The Structure of A Turbulent Jet in A Crossflow-Effect of Jet-Crossflow Velocity

A comprehensive numerical study on the three-dimensional structure of a turbulent jet in crossflow is performed. The jet-to-crossflow velocity ratio (R) varies in the range of 2 - 16; both vertical jets and inclined jets without excess streamwise momentum are considered. The numerical results of the Standard two-equation k-ε model show that the turbulent structure can be broadly categorised according to the jet-to-crossflow velocity ratio. For strong to moderate jet discharges, i.e. R> 4, the jet is characterized by a longitudinal transition through a bent-over phase during which the jet becomes almost parallel with the main freestream, to a sectional vortex-pair flow with double concentration maxima; the computed flow details and scalar mixing characteristics can be described by self-similar relations beyond a dimensionless distance of around 20-60. The similarity coefficients are only weakly dependent on R. The cross-section scalar field is kidney-shaped and bifurcated, vvith distinct double concentr     

珠江口水域化学耗氧量、溶解氧、无机磷与有机磷的三维水质数学模拟

珠江沿岸城市排污量大,对污染源治理能力十分有限,大量污染物通过河流或直接排放到珠江口,河口区半封闭的地形及潮水顶托使得污染物不易输送出外海,致使珠江口水质恶化,原有海洋生态环境遭到破坏,反过来制约了经济的发展.     

Hydrodynamic modeling of flushing time in a small estuary of North Bay, Florida, USA

Freshwater fraction method is popular for cost-effective estimations of estuarine flushing time in response to freshwater inputs. However, due to the spatial variations of salinity, it is usually expensive to directly estimate the long-term freshwater fraction in the estuary from field observations. This paper presents the application of the 3D hydrodynamic model to estimate the distributions of salinity and thus the freshwater fractions for flushing time estimation. For a case study in a small estuary of the North Bay in Florida, USA, the hydrodynamic model was calibrated and verified using available field observations. Freshwater fractions in the estuary were determined by integrating freshwater fractions in model grids for the calculation of flushing time. The flushing time in the North Bay is calculated by the volume of freshwater fraction divided by the freshwater inflow, which is about 2.2 days under averaged flow conditions. Based on model simulations for a time series of freshwater inputs over a 2-year period, a power regression equation has been derived from model simulations to correlate estuarine flushing time to freshwater inputs. For freshwater input varying from 12 m³/s to 50 m³/s, flushing time in this small estuary of North Bay changes from 3.7 days to 1.8 days. In supporting estuarine management, the model can be used to examine the effects of upstream freshwater withdraw on estuarine salinity and flushing time.     

Coastal geomorphic evolution at the Denglou Cape, the Leizhou Peninsula

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层结流体中的非线性惯性重力内波

根据地球流体力学基本方程组,在密度垂直层结的情况下,引进行波坐标,研究非线性定形波在相平面上的几何拓扑结构。严格论证了不存在定形孤立波,并通过Ｈａｍｉｌｔｏｎ函数及其角作用变把行波系统化成最简形式,由此而得到非线性惯性重力内波的解析解。     

灰色关联分析法在海洋环境质量评价中的应用

介绍了灰色关联分析法的原理,说明了其评价步骤。以青岛某海区海水水质评价为例阐明了该方法在海洋环境评价中的应用,并将评价结果与模糊综合评价结果加以比较,结果表明,两种评价方法的评价结果有着较明显的差别,分析了原因。本文还提出了海水污染防治措施,为海洋环境保护提供依据。     

海洋环境荷载下输液立管的静、动力特性研究

考虑管内流动流体和管外海洋环境荷载共同作用 ,建立海洋立管侧向运动微分方程。用Hermite插值函数离散 ,在微机上编写海洋立管静、动力分析程序 ,通过计算分析研究管内流体对立管侧向变形和应力的作用 ;另外 ,探讨管内流体的流动速度和立管顶端的预张力对立管动力特性的影响。结果表明 ,立管变形和应力均随管内流体流动速度增加而增大 ,同时内流速度的增大会降低立管的固有频率 ,但适当增大立管顶端预张力会抵消内流流速增加引起的固有频率下降。     

Correspondence between the distribution of hydrodynamic time parameters and the distribution of biological and chemical variables in a semi-enclosed coral reef lagoon

Hydrodynamic modeling can be used to spatially characterize water renewal rates in coastal ecosystems. Using a hydrodynamic model implemented over the semi-enclosed Southwest coral lagoon of New Caledonia, a recent study computed the flushing lag as the minimum time required for a particle coming from outside the lagoon (open ocean) to reach a specific station [Jouon, A., Douillet, P., Ouillon, S., Fraunié, P., 2006. Calculations of hydrodynamic time parameters in a semi-opened coastal zone using a 3D hydrodynamic model. Continental Shelf Research 26, 1395–1415]. Local e-flushing time was calculated as the time requested to reach a local grid mesh concentration of 1/e from the precedent step. Here we present an attempt to connect physical forcing to biogeochemical functioning of this coastal ecosystem. An array of stations, located in the lagoonal channel as well as in several bays under anthropogenic influence, was sampled during three cruises. We then tested the statistical relationships between the distribution of flushing indices and those of biological and chemical variables. Among the variables tested, silicate, chlorophyll a and bacterial biomass production present the highest correlations with flushing indices. Correlations are higher with local e-flushing times than with flushing lags or the sum of these two indices. In the bays, these variables often deviate from the relationships determined in the main lagoon channel. In the three bays receiving significant riverine inputs, silicate is well above the regression line, whereas data from the bay receiving almost insignificant freshwater inputs generally fit the lagoon channel regressions. Moreover, in the three bays receiving important urban and industrial effluents, chlorophyll a and bacterial production of biomass generally display values exceeding the lagoon channel regression trends whereas in the bay under moderate anthropogenic influence values follow the regressions obtained in the lagoon channel. The South West lagoon of New Caledonia can hence be viewed as a coastal mesotrophic ecosystem that is flushed by oligotrophic oceanic waters which subsequently replace the lagoonal waters with water considerably impoverished in resources for microbial growth. This flushing was high enough during the periods of study to influence the distribution of phytoplankton biomass, bacterial production of biomass and silicate concentrations in the lagoon channel as well as in some of the bay areas.     

Internal wave eigenmodes and their weak nonlinear resonant interaction in a nonlinearly stratified fluid—A preliminary theoretical and experimental study

A preliminary theoretical and experimental study was conducted on internal wave modes and their weak nonlinear resonant interaction in a nonlinearly stratified fluid. An asymptotical solution of the modes and a dispersion relation of internal waves in a stratified fluid with density profile similar to that in our experiment were obtained theoretically. The resonant-interaction mechanism to 2nd order approximation is also discussed. The resonant interaction of the 3rd and 4th mode internal waves excited by the unstable 1st mode wave is analyzed on the basis of data obtained by conductivity probes. The resonant-interaction condition, i.e., ,k ₁+k ₃+k ₄=0, is examined. It is shown that the resonant instability increases with pycnocline thickness and wave maker driving frequency. This work is supported by the National Natural Science Foundation of China.     

第二次土地调查建库过程中数据质量的控制方法

第二次全国土地调查工作正在广泛开展,其中数据库如实、高效、精确的建立是最主要的任务,而数据质量控制程度的高低直接影响了数据库的建设状况。本文以山西省大同市新荣区为例简要叙述了本次土地利用现状调查数据质量的误差来源及影响因素,同时针对这些问题提出了各阶段的数据质量控制方法与措施,从而对本次土地调查建库过程中的数据质量控制方法进行了探究。