磁悬浮位置信号在液浮陀螺仪中的应用

液浮陀螺仪采用磁悬浮是技术上的一个重大突破，磁悬浮除了具有使陀螺输出轴脱离轴承的机械接触而保持定中心，提高陀螺输入轴对准的精度和稳定性以及陀螺标度因数的稳定性元件之外，还可以利用磁悬浮的位置信号观察到浮子在陀螺仪加温、正常工作及降温等各个阶段所处的位置，判断陀螺仪工作是否正常，这对进一步改进陀螺仪的性能以及分析陀螺仪的故障都有很大帮助。     

三浮陀螺仪径向有源磁悬浮位置检测建模与优化设计

针对三浮陀螺仪有源磁悬浮系统位置检测精度低,制约了陀螺浮子高精度悬浮目标的实现,陀螺精度的进一步提升受到了限制这一问题,结合陀螺磁悬浮的应用环境和结构特点,建立了八极式外转子径向磁悬浮元件的位置检测数学模型。基于该模型对元件设计的核心参数绕组匝数、定子外径、零位气隙等进行了优化,使元件在-15～15?m区间内位置检测灵敏度提高了23%,非线性误差降低16%。在此基础上对有源磁悬浮的控制算法进行了调整。仿真与实验结果表明优化后径向磁悬浮输出力学性能有所提升,在输出轴向上和马达轴向上两种姿态下陀螺固定位置漂移平均减小30%～50%,提出的建模与优化设计方法有效地提高了三浮陀螺精度。     

有源磁悬浮的设计和应用

本文首先论述了有源磁悬浮在国内外的发展状况和趋势,接着论述采用有源磁悬浮的目的和对有源磁悬浮的要求,并对时分式直流反馈有源磁悬浮的工作原理、磁悬浮元件、磁悬浮系统的稳定性、时分模拟开关以及对反馈回路的方案进行了分析。实验结果表明,有源磁悬浮应用于陀螺加速度计对仪表精度的提高起到了关键性作用。     

H_∞控制器在变参数有源磁悬浮系统中的应用

建立了液浮陀螺仪浮子有源磁悬浮控制模型,深入地分析了其结构组成及工作原理。针对所建立的数学模型对各个结构参数进行了鲁棒性分析研究,得出了系统鲁棒稳定性对各个参数的要求。在此基础上,建立了系统工作的状态方程,对变参数的阻尼系统进行了分析研究,设计了满足系统动态性能和鲁棒稳定性要求的H∞控制器。最后分别对初始系统和校正系统进行了仿真研究,仿真结果表明,H∞控制器提高了阻尼在一定范围内变化的磁悬浮系统的鲁棒控制性能,增强了系统的抗干扰能力和动态特性。     

基于浮子运动的三浮陀螺仪工作温度标定方法

针对三浮陀螺仪工业生产过程中,工作温度标定方法精度低、耗时长的问题,提出了一种以"浮子运动趋势拐点"作为判据的工作温度标定方法。首先对三浮陀螺仪磁悬浮标定温度进行可行性分析,然后建立陀螺仪浮子受力模型以归纳浮子运动规律,借助磁悬浮控制系统提供的浮子位置信息提出本方法。试验结果表明,该方法工作温度标定精度优于±0.02℃,较现行的"最小加力法"提高15倍以上,平均耗时缩短一半。     

一种小型静电陀螺仪三位一体系统方案

在比较了国外两种小型静电陀螺仪方案的基础上，研究了一种小型静电陀螺仪质量不平衡调制信号读取、数字式支承和电场恒速三位一体工作系统方案。介绍了三位一体系统的工作原理，讨论了系统各组成模块的功能，对制约系统性能的关键因素作了相关分析。分析表明，在抵消变压器线圈阻抗匹配的条件下，可以忽略加力和信号读取之间的相互影响。     

基于位置信号的三浮陀螺仪有源磁悬浮干扰力矩补偿方法

针对高精度三浮陀螺采用有源磁悬浮之后带来新的干扰力矩问题,提出了基于位置信号的干扰力矩补偿法。对有源模式下径向元件电磁模型进行了分析,得出磁悬浮干扰的直接原因为同一坐标方向的两个极下磁场不对称,定、转子几何中心偏移越大这种不对称性也越大。建立了磁悬浮干扰力矩常值部分和随机部分与定中位置、定中精度的关系数学模型,在陀螺测试输出中对其进行补偿。多次实验表明,引入该补偿算法后陀螺固定位置随机漂移精度平均提高了33%~42%,同时也提高了磁悬浮的定中精度,证明此方法有效。     

磁悬浮陀螺仪的对中调整

在磁悬浮陀螺仪中,为确保磁悬浮正常工作,需要对限位机构进行对中调整。本文通过几种对中方法的比较,结合現实条件介绍一种切实可行的调整结构和调整方法。针对调整中容易出现的几种现象进行了简要分析。最后,对调整中微机显示和自动绘迹使用的效果作简单介绍。     

一种车载数字式陀螺寻北仪的研究

－本文介绍一种适合车载雷达等使用的数字式寻北陀螺仪。它立足于国内的现有条件，以计算罗经原理为基础，采用双位置力反馈平衡法和补角修正技术用以消除陀螺常值漂移的影响和在全方位上提高方位角的计算精度。     

多次循环干涉型光纤陀螺仪的实验研究

详细介绍了循环干涉型光纤陀螺仪的实验装置及测试结果，给出了无源和有源补偿的两种敏感环结构下陀蛇分辨率公式。在实验装置中采用了大功率光源和低耦合比输入耦合器，以提高光波在敏感环中的循环次数。实验结果表明：光束在敏感环中循环了2－3次，并达到了较好的零偏稳定性。     

一种基于直接计算高阶奇异积分的断裂力学双边界积分方程分析法

相对于有限元法,边界单元法在求解断裂问题上有着独特的优势,现有的边界单元法中主要有子区域法和双边界积分方程法.采用一种改进的双边界积分方程法求解二维、三维断裂问题的应力强度因子,对非裂纹边界采用传统的位移边界积分方程,只需对裂纹面中的一面采用面力边界积分方程,并以裂纹间断位移为未知量直接用于计算应力强度因子.采用一种高阶奇异积分的直接法计算面力边界积分方程中的超强奇异积分;对于裂纹尖端单元,提供了三种不同形式的间断位移插值函数,采用两点公式计算应力强度因子.给出了多个具体的算例,与现存的精确解或参考解对比,可得到高精度的计算结果.      

汶川地震诱发文家沟巨型滑坡 碎屑流基本特征及成因机制初步分析

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2008年5月12日,汶川M80地震在四川省绵竹市清平乡文家沟内诱发一巨型滑坡。通过现场调查得知,滑坡前后缘高差455m,厚度20～30m,滑面为基岩层面,初始方量2750×107m3。滑体在运动中转化为碎屑流。滑坡-碎屑流总的水平运动距离为4022m,垂直运动距离为1443m,遗留的堆积物体积达5×107m3。滑坡距映秀—北川断裂仅36km,位于其下盘,地震烈度达XI度。滑坡导致文家沟中48人遇害,并形成一条完整的地震次生地质灾害链。初步分析表明滑坡启动速度快,滑坡向碎屑流转化过程明显、地点明确。碎屑流运动过程复杂,伴有强烈的“气垫效应”和“前缘气浪冲击效应”。作者认为,文家沟滑坡的高启动速度是长持时强烈地震动作用的结果,与山体的猛烈碰撞是导致滑体解体并转化为碎屑流的原因。     

Preface: Orbits around asteroid

One of the core issues in modern celestial mechanics is the orbital dynamics in the near-regime gravitational field of as- teroids, which provides deep insights into the mathematical nature of a class of nonlinear systems, and plays as a critical basis for in situ explorations of different science goals. Lots of efforts have been made to reveal the characteristics of orbital motion in the vicinity of asteroids, and to improve the skills of asteroid research in methodology.     

Effet de l'anisotropie élastique cristalline sur la distribution des facteurs de Schmid à la surface des polycristauxInfluence of crystalline elasticity anisotropy on Schmid factor distribution at the free surface of polycrystals

Experimental studies of the plasticity mechanisms of polycrystals are usually based on the Schmid factor distribution supposing crystalline elasticity isotropy. A numerical evaluation of the effect of crystalline elasticity anisotropy on the apparent Schmid factor distribution at the free surface of polycrystals is presented. Cubic elasticity is considered. Order II stresses (averaged on all grains with the same crystallographic orientation) as well as variations between averages computed on grains with the same crystallographic orientation but with different neighbour grains are computed. The Finite Element Method is used. Commonly studied metals presenting an increasing anisotropy degree are considered (aluminium, nickel, austenite, copper). Concerning order II stresses in strongly anisotropic metals, the apparent Schmid factor distribution is drifted towards small Schmid factor values (the maximum Schmid factor is equal to 0.43 instead of 0.5) and the slip activation order between characteristic orientations of the crystallographic standard triangle is modified. The computed square deviations of the stresses averaged on grains with the same crystallographic orientation but with different neighbour grains are a bit higher than the second order ones (inter-orientation scatter). Our numerical evaluations agree quantitatively with several observations and measures of the literature concerning stress and strain distribution in copper and austenite polycrystals submitted to low amplitude loadings. Hopefully, the given apparent Schmid factor distributions could help to better understand the observations of the plasticity mechanisms taking place at the free surface of polycrystals. To cite this article: M. Sauzay, C. R. Mecanique 334 (2006).     

Nonlinear behavior of matrix-inclusion composites under high confining pressure: application to concrete and mortar

This paper is devoted to a micromechanics-based simulation of the response of concrete to hydrostatic and oedometric compressions. Concrete is described as a composite made up of a cement matrix in which rigid inclusions are embedded. The focus is put on the role of the interface between matrix and inclusion which represent the interfacial transition zone (ITZ). A plastic behavior is considered for both the matrix and the interfaces. The effective response of the composite is derived from the modified secant method adapted to the situation of imperfect interfaces. To cite this article: T.H. Le et al., C. R. Mecanique 336 (2008).     

Dynamics and Breakup of Viscoelastic Liquids (A Review)

The phenomena of hydrodynamic breakup of liquid jets, drops, films, bridges, and filaments are reviewed for liquids with viscoelastic properties. The reasons for breakup are capillary instabilities, collisions with rigid obstacles, and other forms of dynamic action. The relationship between the properties of the liquids and the features of the breakup process is discussed.     

Flow stability analysis and excitation using pulsating jets

Classical flow stability applied to transition from laminar to turbulent flow may also describe the behavior of vorticity fluctuations created by a pulsating jet placed along a solid boundary. A numerical laminar flow experiment involving a pulsating jet placed along the surface of a duct with flow separation downstream, resulted in eliminating most part of the separated flow region. Applying the same approach to a turbulent flow, it was possible to develop a turbulent stability flow formulation and apply successfully turbulent pulsating jet flow separation control. To cite this article: D. Skamnakis, K. Papailiou, C. R. Mecanique 333 (2005).