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731.
Zbigniew Sorbjan 《Boundary-Layer Meteorology》2006,119(1):57-79
Forced convection in a quasi-steady atmospheric boundary layer is investigated based on a large-eddy simulation (LES) model.
The performed simulations show that in the upper portion of the mixed layer the dimensionless (in terms of mixed layer scales)
vertical gradients of temperature, humidity, and wind velocity depend on the dimensionless height z/z
i
and the Reech number Rn. The peak values of variances and covariances at the top of the mixed layer, scaled in terms of the interfacial scales, are
functions of the interfacial Richardson number Ri. As a result expressions for the entrainment rates, in the case when the interfacial layer has a finite depth, and a condition
for the presence of moistening or drying regimes in the mixed layer, are derived. Profiles of dimensionless scalar moments
in the mixed layer are proposed to be expressed in terms of two empirical similarity functions F
m
and F
i
, dependent on dimensionless height z/z
i
, and the interfacial Richardson number Ri. The obtained similarity expressions adequately approximate the LES profiles of
scalar statistics, and properly represent the impact of stability, shear, and entrainment. They are also consistent with the
parameterization proposed for free convection in the first part of this paper. 相似文献
732.
One-dimensional turbulence (ODT) is a single-column simulation in which vertical motions are represented by an unsteady advective process, rather than their customary representation by a diffusive process. No space or time averaging of mesh-resolved motions is invoked. Molecular-transport scales can be resolved in ODT simulations of laboratory-scale flows, but this resolution of these scales is prohibitively expensive in ODT simulations of the atmospheric boundary layer (ABL), except possibly in small subregions of a non-uniform mesh.Here, two methods for ODT simulation of the ABL on uniform meshes are described and applied to the GABLS (GEWEX Atmospheric Boundary Layer Study; GEWEX is the Global Energy and Water Cycle Experiment) stable boundary-layer intercomparison case. One method involves resolution of the roughness scale using a fixed eddy viscosity to represent subgrid motions. The other method, which is implemented at lower spatial resolution, involves a variable eddy viscosity determined by the local mesh-resolved flow, as in multi-dimensional large-eddy simulation (LES). When run at typical LES resolution, it reproduces some of the key high-resolution results, but its fidelity is lower in some important respects. It is concluded that a more elaborate empirically based representation of the subgrid physics, closely analogous to closures currently employed in LES of the ABL, might improve its performance substantially, yielding a cost-effective ABL simulation tool. Prospects for further application of ODT to the ABL, including possible use of ODT as a near-surface subgrid closure framework for general circulation modeling, are assessed. 相似文献
733.
There are many reports about the research on near-fault velocity pulses, which focus on the generation of velocity pulse and simplify the velocity pulse so as to be used in the seismic design of structure, However few researches have put emphasis on the characteristics of near-fault ground motions containing velocity pulses, especially the characteristics relevant with the design response spectrum prescribed by the code. Through collection of a large number of near-fault records containing velocity pulses, the response spectra and the characteristic periods of records containing no pulses are compared with those of records containing pulses. Response spectra of near-fault records are compared with standard spectra given by code; furthermore, the response spectra and the characteristic periods of each earthquake are compared with that given by code. The result shows that at long periods (longer than 1.5 s), the response spectrum of pulse-containing records is bigger than the response spectrum of no-pulse-containing records; when the characteristic period of near-fault records is calculated, the method that does not fix frequency is more reasonable because the T1 and T2 have a lagging tendency; regardless of the site Ⅰ and site Ⅱ, the characteristic period of pulse-containing records is over twice bigger than the characteristic period given by the code, 相似文献
734.
Wang Sheng-zu 《中国地震研究》2006,20(3):326-338
INTRODUCTIONAccording to the“netlike plastic-flow (NPF)”continental dynamics model ( Wang, 1993a ,1993b; Wang,et al .,2001c) ,the continental lithosphere generally includes 4 tectonic deformationlayers frombottomtotop:the NPFlayer (i .e .thelowerlithosphere ,includingthelithospheric mantleandlower crust) ,the transitional weak layer distributed discontinuously (i .e .the so-called low-velocity/high-conductivitylayer) ,the shear fracturinglayer (i .e .the seismogenic layer inthe upperc… 相似文献
735.
大庆探区外围盆地中、新生代地层对比及四大勘探层系 总被引:5,自引:0,他引:5
大庆外围盆地的区域对比与组合规律研究,对于揭示东北中、新生代盆地演化规律和拓展油气开发思路具有重要意义.利用岩性特征、古生物化石组合、同位素等资料,对大庆探区外围盆地中、新生代地层进行了对比,总结了地层发育的宏观规律,提出了中-上侏罗统、下白垩统、上白垩统和古近系四大勘探层系,为大庆探区外围盆地进一步的沉积、构造演化及石油地质研究提供了可靠的依据. 相似文献
736.
水对不同岩石声波速度影响的研究 总被引:1,自引:0,他引:1
通过分析不同成因类型岩石的声波速度,提出了水对不同岩石声波速度的影响,从岩石孔隙及隐微裂隙的发育程度及岩石的水理性质解释了在水的作用下岩石声波变化规律,利用这些规律可以初步判断岩石的隐微裂隙发育程度及水理性质。 相似文献
737.
738.
在充分分析米脂—绥德岩盐田地质特征的基础上,对位于其中部的米脂姬家峁矿区O2m65亚段盐矿层赋存特征进行了研究,预测了矿区O2m65亚段岩盐资源储量,并对其开采条件进行了评价。 相似文献
739.
A. A. M. Holtslag G. J. Steeneveld B. J. H. van de Wiel 《Boundary-Layer Meteorology》2007,125(2):361-376
At present a variety of boundary-layer schemes is in use in numerical models and often a large variation of model results
is found. This is clear from model intercomparisons, such as organized within the GEWEX Atmospheric Boundary Layer Study (GABLS).
In this paper we analyze how the specification of the land-surface temperature affects the results of a boundary-layer scheme,
in particular for stable conditions. As such we use a well established column model of the boundary layer and we vary relevant
parameters in the turbulence scheme for stable conditions. By doing so, we can reproduce the outcome for a variety of boundary-layer
models. This is illustrated with the original set-up of the second GABLS intercomparison study using prescribed geostrophic
winds and land-surface temperatures as inspired by (but not identical to) observations of CASES-99 for a period of more than
two diurnal cycles. The model runs are repeated using a surface temperature that is calculated with a simple land-surface
scheme. In the latter case, it is found that the range of model results in stable conditions is reduced for the sensible heat
fluxes, and the profiles of potential temperature and wind speed. However, in the latter case the modelled surface temperatures
are rather different than with the original set-up, which also impacts on near-surface air temperature and wind speed. As
such it appears that the model results in stable conditions are strongly influenced by non-linear feedbacks in which the magnitude
of the geostrophic wind speed and the related land-surface temperature play an important role. 相似文献
740.
Numerical weather prediction models are increasingly employed for providing meteorological data for urban air quality applications.
Model resolution, physiographic parameters and surface-layer parameterisations need to be adapted to the requirements of the
urban boundary layer. The Lokalmodell of the German Weather Service was triple-nested down to a horizontal grid resolution
of 1.1 km, urbanised physiographic parameters were implemented, and an additional anthropogenic heat source was introduced.
Results of a sensitivity study for a spring dust episode in Helsinki show a clear urbanisation effect of these measures on
temperature, humidity and the partitioning of surface fluxes, leading to an increased Bowen ratio and heat storage and an
urban heat island effect. 相似文献