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The analysis of plunging flows using energy dissipation hypothesis is presented in this paper. The classic two-control- volume theory has recently been found questionable and needs to be corrected. In this study, we avoid the questionable part of that framework and use a single control volume for the analysis of plunging flows. Furthermore, we hypothesize that the increase in kinetic energy in the underflow and entrained flow should be no greater than the loss in potential energy as the inflow plunges. In the current framework, the entrained flow rate does not exceed approximately 40% of the total inflow rate. The densimetric Froude number at the plunge point, [F.sub.dp] = q/ [square root of g'[H.sup.3.sub.p]], where q=inflow rate per unit width; g' = reduced gravity of inflow; and [H.sub.p] = flow depth at the plunge point, is typically in the range of 0.3 < [F.sub.dp] < 0.6 for plunging flows in a constant width channel. DOI: 10.1061/(ASCE)HY.1943-7900.0000176 CE Database subject headings: Energy dissipation; Density flow; Lakes; Plunging flow; Reservoirs. Author keywords: Energy dissipation; Density flow; Lakes; Plunging flow; Reservoirs.

The present experimental investigation focuses on energy dissipation and turbulence production in two undeveloped and a partially developed inflow weak hydraulic jumps, measured with micro-ADVs. For the undeveloped inflow jumps, the turbulence production is mostly confined in the shear layer located in the upper part of the water column. For the partially developed inflow jump, two peak turbulence production regions are observed, one in the upper shear layer and the second in the near-wall region. Moreover, the measured energy dissipation distribution in the jumps reveals a similar longitudinal decay of energy dissipation integrated over the flow sections and of maximum turbulence production values from the intermediate jump region toward its downstream section. DOI: 10.1061/(ASCE)HY.1943-7900.0000124 CE Database subject headings: Hydraulic jump; Turbulence; Inflow; Kinetics.

The results of a laboratory study of hydraulic jumps on corrugated beds are presented. Experiments were performed for a range of Froude numbers from 4 to 10. Three values of the relative roughness t/[y.sub.1] of 0.50, 0.43, and 0.25 were studied. It was found that the tailwater depth required to form a jump was appreciably smaller than that for the corresponding jumps on smooth beds. Further, the length of the jumps was about half of those on smooth beds. The integrated bed shear stress on the corrugated bed was about 10 times that on smooth beds. The axial velocity profiles at different sections in the jump were found to be similar, with some differences from the profile of the simple plane wall jet. The maximum velocity [u.sub.m] at any section in terms of the velocity [U.sub.1] of the supercritical stream was correlated with the longitudinal distance x in terms of L, which is the distance where [u.sub.m] = 0.5[U.sub.1], and this relation was the same as that for jumps on smooth beds with the difference that L/[y.sub.1] was much smaller for jumps on corrugated beds. The normalized boundary layer thickness [delta]/b, where b is the length scale of the velocity profile, was equal to 0.45 for jumps on corrugated beds compared to 0.16 for the simple wall jet. The results of this study show the attractiveness of corrugated beds for energy dissipation below hydraulic structures. DOI: 10.1061/(ASCE)0733-9429(2002) 128:7(656) CE Database keywords: Open channel flow; Hydraulic jump; Energy dissipation; Beds.

This paper presents results of an experimental and theoretical study on the use of a high density polyethylene (HDPE) additional pipe inserted downstream of a pump in a hydraulic network as a surge suppressor. The experiments consistently show a reduction of the oscillations with respect to the case without a HDPE device, while in the case of a single pumping pipeline the oscillations can be amplified for small volumes of the additional pipe. Previously calibrated mechanical parameters are considered in the mathematical models whose results are compared with experimental results. Both linear elastic and Kelvin-Voigt viscoelastic behavior of the pipe material and both one-dimensional (1D) and quasi-2D flow models are taken into account. The numerical results show that the viscoelastic model better describes the phenomenon, but the elastic model adequately estimates the maximum and minimum oscillations. Furthermore, the results of the quasi-2D model are in better agreement with the experimental maximum and minimum oscillations than those of the 1D model, but the differences are less important than in the case of networks without a HDPE device. DOI: 10.1061/(ASCE)0733-9429(2002)128:2(238) CE Database keywords: Unsteady flow; Hydraulic networks; Pipes; Polymers; Energy dissipation.

J.S. Montes studied the classical hydraulics problem involving the flow across a planar sluice gate and provided some explanations for the difficulty. He concluded that energy losses induced by the development of upstream vortices in the corners between the side walls and the sluice gate are responsible for the discrepancies. However, there is little sufficient evidence to support his contention and more prototype data need to be examined before a definitive conclusion can be made with regards to the importance of energy losses across a sluice gate structure.

A new model for the computation of unsteady friction losses in transient flow is developed and verified in this study. The energy dissipation in transient flow is estimated from the instantaneous velocity profiles. The ratio of the energy dissipation at any instant and the energy dissipation obtained by assuming quasi-steady conditions defines the energy dissipation factor. This is a nondimensional, time-varying parameter that modifies the friction term in the transient flow governing equations. The model was verified for laminar and turbulent flows and the comparison of measured and computed pressure heads shows excellent agreement. This model can be adapted to an existing transient program that uses the well-known method of characteristics for the solution of the continuity and momentum equations.

This paper introduces the concept of a submerged hydraulic jump being used for energy dissipation. A baffle wall is used to produce a stable deflected surface jet, thereby deflecting the high-velocity supercritical stream away from the bed to the surface. Based on a series of experiments, a diagram was developed that predicts the conditions under which such a surface jet would be produced. A second series of experiments were performed to study the characteristics of the deflected jet, as it travels upward first as a curved turbulent jet to eventually become a turbulent surface jet. The decay of the maximum velocity in the deflected as well as the surface jet was studied and compared with that of a plane turbulent wall jet that is a model for deeply submerged jumps.

Previous studies have shown the occurence of horizontal vortices beneath the pseudo-bottom formed by the external edges of the steps in stepped spillways. These vortices are caused by the transmission of turbulent shear stress between the skimming stream and the recirculating fluid underneath. In addition, the process of maintaining these vortices causes significant amounts of energy to dissipate. Several formulas are given to calculate the amount of energy that dissipates.

Energy loss data for a 90[degrees] sharp-edged combining pipe junction were obtained, using a 37-m long, 444-mm diameter plastic pipe with a branch pipe entering about 35 pipe diameter downstream from the upstream end of the pipe. The data cover ratios of branch to main-pipe cross-sectional areas [A.sub.b]/[A.sub.d] ranging from 0.02 to 0.21 and ratios of branch to main-pipe discharge [Q.sub.b]/[Q.sub.d] ranging from 0 to 1. At flow situations defined by these ranges there are few energy loss data available and no satisfactory theory. The study includes an investigation of specific flow features at the junction including the velocity and pressure distribution in the branch flow at its exit into the main pipe. A momentum analysis is performed to show that a satisfactory description of the momentum balance must include the momentum contributions associated with: (1) The deflection and distortion of the branch-flow velocity distribution prior to the exit of the branch flow into the main pipe; and (2) the increase in wall shear stress in the main pipe due to the local deformation of the main-flow velocity distribution. The data show that the fully developed pipe flow is re-established about 50 pipe diameters downstream from the pipe junction.