基于视觉的水雷目标识别方法研究     

苗锡奎  朱枫  许以军  吴清潇  郝颖明  任申真 《海洋工程》2012,30(4):154-160

水下目标识别一直是目标识别领域的研究热点,为此,以水雷目标识别为需求背景提出了一种基于视觉的水雷目标识别方法。该方法从水雷目标形状的本质特征出发,根据几何矩的物理意义,结合区域特征和边界特征构造了三个适合于水雷目标形状描述子,采用阈值判决的方法,实现水雷目标的识别。实验结果表明,该方法比基于不变矩的方法识别率更高,具有较好的稳定性,尤其适用于水下特定形状的目标识别和目标受到部分遮挡的情况。其中水下图像处理和特征的定义方法对水下目标识别具有指导和借鉴意义。  相似文献   

铁磁形状记忆合金研究进展与展望（Ⅱ）：本构模型   总被引：1，自引：0，他引：1  

李爱群  陈鑫  左晓宝 《地震学刊》2011,(2):117-130

阐述了铁磁形状记忆合金（Ferromagnetic Shape Memory Alloy,简写为FSMA）本构模型研究的重要性。以时间为顺序,重点介绍了FSMA本构模型研究的发展历程和研究现状。仔细分析了各种FSMA本构模型在理论基础、适用范围、精度以及复杂程度等方面的特点,讨论了各种理论应用于FSMA本构模型的局限性,指出了它们在面向应用时存在的问题。研究表明,由于FSMA兼具磁致形状记忆效应、热弹性形状记忆效应等多种独特性能,使对其本构模型的研究存在一定困难,进一步的研究还有待开展。最后指出,对既能揭示FSMA微观机理又能预测其宏观热磁力学行为的本构模型、描述FSMA所有特性的统一模型、面向应用的FSMA简化本构模型等问题,尚有待深入研究。  相似文献   

隧道掘进面接近地质界面时围岩的应力特征研究   总被引：1，自引：1，他引：0       下载免费PDF全文

熊良宵  袁学武 《水文地质工程地质》2012,39(3):38-44

隧道开挖地层中往往呈现出明显的地质变异性,如软硬岩层的不均匀分布等,使隧道开挖后的力学行为十分复杂.本文采用FLAC3D初步分析了隧道掘进面接近地质界面时围岩的应力状态,并探讨侧向应力、纵向应力、断面形式对围岩应力的影响规律.分析结果表明:当隧道由硬岩往软岩或由软岩往硬岩向地质界面掘进时,掘进面前方围岩均有应力集中现象.隧道无论由硬岩往软岩还是由软岩往硬岩掘进至地质界面时,掘进面前方边墙位置围岩径向应力均随侧向应力的增大而增大,掘进面前方拱顶和边墙位置围岩纵向应力均随纵向应力的增大而增大.马蹄彤隧道开挖至硬岩与软岩的地质界面时,掘进面后方边墙位置围岩应力均小于圆形隧道相应位置的围岩应力.  相似文献   

Evaluation of codified elastic design spectrum models for regions of low-to-moderate seismicity     

《Soil Dynamics and Earthquake Engineering》2015

Design spectrum (DS) model is typically specified in a seismic code of practice for structural design. In a region of low-to-moderate seismicity where seismic code does not exist, a DS model in a well established code of practice is usually adopted, while the suitability of such model has seldom been evaluated. In this article, the elastic DS models for reference (rock) site stipulated in six major codes of practice (AS1170.4–2007, EN1998-1:2004, GB50011–2010, IBC–2012, NBCC–2010 and NZS1170.5:2004) have been compared and scrutinized. Three cities of low-to-moderate seismicity, namely, Melbourne (Australia), Hong Kong (China) and Karlsruhe (Germany), have been selected for illustrative purposes. Particular emphasis has been put on the parameterization scheme for DS model. It is found that huge discrepancies (over 100%) exist among the models, especially at the long period range, due to differences in spectral shapes and the recommended corner periods, which would lead to undesirable effects on the use of the displacement-based seismic design approach. It is urged that the values of corner periods should be determined specifically and cautiously based on the regional seismicity pattern and local geological conditions.  相似文献   

DEM modeling of pullout behavior of geogrid reinforced ballast: The effect of particle shape     

《Computers and Geotechnics》2017

The performance of a geogrid reinforced system depends heavily on the properties of interface between the interacting components (i.e., backfill soil and geogrid inclusion). The comprehensive understanding of soil-geogrid interaction requires proper consideration of the true aperture geometry and the discontinuous nature of backfill soil. Based on the calibrated parameters, this paper presents a simulation procedure using PFC3D to reproduce the realistic pull-out behaviors of a triaxial geogrid embedded in various ballast aggregates with diverse particle shapes. The load transfer behaviors across the interacting components have been visualized in terms of the evolution of bond forces along the geogrid and the evolution of contact forces across the particle assembly. Meanwhile, the inherent microscopic changes accounting for the regression of macroscopic strength and the correlation between macro pull-out force and micro anisotropy parameters have been addressed. In addition, the differences in macro performance and the particle responses produced by different shapes of particles are also systematically discussed to justify the significant role of particle geometry. The findings obtained in this study are expected to provide better understanding of soil-geogrid interaction and the improved interlocking caused by irregular ballast geometry.  相似文献   

Numerical investigation of the opening effect on the mechanical behaviours in rocks under uniaxial loading using hybrid continuum-discrete element method     

《Computers and Geotechnics》2017

Openings including their size, shape and distribution in rock play a significant role in the performance of rock related structures. The well-established knowledge in this area can contribute to the engineering practices, for example, underground space design, planning and optimisation in Civil and Mining Engineering and wellbore stability in Drilling Engineering, among others. Thus, understanding the failure mechanism of rock with openings is theoretically and practically meaningful. Laboratory testing on rock or rock-like materials with openings have been studied extensively in the literature, which, however, primarily focuses on the cracks/fractures. In this paper, a comprehensive numerical study on the effect of non-banded openings, i.e., circular, rectangular, and triangular opening, on the rock mechanical behaviour is performed using a hybrid continuum-discrete element method. It is revealed that the proposed simulation method can reproduce reasonably the crack initiation and propagation, and predict well the change of the mechanical behaviour due to the openings. In addition, the influence of the opening shape and opening ratio (=area of opening/specimen area) on the mechanical behaviour is also investigated.  相似文献   

Self‐centering structural systems with combination of hysteretic and viscous energy dissipations     

Weng Yuen Kam  Stefano Pampanin  Alessandro Palermo  Athol J. Carr 《地震工程与结构动力学》2010,39(10):1083-1108

This paper presents an innovative set of high‐seismic‐resistant structural systems termed Advanced Flag‐Shaped (AFS) systems, where self‐centering elements are used with combinations of various alternative energy dissipation elements (hysteretic, viscous or visco‐elasto‐plastic) in series and/or in parallel. AFS systems is developed using the rationale of combining velocity‐dependent with displacement‐dependent energy dissipation for self‐centering systems, particularly to counteract near‐fault earthquakes. Non‐linear time‐history analyses (NLTHA) on a set of four single‐degree‐of‐freedom (SDOF) systems under a suite of 20 far‐field and 20 near‐fault ground motions are used to compare the seismic performance of AFS systems with the conventional systems. It is shown that AFS systems with a combination in parallel of hysteretic and viscous energy dissipations achieved greater performance in terms of the three performance indices. Furthermore, the use of friction slip in series of viscous energy dissipation is shown to limit the peak response acceleration and induced base‐shear. An extensive parametric analysis is carried out to investigate the influence of two design parameters, λ₁ and λ₂ on the response of SDOF AFS systems with initial periods ranging from 0.2 to 3.0 s and with various strength levels when subjected to far‐field and near‐fault earthquakes. For the design of self‐centering systems with combined hysteretic and viscous energy dissipation (AFS) systems, λ₁ is recommended to be in the range of 0.8–1.6 while λ₂ to be between 0.25 and 0.75 to ensure sufficient self‐centering and energy dissipation capacities, respectively. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

深圳海岸壶穴的形态及空间分布特征   总被引：1，自引：1，他引：0  

王为  许刘兵  吴正  黄山 《地理学报》2010,65(3):320-330

对广东深圳西冲湾海滩东侧基岩海岸上壶穴的形态特征进行详细测量并对其位置和高程做三角高程测量。结合野外观测结果从经典统计学和空间统计学的角度定量地描述壶穴的形态和空间分布特征及其在基岩海岸发育过程中的地貌作用。研究得出以下结论：西冲海岸壶穴趋向形成于节理、断裂、层面等岩体软弱带,壶穴的形态和分布受这些软弱带控制,但形成于软弱带的具体位置却是随机的;西冲海岸壶穴的形成、扩大和加深实际上是对二级平台产生破坏,但壶穴以现代低潮线为下蚀极限;海岸壶穴是现代海岸动力侵蚀过程的产物,只要动力、岩石条件适合,壶穴随时都可形成;海岸壶穴的形态不仅与流水动力有关,而且与岩石硬度及壶穴发育过程有关;海岸壶穴与河流壶穴一样,可以在形成于各种类型的岩石,起源于各种各样的凹坑;海岸与河流的水动力差异导致了海岸壶穴和河流壶穴形态差异。  相似文献   

强震作用下超高桥墩动力稳定性理论研究   总被引：4，自引：4，他引：0       下载免费PDF全文

程麦理  李青宁  苗如松 《地震工程学报》2016,38(3):360-365

根据平截面假定,考虑超高桥墩大位移变形产生的几何非线性影响,建立超高桥墩的振动控制微分方程,利用变步长的龙格-库塔法进行求解,结合B-R运动判定准则,对超高桥墩在地震作用下的动力失稳机理进行研究。理论分析表明,超高桥墩的动力失稳与桥墩的几何尺寸、质量分布、边界条件有密切关系;桥墩动力失稳时刻随地震波加速度峰值的增大而减小;失稳时刻与失稳加速度荷载有对应关系。算例结果表明:本文方法正确,利用本文理论能够准确计算超高桥墩的失稳时刻及失稳加速度,对超高桥墩动力失稳的理论分析及工程实践有重要指导意义。  相似文献   

水力劈裂对岩体中自然裂纹的影响研究     

石路杨  李建  许晓瑞  余天堂 《岩土力学》2016,37(10):3003-3010

建立了求解自然裂纹和水力裂纹扩展的扩展有限元法,对裂纹附近区域的节点采用广义形函数,并采用线增函数消除混合单元,以提高裂纹附近的精度。引入水力劈裂的非耦合模型,即假设裂纹中的水压力为均布力;用砂浆法（线段-线段接触法）结合增广型拉格朗日乘子法处理受压裂纹段的接触条件。并通过算例分析了以下内容：计算了受压裂纹和裂纹面分布均布水压力的水力裂纹的应力强度因子,并与解析解进行了比较,结果表明,提出的方法具有很高的精度;模拟了水力裂纹对自然裂纹面的影响,并分析了自然裂纹面上的接触力和接触状态。  相似文献