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101.
102.
We investigate the relative dispersion properties of the well-mixed class of Lagrangian stochastic models. Dimensional analysis
shows that, given a model in the class, its properties depend solely on a non-dimensional parameter, which measures the relative
weight of Lagrangian-to-Eulerian scales. This parameter is formulated in terms of Kolmogorov constants, and model properties
are then studied by modifying its value in a range that contains the experimental variability. Large variations are found
for the quantity, g* = 2gC0− 1, where g is the Richardson constant. 相似文献
103.
基于空间信息网格(SIG)的矿产资源评价 总被引:2,自引:0,他引:2
随着GIS的普及和深化,空间信息的大数据量、高复杂性和难共享的问题对其研究和应用提出了新的挑战.空间信息网格(Spatial Information Grid,SIG)作为创新性的网络空间信息基础设施和技术体系,为解决这些问题提供了新的契机.本文在给出SIG基本定义和基本特征的基础上,就如何实现基于SIG的矿产资源评价进行了有益的探索和实践,并取得了很好的效果,为矿产资源评价提供了新的方法和思路. 相似文献
104.
Turbulence is one of the most common nature phenomena in everyday experience, but that is not adequately understood yet. This article reviews the history and present state of development of the turbulence theory and indicates the necessity to probe into the turbulent features and mechanism with the different methods at different levels. Therefore this article proves a theorem of turbulent transpor- tation and a theorem of turbulent intensity by using the theory of the nonequilibrium thermodynamics, and that the Reynolds turbulence and the Rayleigh-Bénard turbulence are united in the theorems of the turbulent intensity and the turbulent transportation. The macroscopic cause of the development of fluid turbulence is a result from shearing effect of the velocity together with the temperature, which is also the macroscopic cause of the stretch and fold of trajectory in the phase space of turbulent field. And it is proved by the observed data of atmosphere that the phenomenological coefficient of turbulent in- tensity is not only a function of the velocity shear but also a function of temperature shear, viz the sta- bility of temperature stratification, in the atmosphere. Accordingly, authenticity of the theorem, which is proved by the theory of nonequilibrium thermodynamics, of turbulent intensity is testified by the facts of observational experiment. 相似文献
105.
Wusi Yue Marc B. Parlange Charles Meneveau Weihong Zhu René van Hout Joseph Katz 《Boundary-Layer Meteorology》2007,124(2):183-203
Turbulent flow in a corn canopy is simulated using large-eddy simulation (LES) with a Lagrangian dynamic Smagorinsky model.
A new numerical representation of plant canopies is presented that resolves approximately the local structure of plants and
takes into account their spatial arrangement. As a validation, computational results are compared with experimental data from
recent field particle image velocimetry (PIV) measurements and two previous experimental campaigns. Numerical simulation using
the traditional modelling method to represent the canopy (field-scale approach) is also conducted as a comparison to the plant-scale
approach. The combination of temporal PIV data, LES and spatial PIV data allows us to couple a wide range of relevant turbulence
scales. There is good agreement between experimental data and numerical predictions using the plant-scale approach in terms
of various turbulence statistics. Within the canopy, the plant-scale approach also allows the capture of more details than
the field-scale approach, including instantaneous gusts that penetrate deep inside the canopy. 相似文献
106.
Experimental observation on the characteristics of the near-surface turbulence over the Antarctic ice sheets during the polar day period 总被引:1,自引:0,他引:1
Based on the ultrasonic anemometer/thermometer data in the East Antarctic coastal area ice sheets ob-tained first by Chinese
scientists, turbulent intensity, kinetic energy and sensible heat of turbulence, surface roughness height drag coefficient
and normalized variation were calculated and analysed using the eddy-correlation method. The results show that the values
of roughness height and drag coefficient are 4.3 X 10 m and 1.8x 10 -3, respectively. These turbulent parameters have apparent diurnal variations.
Project supported by the National Natural Science Foundation of China (Grant No. 49675252). 相似文献
107.
We investigate the general properties of supernova driven interstellar turbulence using local three-dimensional MHD simulations under Galactic conditions. Our model includes the effects of large-scale shear due to Galactic differential rotation, density stratification, compressibility, magnetic fields, heating via supernova explosions and parameterized radiative cooling of the interstellar medium. In addition to investigating isolated supernova explosions we allow for multiple supernovae distributed randomly in the Galactic disc and exponentially in the vertical direction. Single supernova explosions drive a strong shock, the lifetime of which is approximately 2 Myr in our model. This stage is found to be characterized by a kinetic energy spectrum in the diffuse gas with spectral index consistent with k = –2. Large-scale shear and Coriolis force act on the supernova remnant producing some vorticity inside it, but this process was found to be very weak. In the case of multiple supernova explosions, older remnants have an important role causing density fluctuations in the interstellar medium. In this clumpy medium, the propagation velocity of the shock fronts changes due to the changing density, and vorticity is generated. In the absence of these supernova interactions the kinetic energy spectrum shows a relatively wide shock spectrum with spectral index k = –2, but when the supernova interactions become dominant the classical k = –5/3 spectrum is observed. 相似文献
108.
We discuss the effects of galactic spiral arms on the -coefficient, turbulent diffusivity and turbulent energy density of the interstellar turbulence. We argue that the -coefficient and the dynamo number are larger in the interarm regions, whereas the kinetic energy density of turbulence is larger in the arms; the turbulent magnetic diffusivity can be only weakly affected by the spiral pattern. 相似文献
109.
G. Rousseau H. Chaté & J. Le Bourlot 《Monthly notices of the Royal Astronomical Society》1998,294(3):373-390
Because a comprehensive microscopic treatment of interstellar molecular clouds is out of reach, an alternative approach is proposed in which most of the crucial ingredients of the problem are considered, but at some 'minimal' level of modelling. This leads to the elaboration of a lattice dynamical system , i.e. a time-dependent, spatially extended, deterministic system of macroscopic cells coupled through radiative transfer. Each cell is characterized by a small set of variables and supports a caricatural chemistry possessing the essential dynamical features of more realistic reaction schemes. This approach naturally precludes quantitative results, but allows heretofore unavailable insights into some of the basic mechanisms at play. We focus on the response of the transfer process and the chemistry to a frozen 'turbulent' velocity field. It is shown that the system settles generically into a state where the effective coupling between cells is neither local nor global, and for which no single length-scale exists. The spectral lines reconstructed from the spatiotemporal evolution of our model may, depending on the velocity field, exhibit profiles ranging from Gaussian to bimodal with strong realization effects. In the bimodal case, the model intrinsically displays an energy cascade transport mechanism to the cells that cool most efficiently: the feedback of chemistry on radiative transfer cannot be neglected. Finally, extensions of this work are discussed and future developments are outlined. 相似文献
110.
给出了正交曲线坐标系下平面二维非恒定动床紊流模型基本方程组,即水流运动方程及潮汐水流不平衡输沙方程。对计算中的有关问题提出了处理方法,如基本资料及代表潮过程选取、糙率的确定、悬沙粒径及沉速、挟沙能力恢复饱和系数及河床冲淤判别条件等。以甬江口为例,计算了镇海弯道至大游山口门约5km河段潮汐水流潮位及流速过程、丁坝作用下的回流域及疏浚与整治相结合的河床变形,计算结果与野外资料吻合良好。在此基础上,计算了宁波大桥桥墩作用下的水流结构变化及对镇海港航道的冲淤影响。 相似文献