束。仿真结果表明,与现有时间约束推理方法相比,所提出方法提高了时间约束推理效率,进而可为小天体柔性着陆任务规划提供支撑。

低蛋白日粮对朗德鹅生产性能及健康状况的影响

试验旨在研究低蛋白日粮对朗德鹅生长性能和健康状况的影响,为低蛋白日粮在朗德鹅生产中的应用提供参考。选择480只18日龄朗德鹅,随机分为4组,分别为14.6%组、14.8%组、15.0%组和18.0%组,每组6个重复,每个重复20只,其中14.6%组、14.8%组和15.0%组为低蛋白组,18.0%组为对照组。结果表明:低蛋白组的平均末重、平均日采食量和料重比与对照组差异均不显著(P>0.05),低蛋白组的平均日增重均低于对照组,且14.6%组与对照组差异显著(P<0.05),14.8%组、15.0%组与对照组差异不显著(P>0.05),低蛋白组中14.6%组的平均日增重最低,为65.06 g,与14.8%组差异显著(P<0.05),与15.0%组差异不显著(P>0.05);低蛋白组死淘率、发病率均低于对照组,且与对照组差异显著(P<0.05)。说明低蛋白日粮虽然会降低朗德鹅的日增重,影响其生长性能,但也降低了朗德鹅患病风险,提高了其成活率。

IM公司奥德修斯号月面着陆器任务浅析

针对M公司的Nova-C级月面着陆器奥德修斯号开展了分析,从整器构型、飞行过程、载荷配置、任务评价4个方面进行了介绍,并对此次任务中遇到的故障以及处置措施进行了梳理,剖析了商业航天的特征,最后总结了商业航天运营模式对于我国航天事业发展的启示,以及本次飞行任务中的亮点和故障情况对我国月球探测任务的启示,并给出了几点思考与建议。

可行走着陆器的牛顿-欧拉法动力学研究

基于一种具有串并联混合腿足机构的四足可行走着陆器,为摸清其行走过程中的关节能耗问题,采用牛顿-欧拉方法进行了动力学建模研究。首先,采用D-H法建立串并联混合腿足机构的关节坐标系,进行正向运动学和逆向运动学的推导;然后在运动学模型的基础上,采用牛顿-欧拉方法建立着陆器整机的全状态动力学模型,该模型以足端相对轨迹为输入,获取着陆器在运动过程中各关节受力情况的变化曲线;最后,采用五次样条插值法规划一段运动轨迹,用ADAMS仿真软件进行着陆器虚拟样机仿真。经验证,该动力学模型理论计算数值和虚拟样机仿真数值具有相同的变化趋势,证明了模型的有效性,可以作为后续能耗模型建立和优化的基础。

Soft landing stability analysis of a Mars lander under uncertain terrain

Safe soft landing of the lander is vital to the Mars surface exploration mission. Analysis and verification of the landing stability under uncertain terrain play an important role in lander design. However, the effect of uncertain terrain is ignored in most existing studies, making the analysis incomprehensive and increasing the risk of landing failure in practice. In this paper, a Mars lander with 10 attitude control thrusters is introduced and its dynamics model is then established considering plastic deformation parts and nonlinear contact forces. The effectiveness and accuracy of the dynamics modeling method are verified by experiments with an average relative error of 10%.In order to carry out the dynamics simulation with high-fidelity terrain, a terrain generation method based on statistical data is proposed. Through Monte Carlo simulation under a 50 m × 50 m randomly generated landing terrain, the stability of the lander and the effects of attitude control thrusters are analyzed. The results show that the failure rate is 5.5%, in which the primary failure forms are overturning and abnormal attitude. When the landing simulations are repeated without thrusters, the stable ratio decreases from 94.5% to 90.7%, suggesting the positive effects of attitude control thrusters in improving landing stability under rough terrain.

Sean Landers：借用毕加索

Sean Landers是一个很聪明的艺术家，虽然某些人会说他有些聪明过头了。他早期的自我思索式的文字绘画中虽然充满了拼写错误、语法错误和杂乱的思想，但却非常优秀，而且常常十分滑稽。此后他举办了一系列良莠不齐的展览，一部分还不错，一部分却让人失望。但Landers又再一次取得了进步。某些艺术家以自己的身体、性取向或是个人的政治倾向作为创作的素材，我们不得不疑惑他们是否自负过度以及为什么我们要去关心这些。