Computational materials: Multi-scale modeling and simulation of nanostructured materials

The paper provides details on the current approach to multi-scale modeling and simulation of advanced materials for structural applications. Examples are given that illustrate the suggested approaches to predicting the behavior and influencing the design of nanostructured materials such as high-performance polymers, composites, and nanotube-reinforced polymers. Primary simulation and measurement methods applicable to multi-scale modeling are outlined. Key challenges including verification and validation are highlighted and discussed.     

基于遥感案例推理的海岸带养殖信息提取

目前基于目视解释或光谱分类的养殖信息提取效率低,难以克服由于地物混杂带来的“椒盐”噪声现象且难以融合地学知识。针对养殖信息提取中存在的问题,首先在分析现有养殖信息提取方法和案例推理CBR(Case\|Based Reasoning)用于遥感图像处理的基础上,提出基于遥感案例推理的海岸带养殖信息提取的研究思路;其次,结合养殖区域的空间特征和属性特征,构建案例的表达模型以及CBR相似性推理模型;最后,对不属于案例构建区的粤西沙田镇进行养殖信息提取的CBR实验,精度达到84.56%。对比CBR方法和传统监督分类方法可知,CBR方法是实现海岸带养殖信息快速准确提取的一种有效手段。     

基于双缓冲机制的多尺度导航电子地图显示设计

为了提高电子地图数据的精度和画面显示的速率,对地图数据格式加以改进,新增isvl参数准确标识出被描绘数据情报的尺度,对检索的数据缓存做了优化性能管理,依据地图数据的格式提出了坐标变换、数据解析和描画范围定位的准确算法,采用双缓冲机制绘制地图;经实验证明,使用该套方案实验的结果,具有以下特性:1)高精度,多尺度;2)画面合理的表达了空间关系;3)支持实时动态快速显示;可应用到电子地图的研发中。     

一种新的红外图像快速分割方法研究

研究红外图像目标分割快速优化问题。在高分辨率红外图像的分割中,红外图像存在数据量大、目标的边缘模糊和噪声较大等导致分辨率低和实时性差。为了快速准确分割,提出基于低尺度分割阈值预测的快速红外图像分割方法(LFIRS)。首先建立尺度阶数计算模型以确定保留原始红外图像目标基本信息所需的最小尺度,在分析多尺度过程对具有目标/背景强相关特性的红外图像进行分割阈值,建立多尺度红外图像分割阈值的相关模型(CLM),结合经典二维阈值法得到的最低两个尺度的阈值CLM模型参数,可以通过CLM模型与最小尺度的快速获取原始尺度的分割阈值,实现红外图像的快速分割。实验结果表明,改进方法提高了图像分辨和分割速度,且改善了分割效果。     

Explicit numerical simulation of suspension flow with deposition in porous media: influence of local flow field variation on deposition processes predicted by trajectory methods

A new explicit numerical simulation (ENS) method based on lattice-gas automata (LGA) is introduced here for the flow of solid/fluid suspensions with deposition in porous media. The ENS method explicitly resolves the dynamics of the individual solid particles and the suspending fluid in the domain defined by the pore walls and solid particle surfaces. After describing the new method, it is applied to the study of solid/fluid suspension flow with deposition in a constriction and in a model random porous solid. This study clearly demonstrates that the deposits strongly influence the local flow fields, which in turn affect the deposition process indicating that this interplay should be modelled if accurate results are desired from trajectory methods.     

Multi-loop design of multi-scale controllers for multivariable processes

Based on the recently proposed (SISO) multi-scale control scheme, a new approach is introduced to design multi-loop controllers for multivariable processes. The basic feature of the multi-scale control scheme is to decompose a given plant into a sum of basic modes. To achieve good nominal control performance and performance robustness, a set of sub-controllers are designed based on the plant modes in such a way that they are mutually enhanced with each other so as to optimize the overall control objective. It is shown that the designed multi-scale controller is equivalent to a conventional PID controller augmented with a filter. The multi-scale control scheme offers a systematic approach to designing multi-loop PID controllers augmented with filters. Numerical studies show that the proposed multi-loop multi-scale controllers provide improved nominal performance and performance robustness over some well-established multi-loop PID controller schemes.     

Generalized multi-scale control scheme for cascade processes with time-delays

The cascade control is a well-known technique in process industry to improve regulatory control performance. The use of the conventional PI/PID controllers has often been found to be ineffective for cascade processes with long time-delays. Recent literature report has shown that the multi-scale control (MSC) scheme is capable of providing improved performance over the conventional PID controllers for processes characterized by long time-delays as well as slow RHP zeros. This paper presents an extension of this basic MSC scheme to cascade processes with long time-delays. This new cascade MSC scheme is applicable to self-regulating, integrating and unstable processes. Extensive numerical studies demonstrate the effectiveness of the cascade MSC scheme compared with some well-established cascade control strategies.     

Multi-scale finite element modelling using bubble function method for a convection-diffusion problem

Due to the multi-scale nature of the convection-diffusion equation the standard Galerkin method fails to predict accurate and stable results. A multi-scale finite element method based on the bubble function approach has been developed and applied to this problem. Finite element formulations based on the discontinuous weighting functions including the streamline upwind Petrov-Galerkin (SUPG) method are also evaluated. The results show that the multi-scale method provides stable and accurate results and matches very well the analytical solution.     

Pavement crack detection using hessian structure propagation

Pavement images are widely used in transportation agencies to detect cracks accurately so that the best proper plans of maintenance and rehabilitation could be made. Although crack in a pavement image is perceived because the intensity of crack pixels contrasts with that of the pavement background, there are still challenges in distinguishing cracks from complex textures, heavy noise, and interference. Unlike the intensity or the first-order edge feature of crack, this paper proposes the second-order directional derivative to characterize the directional valley-like structure of crack. The multi-scale Hessian structure is first proposed to analytically adapt to the direction and valley of cracking in the Gaussian scale space. The crack structure field is then proposed to mimic the curvilinear propagation of crack in the local area, which is iteratively applied at every point of the crack curve to infer the crack structure at the gaps and intersections. Finally, the most salient centerline of the crack within its curvilinear buffer is exactly located with non-maximum suppression along the perpendicular direction of crack. The experiments on large numbers of images of various crack types and with diverse conditions of noise, illumination and interference demonstrate the proposed method can detect pavement cracks well with an average Precision, Recall and F-measure of 92.4%, 88.4%, and 90.4% respectively. Also, the proposed method achieves the best performance of crack detection on the benchmark datasets among methods that also require no training and publicly offer the detection results for every image.     

基于EMD和小波分析的多尺度边缘检测

提出了一种基于EMD(Empirical Mode Decomposition)与小波分析相结合的多尺度边缘检测方法。首先将图像信号进行EMD分解,将其分解成n个IMF(Intrinsic Mode Function)函数,再对每个IMF函数进行小波变换。将该方法应用于图像的边缘提取,较好地得到了图像的边缘信息。