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81.
采用变量代换的方法,处理水波的自由边界,获得了新的水波控制方程和边界条件。以摄动法解非线性偏微分方程的近似解析解,求得了与三阶斯托克斯波略有差别的非线性波面和包含振幅的非线性水波色散关系,并且得出了二阶以上的波动势函数在深水情况下不为零的结论。 相似文献
82.
Southern resident killer whales in British Columbia and Washington are exposed to heavy vessel traffic. This study investigates their exposure to exhaust gases from whale-watching vessels by using a simple dispersion model incorporating data on whale and vessel behavior, atmospheric conditions, and output of airborne pollutants from the whale-watching fleet based on emissions data from regulatory agencies.Our findings suggest that current whale-watching guidelines are usually effective in limiting pollutant exposure to levels at or just below those at which measurable adverse health effects would be expected in killer whales. However, safe pollutant levels are exceeded under worst-case conditions and certain average-case conditions. To reduce killer whale exposure to exhaust we recommend: vessels position on the downwind side of whales, a maximum of 20 whale-watching vessels should be within 800 m at any given time, viewing periods should be limited, and current whale-watch guidelines and laws should be enforced. 相似文献
83.
Following the collapse of the New York World Trade Center (WTC) towers on September 11, 2001, Local, State, and Federal agencies initiated numerous air monitoring activities to better understand the ongoing impacts of emissions from the disaster. The collapse of the World Trade Center towers and associated fires that lasted for several weeks resulted at times in a noticeable plume of material that was dispersed around the Metropolitan New York City (NYC) area. In general, the plume was only noticeable for a short period of time following September 11, and only apparent close to the World Trade Center site. A study of the estimated pathway which the plume of WTC material would likely follow was completed to support the United States Environmental Protection Agency’s 2002 initial exposure assessments. In this study, the WTC emissions were simulated using the CALMET-CALPUFF model in order to examine the general spatial and temporal dispersion patterns over NYC. This paper presents the results of the CALPUFF plume model in terms of plume dilution and location, since the exact source strength remains unknown. Independent observations of PM2.5 are used to support the general dispersion features calculated by the model. Results indicate that the simulated plume matched well with an abnormal increase (600–1000% of normal) in PM2.5 two nights after the WTC collapse as the plume rotated north to southeast, towards parts of NYC. Very little if any evidence of the plume signature was noted during a similar flow scenario a week after September 11. This leads to the conclusion that other than areas within a few kilometers from the WTC site, the PM2.5 plume was not observable over NYC’s background concentration after the first few days. 相似文献
84.
A barrier system based on the hydraulic trap design concept for a landfill was proposed. To study the field scenario in which
a clay liner is underlain by a granular layer functioning as a secondary leachate drain layer, a laboratory advection–diffusion
test was performed to investigate factors controlling the transport of contaminants in a two-layer soil system. The soils
used for this study were Ariake clay and, the underlying layer, Shirasu soil from the Kyushu region of Japan. Potassium (K+) was selected as the target chemical species with an initial concentration of 905 mg L−1. The effective diffusion coefficients (D
e) of K+ for Ariake clay and Shirasu soil were back-calculated using an available computer program, Pollute
V 6.3. Values of D
e derived from this experiment are consistent with previously published ones. The Ariake clay has lower D
e than the Shirasu soil. The hypothesis that mechanical dispersion can be considered negligible is reasonable based on both
the observation that the predicted values well fit the experimental data and the analyses of two dimensionless parameters.
Parametric analyses show that transport of K+ through soils is controlled by advection–diffusion rather than diffusion only, whereas at low Darcy velocity (i.e., ≤10−9 m s−1), transport of K+ will be controlled by diffusion. Applications of the test results and parametric analysis results in practical situations
were reviewed. 相似文献
85.
Large-eddy Simulation of the Dispersion of Solid Particles in a Turbulent Boundary Layer 总被引：2，自引：2，他引：2
Ivana Vinkovic Cesar Aguirre Michel Ayrault Serge Simoëns 《Boundary-Layer Meteorology》2006,121(2):283-311
A large-eddy simulation (LES) with the dynamic Smagorinsky-Germano subgrid-scale (SGS) model is used to study the dispersion of solid particles in a turbulent boundary layer. Solid particles are tracked in a Lagrangian way. The instantaneous velocity of the surrounding fluid is considered to have a large-scale part (directly computed by the LES) and a small-scale part. The SGS velocity of the surrounding fluid is given by a three-dimensional Langevin model written in terms of SGS statistics at a mesh level. An appropriate Lagrangian correlation time scale is considered in order to include the influences of gravity and inertia of the solid particle. Inter-particle collisions and the influence of particles on the mean flow are also taken into account. The results of the LES are compared with the wind-tunnel experiments of Nalpanis et al. (1993 J Fluid Mech 251: 661–685) and of Tanière et al. (1997 Exp in Fluids 23:463–471) on sand particles in saltation and in modified saltation, respectively. 相似文献
86.
基于有关粗糙界面的Rayleigh假设，讨论了平面声波按余弦规律快速变化的小尺度粗糙界面上的反射特征.研究表明：这类界面与位于该位置的一个过渡地层的作用相当.该过渡层的厚度为粗糙界面的起伏幅度，速度和密度为上下两层介质相应量的平均值.研究了埋藏很深的微粗糙界面所引起的地震反射（绕射）波的频散特性和走时的构成，即包含零炮检距反射时间、正常时差和界面粗糙时差三部分内容.该粗糙时差与空间坐标和时间坐标无关，与绕射波的阶次有关，绕射波尾随在反射波之后以某一固定的时差出现.且只有当界面的粗糙波长与地震波的波长相当时，才能观测到这类绕射波.该结论为粗糙界面地震反射资料的处理方法提供了理论依据. 相似文献
87.
在计算面波频散问题的广义反射-透射系数方法基础上研究了含有低速层的均匀平层固体地球模型的面波的频散曲线以及简正振型的计算问题. 当不存在低速层时，仅利用陈晓非1993年提出的单一的久期函数对求解这两个问题已经足够. 但是当模型中存在低速层时，该单一久期函数在数值求解较低阶模式很困难. 本文提出用久期函数族代替该单一久期函数、对不同的简正振型模式采用对应的久期函数来求解的方法，从而更加容易有效地求解较低阶的模式，完善了利用广义反射-透射系数方法求解面波频散问题的理论和算法. 相似文献
88.
89.
Simultaneous measurement of coupled water, heat, and solute transport in unsaturated porous media is made possible with the multi-functional heat pulse probe (MFHPP). The probe combines a heat pulse technique for estimating soil heat properties, water flux, and water content with a Wenner array measurement of bulk soil electrical conductivity (ECbulk). To evaluate the MFHPP, we conducted controlled steady-state flow experiments in a sand column for a wide range of water saturations, flow velocities, and solute concentrations. Flow and transport processes were monitored continuously using the MFHPP. Experimental data were analyzed by inverse modeling of simultaneous water, heat, and solute transport using an adapted HYDRUS-2D model. Various optimization scenarios yielded simultaneous estimation of thermal, solute, and hydraulic parameters and variables, including thermal conductivity, volumetric water content, water flux, and thermal and solute dispersivities. We conclude that the MFHPP holds great promise as an excellent instrument for the continuous monitoring and characterization of the vadose zone. 相似文献
90.