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While analysing a real network, the assumption of zero minimum pressure head as the elevation of demand node may lead to unrealistic results as some residual pressure is necessary to derive any outflow at the node. A more realistic minimum pressure head plays an important role for analysis of an existing or proposed network. The present study extends a novel method of pressure-dependent volume driven-analysis by investigating the effects of realistic minimum pressure heads. The novelty of the proposed method is to evaluate the practical impact of the zero minimum pressure head assumption under pressure-deficient condition in water distribution networks considering pipe isolation, fire demand, and altering total reservoir heads. The results obtained from the present method are compared with the results based on the more optimistic traditional assumption of zero minimum residual pressure-head. It is observed that time to fill the storage tanks under both normal and pressure-deficient conditions for non-zero minimum pressure head is higher. All the simulations were performed using graphical user interface of EPANET 2. Thus, the proposed approach can be used readily by researchers and practitioners without requiring any additional computational codes development.

Forestry eco-hydrology is closely related to root architecture, and soil water infiltration has been always associated with root architecture. In this study, dye infiltration experiments and HYDRUS-1D were used to quantify the effects of different root architectures on the dynamics of soil water infiltration, volumetric water content, and soil water pressure head. The results provide evidence that root channels acted as preferential flow paths for water infiltration and percolation into the soil. Maize fibrous roots, rubber trees fine roots, and Spartina alterniflora smooth roots easily penetrated the plough layer of an agriculture site, the hard soil layer of a forest site, and the alternating sandy and mud layers of an intertidal zone, respectively. The initial and final infiltration rates were significantly different between the rooted and rootless soil profiles. The root-induced infiltration events lowered the propagation time of the wetting front across the rooted soil profile by 33%–113% than the rootless soil (p < 0.05), and the volumetric water content of the saturation zone of the rooted soil profile increased by 12%–19% relative to the rootless soil (p < 0.05). Furthermore, the soil water pressure head increased from negative (i.e., unsaturated) to positive (i.e., saturated) in the saturated soil. This change was more pronounced in the maize fibrous roots soil profile, but less pronounced in the rubber fine roots’ soil profiles or the S. alterniflora smooth roots. The results indicate that the downward movement, volumetric water content, and soil water pressure head were higher in soil profiles having plant roots than the rootless soil, and the degree of roots effects depended on roots architectures, soil hardness, and soil layer configuration. The findings provide evidence that root channels can act as preferential flow paths for water infiltration and percolation into the soil.

Ski jump spillways are frequently implemented to dissipate energy from high-speed flows. The general feature of this structure is to transform the spillway flow into a free jet up to a location where the impact of the jet creates a plunge pool, representing an area for potential erosion phenomena. In the present investigation, several tests with different ski jump bucket angles are executed numerically by means of the OpenFOAM® digital library, taking advantage of the Reynolds-averaged Navier–Stokes equations (RANS) approach. The results are compared to those obtained experimentally by other authors as related to the jet length and shape, obtaining physical insights into the jet characteristics. Particular attention is given to the maximum pressure head at the tailwater. Simple equations are proposed to predict the maximum dynamic pressure head acting on the tailwater, as dependent upon the Froude number, and the maximum pressure head on the bucket. Results of this study provide useful suggestions for the design of ski jump spillways in dam construction.

This study investigates the water hammer phenomenon using ANSYS Fluent, comparing numerical results with analytical models (Quasi, Zielke, and Brunone) and experimental data from a laboratory setup. The standard k - ε turbulence model was employed to simulate turbulent flow conditions. The findings reveal that the ANSYS-based water hammer simulation shows excellent agreement with both the experimental data and Brunone’s analytical model. Pressure variations were analyzed at two critical locations: the pipe midpoint and the valve vicinity, across different flow velocities. For instance, at a flow velocity of 0.1 m/s, the numerical model predicted a pressure head of 47.263 m near the valve, closely matching the experimental value (46.403 m) and outperforming the Zielke (45.307 m), Brunone (45.526 m), and Quasi (45.521 m) models. These results highlight the high accuracy and reliability of the numerical simulation in capturing water hammer dynamics, suggesting its effectiveness for practical hydraulic system analysis.

Aiming at the gas injection technique for maintaining the performance of liquid-propellant rocket engines over a wide throttling range, an experimental study was conducted using the head cavity of a certain type gas generator as the object. White oil and water were selected as the substitute working liquids, while gaseous helium (GHe) and gaseous nitrogen (GN2) were used as injected gases. Pressures at typical positions were measured, and the phase distribution at the head cavity inlet and nozzle outlets was visually captured. The effects of flow rate, gas type and liquid type were tested and compared. The results indicate that, injecting gas could significantly increase the pressure of head cavity, and improve the nozzle atomization effect at low-thrust conditions. The nozzle pressure drop increases linearly with the gas injection rate at a given liquid flow rate. Across varying liquid flow rates, a fixed amount of gas injection results in nearly constant multiplicative increases in the nozzle pressure drop. GHe is recommended as the preferred injecting gas due to its superior pressurization capability compared to GN2. This work could provide fundamental data for understanding gas injection mechanisms and promote its mature application in the development of deep-throttling technology.

Determining the water permeability of concrete in structures remains a conundrum because of difficulties in removing the influences of moisture. This study describes the extended flow-net theory developed on the basis of the two-pressure-head concept, which provides a means of measuring permeability under the partially saturated condition. Surface-mounted tests and standard laboratory water penetration tests were carried out to verify this approach. Before determining the water permeability, steady-state flow rates at two different pressure levels were evaluated and the effects of initial moisture conditions on flow behavior were investigated. The results indicate that the proposed approach does offer a useful means of determining the water permeability of structural concrete, although it cannot be claimed tobe universally applicable for all moisture conditions likely to be encountered in practice. Keywords: extended flow-net theory; in-place water permeability; two-pressure-head test; unsaturated flow.

Dissipation basins are usually constructed downstream of spillways to dissipate energy, causing large pressure fluctuations underneath hydraulic jumps. Little systematic experimental investigation seems available for the pressure parameters on the bed of the US Department of the Interior, Bureau of Reclamation (USBR) Type II dissipation basins in the literature. We present the results of laboratory-scale experiments, focusing on the statistical modeling of the pressure field at the centerline of the apron along the USBR Type I and II basins. The accuracy of the pressure transducers was ±0.5%. The presence of accessories within basinII reduced the maximum pressure fluctuations by about 45% compared to basinI. Accordingly, in some points, the bottom of basinII did not collide directly with the jet due to the hydraulic jump. As a result, the values of pressure and pressure fluctuations decreased mainly therein. New original best-fit relationships were proposed for the mean pressure, the statistical coefficient of the probability distribution, and the standard deviation of pressure fluctuations to estimate the pressures with different probabilities of occurrence in basinI and basinII. The results could be useful for a more accurate, safe design of the slab thickness, and reduce the operation and maintenance costs of dissipation basins.

Predicting soil–water dynamics in Moistube irrigation (ΜΤΙ) favours understanding ΜΤΙ functioning mechanisms and technical parameter design. This study proposed a physically based infiltration (PH) model extending the Green–Ampt (GA) model to a two-dimensional polar coordinate system. We treated Moistube as a clay and considered the infiltration from internal Moistube to surrounding soils. The performances of the PH model, together with a semi-physical–empirical (PH–EM) model and a numerical simulation (NUM) model, were evaluated based on regulated working pressure head (WPH) experiments. A HYDRUS 2D model was used based on experimental design to reproduce the soil–water dynamics by assigning Moistube and soil two sets of hydraulic parameters. WPH increase or decrease treatments were applied to Moistube. The Moistube discharge rate, infiltration volume, and wetting front (WF) advance were analyzed and predicted by three models. The results showed that cumulative infiltration, Moistube discharge, and effective saturation around Moistube were enhanced or abated under WPH increase or decrease, with WF accelerating or decelerating. The modelled effective saturation varied between 0.45 and 0.70, providing suitable moist conditions for crops. Percentage of bias (PBIAS) and mean absolute percentage relative error (MAPRE) were employed to evaluate model performances. Three models well-predicted infiltration characteristics and WF advance but differed in accuracy. The PH model overestimated and underestimated the Moistube discharge rate in early and later phases. The prediction accuracy in WF varied across infiltration phases and WPH modes. The PH–EM model yielded accurate results due to its empirical attribute. The NUM model produced novel phenomena of infiltration characteristics at WPH adjustment points, i.e., the discharge rate exponentially decreased over time after the WPH increased but presented restraining followed by rebounding trends after the WPH decreased. The NUM model strongly depended on the selection of the Moistube hydraulic parameters. Extending the GA model to a two-dimensional polar coordinate system by treating Moistube as a clay was practicable in modelling soil water dynamics, thereby contributing to designing and optimizing MTI technical indexes.

The embedment of steel spiral cases within concrete under a pressurized condition is a kind of construction approach that widely used in pump-turbines. There will be an initial preloading clearance between the spiral case and surrounding concrete after the construction. The clearance is directly determined by the preloading water head and changes with the variation in operational hydraulic pressure, which will effect the combined load transmission mechanism. This paper investigates the clearance evolution of preloading filling spiral cases and surrounding concrete under different internal pressure. The effect of the preloading water head on the initial clearance, the contact characteristics and the combined load transmission mechanism under different internal pressure are numerically studied. The results show that the initial clearance between the spiral case and concrete increases with the rise of the preloading water head. The maximum clearances are all located at the waist of the spiral case. The clearance during operation presents uneven distribution characteristics in spatial and temporal scales. Before the internal water pressure comes to the preloading water head, the inlet, outer part in the direction of 45° and the sectional area are the first to close, the outer part of the waist follows, while the outer area of the spiral case middle remains open when the pressure reaches the preloading water head. The contact pressure distribution is consistent with the contact status characteristic. The conclusion of this paper aims to improve the understanding of the effect of the clearance between the preloading filling spiral case and concrete, so as to provide theoretical reference for safe and stable operation of pump-turbine units.

To improve the cavitation performance of a single-stage, single-suction centrifugal pump, this study compared the effects of an equal-pitch inducer and a variable-pitch inducer. Experimental results revealed that the NPSH 3 of the pump without an inducer is 4.6m for operation at Q=80m 3 /h, while with an equal-pitch inducer and a variable-pitch inducer are respectively 2.6m and 2.2m. Both two inducers significantly increase the shut-off heads, while the BEP shift towards smaller flow rates, with the maximum efficiency value reduced by about 3%. The CFD simulation analysis show that when the inlet total pressure is greater than 4m, the equal-pitch inducer has better anti-cavitation performance, while the variable-pitch angle inducer has a better inhibitory effect on cavitation development which the inlet total pressure is less than 4m. To further enhance the pump’s cavitation performance, filing blade inlet suction side of the variable-pitchinducer is necessary to reduce the NPSH 3 from 2.2m to 1.7m, resulting in a 22% improvement in cavitation performance.