雷达光电测速无偏转换误差分析及数据融合

为改善雷达光电跟踪系统目标运动参数估计性能,提出了一种考虑测速无偏转换的数据融合算法。基于雷达多普勒径向速度量测与光电跟踪系统角速度信息,推导了测速信息在笛卡尔坐标系下的无偏转换量测,分析了转换后量测噪声的统计特性,给出了基于解耦序贯更新滤波的数据融合算法。仿真表明,本文方法改善了目标运动参数估计精度,提高了速度分量估计误差收敛速度,研究结果亦可为航迹起始、目标威胁度初判提供参考。     

基于被动式传感器的目标跟踪算法研究

仅有角度量测的被动式单传感器跟踪搜索系统有广泛的应用前景,但现有的针对性跟踪算法并不能很好的处理实际问题,失跟现象常常发生。本文对现有算法所存在的问题进行了深入研究,并提出了相应的改进算法。通过对机动目标运动分析,总结出角度向量在时间域中的变化规律,通过引入新的计算向量,对原算法残差计算进行了修正。它对基于单个被动传感器的纯方位跟踪问题的处理提供了新的思路。仿真实验及实际应用已证明了该算法有效性。     

方位角准确预测法在光电跟踪中的应用研究

本文通过基于卡尔曼滤波和一步预测理论建立适当的数学模型，提出了一种应用于舰载光电跟踪设备的拟线性目标方位预测算法，并对不同的运动目标的进行了仿真计算。结果表明该方法有较高的精度，能预测出光电跟踪设备在丢失目标情况下的目标航迹，可满足其在炮振丢失目标情况下的预测要求。     

一种多目标自动跟踪的逻辑关联方法

目标跟踪是被动声纳系统的主要功能之一,跟踪器为目标运动分析和目标识别等后置处理提供输入数据。声纳操作员利用人脑独特的认知模式、先验知识和视觉的迹迹相关效应,能够很好地在声纳显示方位历程图上发现目标并录取跟踪。但实际应用中由于低信噪比、航迹交叉和转向等复杂多目标情形,声纳系统实现多目标自动跟踪十分困难。给出一种多目标自动跟踪的逻辑关联方法,利用被动声纳宽带波束输出数据,通过点迹与航迹关联、航迹评价管理和交叉处理等过程,可以较好实现多目标自动跟踪。试验数据的处理结果验证了所提方法的有效性,能够在声纳装备中得到工程应用。     

矢量水听器阵列自适应子空间跟踪算法

矢量水听器能同时共点获得声场中声压和振速,与其他水听器相比,能获得更多的信息量,具有很好的应用前景。矢量水听器阵列的MUSIC算法能实现360°无模糊方位估计,然而对于方位时变的目标源,该算法很难完成对上述目标源方位进行实时跟踪估计。鉴于此,将MALASE算法和MUSIC算法相结合,提出了一种矢量水听器阵列的自适应子空间跟踪算法。仿真结果表明,该算法既保留了MUSIC算法的性能,又实现了对目标源进行实时跟踪估计,且方位估计误差仅为0．4°左右。     

规避目标的纯方位被动跟踪

构造了基于笛卡耳曼滤波器的改进极坐标扩展卡尔曼跟踪滤波器。提出了应用于方位角测量的规避目标的跟踪算法，对提出的算法进行了相应的仿真实验。仿真结果表明，该算法非常适合于规避目标的纯方位跟踪，具有很好的工程应用前景。     

单预警机静态航迹规划建模与仿真

预警机作为空军预警探测的重要组成部分,飞行前对其进行航迹规划是至关重要的.在分析预警机航迹规划与目前已研究的飞行器航迹规划区别的基础上,研究了单架预警机静态航迹规划问题.首先,结合当前预警机的作战运用模式,综合考虑对预警机跟踪监视目标性能有影响的各种主要因素,将预警机航迹规划划分为2个阶段;然后,对影响各阶段航迹规划的主要因素分别进行数学建模并得出代价函数,设计了各阶段具体的航迹规划步骤,并基于改进的粒子群算法对飞行段航迹进行搜索.通过Matlab仿真证明了所设计的方法能够根据目标分布情况自动生成质量优越的航迹.     

一种纯方位跟踪中的自适应滤波算法

针对纯方位被动目标跟踪中扩展卡尔曼滤波算法易发散的不足，提出了一种自适应的改进算法。该算法利用极大后验噪声估计器Sage-Husa对虚拟观测噪声进行实时在线估计，动态补偿线性化带来的误差。算法的对比仿真分析结果表明，AEKF较之EKF滤波效果有所改善，增强了稳定性，提高了精度，为ST纯方位被动目标跟踪的实现提供一种新的方法。     

多阵方位-频率目标运动分析算法研究

利用两接收阵的大空间跨度，可以得到对同一个目标有较大差异的DOA估计，利用这些角度差可直接对目标进行三角定位和跟踪。在多阵条件下，即使只有一种目标方位参量，也能在不需要本艇机动下对目标进行跟踪。但当目标处于两阵连线上时，目标仍容易发散。为解决这一问题，我们提出了多阵方位．频率目标运动分析算法，对其可观察性进行了分析。理论分析证明多阵方位-频率TMA的不可观察性条件在多阵纯方位TMA的不可观察性条件[θ1(t)-θ2(t)]=kπ上增加了一个附加条件θ1′=0。这个附加条件不仅弱化了不可观察性的约束条件，还在一定程度上增加了目标跟踪的稳定性。最后给出了三种情况下的计算机模拟．并与多阵纯方位目标运动分析算法作了比较。     

基于跟踪起始准则的多基地声呐阵位优化算法

针对水下区域监视多基地声呐（如浮标等）发射、接收节点阵位布置问题,提出了一种基于跟踪起始准则的多基地声呐阵位优化算法。该算法首先在分布式和集中式两种多基地融合处理模式下,推导了目标跟踪起始概率计算准则,然后,基于区域目标成功跟踪起始覆盖率,建立了多基地声呐阵位优化数学模型,并采用粒子群算法来优化求解该非凸数学模型,从而得到全局最优的多基地声呐发射-接收阵位。仿真结果表明,在两种多基地融合处理模式下,优化后多基地声呐节点阵位,其区域目标跟踪起始覆盖率比典型经验方案有较大提高。     

多亮点声纳目标轨迹起始技术

高分辨率声纳目标具有多亮点分布特性,传统轨迹起始算法很难有效对其轨迹起始。针对声纳目标多亮点分布特性,设计了基于蒙特卡洛方法的轨迹起始算法,其根据跟踪门内每个分布亮点的特性,估计目标的概率分布,推出目标位置信息。由于轨迹起始算法考虑了声纳目标的多亮点属性和每个亮点的信息,并在轨迹起始过程中没有将速度、加速度、角度等作为轨迹起始的限制条件,而是在确认阶段,作为限制条件,对不符合逻辑的轨迹进行淘汰,对符合逻辑的进行动静分类。所以此轨迹起始算法克服了传统算法容易将多亮点目标起始为多个轨迹或轨迹起始错误的缺点。用不同方法对多亮点分布声纳目标数据进行了轨迹起始,结果验证了该方法的有效性。     

Incorporation of microdosimetric concepts into a biologically-based model of radiation carcinogenesis

The generalised state-vector model of radiation carcinogenesis (SVM) simulates radiation induced biological effects by expressing the transition rates between the various initiation and promotion stages in terms of dose rate for low and high linear energy transfer (LET) particles. In the present work, the SVM has been reformulated to incorporate single track characteristics of particles with varying LET. Transition rates of the initiation phase were expressed as functions of LET by describing the complexity and clustering of DNA double strand breaks (DSBs) and its effect on repair kinetics, while the promotion phase was reformulated based on a multi-target single-hit hypothesis. Such an approach allows the consideration of hit frequencies and the variability of the specific energy and LET spectra of radon progeny alpha particles in bronchial target cells for different exposure conditions.     

Vibrations of a track caused by variation of the foundation stiffness

The paper deals with the stochastic analysis of a single-degree-of-freedom vehicle moving at constant velocity along a simple track structure with randomly varying support stiffness. The track is modelled as an infinite Bernoulli–Euler beam resting on a Kelvin foundation, which has been modified by the introduction of a shear layer. The vertical spring stiffness in the support is assumed to be a stochastic homogeneous field consisting of a small random variation around a deterministic mean value. First, the equations of motion for the vehicle and beam are formulated in a moving frame of reference following the vehicle. Next, a first-order perturbation method is proposed to establish the relationship between the variation of the spring stiffness and the responses of the vehicle mass and the beam. Numerical examples are given for various parameters of the track. The response spectra obtained from the perturbation analysis are compared with the numerical solution, in which finite elements with transparent boundary conditions are used. The circumstances, under which the first-order perturbation approach provides satisfactory results, are discussed.     

The fracture behaviour of a welded tubular joint—an ESIS TC1.3 round robin on failure assessment methods: Part VI: application of WES 2805-1997

The Japanese flaw assessment method WES 2805-1997 is applied to the fracture tests on welded tubular T-joints presented in Engineering Fracture Mechanics (2002;69). The approach is shown to yield conservative results for small amounts of stable crack growth but it overestimates the load carrying capacity for larger amounts of stable crack growth. As a consequence it is proposed to restrict the application to ductile crack initiation and to brittle fracture below or at stable crack initiation.     

Dynamic finite element modeling and fatigue damage analysis of thermite welds

Railway track comprises of continuous welded rail mounted with rail clips on sleepers integrated to a ballast track form system. Modeling the rail structure with thermite weld subjected to the complex dynamic loadings is a challenging problem. Fatigue failures at the head‐to‐web, web‐to‐foot, and foot regions of weld collar are investigated. In this paper, a combined method of multibody system dynamic analysis and dynamic finite element analysis was used. A train roll‐in experiment was conducted at a train depot test track to validate modeling results predicted at the strain gauge location. Three critical plane‐based multiaxial fatigue criterions incorporated with a smallest enclosing circle algorithm were implemented in Python code to study the fatigue behavior at weld collar. Parametric studies were also conducted to investigate the effects of track component materials, track curvature, and train velocity. This approach provides a method for predicting the failures of thermite welded joints in railway tracks.     

Multi-Target Track Initiation in Heavy Clutter

In the heavy clutter environment, the information capacity is large, the relationships among information are complicated, and track initiation often has a high false alarm rate or missing alarm rate. Obviously, it is a difficult task to get a high-quality track initiation in the limited measurement cycles. This paper studies the multi-target track initiation in heavy clutter. At first, a relaxed logic-based clutter filter algorithm is presented. In the algorithm, the raw measurement is filtered by using the relaxed logic method. We not only design a kind of incremental and adaptive filtering gate, but also add the angle extrapolation based on polynomial extrapolation. The algorithm eliminates most of the clutter and obtains the environment with high detection rate and less clutter. Then, we propose a fuzzy sequential Hough transform-based track initiation algorithm. The algorithm establishes a new meshing rule according to system noise to balance the relationship between the grid granularity and the track initiation quality. And a flexible superposition matrix based on fuzzy clustering is constructed, which avoids the transformation error caused by 0–1 voting method in traditional Hough transform. In addition, the algorithm allows the superposition matrixes of nonadjacent cycles to be associated to overcome the shortcoming that the track can’t be initiated in time when the measurements appear in an intermittent way. And a slope verification method is introduced to detect formation-intensive serial tracks. Last, the sliding window method is employed to feedback the track initiation results timely and confirm the track. Simulation results verify that the proposed algorithms can initiate the tracks accurately in heavy clutter.     

A probabilistic nonlocal model for crack initiation and propagation in heterogeneous brittle materials

A probabilistic damage model is developed to study crack initiation and growth in quasi‐brittle materials. Two different thresholds are considered to describe these mechanisms. A Weibull model is used to account for the randomness of crack initiation(s) and then a fracture mechanics based threshold is considered to model crack propagation. The model is integrated in a finite element code via a nonlocal damage approach. A regularization operator based on a stress regularization is introduced. Both damage thresholds are checked using the ‘regularized’ stress field to avoid mesh dependence. The interaction between propagating cracks and potential initiation sites is accounted for. Copyright © 2012 John Wiley & Sons, Ltd.     

被动传感器航迹起始算法

为解决杂波、未知数目和被动传感器测量精度不一致情况下的航迹起始问题,提出了一种适用于被动传感器系统的航迹起始算法.该算法首先根据启发式规则消除一部分虚假定位点,然后利用概率网格的思想将观测空间划分为同一大小的网格,同时根据被动传感器的测量精度计算得到每个网格内出现目标的概率,最后利用序列Hough变换进行航迹的检测.仿...     

Fatigue life prediction for stainless steel welded plate CCT geometry based on Lawrence''s local-stress approach

In the present study, the effect of welding process and procedure on fatigue crack initiation from notches and fatigue crack propagation in AISI 304L stainless steel welds was experimentally investigated. Full penetration, double-vee butt welds have been fabricated and CCT type specimens were used. Lawrence's local-stress approach (a two-stage model) is used to predict the fatigue life. The notch-root stress method was applied to calculate the fatigue crack initiation life, while the fatigue crack propagation life was estimated using fracture mechanics concepts. The fatigue notch factor is calculated using Lawrence's approach. Constant amplitude fatigue tests with stress ratio, R=0 were carried out using 100 kN servo-hydraulic DARTEC universal testing machine with a frequency of 30 Hz. The predicted lives were compared with the experimental values. A good agreement has been reached. It is found that the weld procedure has a stronger effect on lives to initiation than on propagation lives.