Search Results (599)

This paper investigates the evolution of the microstructure, mechanical performances, and corrosion resistance of selective laser melting (SLM) 304 steel under different intermittent stretching deformation step sizes, revealing the underlying evolution patterns. The results indicate that the intermittent deformation step size significantly affects the microstructure and performance of SLM 304 steel. Larger step sizes result in more complete molten pool contours, less deformation of grain and cellular structures, and a lower martensite volume fraction; smaller step sizes lead to distorted molten pools, fragmented grains, exacerbated cellular structure distortion, and increased martensite content. In terms of mechanical performances, tensile strength, nano-hardness, and elastic modulus decrease with increasing step size, while elongation increases accordingly. Corrosion resistance improves with larger step sizes, with specimens exhibiting more complete and thicker oxide films on the surface and superior pitting resistance; continuous stretching specimens exhibit the worst corrosion resistance, while the original specimens are the best. Intermittent deformation optimizes properties by regulating microstructure, providing a basis for the design of high-performance SLM 304 steel. This study provides theoretical support for the design and application of additive manufacturing stainless steel components, facilitating the engineering and industrial application of SLM technology in high-end equipment manufacturing. Full article

During frequent peak-regulation operation, pumped storage units inevitably operate under off-design conditions. Variations in draft tube flow structures under different load conditions may alter the hydraulic loading acting on the runner and shaft system. In this study, a model pump-turbine was investigated using unsteady numerical simulations combined with finite element structural analysis. Analyses were conducted under 70%, 100%, and 105% load conditions, representing typical part-load, rated, and overload operating states. The results show that under 70% load, the draft tube flow exhibits an eccentric structure with strong circumferential pressure non-uniformity. At the rated condition (100% load), the flow field is closest to axisymmetric with the most uniform pressure distribution. Under 105% load, a concentrated central vortex forms, and the degree of non-uniformity is intermediate. The hydraulic loads under different conditions lead to significant differences in the stress and deformation characteristics of the shaft system. The maximum equivalent stress increases from 1.84 MPa at the rated condition to 3.33 MPa under overload conditions, while more pronounced flow asymmetry and pressure non-uniformity occur at part-load operation. These findings clarify the relationship between load variation, draft tube flow structures, and the mechanical response of the shaft system. Full article

Cavitation in rotating hydraulic machinery—such as industrial pumps and hydropower turbines—can cause blade and casing erosion, excessive vibration, noise and efficiency loss, posing significant operational and economic risks across industrial sectors. Reliable and scalable monitoring strategies are therefore essential, particularly under variable operating conditions in real-world environments. Recent advances in machine learning (ML) and deep learning (DL) have enabled data-driven approaches for cavitation detection based on operational sensor signals, yet a structured synthesis of these developments is lacking. This scoping review systematically analyzes measurement-based ML and DL approaches for cavitation monitoring, with the aim of identifying key trends, challenges and future research directions. Following PRISMA-ScR and JBI guidelines, 52 peer-reviewed studies published between 1996 and 2025 were evaluated, covering laboratory and field investigations across pumps and turbines and a wide range of model architectures. The analysis reveals that most studies are laboratory-based (∼80%), focus on pumps (∼70%) and rely on single-machine datasets (>80%), limiting generalization across machines and operating conditions. Classical ML approaches remain relevant due to interpretability and robustness with limited data, while DL enables end-to-end learning from raw or time–frequency transformed signals, frequently achieving diagnostic accuracy above 95%. Hybrid frameworks combining DL-based feature extraction with classical classifiers are increasingly adopted. Key limitations across the literature include domain shifts between laboratory and field data, scarce or inconsistent labeling and a predominant focus on categorical cavitation severity levels. Full article

Typhoon-induced extreme weather poses a severe threat to power systems with high offshore wind penetration. Source-side wind turbine tripping and grid-side transmission line failures are likely to occur simultaneously, which may trigger cascading outages and large-scale load shedding. A multi-level source-grid-load-storage preventive resilience dispatch strategy is proposed. A typhoon spatiotemporal evolution model is first established based on the Batts gradient wind model. Failure probability models for offshore wind turbines and overhead transmission lines are developed while considering strong wind and lightning strike effects. The most probable and severe fault scenario is identified using an entropy-based quantification method. A two-stage robust preventive dispatch model is subsequently formulated. In the day-ahead stage, unit commitment, multi-type reserve allocation, and pumped storage scheduling are optimized at a 1 h resolution. In the real-time stage, combined wind-storage systems are coordinated at a 10 min resolution to accommodate rapid wind power ramps caused by high-wind shutdown events. The model is reformulated through Lagrangian duality and solved by the Benders decomposition algorithm. Case studies on a modified IEEE-RTS 24-bus system with three offshore wind farms demonstrate that the proposed strategy reduces wind curtailment by 66.3%, load shedding by 74.6%, and total cost by 14.8% compared with the case without energy storage. The combined operation cost of storage resources accounts for only 3.1% of the total cost, confirming its favorable cost-effectiveness for resilience enhancement. The proposed strategy contributes to the sustainable integration of offshore wind energy by ensuring a reliable power supply during extreme weather events. Full article

The development of renewable energy and the increasing demand for electricity underscore the importance of pumped storage for grid stability. Under low-flow pump operating conditions, pump-turbines frequently exhibit hump characteristics, causing severe hydraulic instability and strong pressure pulsations. This study investigates the formation of a hump using full-channel numerical simulations based on the Scale-Adaptive Simulation turbulence model. The numerical flow–head characteristics were validated against the available experimental H–Q data, while the pressure pulsation results were used for qualitative mechanism analysis. The results reveal three major mechanisms: pre-swirl and spiral backflow in the draft tube, non-uniform runner inflow, and vortex flow-induced separation in the wicket gates. An analysis of entropy production reveals that vortex dissipation is responsible for as much as 71% of hydraulic losses in the hump region. In order to mitigate these effects, four stabilizing fins were installed inside the draft tube. The simulations indicate that the fins possess the capability to inhibit swirl and backflow, confine the vortices within the fin–runner interface, improve inflow uniformity and reduce overall hydraulic losses. As a result, the structural modification significantly attenuates the pressure pulsation amplitudes at key monitoring points and visibly shortens the recovery periods. The region of the hump and positive slope of the performance curve are considerably reduced while the head near the region of the hump is increased. Although the intrinsic hump characteristic is still present, the fin-based flow-control strategy can effectively improve the performance and stability of the pump-turbine, which can guide the design and optimization of high-efficiency pumped-storage plants. Full article

Samothrace is a Greek island in the northern Aegean Sea. Though connected to the mainland grid and demonstrating strong wind potential, it is challenged by seasonal shortages in both electricity and potable water. This study assesses a Hybrid Renewable Energy System designed to meet local energy and water demands while maintaining economic viability. The system consists of 10 wind turbines (23.5 MW), a reverse osmosis desalination plant yielding 876,000 m³/year, and four alternative storage configurations: green hydrogen, pumped hydro, lithium-ion batteries, and a combined green hydrogen–pumped hydro option. Using identical climatic and demand data, system performance was simulated for the years 2011–2020. Wind generation reached 113,000 MWh annually, of which 81–84% was exported to the mainland. Potable water demand was met at a rate of 99% in all scenarios, with monthly production ranging from 17,500 m³ in February to almost 50,000 m³ in August, thus requiring 1.80% of wind output. Investment costs ranged from 34.4 M € to 39.8 M €; net present values remained around 75 M € for all scenarios. Results demonstrate that complete autonomy can be achieved; however, economic sustainability is maximized by leveraging the interconnection and sizing storage below full-autonomy levels. Full article

The transition toward sustainable aviation fuels requires dedicated experimental platforms capable of evaluating alternative fuels under realistic propulsion conditions. This study presents the development and laboratory experimental validation of a modular testing installation designed for sustainable fuels derived from plastic waste pyrolysis, intended for aerospace engine applications. The proposed system is conceived as an integrated small-scale gas turbine assembly that reproduces the functional characteristics of a jet engine and enables controlled laboratory investigations of dynamic behavior, combustion stability, and performance. The installation comprises a compressor, annular combustion chamber, and turbine mounted on a common shaft, along with a fully autonomous fuel supply system equipped with electronically controlled pumping, safety devices, and thermal conditioning of the fuel mixture via an attached Stirling engine. Combustion processes are continuously evaluated using an exhaust gas analysis system to assess fuel composition and combustion quality, while a high-speed camera operating at 50,000 fps enables detailed visualization of flame stability. Operating parameters, including temperatures, pressures, rotational speed, mass flow rates, and thrust, are monitored and recorded through an integrated control and data acquisition system with real-time analysis capabilities. Experimental results demonstrate stable operation and reliable ignition using alternative fuel mixtures, confirming the suitability of the modular installation as a versatile research platform for the assessment and comparative analysis of sustainable aerospace fuels. Full article

Pump-turbines are critical for maintaining power grid stability, but they frequently suffer from flow instabilities induced by cavitation due to frequent operating condition changes. This study employs numerical simulations to systematically analyze the internal flow characteristics and changes in runner forces within a model pump-turbine under varying guide vane openings and cavitation coefficients. Results indicate that, under low opening conditions, a spiral vortex rope forms within the draft tube, inducing significant low-frequency pressure fluctuations. As cavitation intensifies, the vortex rope undergoes substantial expansion. At guide vane openings of 30.6 degrees and 37.3 degrees, the draft tube vortex rope exhibits a straight conical shape, with its dimensions increasing as flow rate rises. Additionally, the radial force on the runner is dominated by low-frequency fluctuations generated by the draft tube at low opening conditions, shifting to high-frequency characteristics caused by rotor–stator interaction at high opening conditions. Meanwhile, the expansion and contraction of the cavity volume induce low-frequency fluctuations in the axial force on the runner. These findings reveal the mechanism of vortex rope evolution on runner forces, emphasizing the impact of cavitation on the flow characteristics and force characteristics of the unit. Full article

The runner of a pump turbine features a relatively flat structural configuration. The clearance cavities formed between the upper crown, lower band, and surrounding stationary components play a critical role in its dynamic behavior and operational stability. Consequently, a detailed modal analysis of the runner is essential to ensure safe and stable operation. In this study, an acoustic–structure coupling method is adopted to investigate the wet modal characteristics of the pump-turbine runner, explicitly accounting for the added mass effect induced by the fluid in the external flow passages. By systematically varying the geometric parameters of the upper crown clearance cavity, the influence of seal clearance dimensions on the runner’s modal characteristics is examined. The results demonstrate that the radial clearance and the axial height of the seal cavity are the most influential parameters, reducing natural frequencies by up to 15.85% and 16.93%, respectively. The pitch of the seal teeth shows a secondary yet notable effect, inducing a frequency variation of 13.73%. In contrast, local labyrinth seal parameters, such as the number of teeth and tooth width, have a comparatively limited effect. This study provides practical guidance for vibration risk prediction, anti-resonance design, and operational stability assessment of high-head, large-capacity turbine runners by revealing the quantitative relationship between geometric parameters and modal frequencies. Full article

This study employs CiteSpace 6.3 R1 software to conduct a quantitative analysis of 645 cavitation-related centrifugal pump publications from the Web of Science Core Collection database (2007–2025) using bibliometric methods. The analysis encompasses publication volume statistics, keyword co-occurrence analysis, and keyword clustering. The results indicate that research on centrifugal pump cavitation is currently in a phase of rapid development. The annual number of publications related to centrifugal pump cavitation shows an overall fluctuating upward trend, with Jiangsu University emerging as the leading research institution. The research hotspots include fault diagnosis, impeller design, numerical simulation, and validation, forming four major developmental pathways. Research on cavitation in centrifugal pumps has gradually shifted its focus from numerical simulation to practical engineering issues such as pressure pulsation and cavitation, with hot topics evolving at an accelerated pace. Future efforts must address challenges like cavitation monitoring and high-precision simulation to comprehensively enhance the anti-cavitation performance and operational reliability of centrifugal pumps. Full article

Impeller blades are one of the main parts of a centrifugal pump that affect the performance of the pump. The presence of solid particles in seawater, transported through a centrifugal pump, causes wear in the blade surface that reduces blade lifetime. In the orthogonal direction, this wear is an erosion thickness of the blade. Assuming that these particles have a spherical shape, the erosion rate depends on their velocity, size, impingement angle, and material hardness index. In this work, we investigate the erosion thickness of a low-head centrifugal pump operating in pump and turbine modes, with a particle radius ranging from 4 μm to 50 μm. The numerical simulation used an RNG k–ε turbulence model, assuming a perfect bounce collision between the particle and the rotating solid wall. The study shows that the blade pressure side is impacted by a solid particle concentration higher than the suction side. In pump mode, the erosion thickness on the blade sides increases if the particle radius is above 4 μm and reaches a maximum at 40 μm. In turbine mode, the erosion thickness decreases when the particle radius is greater than 5 μm. The thickness loss is greater in turbine mode than in pump mode. The influence of particle flow rate was investigated. Below a particle radius of 10 μm, particles follow the flow directions and reside for a longer time in the blade channel. Passing from a particle radius of 50 μm to 100 μm, the blade lifetime was decreased by a factor of 11. Full article

The optimal control of sustainable energy supply systems, including renewable energies and energy storage, takes a central role in the decarbonization of industrial systems. However, the use of fluctuating renewable energies leads to fluctuations in energy generation and requires a suitable control strategy for the complex systems in order to ensure energy supply. In this paper, we consider an electrified power-to-heat system which is designed to supply heat in the form of superheated steam for industrial processes. The system consists of a high-temperature heat pump for heat supply, a wind turbine for power generation, a sensible thermal energy storage for storing excess heat, and a steam generator for providing steam. If the system’s energy demand cannot be covered by electricity from the wind turbine, additional electricity must be purchased from the power grid. For this system, we investigate the cost-optimal operation, aiming to minimize the electricity cost from the grid by a suitable system control depending on the available wind power and the amount of stored thermal energy. This is a decision-making problem under uncertainty regarding the future prices for electricity from the grid and the future generation of wind power. The resulting stochastic optimal control problem is treated as finite-horizon Markov decision process for a multi-dimensional controlled state process. We first consider the classical backward recursion technique for solving the associated dynamic programming equation for the value function and compute the optimal decision rule. Since that approach suffers from the curse of dimensionality, we also apply reinforcement learning techniques, namely Q-learning, that are able to provide a good approximate solution to the optimization problem within reasonable time. Full article

This study aims to clarify the influence mechanisms of core operating and structural parameters and provide targeted theoretical support for the optimized design and industrial application of metal hydride (MH) hydrogen storage systems. For this purpose, a two-dimensional axisymmetric numerical model was established to characterize the MH adsorption/desorption processes, which was validated by its consistency with previous experimental data. The innovation lies in clarifying the optimization sensitivity and priority of each parameter in the hydrogen adsorption and desorption processes and further revealing the intrinsic mechanism of parameter coupling on the system’s reaction and thermal performance. Results show that the initial temperature is most critical: 303 K shortens adsorption time by 30% (vs. 323 K), while 323 K cuts desorption time by 50%. Optimal adsorption pressure is 8–10 bar; 0.4 bar outlet pressure reduces desorption time by 37%. Enhancing heat transfer and thermal conductivity significantly shortens reaction times, while porosity has a limited impact. These findings advance the fundamental understanding of metal hydride systems and facilitate their transition from laboratory-scale research to industrial implementation. Full article

Cavitation erosion is a critical problem for many engineering components, such as ship propellers, diesel engine exhaust valves, cylinder liners, pump impeller blades, hydraulic turbines, and bearings, which are exposed to high-velocity flowing fluids or to vibratory fluid motion. It represents a mechanical degradation of the surface caused by the continuous collapse of bubbles in the surrounding liquid, which seriously affects flow efficiency and component service life, increasing maintenance frequency and refurbishment costs. The intensity and evolution of the cavitation erosion phenomenon depend on the hydrodynamic conditions to which the component surface is exposed, the properties of the liquid, and the judicious selection of the most suitable material. This paper aims to modify the microstructure of a Ni-based superalloy by applying recrystallization annealing heat treatment in order to obtain surfaces resistant to cavitation erosion for components that handle fluids under local pressure fluctuations. Experimental tests are carried out using a vibratory apparatus with piezoceramic crystals operating at a frequency of 20 kHz and an amplitude of 50 µm. The cavitation erosion performance of the Ni-based superalloy INCONEL 625, heat treated by recrystallization annealing, are compared with that of austenitic stainless steel AISI 316L subjected to solution treatment. For both metallic alloys, based on mass loss measurements, the characteristic time-dependent curves of the mean cumulative erosion penetration depth, MDE(t), and the mean erosion rate, MDER(t), are determined. The comparison of these curves and of the parameters defined and recommended by the ASTM G32 standard demonstrates that, for the Inconel 625 superalloy, resistance to cavitation erosion increases by 77–81% compared to that of AISI 316L austenitic stainless steel. X-ray diffraction analyses (XRD) show that, in the microstructure of the Inconel 625 superalloy, in addition to austenite, MC-type carbides, M₂₃C₆ carbides, and intermetallic phases γ″ = Ni₃(Nb, Al, Ti) and δ = Ni₃(Nb, Mo) are also present. Full article

This study investigates the aerodynamic and structural behavior of a traditional horizontal-axis windmill equipped with a passively controlled fabric-sail rotor system, representative of the historic Lasithi Plateau windmills of Crete. The traditional windmill of the Lasithi Plateau, historically employed for water pumping to support irrigation and domestic water supply, constituted the conceptual basis for its further development into a wind energy system capable of electrical power generation. To this end, the structural and constructional characteristics of the traditional windmill are thoroughly investigated, with the objective of defining the technical specifications required for the design of a new product, namely a small-scale wind turbine incorporating a sail-based rotor configuration. First, the local meteorological conditions in the area are assessed using a long-term mesoscale to microclimatic approach. These parameters determine the operational and extreme working conditions of the windmill. Then emphasis is placed on understanding how important design features—such as the sail geometry, the supporting framework, and the passive aeroelastic deformation mechanism—govern the rotor’s performance and operational robustness. The sail’s ability to deform substantially plays a central role in regulating aerodynamic loading, serving as an inherent load-shedding mechanism that enhances survivability during high-wind events up to 40 m/s. The observed nonlinear trends in torque and thrust with increasing wind speed highlight the importance of aeroelastic effects in the functional design of fabric-sail rotors. Particular attention is given to the behavior of the woven polyester sail material, which enables large reversible deformations without mechanical failure, thereby preserving structural integrity and operational continuity. Overall, this study provides insight into the design principles and operational characteristics of flexible-sail windmills, illustrating how traditional configurations can inform the development of resilient, low-cost wind-driven systems. Full article