Three-dimensional ocean sensor networks: A survey   总被引：1，自引：0，他引：1  

WANG Yu  LIU Yingjian  GUO Zhongwen 《中国海洋大学学报(英文版)》2012,11(4):436-450

The past decade has seen a growing interest in ocean sensor networks because of their wide applications in marine research,oceanography,ocean monitoring,offshore exploration,and defense or homeland security.Ocean sensor networks are generally formed with various ocean sensors,autonomous underwater vehicles,surface stations,and research vessels.To make ocean sensor network applications viable,efficient communication among all devices and components is crucial.Due to the unique characteristics of underwater acoustic channels and the complex deployment environment in three dimensional(3D) ocean spaces,new efficient and reliable communication and networking protocols are needed in design of ocean sensor networks.In this paper,we aim to provide an overview of the most recent advances in network design principles for 3D ocean sensor networks,with focuses on deployment,localization,topology design,and position-based routing in 3D ocean spaces.  相似文献   

天津滨海新区浅层超软土加固技术现场对比试验     

董志良  周琦  张功新  邱青长  罗彦  李燕 《岩土力学》2012,33(5):1306-1312

分析天津滨海新区浅层超软土加固处理存在的问题,提出常规方案、单排单管方案和单排单管加密方案。依托天津滨海新区某工程,开展现场对比试验。结合各种监测检测成果,对比分析3种方案加固效果,并提出进一步优化改进建议。工程实践表明,经过3种方案加固处理,吹填淤泥表层会形成具有一定强度和厚度的硬壳层,土体物理力学性质明显改善,均能满足后续吹填砂垫层和机械插板的施工要求。另外,单排单管方案和加密方案加固效果明显优于常规方案,尤其有利于硬壳层厚度的形成。从长远加固效果角度出发,单排单管方案及加密方案更可取。  相似文献   

基于Hewlett理论的支护桩桩间距计算方法研究     

史海莹  龚晓南  俞建霖  连峰 《岩土力学》2011,32(Z1):351-0355

基坑支护桩桩间距设计通常基于经验取值,并不考虑土拱的作用和桩间土的稳定性。基于Hewlett理论分析了基坑支护桩桩间土拱效应,并开展了对桩间土整体稳定性的研究,分别得出了满足两种稳定条件的桩身荷载分担比公式和桩间距公式。通过对设置在四种土质中的支护桩桩间土拱的计算分析发现：对于强度指标较高的黏土、粉土,桩宽比为0.5时,荷载分担比即达到100%,而对于强度指标较低的淤泥质黏土,桩宽比为0.8时,荷载分担比方达到100%;桩间土整体稳定性对于桩间距的要求较为宽松。对于常规桩径的支护桩,桩间距的设计应按土拱稳定为控制准则,但对于设置在内摩擦角较大而黏聚力较小土层中的大直径桩,应按桩间土整体稳定为控制准则  相似文献   

A Fourth Order Accurate SH-Wave Staggered Grid Finite-difference Algorithm with Variable Grid Size and VGR-Stress Imaging Technique     

J. P. Narayan  S. Kumar 《Pure and Applied Geophysics》2008,165(2):271-294

This article presents a new approach for the implementation of a planar-free surface boundary condition. It is based on a vertical grid-size reduction above the free surface during the explicit computation of a free surface boundary condition. This technique is very much similar to the well-known stress imaging technique. VGR-stress imaging technique name is proposed for this new free surface boundary condition (VGR stands for ‘vertical grid-size reduction’). To study the performance of the proposed VGR-stress imaging technique, it was implemented in a newly developed second order accurate in time and fourth-order accurate in space (2, 4) staggered grid SH-wave finite-difference (FD) algorithm with variable grid size. It was confirmed that the effective thickness (ETH) of first soil layer becomes less by one-half of vertical grid size than the assigned thickness (ATH), if stress imaging technique is used as a free surface boundary condition. The qualitative and quantitative results of various numerical experiments revealed that the proposed VGR-stress imaging technique is better than the stress imaging technique since it is free from the thickness discrepancy arising due to the use of images of stress components across the free surface. On the basis of iterative numerical experiments, it was confirmed that the stability condition for this FD scheme with variable grid size is It was also inferred that at least five to six grid points per shortest wavelength are required to avoid the grid dispersion. The maximum grid-spacing ratio up to 12.5 or even more did not affect the accuracy of (2,4) SH-wave algorithm. The obtained reduction of 10.46 and 5.38 folds in the requirement of computational memory and time for a particular basin-edge model, as compared with the homogeneous grid size, reflects the efficacy of the new FD algorithm.  相似文献   

A methodology to assess the delivery of road runoff in forestry environments   总被引：1，自引：0，他引：1  

I. Takken  J. Croke  P. Lane 《水文研究》2008,22(2):254-264

This paper outlines a conceptual and methodological approach to evaluating the risk of road derived runoff delivery, which is based on the principle of hydrological connectivity. Three different types of runoff delivery pathways are identified (stream crossings, gullied pathways and diffuse pathways) and the volume of runoff that may reach the stream through these pathways during a one in 10 year 30 minute event is estimated. The methodology is applied to three catchments of contrasting forest use, both plantation and native. Results show that degree of connectivity of a road depends on catchment characteristics such as the topography, road placement, drain spacing and road and drainage density. Maps outlining the distribution of different delivery pathways within a catchment are used to assess the potential for runoff connectivity. In one of the selected study catchments, the Albert River, greatest potential connectivity can be isolated to a single road. The upper part of this road crosses many tributaries resulting in high connectivity via stream crossings, whereas the lower part of the road is located within the valley bottom, where the majority of drains will contribute runoff during a one in 10 year event through diffuse overland flow. The presented methodology is also used to highlight hot‐spots in terms of runoff and sediment delivery through the creation of risk assessment maps, which allows for the evaluation of different procedures for road rehabilitation. Using examples from the Albert River catchment, we demonstrate that minimizing diffuse overland flow can generally be achieved by the placement of additional road drains, whereas at highly connected road segments the relocation of the road might be the only option. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

复杂环境中大规模桩筏基础的优化设计方法研究     

谢芸菲  迟世春  周雄雄 《岩土力学》2019,40(Z1):486-493

变刚度优化设计对于复杂环境中的大规模桩筏基础始终是一个重要难题。基于有限元分析提出一种两阶段优化设计方法,该方法首先根据传统均匀布桩方案的桩顶应力分布对群桩进行分区,然后依据每个子区域桩顶应力之间的关系确定基桩数量调整系数,最后通过调整桩间距来改变各子区域的基桩数量,从而实现变刚度优化设计。运用该方法对多层土体中承担非均匀上部结构荷载的大规模桩筏基础进行变刚度优化设计,计算结果表明优化设计后筏板的差异沉降、平均整体弯矩和群桩顶部的差异应力均显著降低。该方法计算简单,应用范围广,且不受复杂土层条件、非均匀上部结构荷载以及桩基础规模大小形状的限制。  相似文献   

利用直达P波测定地方震震源深度的探讨   总被引：2，自引：0，他引：2  

王登伟 《地震地磁观测与研究》2010,31(5):45-48

震源深度是地震时空参数中的基本参数,是目前最难测准的参数之一。可以使用直达P波测定震源深度。要确保测定结果的精度,必须加密台网观测点,使台间距的大小与震源深度相当。利用四川省西昌和冕宁大桥水库两个遥测地震台网的直达P波资料,测定发生在其监控区域内137个地震的震源深度。结果发现,该区域地震的平均深度和深度下限存在随震级增大而增加的现象。其中有部分地震的震源深度,利用本研究方法测定的结果与使用遥测地震台网计算机定位程序输出的结果相差较大。作者认为,这部分地震使用计算机定位程序得出的震源深度有较大的误差。  相似文献   

深海布放缆不同材料属性下应力波自由传播频率特性影响研究     

吴丞昊  杨建民  田新亮  胡智焕  彭涛 《海洋工程》2017,35(5):12-22

在频域对深海布放缆系统内应力波自由传播特性进行了分析。在布放缆数学建模时使用了哈密顿原理,并在建模时考虑布放缆的曲率。计算过程中保留了缆绳曲率与其弧长坐标之间的非线性关系,并最后得到了其上传播的应力纵波与应力横波的特性。通过计算得到布放缆属性和缆绳内竖直张力等参数对缆绳内自由传播频率特性的影响曲线。结果表明,这些因素对自由传播应力波的频率关系、色散关系、相速度与群速度影响显著。对于应力纵波,整个频域可被两个截止频率与一个行波截止频率分成四个区域。除了通频带之外,在低频时亦存在抑止带和行波抑止带。应力纵波仅能在通频带中以行波形式传播,而应力横波则可以在所有频率范围内以行波形式传播。  相似文献   

不同围岩类别小间距隧道施工过程模拟研究   总被引：26，自引：6，他引：20  

李云鹏  王芝银  韩常领  霍明  艾传志 《岩土力学》2006,27(1):11-16

从不同围岩类别出发,对3车道小间距隧道采用典型双侧导坑法的开挖施工过程进行了数值模拟研究。给出了不同围岩类型下的3车道小间距隧道在施工过程中的围岩破坏特征及其变形规律和变形规律的相似性,获得了洞周最大变形量值之间的相对比值关系。通过中隔墙的变形与塑性破坏规律分析,比选出了3车道隧道中隔墙最小间距的工程设计参考值。分析表明：II类围岩合理间距不应小于0.45B,III类围岩应在0.35～0.45B之间,IV,V类围岩可在0.2～0.35B之间选择,对信息化反馈施工,指出了必须重点监控与关注的位置。为小间距隧道的发展和施工设计提供了较确切的参考数据和理论依据。  相似文献   

某水电站地下厂房围岩稳定性分析     

隋斌  朱维申  张欣  王刚 《岩土力学》2006,27(Z1):416-420

对某水电站地下厂房采用有限元方法反演厂区初始地应力场。分别对地下厂房洞室群3个平行洞室的不同间距、洞室开挖的不同顺序以及施加锚杆和锚索后的方案与毛洞方案进行了分析比较。计算结果表明,经过适当优化后该洞室群在洞室布局、开挖顺序和支护参数等方面是安全可行的,各主要洞室群的稳定性总体较好。  相似文献