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To address the wave control challenges in the surge tanks of hydropower plants with ultra-long headrace tunnels, this study proposed a surge tank configuration with three large-volume water chambers. The transient characteristics under critical operational scenarios such as load acceptance and rejection were analyzed using the one-dimensional method of characteristics (1D MOC). Additionally, the 1D MOC and three-dimensional fluid dynamics (3D CFD) coupled simulation method was applied to analyze the flow patterns in the surge chambers under controlled conditions. The results demonstrate that the well-designed multi-chamber geometry effectively confines water-level fluctuations within acceptable limits. Both water and air phases exhibit favourable flow patterns without significant air-pocket entrapment. These findings provide valuable insights for improving transient processes in long-distance hydropower systems and offer guidance for surge tank design optimization.

An increasing reliance on groundwater resources has been observed worldwide during the past 50–70 years and has led to unsustainable groundwater abstraction in many regions, especially in semi-arid and arid alluvial groundwater basins. Managed aquifer recharge (MAR) has been promoted to replenish overdrafted groundwater basins and augment surface water supply. However, MAR feasibility in alluvial groundwater basins is complicated by complex geologic architecture that typically includes laterally continuous, fine-texture confining units that can impede both recharge rates and regional propagation of increases in the hydraulic head. A greater feasibility of MAR hinges on identifying locations where rapid, high-volume recharge that provides regional increases in pressure head are possible, but relatively little research has evaluated the factors that control MAR feasibility in alluvial groundwater basins. Here, we combine a transition probability Markov chain geostatistical model of the subsurface geologic heterogeneity of the eastern side of the northern Central Valley, California, with the three-dimensional, variably saturated water flow code ParFlow to explore the variability of MAR feasibility in this region. We use a combination of computationally efficient local- and global-sensitivity analyses to evaluate the relative importance of factors that contribute to MAR feasibility. A novel proxy parameter approach was used to describe the configuration and proportions of subsurface hydrofacies and the water table depth for sensitivity analyses, and results suggest that recharge potential is relatively more sensitive to the variability of this proxy parameter than to the variability of individual hydrofacies hydraulic properties. Results demonstrate that large variability of MAR feasibility is typical for alluvial aquifer systems and that outsized recharge rates are possible in select locations where interconnected, coarse-texture hydrofacies occur.

See the retraction notice E3S Web of Conferences 420 , 00001 (2023), https://doi.org/10.1051/e3sconf/202342000001

In order to analyze the response of a hydraulic turbine to a variation in the operating conditions, different laws of variation in time of the mass flow rate have been considered. After validating the overall numerical framework through comparison with relevant experiments, the performances of the considered turbine have been analyzed from a fluid-dynamic point of view. The results show that different time profiles of the mass flow rate (in this work, for simplicity, referred to as “transition functions”) have a varying influence on the transient behavior of the turbine. When a quadratic function is considered for the case of large flow, the transient head and torque increase gradually with time, the fluctuation amplitude of the transient hydraulic efficiency at the main frequency is the largest, and the fluctuation amplitude of the radial force is the smallest. For the small flow case, the time profile with exponential nature leads to the best results. The transient head and torque decrease gradually with time, the pulsation amplitude of the transient hydraulic efficiency is the largest at the main frequency, and the pulsation amplitude of the radial force is the smallest.

Due to the uneven distribution of water resources, there are many water diversion projects around the world, such as the South-to-North Water Diversion Project in China, especially in some plain areas. To transfer water from low to high areas, large low-head pumps have been widely used. The transition process of the pumping station is mainly caused by the sudden change in the flow velocity and pressure of the fluid in the pipeline of the pumping station system caused by the start-up and shutdown processes. The previous research has mainly been based on the one-dimensional characteristic line method. However, due to the characteristics of the low-lift pumping station, the flow passage is short and irregular, and the calculation results often cannot guarantee the accuracy of the calculation. In addition to some faults in the actual operation process, in some pumping stations, accidents or operation-scheduling faults are caused by transient processes, such as a high degree of water hammer, the inability to initiate backward flow, the shutdown load rejection runaway exceeding the standard, and decreased hydraulic efficiency. To avoid transition process failures in the newly designed pumping stations and the modified pumping stations, it is necessary to carry out a research review of the three-dimensional transition process of large low-lift pumps. Especially with the development of computing technology, CFD numerical simulation technology has become the main research method for analyzing the pump transition process. The research on the transition process is mainly based on the combination of numerical simulations and experiments. The reliability of a numerical simulation is verified by an experiment. A numerical simulation can measure some parameters that cannot be measured by an experiment. Dynamic mesh technology has become the main technical means for using CFD numerical simulation to study the three-dimensional transition process, and the secondary development of computing software has become the main trend of future development. This paper analyzes and summarizes the research status of the start–stop transition process of large low-lift pump stations and provides a reference for the protection of the start–stop transition process of pump stations.

Understanding the change in soil hydraulic conductivity with temperature is key to predicting groundwater flow and solute transport in cold regions. The most commonly used models for hydraulic conductivity during freeze‒thaw cycles only consider the flow of capillary water in the soil and neglect water flowing along thin films around the particle surface. This paper proposed a new hydraulic conductivity model of frozen soil via the Clausius–Clapeyron equation based on an unsaturated soil hydraulic conductivity model over the entire moisture range using an analogy between freeze‒thaw and dry‒wet processes in soils. The new model used a single equation to describe the conductivity behaviors resulting from both capillary and adsorption forces, thus accounting for the effect of both capillary water and thin liquid film around soil. By comparison with other existing models, the results demonstrated that the new model is applicable to various types of soils and that the predicted hydraulic conductivity is in the highest agreement with the observed data, while reducing the root mean square error by 38.9% compared to the van Genuchten–Mualem model. Finally, our new model was validated with thermal–hydrological benchmark problem and laboratory experiment result. The benchmark results indicated that the advective heat transfer was more significant, and the phase change was completed earlier when considering both capillary and adsorption forces than when only considering capillary forces. Furthermore, the coupled flow–heat model with the new hydraulic conductivity expression replicated well the results from a laboratory column experiment. Key Points A new model accounting for both capillary and film water was developed to estimate soil hydraulic conductivity during freeze‒thaw process The new model based on physical mechanism has a simpler form and needs fewer parameters than existing model The new model was coupled with flow‒heat transport equations that successfully replicate the laboratory experiment data

With the growing development and utilization of underground space and resources, rock masses exposed to high stresses and pore pressure, large temperature changes, and complex hydraulic–chemical environments have become a research topic of wide interest. Such coupled physical and chemical processes strongly impact the rock mass’s mechanical properties and structural failure. Analyzing and studying rock’s mechanical properties and damage under multi-physics coupled environment can help ensure the safety and efficiency of exploiting underground mineral resources and developing underground space. Thermal–hydraulic–mechanical–chemical (THMC) coupled processes in rock masses have become a hot research topic, and the related numerical and experimental methods have made significant progress. This paper comprehensively reviews and evaluates the latest research progress on THMC coupling models and numerical methods. Finally, we summarize the key points, difficulties, and future THMC multi-physics coupling research directions and provide references for influencing mechanisms research and engineering practice.

Abrasive waterjet (AWJ) cutting technology is widely used for nonconventional cold machining of ductile or brittle materials in various manufacturing fields. However, this technology has a significant limitation in terms of the effective depth of cut. As a solution, in this study, a model for the effective depth of cut is proposed based on the Gaussian distribution of the cut profile curve. The proposed model is used to investigate the dynamic evolution of the depth of cut and its influence mechanism. First, a prediction model for the effective depth of cut is established using the material removal mechanism and single particle erosion theory. In addition, an experimental analysis is conducted to improve and optimize the cutting performance of the AWJ considering the effect of machining parameters on (i) the effective depth of cut and (ii) cutting performance. The key factors that affect the geometric profile characteristics of the kerf are investigated, and the optimal parameters for achieving the effective depth of cut model are further determined. According to the AWJ cutting performance experiments conducted by using Ti-6Al-4 V, the prediction model is strongly correlated with the experimental data, and the average difference between the prediction model and experimental results is 6.46% of the effective depth of cut. Notably, this model can predict the effective depth of a cut for different cutting parameters. Furthermore, it exhibits significant industrial value by expanding the application fields of finishing machining using AWJ technology.

The internal pore structural characteristics and microbubble distribution features of concrete have a significant impact on its frost resistance, but their size is relatively small compared to aggregates, making them difficult to visually represent in the mesoscopic numerical model of concrete. Therefore, based on the ice-crystal phase transition mechanism of pore water and the theory of fine-scale inclusions, this paper establishes an estimation model for effective thermal conductivity and permeability coefficients that can reflect the distribution characteristics of the internal pore size and the content of microbubbles in porous media and explores the evolution mechanism of effective thermal conductivity and permeability coefficients during the freezing process. The segmented Gaussian integration method is adopted for the calculation of integrals involving pore size distribution curves. In addition, based on the concept that the fracture phase represents continuous damage, a switching model for the permeability coefficient is proposed to address the fundamental impact of frost cracking on permeability. Finally, the proposed estimation models for thermal conductivity and permeability are applied to the cement mortar and the interface transition zone (ITZ), and a thermal–hydraulic–mechanical coupling finite element model of concrete specimens at the mesoscale based on the fracture phase-field method is established. After that, the frost-cracking mechanism in ordinary concrete samples during the freezing process is explored, as well as the mechanism of microbubbles in relieving pore pressure and the adverse effect of accelerated cooling on frost cracking. The results show that the cracks first occurred near the aggregate on the concrete sample surface and then extended inward along the interface transition zone, which is consistent with the frost-cracking scenario of concrete structures in cold regions.

Two-dimensional (2-D) quadrant analysis is generally used for investigating flow and sediment dynamics around a rigid structure in open channel flows. Given that particle distribution around rigid obstacles is not spatially uniform and changes in time, while vortices evolve to become three-dimensional (3-D) structures, 2-D quadrant analysis might be unsuitable to completely determine the sediment transport. Hence, 3-D quadrant and 3-D octant analyses should be considered, using the 3-D instantaneous velocity data and relative 3-D bursting process to define sediment transport surrounding the submerged square and circular cylinders. The turbulent kinetic energy (TKE), transition probabilities, occurrence probabilities, stress fraction and angles of inclination of 3-D bursting events are considered to quantify the coherent structures surrounding the cylinders and their interaction with bed particles. Experiments were conducted at the Hydraulics and Water Resources Engineering Laboratory, School of Infrastructure, Indian Institute of Technology, Bhubaneswar, Odisha, India, and velocity data were recorded at different cross-sections around the submerged cylinders using an acoustic Doppler velocimeter. Results show that the TKE is greater for internal ejection, external ejection, and internal sweep, external sweep in the upstream of the circular and square cylindrical structures. On the other part, the TKE is significant for internal ejection, external ejection, and internal sweep, external sweep in the downstream of the aligned square cylindrical structures, which justifies the highest scour depth that occurred upstream of the circular and square cylindrical structures and downstream of the aligned square cylindrical structure. The transition probability of the bursting events was determined using the Markov process from the measured velocity data to investigate the consecutive occurrence of bursting events. Further, the importance of sweeps and ejections on sediment erosion surrounding the cylinders within the scour hole at various stages of its development was investigated via 3-D quadrant analysis of the bursting occurrences. The outcomes show that external sweep and internal ejection events are active mechanisms for bed particle transport surrounding the cylinder. The maximum transition probability values are found around aligned cylindrical structures in comparison with the circular and square cylindrical structures in the transverse direction. This depicts the formation of a trailing vortex on both sides of the aligned square cylindrical object. The results reveal that the effect of inclination angles with respect to the water flow is greater for internal ejection and external sweep from upstream to downstream within the scour hole surrounding the cylindrical structures at various phases of development as horseshoe vortices and downflow develop upstream of the cylindrical structures while trailing vortices and wake vortices form at the top and downstream of the cylindrical structures. Internal and external ejection have a higher stress fraction than an internal and external sweep for square cylinders with alignment angles of 0°, 20° and circular cylinders over underdeveloped and developed scoured beds, respectively. With the higher percentage of fractional contributions for internal sweeps, the external sweep is predicted close to the cylindrical objects in comparison with the internal ejection and external ejection events because of the formation and warping of the horseshoe vortex close to the cylindrical objects, suggesting a significant probability of 3-D bursting occurrences with sediment movement near the cylindrical structures.