Advanced system‐level simulation paradigm for ultra‐wideband systems using SCERNE platform

In this article, a progressive system‐level simulation framework is developed based on Simulation de Chaînes d'Emission/Réception Nouvelle gEnération (SCERNE) platform to simulate an ultra‐wideband (UWB) impulse radar transmitter and accurately predict its performance. With the purpose of demonstrating the usefulness of the SCERNE ability in system‐level modeling, we present and simulate a simplified structure of UWB impulse radar transmitter. First, after simulation each component in different circuit‐level tools such as ADS, CST, and HFSS, each part has been modeled by using different modeling methods to transfer their data into MATLAB environment. Then, we duplicate the transmitter structure in SCERNE toolbox to validate the results. The advantage conferred by the proposed SCERNE toolbox is that fast and accurate bilateral modeling method is available at multi‐medium structures in contrast with conventional unilateral modeling, and so a lower memory and higher accuracy of the behavioral model is achieved. It can also be beneficial when the user is looking for system‐level, as the increased components amounts can help as a surrogate model. The system model can be easily extended to other UWB radar systems by simply changing the input pulse shape, UWB channel environment, transceiver topology, etc. Various effects such as signal quality, and pulse shape that can easily investigate and re‐optimize for high performance are using the developed model. To validate the practicality of the proposed paradigm, the simulations and predictions through model results are being outlined.     

Improving mine recognition through processing and Dempster-Shafer fusion of ground-penetrating radar data

A method for modeling and combination of measures extracted from a ground-penetrating radar (GPR) in terms of belief functions within the Dempster-Shafer framework is presented and illustrated on a real GPR data set. A starting point in the analysis is a preprocessed C-scan of a sand-lane containing some mines and false alarms. In order to improve the selection of regions of interest on such a preprocessed C-scan, a method for detecting suspected areas is developed, based on region analysis around the local maxima. Once the regions are selected, a detailed analysis of the chosen measures is performed for each of them. Two sets of measures are extracted and modeled in terms of belief functions. Finally, for every suspected region, masses assigned by each of the measures are combined, leading to a first guess on whether there is a mine or a non-dangerous object in the region. The region selection method improves detection, while the combination method results in significant improvements, especially in eliminating most of the false alarms.     

基于MATLAB与VC混合编程的飞机刹车系统仿真

MATLAB／VC＋＋的混合编程是基于MATI。AB／Simulink的仿真工程处理要求,结合两种软件工具的特性,采取以代码交互和MATLAB函数模块调用为主,配合外部应用程序接口函数所构建的一种用户接口编程模式;文中以某型军机为背景,依据飞机刹车系统在降落过程中的动力学特性,建立了逼真的数学模型,通过分析6种VC＋＋调用MATLAB方法的原理及特点,详细探讨了使用MATLAB引擎调用方式进行VC＋＋与MATLAB混合编程的方法,并将该方法应用在飞机刹车系统建模与仿真中,通过实例实现了MATLAB模块在VC＋＋环境中的集成,说明了该方法的可行性。     

Hybrid-interface element for thick laminated composite plates

A novel 27-node three-dimensional hexahedral hybrid-interface finite element (FE) model has been presented to analyze laminated composite plates and sandwich plates using the minimum potential energy principle. Fundamental elasticity relationship between components of stress, strain and displacement fields are maintained throughout the elastic continuum as the transverse stress components have been invoked as nodal degrees of freedom. Continuity of the transverse stresses at lamina interface has been maintained. Each lamina is modeled by using hybrid-interface elements at the top and the bottom interfaces and conventional displacement based elements sandwiched between these interfaces. Results obtained from the present formulation have found to be in excellent agreement with the elasticity solutions for thin and thick composite cross-ply, angle-ply laminates, as well as sandwich plates. Additional results have also been presented on the variation of the transverse strains to highlight magnitude of discontinuity in these quantities due to difference in properties of face and core materials of sandwich plates. Present formulation can be used effectively to interface hybrid formulation that uses transverse stresses and displacements as degrees of freedom with conventional purely displacement based formulation for realistic estimates of the transverse stresses.     

超宽带探地雷达目标回波信号特征提取与材质识别

基于探地雷达信号传输机理,建立了超宽带探地雷达宽带回波模型,揭示了多谱分量对目标回波信号特征提取与材质识别的影响。超宽带探地雷达由于回波信号信息丰富的特点,特征向量的选取成为目标识别的关键。利用子波变换在宽相关处理中的应用,对回波信号进行滤波和典型数据提取。提取纵向和横向典型数据用于目标形状识别;提取回波道数据进行Welch功率谱分析,用于目标材质识别。     

Anistropic creep modeling based on elastic projection operators with applications to CMSX-4 superalloy

This paper presents a unified framework for creep modeling of anisotropic materials, which is specified in more detail to the cases of isotropy, cubic symmetry and transverse isotropy. To this end an additive decomposition of the elastic and inelastic strain tensors into dilational and isochoric Kelvin modes is assumed. Each of these modes is obtained from fourth-order projection operators, resulting from solution of the eigenvalue problem for the anisotropic fourth-order elasticity tensor. The amount of strain rate for each mode is modeled with a Norton-type ansatz in terms of an equivalent stress. The formulation for the equivalent stress in terms of quadratic forms with aid of the projection operators is compared with polynomial expressions from the literature. The experimental phenomenon of primary creep is taken into account by a back stress tensor of Armstrong–Frederick type, which is also decomposed into Kelvin modes. As a consequence of the mode decomposition the classical radial-return method of isotropic elasto-plasticity is generalized to the different cases of anisotropy. Furthermore the implications on parameter identification are addressed. Two numerical examples are concerned with a superalloy CMSX-4.     

Feature and decision level sensor fusion of electromagnetic induction and ground penetrating radar sensors for landmine detection with hand-held units

Strategies for fusion of electromagnetic induction (metal detector (MD)) and ground penetrating radar (GPR) sensors for landmine detection are investigated. Feature and decision level algorithms are devised and compared. Features are extracted from the MD signals by correlating with weighted density distribution functions. A multi-frequency band linear prediction method generates features for the GPR. Feature level fusion combines MD and GPR features in a single neural network. Decision level fusion is performed by using the MD features as inputs to one neural network and the GPR features as inputs to the geometric mean and combining the output values. Experimental results are reported on a very large real data set containing 2315 mine encounters of different size, shape, content and metal composition that are measured under different soil conditions at three distinct geographical locations.     

基于MUSIC谱估计的探地雷达回波处理方法

为了克服现有信号处理算法对探地雷达噪声及杂波滤除的不足,提出了一种基于MUSIC谱估计时域与频域联合滤波方法。利用常用的去直流波和均值滤波抑制方法进行雷达信号预处理,在此基础上,引入谱分析中信号子空间与噪声子空间的概念,将MUSIC算法与最小二乘法相结合来进行探地雷达杂波及噪声处理。仿真及实验结果表明,提出的回波处理方法可以有效地抑制雷达信号中的噪声和杂波,能提高测量数据的精度,具有较高的实用性和可用性。     

MATLAB 与STM32 CubeMX联合的嵌入式开发方法

利用专门的软件STM32CubeMX与 MATLAB进行嵌入式建模与仿真,仿真成功后,在编译器中将其翻译为高效的 MDK C语言代码,大大提高了嵌入式程序的开发效率,缩短了开发周期,并且可以同时利用 MATLAB的代码优化工具箱,提高代码质量。实验结果表明,利用 MATLAB与STM32CubeMX生成的代码在目标系统中运行良好,在设计效率和易维护性方面优于手工编写的代码。     

一种雷达回波实时仿真的软件实现方法研究

为了便于将雷达回波仿真应用于实践,提出一种雷达回波实时仿真的软件实现设计方法。按照雷达信号接收处理的工作原理,对雷达工作方式和战场环境分别建模并作适当简化,利用软件编程实现雷达回波仿真。利用软件实现的便捷性特点,在仿真中设计了一些交互接口,可接收对雷达工作状态的调整指令以及对模拟战场环境的修改信息。这样可实时更新生成不同环境下的动态回波信号,提高仿真应用的灵活性与通用性。仿真结果验证了该方法的可用性和有效性。     

Identifying underground voids using a GPR circular-end bow-tie antenna system based on a support vector machine

This article presents a pattern recognition approach based on discrete cosine transform (DCT) and polarization attributes to identify voids underground in ground penetrating radar (GPR) images. Features vectors composed of DCT coefficients supplying to the support vector machine classifier are studied, together with their linearity. To evaluate the proposed method, we hold an experimental study of GPR data obtained by numerical modelling of a GPR circular-end bow-tie antenna system using the finite-integration technique based simulator. In order to form the database of features, different acquisition scenarios of GPR models are achieved by varying buried object’s material type, position, shape, size parameters, and electric characteristics of subsurface medium. The robustness of the proposed system towards degradation of the generated GPR data is tested by introducing Gaussian and speckle noise. The experimental results show the proposed approach exhibits encouraging performance in terms of void identification with errors of object apex position in GPR images.     

基于多标签层次聚类的GPR 图像双曲波提取方法

探地雷达(GPR)图像双曲波提取是分析地下目标位置和结构的重要方法,但在真 实环境中,由于噪声和杂波的干扰,使得提取出的双曲波存在结构不完整、碎片化和形状异 常等问题,不利于数据分析和三维建模等后续操作。为此,提出了一种基于多标签层次聚类 的双曲波提取方法(MHCE)。首先通过信息熵评价像素邻域的稳定性,构造了基于信息熵的 距离度量来进行层次聚类;然后利用聚类后的邻接空间进行多标签聚类以降低杂波和噪声对 双曲波提取的影响;最后结合多标签聚类结果的拟合形状和纹理方向提取双曲波。实验表明, 该方法对于真实GPR 图像双曲波具有较好的鲁棒性,能够获得规范化的双曲波形状和位置 参数。     

Dynamic delamination modelling using interface elements

Existing techniques in explicit dynamic Finite Element (FE) codes for the analysis of delamination in composite structures and components can be simplistic, using simple stress-based failure function to initiate and propagate delaminations.This paper presents an interface modelling technique for explicit FE codes. The formulation is based on damage mechanics and uses only two constants for each delamination mode; firstly, a stress threshold for damage to commence, and secondly, the critical energy release rate for the particular delamination mode. The model has been implemented into the LLNL DYNA3D Finite Element (FE) code and the LS-DYNA3D commercial FE code.The interface element modelling technique is applied to a series of common fracture toughness based delamination problems, namely the DCB, ENF and MMB tests. The tests are modelled using a simple dynamic relaxation technique, and serves to validate the methodology before application to more complex problems.Explicit Finite Elements codes, such as DYNA3D, are commonly used to solve impact type problems. A modified BOEING impact test at two energy levels is used to illustrate the application of the interface element technique, and it’s coupling to existing in-plane failure models. Simulations are also performed without interface elements to demonstrate the need to include the interface when modelling impact on composite components.     

Detecting,locating, and characterizing voids in disaster rubble for search and rescue

After natural and man-made disasters such as earthquakes, hurricanes, and explosions, victims may survive in voids that are formed naturally in collapsed structures. First responders need to identify and locate these critical voids for rapid search and rescue operations. Due to the complex and unstructured occlusions in disaster areas, visual and manual search is time-consuming and error-prone. In this study, we proposed a novel method to automatically detect, locate, and characterize voids buried in disaster rubble using ground penetrating radar (GPR). After preprocessing the collected radargrams, the boundaries of potential voids are segmented based on radar signal patterns, and the 95% confidence intervals are constructed around the segmented boundaries to account for uncertainties. To improve the detection accuracy, the geometric relations of the detected boundaries and their signal characteristics are examined to confirm the void existence. Then, the void location and dimension are estimated based on calibrated velocity of radar wave and its travel time. The effectiveness and efficiency of the proposed method were manifested by its performance in laboratory and field experiments. The contribution of this study is twofold. First, the feasibility of using GPR to detect, locate, and characterize voids in collapsed structures is experimentally tested, innovatively extending the application of GPR to search and rescue operations. Second, algorithms are developed to process non-intuitive radargrams to provide first responders actionable information.     

杂波环境下雷达信号处理的SystemVue建模与仿真方法研究

对雷达信号处理的仿真建模方法进行研究,利用SystemVue仿真平台中专用的雷达模型库构建雷达系统仿真模型,并对杂波环境下的雷达信号处理过程进行雷达系统的建模与仿真实现。首先,分析雷达回波生成过程及雷达信号处理的基本原理;其次,研究雷达仿真模型库中目标模型、杂波/噪声模型、脉冲压缩模型、MTD模型、CFAR模型的功能作用及参数设置;最后,利用SystemVue仿真平台搭建杂波环境下雷达系统仿真模型,并基于矩阵类型的数据对雷达信号处理过程进行仿真。经过仿真,雷达系统模型的信号处理结果与理论相符,验证了该仿真模型的正确性。     

A study of moderately thick quadrilateral plate elements based on the absolute nodal coordinate formulation

Finite element analysis using plate elements based on the absolute nodal coordinate formulation (ANCF) can predict the behaviors of moderately thick plates subject to large deformation. However, the formulation is subject to numerical locking, which compromises results. This study was designed to investigate and develop techniques to prevent or mitigate numerical locking phenomena. Three different ANCF plate element types were examined. The first is the original fully parameterized quadrilateral ANCF plate element. The second is an update to this element that linearly interpolates transverse shear strains to overcome slow convergence due to transverse shear locking. Finally, the third is based on a new higher order ANCF plate element that is being introduced here. The higher order plate element makes it possible to describe a higher than first-order transverse displacement field to prevent Poisson thickness locking. The term “higher order” is used, because some nodal coordinates of the new plate element are defined by higher order derivatives. The performance of each plate element type was tested by (1) solving a comprehensive set of small deformation static problems, (2) carrying out eigenfrequency analyses, and (3) analyzing a typical dynamic scenario. The numerical calculations were made using MATLAB. The results of the static and eigenfrequency analyses were benchmarked to reference solutions provided by the commercially available finite element software ANSYS. The results show that shear locking is strongly dependent on material thickness. Poisson thickness locking is independent of thickness, but strongly depends on the Poisson effect. Poisson thickness locking becomes a problem for both of the fully parameterized element types implemented with full 3-D elasticity. Their converged results differ by about 18 % from the ANSYS results. Corresponding results for the new higher order ANCF plate element agree with the benchmark. ANCF plate elements can describe the trapezoidal mode; therefore, they do not suffer from Poisson locking, a reported problem for fully parameterized ANCF beam elements. For cases with shear deformation loading, shear locking slows solution convergence for models based on either the original fully parameterized plate element or the newly introduced higher order plate element.     

基于STD标准的LFM脉冲信号建模与应用

信号和测试定义(STD)标准是面向信号自动测试工程应用的理论基础,但目前该标准中提供的基本信号模型并不能满足雷达告警设备检测需求。针对此问题,依据标准要求扩展线性调频(LFM)脉冲信号类型,并进行信号仿真。基于MATLAB APP Designer工具设计开发测试信号模型加载和实例创建软件,创建信号实例,并通过矢量信号源模拟产生雷达信号,送至雷达告警接收机前端,进行信号的有效性验证。实验证明,扩展的线性调频脉冲信号模型可以满足实际测试需求,为未来雷达信号标准化建模奠定了良好基础。     

Multidisciplinary aircraft design and evaluation software integrating CAD,analysis, database,and optimization

The development of an overall strategy to design the aircraft using analysis codes is presented. The procedure is automated through the integrated software MADE (multidisciplinary aircraft design and evaluation) developed in this research that enables the determination of an optimum set of aircraft configurations. The core ingredients of MADE are (i) analysis codes, which utilizes initial sizing, aerodynamics, mass, stability and control, propulsion, performance, and RCS (radar cross section) analyses, (ii) optimization utilizing gradient-based optimization technique, response surface modeling, and Carpet plot, (iii) database utilizing commercial Oracle 8i database management system (DBMS) and OCI (Oracle call interface) to save design parameters and aircraft configurations. The complexity of input and output containing massive amounts of data has previously placed severe limitations on the use of aircraft analysis codes by the general aerospace engineering community. By using C++ and the Microsoft Foundation Classes to develop a graphical user interface (GUI) and using DBMS, it is believed that use of MADE can avoid the additional cumbersome, and sometimes tedious, task of preparing the required input files manually and can make the transition to general usability in an aerospace engineering environment. For detail explanation, examples of E–R diagram, class diagram, and data flows between codes for the MADE are also presented.     

超宽带雷达的发展、现状及应用

超宽带雷达以其高距高分辩率、强穿透国、低截获率与强抗干扰性在军事、商业、环保等领域得到日益关注。本文综述了超宽带雷达的发展历史,结合国外实际超宽带合成孔径雷达系统阐明了超宽带合成孔径雷达的现状,并深入探讨了超宽带雷达的特性及其应用前景。超宽带雷达经过几十年的发展仍存在一些值得深入研究的问题,本文简要分析了部分技术难点,指出了超宽带雷达今后的发展和应用方向。