摘要:

The degree of contraction of jets issuing from conduits depends upon the geometry of the approach flow, particularly upon (1) the angle of convergence of the walls and (2) the ratio of the area of the jet opening to that of the approach flow. The work of Von Mises, which provided coefficients of contraction for the convergence angles that are multiples of π/4, has been extended to include all multiples of π/12. The analysis of the two-dimensional, irrotational flow is based on the classical free-streamline technique of Helmoltz and Kirchoff. Plots of the tabulated values ofCcfor the various angles and area ratios illustrate the trends and assist with interpolations. The computed coefficients have applications, to a useful approximation, to a wide variety of flows encountered in practice, including flows that are neither two-dimensional nor entirely free from effects of viscosity. Among them are flow through valves and gates in conduits and flow under floating bridges.

ISSN:0022-1686    

DOI:10.1080/00221689309498771

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Turbulent flow in a pipe with a 21° gradual contraction is studied experimentally and numerically. Velocity and turbulence measurements were taken with a Laser-Doppler-Anemometry (LDA) and a Hot-wire (H-W) at two representative stations 1D2and 10D2after the contraction and also at one station 2D1, upstream of the contraction. Calculations of the flow characteristics at the two downstream stations indicate that using a step wise approximation of the inclined contraction wall affects slightly the results. Predictions of velocity by the standardk-εmodel of turbulence for high Reynolds numbers are in satisfactory agreement with those measured by both LDA and H-W. Also, a low-Reynolds number model, proposed by Launder and Sharma, gives similar predictions. Measurements and calculations were performed for two Reynolds 100,000 and 150,000 and indicate a weak dependence of the flow characteristics on the Reynolds number.

ISSN:0022-1686    

DOI:10.1080/00221689309498772

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A simple one-dimensional formulation on the basis of momentum and continuity equation is proposed to predict the transitional flow at a channel junction. The findings are compared with the results of an earlier one-dimensional formulation and experiments. It is found that the present formulation agrees better with experiments. The equation derived on the basis of the present analysis allows computation of the transitional junction flow.

ISSN:0022-1686    

DOI:10.1080/00221689309498773

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The velocity characteristics of the submerged jet produced by a rotating ship propeller are described in terms of the maximum velocity measured on the propeller plane. Detailed measurements of velocities have been taken in the zone of the wash close to the propeller. The maximum velocity has been found to decay with distance from the propeller source. The maximum velocity in the zone of formation of the propeller jet has been shown to depend upon the efflux velocity and the blade area ratio for the propeller.

ISSN:0022-1686    

DOI:10.1080/00221689309498774

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A morphological model for the development of local-scour holes behind structures is developed, based on the 2-D Navier Stokes and convection-diffusion equations. The bed-load (transport) and the concentration at a reference level close to the bed are prescribed using a stochastical approach for the instantaneous bed shear-stress. The standard deviation of the latter is closely related to the turbulence energy in the mixing layer and to the bed turbulence.

ISSN:0022-1686    

DOI:10.1080/00221689309498775

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Through a spectral analysis of the linearized Saint Venant equations, it is shown that any space-limited perturbation of an otherwise steady flow evolves into a gaussian form which attenuates smoothly with time, being the result of the contribution of the longest forward spectral components. It is also shown that the shortest forward and backward spectral component contributions, relevant for intermediate times, preserve the initial wave form but attenuate exponentially. Nonlinear effects are briefly discussed. It is postulated that, due to the filtering behaviour of open channels, it is expected that, in addition to a gaussian wave form, only steps and sinusoids should be observed asymptotically.

ISSN:0022-1686    

DOI:10.1080/00221689309498776

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Wave pressure reduction due to a submerged horizontal plate placed before a vertical wall was investigated both numerically as well as experimentally. Pressure-reduction due to the submerged plate for short period waves was clearly evident. For all the case studies, the optimal submergence depth was found to be equal tod= 0.20hrather than 0.45h, wherehis the total water depth. However, at this depth,d= 0.20/;, the pressurereduction effect will vary according to wave conditions, the width of the plate, (l), and the distance of the plate away from the vertical wall (w). Furthermore, it was found that the wider the plates, the longer the waves that will be affected. Calculated reflection coefficients were found to be in satisfactory agreements with experiments for nonbreaking waves.

ISSN:0022-1686    

DOI:10.1080/00221689309498777

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A recently developed numerical method is applied to the study of transient, nonlinear wave propagation in a laboratory flume. The nonlinear free surface boundary conditions and the wave generator boundary condition are expanded about the corresponding equilibrium positions by perturbation expansions. The Sommerfeld radiation condition applied on the downwave control surface is modified to incorporate a time-dependent celerity to account for transient effects. The boundary conditions are then satisfied to second order by a numerical integration in time, and the field solution at each time step is obtained by an integral equation method based on Green's theorem. The accuracy of the numerical solution is first assessed in term of the condition number. The propagation characteristics of regular and irregular waves are studied. To verify the numerical model, a series of laboratory tests have been performed. For the case of an irregular wave packet, the experimental results of the free surface elevations obtained at twelve different locations along the flume are compared with the corresponding numerical predictions and favourable agreement is indicated.

ISSN:0022-1686    

DOI:10.1080/00221689309498778

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Motion within a soft muddy bottom under small amplitude wave action is briefly examined using an analytical approach to gain insight into the mechanism by which coastal mud responds to water waves. The bed is modelled as a viscoelastic body using the Voigt model. The model's results on interface shear stress and wave damping show acceptable agreement when compared to laboratory data. This model is an extension of the one developed by MacPherson [3], since it considers the continuity of the shear stress through the watermud interface, taking into account a thin water boundary layer upon the interface. It can be concluded that:

ISSN:0022-1686    

DOI:10.1080/00221689309498779

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Surge waves in open channels can be simulated well by solitary waves if the peak values of the bottom attack are the goal of the investigation. In this paper, a theoretical model is presented for calculation of the bottom shear stress due to solitary waves. The wave parameters and the bottom roughness can be given arbitrarily. The model has been verified and calibrated by experiments using a shear plate. In a second step, the calculation model is employed on solitary waves causing onset of movement of a given sediment. The resulting peak shear stress under these waves is found to exceed the well-known Shields value considerably.

ISSN:0022-1686    

DOI:10.1080/00221689309498780

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor