用于新型等效原理空间实验检验的静电加速度计设计

等效原理是爱因斯坦广义相对论的基本假设之一,在更高精度上检验等效原理是否成立可以预言新型基本相互作用力。新型等效原理是我国科技工作者提出的一种假设,通过检验两个相同材料但自旋状态不同的宏观物体的自由落体运动来检验等效原理可能存在的破坏。提出了一种面向空间检验新型等效原理的差分静电加速度计设计方案,给出了地面实验用原理样机的结构设计,对结构模态和温度应力进行了有限元仿真;依据支承刚度和量程约束条件,对径向和轴向静电支承控制回路进行了设计和仿真分析;建模分析了高真空下转子静电加转驱动回路的主要性能,仿真结果表明启动过程中达到目标转速(10~4 rpm)的启动时间为36.9 min。     

静电加速度计悬浮质量块质心偏移量在轨标定

高精度静电加速度计已广泛地应用于航天任务中,用于测量作用于航天器的非引力加速度。如果静电加速度计悬浮质量块的质心与航天器的质心安装有偏差时,重力梯度力、姿态耦合产生的干扰加速度,静电加速度计控制系统引入的干扰加速度等干扰力会夹杂在测量数据中。针对这一问题,研究了航天器小质量特性变化情况下,当静电加速度计处于动态设计良好并进入稳态后,利用静电加速度计、陀螺仪和磁强计作为敏感元件,基于非线性卡尔曼滤波理论的静电加速度计悬浮质量块质心偏移量的在轨标定。仿真结果表明,该方案的精度J向可以达到0．1mm,Y和Z向能达到0．04mm。     

大冲击后力反馈微加速度计吸合失效与防止

冲击载荷强迫微加速度计的敏感质量大大偏离平衡位置,使差动静电力发生器的非线性效应体现出来,其结果是使正常工作时敏感质量仅在平衡位置附近有微小位移的状况下成立的负反馈闭环系统模型不再适用,敏感质量的受控特性可能变为正反馈,从而使微加速度计失效。为提高微加速度计受外界大载荷冲击后的可靠性,分析了加速度计的敏感质量在不同限制的静电反馈力下的受控特性及对应的闭环系统特性,推导了在已知止挡机械参数下确定微加速度计相应电气参数从而避免此类失效的防吸合准则。多次的验证实验表明,按防吸合准则设计了系统参数的静电力反馈加速度计,在受到远超过其本身量程的载荷冲击后,可以100%地防止吸合现象的出现。     

一种谐振式微加速度计表芯非线性动力学分析及实验

在研制基于静电刚度谐振式微加速度计过程中,发现增大激励电压可以提高输出信噪比,但响应的振动幅度将不稳定,同时谐振频率也将会出现漂移。针对上述问题,建立了静电驱动微机械谐振系统等效行为模型,非线性动力学理论分析结果与实验现象一致,总结出需要从加速度计结构参数优化和减小激励电压两个方面来减小频率漂移和提高分辨率。将结构优化准则应用到制造的微加速度计上,实验结果表明:在5 V敏感电压下,闭环条件下单梁加速度计灵敏度为58 Hz/g,分辨率为3.5 mg。     

硅微静电加速度计的支承刚度特性

静电加速度计通过降低带宽和量程在空间微重力环境下可以实现极高的分辨率。设计了一种采用玻璃-硅-玻璃"三明治"结构、平行六面体状检验质量、体硅加工工艺的三轴硅微静电加速度计,推导并讨论了静电支承回路的典型刚度特性与控制参数之间的关系式。采用基于DSP的数字控制器,实现了敏感质量的六自由度稳定支承,在大气环境下测试了静电支承回路的主要性能。分析与测试结果表明,在支承系统频带内,支承刚度特性与控制器参数及气膜阻尼系数密切相关;同时,改变预载电压可以在较大范围内在线调整加速度计的量程和支承刚度等指标。     

六轴硅微静电加速度计的悬浮回路设计

传统的静电加速度计在空间微弱加速度测量方面可以获得极高的分辨率。提出了一种采用静电悬浮、可实现六轴加速度测量的微静电加速度计。敏感组合件采用玻璃-硅-玻璃三层键合结构、体硅加工工艺;检测质量采用"回"字形结构,以提高加速度计的径向量程和刚度。利用有限元软件分析了大气环境下检验质量的气模阻尼特性,对六自由度静电悬浮回路进行了建模与分析,提出了实现六轴加速度检测的控制方案。给出了静电悬浮回路的仿真结果,评估了六轴加速度计的性能。     

静电伺服微加速度计的量程设计

详细推导了静电伺服加速度计在定极板上施加直流偏压、交流驱动电压，动极板上有反馈直流电压和交流检测电压的情况下，检测质量(动极板)受到的静电力。通过对静电力的分析，得出静电伺服彻。速度计的量程除了受系统能提供的最大静电力限制外，还需满足电刚度小于与机械刚度的条件，该电刚度是极板上所有的直流电压、交流电压产生的电刚度之和。离心实验证明，利用该原则设计的“叉指”结构静电伺服微加速度计的量程达到了设计值。该设计原则可以为此类加速度计的设计提供参考。     

静电负刚度调谐加速度计的力平衡闭环检测控制方法

静电负刚度调谐加速度计(EFMA)在设计原理上具有兼顾电容式加速度计和谐振式加速度计相关优点的潜力.然而由于静电刚度对应的极板位移具有明显的非线性效应,使得EFMA在大量程应用中标度因数非线性较差,成为了当前制约EFMA量程提升的重要因素.基于EFMA频率输出的特点,推导了力平衡控制量并开展了力平衡控制环路的设计与研究...     

基于静电悬浮的零刚度隔振减振控制方法

基于静电悬浮的双级无拖曳天基超静平台是一种新型的隔振减振平台,但由于静电负刚度的耦合效应,会残留微振动传递路径,从而难以达到理想的隔振效果。首先,建立了基于静电悬浮的双级无拖曳天基超静平台的系统模型,分析了静电负刚度的产生机制。然后,提出基于反馈电压反函数调制、非对称调制的两种绝对零刚度构造方法,并将其与基于刚度并联的准零刚度构造方法进行了比较。接着,给出了基于反馈电压调制的绝对零刚度隔振控制与主动减振控制的一体化兼容设计流程。最后,基于Matlab/Simulink建立了系统仿真模型,对所提方法进行了隔振性能和鲁棒性方面的仿真实验。实验结果表明,基于反馈电压调制的绝对零刚度隔振方法能完全隔绝卫星微振动对载荷平台的扰动;在系统参数误差达10%的条件下,所提方法仍可获得比无刚度补偿系统优1～2个量级的隔振性能。     

分数阶拟周期Mathieu方程的动力学分析

分数阶微积分有着诸多优异的特点, 目前在动力学领域主要用来提高非线性系统振动特性研究的准确性. 本文在拟周期Mathieu方程的基础上, 引入分数阶微积分理论, 研究了分数阶微分项参数对方程稳定性的影响. 首先, 采用摄动法得到方程稳定区和非稳定区分界线(即过渡曲线)近似表达式, 利用数值方法验证了解析结果的准确性, 图像显示两者吻合较好. 随后, 通过归纳总结不同情况下的过渡曲线近似表达式, 发现在系统中分数阶微分项以等效线性刚度和等效线性阻尼的方式存在. 根据这一特点, 得到了系统等效线性阻尼和等效线性刚度的一般形式, 并且定义了非稳定区域厚度. 最后, 通过数值仿真直观地分析了分数阶微分项参数对方程稳定区域大小和过渡曲线位置的影响. 结果发现, 分数阶微分项不仅具有阻尼特性还具有刚度特性, 并且以等效线性刚度和等效线性阻尼的方式影响着方程稳定区域大小和过渡曲线位置. 合理选择分数阶微分项参数可以使其呈现不同程度的刚度特性或阻尼特性, 方程稳定区域的大小和过渡曲线的位置也因此产生了不同程度的变化.      

Electrogas- and electrohydrodynamic control of gas and liquid jets and flows

The physical and mathematical principles of the method of electrogas-and electrohydrodynamic conversion of electrical signals to pneumatic (hydraulic) signals and vice versa for control of gas and liquid jets and flows in electropneumohydraulic systems are considered. St. Petersburg State Technical University, St. Petersburg 195251. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 41, No. 2, pp. 25–31, March–April, 2000.     

Fatigue and static strength of notched and unnotched aluminum-alloy and steel specimens

This paper describes a method of presentation of fatigue data on three commonly used aircraft materials, 2024-T3 and 7075-T6 aluminum alloys and normalized SAE 4130 steel, such that variations in fatigue strength with stress-concentration factor can be shown. Comparisons of the fatigue strengths of 2024-T3 and 7075-T6 aluminum are made for the most useful range of stress-concentration factors. Static-strength results of notched and unnotched specimens of the three materials are presented to show how the strength varies with some parameters of the stress concentration. Comparison of the data with one theory for the strength of cracked specimens was made.     

STICTION AND ANTI—STICTION IN MEMS AND NEMS

Stiction in microelectromechanical systems (MEMS) has been a major failure mode ever since the advent of surface micromachining in the 80s of the last century due to large surfacearea-to-volume ratio. Even now when solutions to this problem are emerging, such as self-assembled monolayer (SAM) and other measures, stiction remains one of the most catastrophic failure modes in MEMS. A review is presented in this paper on stiction and anti-stiction in MEMS and nanoelectromechanical systems (NEMS). First, some new experimental observations of stiction in radio frequency (RF) MEMS switch and micromachined accelerometers are presented. Second, some criteria for stiction of microstructures in MEMS and NEMS due to surface forces (such as capillary, electrostatic, van der Waals, Casimir forces, etc.) are reviewed. The influence of surface roughness and environmental conditions (relative humidity and temperature) on stiction are also discussed. As hydrophobic films, the self-assembled monolayers (SAMs) turn out able to prevent release-related stiction effectively. The anti-stiction of SAMs in MEMS is reviewed in the last part. The project supported by the Distinguished Young Scholar Fund of NSFC (10225209), key project from the Chinese Academy of Sciences (KJCX2-SW-L2) and National “973” Project (G1999033103)     

水和水蒸汽热力学物性参数及导数的计算与应用

本文针对现代换热设备设计、两相流动与传热研究的需要,介绍了可供科研使用的水和水蒸汽物性计算方法,完善了计算程序。根据超临界锅炉设计中的超临界水的物性计算,两相流研究和换热设备动态特性研究中对物性导数计算的需要,提供了两个算例,并进行了定性分析。     

Legal and policy issues in genetics and insurance

Genetic screening and testing techniques provide a powerful diagnostic tool for the acquisition of predictive information. The potential value of such diagnostic techniques cannot be overstated. However, commercial organisations such as insurance companies and employers are also highly interested in the acquisition and use of genetic information. Concerns about the potential abuse of genetic information have stimulated a counter-current of public pressure for restrictions on the use which can be made of genetic diagnostic information. In a number of countries this pressure has generated enough concern to stimulate legislatures to enact laws which curtail the use and acquisition of genetic information. This pattern has clearly emerged in the United States of America and there are indications that similar trends are developing in Europe. This paper examines the law and policy issues arising from the interface between genetics and insurance.     

Microcanonical Entropy and Mesoscale Dislocation Mechanics and Plasticity

A methodology is devised to utilize the statistical mechanical entropy of an isolated, constrained atomistic system to define constitutive response functions for the dissipative driving-force and energetic fields in continuum thermomechanics. A thermodynamic model of dislocation mechanics is discussed as an example. Primary outcomes are constitutive relations for the back-stress tensor and the Cauchy stress tensor in terms of the elastic distortion, mass density, polar dislocation density, and the scalar statistical density.     

Sound and vorticity interactions: transmission and scattering

We review several aspects of the propagation of sound in vortical flows. We restrict ourselves to isothermal, humidity-free flows at low Mach number M. Since vorticity plays a major role in vortex-flow interactions we focus on vortical flows. We consider two main canonical situations. The first concerns the transmission of sound. We analyze the evolution of acoustic wavefronts as they propagate across a single vortex. The second situation addresses the scattering of sound waves by nonstationary vortices. We study the evolution of the acoustic pressure emitted in the far field, at an angle with the initial direction of propagation. In this geometry one performs direct spectroscopy of the flow vorticity field. In each case, we review theoretical results and compare with experimental measurements and numerical simulations when available. We also briefly report how the following new acoustic techniques have recently been used to study complex or turbulent flows: time-resolved acoustic spectroscopy, speckle interferometry and Lagrangian particle tracking. PACS 43.25, 43.28, 47.32, 67.40