航天器动力学与控制的研究进展与展望

开展航天器动力学与控制的研究在航天技术的发展中起到举足轻重的作用, 其目的在于发展有效的方法促使航天器在各阶段平稳可靠地运行. 航天器技术发展迅速, 其形式日趋多样化, 功能与构造日趋复杂,已经向大型空间站、微小卫星、深空探测等方向发展. 航天器结构表现出多耦合、非线性、极端外界环境, 以及大尺度柔性结构等特征, 由此激发起航天器动力学与控制领域各方向的深入研究. 航天器动力学与控制的研究方法覆盖理论分析、数值仿真, 以及实验模拟等诸多方面, 研究内容十分丰富. 本文概括介绍了近年来航天器动力学与控制研究方面的发展状况, 综述了跨航天器动力学与控制、航天器系统级动力学与振动控制、航天器部件级动力学与振动控制等航天领域中的若干基础问题. 内容主要集中于航天领域中不同应用范围、不同层次结构的航天器动力学模型的建立和动力学响应与振动控制的研究方法及已取得的成果. 最后, 提出了该领域中值得进一步考虑的科学问题及未来的发展方向.      

颗粒流润滑过程中粉末层的微观破坏形式和机理分析

将松散的石墨粉末导入到面接触摩擦副间隙中,对粉末层形成和破坏过程的宏、微观现象进行了跟踪和分析.通过对粉末层的电子、光学显微镜观察及能谱分析发现粉末层典型的生命周期包含完整、轻微破损、严重剥落和完全破坏4个阶段.利用光学显微镜观察到粉末层的鼓包、部分剥落、分层剥落和擦伤等微观现象,这些现象代表粉末层不同阶段的破坏状态和磨损程度.鼓包、部分剥落、分层剥落是粉末层破坏的早期形式.擦伤是粉末层破坏的严重形式,表明上试件和下试件发生了表面的直接接触并产生磨损,通常能够在粉末层完全破坏之前观察到.     

城市地质图的特点·编图原则·方法

论述了城市地质图的主要特点、编图原则和方法, 其主要内容概括如下: (1)编制城市地质图的重要意义首先在于为不断完善和适应城市建设和发展的需要, 更好地使地质工作为城市建设总体规划和政府决策服务, 同时为具体工程设计和施工提供基础资料。其次为合理地开发利用城市土地资源、保护城市地质环境提供科学依据。(2)城市地质图是一个具有以专业地质规划目标与工程地质要求、城市发展总体效益评估为内容的系列图件, 是一个分别具有适应于地质专业人员、城市规划设计工程师和政府决策管理官员需要的多功能特点的系统性图件。(3)城市地质图编制原则, 第一在于客观性; 第二为评价性; 第三为预测性; 第四为实用性。前三项是前提和基础, 后者为目的。力求做到内容准确、明晰可读、易懂, 紧紧围绕城市规划设计和政府决策对地质技术的要求进行。(4)城市地质图包容了基础地质图类、分析评价图类、效益决策评估类三个等级的功能各异的图件, 在制图方法和程式上体现了图件的等级—内容—性质—用途的统一、技术性与管理决策的统一。     

小行星撞击地球的超高速问题

小行星撞击地球是人类生存面临的潜在威胁之一.在小行星进入地球大气与撞击地球表面过程中,存在烧蚀、解体、空中爆炸、火球、撞击成坑、反溅碎片云、地震以及海啸等一系列复杂的物理化学和力学现象.本文梳理和归纳了与这些现象相关的超高速空气动力学问题和超高速碰撞动力学问题.小行星进入地球大气的超高速空气动力学问题有:极高速($V = 12 ~ 20$km/s)进入条件下的气动力与轨迹,极高速进入条件下的小行星气动加热与烧蚀机理,极高速气动加热条件下的小行星结构传热与热响应,极高速进入条件下的高温气体效应,小行星进入过程的物理特征.小行星撞击地球的超高速碰撞动力学问题有:陆地撞击成坑与反溅碎片云,海洋撞击与海啸,撞击过程的地震效应.由于小行星撞击地球与超高速飞行器的再入过程在速度、材料和结构上存在较大差异,针对这些超高速问题,现有的研究手段在地面试验和数值计算两方面都存在不足.最后,从小行星进入地球大气的弹道方程、质量损失方程、解体判据和解体模型等出发,初步建立了小行星进入与撞击效应分析评估模型,并对Chelyabinsk和Tunguska两次流星事件进行了分析,重构了进入与爆炸解体过程,评估了空爆火球在地面所导致的超压和热辐射损伤.      

折纸结构和折纸超材料动力学研究进展

折纸结构和折纸超材料由于其无穷的设计空间,突出的变形状、变大小、变拓扑特性,以及由折叠诱发的超常规力学特性,在最近几年迅速成为数学、物理和工程学科的研究前沿和热点.折纸结构和折纸超材料在航天、医疗、材料、机器人等众多工程领域具有广泛的应用前景,其典型的代表包括大型空间可展开结构、自折叠可重构机器人、微型可折叠器械等.随...     

Finite rise time step strain modeling of nearly monodisperse polymer melts and solutions

The step shear strain experiment is one of the fundamental transient tests used to characterize the rheology of viscoelastic polymer melts and solutions. Many melts and solutions exhibit homogeneous deformation and stress relaxation; in these cases the transient dynamics can be modeled by completely ignoring momentum effects and imposing singular kinematics. Recently, however, it has been observed that there are certain classes of nearly monodisperse melts and solutions that exhibit anomalous nonhomogeneous deformation and stress relaxation (Morrison and Larson (1990), Larson, Khan, and Raju (1988), Vrentas and Graessley (1982), and Osaki and Kurata (1980)). We demonstrate that, for these classes, a finite rise time must be incorporated, some source of inhomogeneity must be present, and a small amount of added Newtonian viscosity is necessary. We examine five nonlinear and quasilinear models; the Johnson-Segalman, Phan Thien Tanner, Giesekus, White-Metzner, and Larson models. We determine which mathematical features of the models are necessary and/or sufficient to describe the observed experimental behavior.     

中国高速列车研发与展望

十几年来, 以高速列车为代表的高速铁路装备在长期技术积累和自主研发的基础上,经过引进消化吸收再创新、自主提升创新、全面创新和持续创新,成功研制了多代先进的高速列车产品. 通过不断的技术创新,突破了高速列车系列关键技术, 形成了自主研发能力,不断提升高速列车的安全性、可靠性、经济性、环保性及智能化.我国高速列车的运行速度、综合舒适度、安全性、可靠性、节能环保等各项综合性能指标优良,部分指标达到国际领先水平.论文系统回顾了我国和谐号动车组、复兴号动车组、城际动车组、前沿动车组产品的发展成就及主要技术突破,分析了高速列车研发过程中面临的复杂环境适应性、大系统复杂耦合作用、安全可靠设计、智能化应用等关键技术挑战,系统概述了高速列车故障预测与健康管理技术、车体轻量化技术、被动安全防护技术、碳纤维复合材料应用、气动外形设计技术、高速转向架技术、噪声控制技术、牵引制动技术等关键技术的研究进展及主要技术突破, 并展望了高速列车动力学技术、结构安全技术、被动安全防护技术、流固耦合技术、牵引制动技术、智能控制安全技术、故障预测与健康管理技术、综合节能技术等关键技术的未来发展方向.      

人体生物摩擦学的研究现状与展望

介绍了人体生物摩擦学的概念,分析了头发、眼睛、皮肤、牙齿和关节等系统的生物摩擦学研究现状,就血液、人工心脏泵、人工心脏瓣膜和食品味觉的生物摩擦学研究方向进行了展望.指出当前人体生物摩擦学研究的关键科学问题主要包括人体摩擦副的特殊摩擦学行为及机理、模拟人体生物环境条件的人工器官摩擦磨损试验方法研究、人工材料在体内的生物摩擦学行为反应预测及磨粒在体内的生物反应和临床病症的评定.     

Development and implementation of an IOT based instrumentation system for computing performance of a tractor-implement system

A high precision and compact IOT based digital instrumentation setup to measure, display and record various tractor and implement system performance parameters was developed and installed on a 28.3 kW Tractor. The setup was capable of continuous monitoring and wirelessly transmitting tractor-implement performance parameters on a cloud platform such as engine speed, radiator fan speed, fuel consumption, draft, forward speed, lift arm angle, wheel slip, wheel slip, PTO speed, geo-location/position of the tractor, choking of seeds in the implement and vibrations experienced by the implement. For precision measurements, commercial transducers used in the system were calibrated and assessed under both static and dynamic conditions. The average calibration constant for fuel consumption, forward speed, lift arm angle and load cell were 0.00009804 L/pulse, 0.01610306 km/h/pulse, 0.056 mA/degree and 0.2575 mV/kN respectively. The system based on DataTaker DT 85 Data logger connected to a micro-computer through transducers capable of transferring data wirelessly was installed on John Deere 5038 tractor and was tested with a Spatially Modified No-Till Drill in agricultural field with varied implement depth.     

不同心排出量下主动脉瓣血流动力学的PIV实验研究

主动脉瓣发生病变时导致心排出量(cardiac output, CO)减少,而心排出量减少与主动脉瓣血流动力学耦合作用, 引发瓣膜继发性疾病.本文基于医学影像数据三维重构带有冠状动脉的主动脉根部,制备高度光滑和透明的主动脉根部实验模型, 构建体外脉动循环模拟系统,利用粒子图像测速技术(particle image velocimetry,PIV)研究冠状动脉存在时心排出量对主动脉瓣速度分布、黏性剪应力(viscous shear stress, VSS)和雷诺剪应力(Reynolds shear stress, RSS)等血流动力学的影响.研究结果表明: 冠状动脉的存在改变了主动脉窦中的涡旋运动和涡度,冠状动脉存在时流体经由冠状动脉流出, 主动脉窦中的涡旋运动逐渐消失,涡度较早开始减小. 峰值期, 中心对称流动两侧区域存在正、负高黏性剪切区域,存在冠状动脉一侧的升主动脉下游存在高雷诺剪应力区域.心排出量显著影响主动脉瓣的速度分布、VSS和RSS等血液流动和受力状况.随着心排出量增大, 冠状动脉存在时峰值期的最大速度、VSS和RSS增大, 即$CO=2.1$, 2.8, 3.5和4.2 l/min时, 最大速度分别为0.98, 1.13, 1.21和1.37 m/s, 最大VSS分别为0.87, 0.95, 0.96和1.02 N/m$^{2}$, 最大RSS分别为103.76, 116.25, 138.68和146.55 N/m$^{2}$. 心排出量较低时,主动脉瓣较低的跨瓣流动速度和黏性剪应力易导致血栓形成,研究结果可为主动脉瓣置换术提供理论参考.      

Dynamics of firing patterns, synchronization and resonances in neuronal electrical activities： experiments and analysis

Recent advances in the experimental and theoretical study of dynamics of neuronal electrical firing activities are reviewed. Firstly, some experimental phenomena of neuronal irregular firing patterns, especially chaotic and stochastic firing patterns, are presented, and practical nonlinear time analysis methods are introduced to distinguish deterministic and stochastic mechanism in time series. Secondly, the dynamics of electrical firing activities in a single neuron is concerned, namely, fast-slow dynamics analysis for classification and mechanism of various bursting patterns, one- or two-parameter bifurcation analysis for transitions of firing patterns, and stochastic dynamics of firing activities （stochastic and coherence resonances, integer multiple and other firing patterns induced by noise, etc.）. Thirdly, different types of synchronization of coupled neurons with electrical and chemical synapses are discussed. As noise and time delay are inevitable in nervous systems, it is found that noise and time delay may induce or enhance synchronization and change firing patterns of coupled neurons. Noise-induced resonance and spatiotemporal patterns in coupled neuronal networks are also demonstrated. Finally, some prospects are presented for future research. In consequence, the idea and methods of nonlinear dynamics are of great significance in exploration of dynamic processes and physiological functions of nervous systems.     

流体力学与国土安全

国土安全涉及到流体力学的广泛应用, 并为其研究发展提供了诸多机遇. 本 评论选择列举了流体力学在反恐领域的各类课题, 还建议了今后的研究方向. 课题范围从防 备、遏制策划中的恐怖袭击, 一直到探测、应对和恢复. 具体的内容则包括飞机加固, 爆炸 缓冲, 传感器取样, 爆炸物探测, 微流控和芯片实验室, 城市环境中化学羽流弥散以及建筑 物通风等. 此外, 本文还讨论了蒸气羽流与远距探测, 非致命武器, 疾病空气传播, 人员防 护装备以及污染移除问题. 涉及这类的应用, 要求流体力学家跨越传统领域的边界, 进行交 叉学科研究, 特别是要结合化学、生物学、气溶胶学与大气科学协同工作.     

Unsteady bio-fluid dynamics in flying and swimming

Flying and swimming in nature present sophisticated and exciting ventures in biomimetics, which seeks sustainable solutions and solves practical problems by emulating nature's time-tested patterns, functions, and strategies. Bio-fluids in insect and bird flight, as well as in fish swimming are highly dynamic and unsteady; however, they have been studied mostly with a focus on the phenomena associated with a body or wings moving in a steady flow. Characterized by unsteady wing flapping and body undulation, fluid-structure interactions, flexible wings and bodies, turbulent environments, and complex maneuver, bio-fluid dynamics normally have challenges associated with low Reynolds number regime and high unsteadiness in modeling and analysis of flow physics. In this article, we review and highlight recent advances in unsteady bio-fluid dynamics in terms of leading-edge vortices, passive mechanisms in flexible wings and hinges, flapping flight in unsteady environments, and micro-structured aerodynamics in flapping flight, as well as undulatory swimming, flapping-fin hydrodynamics, body–fin interac-tion, C-start and maneuvering, swimming in turbulence,collective swimming, and micro-structured hydrodynamics in swimming. We further give a perspective outlook on future challenges and tasks of several key issues of the field.     

骨陷窝-骨细胞形状和方向对骨单元内液体流动行为的影响

骨组织内的流体流动不仅为骨细胞的生存提供了充足营养供应及代谢物排放途径,也在骨重建过程中起到关键作用. 为了更精确地阐明骨内液体流动的具体形式,这项研究利用骨陷窝-骨细胞的密度,形态和方向等参数来计算骨单元内液体的流动行为. 首先,计算出不同形状和方向的骨陷窝周围骨小管的数量及分布情况,其次利用算出的参数以及骨组织其他微结构数据来估计骨组织的渗透率和孔隙率等参数,最后根据计算所得的参数建立骨单元的多孔弹性力学有限元模型,并分析了在轴向位移载荷作用下骨陷窝形状和方向对骨单元内液体渗流行为的影响. 结果表明,在所研究的参数范围内不同骨单元模型的相同区域上,骨陷窝形状影响下的骨单元最大压力和流速比最小的分别增加了86%和18%;骨陷窝方向影响下的最大压力和流速比最小的分别增加了125%和56%. 伸长形骨陷窝对单个骨单元局部压力的影响远大于扁平形和圆形骨陷窝. 骨陷窝从0°绕$x$轴旋转到90°过程中压力是逐渐降低的,且30°,45°和60°的模型对骨单元内局部流速有显著影响. 该模型表示骨陷窝的形状和方向以及骨小管的三维分布对骨单元内液体压力和流速幅值及沿不同方向的流动差异有显著的影响. 这项研究将有助于精确量化描述骨内液体的流体行为.      

地球流变学研究现状

地球流变学研究地球介质的流变学性质、地质构造的形成和演化、地震的前兆及其发展、泥石流、岩浆流、冰川运动等地学问题。它是介于地球科学和力学之间的边缘学科。本文介绍地球流变学的进展,包括:岩石蠕变实验,利用观测数据反演地球流变学性质,岩石圈变形分析,动力热体系,地质构造、矿物颗粒的定向分布以及地震过程与流变学的关系。      

Experimental study and analysis on driving wheels’ performance for planetary exploration rovers moving in deformable soil

Planetary rovers are different from conventional terrestrial vehicles in many respects, making it necessary to investigate the terramechanics with a particular focus on them, which is a hot research topic at the budding stage. Predicting the wheel-soil interaction performance from the knowledge of terramechanics is of great importance to the mechanical design/evaluation/optimization, dynamics simulation, soil parameter identification, and control of planetary rovers. In this study, experiments were performed using a single-wheel testbed for wheels with different radii (135 and 157.35 mm), widths (110 and 165 mm), lug heights (0, 5, 10, and 15 mm), numbers of lugs (30, 24, 15, and 8), and lug inclination angles (0°, 5°, 10°, and 20°) under different slip ratios (0, 0.1, 0.2, 0.3, 0.4, 0.6, etc.). The influences of the vertical load (30 N, 80 N, and 150 N), moving velocity (10, 25, 40, and 55 mm/s), and repetitive passing (four times) were also studied. Experimental results shown with figures and tables and are analyzed to evaluate the wheels’ driving performance in deformable soil and to draw conclusions. The driving performance of wheels is analyzed using absolute performance indices such as drawbar pull, driving torque, and wheel sinkage and also using relative indices such as the drawbar pull coefficient, tractive efficiency, and entrance angle. The experimental results and conclusions are useful for optimal wheel design and improvement/verification of wheel-soil interaction mechanics model. The analysis methods used in this paper, such as those considering the relationships among the relative indices, can be referred to for analyzing the performance of wheels of other vehicles.     

油气井密封结构的变形与失效行为研究进展

在今后相当长一个时期,石油和天然气依然是人类的主要能源.油气井密封是油气开采中最重要的作业之一,在水平钻井、水力压裂等最新的油气开采技术中发挥着重要的作用,促进了页岩气等非常规油气开采的发展.密封质量会直接影响油气井的安全和生产效率,密封元件的失效可造成严重的环境污染和生命财产损失.因此,深入理解密封元件的失效行为,对于油气井安全评估具有重要意义.水泥和可溶胀高弹体密封是两种最主要的密封方式.水泥密封已有百余年历史,溶胀式高弹体密封则是一种相对较新的密封技术.本文介绍这两种油气井密封结构变形与失效行为的国内外最新研究进展.首先,介绍固井水泥环固化过程中的应力演化、生产作业导致的应力、水泥环的失效模式和失效判据方面的研究进展;然后,介绍溶胀式高弹体封隔器的基本原理、力学理论、测试方法、失效模式及失稳等方面的研究进展.      

合成射流技术及其在流动控制中应用的进展

流动控制是流体技术最主要的研究领域,21世纪的空气动力学将在流动控制领域取得重大突破; 合成射流是一种基于旋涡运动的零质量射流,是流动控制领域近10年来最热门活跃的流动主动控制技术.首先介绍了合成射流激励器及激励器的基本类型,并概括了激励器的主要发展方向,即宽频域、高动量、``强壮'的合成射流激励器和微小型激励器.尔后,对合成射流激励器工作原理、合成射流结构以及合成射流独特的流场特征和合成射流技术的特点进行了综述.最后着重对合成射流技术主要和潜在应用,如流动分离及气动力控制、射流矢量控制、增强掺混及加强传热和传质、抑制噪声、微流体控制、飞行控制以及粒子的散布控制、合成射流陀螺仪技术等进行了介绍和综述,同时对其在各应用领域的控制机理进行了归纳总结.      

Protein Mechanics: A New Frontier in Biomechanics

Proteins play essential roles in all aspects of cellular processes, such as biosynthesis, division, growth, motility, metabolism, signaling, and transmission of genetic information. Proteins, however, could deform under mechanical forces, thus altering their biological functions. Here we present protein deformation as a possible molecular basis for mechanosensing and mechanotransduction, elucidate the important features of protein mechanics including protein deformation mode and dynamics, illustrate how protein deformation could alter biological function, and describe the important roles of protein deformation in force-sensing, force transducing and mechanochemical coupling in cells. The experimental and modeling challenges in protein mechanics are discussed.     

Application of Modelica/MWorks on modeling,simulation and optimization for electro-hydraulic servo valve system

Electro-hydraulic servo valve is a typical complicated multi-domain system constituted by mechanical, electric, hydraulic and magnetic components, which is widely used in electro-hydraulic servo systems such as construction machinery, heavy equipment, weapon and so forth. The traditional method of modeling and simulation of servo valve is based on block diagram or signal flow, which cannot describe the servo valve system from components level nor be used in modeling and simulation of overall servo systems. In the procedure of traditional method, computational causality must be involved in modeling of servo valve, which is inconvenient to execute modification on components or parameters. Modelica is an object-oriented modeling language which is suited for large, complex, heterogeneous and multi-domain systems. The key features of Modelica are multi-domain, object-oriented and non-causal, which are suitable for modeling of servo valve and make the model readable, reusable, and easy to modify. The simulation results show similar curves with traditional method. This new servo valve modeling and simulation method can provide the engineers a more efficient way to design and optimize a servo valve and an overall servo system.