激光陀螺组合体自主测量船体角变形的最优估计法

根据激光陀螺组合体测量的角增量计算得到的惯性姿态匹配测量方程,结合动态变形模型和静态变形模型,构建了船体角变形测量的最优滤波器,实现了角变形的最优估计。该方法将角变形和激光陀螺的随机漂移误差近似为平稳随机过程并分别构建滤波器,静态变形建模为白噪声驱动的一阶随机游走过程,动态变形建模为二阶马尔可夫平稳随机过程。通过角速度匹配测量方程进行了角变形的观测性分析得知:动态变形的估计精度与激光陀螺的测量精度相当,静态变形的估计精度依赖于船体摇摆频率和幅度,因此最优估计法的误差主要为静态角变形模型的估计误差。仿真结果表明,通过设置合适的静态角变形模型参数,该最优估计法测量角变形的误差小于10"。     

机抖激光陀螺动力学特性研究

在构建激光陀螺捷联系统时,三个激光陀螺安装在同一个基座上.由于三个陀螺振子都在进行高频角振动,激励基座产生耦合振动,造成陀螺是在振动基座环境下工作,引起激光捷联系统的抖动耦合误差,导致系统导航精度下降.采用有限元方法研究了机抖激光陀螺的动力学特性和振动模态,以及机抖激光陀螺的振子抖动对基座的影响和外界激励条件下陀螺的响应.通过压电陶瓷激励下陀螺的频率响应分析,实现了激光陀螺工作状态下的动力学仿真,可以获得陀螺工作时激光陀螺任意位置的动力学响应信息,从而为激光陀螺和基座的结构设计提供评判依据,也为分析激光捷联系统的抖动耦合误差开辟了新途径.     

基于姿态匹配的船体形变测量方法

针对激光陀螺船体形变测量系统,提出了一种新的基于姿态匹配的形变测量解算方法。该方法不同于以角速度差作为观测量的惯性测量匹配法,而是基于两套激光陀螺系统的姿态信息。确立了新的形变测量滤波观测量,并建立线性量测方程。两套激光陀螺系统直接利用激光陀螺输出的角增量数据相对于惯性空间进行姿态更新,惯性坐标系取为各自初始时刻的载体坐标系,完全回避了系统初始对准问题,且充分利用了激光陀螺角度测量精度高的特点。仿真结果表明,该方法能够有效实现船体形变的高频精确测量,仿真测量精度优于15″,为激光陀螺船体形变测量技术进入工程应用打下了基础。     

速率偏频激光陀螺标定方法讨论

三轴整体式速率偏频激光陀螺由于总是绕其对称轴做等速率的正负旋转运动,通过传统的位置法和旋转法无法对用其构成的捷联式惯导系统进行标定。中讨论了速率偏频激光陀螺在系统中的精确标定方法,指出该方法需要特殊的转台设备,目前尚无法满足,因此提出了一种结合光学方法测量陀螺安装误差角。这种方法利用速率偏频转台自身的旋转角速率对陀螺刻度系数和常值漂移进行简易标定的方法,实验表明该方法可满足系统导航要求。     

激光陀螺POS惯性数据滤波及时延补偿

激光陀螺作为位置姿态测量系统(POS)的核心传感器,其精度直接决定激光陀螺POS系统精度,围绕机抖激光陀螺信号去噪的需求,基于FIR滤波器建模的方法,设计了FIR数字低通滤波器;针对滤波器导致的信号延迟问题,根据FIR数字滤波器群延迟特性建模,提出了激光陀螺POS数据时延补偿方法。静态实验结果表明,设计的FIR数字低通滤波器降低了激光陀螺抖动噪声功率达80dB。进一步通过飞行实验表明,提出的方法降低了激光陀螺POS系统姿态角误差,与POS/AV510相比航向角误差由0.017°降低到0.01°,俯仰角误差由0.007°降低到0.005°,横滚角误差由0.016°降低到0.005°,满足了机载InSAR对激光陀螺POS精度要求。     

基于激光陀螺自适应补偿的船体变形测量方法

基于长期变形、动态挠曲变形以及陀螺随机零偏的状态方程,构建了激光陀螺测量的惯性姿态匹配最优滤波器,可以实时地估计出船体变形角。针对实时估计的长期变形角具有偏置误差的问题,推导了惯性姿态匹配的误差方程,指出动态挠曲变形角与船体惯性姿态角之间具有长时间的交叉相关耦合作用导致了长期变形角估计具有偏置误差,并提出了对输入到最优滤波器的激光陀螺角增量进行自适应补偿的方法来抑制偏置误差。实验结果表明,补偿后俯仰角、横滚角和艏挠角的偏置误差均方根均小于5″,较补偿前降低均方根误差约为5″,该自适应补偿方法可有效地抑制偏置误差,提高惯性姿态匹配方法在船体变形测量应用中的有效性。     

船体变形测量中激光陀螺误差的抑制机理

针对激光陀螺测量误差对船体自主变形测量精度的影响问题,在角速度匹配方程基础上提出了一种信号同步积分求解变形角的方法。根据船体角运动的周期特性,利用实测船体运动角速度信号产生时序同步信号,并与角速度匹配方程相乘得到新的测量方程,使得包含变形角信息的有用信号通过积分得到增强,而陀螺误差则被调制为随机信号,积分后被抑制,从而提高了测量方程的信噪比。仿真结果表明:当积分时间大于5 min时,变形角测量误差的均方根值(RMS)小于10",且随着积分时间的增加,测量精度将会提高。这种同步积分方法不需要对陀螺误差建模即可实现对船体变形的高精度测量,而且直观地解释了在激光陀螺误差存在条件下自主变形测量误差不随时间发散的原因。     

激光捷联系统中的优化圆锥误差补偿算法

激光捷联系统中采用低通滤波器消除激光陀螺角增量输出中机械抖动引入的干扰信号,同时也对陀螺敏感的外界惯性输入角速度信号进行了频率整形,产生了视在圆锥误差,此时传统圆锥补偿算法未考虑滤波器影响补偿精度严重降低.针对本系统采用了31阶低通滤波器对陀螺的角增量输出整形,分析了其引入的视在圆锥误差,基于滤波器的频率特性,采用五子样圆锥误差补偿算法,即在旋转矢量更新周期内有五个陀螺采样信号,可以构成四种不同时间间隔的陀螺输出角增量信号的叉积,利用这些叉积的线性组合更新旋转矢量.仿真结果表明,对经过滤波器整形的陀螺输出角增量进行补偿,优化的圆锥补偿算法的补偿精度明显优于传统圆锥补偿算法,使系统姿态角的精度提高了两个数量级.     

非共面四频激光陀螺变温零偏周期性波动

非共面四频激光陀螺的零偏随温度周期变化直接影响陀螺性能,提出了一种采用对法拉第旋光元件参数优化有效降低零偏波动幅值的方法。根据非共面四频激光陀螺的振荡光束频率特性,结合腔内旋光元件表面反射光束和散射光束的耦合效应以及旋光元件磁光效应,理论分析确定了导致陀螺变温零偏周期性波动的主要因素。采用对旋光元件楔角、微扰角度以及方位角三项参数的理论计算及仿真分析,确定了参数优化方法和优化验证参数,经验证与理论分析结果一致,有效消除了陀螺变温零偏周期性波动,结合温度补偿模型,实现70°C变温范围内零偏最大变化由1.5(°)/h降低为0.11(°)/h。     

激光陀螺的光强稳定控制

针对国内稳流激光电源与激光陀螺理论要求不符这一问题,对激光陀螺光强稳定控制的理论、意义、难点及实现等各个方面的问题进行详细的讨论,提出抑制三种控制之间耦合效应的解决方案,根据所提方案设计完成基于TMS320F2812的激光陀螺三稳定全数字一体化电路系统,在国内首次实现激光陀螺光强稳定电源。最后用设计的电路系统对某型四频激光陀螺进行了各种实验。结果表明:电路系统在抑制三种稳定控制之间耦合效应方面是有效的、实用的;同时有效抑制了稳流电源下某型四频激光陀螺在高低温实验中零漂的剧烈振荡。理论和实验均证实稳流电源是不符合原理要求的,国内从激光陀螺开始研制至今仍然采用的稳流电源应该更换为光强稳定控制电源。     

Discrete and Continuous Random Walk Models for Space-Time Fractional Diffusion

A mathematical approach to anomalous diffusion may be based on generalized diffusion equations (containing derivatives of fractional order in space or/and time) and related random walk models. A more general approach is however provided by the integral equation for the so-called continuous time random walk (CTRW), which can be understood as a random walk subordinated to a renewal process. We show how this integral equation reduces to our fractional diffusion equations by a properly scaled passage to the limit of compressed waiting times and jumps. The essential assumption is that the probabilities for waiting times and jumps behave asymptotically like powers with negative exponents related to the orders of the fractional derivatives. Illustrating examples are given, numerical results and plots of simulations are displayed.     

Discrete and Continuous Random Walk Models for Space-Time Fractional Diffusion

A mathematical approach to anomalous diffusion may be based on generalized diffusion equations (containing derivatives of fractional order in space or/and time) and related random walk models. A more general approach is however provided by the integral equation for the so-called continuous time random walk (CTRW), which can be understood as a random walk subordinated to a renewal process. We show how this integral equation reduces to our fractional diffusion equations by a properly scaled passage to the limit of compressed waiting times and jumps. The essential assumption is that the probabilities for waiting times and jumps behave asymptotically like powers with negative exponents related to the orders of the fractional derivatives. Illustrating examples are given, numerical results and plots of simulations are displayed.     

海冰动力学数值模拟中改进的PIC方法

为了准确地模拟海冰的动力过程,需要建立精确有效的数值方法。本文结合质点网格法(PIC)和光滑质点流体动力学方法(SPH)发展了一种改进的PIC方法。该方法在欧拉坐标下对海冰动量方程进行差分计算,在拉格朗日坐标下进行海冰质点位移、厚度和密集度计算,并采用Gauss函数进行欧拉网格点与拉格朗日质点间海冰参数的交互插值。采用改进的PIC方法对规则区域内的海冰堆积过程进行了数值试验,对渤海海冰的动力过程进行了72小时数值模拟。计算结果均表明改进的PIC方法具有计算量小,计算结果平稳精确的优点,可很好地适用于海冰动力作用过程的数值模拟。     

Numerical analysis of effective elastic properties of geomaterials containing voids using 3D random fields and finite elements

The purpose of the study is to investigate the influence of porosity and void size on effective elastic geotechnical engineering properties with a 3D model of random fields and finite element. The random field theory is used to generate models of geomaterials containing spatially random voids with controlled porosity and void size. A “tied freedom” analysis is developed to evaluate the effective Young’s modulus and Poisson’s ratio in an ideal block material of finite elements. To deliver a mean and standard deviation of the elastic parameters, this approach uses Monte-Carlo simulations and finite elements, where each simulation leads to an effective value of the property under investigation. The results are extended to investigate an influence of representative volume element (RVE). A comparison of the effective elastic stiffness of 2D and 3D models is also discussed.     

Stress concentration factors of periodic notches determined from the strain energy density

Stress concentration factors (SCFs) of a number of flat plates and round bars with periodic U- and V-notches are evaluated. Tension, bending and torsion loadings are considered in the investigation. The main objective of the investigation is to take advantage of the local strain energy density (SED) averaged on a control volume surrounding the tip of the middle notch and to estimate the SCF of each component by using a relatively coarse mesh. The unique advantage of SED method is the most prominent application of such a technique in the current study. Systematic FE simulations by considering a wide range of notch acuity and relative frequency of periodic U- and V-notch components are performed. More than two hundred and fifty models have been examined. The results of this study are compared with those provided by other researchers in the past and recent literature. Two new expressions of the notch depth reduction factor for the case of normal stresses (tension and bending) and torsion are also proposed to match the results from SED approach.     

Unified proof to oscillation property of discrete beam

The oscillation property （OP） is a fundamental and important qualitative property for the vibrations of single span one-dimensional continuums such as strings, bars, torsion bars, and Euler beams. Any properly discretized continuum model should keep the OP. In literatures, the OP of discrete beam models is discussed essentially by means of matrix factorization. The discussion is model-specific and boundary-condition- specific. Besides, matrix factorization is difficult in handling finite element （FE） models of beams. In this paper, according to a sufficient condition for the OP, a new approach to discuss the property is proposed. The local criteria on discrete displacements rather than global matrix factorizations are given to verify the OP. Based on the proposed approach, known results such as the OP for the 2-node FE beams via the Heilinger- Reissener principle （HR-FE beams） as well as the 5-point finite difference （FD） beams are verified. New results on the OP for the 2-node PE-FE beams and the FE Timoshenko beams with small slenderness are given. Through a simple manipulation, the qualitative property of discrete multibearing beams can also be discussed by the proposed approach.     

Micromechanical analysis of kinematic hardening in natural clay

This paper presents a micromechanical analysis of the macroscopic behaviour of natural clay. A microstructural stress–strain model for clayey material has been developed which considers clay as a collection of clusters. The deformation of a representative volume of the material is generated by mobilizing and compressing all the clusters along their contact planes. Numerical simulations of multistage drained triaxial stress paths on Otaniemi clay have been performed and compared the numerical results to the experimental ones in order to validate the modelling approach. Then, the numerical results obtained at the microscopic level were analysed in order to explain the induced anisotropy observed in the clay behaviour at the macroscopic level. The evolution of the state variables at each contact plane during loading can explain the changes in shape and position in the stress space of the yield surface at the macroscopic level, as well as the rotation of the axes of anisotropy of the material.     

Jacobian-free Newton-Krylov subspace method with wavelet-based preconditioner for analysis of transient elastohydrodynamic lubrication problems with surface asperities

This paper presents an investigation into the effect of surface asperities on the over-rolling of bearing surfaces in transient elastohydrodynamic lubrication(EHL) line contact. The governing equations are discretized by the finite difference method. The resulting nonlinear system of algebraic equations is solved by the Jacobian-free Newtongeneralized minimal residual(GMRES) from the Krylov subspace method(KSM). The acceleration of the GMRES iteration is accomplished by a wavelet-based preconditioner.The profiles of the lubricant pressure and film thickness are obtained at each time step when the indented surface moves through the contact region. The prediction of pressure as a function of time provides an insight into the understanding of fatigue life of bearings.The analysis confirms the need for the time-dependent approach of EHL problems with surface asperities. This method requires less storage and yields an accurate solution with much coarser grids. It is stable, efficient, allows a larger time step, and covers a wide range of parameters of interest.     

旋转圆管湍流的大涡模拟数值研究

采用大涡模拟（LES）方法,并结合动力学亚格子尺度应力（SGS）模型,通过数值求解柱坐标系下的滤波Navier-Stokes方程,研究了绕管轴旋转圆管内的湍流流动特性.为验证计算的可靠性,以及动力学SGS模型对于旋转湍流的适用性,将大涡模拟计算所得的结果,与相应的直接模拟（DNS）结果和实验数据进行了对比验证,吻合良好.进一步对旋转圆管湍流的物理机理进行了探讨,研究了湍流特性随旋转速率的变化规律.当旋转速率增加时,湍流流动有层流化的发展趋势.基于湍动能变化的关系,分析了旋转效应对湍流脉动生成的抑制作用.     

用于先进半导体制程的光刻反向计算技术(ILT)

此篇论文将介绍一个用于半导体光罩上图样设计以及可用于实际生产的光刻反向计算技术（ILT）。在论文中将讨论有关ILT的最新发展，包括在超成像极限协助图样（SRAF）的生成，可增加制程宽容度的ILT，以及如何生成满足光罩生产标准的图样等方面。从内部的研究结果和客户的使用结果可以看出，ILT已经不再只是一种用于研究的工具，而是已经可以用于先进半导体制程的大规模生产。在对各个环节优化之后，ILT可以增加制程的宽容度，同时将光罩的成本控制在可以接受的水平。