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661.
Constant sets for several turbulence closure models,based on data for the atmospheric boundary layer, areproposed. They differ from those currently used inengineering situations but are self-consistent andtuned to represent atmospheric boundary-layerturbulence. The proposed constant sets are tested in a simple,one-dimensional, neutrally-stratified planetaryboundary-layer flow over a horizontally homogeneousand aerodynamically rough flat surface. Comparisons ofmodel results with similarity theory and large-eddysimulation show promise for improving boundary-layerpredictions. 相似文献
662.
通过对大量的实测数据计算统计分析表明:在三、四、五等水准测量时,利用上丝和下丝读数同时参与测站高差的计算以及在内业平差计算时同时顾及各测段之间测站数和距离两者的关系,能有效提高其成果质量。 相似文献
663.
D. Keith Wilson 《Boundary-Layer Meteorology》1997,85(1):35-52
A three-dimensional model for correlation functions and spectra in theatmospheric, convective boundary layer (CBL) is presented. The modelincludes vertical inhomogeneities introduced by eddy-blocking at the ground.By assuming the disturbance to the turbulent flow resulting from the groundblocking is irrotational, an equation is developed which allows one to writethe inhomogeneous, two-dimensional (2D) cross spectra for the blocked flowin terms of the 2D cross spectra for a homogeneous flow. VonKármán's energy spectrum then is used to determine thehomogeneous, 2D cross spectra. Although there are only two adjustableparameters in the model, the variance and a length scale, the model is shownto agree quite well with a diversity of previous results for the CBL. 相似文献
664.
A three-dimensional numerical model of hydrodynamics and water quality in Hakata Bay 总被引:1,自引:0,他引:1
The hydrodynamics and water quality in Hakata Bay, Japan, are strongly affected by the seasonal variations in both the gravitational circulation and the stratification in the bay. The three-dimensional hydrodynamics and water quality model has been developed to simulate the long-term transport and fate of pollutants in the system. The model is unique in that it completely integrates the refined modelling of the hydrodynamics, biochemical reactions and the ecosystem in the coastal areas. It is a 3-dimensional segmented model which is capable of resolving mean daily variations in all the parameters relevant to pollution control. It predicts daily fluctuations in the oxygen content at different depths in water throughout the year. It takes into account transport and settling of pollutant particles. It predicts light penetration from computed turbidity variations. It includes interactions between the ecosystem and water quality, through nutrient cycling and photosynthesis. The model has been calibrated well against the data set of historical water quality observations in Hakata Bay. 相似文献
665.
Estimates of Energy Dissipation Rates in the Three-Dimensional Deep Ocean Internal Wave Field 总被引:2,自引:0,他引:2
Using the “Eikonal Approach” (Henyey et al., 1986), we estimate energy dissipation rates in the three-dimensional Garrett-Munk internal wave field. The total energy dissipation rate within the undisturbed GM internal wave field is found to be 4.34 × 10−9 W kg−1. This corresponds to a diapycnal diffusivity of about 0.3 × 10−4 m2s−1, which is less than the value 10−4 m2s−1 required to sustain the global ocean overturning circulation. Only when the high vertical wavenumber, near-inertial current shear is enhanced can diapycnal diffusivity reach ∼10−4 m2s−1. It follows that the energy supplied at low vertical wavenumbers and low frequencies is efficiently transferred to high vertical wavenumbers and near-inertial frequencies in the mixing hotspots in the real ocean. 相似文献
666.
Tetjana Ross Rolf Lueck 《Deep Sea Research Part I: Oceanographic Research Papers》2005,52(12):2353-2365
Recent work has suggested the possibility of using high-frequency (10 kHz to 1 MHz) acoustics to remotely sense turbulent microstructure in the ocean. Once developed, this technique will provide a powerful tool for examining the spatial and temporal distributions of ocean mixing in a way not possible using traditional microstructure methods. In this paper turbulent dissipation rates are estimated through an inversion of 307 kHz acoustic scattering data collected in the lee of a sill in Knight Inlet, British Columbia. These data have been shown previously to be strongly correlated with temperature and shear microstructure measurements. Here we show that inversion methods can be used to get turbulent dissipation rates from acoustic backscatter, provided that independent measurements of temperature and salinity stratification are available. The temperature–salinity characteristics of the environment, however, can place limitations on the inversion technique. The strong negative salinity gradient in Knight Inlet decreases the slope of the functional relationship between dissipation rate and scattering cross-section for high dissipation rates and increases the uncertainty of the inversion. This limitation on the inversion technique is not an issue throughout most of the world's oceans (where dT/dS>0) and, in places where it could be a problem, the limitation can be overcome by using multi-frequency techniques. 相似文献
667.
Turbulence and zooplankton production: insights from PROVESS 总被引:1,自引:0,他引:1
Zooplankton are directly influenced by turbulence in both a passive and an active manner. Passively, zooplankton are at the mercy of turbulence in how it affects their vertical mixing, encounter rate, detection abilities and feeding current efficiency. Many zooplankton species, however, are actively able to mitigate the effects of turbulence by modifying their behaviour, e.g. vertical migration, prey switching and habituation to hydromechanical stimuli. Both theoretical treatments of these processes and field observations from the northern North Sea are examined. Field observations show that some copepod species actively migrate to avoid high turbulence levels in surface waters. Furthermore, observations show a negative relationship between turbulence and zooplankton ingestion rates. This supports the paradigm of a dome-shaped response for zooplankton production with environmental turbulence. A theoretical treatment shows that the reaction distance, R, for an ambush-feeding copepod feeding on swimming organisms follows R ∝ −1/6 where is the turbulent dissipation rate, a result that shows close agreement with previously reported experimental results. 相似文献
668.
Among well-mixed multi-dimensional Lagrangian stochastic (LS) dispersion models, we observe that those in poorest agreement with observations produce spiralling trajectories, with an associated reduction in dispersion. We therefore investigate statistics of increments d ' to the orientation '= arctan(W'/U') of the Lagrangian velocity-fluctuation vector – as a possible means to distinguish the better LS models within the well-mixed class. Zero-spin models, having d' = 0, are found to provide best agreement with observations. It is not clear however, whether imposition of the zero-spin property selects (in conjunction with the well-mixed condition) a unique model. 相似文献
669.
Multi-phase simulations of turbulent driven flow in a dense medium cyclone with magnetite medium have been conducted in Fluent, using the Algebraic Slip Mixture model to model the dispersed phases and the air-core, and both the Large Eddy Simulation turbulence model (LES) and Reynolds Stress Models (RSM) for turbulence closure. The predicted air-core shape and diameter were found to be close to the experimental results measured by gamma ray tomography. It is possible to use the LES turbulence model with ASM multi-phase model to predict the air/slurry interface accurately. Multi-phase simulations (air/water/medium) show appropriate medium segregation effects but over-predict the level of segregation compared to that measured by gamma ray tomography near the wall. This is believed to be because of unaccounted back-mixing of the dispersed phase due to turbulence in the basic Algebraic Slip Mixture model. The predictions of accurate axial segregation of magnetite medium are investigated using the LES turbulence model in conjunction with the multi-phase mixture model and viscosity corrections according to the feed particle loading factor. At higher feed densities the agreement between the Dunglison [Dunglison, M.E., 1999, A general model of the dense medium cylone, PhD thesis, JKMRC, University of Queensland] correlations and experimental measurements and the CFD is reasonably good, but the overflow density is lower than the model predictions. It is believed that the excessive underflow volumetric flow rates are responsible for under prediction of the overflow density. The effect of size distribution of the magnetite has been fully studied. As expected, the ultra-fine magnetite sizes (i.e. 2 and 7 microns) are distributed uniformly throughout the cyclone. As the size of magnetite increases, more segregation of magnetite occurs close to the wall. 相似文献
670.
Peter Hurley 《Boundary-Layer Meteorology》2007,125(3):525-536
The treatment of turbulence closure in atmospheric models is examined in the context of the dry convective boundary layer
(CBL) and the eddy-diffusivity/mass-flux (EDMF) approach. The EDMF approach is implemented into a model called TAPM to use
a coupled two-equation prognostic turbulence closure and the mass-flux approach to represent turbulence in the CBL. This work
also extends the range of turbulence variables that can be derived from the mass-flux component of the model and uses these
along with their values from the prognostic scheme to provide total turbulence fields that can be used to compare to data
and/or to feed into other components of TAPM, including those needed to drive Eulerian and Lagrangian air pollution dispersion
modules. Model results are presented for the afternoon of a simulated summer day and are compared to both laboratory and field
observations in a mixed-layer scaled framework. The results show that the EDMF approach works well within TAPM and can provide
good predictions of mean and turbulence fields, including in the upper levels of the CBL. The EDMF approach has several attractive
features, including the potential to be one approach to unify the treatment of turbulence and dry and moist convection in
atmospheric models. 相似文献