基于自适应参数估计的三轴磁传感器实时校正方法

针对传统基于椭球模型三轴磁传感器无法实时校正的问题,设计了基于自适应参数估计的三轴磁传感器实时校正方法,通过对参数的实时估计与处理,实现了三轴磁传感器误差的校正。首先,对三轴磁传感器全误差模型进行分析与处理,建立了基于模值的参数估计方程;其次,详细分析了参数模型的噪声特性,针对非高斯状态相关噪声,提出了采用自适应参数估计方法;最后,设计仿真与实验分析,完成三轴磁传感器误差校正。实验结果表明,所提出的算法可以实现误差参数的实时校正,提升了磁传感器误差校正的自主性。同时,基于自适应参数估计方法,使得校正结果模值标准差相较于传统方法减小了3倍。     

基于椭球拟合的磁梯度张量系统集成校正

为了提高磁梯度张量系统测量精度,针对磁传感器轴位偏差、标度因子与非正交性,传感器阵列间非对准误差以及载体磁干扰等误差因素,提出了基于椭球拟合的磁梯度张量系统集成校正方法。根据硬、软磁材料磁场数学模型,将磁传感器系统误差和硬、软磁干扰误差构建为集成误差系数矩阵和集成零漂向量两部分,基于最小二乘椭球拟合建立了集成补偿模型以此校正传感器输出。通过正交系间旋转矩阵构建非对准参数的线性方程组并得到最小二乘估计,以此对准张量系统。研究结果表明:仿真校正后传感器总磁场强度(TMI)和系统张量分量有效收敛于预设测量噪声;实验校正后各传感器输出具有较高重合与同轴性,总磁场强度均方根误差(RMSE)降至约5nT,张量分量均方根误差限制在20nT/m内。该方法能够稳定可靠地提高磁梯度张量系统测量精度。     

不受姿态误差影响的惯性/磁感应融合定位方法

针对传统电磁信标导航定位系统中由惯性元件解算磁传感器姿态误差导致定位性能下降问题,提出了一种不受传感器姿态影响的改进惯性/磁感应定位融合定位方法,避免了姿态误差对定位结果的影响。首先,基于磁信标磁场分布规律与特征矢量构建了与传感器姿态无关的非线性磁感应定位模型;然后,结合惯性元件对载体目标的状态估计提出了改进的惯性/磁感应定位模型,降低了累计误差、提高了定位精度与结果的输出速度;最后,利用无迹卡尔曼滤波（UKF）对融合数据进行处理,实现对动态目标的位置估计。分别通过实验和仿真验证了不受姿态影响的磁感应定位模型以及惯性/磁感应定位方法的有效性。实验结果表明磁感应定位模型能够不受传感器姿态误差的影响实现定位;数值仿真结果表明惯性元件解算姿态辅助磁信标定位方法的最大误差为7.29 m,基于改进的惯性/磁感应融合定位方法最大误差0.77 m。     

姿态检测地磁传感器误差分析与补偿方法

针对磁环境下的地磁传感器测量精度不足的问题,为了补偿地磁传感器存在的各种误差,在分析地磁传感器的自身误差和环境干扰误差的基础上,建立了地磁传感器误差校正模型,利用最大似然估计法将误差校正模型转化成多项式最小二乘拟合的基本方程形式,提出了基于QR因子分解法的补偿系数快速解算方法。分别求取仿真误差模型和实验误差模型的补偿系数,然后对地磁场矢量进行校正。结果表明,校正后的磁场强度和实际磁场强度基本一致,滚转角精度提高了近5倍,能够满足相关需求。     

多传感器融合技术在低成本车辆组合导航定位系统中的应用

采用多传感器信息融合技术，运用位置/航向的输出校正和元件参数误差的补偿校正的方法，利用一阶马尔可夫模型建立了传感器参数的误差模型，提出了基于集中卡尔曼滤波的GPS/INU车辆组合导航算法。仿真结果表明上述方法是行之有效的。     

基于微小型传感器的惯性/卫星/天文组合导航方法

为了实现基于微小型传感器的高精度导航,针对微小型导航传感器精度相对较低、误差相对较大的特点,对微小型惯性测量单元(MIMU)、微GPS卫星接收机、微小型星敏感器的测量误差进行了建模与分析;对多传感器的导航信息进行分散化处理,采用卡尔曼滤波进行局部估计;提出了基于部分信息融合的联邦滤波算法进行全局融合;并给出了利用全局融合结果对MIMU导航误差进行输出校正的算法.仿真结果表明,该组合导航方法能够利用微小型传感器实现较高精度的导航定位.     

基于非线性最小二乘估计的eLoran/INS/磁传感器组合导航方法

为实现不依赖GNSS系统的高精度导航系统,提出了一种基于非线性最小二乘估计的e Loran/INS/磁传感器组合导航方法。利用INS/磁传感器等传感器稳定性好,高频噪声低的特点,降低eLoran导航系统受传播路径影响导致的定位误差;同时所提方法可以校准其它传感器的零点偏移。首先利用INS系统估计载体当前的状态(包括姿态、位置),再通过高斯-牛顿法,求解载体状态的最小二乘解,从而使各物理量(磁场矢量、重力矢量和位置)在当前估计的载体坐标系内计算的数值与传感器的测量结果之间误差达到最小。最后,利用传感器的零点偏移在误差项中变化缓慢的特点,通过低通滤波估计零点偏移并进行校准。所提方法具有运算量小,解算精度高的特点。仿真试验结果显示所提出方法可将罗兰导航系统定位误差从100 m提高至6.1 m(2σ),证明了该系统具备独立于GNSS系统提供高精度导航定位的潜力。     

基于光学自准直技术的导航系统姿态输入输出方法

基于光学陀螺的单轴旋转式捷联惯性通常采用角度传感器来实现方位角的输出,但其测量结果受角度传感器自身精度、回转轴系、橡胶减震器及防冲击减震器的影响较大。为提高姿态传递精度,提出一种基于自准直仪和多面镜的光学传递方案,通过光学方法将输出平面与惯组直接建立关系,从而减少中间环节,消除角度传感器误差对系统方位角输出带来的误差,可有效避免传统测量中各种因素的影响。通过模拟试验该方案三个姿态角的传递精度均可达到5″以内,满足惯性系统的高精度姿态传递需要。     

基于姿态角估计的四旋翼飞行器多传感器故障诊断方法

针对无法直接测量得到姿态角的四旋翼飞行器多传感器偏差故障检测与诊断问题,提出一种基于姿态角估计的多传感器故障同时发生的故障检测与隔离以及故障偏差值估计的方法。首先,在考虑模型误差的前提下,建立四旋翼飞行器动力学模型和传感器模型,构建四旋翼飞行器故障检测与诊断系统。其次,在利用基于滑模观测器得到姿态角估计值的基础上,设计非线性故障观测器对故障进行检测与隔离。最后,构建非线性自适应观测器实现未知故障偏差值的估计,并证明自适应律的稳定性和参数收敛性。实验结果表明,该方法能实现多传感器偏差故障检测与隔离,并在5 s之内实现对传感器多故障偏差的估计与跟踪,且估计误差有界,该方法有效性得以验证。     

基于压力传感器辅助的行人室内定位零速修正方法

针对现有行人室内定位导航系统定位精度差的问题,设计了一种压力传感器辅助微惯性测量单元的多条件约束零速修正方法。将微惯性测量单元和压力传感器固连在鞋上,用来测量人体脚部运动信息。在经典捷联解算基础上通过对行走时微惯性测量单元和压力传感器的统计特性进行分析,对加速度模值、滑动方差、角速度模值、足底压力设定阈值,用以检测行走过程中的零速区间,通过基于零速修正的卡尔曼滤波估计姿态误差、速度误差和位置误差,反馈校正后对微惯性测量单元的累积误差进行修正。最后通过对比试验证明了压力传感器辅助下的零速修正方法提高了系统导航定位精度,步行和跑动时的水平定位精度优于1%D。     

自适应滤波方法在陀螺软故障检测中的应用

采用自适应滤波方法对影响故障检测及隔离(FDI)性能的传感器误差进行了补偿，同时提出了故障检测与隔离的自适应滤波方法(AET)。该方法可以对多个传感器同时出现故障的情况进行检测与隔离。中以六个陀螺冗余惯性导航系统的仿真结果验证了该算法的有效性。     

A joint encryption and error correction scheme based on chaos and LDPC

Although some cryptosystems based on error correction code have been presented, the security and efficiency must be overcome before it can be realized. In this paper, a novel method of combined encryption and error correction based on hyperchaotic system and lower-density parity check (LDPC) code is proposed to provide both of the security and efficiency. The proposed system adopts a pseudorandom sequence generator based on hyperchaotic system for scrambling the plaintext and constructing the dynamic permutation box. The message is encoded by the LDPC encoder after it was scrambled and then encrypted by the permutation box. Different permutation patterns generated for different message blocks help to provide high security, while the encoder helps to provide capacity of error correction. MATLAB simulations reveal that the proposed scheme is more secure and effective than the existing joint encryption and error correction coding scheme. Moreover, the full error correction ability of LDPC is kept without confliction. So, the proposed scheme is suitable for secure communication system.     

损伤识别一种改进的残余力向量法

提出了一种改进的残余力向量法用于工程结构损伤识别.分析了利用结构有限元模型缩聚技术给残余力向量法所造成的误差,提出了一种改进的残余力向量法.以平面桁架结构为算例,比较了改进方法与原方法的损伤识别结果.结果表明,改进的方法合理可靠、精度高.     

The method of dynamic mode decomposition in shallow water and a swirling flow problem

In this paper, a new vector‐filtering criterion for dynamic modes selection is proposed that is able to extract dynamically relevant flow features from dynamic mode decomposition of time‐resolved experimental or numerical data. We employ a novel modes selection criterion in parallel with the classic selection based on modes amplitudes, in order to analyze which of these procedures better highlight the coherent structures of the flow dynamics. Numerical tests are performed on two distinct problems. The efficiency of the proposed criterion is proved in retaining the most influential modes and reducing the size of the dynamic mode decomposition model. By applying the proposed filtering mode technique, the flow reconstruction error is shown to be significantly reduced. Copyright © 2016 John Wiley & Sons, Ltd.     

PIV速度场坏矢量的本征正交分解处理技术

介绍了一种针对粒子图像测速(PIV)基于本征正交分解(POD)的速度场后处理技术.该技术改变了现在后处理技术将速度场坏矢量识别和修正分开实现的局面,通过迭代方法有效地实现了速度场坏点统一的识别和修复算法.算法利用POD分解的低阶模态信息重构出可以用于坏矢量识别的参考速度场,利用该参考速度场对全流场进行坏点识别并完成修正.通过对一套光滑的PIV速度场数据引入高斯分布的随机误差,测试验证了该POD方法的优越性.在坏矢量识别方面新方法较归一化中值检验有更高的正确性,能识别大面积出现的坏矢量区域.在坏矢量修补的插值算法中,新方法的计算效率又高于传统Gappy POD方法,且计算精度优于常见的矢量场内插数学方法.特别是在数据缺失的大连通区域,该方法对物理流场有很好的预测效果.     

A new adaptive fuzzy sliding mode observer for a class of MIMO nonlinear systems

In this paper, a new adaptive fuzzy sliding mode (AFSM) observer is proposed which can be used for a class of MIMO nonlinear systems. In the proposed algorithm, the zero-input dynamics of the plant could be unknown. In this method, a fuzzy system is designed to estimate the nonlinear behavior of the observer. The output of fuzzy rules are tuned adaptively, based on the observer error. The output connection matrix is used to combine the observer errors of individual subsystems. A robust term, which is designed based on the sliding mode theory, is added to the observer to compensate the fuzzy estimation error. The estimation error bound is adjusted by an adaptive law. The main advantage of the proposed observer is that, unlike many of the previous works, the measured outputs is not limited to the first entries of a canonical-form state vector. The proposed observer estimates the closed-loop state tracking error asymptotically, provided that the output gain matrix includes Hurwitz coefficients. The chattering is eliminated by using boundary layers around the sliding surfaces and the observer convergence is proved using a Lyapunov-based approach. The proposed method is applied on a real multilink robot manipulator. The performance of the observer shows its effectiveness in the real world.     

A consistent closure method for non-linear random vibration

—A closure method is proposed for calculating moments of the state vector of a non-linear system satisfying an Itô stochastic differential equation. It is based on a finite set of moment equations and a sequence of probabilities converging to the exact distribution of the state vector that is obtained by the minimization of an objective function. Numerical results for one-dimensional diffusion processes show that the proposed closure technique is robust in the sense that resultant moments are satisfactory even when crude approximations are used for the probability of the state vector.     

Hummingbirds generate bilateral vortex loops during hovering: evidence from flow visualization

This article derives a method to estimate and correct the bias error of the shift vector’s absolute length in the presence of curved streamlines. The main idea is to identify the most likely streamline with constant curvature from the second-order shift vector and its gradient. The work establishes a theoretical framework including the systematic errors of the first-order and second-order shift vector’s absolute value and angle. Synthetic images of a stationary vortex are used to validate the proposed method. The curvature-correction is also applied to a synthetic flow field with non-constant curvature to demonstrate its potential for more realistic flow fields. The results reveal that second-order accurate vector fields suffer from a biased shift vector length depending on the streamline’s curvature and on the shift vector length. The bias error is negligible for vector fields with a shift vector length below the streamline curvature radius. For large shift vectors or strong curvatures, the bias error can be significantly reduced with the developed method. The approach is very general and can be applied to any vector field obtained from window-correlation particle image velocimetry (PIV), single-pixel ensemble-correlation PIV, particle tracking velocimetry or optical flow methods. It also works for all 3D extensions of the techniques, such as 3D-PTV or tomographic PIV.     

基于极大似然比的多故障卫星完好性检测

针对多星座情况下多卫星同时故障时的接收机自主完好性检测的问题,分析了多卫星同时故障的原因及特点,提出基于极大似然比的分层完好性检测方法.通过奇偶向量矩阵的计算,根据极大似然估计,进行故障检测与隔离,利用全量检验统计值与部分检验统计值之间的关系进行故障卫星的确定,并利用接收机的数据进行仿真验证.仿真结果表明,本方法可以快速有效地实现多星座情况下的接收机自主完好性检测,检测出并隔离故障卫星.     

等参管单元及其在热传导问题边界元法中的应用Isoparametric tube elements and their application in heat conduction BEM analysis

采用边界元法（BEM ）求解实际工程问题时,很大一部分误差来自于离散误差。为此,本文基于Lagrange插值原理,提出了一种三维等参管单元边界元算法,该单元能很好地模拟管状结构的几何外形并对物理量进行高阶插值,大大地消除了离散误差。另外,当在边界元法中使用等参管单元时,提出了一种在等参平面内消除积分奇异性的方法。算例表明,本文算法具有划分网格少,求解精度高的优点。