深海汇聚区的焦散结构与声能分布特征     

阎肖鹏 《海洋通报》2012,31(3):283-289

在深海汇聚区声场中,不同初始角的声线在传播过程中因折射程度差异形成特定的焦散结构。根据射线理论推导了线性剖面条件下用F算子表示的声线轨迹模型,并讨论了焦散结构与掠射角及声源-接收深度配置的变化关系。折射型焦散线由0°~5°的小角度声线构成,为波导结构;反射型焦散线由掠射角为±(5°~10°)的声线构成,为折线结构,且上行与下行声线的焦散线结构明显不同。应用BELLHOP模型分析得出了汇聚区增益与声源-接收深度条件的变化关系,并根据射线到达结构和焦散特征提出了一种确定汇聚区位置和范围的方法。  相似文献   

Transmission Sources of Waterborne Viruses in South Sudan Refugee Camps          下载免费PDF全文

Laura Guerrero‐Latorre  Ayalkibet Hundesa  Rosina Girones 《洁净——土壤、空气、水》2016,44(7):775-780

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输电线路掏挖基础机械成孔过程中孔壁土体稳定性分析   总被引：2，自引：0，他引：2  

崔强  何西伟  曹丹京  苏鼎  徐震 《冰川冻土》2016,38(4):922-928

针对输电线路掏挖基础成孔过程中孔壁稳定性的问题,以机械化旋挖钻机成孔的掏挖基础孔壁土体为研究对象,采用FLAC3D数值模拟软件,对旋挖钻机成孔过程中孔壁土体的变形破坏过程进行模拟分析,研究了开挖过程中掏挖基础孔壁土体的稳定性及影响因素.研究结果表明,钻机的自重荷载与开挖卸荷作用对孔口处和扩大头处土体的水平向位移影响较为明显;不同埋深基础的孔壁土体塑性区的分布面积和延伸范围均存在差异,随着埋深的增加,基础扩大头处的塑性区面积和延伸范围也随之增大,因此,现场机械化开挖施工过程中应重点关注孔口和扩大头附近部位的变形破坏.该研究成果可为机械化旋挖钻机成孔技术在我国输电线路工程杆塔掏挖基础施工的应用提供理论依据.  相似文献   

基于数字图像相关方法的动载颗粒体系力链破坏机制初探     

陈凡秀  庄琦  王日龙 《岩土力学》2016,37(2):563-573

颗粒物质是具有复杂力链网络的常见体系,其平衡和稳定性取决于内部力链骨架的几何结构和力学性能。为恰当刻画颗粒体系的微细观力学行为,从颗粒局部排列形态、颗粒间接触力和颗粒及外荷载的物理参数出发,展开基于二维数字图像相关技术（2D-DIC）的集中力作用下颗粒体系变形的试验。通过结合DIC的试验方法,应用牛顿力学理论及颗粒线性动量平衡获得颗粒间接触力的大小和方向,确定力链的动力学规律;得到颗粒间接触力大小分布变化并提取颗粒体系力链;提出颗粒排布的两种状态：横向传力和纵向传力状态;分析颗粒接触面法线与水平轴的夹角?、传力角?,讨论了?、? 对力链断裂破坏的影响;分析颗粒直径d与外荷载压条直径D的比值R以及压条下表面能直接接触的最大颗粒数N等参数,为描述力链的演化和破坏重构机制提供参考基础;简单阐述了力链网络在外荷载下的微细观统计效应对体系宏观力学性质的影响规律。  相似文献   

A new numerical technique for simulating the coupled seismic and electromagnetic waves in layered porous media          下载免费PDF全文

Hengxin Ren  Qinghua Huang  Xiaofei Chen 《地震科学（英文版）》2010,23(2):167-176

Chen's technique of computing synthetic seismograms,which decomposes every vector with a set of basis of orthogonality and completeness before applying the Luco-Apsel-Chen(LAC)generalized reflection and transmission coefficients method,is confirmed to be efficient in dealing with elastic waves in multi-layered media and accurate in any frequency range.In this article,we extend Chen's technique to the computation of coupled seismic and electromagnetic(EM)waves in layered porous media.Expanding the involved mechanical and electromagnetic fields by a set of scalar and vector wave-function basis,we obtain the fundamental equations which are subsequently solved by using a recently developed version of the LAC generalized reflection and transmission coefficients method.Our approach and corresponding program is validated by reciprocity tests.We also show a numerical example of a two-layer model with an explosion source.The P-to-EM conversion waves radiated from the interface may have potential application.  相似文献   

DESIGN OF MODULATION AND COMPRESSION CODING IN UNDERWATER ACOUSTIC IMAGE TRANSMISSION     

程恩  余丽敏  林耿超 《中国海洋湖沼学报》2002,20(3):202-207

This paper describes the design of modulation, compression coding and transmission control in underwater acoustic color image transmission system. This design adapts a special system of modulation and transmission control based on a DSP(Digital Signal Processing) chip, to cope with the complex underwater acoustic channel. The hardware block diagram and software flow chart are presented.  相似文献   

低纬子午环的方位传动   总被引：3，自引：3，他引：0  

陈林飞  铁琼仙 《天文研究与技术》1997,(Z1)

介绍了低纬子午环上设置方位机构的必要性和这套机构的结构，分析了在仪器升降和转置过程中，引起三个支承螺杆晃动的原因和对仪器方位定向的影响，叙述了减小晃动的办法和克服剩余影响的临时措施。  相似文献   

Effective solutions to a global 3D visual system in networking environments   总被引：2，自引：0，他引：2  

ZHANG Liqiang    ZHANG Yan  YANG Chongjun  LIU Suhong  REN Yingchao  RUI Xiaoping & LIU Donglin . State Key Laboratory of Remote Sensing Sciences  School of Geography  Remote Sensing  Beijing Normal University  Beijing  China  . State Key Laboratory of Remote Sensing Sciences  Institute of Remote Sensing Applications  Chinese Academy of Sciences  Beijing  China  . Institute of Geographical Sciences  Natural Resources Research  Chinese Academy of Sciences  Beijing  China   《中国科学D辑(英文版)》2005,48(11):2032-2039

Today, with the proposal of digital earth, digital city and digital community, and rapid advances in informa-tion technologies and collection of spatial data, to a great degree, the traditional 2D GIS is promoted to Web and 3D GIS, which greatly challenges the capaci-ties of the system in transmitting and handling massive datasets. A great number of 3D GIS prototype systems have been developed and applied in such areas as mine resource management, digital cities. However, appli-cation sys…  相似文献   

Attenuation characteristics of ground motion intensity from earthquakes with intermediate depth     

A.?JoshiEmail author  S.?Midorikawa 《Journal of Seismology》2005,9(1):23-37

Data of the intermediate depth (the Geioyo and the Shizuoka) earthquakes in Japan recorded in a dense network is analysed and compared with various available attenuation relations. The approach of Midorikawa (Midorikawa S., 1993, Technophysics 218, 287–295) based on the empirical Greens function technique of Irikura (Irikura, K., 1986, Proceedings of the 7th Japan Earthquake Engineering Symposium, pp. 151–156.) has been used to model the rupture responsible for these earthquakes and peak ground acceleration are simulated at selected observation points. The method presented in this work includes the transmission effect in a multiple layer crustal model for a finite fault earthquake source model. Sharp attenuation rate is seen for such intermediate depth earthquakes which is difficult to explain through conventional attenuation relations. Detail study of the methodology and comparison of results shows that the transmission factor plays an important role for the sharp attenuation rate for intermediate-to deep-focus earthquakes.  相似文献   

分频输电系统中变频变压器的两种新型结构     

施汉基 《广东海洋大学学报》1997,(2)

分析了星-开口三角型三相铁磁三倍叛变压器的移相原理和用于分频输电系统时可能出现的问题，提出了两种新型的铁磁三倍频变压器的结构方案，并论述了它们的工作原理和优点。指出对铁磁三倍频变压器仍需进行更深入研究的若干问题．  相似文献