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This paper explores the impacts of reconfiguration and leaf morphology on the flow downstream of a flexible foliated plant. 3D acoustic Doppler velocimetry and particle image velocimetry were used to experimentally investigate the hydrodynamic interaction between a foliated plant and the flow, testing two plants with different leaves morphology under different bulk flow velocities. The model vegetation was representative of riparian vegetation species in terms of plants hydrodynamic behavior and leaf to stem area ratio. To explore the effects of the seasonal variability of vegetation on the flow structure, leafless conditions were tested. Reconfiguration resulted in a decrease of the frontal projected area of the plants up to the 80% relative to the undeformed value. Such changes in plant frontal area markedly affected the spatial distributions of mean velocity and turbulence intensities, altering the local exchanges of momentum. At increasing reconfiguration, the different plant morphology influenced the mean and turbulent wake width. The leafless stem exhibited a rigid behavior, with the flow in the wake being comparable to that downstream of a rigid cylinder. The study revealed that the flexibility-induced reconfiguration of plants can markedly affect the local distribution of flow properties in the wake, potentially affecting transport processes at the scale of the plant and its subparts.

Although pressure regulation valves (PRVs) are commonly used for reducing leakage in water distribution networks (WDNs), in recent years, many studies have highlighted the opportunity of using pumps as turbines (PATs) so as to couple pressure reduction (and thus leakage reduction) with hydropower generation. Unlike in water transmission systems however, flow discharge in a WDN varies continuously, consequently requiring real-time control (RTC) of pressure. Nevertheless, RTC of a PAT in a WDN remains an open issue, due to the lack of information and knowledge about PAT operation in a real environment. Whereas previous experimental studies have described PAT installation with a frequency converter in which the power produced gets dissipated through electrical resistance, in the hydraulic regulation layout, impeller speed depends on the electrical grid. Consequently, this paper proposes a comprehensive algorithm to both control the pressure at the control node of a WDN and produce power through a PAT directly connected to the electrical grid. The operation of the prototype was considered under hydraulic regulation, demonstrated by several studies to represent the most effective trade-off between costs and benefits. Further testing by means of laboratory experiments designed to simulate the operation of a grid-connected PAT installed in a WDN effectively validated the robustness of the proposed method. The results proved the ability of the prototype and algorithm to couple hydropower generation with pressure control even when the flow varied suddenly. [ABSTRACT FROM AUTHOR]

A pressurized water system may be subjected to high pressure surges because of the expulsion of a trapped air pocket through an orifice at the downstream end of the pipe. Results are presented of laboratory experiments, in which pressure histories were recorded for different upstream heads, air pocket volumes, and orifice sizes. The resulting pressure oscillation pattern was divided into two distinct stages: a first phase of low-frequency pressure oscillation during the air release, followed by a sudden pressure increase with water hammer characteristics when the water column reaches the orifice. The experimental results show that the duration of the first phase decreases substantially with increasing upstream head and orifice size, and increases with air pocket volume. A simple relationship was deduced, which agrees well with experimental data. The maximum pressure peaks, always observed in the water hammer phase, increased with upstream head and orifice size, whereas the volume of the air pocket appeared to be a less significant factor in the range investigated. A simple predictive equation was deduced based on Allievi-Joukowski results. DOI: 10.1061/(ASCE)0733-9429(2008) 134:9(1395) CE Database subject headings: Water pressure; Water hammer; Air flow; Water pipelines; Hydraulic transients.

Seepage erosion phenomena can arise when particles of soil are transported underneath any hydraulic structure by the seepage flow, as a consequence of the difference in the surface elevation upstream and downstream of the hydraulic structure. To assess the stability of hydraulic structures against seepage erosion computational models are available varying from simple empirical rules to advanced models. In this paper, the safety coefficient is assessed by comparing the exit gradient with the critical gradient: the former represents the hydraulic gradient at the exit point along the downstream ground surface, whereas the latter is the gradient at which upward drag forces on the soil particles equal the submerged weight of the soil particles and a quicksand condition originates. An experimental research was carried out to analyze different thickness sheet piles embedded in sandy soils, resulting in agreement between experimental data and theoretical values if the thickness of the sheet pile and the ground surface deformation are properly taken into account. DOI: 10.1061/(ASCE)0733-9429(2008)134:6(794) CE Database subject headings: Filtration; Seepage; Soil erosion; Heaving; Hydraulic models; Experimentation; Sand.

Transients generated by expulsion of air pockets in water pipelines represent a key issue in the management of water systems. Severe pressure surges may arise, with detrimental effects on pipelines, valves and other devices. To analyze the transient and predict the resulting pressure surge, both theoretical and experimental studies have been developed in the literature. However, most studies consider horizontal or vertical pipelines, whereas the actual profile in the real field environment is a sequence of ascending and descending pipes. Consequently, this paper summarizes laboratory experiments carried out on an undulating pipeline, with an orifice fitted at the high point to simulate an air release valve. In the experiments, the orifice diameter, the supply pressure and the air volume entrapped in the descending pipe were varied. In almost all the runs, the peak pressure was achieved during the mass oscillation transient. Water hammer only occurs because of the expulsion of air bubbles within the water column, but generally the effect on the transient is fairly negligible. Results also showed that pressure surges decrease upon increasing the orifice diameter, except for high supply pressure and small-entrapped volume, for which an intermediate 'critical' orifice diameter can be identified. [ABSTRACT FROM AUTHOR]