摘要:

If ocean outfalls are to function effectively it is necessary that seawater be fully purged from the system. Consequently a basic design requirement of an outfall is that it has purging capability. This paper describes model studies designed to investigate the detailed nature of the purging process in outfalls with high risers. Both purging of seawater from the outfall and its subsequent intrusion into the outfall following cessation of effluent flow were investigated. The results of the study are presented in non-dimensional terms and are compared with existing theoretical models.

ISSN:0022-1686    

DOI:10.1080/00221689209498881

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

In this work, some considerations about the problem of the unsteady flow simulation at a junction of open channels are presented. When simulating unsteady flow through junctions, the usual technique is to assume the equality of water stages. Following the theory of characteristics, we explain that this is a valid approximation for low Froude numbers but impossible to apply in other general cases. A theoretical approach of the steady state at a junction is used to state the unsteady compatibility conditions to be used. A time evolution modelling including supercritical flows, hydraulics jumps and shock propagation through the junction becomes possible and a useful tool to improve complex dam break simulations involving tributaries.

ISSN:0022-1686    

DOI:10.1080/00221689209498882

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Field data obtained in the measurement of typhoon-generated waves in Gulf of Bei Bu, a semi-enclosed shallow water bay, is used in the validation of a 'third generation' spectral model which employs an accurate numerical solution algorithm. The linear bottom dissipation expression obtained in the JONSWAP study is adopted since it produces a more reasonable wave growth characteristics in an ideal test case as compared to the dissipation formulation based on quadratic friction law. Computational efficiency of the model is enhanced by employing digital filtering technique to suppress the numerical instability arisen from using large time step (up to about 30 minutes) and to maintain an acceptable accuracy. The performance of the model is good and provides a further support to the 'third generation' formulation of spectral models.

ISSN:0022-1686    

DOI:10.1080/00221689209498883

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Experimental runs were carried out in the open recirculating channel in the Hydraulics Laboratory of the Kuwait Institute for Scientific Research to study variations in velocity distribution and suspended-sediment concentration due to currents, waves and combinations of these. A laser Doppler anemometer was used to measure the velocities at different water depths for three wave conditions, three current conditions and nine wave-current coexistence cases. Measurements showed that the familiar logarithmic current profile can be used to represent the change in velocity with water depth in currents without waves and in current-wave coexistence fields. The coefficient values in such a distribution depend on the ratio between the average current speed and the wave-induced current value. For the study of suspended sediment concentration, a specially designed suction instrument was manufactured in the laboratory workshop to collect the watersand mixture with variable-speed pumps that allowed average space and time concentrations to be obtained at different water depths. Measurements revealed two regions: of high concentration close to the bed, and of low concentration away from the bed. Two empirical expressions were developed to represent these distribution concentrations, together with an expression to obtain the thickness of the high-concentration layer. These expressions can be used in numerical model studies to estimate the suspended-sediment transport rate along the coasts.

ISSN:0022-1686    

DOI:10.1080/00221689209498884

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

If stratified soil structures are not designed according to conventional filter criteria, a flow of ground water may erode and transport an underlying, finer material through the pore system of the coarser stratum above. A constitutive equation for interfacial transport rate is derived from physical principles and verified through laboratory experiments. The relationship is incorporated in a mathematical formulation for interfacial erosion processes analogous to the one commonly applied to alluvial streams. Both analysis and experiments indicate that interfacial erosion depends strongly on variation in the grain size ratio between the two strata and the porosity of the coarser stratum. A simulation example demonstrates a case in which the core in an earth-fill dam is subjected to overflow and the crest of the core is eroded.

ISSN:0022-1686    

DOI:10.1080/00221689209498885

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

In this paper, the ability of a laminar pipe-flow model to reproduce the hydrodynamic transport of contaminated groundwater in fractured rock is investigated. It is assumed that the cross-section areas are circular and that the flow is laminar. The molecular diffusion is neglected as well as the impact of variations in velocity over the cross-section area. It is assumed that the cross-section areas in an ensemble of tubes have a gamma distribution. The model is applied to field tracer experiments at two sites. It is shown that the mean size of the cavities is smaller deeper into the ground and that the distribution is narrower. Different values of the parameter of the gamma distribution were used to reproduce the breakthrough course at the different sites. It was shown that there is no general relation between conductivity of a porous medium and its porosity when the pore size distribution is not taken into account.

ISSN:0022-1686    

DOI:10.1080/00221689209498886

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Experiments on settling of cohesive sediments were carried out in turbulent flows in an annular flume using kaolinite clay as well as a natural river sediment. Results indicate that the finer fractions were able to deposit because they were settling as floes. Data on concentration and size distribution of dispersed samples were used to calculate the effective settling velocities for the different size fractions.

ISSN:0022-1686    

DOI:10.1080/00221689209498887

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Local scour downstream of an apron with a swept-out hydraulic jump is shown to develop very rapidly, that is in less than 1% of the time to reach the ultimate scour depth. The short-term scour although not as deep as the long-term scour, occurs much closer to the apron. The limiting short-term scour depth is found to be related to flow regime or type of hydraulic jump that dominates the flow in the scour hole. The deepest shortterm scour was associated with the plunging jump (B-jump) and the adverse jump regimes. A modification of the B-jump equation of Hager and Bretz is proposed to estimate the limiting depth of short-term local scour.

ISSN:0022-1686    

DOI:10.1080/00221689209498888

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Considering the primary vortex in front of the pier to be the prime agent causing scour at bridge piers, a scheme has been proposed for computation of the temporal variation of scour depth during live-bed condition. An equation has also been developed for the computation of maximum scour depth around circular bridge piers in uniform sediments during live-bed condition. The equation follows logically from the scheme proposed for the computation of the temporal variation of scour. The effect of unsteadiness of flow on scour depth has been also studied.

ISSN:0022-1686    

DOI:10.1080/00221689209498889

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

ISSN:0022-1686    

DOI:10.1080/00221689209498890

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor