河口水流、波浪、潮流、泥沙、河床变形二维数学模型

根据河口“波浪掀沙，潮流输沙”的泥沙运动机制，引入“波浪幅射应力”反应波浪对水体和泥沙的驱动力．考虑波浪对底部泥沙作用力、波浪对水流挟沙能力的影响及风场对水流和泥沙运动的影响．同时考虑泥沙粒径大小、水体含盐度、含沙量及水流紊动程度等因素对絮凝沉速的影响．用ＡＤＩ算法求解沿水深平均方程，破开算子法解悬移质不平衡输沙方程及河床变形方程，引入通度概念处理岸滩不规则边界，建立河口水流、波浪、潮流、泥沙、河床变形二维数学模型．通过实测资料及卫星摇感图像对所建数学模型进行检验，表明它可以较好地预测河口泥沙的运动     

AN EXTENDED MODELING OF TIDE-WAVE MOTION

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内孤立波环境下柱体的受力特性

针对以往孤立波对柱体作用研究多只针对柱体的整体受力开展,少有研究精细获取柱体不同部位受力特性的问题,借助三维大涡模拟(LES)数值波浪水槽,通过提取柱周流场及压强分布,得到柱体所受压差阻力及黏滞力的垂向分布,对柱体在孤立波环境中的受力特性进行了分析,并采用多元线性回归分析,构造综合影响参数分析了柱体受力特性,构建了柱体受力系数经验表达式。结果表明:上下层水体中方柱所受压差阻力约分别为圆柱的1.5倍和3.5倍;作用于柱体上的黏滞力比压差阻力小1或2个数量级,可忽略流体的黏性效应;综合影响参数与相对波幅正相关,与上下水深比负相关。     

中国企业人力资本产权变革三次浪潮评析

人力资本股权化是现代企业产权制度变革的基本逻辑和大趋势.如何在实际操作层面解决"两权分离"悖论,不仅是现代公司制度运作和发展的主题,也是中国企业人力资本产权制度变革的逻辑起点、核心问题和主要矛盾.1992年以来,中国企业人力资本产权变革经历了三次浪潮.目前,对于中国企业来说,实现人力资本股权化、稚行股权激励计划,已经不是什么"理论"问题而是如何实际"行动"的问题.基于人力资本产权制度变革积极推行股权激励计划,是未来中国企业必然而明智的战略选择.     

Roll Waves in High Gradient Channels

Abstract

Vedernikov's number quantifies the allowable capacity that can be sustained as a stable uniform flow in a high gradient channel, but it does not provide any guidance to the design of freeboard when roll waves exist. Without considering roll waves, high gradient channels are undersized using the uniform flow approach and fail to maintain design integrity. This paper presents revised design curves to determine the stability of flow in high gradient channels. When the design condition exceeds the limiting condition, roll waves should be considered in design. This study applies the model of moving hydraulic jump to simulate roll waves. It provides estimations for wave heights when Froude number is greater than 1.50.     

NUMERICAL SIMULATION OF PROPAGATION AND BREAKING PROCESSES OF A FOCUSED WAVES GROUP

A two-dimensional numerical wave flume is developed to study the focused waves group propagation and the consequent breaking processes. The numerical model is based on the Reynolds-Averaged Navier-Stokes (RANS) equations, with the standard k-ε turbulence model to simulate the turbulence effects. To track the complicated and broken free-surface, the Volume Of Fluid (VOF) method is employed. The numerical model combines the "Partial Cell Treatment (PCT)" method with the "Locally Relative Stationary (LRS)" concept to treat the moving wave paddle so that various waves can be generated directly in a fixed Cartesian grid system. The theoretical results of the linear and nonlinear waves are used to validate the numerical wave flume firstly, and then a plunging breaking wave created by a focused waves group is simulated. The numerical results are compared to the experimental data and other simulation results, with very good agreements. The turbulence intensity, the flow field and the energy dissipation in the breaking processes are analyzed based on the numerical results. It is shown that the present numerical model is efficient and accurate for studying the waves group generation, the waves packet propagation, and the wave breaking processes.     

BOUSSINESQ MODELLING OF NEARSHORE WAVES UNDER BODY FITTED COORDINATE

A set of nonlinear Boussinesq equations with fully nonlinearity property is solved numerically in generalized coordinates,to develop a Boussinesq-type wave model in dealing with irregular computation boundaries in complex nearshore regions and to facilitate the grid refinements in simulations.The governing equations expressed in contravariant components of velocity vectors under curvilinear coordinates are derived and a high order finite difference scheme on a staggered grid is employed for the numerical implementation.The developed model is used to simulate nearshore wave propagations under curvilinear coordinates,the numerical results are compared against analytical or experimental data with a good agreement.     

VERTICAL DISTRIBUTION OF LONGSHORE CURRENTS OVER PLANE AND BARRED BEACHES

Experiments were conducted to determine the vertical profile of the longshore currents over plane and barred beaches. The logarithmic law is applied to fit the data for the region below the wave trough and an adjusted logarithmic profile without the mass transport velocity is applied to the region above the wave trough. The results indicate that the logarithmic law fits the data well for both plane and barred beaches. The friction velocity and the relative roughness obtained by the data fitting are compared with relevant calculated results.     

Waves and Determinants in Mergers and Acquisitions: The Case of Latin America

This article contributes to the current literature on mergers and acquisitions (M&As) by identifying the existence of waves and the determinants of M&A activity in the economies of Argentina, Brazil, Chile, Colombia, Mexico, and Peru. From a sample of 2,391 M&A announcements reported by Thomson One on these countries, applying the methodology proposed by Harford (2005), evidence of M&A waves is found for the periods 1995–2002 and 2003–2010, as reported for other regions in various international studies. After controlling for economic and business environment variables, as well as for profitability and book-to-market variables at the industry level, we find evidence that supports neoclassical theory as a main explanation for M&A activity but not for the misvaluation effect.     

Vertical oscillations of the thermocline caused by internal waves modify coldwater pelagic fish distribution: Results from a large stratified lake

Fishes typically occupy a species-specific temperature range, with their occupied depth being related to the lake’s temperature profile. When a fish’s preferred temperature range coincides with the thermocline, the location of their preferred thermal habitat is influenced by the rise and fall of internal waves, leading to possible changes in fish depth. These internal waves are common in large, stratified lakes, yet we do not know how they affect the spatial distribution and behavior of freshwater fishes. We conducted nighttime hydroacoustic surveys in a large, deep embayment of a large thermally stratified lake to observe whether pelagic fish respond to vertical oscillations of the thermocline caused by internal waves. The coldwater pelagic fish in our study (primarily cisco, Coregonus artedi) typically occupied a narrow vertical band approximately 5–8 m thick and temperatures between 10.8 ± 0.8–13.6 ± 1.6 °C (fishes sized 106–500 mm), just below the thermocline (centered around 15–17 °C). Importantly, the upper bound of fish depth varied in response to vertical thermocline movements associated with internal waves, suggesting fish respond to changes in their physical environment on timescales commensurate with basin-scale internal wave periods (hours to days), to remain within their preferred thermal habitat. Dissolved-oxygen levels were typically above avoidance thresholds of these fish, thus not likely exerting a strong influence on fish location. Our findings emphasize the need to account for internal waves when designing hydroacoustic and netting surveys, as thermocline movements can influence where fish are located.