A multi-frequency Acoustic Concentration and Velocity Profiler (ACVP) for boundary layer measurements of fine-scale flow and sediment transport processes

The use of acoustics to measure sediment transport boundary layer processes has gained increasing acceptance over the past two decades. This has occurred through the development of increasingly sophisticated measuring systems and theoretical developments, which have enabled flow and suspended sediment parameters to be obtained from acoustic data with a high degree of accuracy. Until relatively recently, separate acoustic systems were used to measure flow and suspended sediment concentration. Over the past few years, however, the technology has become sufficiently advanced so that flow and sediment measurements can be integrated into a single system. This integration provides, quasi-instantaneous, non-intrusive, co-located, high temporal-spatial resolution measurements of benthic flow and sediment processes. Here the development of such an instrument, the Acoustic Concentration and Velocity Profiler (ACVP) is described. The theory underpinning its application is outlined, new approaches to velocity de-aliasing and suspended sediment inversion instabilities using multi-frequency capabilities are presented and the application of the system to sediment transport processes over a sandy ripple bed is illustrated. The observations clearly show the value of such instrumentation for studying the dynamical interaction between the bed, the flow and the sediments at and within the bottom boundary layer.     

Outcome regimes of binary raindrop collisions

This study delineates the physical conditions that are responsible for the occurrence of main outcome regimes (i.e., bounce, coalescence, and breakup) for binary drop collisions with a precipitation microphysics perspective. Physical considerations based on the collision kinetic energy and the surface energies of the colliding drops lead to the development of a theoretical regime diagram for the drop/raindrop collision outcomes in the We–p plane (We — Weber number, p — raindrop diameter ratio). This theoretical regime diagram is supported by laboratory experimental observations of drop collisions using high-speed imaging. Results of this fundamental study bring in new insights into the quantitative understanding of drop dynamics, applications of which extend beyond precipitation microphysics. In particular, results of this drop collision study are expected to give impetus to the physics-based dynamic modeling of the drop size distributions that is essential for various typical modern engineering applications, including numerical modeling of evolution of raindrop size distribution in rain shaft.     

关于地震波散射波场属性的基本研究

当地震波传播过程中遇到异常体时往往会在间断点处产生绕射现象,这是识别断层及其他构造的一个重要因素。然而,在实际情况下,绝大多数异常体尤其是金属矿藏,由于其形态并不是规则的,且尺度较小,从而无法产生很好的绕射波,取而代之的却是大量富含介质不规则信息的散射现象.近年来,特别是在金属矿地震勘探中,很多人错误地将散射理解为绕射。通过对一个特殊模型的正演模拟,系统地说明二者之间的差别以及散射波场的一些基本特征。     

近百年来的南极绕极波变化特征

采用2011年发布的20世纪全球大气环流再分析资料,结合长期观测序列,分析了百余年来大气中南极绕极波的强弱变化和传播过程。结果显示,南极绕极波有显著的年代际变化,在1940~1960年和1980~2000年附近出现和活跃,而在其他年代消失。东南太平洋南极绕极波振幅最强,该区域的海气耦合过程可能是绕极波信号增强的关键之一。初步揭示了百年来南极绕极波和南极涛动的对应关系,偏强的南极涛动有利于南极绕极波的出现,但并非决定绕极波产生的唯一因素。     

OPAL不透明度对恒星结构和演化模型的影响

本文利用国际上最新公布的OPAL不透明度表及相应的化学丰度，计算了三颗不同初始质量的星族互恒星的非守恒演化模型，并和过去长期采用的LAOL不透明度的结果进行详细比较，得出以下主要结论：（1）恒星HR图中的演化轨迹光度降低，主序位置明显向红方向移动；（2）恒星中心H，He燃烧寿命大大延长了；（3）小质量星氢燃烧核和对流核都变小，大、中质量星的中心对流核和燃烧核都有所增大；（4）恒星中心温度－密度关系基本不受影响．     

串联F-K加相移插值法偏移

本文介绍的偏移成像方法为递归F-K法、相移插值法及串联偏移技术的有效结合,简称CFPI法.该方法中,波场外推采用相移插值法中递归向下延拓方式,而每一延拓层间的成像则用文中给出的常速F-K加剩余速度F-K偏移,通过与横向速度变化有关的插值来实现,该过程用FFT完成.该方法可采用较大的延拓步长速归向下外推与成像.理论分析及实际计算结果比较表明,该算法效率远高于相移插值法偏移.     

A model of inter-annual variability in beach levels

Beach profile data, collected twice per year at 19 stations over a 25 km length of coastline in Tremadoc Bay, have been analysed to quantify the inter-annual variability in beach levels over a 7 year period and the results compared against the output of a numerical model. Using hourly wind data as forcing, the morphological development of northern Tremadoc Bay was simulated by wave, tidal, longshore transport, total transport and bed level change models. The modelling methodology was efficient and innovative, allowing realistic simulations of long duration with a time step of 1 h, hence capturing the high frequency nature of wind events. The model was run for each of the 7 autumn/winter periods (generally November–April) and the modelled net change in beach levels compared with the data from all 19 stations. The model results had reasonable agreement with the beach profile surveys. However, the observed magnitude of bed level change in the bay lagged the model output by 1 year, indicating that sediment processes acting over a larger area are important in a relatively localised study of inter-annual variability.     

Nonlinear heave radiation forces on two-dimensional single and twin hulls

A study of nonlinear heave radiation of two-dimensional single and double hulls has been carried out in the time domain. The problem is analyzed by means of a fully nonlinear mathematical model, referred to as the mixed Eulerian–Lagrangian (MEL) model, which is based on an integral relation formulation coupled with time-integration of the nonlinear free-surface boundary conditions. The integral equation solver is based on a cubic-spline boundary-element scheme in which both potential and velocity continuity conditions can be enforced through the intersection points. The body undergoes periodic forced heave oscillation. By implementing effective wave-absorbing beaches at the two ends of the rectangular numerical tank, long-term steady-state force-histories could be achieved consistently in all computations.Results in terms of radiation forces for rectangular and triangular single- and twin-hull geometries are presented and discussed. Linear hydrodynamic forces in terms of added-mass and damping are validated for the rectangular hull. The Fourier-analyzed results reveal the extent of nonlinear (higher-order) components in the force-signals over different parameters which include the amplitudes of oscillation, hull-spacing for the twin-hulls and water depth.     

尕海DG03孔元素地球化学特征及其环境意义

通过对柴达木盆地尕海DG03孔沉积物的Ti、V、Cr、Mn、Ni、Zn、C、N等元素含量变化以及m(C)/m(N)、m(Sr)/m(Ba)比值变化的测定,结合DG03孔沉积序列的年代学测定和沉积物分布特征,分析了尕海地区11·52ka BP以来的气候环境变化过程。研究表明尕海地区在11·52ka BP以来存在明显的气候波动;4·70kaBP以来的全新世晚期气候波动频率加大,存在5次较为明显的冷干和暖湿的气候旋回,并且表现出冷干气候时段长,暖湿气候时段短的特征。