摘要:

Debris deposit laying over an impermeable high slope surface (e.g. in steep streams and gullies) could develop a water sediment mixture flow (usually known as debris flow) when a high enough water flow is flowing over the sediment bed. In particular the rainfall first saturates the debris deposit and then mobilizes it by an overland flow.

ISSN:0022-1686    

DOI:10.1080/00221680009498343

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Experimental results are presented about long term local scouring downstream of bed sills in monogranular gravel beds. Two sets of tests were performed in a tilting flume at HR Wallingford, UK, in 1996 and 1997, the main difference between the sets of tests being the size of sediments used. A dimensional analysis of the problem of local scour at bed sills was carried out and used to analyse the experimental results. The introduction of a new variable, the 'morphological jump', permits the derivation of two empirical formulas to predict the maximum depth and length of the scour hole at equilibrium. In addition, the Froude number seems to have no influence on the dimensions of the scour hole, but does have an effect on the development of a 'sill step' upstream of each sill. Non-dimensional scour hole profiles were found to be affine. As a consequence, it is possible to predict the location of the deepest scour relative to the bed sill.

ISSN:0022-1686    

DOI:10.1080/00221680009498344

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

We provide new theoretical arguments which together with recent measurements by Gong et al. [1996], strongly support the existence of the jet flow regime [Giménez-Curto and Corniero, 1996]. The theoretical arguments refer in particular to the introduction of a formal condition for flow separation from uneven surfaces for laminar and turbulent flow as well. This condition, which is a first requirement of the jet regime flow model, is compared with existing information.

ISSN:0022-1686    

DOI:10.1080/00221680009498345

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A multiple-point hybrid model for predicting the behavior of merging jets in a coflowing ambient fluid is presented. The hybrid model combines themodular structure of a length-scale model with the reduced empiricism of an Eulerian-integral model. Integral models of merging behavior are cumbersomebecause of the need to sum the momentum of individual jets during the merging process. A length-scale approach simplifies the model significantly,but details of the merging process are lost. A significant limitation of length-scale models is the assumption that the transition between flowregimes occurs at a single point. This difficulty can be overcome by allowing the transition to occur in stages and this leads to the use of the multiplepointapproach. Predictions from the multiple-point hybrid model are compared with an equivalent single-point hybrid model and an Eulerian-integralsolution for the same problem. The multiple-point approach significantly reduces transition errors when compared to the single-point model. These transitionerrors can result in inaccurate predictions of merging behaviour. Predictions from the multiple-point hybrid model are in good agreement with theintegral solution.

ISSN:0022-1686    

DOI:10.1080/00221686.2000.10525035

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A numerical model to calculate three-dimensional turbulent flew In open channels ef arbitrary cress-section is developed and validated: The model selves the incompressible, Reynolds-averaged Navier-Stekes (RANS) equations, formulated in generalised curvilinear coordinates, in conjunction with the fcg turbulence closure. The free-surface elevation is determined by allowing the gomputatienal mesh to deform during the iterative solution procedure so that the proper kinematic and dynamic conditions are satisfied at convergence- The numerical model is validated by application to simulate the flow through meandering open channels for which detailed experimental measurements are available. Comparisons of the computed solutions with experimental data reveal that the model predicts the details of the velocity field, including changes in secondary motion, the distribution ef bed shear, and variations of flow depth in both the transverse and longitudinal directions.

ISSN:0022-1686    

DOI:10.1080/00221680009498346

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

This paper reports a finite volume TVD-MacCormack scheme for the computation of two-dimensional open channel flows with abrupt changes. The algorithm modified the widely-used MacCormack scheme by implementing a conservative dissipation step to avoid the unphysical oscillation in the vicinity of strong gradients in the numerical solution. Compared with other numerical models, this scheme does not bring in any additional difficulty in dealing with the source terms. Furthermore, this algorithm remains second-order accuracy in both space and time. A series of simulation, such as oblique hydraulic jump, circular dambreak and two-dimensional dambreak are carried out to demonstrate its robustness and stability in capturing strong gradients and discontinuities in open channel flows, The accuracy of numerical scheme is also verified with two laboratory dambreak experiments.

ISSN:0022-1686    

DOI:10.1080/00221680009498347

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The paper presents generalisation of the old Prandtl mixing-length hypothesis (MLH) for three-dimensional (3D) flows to provide engineers with a new tool to calculate the mean velocity distribution in turbulent open channel flows. These flows are usually not isotropic, i.e. turbulence may have different length scales in different directions. Hence, at every point of the flow a symmetrical second-order tensor with dimension of length should be given. The components of this tensor are specified based on the structure of the largest turbulent eddies. To demonstrate the usefulness of the proposed model, the Reynolds equations with the new turbulence model are solved and calculated streamwise velocity contours are compared with the measurement results. The importance of turbulent structure (sizes of the largest eddies and their growth rate) in forming the streamwise velocity contours is shown.

ISSN:0022-1686    

DOI:10.1080/00221680009498348

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The Craik-Leibovich equations including vortex forcing terms and a pressure gradient force in x-momentum are integrated numerically. Some typical environmental problems with strong longitudinal currents are analysed.

ISSN:0022-1686    

DOI:10.1080/00221680009498349

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The increase in dissolved gas concentration downstream of hydraulic structures such as dam spillways can be harmful to most fish species. Such increases have been noted at numerous hydroelectric dams on the Columbia and Snake Rivers in Washington State, and there is fear that this total dissolved gas (TDG) "supersaturation" will increase mortality in juvenile and adult salmonids. Modifications to the spillway and/or its tailrace at some of these dams have or will be installed to help lower the concentration of total dissolved gas downstream of the dams. At Wanapum Dam on the mid-Columbia River, spillway modifications were designed and evaluated using a combination of physical and numerical models. The physical model provided information about the hydraulics associated with different spillway modifications. The numerical model calculated the concentration of total dissolved gas based upon hydrodynamic data from the physical model and mass transport relations developed for air-water flows. This article describes the numerical model development and application. A companion article (Mannheim and Weber, 1998) describes the physical modeling efforts made to evaluate the performance of the proposed spillway modifications at the dam.

ISSN:0022-1686    

DOI:10.1080/00221680009498350

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

ISSN:0022-1686    

DOI:10.1080/00221680009498342

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor