Finite element method for strong reflection of water waves

In this study, the propagation of monochromatic water waves over an arbitrarily varying topography is numerically investigated. A finite element model is developed by formulating the diffraction of waves caused by depth changes. Not only the propagating mode but also the evanescent modes are included in the model. The model developed is applied to the study of strong reflection of monochromatic waves over a sinusoidally varying topography. Predicted reflection coefficients are compared with those of available laboratory experiments and the eigenfunction expansion method. A very good agreement is observed.     

Performance of solid and perforated U-type breakwaters under regular and irregular waves

An experimental investigation of U-type breakwaters was carried out in a laboratory channel. Both regular and irregular waves were used during testing. Two types of breakwaters such as solid and perforated were studied to analyse the porosity effect of structures. In order to investigate performance of these breakwaters for different immersion depths, four depths of immersions of the solid and perforated breakwaters were selected. Different wave groups were generated over these breakwaters, and the transmission, reflection and energy dissipation characteristics of each breakwater were determined. Three coefficients such as transmission, reflection and energy dissipation coefficients, which were named as C_t, C_r, and C_l, respectively, were used during the evaluation of the test results. The most important parameters governing performance of these breakwaters were determined by using earlier investigations and experimental results. These parameters were expressed as a dimensionless group by using π theory. Based on the test results, empirical expressions were formulated to describe the C_t, C_r, and C_l for different immersion depths of solid and perforated breakwaters under regular and irregular waves.     

云南西部地壳深部结构特征

在云南西部,穿过红河、小江断裂带完成了一条长360 km、呈北东向的深地震宽角反射/折射剖面.通过对该测线的观测资料进行一维、二维模拟解释,得到了沿剖面的二维地壳速度模型.研究结果显示,沿测线Moho界面埋深横线变化大,其西南侧Moho埋深约35 km,东北侧Moho最大埋深可达43 km.沿剖面从西南到北东方向,地壳平均P波速度从5.9 km/s逐渐增加到6.13 km/s,但显著低于全球大陆平均值.结合以往的接收函数和面波联合反演结果,我们推算沿测线从西南到东北,其下方地壳泊松比介于0.23~0.25之间.剖面西南侧上地壳具有异常低的P波速度和泊松比,暗示其下方上地壳以α-相长英质组分为主;而剖面东北上地壳相对较高的P波速度和泊松比则暗示其物质组成以花岗岩-花岗闪长岩为主.研究区下地壳的P波速度和泊松比分别介于6.25~6.75 km/s和0.24~0.26 km/s之间,暗示其上部组成以花岗岩相的片麻岩为主,而下部组成则以角闪石类岩石为主.红河断裂两侧地壳速度显著不同,从浅到深其速度差异逐渐变弱,但红河断裂两侧地壳厚度变化较大.而小江断裂下方两侧地壳速度和地壳厚度变化并没有红河断裂那么明显.     

南海南部海域中中新世(T3界面)构造变革界面地震反射特征及构造含义

南海南部海域油气资源丰富,由于盆地沉积厚度大、沉积相横向变化快和构造演化复杂等原因,致使该海域新生代地层的划分方案差异大,地层时代的认识也存在较大分歧,这极大地制约了对盆地油气资源评价的正确认识.本文在总结国内外不同分层方案基础上,通过收集国外在南海南部深水区两口关键钻井的资料,开展曾母和北康两盆地重处理二维地震剖面的构造-地层解译,以及联井剖面的井震对比,重新识别和标定新生代重要构造变革面的地震反射特征.根据海域钻井、地层岩性、沉积环境、构造应力体系和古生物资料的综合对比研究,结合婆罗洲陆地测年结果和区域构造事件,重新厘定中中新世T₃构造变革面的发育时代,年龄为15～17 Ma,分析了该界面的构造含义,认为其是南海海底扩张停止的一个构造响应界面,在南海南部海域对应南沙运动,在北婆罗洲地区表现为沙巴造山运动.     

深地震反射剖面揭示的渭河盆地西安坳陷的地壳精细结构

2005年,跨西安坳陷完成一条NW方向,69 km长的深地震反射剖面,首次获得该区域的地壳精细结构、主要断裂展布和深、浅构造关系图像.地震反射CMP叠加时间剖面显示,以反射事件C为界,地壳被分成上下两部分.上地壳由多组近水平反射带组成,具有分段连续性好、局部存在反射带明显错断或形态突变等特征,清晰地刻画出西安坳陷新生代沉积分层、坳陷底界、渭河断裂带、临潼-长安断裂带和秦岭山前断裂带的几何形态和关系.反射事件C是结晶地壳内宽度约0.5 s的反射带,最深处位于桩号30 km,底界约6.5 s,向西北缓慢抬升至5.5 s,向南东迅速抬升至5.5 s.下地壳有两个明显的反射事件RA、RB: RB是位于桩号40~47 km之间的局部反射团, 而RA为宽度约2 s、向坳陷倾斜的反射带.以桩号38 km为界,反射Moho形态截然不同,而且出现了显著的错断:大桩号方向,反射Moho为位于双程走时11~14 s水平的反射分段连续的过渡带,宽度约3 s;小桩号方向,反射Moho为一宽度约2 s、并向大桩号倾斜的反射分段连续的过渡带,其形态和反射事件RA相同.根据地震波速度资料,求得这几个反射带顶界的深度分别为:10.5~13.5 km(反射带C)、20.3~21.5 km(反射带RB)、16.8~34.3 km(反射带RA)和32~36.7 km(反射带Moho)左右.作者认为形态一致的反射事件RA和反射Moho很可能是古秦岭洋向华北地台俯冲的遗迹.此外,西安坳陷内错断新生界深达反射事件C的渭河和临潼-长安断裂带和莫霍错断的存在,表明该地区地壳现今活动性很强,是未来强震发生值得注意的地区.     

Evidence of chaos in the rainfall-runoff process

Abstract

The transformation of rainfall into runoff is one of the most important processes in hydrology. In the past few decades, a wide variety of automated or computer-based approaches have been applied to model this process. However, many such approaches have an important limitation in that they treat the rainfall-runoff process as a realization of only a few parameters of linear relationships rather than the process as a whole. What is required, therefore, is an approach that can capture not only the overall appearance but also the intricate details of the nonlinear behaviour of the process. The purpose of this study is to investigate the possibility of understanding the dynamics of the rainfall-runoff process from a new perspective, as a chaotic process. The possible existence of chaotic behaviour in the rainfall-runoff process is studied by investigating the rainfall and runoff time series: (a) separately; and (b) jointly (using the runoff coefficient). Monthly rainfall and runoff observed over a period of 131 years (January 1807-December 1937) at the Göta River basin in the south of Sweden are analysed. The correlation dimension method is employed to identify the presence of chaos. The correlation dimensions obtained for the rainfall and runoff time series are 6.4 and 5.5, respectively. The finite dimensions obtained for the rainfall and runoff time series indicate the possible existence of chaos in these processes, implying that the joint rainfall-runoff process might also exhibit chaotic behaviour. The correlation dimension of about 7.8 obtained for the runoff coefficient also indicates the possible presence of chaos and supports the above results.     

关于转变测绘地理信息行政管理职能的思考

政府职能转变已成为新时期深化行政管理体制改革的重要内容。适应形势发展需要,客观分析当前我国测绘地理信息行政管理职能转变的必要性,明确测绘信息地理行政管理职能转变的重点,对于深化我国测绘地理信息行政管理体制改革,促进测绘地理信息事业科学发展具有十分重要的意义。     

双消浪室局部开孔沉箱防波堤反射特性的理论与试验研究

双消浪室局部开孔沉箱防波堤具有低反射、结构受力小、适宜较大水深和工程造价低等优点。为明确双消浪室局部开孔沉箱水动力特性的主要影响因素,采用理论分析和物理模型试验相结合的方法,对规则波和不规则波作用下双消浪室局部开孔沉箱防波堤的反射特性进行研究。基于势流理论,建立规则波和不规则波对局部开孔沉箱防波堤作用的三维解析解,采用二次压力损失边界条件考虑沉箱开孔墙对波浪运动的影响,利用周期性边界条件考虑防波堤结构沿长度方向的周期性变化。开展相应规则波和不规则波物理模型试验,验证理论模型的合理性。通过算例分析,研究不同波浪要素和结构参数对防波堤反射特性的影响。研究表明:双消浪室局部开孔沉箱相对消浪室宽度取值为0.08~0.20,沉箱前墙开孔率大于后墙开孔率时,防波堤在较大波浪频率范围内消波效果显著;当前后墙的开孔率相等时,防波堤反射系数的最小值随着开孔率增大而减小。     

Thermohaline structures across the Luzon Strait from seismic reflection data

A legacy seismic section across the Luzon Strait was reprocessed using the pre-stack depth migration method to reveal thermohaline structures in the water column. Distinct finescale and mesoscale features can be seen from the seismic image. Vertically, reflective patterns are associated with three water layers: upper layer, intermediate layer, and deep layer. The upper layer can be divided into three areas by two opposing weak-to-transparent zones from west to east with individual thicknesses: ～400, 550, and 700 m. They are interpreted as the South China Sea upper water, the Kuroshio water, and the Pacific upper water, respectively, separated by two Kuroshio frontal zones. Internal waves are ubiquitous in the Kuroshio water fluctuating in different amplitudes and wavelengths laterally. The finestructure shows the western Kuroshio front zone is composed of three subparallel blanking zones with an average eastward dipping angle of 2.3°. They are regarded as the well-mixed frontal interfaces developed in and along a multi-frontal frontal zone. The transparent reflection of the intermediate water above the Hengchun is suggestive of a well-mixed layer by the near-bottom turbulence. In the Pacific intermediate water near the eastern mouth of the Bashi Channel, there is an inverted crescent-shaped structure, which is likely associated with the intrusion of the South China Sea intermediate water through the Bashi Channel. These imaged features are consistent with the observed oceanographic phenomena in the region.     

蒙古国塔南凹陷下白垩统铜钵庙组地震反射特征

铜钵庙组是塔南凹陷的重要含油气层位,精细研究其层序地层,有助于进一步对油气藏进行勘探和开发。主要利用地震反射特征,结合单井资料,对铜钵庙组进行了层序界面的识别,并首次在本区对层序内部体系域地震反射特征进行详细研究。铜钵庙组顶、底界面( T3、T5) 为区域不整合面,分别表现为高角度不整合和“上超下剥”的反射特征; 内部以T3--1 为界分为2 个三级层级( SQ1、 SQ2) 。T3--1 为局部不整合面,主要表现为上超。体系域在本区东次凹上部层序SQ2 中发育完整,被首次上超面、末次上超面和顶部的下超面分为LST、TST、HST 和RST。在此基础上分析了铜钵庙组的内部反射结构,认为本区存在5 种主要反射结构,其中,杂乱反射、楔状反射、前积反射地震相出现在山( 陆架) 前地区,代表扇三角洲沉积; 亚平行反射、波状反射代表滨浅湖沉积或三角洲平原沉积; 平行反射位于盆地地堑中心,代表半深湖、深湖沉积。