Assessing impaired benthic communities using sediment toxicity and contaminant concentrations from reference sites inside the Niagara River Area of Concern

Anthropogenically degraded benthic-macroinvertebrate communities (benthos) are one of seven beneficial use impairments (BUIs) in the Niagara River Area of Concern (AOC). Over the last 50 years, upgrades to waste-water treatment, industry closures, and sediment remediations reduced contaminant levels throughout the system. Improvements in benthic communities and sediment toxicity, however, were difficult to assess because there are no comparable reference reaches outside the AOC. A multi-phase study was initiated in 2015 to determine if data from inside the AOC could identify reference conditions, if toxicity and benthic-community data from these sites differed from other AOC sites, and if further remediation efforts were warranted in parts of the AOC. Concentrations or quotients of PAHs, PCBs, dioxins and furans, pesticides, and most metals were below their New York Sediment Class A Guidance Values at 10 sites that were subsequently designated as reference sites. Survival and growth data from Chironomus dilutus and Hyalella azteca bioassays indicated that sediments from only a few individual AOC-impact sites were toxic or significantly different from reference sites, and that mean toxicity at pooled AOC-impact and reference sites did not differ significantly. Similarly, New York Biological Assessment Profile scores and chironomid mentum deformity scores at only a few individual sites differed significantly from corresponding indices at reference sites, but neither metric differed significantly in comparisons between pooled AOC-impact and reference sites. Most analyses indicated that benthic communities were unimpaired and that removal criteria for the benthos BUI were largely met in much of the upper Niagara River AOC.     

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.     

内河航道中船行波在岸坡爬高的数值模拟

该文基于RANS方程、RNG k-ε湍流模型建立数值波浪水池,用VOF法追踪自由面的位置,并模拟了内河航道中船行波的生成、传播、爬高和岸壁反射过程,且与典型断面航道中船行波在岸坡最大爬高和回落的现场测量值进行了比较,验证了数值模型的有效性。通过对航道中船行波进行数值模拟,获得了船行波的波形及其在岸坡上爬高与回落的最大值。分析了船舶吃水、航速和航道岸坡倾角对特征波高以及最大爬高与回落的影响。最后建立了计算船行波特征波高、爬高和回落的经验公式。     

多向聚焦破碎波的实验研究

该文采用两种不同频谱形式(等波陡和等波幅)、不同水深,通过波浪聚焦的方法在水池中产生多向聚焦波和破碎波,实验研究了破碎波的波面特性、破碎波的破碎指标及传播过程中的频谱变化,结果表明频谱形式、水深及方向分布对破碎波浪特性有明显的影响;波浪传播过程中频谱高频部分有明显的变化;波浪破碎过程中的能量损失主要来自波浪频谱高频部分。     

不规则波抛物型缓底坡波动方程

使用Kubo近似，导出了不规则波抛物型缓底坡波动方程的折射绕射联合模型。对不规则波抛物型缓底坡波动方程进行数值模拟，并对结与实验进行比较。不规则波抛物型缓底坡波动方程能很好地描述波浪传播过程中的变化，由此，可以预测波浪在传播过程中受到地形及波浪间相互用作而发生的变化。     

基于SWASH模型的近岸波浪传播变形数值模拟

SWASH模型是一种新型的非静压时域波浪模拟。为了探讨SWASH模型对于解决近岸波浪传播变形问题的适用性,在对其控制方程、边界条件、数值解法等进行介绍的基础上,采用该模型分别模拟了正向规则波、斜向规则波和斜向不规则波入射条件下L形防波堤附近水域的波浪场和波生流场,并与物理试验结果进行对比。结果表明,SWASH模型较好地复演了波浪在近岸区域所发生的浅水变形、折射、破碎,以及堤前反射、堤内绕射等物理现象,波高沿断面的定量分布与试验结果吻合良好,同时较好地模拟了不同波况下防波堤附近水域的波生流场,说明该模型适用于复杂岸线和地形条件下波浪传播变形的数值模拟。     

改进的非线性波传播数值模型的验证和应用

基于吸收入射边界上反射波的方法,并通过将统一边界条件表达式推广到适应不规则波的情况,改进了非线性波传播的数值模型.将利用模型的线性版本(略去非线性项)所计算得到的台阶地形上波浪的反射和透射系数与相应的解析解进行了定量比较.在斜坡地形上数值模拟了不规则波的传播,并将数值结果和物理模型实验值进行了比较.在下游边界分别为开边界和全反射边界的等水深的水槽内数值模拟了不规则波的传播变形,讨论了非线性作用的影响.在侧边界和下游边界均为全反射的固壁边界、二维的等水深水域内,数值模拟了波浪斜向入射时所产生的波浪变形.计算结果表明,对上述各种算例,改进后的非线性波传播数值模型均能进行有效地数值模拟.     

Nearshore-offshore exchanges in multi-basin coastal waters: Observations and three-dimensional modeling in Lake Erie

Nearshore-offshore exchanges through upwelling events and subsequent formation of internal Kelvin waves and coastal-jets are expected in the multi-basin coastal waters of Lake Erie; however, these phenomena have yet to be confirmed in the field or numerically modeled. Here, we demonstrate these physical processes in Lake Erie through extensive field data analysis and high-resolution three-dimensional hydrodynamic modeling. The validated model successfully reproduces dominant physical processes in the offshore and nearshore waters including surface seiches (~14?h), near-inertial waves (~17?h) and upwelling events (5–10?days). We show that upwelling events are the predominant nearshore physical processes, and are energized when winds accelerate the epilimnetic waters to the south, causing the thermocline front to move up into the north shore. After the wind subsides, the elevated thermoclines simultaneously form two separate cyclonically propagating internal Kelvin waves in the central and the eastern basins following by two coastal-jets at phase speeds of 0.22?ms^?1 and 0.37?ms^?1 within 5–15?km off the shoreline, respectively. The predominant south-west winds limit the presence of Kelvin waves only to the northern parts of each basin, where the bathymetry allows, and disappear when shoreline morphology no longer maintain these waves due to nonzero cross-shore transports at the coastal boundary layer. Intrusions of hypolimnetic waters through upwelling events contribute 10–30% to the net cross-shore transport, and are most pronounced in May and June when the offshore thermocline is shallow. The intermittent strong westward nearshore currents by Kelvin waves are in the opposite direction of seasonal eastward currents.     

Kelvin waves in Lake Geneva

The passage of Kelvin waves in Lake Geneva after strong wind events was experimentally investigated in 1987 and 2002 using thermistor chains, current meters and Acoustic Doppler Current Profilers (ADCP) probing the whole water column, including the bottom boundary layer. Characteristics of these internal waves such as period, amplitude, exponential decay with distance from the shore and damping were determined. A significant increase of shear was observed in the thermocline region during the passage of a Kelvin wave crest. The passage of a Kelvin wave crest also led to a well-mixed bottom boundary layer characterized by a logarithmic velocity profile, complying with the so-called “law of the wall” up to an average height of 11 m. A bottom drag coefficient of 2.5 × 10^− 3 was determined from our measurements. We estimated that ~ 70% of the Kelvin wave energy is dissipated in the bottom boundary layer. This study shows that the passage of Kelvin waves energizes the thermocline and near bed region and that this process is of fundamental importance in the dynamics of the nearshore region of mid-latitude large lakes.     

单相与多相介质中弹性波波速相关问题对比研究

从单相介质到双相及三相多孔介质，通过研究Rayleigh波波速与体波波速之间的关系，得到了三种介质下半空间表面Rayleigh波存在所需满足的条件，以及分析了其理论求解过程之间的联系与差异。对由两种不同定义式得到的平面弹性波传播速度进行了理论分析，并以双相多孔介质为例，通过数值计算直观地对两者进行了比较，结果表明：（1）对于快纵波（P1）、剪切波（S），两种传播速度随频率的变化曲线（即弥散曲线）重叠；（2）对于慢纵波（P2）、Rayleigh波，两条弥散曲线分离，两种传播速度在数值上存在一定差异；（3）两者随频率的变化趋势基本一致。弹性波波数虚部与实部的比值的数值计算结果验证了上述结论。     

NUMERICAL SIMULATION OF EXTREME WAVE GENERATION USING VOF METHOD

Numerical simulations of extreme wave generation are carried out by using the Volume Of Fluid (VOF) method. Extreme waves are generated based on wave focusing in a 2-D numerical model. To validate the capability of the VOF-based model described in this article, the propagation of regular waves is computed and compared with the theoretical results. By adjusting the phases of wave components, extreme waves are formed at given time and given position in the computation. The numerical results are compared with theoretical solutions and experimental data. It is concluded that the present model based on the VOF technique can provide acceptably accurate numerical results to serve practical purposes.     

基于CIP法的波物相互作用强非线性数值模拟

极端波浪环境作用下,浮体易发生上浪拍击等强非线性现象,这一问题也是波浪与浮体相互作用研究的难点之一。该文基于高阶CIP(Constrained Interpolation Profile)法,采用THINC(Tangent of Hyperbola for Interface Capturing)数值技术精确捕捉自由液面,建立了二维多相流强非线性数值水槽模型。通过模拟线性波和孤立波的生成、传播过程,对该模型的收敛性、稳定性及造波性能进行了全面的验证与分析。利用该数值模型模拟和分析了极端波浪对浮体的强非线性作用。     

南海东北部陆架波折处潮-地作用激发非线性内波的数值模拟

南海东北部陆架波折处是大振幅内孤立波的频发地带.普遍的观点认为,这些内孤立波主要源自于吕宋海峡处潮流与海脊的相互作用;而对局地潮流-陆架波折相互作用的生成过程了解较少.本文通过一个二维非静力近似海洋数值模式,模拟了南海东北部陆架波折处潮流-地形相互作用激发内波及内波的演化过程,探讨了潮流周期、跃层深度对内波生成过程的影响.研究表明,潮流与地形相互作用能够激发向岸传播的内孤立子波列,证实了该海区内孤立波局地生成的可能性,但是相比于从吕宋海峡处传入的大振幅内孤立波,局地生成的内孤立波振幅要小得多.     

滑坡涌浪垂面二维数值模拟

 根据可压缩流连续方程和Navier-Stokes方程，推导出滑坡涌浪的控制方程，并建立了垂面二维滑坡涌浪数学模型。采用非规则贴体网格有限体积法和显示MacCormack法步进求解方程，并且利用新滩滑坡的相关资料进行了验证。结果表明，模型的计算值与原型观测值吻合较好。     

FREE LONG WAVES INDUCED BY WEAKLY NONLINEAR STOKES WAVES PROPAGATING OVER STRONG AMBIENT CURRENT AND AN UNEVEN BOTTOM

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风对二维极值波作用的数值研究

实际海域中风浪往往共存,当极值波浪出现时,风会对其特性产生很大影响。为了研究风对极值波浪特性的影响规律,该文基于势流理论建立自由水面满足完全非线性边界条件的风浪混合作用数值水槽模型,通过实时模拟造波板运动产生入射波,并基于波群聚焦原理定点产生极值波浪,利用改进的杰弗里斯遮蔽原理(Jeffreys'sheltering mechanism)将风压引入到自由水面动力边界条件中。在时域模拟中,采用混合欧拉-拉格朗日方法追踪瞬时水面,利用格林第二定理建立了边界积分方程,采用高阶边界元方法进行离散求解。通过与已发表实验结果对比验证模型的准确性,进而开展数值实验研究风对极值波浪水动力特性的影响,包括聚焦幅值、聚焦位置和极值波高随风速的变化以及波群聚焦和解焦过程波浪演变特性等。     

Development of a hybrid particle-mesh method for simulating free-surface flows

In this work the feasibility of a numerical wave tank using a hybrid particle-mesh method is investigated.Based on the fluid implicit particle method(FLIP)a formulation for the hybrid method is presented for incompressible multiphase flows involving large density jumps and wave generating boundaries.The performance of the method is assessed for a standing wave and for the generation and propagation of a solitary wave over a flat and a sloping bed.A comparison is made with results obtained with a well-established SPH package.The tests demonstrate that the method is a promising and attractive tool for simulating the nearshore propagation of waves.     

SLOW DRIFT DAMPING FORCE ACTING ON A CYLINDER IN WAVES

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SAR IMAGING SIMULATION OF HORIZONTAL FULLY TWO-DIMENSIONAL INTERNAL WAVES

1. INTRODUCTION The ability of Synthetic Aperture Radar (SAR) to measure ocean waves has been widely proved since the launch of Seasat in 1978[1] Compared with traditional in-situ instruments, SAR is superior for its wide spatial coverage and high spatial…