二频机抖激光捷联系统结构振动分析

二频机抖激光捷联系统中三个激光陀螺抖动会引起惯性器件的耦合振动,产生系统抖动耦合误差,导致惯导系统导航精度下降。二频机抖激光陀螺捷联惯导系统机械结构较为复杂,很难通过解析法求解其振动特性。作者采用有限元方法对二频机抖激光陀螺进行了正弦信号驱动下的瞬态响应分析,并在正弦信号中加入了抖动随机信号,实现了机抖激光陀螺工作状态的仿真。此外,还对二频机抖激光捷联系统的振动特性进行了瞬态响应分析,掌握了系统的耦合振动情况,并进行了功率谱分析。这为激光捷联系统的频率搭配最优化提供了分析方法,对高精度二频机抖激光捷联系统的设计有重要意义。     

激光陀螺捷联惯导减振系统动力学建模与仿真

由于激光陀螺固有机抖频率的存在,以及导弹运输、装卸、发射与飞行过程经历的动态环境中振动、冲击、过载等激励,导致激光陀螺在导弹上使用输出精度差。应用多体系统传递矩阵法,建立了激光陀螺捷联惯性测量组合减振多体系统动力学模型,分析激光陀螺固有抖动和导弹振动冲击对激光陀螺输出精度的影响。通过对减振系统动力学模型进行仿真,获得了激光陀螺抖动和导弹冲击环境下激光陀螺捷联惯性测量组合减振系统动态响应。该仿真结果为激光陀螺捷联惯性测量组合减振设计提供理论依据,该分析方法为激光陀螺捷联惯组在导弹上应用提供理论基础。     

圆锥误差补偿算法在三轴激光捷联惯导系统中的应用

圆锥误差是影响捷联惯导系统姿态算法精度的原理性误差,其对三轴激光捷联惯导系统精度的影响显著.对三轴机抖激光陀螺捷联惯导系统,除了弹体运动可能引入圆锥运动外,三轴机抖激光陀螺产生的机械抖动也会在惯导系统中引入圆锥运动.文中分析了两种圆锥运动在三轴激光捷联惯导系统中产生的机理,并给出了圆锥误差补偿算法在不同试验条件下的应用效果.     

机抖激光陀螺敏感轴动态偏移误差参数估计与补偿

针对振动环境下机抖激光陀螺敏感轴产生动态偏移造成惯导系统精度下降的问题,从理论上推导了机抖激光陀螺敏感轴动态偏移误差模型,并结合工程实际建立了简化的误差模型;在此简化误差模型基础上,推导了陀螺敏感轴动态偏移造成的等效陀螺漂移与比力、角速度的耦合关系;将机抖激光陀螺敏感轴动态偏移误差归结为9个待辨识参数,针对该模型中的待辨识参数设计了标定方法,并给出了标定实验设计原则;以姿态误差为观测量进行振动实验对待辨识参数进行估计,振动实验结果表明,在10 min线振动时间内,机抖激光陀螺敏感轴动态偏移误差补偿后,捷联惯导系统纯惯导速度误差减小30%以上。     

多凹点滤波器在LINS中的应用

分析了激光捷联惯性导航系统中的激光陀螺频谱特性,指出激光捷联惯性导航系统中三个激光陀螺的抖动频率会互相干扰。提出一种多凹点有限冲击响应低通滤波器频域设计方法,通过指定三个抖动频率点幅值为小量,在幅频特性曲线上产生三个凹陷点。该滤波器采用标准滤波算法,同时实现了对激光捷联惯性导航系统三个激光陀螺的滤波和机抖信号的陷波。给出了一个24阶多凹点滤波器设计实例,幅频特性分析说明,由于三个陷波点的集中,该滤波器还可以在机抖频率可能存在的频段上,提供额外的80 d B以上的衰减,可防止激光陀螺抖动频率漂移后陷波性能下降。试验结果表明,多凹点滤波器输出数据波动幅度比原激光捷联惯性导航系统使用的滤波器结果减小5~8倍,三轴摇摆试验的导航精度也有一定提高。     

机抖温度特性对激光陀螺零偏稳定性的影响

机抖机构是一个工作于谐振状态的精密机电元件,当环境温度发生变化时,机抖的抖动偏频量将发生变化,这将引起角度随机游走误差的变化,并导致激光陀螺的零偏稳定性变差。本文推导了机械抖动激光陀螺的抖动速率与激光陀螺输出误差的关系表达式,提出了均方意义下的等抖动速率控制保持激光陀螺零偏稳定性的方法,并且通过实验具体研究了电磁式机械抖动装置的温度特性及其对激光陀螺零偏稳定性的影响。仿真实验与实测数据结果表明:在全温度范围内保持机抖机构抖动速率的一致性能有效地提高激光陀螺的零偏稳定性。     

结构参数对捷联惯导系统静态圆锥运动的影响

以采用整体隔振措施的配重式三轴机抖激光陀螺捷联惯导系统为研究对象,利用数值仿真方法,重点讨论了惯导系统的静不平衡、动不平衡、转动惯量以及隔振器刚度和阻尼对静态环境条件下由于陀螺抖动机构的不平衡引起的圆锥运动（细分为三类）的影响规律。研究认为,惯导系统的静平衡性和动平衡性只影响第三类圆锥运动,对一二类圆锥运动的影响甚微;惯导系统转动惯量的增大将会使圆锥运动减小;系统隔振频率越靠近陀螺抖动频率,圆锥运动越强烈;系统隔振器阻尼对圆锥运动的影响较小。研究成果可为机抖激光捷联惯导系统的结构设计及圆锥误差的事前控制提供理论指导。     

二频机抖激光陀螺抖动动力学模型

以国产某型二频机抖激光陀螺为对象，采用有限元方法，求得激光陀螺各个方向上的刚度系数和耦合刚度系数，建立陀螺的抖动动力学模型，分析了陀螺的幅频特性。对动力学模型中求得的各个方向上的固有模态进行了验证，证明了激光陀螺抖动动力学模型的正确性。     

弹载激光陀螺惯导系统安装支架设计

以某型号武器控制系统使用激光陀螺的任务为背景,针对激光陀螺捷联惯导系统在地面动态导航测试中圆概率误差偏大的现象,要求给激光陀螺捷联惯导系统设计出性能优良的减振系统。通过双自由度分析法以及振动试验,指出原安装板刚性不足,导致谐振频率出现在激光陀螺的机抖频率附近以及其它需要减振的频率段,这些成为导航误差偏大的主要原因。把安装支架作为减振系统的一部分,应用有限元动态优化法设计出刚性增强的安装板和动态结构性能良好的安装支架来改善减振效果。经地面振动试验验证,新构建的减振系统的减振效果达到预期的设计要求,在国内战术武器激光陀螺应用方面取得很大进展,可以在飞行器上使用。     

机抖激光陀螺方波驱动方式的谐波分析

针对方波驱动方式下机械抖动激光陀螺抖动幅度控制的问题,对机抖陀螺抖动的稳态幅度和驱动信号的维持时间之间的关系进行了研究。分析了某型机抖激光陀螺抖动机构的工作特性,通过谐波分析法证明了方波驱动波形在驱动效果上可以近似的由其一次谐波来等效进行分析,得出了方波驱动方式下抖动稳态幅度与方波驱动信号维持时间之间满足正弦函数关系的结论。分析了某型机抖激光陀螺实际驱动信号波形,证明了实际情况下上述结论的有效性;通过仿真对文中的结论进行了验证。     

Preface: Current research progress on mechanics of high speed rail

The construction and operation of high-speed rail（HSR）grid within the past two decades in China,in terms of the scale,may be possibly comparable to any national-wide construction in the history of China,even the Great Wall.By counting railways with commercial train service at the speed of200 km/h,China has the world’s longest HSR network with over 19 369.8 km of track in service today and this number     

ACTA MECHANICA SINICA 2014 ANNUAL SUBJECT INDEX

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人造地震动合成中的位移误差分析

三角函数级数法是合成人工地震动常用算法之一,但是通过对加速度积分求取位移时,却存在与零线漂移相类似的位移漂移现象。     

Hermitian space-time finite elements for estuarine mass transport

Space-time finite element solutions of the convection–dispersion equation using higher-order nodal continuity and Hermitian polynomial shape functions are described. Five separate elements ranging from a complete linear element with C^0,0 nodal continuity to a complete first-order Hermitian element with C^1,1 nodal continuity are subjected to detailed analysis. Wave deformation analyses identify the source of leading or trailing edge oscillations, trailing edge oscillations being the major source of difficulty. These observations are confirmed by numerical experiments which further demonstrate the potential of higher-order nodal continuity. The performance of the complete first-order Hermitian element is quite satisfactory and measurably superior to the linear element.     

Rainwater rivulets on a cable subject to windFilets d'eau de pluie sur un câble soumis au vent

Rainwater rivulets appear on inclined cables of cable-stayed bridges when wind and rain occur simultaneously. In a restricted range of parameters this is known to cause vibrations of high amplitudes on the cable. The mechanism underlying this effect is still under debate but the role of rainwater rivulets is certain. We use a standard lubrication model to analyse the dynamics of a water film on a cylinder under the effect of gravity and wind load. A simple criterion is then proposed for the appearance and position of rivulets, where the Froude number is the control parameter. Experiments with several geometries of cylinder covered with water in a wind tunnel show the evolution of the rivulets with the Froude number. Comparison of the prediction by the model with these experimental data shows that the main mechanism of rivulet formation and positioning is captured. To cite this article: C. Lemaitre et al., C. R. Mecanique 334 (2006).     

Cristallisation par onde acoustique : le cas de l'héliumCrystallization by acoustic waves: the case of helium

We establish a theoretical model to explain the nucleation of a crystal of helium by an acoustic over-pressure. We explain the interfacial laws for this ultra-fast cristallization, close to the sound speed. Assuming spherical symmetry and taking into account the experimental data, we recover the dynamics of the growth and melting during an over-pressure impulse. To cite this article: M. Ben Amar et al., C. R. Mecanique 331 (2003).     

Structure initiale et propriétés de liquéfaction statique d'un sableInitial structure and static liquefaction properties of sand.

Based on the use of two different preparation procedures for reconstituting triaxial samples of sand, i.e. wet tamping and dry pluviation, significant differences in associated mechanical behaviour are observed on a reference sand with respect to the phenomenon of ‘static’ liquefaction. Wet tamping favours the initiation of liquefaction instability, whereas dry pluviation favours a more stable behaviour, less susceptible to liquefaction. Microscopic observation of corresponding sand specimens allows us to identify two well differentiated structures, i.e., for wet tamping, an irregular structure with predominance of aggregates (aggregated grains) and macropores, very contractant and unstable and, for dry pluviation, a more regular structure, without macropores, more dilatant and more stable. These observations show the importance of further characterization, based on the introduction of appropriate parameters, of the initial structure of sandy materials, strongly dependant upon their mode of formation (natural or artificial). To cite this article: N. Benahmed et al., C. R. Mecanique 332 (2004).     

Sources of Complexity in Human Systems

Complex is a special attribute we can give to many kinds of systems. Although it is used often as a synonym of difficult, it has a specific epistemological meaning, which is going to be shared by the incoming science of complexity. Difficult is an object which, by means of an adequate computational power, can be deterministically or stochastically predictable. On the contrary complex is an object which can not be predictable because of logical impossibility or because its predictability would require a computational power far beyond any physical feasibility, now and forever. For complexity refers to some observing system, it is always subjective, and thus it is defined as observed irreducible complexity. Human systems are affected by several sources of complexity, belonging to three classes, in order of descending restrictivity. Systems belonging to the first class are not predictable at all, those belonging to the second class are predictable only through an infinite computational capacity, and those belonging to the third class are predictable only through a trans-computational capacity. The first class has two sources of complexity: logical complexity, directly deriving from self-reference and Gödel's incompleteness theorems, and relational complexity, resulting in a sort of indeterminacy principle occurring in social systems. The second class has three sources of complexity: gnosiological complexity, which consists of the variety of possible perceptions; semiotic complexity, which represents the infinite possible interpretations of signs and facts; and chaotic complexity, which characterizes phenomena of nonlinear dynamic systems. The third class coincides with computational complexity, which basically coincides with the mathematical concept of intractability. Artificial, natural, biological and human systems are characterized by the influence of different sources of complexity, and the latter appear to be the most complex.