A vortex-tube model of eddies in the inertial range     

Stephen Childress 《地球物理与天体物理流体动力学》2013,107(1-4):29-64

Abstract

A vortex-tube geometry of the cascade of energy to small-scale eddies, in the inertial range of fully-developed turbulence, is proposed. The model is a special case of the beta model of Frisch, Sulem and Nelkin (1978). We require that the cascade conserve the principal invariants of inviscid, incompressible flow, namely volume, topological knottedness, circulation, and, at discrete times marking the termination of steps in the cascade, energy. The process terminates in a finite time, as in any beta model, leaving behind a self-similar network of “inactive” tubes. We associate a self-similar scaling dimension D with the structure, equal to the Hausdorff dimension of the set of “active” tubes at the termination of the cascade. Because circulation Λ plays a key role in the analysis of the cascade, we refer to these vortex-tube geometries as “gamma models”. The viewpoint throughout is entirely deterministic.

We describe two examples of gamma models. In the ring geometry, an eddy is a vortex ring, and the cascade produces “rings upon rings”, so we allow cutting and fusing of tubes while conserving total helicity. In the preferred helical model, no cutting is needed, and the cascade produces an infinite progression of braided “coils upon coils”. We suggest that latter geometry as a candidate for the topology of a singularity of the inviscid limit of a Navier-Stokes flow, when modeled by discrete vortex tubes.

A crucial ingredient of a gamma model, not explicitly present in a beta model, is the possibility of “splitting” a vortex tube into sub-tubes carrying smaller circulation. We suggest a dynamical basis for this process, as an instability of tubes whose cores violate the Rayleigh criterion.

The parameters describing a gamma model are not uniquely determined by our study, but there is a “simplest” helical gamma model, involving minimal splitting and distortion of tubes. The dimension D of the structure is 13/5, with a scale factor Λ = 2^?5/4. This value of D agrees with that suggested by Hentschel and Procaccia (1982), by analogy with established results for certain branched polymers.  相似文献   

On the growth of disturbances to forced and dissipated barotropic flows     

Jieping Zou  John Fyfe 《地球物理与天体物理流体动力学》2013,107(1-4):41-56

Abstract

We consider the growth of disturbances to large-scale zonally-asymmetric steady states in a truncated spectral model for forced and dissipated barotropic flow. A variant of the energy method is developed to optimize the instantaneous disturbance energy growth rate. The method involves solving a matrix eigenvalue problem amenable to standard numerical techniques. Two applications are discussed. (1) The global stability of a family of steady states is assessed in terms of the Ekman damping coefficient r. It is shown that monotonic global stability (i.e., every disturbances energy monotonically decays to zero) prevails when r≥r_c . (2) Initially fastest-growing disturbances are constructed in the r<r_c regime. Particular attention is paid to a subregion of the r<r_c regime where initially-growing disturbances exist despite stability with respect to normal modes. Nonlinear time-dependent simulations are performed in order to appraise the time evolution of various disturbances.  相似文献   

Prediction of the consumption rates for juvenile Atlantic salmon (Salmo salar L.) on the scale of habitat patches: Development of empirical models based on stomach contents     

Frédéric Burton  Daniel Boisclair 《Limnologica》2013,43(5):332-338

Rivers and streams are unstable environments in which estimation of energetic costs and benefits of habitat utilization are the daunting exercise. Empirical models of food consumption may be used to estimate energetic benefits based on abiotic and biotic conditions in patches of habitat. We performed thirty daily surveys of fish stomach contents to estimate the consumption rates for juvenile Atlantic salmon (Salmo salar) in a river. The data were used to assess whether variations of daily consumption rates existed within the river, and to develop empirical models that could predict fish consumption rates using abiotic and biotic conditions as independent variables. Daily consumption rates based on stomach content surveys in the field (range: 0.15–1.49 g dry/(100 g wet day)) varied significantly depending on habitat patch (500–1000 m²), summer period, and sampling year. Variables such as water temperature, numerical density of salmon, water depth and moon phase explained 83–93% of the variations in daily food consumption rates. Daily consumption rates tended to increase with water temperature and depth, and were also higher near a full moon. However, they tended to decrease with the numerical density of salmon. Our work suggests that empirical models based on independent variables that are relatively simple to estimate in the field may be developed to predict fish consumption rates in different habitat patches in a river.  相似文献   

Discussion of “Challenges in operationalizing the water–energy–food nexus”*     

Olli Varis  Marko Keskinen 《水文科学杂志》2013,58(12):1863-1865

ABSTRACT

We greatly enjoyed reading the paper by Liu et al., which is both timely and rich in insight, as it discusses the challenges in operationalizing the water–energy–food security (WEF) nexus. The nexus approach is gaining increasing attention, both in research and in policy documents, as reflected in the number and content of published documents in the past years and highlighted by the authors.  相似文献   

近45年全球海域波浪能资源研究及等级区划     

郑崇伟 《亚热带资源与环境学报》2013,(1):18-24

基于来自ECMWF的资料将1957年09月---2002年08月风浪、涌浪分离的ERA-40 wave reanalysis,对全球海域的波浪能资源进行重新审视．充分依据涌浪具有能量大、稳定性好等优点,利于波浪能的采集与转换,从提高波浪能资源有效利用率的角度出发,综合考虑能流密度的大小、能级频率、能流密度的稳定性和长期变化趋势等,对全球海域的波浪能资源进行系统性研究,并构建一套波浪能资源评估系统,对全球海域的波浪能资源进行功能区划,为海浪发电、海水淡化等波浪能资源开发工作提供科学依据．  相似文献   

中国生物质能产业发展面临的矛盾和挑战     

蔺雪芹  司月芳  王岱 《资源与生态学报(英文版)》2013,(4):353-360

本文在分析中国生物质能产业发展现状的基础上,认为当前中国生物质能产业发展受到资源家底不清、政策环境不完善和生态保护压力等因素制约,存在着产业发展总体水平低,产业体系不健全,生产成本高,产业技术水平低,行业发展无序等问题。结合这些问题,立足我国资源环境承载能力,适应市场需求变化和科技进步趋势,本文提出今后重点加强生物质能产业发展政策扶持,生物质能原料资源调查评估,生物质能转化利用技术开发和能源产业示范基地建设,以期促进生物质能产业健康快速发展。  相似文献   

Laboratory experiments of sediment transport from bare soil with a rill     

Hafzullah Aksoy  N. Erdem Unal  Sevket Cokgor  Abdullah Gedikli  Kaan Koca 《水文科学杂志》2013,58(7):1505-1518

Abstract

Mathematical models developed for quantification of sediment transport in hydrological watersheds require data collected through field or laboratory experiments, but these are still very rare in the literature. This study aims to collect such data at the laboratory scale. To this end, a rainfall simulator equipped with nozzles to spray rainfall was constructed, together with an erosion flume that can be given longitudinal and lateral slopes. Eighty experiments were performed, considering microtopographical features by pre-forming a rill on the soil surface before the start of each experiment. Medium and fine sands were used as soil, and four rainfall intensities (45, 65, 85 and 105 mm h^-1) were applied in the experiments. Rainfall characteristics such as uniformity, granulometry, drop velocity and kinetic energy were evaluated; flow and sediment discharge data were collected and analysed. The analysis shows that the sediment transport rate is directly proportional to rainfall intensity and slope. In contrast, the volumetric sediment concentration stays constant and does not change with rainfall intensity unless the slope changes. These conclusions are restricted to the conditions of experiments performed under rainfall intensities between and 105 mm h^-1 for medium and fine sands in a 136-cm-wide, 650-cm-long and 17-cm-deep erosion flume with longitudinal and lateral slopes varying between 5 and 20%.

Editor Z.W. Kundzewicz; Associate editor G. Mahé

Citation Aksoy, H., Unal, N.E., Cokgor, S., Gedikli, A., Yoon, J., Koca, K., Inci, S.B., Eris, E., and Pak, G., 2013. Laboratory experiments of sediment transport from bare soil with a rill. Hydrological Sciences Journal, 58 (7), 1505–1518.  相似文献   

Can satellite land surface temperature data be used similarly to river discharge measurements for distributed hydrological model calibration?     

C. Corbari  M. Mancini  J. Li  Z. Su 《水文科学杂志》2013,58(2):202-217

Abstract

A new methodology is proposed for the calibration of distributed hydrological models at the basin scale by constraining an internal model variable using satellite data of land surface temperature (LST). The model algorithm solves the system of energy and mass balances in terms of a representative equilibrium temperature that governs the fluxes of energy and mass over the basin domain. This equilibrium surface temperature, which is a critical model state variable, is compared to operational satellite LST, while calibrating soil hydraulic parameters and vegetation variables differently in each pixel, minimizing the errors. This procedure is compared to the traditional calibration using only discharge measurements. The distributed energy water balance model, Flash-flood Event-based Spatially-distributed rainfall–runoff Transformation – Energy Water Balance model (FEST-EWB), is used to test this approach. This methodology is applied to the Upper Yangtze River basin (China) using MODIS LST retrieved from satellite data in the framework of the NRSCC-ESA DRAGON-2 Programme. The calibration procedure based on LST seems to outperform the calibration based on discharge, with lower relative error and higher Nash-Sutcliffe efficiency index on cumulated volume.