基于MATLAB的GPS软件接收机捕获与跟踪算法实现

研究了GPS软件接收机的捕获和跟踪算法,并基于Matlab软件平台和射频前端在PC上实现了GPS软件接收机样机。介绍了GPS软件接收机的结构和数据采集硬件,讨论了GPSC/A码的特性、产生原理以及捕获过程。针对传统的串行搜索算法慢的缺点以及高动态GPS软件接收机的特点,在该样机中实现了快速的基于循环卷积的并行捕获算法,并联合使用超前滞后环和对相位反转不敏感的科斯塔斯锁相环分别对码相位和多普勒频偏进行跟踪,解调得到导航电文。仿真和测试结果表明,使用GPS软件接收机进行信号处理的思想使用户在算法处理和软件升级等方面具有更大的灵活性,可应用于下一代任何全球导航卫星定位系统(GNSS)和空基增强系统(SBAS)接收机的设计。     

Efficient computation for dynamic responses of systems with time-varying characteristics

Based on Neumman series and epsilon-algorithm, an efficient computation for dynamic responses of systems with arbitrary time-varying characteristics is investigated. Avoiding the calculation for the inverses of the equivalent stiffness matrices in each time step, the computation effort of the proposed method is reduced compared with the full analysis of Newmark method. The validity and applications of the proposed method are illustrated by a 4-DOF spring-mass system with periodical time-varying stiffness properties and a truss structure with arbitrary time-varying lumped mass. It shows that good approximate results can be obtained by the proposed method compared with the responses obtained by the full analysis of Newmark method.     

An embedded boundary framework for compressible turbulent flow and fluid–structure computations on structured and unstructured grids

The finite volume method with exact two‐phase Riemann problems (FIVER) is a two‐faceted computational method for compressible multi‐material (fluid–fluid, fluid–structure, and multi‐fluid–structure) problems characterized by large density jumps, and/or highly nonlinear structural motions and deformations. For compressible multi‐phase flow problems, FIVER is a Godunov‐type discretization scheme characterized by the construction and solution at the material interfaces of local, exact, two‐phase Riemann problems. For compressible fluid–structure interaction (FSI) problems, it is an embedded boundary method for computational fluid dynamics (CFD) capable of handling large structural deformations and topological changes. Originally developed for inviscid multi‐material computations on nonbody‐fitted structured and unstructured grids, FIVER is extended in this paper to laminar and turbulent viscous flow and FSI problems. To this effect, it is equipped with carefully designed extrapolation schemes for populating the ghost fluid values needed for the construction, in the vicinity of the fluid–structure interface, of second‐order spatial approximations of the viscous fluxes and source terms associated with Reynolds averaged Navier–Stokes (RANS)‐based turbulence models and large eddy simulation (LES). Two support algorithms, which pertain to the application of any embedded boundary method for CFD to the robust, accurate, and fast solution of FSI problems, are also presented in this paper. The first one focuses on the fast computation of the time‐dependent distance to the wall because it is required by many RANS‐based turbulence models. The second algorithm addresses the robust and accurate computation of the flow‐induced forces and moments on embedded discrete surfaces, and their finite element representations when these surfaces are flexible. Equipped with these two auxiliary algorithms, the extension of FIVER to viscous flow and FSI problems is first verified with the LES of a turbulent flow past an immobile prolate spheroid, and the computation of a series of unsteady laminar flows past two counter‐rotating cylinders. Then, its potential for the solution of complex, turbulent, and flexible FSI problems is also demonstrated with the simulation, using the Spalart–Allmaras turbulence model, of the vertical tail buffeting of an F/A‐18 aircraft configuration and the comparison of the obtained numerical results with flight test data. Copyright © 2014 John Wiley & Sons, Ltd.     

新型纳米结构金属材料的力学性能及变形机制

“纳米结构” 化是金属及其合金材料获得优异力学性能的有效途径.纳米结构金属材料表面或内部的缺陷, 包括晶界、位错、孪晶、孔洞、裂纹、第二相等, 其形核、演化及互相作用对材料的强度和韧性具有重要影响. 该文综述了与上述科学问题相关的新型纳米结构金属材料的微观组织结构表征及力学性能测试、强韧化机制计算模拟方面的研究进展. 并讨论了急需从微观尺度上就新型纳米结构金属材料的特征力学行为和关键变形机制开展深入、系统研究.      

贝雷砂岩射孔孔道流动效应正交计算分析

对射孔孔道流动效应进行了量纲分析,建立了轴向和径向流量与影响流量因素间的工程表达式。综合考虑影响流动效应的主要因素和取值范围,设计了数值模拟计算工况的正交计算方案,并利用ANSYS/FLOTRAN流体程序进行了带损伤区贝雷砂岩流量数值模拟研究,获得了各个计算方案的径向流量和轴向流量,用以确定出流量公式的系数。最终确定的流量公式表明,各要素对流量影响的重要顺序依次为固有渗透率、损害区厚度、孔深、渗透率剩余百分数和孔径。     

液体火箭发动机健康诊断系统设计与实现

设计和实现了液体火箭发动机健康诊断系统,基于两种现役液体火箭发动机3种类型的20余次地面热试车数据,提取了200个特征参数,初步确定了针对不同健康状态的权重向量,建立了基于案例和基于规则的综合诊断,生成健康诊断报告.系统现已投入某型液体火箭发动机的科研与生产,为火箭发动机的校准试车后不分解交付提供依据.     

基于2D开源视频分析和建模软件Tracker研究抛体运动实验

以抛体运动实验的视频分析为例,具体介绍如何使用开源视频分析和建模软件Tracker对抛体运动实验进行分析,期望能在国内物理教学中,推广使用这类低成本的开源软件,激发学生探索隐藏在物理实验背后的物理规律的兴趣,扩展分析物理实验的手段.     

机、电、微机控制一体化

通过平面电机绘图机系统的设计,描述了机、电、微机控制技术一体化的优越性。一个重要的优点是机械、电气技术的结合将会大大地简化平面电机绘图系统的结构和制造工艺,因而降低了成本。另一个重要优点是微机控制技术将会大大地扩大机电产品的功能。最后结论:机、电、微机控制技术一体化是机电产品今后的发展趋势。     

保护私有信息的一般线性方程组计算协议

作为科学计算的一个重要问题,保护私有信息的线性方程组的求解在金融、机械及通信等领域有着广泛的应用.在不经意传输的意义下,利用有限域上计算Moore-Penrose伪逆矩阵的概率算法,设计新的安全协议,解决了隐私保护的一般线性方程组在有限域上的安全两方计算问题,并利用模拟范例证明该协议在半诚实模型下是安全的.     

Variational Bayes With Intractable Likelihood

Variational Bayes (VB) is rapidly becoming a popular tool for Bayesian inference in statistical modeling. However, the existing VB algorithms are restricted to cases where the likelihood is tractable, which precludes their use in many interesting situations such as in state--space models and in approximate Bayesian computation (ABC), where application of VB methods was previously impossible. This article extends the scope of application of VB to cases where the likelihood is intractable, but can be estimated unbiasedly. The proposed VB method therefore makes it possible to carry out Bayesian inference in many statistical applications, including state--space models and ABC. The method is generic in the sense that it can be applied to almost all statistical models without requiring too much model-based derivation, which is a drawback of many existing VB algorithms. We also show how the proposed method can be used to obtain highly accurate VB approximations of marginal posterior distributions. Supplementary material for this article is available online.