APPLICABILITY OF SEDIMENT TRANSPORT FORMULAS

1 INTRODUCTIONThe selection of aPPropriate sediment transport fOrmulas under different flow and sedfornt conditions isimPoftant tO the sedimen tusPort and river morphologic stUdies of a river. There are numrousWlas published in professional joumals and summarized in sediment transPort texthooks. Mosttextbooks shy away from direct comPallsons of the accuracies of transPort formulas. ComPllted resultsbased on differnt transport formulas may differ significanly from each other and from …     

热力学基本关系式和化学势及过程的不可逆性浅析

本文从可逆过程有最大功出发，分析热力学基本关系式的适用体系，说明了化学势和过程不可逆性的物理意义。     

秦巴地区次生金异常地表含矿性判别及矿体定位估算

在分析金粒在水系中运移、落淤和在土壤中扩散动力条件的基础上,本文建立了五万分之一水系沉积物测量金异常地表含矿性的判别公式,阐述了推算异常内矿石最高金品位的方法并计算了秦巴地区的判别指数;总结出万分之一土壤测量矿致金异常的标志特征、矿体定位的估算公式及各级次地形坡度角的系数和常数。这些公式、方法,有较大的实用意义。     

Finite-element computation of wave impact load due to a violent sloshing

A nonlinear sloshing problem is numerically simulated. During excessive sloshing, the sloshing-induced impact load can cause a critical damage on the tank structure. Recently the problem becomes an important research topic in LNG (Liquefied Natural Gas) Tanker and FPSO (Floating Production Storage Offloading) design. In this study, the wave impact load on the structure is obtained numerically by imposing the exact nonlinear free surface conditions and compared with that predicted by Morison's formula. As a theoretical model, a three-dimensional free surface flow in a tank is formulated in the scope of potential flow theory with the exact nonlinear free-surface conditions. A finite-element method based on Hamilton's principle is employed as a numerical method. The problem is treated as an initial-value problem. The nonlinear problem is numerically solved through an iterative scheme at each time step.     

Numerical Study on Breaking Criteria for Solitary Waves

Studies of the breaking criteria for solitary waves on a slope are presented in this paper. The boundary element method is used to model the processes of shoaling and breaking of solitary waves on various slopes. Empirical formulae that can be used to characterize the breaking of solitary waves are presented. These include the breaking index, the wave height, the water depth, and the maximum particle velocity at the point of breaking. Comparisons with the results of other researches are given.     

任意曲线边界条件下缓变水深水域波浪传播的数值模拟

缓坡方程被广泛地应用于描述波浪的传播变形计算,目前一般采用矩形网格求解.将计算域剖分为任意四边形网格,以格林公式为基础,在变量沿单元边界线性变化的假定下,对双曲型的波能守恒方程、波数矢无旋性方程进行离散,同时通过等参单元变换推求节点偏导数值以离散椭圆型光程函数方程,从而建立了任意曲线边界条件下缓变水深水域波浪传播的数值模拟模型.将模型应用于平行直线型等深线地形,并将计算域剖分为不规则四边形网格,对不同入射角、底坡、波高等多种组合情况比较了数值解与解析解,结果表明两者一致.应用于复杂边界的实例,数值模拟结果与物模实验值基本吻合.     

风浪场波生横向彻体切应力的分析

使用风浪经验公式和风浪传入近岸的小振幅波动理论计算并分析了地转条件下波生横向彻体切应力随风速、风区、水深等因素的变化规律。结果表明，彻体切应力随风速、风区的增大而增大，直到波浪达到完全成长状态，但增长速度并不规则；为更加直观的显示彻体切应力的海流驱动作用，将其与定常Ekman漂流中的风生湍粘性力进行了有意义的比较，结果表明，在中、高纬度的通常海况下两者具有相同量级，因此，在有波浪场存在的条件下，由风、浪共生海流的总体强度将比理论Ekman漂流大，并且不会完全符合Ekman漂流理论的转向规律，在表层尤其明显。由此说明，在一定情况下在风生漂流研究中考虑由地转引起的波生横向彻体切应力是非常必要的。     

河道水位流量预报方法研究

论述了加里宁-米尔加科夫洪水演进方法，通过“虚设下游断面”的概念和变特征河长演进的思路将其改进。结合洪水波的运动波近似值，建立了河道洪水流量和水位预报方法。将该方法用于小清河干流济南城区规划河段，得到了孟家节制闸处的洪水流量和水位变化过程，为河道的规划设计和防洪调度提供了决策依据。     

Along-wind dispersion of puffs released in a built-up urban area

The SF₆ gas tracer observations for puffs released near the ground during the Joint Urban 2003 (JU2003) urban dispersion experiment in Oklahoma City have been analysed. The JU2003 observations, at distances of about 100–1,100 m from the source, show that, at small times, when the puff is still within the built-up downtown domain, the standard deviation of the concentration time series, σ_t, is influenced by the initial puff spread due to buildings near the source and by hold-up in the wakes of large buildings at the sampler locations. This effect is parameterised by assuming an initial σ_to of about 42 s, leading to a comprehensive similarity formula: σ_t = 42 + 0.1t. The second term, 0.1t, is consistent with an earlier similarity relation, σ_t = 0.1t, derived from puff observations in many experiments over rural terrain. The along-wind dispersion coefficient, σ_x, is assumed to equal σ_t u, in which u is the puff speed calculated as the distance from the source to the sampler, x, divided by the time after the release that the maximum concentration is observed at the sampler. σ_x can be expressed as σ_x = σ_xo + 0.14x, with the initial σ_xo of 45 m. This initial σ_xo agrees with the suggestion of an initial plume spread of about 40 m, made by McElroy and Pooler from analysis of the 1960s’ St. Louis urban dispersion experiment. The puff speeds, u, are initially only about 20% of the observed wind speed, averaged over about 80 street-level and rooftop anemometers in the city, but approach the mean observed wind speed as the puffs grow vertically. The scatter in the σ_t data is about ± a factor of two or three at any given travel time. The maximum σ_t is about 250 s, and the maximum duration of the puff over the sampler, Dt, sometimes called the retention time, is about 1,100 s or 18 min for these puffs and distances.     

19562000年中国潜在蒸散量变化趋势

利用1956²000年全国580个气象站的逐月气候资料,采用FAO推荐的彭曼-孟蒂斯公式计算潜在蒸散量,对中国及十大流域这45年的潜在蒸散量时空分布特征和变化趋势进行了分析,并采用偏相关分析方法,对造成潜在蒸散量变化的主要气候影响因子进行了探讨。结果表明:45年中除松花江流域外,全国绝大多数流域的年和四季的潜在蒸散量均呈现减少趋势,南方各流域（西南诸河流域除外）年和夏季潜在蒸散量减少趋势尤其明显。1980²000年和1956¹979年两时段多年平均年潜在蒸散量差值表明,我国大部地区1980²000年时段较前一时段减少,山东半岛、黄河和长江源区、西南诸河的中西部以及宁夏等地则增多。分析还表明,全国及大多数流域的年和四季潜在蒸散量与日照时数、风速、相对湿度等要素关系密切,但这45年日照时数和/或风速的明显减少可能是导致大多数地区潜在蒸散量减少的主要原因。