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1.
In this paper, we have attempted a diagnostic study of the turbulence characteristics of the ABL by means of two one-dimensional models. The first model uses a first order non-local closure, based on the Transilient Turbulence Theory, for parameterizing turbulent fluxes. while the second model uses second order local closure for parameterizing these. The models have been applied to conduct case studies using the Kytoon data taken at Kharagpur, during 17th–21st June, 1990, as part of the MONTBLEX programme. Our findings bring out various interesting features regarding the non-local and local turbulent statistics such as kinematic fluxes, turbulence kinetic energy, vertical velocity variance, the contribution of the eddies of various sizes to the fluxes at different level and the mixing lengths. The one-dimensional anisotropy of the turbulent eddies has been revealed by the findings from the transilient model. The vertical variation of the turbulence kinetic energy, as computed directly by the second order model, is found to be strongly correlated with the vertical velocity variance. In particular, for stably stratified boundary layers, identification of two distinct zones of the turbulence kinetic energy and corresponding vertical velocity maxima is possible, which has been interpreted as positive evidence of patchy turbulence in the boundary layer. 相似文献
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运用Micro ADV测速系统,对3种工况下滩地植被化的复式断面横流环境中三维圆形水平射流的特性进行了试验研究.试验测得的射流典型横断面速度场及湍动能的成果表明,射流与来流的相互作用表现出明显的分叉现象,其分叉半角为5.71°;复式断面二次流具有加速射流分叉的作用,滩地植被具有减缓射流分叉的效应.对射流出口平面的速度场及湍动能的分析表明,射流轨迹曲线的弯曲程度、射流中心线的位置主要取决于射流与来流流速比.流动横断面流速和湍动能特性表明,射流在整个流场中是各向异性的. 相似文献
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This paper deals with eddies generated by a shear flow instability in the tidal Potomac River, Maryland-Virginia, USA. An
evolution sequence of this robust phenomenon is synthesized using ASTER and Landsat visible imagery, and its growth from small-amplitude
waves into mature eddies is shown. Using feature tracking between two nearly contemporaneous ASTER and Landsat images, an,
along-river surface velocity profile is computed. Archived velocity and density profiles, taken during accelerating ebb at
locations up-river and down-river of the study area indicate the water column is relatively homogenous up-river, but resembles
a two-layer fluid down-river where estuarine stratification is present in the lower water column. Velocity variation with
depth in the upper water column is relatively small, deviating at mid depth from the near-surface value by only 9–15% at both
sites. We examined the horizontal stability properties of this flow by modeling it as inviscid and barotropic., and predicted
rapidly growing unstable waves with wavelengths close to the observed ones. Their proximity to the coast, as well as the precise
details of the coastline configuration, are shown to have a negligible effect in determining the observed unstable wavelengths. 相似文献
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采用三维湍流模型及其混合有限分析解法进行横流中湍射流这一复杂三维流动的研究。在利用实验数据对模型及其计算方法验证的基础上,对多种喷口形式和流速比工况下的流速场和涡量场进行了数值计算,模拟得到了其旋涡结构发展演化特性。在射流初始阶段,横流在射流背流面形成绕流分离旋涡,其结构与射流喷口形式和流速比有关。射流主轴沿流向布置的窄缝射流产生的旋涡最为特殊和复杂,在喷口侧面存在4个分离点,从而形成4个旋涡。在射流远区,流动主要由反向旋转涡对所控制,并诱导出二次涡对。分析得出了射流喷口形式及流速比对反向旋转涡对涡核位置和旋转强度的影响。 相似文献
8.
Mesoscale eddies, which are widely found in the oceans, play a vital role in momentum, energy, heat and mass transport. The Euler method for identifying mesoscale eddies using satellite altimeter data was presented in detail, including closed SLA contours, OW numbers, Winding-Angle and flow vector methods. The results show that mesoscale eddies are almost nonlinear and solid-body rotation. The long-lived eddies with lifetimes ≥16 weeks have an average lifetime of 32 weeks and an average propagation distance of 550 km. Their mean amplitude and a speed-based radius scale as defined by the automated procedure are 8 cm and 90 km, respectively. The method combining with SLA and Argo profiles to composite the three-dimensional structure were addressed. Due to the different temperature and salt structure in the various oceans of the world, the eddies in different oceans show different three-dimensional structures, which are influenced by both the generation and local temperature and salinity. Two special types of eddies were introduced from the perspective of generation, evolution and dissipation processes, namely the Loop Current Ring in the Gulf of Mexico and Mediterranean eddy in the Atlantic Ocean. Finally, issues including submesoscale processes, dissipation of eddies and subthermocline eddies were discussed, and some future research directions were proposed. 相似文献
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利用回归模型模拟卫星跟踪海洋漂流浮标轨迹 总被引：5，自引：1，他引：4
分析浮标漂流速度和表层地转流、风海流结果表明：浮标漂流速度和表层地转流具有良好相关性。针对卫星跟踪漂流浮标运动的准地转性,建立了以海表地转流为主要回归自变量的几种回归模型,用以模拟浮标漂流轨迹,以期对浮标运动特性有进一步的认识。对南海中伴随涡旋运动的2个浮标模拟试验显示,诸多模型中以海表地转流、风海流及背景流为自变量的回归模型模拟浮标漂流轨迹效果较好。利用该回归模型,模拟出南海2个漂流浮标轨迹和真实轨迹距离偏差较小且二者运动趋势基本一致。通过分析回归模拟所得风海流、海表地转流及背景流发现：涡旋中心附近浮标漂移主要受地转流的控制,而涡旋边缘处风海流起到关键性作用,正是这部分贡献使得浮标能够进入（脱离）涡旋。背景流的空间分布决定着浮标漂移的最终去向,特别是背景流方向改变的区域,背景流的存在使得模拟浮标轨迹能够像真实轨迹一样运移。 相似文献
10.
以k-ε紊流模型为基础,针对浅水环境垂向射流的水面会有明显突起情况,采用VOF(Volume of Fluid)方法追踪自由面,建立了适合浅水环境垂向平面紊动射流的二维数学模型.对不同入射速度、水深、入射口宽度组合进行了大量的数值模拟实验,对整个流场的分布作了分析,发现自由面的分布特点和速度矢量场的分布特点相对应;中轴线附近的自由面隆起具有自相似性,文中给出了拟合表达式;由于水面的阻滞,中轴线上垂向速度的衰减较自由射流快,衰减规律随水深和射流宽度而异. 相似文献
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Finite element cavity expansion analysis investigating the effect of penetration rate on piezocone tests in clay is presented. A coupled analysis was performed, in which the rate of cavity expansion was linked to the penetration rate of the cone and the cone angle, using the assumption that the deformation was wholly radial, and took place only between the cone tip and the cone shoulder. The soil was modelled using modified cam clay with two sets of parameters and varying values of overconsolidation ratio (OCR). The influence of penetration rate on the stress and pore pressure distributions was examined. For slower penetration rates, the excess pore pressure at the cone shoulder is lower since consolidation is permitted coincident with penetration. The radial profiles of post‐penetration voids ratio demonstrate that partially drained penetration is permitted by volume change in the near field, in addition to radial movement in the far field. The radial distribution of excess pore pressure after slow penetration differs from the undrained case, with a relatively low radial gradient existing at the cone face. As a result, the dissipation curves after slow penetration lag behind those following fast penetration. The cone velocity is made dimensionless by normalizing with the coefficient of consolidation and the cone diameter. ‘Backbone’ curves of normalized velocity against normalized tip resistance and excess pore pressure capturing the transition from undrained to drained penetration are derived. The normalized pore pressure backbone curve is unique, whilst the normalized tip resistance shows a small dependency on OCR. These backbone penetration curves are compared with centrifuge model piezocone tests conducted at varying rates, and subsequent dissipation tests. The numerical and experimental results suggest that the value of consolidation coefficient operative during the dissipation phase is 2–4 times higher than the virgin compression value due to changes in the operative soil stiffness, as demonstrated from the stress paths of individual soil elements. The use of multi‐rate penetration tests to deduce values of consolidation coefficient is discussed, in light of these differences. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
13.
In order to capture the influence of the cavity expansion velocity, this paper presents a semianalytical solution for dynamic spherical cavity expansion in modified Cam Clay (MCC) soil. The key problem is solving the six coupled partial differential equations (PDEs) of cavity expansion, in which the dynamic term is considered in the stress equilibrium equation. The similarity transformation technique is used to transform the PDEs into ordinary differential equations (ODEs). Subsequently, the numerical method using the function “ODE45” in MATLAB is selected to solve the ODEs, which allows the stress and excess pore pressure around the expanding spherical cavity wall to be obtained. The proposed semianalytical solution for dynamic spherical cavity expansion was validated by comparting the degenerate solution with the published quasistatic solution for the MCC model. Parametric study was then conducted to capture the influence of the cavity wall velocity on the cavity expansion response. The proposed solution has potential application to geotechnical problems such as dynamic pile driving, the dynamic cone penetration test, and so forth. 相似文献
14.
On the influence of spatial heterogeneity on an internal boundary layer at a short fetch 总被引：1，自引：0，他引：1
B. S. Murthy R. Latha Cini Sukumaran A. Shivaji S. Sivaramakrishnan 《Journal of Earth System Science》2009,118(1):61-70
Surface layer meteorological data collected at a coastal site, at Vasco-Da-Gama (15°21′N, 73°51′E, 58.5m MSL) (13–18 July,
2002) with prevailing southwesterly surface winds are analyzed to study the characteristics of internal boundary layer at
a short fetch using an instrumented tower (9 m). The spectral and turbulence characteristics of wind are compared with earlier
measurements made at a comparatively homogeneous terrain and the standards available in literature. The study show the smaller
eddies in the vertical velocity spectrum attains equilibrium with the underlying surface at a short fetch itself and follows
spectral similarity. However, this is not followed by longitudinal and transverse velocity spectra under unstable as well
as stable conditions. 相似文献
15.
B. N. Goswami 《Journal of Earth System Science》1985,94(3):219-235
A zonally averaged version of the Goddard Laboratory for Atmospheric Sciences (GLAS) climate model is used to study the sensitivity of the northern hemisphere (NH) summer mean meridional circulation to changes in the large scale eddy forcing. A standard solution is obtained by prescribing
the latent heating field and climatological horizontal transports of heat and momentum by the eddies. The radiative heating
and surface fluxes are calculated by model parameterizations. This standard solution is compared with the results of several
sensitivity studies. When the eddy forcing is reduced to 0.5 times or increased to 1.5 times the climatological values, the
strength of the Ferrel cells decrease or increase proportionally. It is also seen that such changes in the eddy forcing can
influence the strength of theNH Hadley cell significantly. Possible impact of such changes in the large scale eddy forcing on the monsoon circulation via
changes in the Hadley circulation is discussed. Sensitivity experiments including only one component of eddy forcing at a
time show that the eddy momentum fluxes seem to be more important in maintaining the Ferrel cells than the eddy heat fluxes.
In the absence of the eddy heat fluxes, the observed eddy momentum fluxes alone produce subtropical westerly jets which are
weaker than those in the standard solution. On the other hand, the observed eddy heat fluxes alone produce subtropical westerly
jets which are stronger than those in the standard solution. 相似文献
16.
The Ilchulbong tuff cone, Cheju Island, South Korea 总被引：3，自引：0，他引：3
The Ilchulbong mount of Cheju Island, South Korea, is an emergent tuff cone of middle Pleistocene age formed by eruption of a vesiculating basaltic magma into shallow seawater. A sedimentological study reveals that the cone sequence can be represented by nine sedimentary facies that are grouped into four facies associations. Facies association I represents steep strata near the crater rim composed mostly of crudely and evenly bedded lapilli tuff and minor inversely graded lapilli tuff. These facies suggest fall-out from tephra finger jets and occasional grain flows, respectively. Facies association II represents flank or base-of-slope deposits composed of lenticular and hummocky beds of massive or backset-stacked deposits intercalated between crudely to thinly stratified lapilli tuffs. They suggest occasional resedimentation of tephra by debris flows and slides during the eruption. Facies association III comprises thin, gently dipping marginal strata, composed of thinly stratified lapilli tuff and tuff. This association results from pyroclastic surges and cosurge falls associated with occasional large-scale jets. Facies association IV comprises a reworked sequence of massive, inversely graded and cross-bedded (gravelly) sandstones. These facies represent post-eruptive reworking of tephra by debris and stream flows. The facies associations suggest that the Ilchulbong tuff cone grew by an alternation of vertical and lateral accumulation. The vertical buildup was accomplished by plastering of wet tephra finger jets. This resulted in oversteepening and periodic failure of the deposits, in which resedimentation contributed to the lateral growth. After the eruption ceased, the cone underwent subaerial erosion and faulting of intracrater deposits. A volcaniclastic apron accumulated with erosion of the original tuff cone; the faulting was caused by subsidence of the subvolcanic basement within the crater. 相似文献
17.
A cavity expansion–based solution is proposed in this paper for the interpretation of CPTu data under a partially drained condition. Variations of the normalized cone tip resistance, cone factor, and undrained-drained resistance ratio are examined with different initial specific volume and overconsolidation ratio, based on the exact solutions of both undrained and drained cavity expansion in CASM, which is a unified state parameter model for clay and sand. A drainage index is proposed to represent the partially drained condition, and the critical state after expansion and stress paths of cavity expansion are therefore predicted by estimating a virtual plastic region and assuming a drainage-index–based mapping technique. The stress paths and distributions of stresses and specific volume are investigated for different values of drainage index, which are also related to the penetration velocity with comparisons of experimental data and numerical results. The subsequent consolidation after penetration is thus predicted with the assumption of constant deviatoric stress during dissipation of the excess pore pressure. Both spherical and cylindrical consolidations are compared for dissipation around the cone tip and the probe shaft, respectively. The effects of overconsolidation ratio on the stress paths and the distributions of excess pore pressure and specific volume are then thoroughly investigated. The proposed solution and the findings would contribute to the interpretation of CPTu tests under a random drained condition, as well as the analysis of pile installation and the subsequent consolidation. 相似文献
18.
Continuous observations since 1991 by using synthetic aperture radar (SAR) on board the Almaz1, ERS-1/2, JERS-1, and RADARSAT
satellites support the well-known fact that oceanic eddies are distributed worldwide in the ocean. The paper is devoted to
an evaluation of the potential of SAR for detection of eddies and vortical motions in the ocean. The classification of typical
vortical features in the ocean detected in remote sensing images (visible, infrared, and SAR) is presented as well as available
information on their spatial and temporal scales. Examples of the Almaz-1 and ERS-1/2 SAR images showing different eddy types,
such as rings, spiral eddies of the open ocean, eddies behind islands and in bays, spin-off eddies and mushroom-like structures
(vortex dipoles) are given and discussed. It is shown that a common feature for most of the eddies detected in the SAR images
is a broad spectrum of spatial scales, spiral shape and shear nature. It is concluded that the spaceborne SARs give valuable
information on ocean eddies, especially in combination with visible and infrared satellite data. 相似文献
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横流中多孔射流的流动特性是揭示其输移扩散机理的基础。利用粒子图像测速技术PIV测量了横向流动条件下单孔、两孔和四孔射流的速度场,对射流主体范围内、射流的迎流面和各个射流之间的流场进行了研究。实验研究表明,多个射流中的第1个射流迎流面卷吸强度明显大于单个射流情况;两个射流之间的区域可分为两个部分,上游部分水体被卷吸进入上一个射流,下游部分水体被卷吸进入下一个射流;后面射流迎流面的横向流速明显低于第1个射流迎流面的横向流速,揭示了导致后面射流弯曲的横向有效流速沿程发展变化过程;揭示了横向有效流速的沿程变化规律。 相似文献