Suppressing GPR Clutter from Randomly Rough Ground Surfaces to Enhance Nonmetallic Mine Detection

This study attempts to quantify the ground penetrating radar rough ground surface clutter by numerical modeling of wave scattering, and establish a strategy to suppress the clutter for given test signals. The goal is to improve the GPR detection statistics for small, buried, low-contrast nonmetallic antipersonnel mines. Using a model of an experimentally measured impulse GPR signal, we simulate the ground surface and buried low-contrast mine target scattered responses. We employ a 2D finite difference time domain (FDTD) method to analyze the pulse shape, delay, and amplitude characteristics of the scattered waves—with and without buried nonmetallic mine targets—as a function of roughness parameters. Five hundred Monte Carlo simulations of various test cases of specified ground root mean square height and correlation length were run to generate statistics for the clutter and target signal variations. In addition, the effectiveness of identifying and removing the ground surface clutter signal for detecting subsurface targets is presented. Results indicate that even with moderate roughness, statistics can be generated to enhance the detection of small, shallow, low-contrast targets.     

Using the PML ABC for Air/Soil Wave Interaction Modeling in the Time and Frequency Domains

The Perfectly Matched Layer (PML) and absorbing boundary condition (ABC) is applied to two-dimensional Finite Difference Time Domain (FDTD) and Finite Difference Frequency Domain (FDFD) simulations of wave interactions with a two-layer air and soil geometry. Since the soil medium is lossy and dispersive, modeling of wave propagation and scattering is significantly more difficult than for free space and pure dielectrics. In addition, specifying an ABC which efficiently prevents reflections from both the free space termination and the adjacent soil is challenging. The theoretical basis for terminating dispersive media for both the time and frequency domains is presented, and simulation results for plane wave and point source excitations are demonstrated. For the former case, scattering is computed from a buried mine-like target. Although the absorbing characteristics of the PML for the air/soil interface are not as good as for free space, it is shown that maximum local reflections of as low as –15dB for FDTD and –50dB for FDFD are possible.     

面向结构建模的产品族EAC模型及应用研究

提出基于实体-属性-约束（entity--attribute--constraint，EAC）模型的产品族建模方法，将产品族表达为实体、属性、约束三元组。实体是产品族的物理对象及其抽象；属性是对物理对象的特性描述；约束是维护产品族实体对象和属性对象的关系集合。提出基于VGBOM的产品族描述模型，该模型除了能表示一族产品的结构和关系，涵盖产品所有可能的产品变型的特点外，还具有变量化的特点，使得产品族通过配置更易于实现产品变型。     

An Object-Oriented Approach for Flexible Manufacturing Control Systems Analysis and Design Using the Unified Modeling Language

In reacting to global competition and rapidly changing customer demands, industrial business organizations have developed a strong interest in flexible automation. The aim of flexible automation focuses on achieving agility in handling uncertainties from internal or external environments. Modeling complex structures, promoting reuse, and shortening the development time cycle are particularly significant aspects in the analysis and design of CIM systems, where heterogeneous elements have to be integrated in a complex control architecture. The design methodology for FMS control software involves the abstraction of an FMS and the estimation of the system performances. The aim of this activity is to suggest the optimal configuration of an FMS for given specifications, through simulation tools. In the software engineering field, object-oriented (OO) approaches have proven to be a powerful technique with respect to such aspects. The unified modeling language (UML), by using OO design methodologies, can offer reusability, extendibility, and modifiability in software design. Also, it bridges the gap that exists between the OO analysis and design area and the area of OO programming by creating an integrative metamodel of OO concepts. The specific goal of this paper is to formulate a new methodology for developing reusable, extendible, and modifiable control software for an FMS in an object-oriented environment. It is demonstrated that, with few diagrams, UML can be used to model such systems without being associated with other modeling tools.