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Drop manholes are hydraulic devices typically employed to dissipate flow energy in high slope, urban drainage systems. The use of several drops of small height placed in series (drop manhole cascade) is a more economical and effective method for controlling velocity and kinetic energy than a single drop of large height. An experimental campaign was specifically designed to investigate hydraulics of drop manhole cascades at the LIA Laboratory, University of Cassino and Southern Lazio. Results were summarized in equations that quantify overall dissipation performance and describe the hydraulics of the downstream flow in terms of outflow depth and energy head. The performance of single drops and a three-drop cascade are compared. The data show how the energy of the stream passing through the dropshaft cascade quickly achieves a new equilibrium condition downstream from the second manhole. Finally, the energy dissipation of a drop manhole cascade was compared with that of smooth and roughened chutes to highlight similarities and differences between different dissipation structures. [ABSTRACT FROM AUTHOR]

The hydraulics of supercritical flow across manholes in sewers is explored using systematic experimentation. Due to the expansion at the manhole entrance an in-manhole wave is generated. Further, at the downstream manhole end, flows with a sufficiently large filling ratio impinge on the wall and lead to a so-called swell. In addition, due to shock wave generation in the downstream sewer, a sewer wave is generated. The heights and locations of these three waves were determined in terms of basic hydraulic quantities. More importantly, the capacity of the manhole and the downstream sewer under wave action was quantified. It was found that in order for free surface flow to be maintained the common design standard for sewers with a supercritical approach flow have to be revised. These implications have to be accounted for in future designs. DOI: 10.1061/(ASCE)0733-9429(2002)128:11(1014) CE Database keywords: Supercritical flow; Hydraulics; Sewers; Flow resistance; Manholes.

Undular hydraulic jumps in circular conduits are considered with an experimental approach. Based on previous findings in rectangular channels, this research indicates differences in terms of shape effects. All present results depend on the filling ratio of the upstream conduit flow in addition to the upstream Froude number. The results include information on the wave crests and troughs, wave lengths, and generalized axial surface profiles. The wall surface profile is shown to be similar to the axial wave profile, but with smaller wave extrema and a wave shift. The design of conduits containing undular jumps should be avoided because of unstable flow. It is also demonstrated that conduits may choke in the presence of undular jumps, with a previously established choking number relating to a design limit. For flows with choking numbers in excess of 1, choking occurs associated with a transition from the free surface to the pressurized conduit flow. DOI: 10.1061/(ASCE)0733-9429(2002)128:11(1008) CE Database keywords: Hydraulic jumps; Water conduits; Sewers; Channel flow; Water tunnels.

This paper presents a methodology to evaluate the reliability of water distribution systems that can be used in the design phase and for identifying repair works to be carded out on existing systems. The methodology is based on the statistical analysis of dimensionless performance indices (hydraulic performance indices) derived from a large number of simulations of various water system demand scenarios and/or operating conditions. The hydraulic reliability index is assumed as the probability that, under a given operating condition, the hydraulic performance index will be above a certain threshold. Finally, the system's overall reliability (mechanical + hydraulic) is estimated using the overall reliability index, which is defined by the weighted mean of the hydraulic performance indices obtained for the various operating conditions. A case study using this methodology shows the concrete possibilities of applying this approach to a wide spectrum of cases, and the small influence on overall system reliability normally exerted by such events as the failure of links, pipes, and valves.

Featured Application: The paper presents new equations for predicting 3D scouring patterns at subsea pipelines under wave-only conditions. These equations are more reliable than conventional approaches and exhibit a clear physical consistence. Subsea pipelines carry oil or natural gas over long distances of the seabed, but fluid leakage due to a failure of the pipeline can culminate in huge environmental disasters. Scouring process may take place beneath pipelines due to current and/or wave action, causing pipeline suspension and leading to the risk of pipeline failure. The resulting morphological variations of the seabed propagate not only below and normally to the pipeline but also along the pipeline itself. Therefore, 3D scouring patterns need to be considered. Mainly based on the experimental works at laboratory scale by Cheng and coworkers, in this study, Artificial Intelligent (AI) techniques are employed to present new equations for predicting three dimensional current- and wave-induced scour rates around subsea pipelines. These equations are given in terms of key dimensionless parameters, among which are the Shields' parameter, the Keulegan–Carpenter number, relative embedment depth, and wave/current angle of attach. Using various statistical benchmarks, the efficiency of AI-models-based regression equations is assessed. The proposed predictive models perform much better than the existing empirical equations from literature. Even more interestingly, they exhibit a clear physical consistence and allow for highlighting the relative importance of the key dimensionless variables governing the scouring patterns. [ABSTRACT FROM AUTHOR]

A novel application of spline curves was developed for tracing average daily trends of water demand. These trends were used as input of a stochastic model to generate synthetic time series considering the number of water users as the main input parameter. Hermite polynomials were used for a piecewise interpolation of some known points of the daily trend which were obtained through reliable equations from the literature, whereas unknown points were deduced based on the mathematical properties of the demand pattern. Daily demand time series were generated for different time resolutions using a Monte Carlo approach based on a mixed probability distribution. Results were compared with real observed demand data to validate the effectiveness of the proposed approach, showing encouraging results. [ABSTRACT FROM AUTHOR]