Search Results (1,543)

The integration of grid-forming wind turbines introduces forced oscillations and harmonic/inter-harmonic interference, which degrades the accuracy of traditional energy-flow-based source localization methods. To address this issue, this paper proposes a novel method based on improved complete ensemble empirical mode decomposition with Adaptive Noise (ICEEMDAN) and an improved Teager energy operator (ITEO). The proposed method first employs ICEEMDAN to adaptively decompose wide-area measurement signals, effectively suppressing mode mixing and noise. Then, ITEO is utilized to extract the dominant oscillation components. By incorporating an adjustable computation window, ITEO enhances frequency selectivity, amplifying force oscillations while suppressing high-frequency noise, leading to robust energy estimation. Following this, the dissipative modal energy flow is calculated from the reconstructed time-domain waveforms. Ultimately, the disturbance source is precisely identified based on the dissipative energy flow theory. The method is validated through extensive simulations on a multi-bus test system with grid-forming wind turbines, considering disturbances from both synchronous generator excitations and wind turbine internal controls, as well as in high-noise environments. Additional validation using a real-world oscillation event from the ISO New England system confirms that the proposed method achieves superior accuracy and robustness compared to conventional methods. Full article

In this paper, an emission- and reliability-aware stochastic optimization model is proposed for the economic planning of electric bus parking lots (EBPLs) with photovoltaic (PV) and wind-turbine (WT) resources in an 85-bus radial distribution network. The model simultaneously minimizes operating, emission, and energy-loss costs while increasing system reliability, measured by energy not supplied (ENS), and uses a fuzzy decision-making approach to determine the final solution. To address optimization challenges, a new multi-objective entropy-guided Sinh–Cosh Optimizer (MO-ESCHO) is proposed to efficiently mitigate premature convergence and produce a well-distributed Pareto front. Also, a hybrid forecasting architecture that combines MO-ESCHO and artificial neural networks (ANN) is proposed for accurate prediction of PV and WT power and network loading. The framework is tested across five cases, progressively incorporating EBPL, demand response (DR), forecast information, and stochastic simulation of uncertainties using a new hybrid Unscented Transformation–Cubature Quadrature Rule (UT-CQR) method. Comparative analyses against conventional methods confirm superior performance in achieving better objective values and ensuring computational efficiency. The outcomes indicate that the combination of EBPL with RES reduces operating costs by 5.23%, emission costs by 27.39%, and ENS by 11.48% compared with the base case with RES alone. Moreover, incorporating the stochastic model increases operating costs by 6.03%, emission costs by 5.05%, and ENS by 7.94% over the deterministic forecast case, reflecting the added complexity of uncertainty. The main contributions lie in coupling EBPLs and RES under uncertainty and proposing UT-CQR, which exhibits robust system performance with reduced variance and lower computational effort compared with Monte Carlo and cloud-model approaches. Full article

This study presents a comprehensive numerical and theoretical analysis comparing the aerodynamic performance of a racetrack trajectory vertical axis wind turbine with a baseline VAWT. The racetrack trajectory comprises two parallel straight segments connected by semicircular arcs. However, two critical research gaps remain: the aerodynamic performance of this non-axisymmetric rotor, especially its sensitivity to inflow direction, is not well understood, and a computationally efficient theoretical model for its rapid design is lacking. Using unsteady Reynolds-Averaged Navier–Stokes (URANS) simulations to systematically quantify this sensitivity, and developing an adapted double multiple streamtube (DMST) model, the performance of both turbines is evaluated across tip speed ratios (TSRs) of 1.5–4 and inflow angles β = 0–90°. Results indicate that the racetrack turbine achieves a peak power coefficient of 0.49 at TSR = 2.5 and β = 90°, 16.7% higher than the baseline VAWT. Its performance is highly sensitive to inflow direction, whereas the baseline operates more uniformly across angles. Flow field and wake analyses reveal that the racetrack turbine exhibits faster wake recovery and lower turbulence intensity downstream under optimal inflow. This study demonstrates the potential of racetrack turbines for enhanced directional efficiency in marine wind conditions and validates the adapted DMST model as a reliable tool for preliminary design. Full article

A clearance necessarily exists between the blade tip and the casing in turbines. A leakage flow, formed by the accelerated gas through the tip clearance, is a major cause of turbine stage efficiency loss. Severe heat loads on the blade tip surface also result from a leakage flow, a primary cause of blade damage. Although the understanding of leakage flow mechanisms is mature after years of research, the continuous rise in turbine inlet temperature, pursuing higher engine thrust, requires more effective cooling methods for the blade tip region. This paper presents a review of research on three fundamental tip structures (flat tip, squealer tip, and winglet tip) to explain their design concepts, analyze their respective flow mechanisms as well as heat transfer characteristics, and introduce various modified designs. Various film cooling arrangements applied to these tip structures are examined to identify effective strategies that strengthen the advantages of structural optimization. In view of engineering applications, this paper reviews research on unsteady wake interactions as the aforementioned framework, hoping to provide readers a more comprehensive understanding. Full article

This paper provides a comprehensive analysis of the development, implementation, and evolution of the circular economy indicator (CEI) in the context of hydroelectric turbine refurbishment over the past five decades. By systematically examining publications indexed in the Web of Science database between 1975 and 2025, the study traces the conceptual origins of the CEI, highlights methodological advances, and analyzes practical applications. The analysis focuses on key aspects such as material circularity, energy efficiency, including the share of renewable sources, and the extension of operational lifetime achieved through refurbishment. The paper also identifies persistent methodological gaps, in particular regarding the integration of social and governance dimensions, as well as the lack of standardization across projects, proposing strategies to increase the reliability and applicability of the indicator. The results provide guidance for integrating circular economy principles into hydroelectric refurbishment processes, outline good practices, and set priorities for future research oriented towards more holistic and multidimensional assessments of circularity. Full article

This study examines outflow boundary conditions (BCs) in computational fluid dynamics (CFD) simulations of a transition duct with and without guide vanes that converts supersonic flow exiting a rotating detonation combustor (RDC) to subsonic flow to drive a turbine. Since the flow exiting the transition duct has swirling shock waves with significant spatial and temporal variations in pressure, temperature, and Mach number, imposing proper BCs poses a challenge. To ensure all swirling shock waves exit the transition duct without creating non-physical reflected waves at its outlet, this study examined three outflow BCs: (1) the average pressure imposed at the duct’s outlet, (2) a nonreflecting BC (NRBC) with a specified average pressure imposed at the duct’s outlet, (3) the average pressure imposed at the outlet of an extension duct made up of a buffer layer and a sponge layer. This study is based on the three-dimensional, unsteady density-weighted-ensemble-averaged continuity, Navier–Stokes, and energy equations for a thermally perfect gas closed by the realizable k–ε model and “enhanced” wall functions. The results obtained show that imposing an average pressure at the transition duct’s outlet produces spurious waves that degrade the physical meaningfulness of the solution. When the NRBC was applied, swirling shock waves exited the duct’s outlet without creating spurious waves. However, its usage requires the gas to be thermally, as well as calorically, perfect, which this study shows could be a concern. By imposing the average pressure at the outlet of an extension duct, the gas does not need to be calorically perfect. The results obtained show the effects of the sponge layer’s length and coarsening ratio on damping nonuniformities in non-physical reflected waves to ensure the flow exiting the transition duct’s outlet can do so as if there are no boundaries present and has the desired average pressure—even though the BC is applied at the extension duct’s outlet. Full article

Sediment erosion is a persistent problem that leads to the deterioration of hydro-turbines over time, ultimately causing blade failure. This paper analyzes the dynamics of sediment in water and its effects on a small Kaplan turbine. Flow data is obtained independently and transferred to a separate Lagrangian-based finite element code, which tracks particles throughout the computational domain to determine local impacts and erosion rates. This solver uses a random walk approach, along with statistical descriptions of particle sizes, numbers, and release positions. The turbine runner features significantly twisted blades with rounded corners, and complex three-dimensional (3-d) flow related to leakage and secondary flows. The results indicate that flow quality, particle size, concentration, and the relative position of the blades against the vanes significantly influence the distribution of impacts and erosion intensity, subsequently the local eroded mass is cumulated for each element face and averaged across one pitch of blades. At the highest concentration of 2500 mg/m³, the results show a substantial erosion rate from the rotor blades, quantified at 4.6784 × 10⁻³ mg/h and 9.4269 × 10⁻³ mg/h for the nominal and maximum power operating points, respectively. Extreme erosion is observed at the leading edge (LE) of the blades and along the front part of the pressure side (PS), as well as at the trailing edge (TE) near the hub corner. The distributor vanes also experience erosion, particularly at the LE on both sides, although the erosion rates in these areas are less pronounced. These findings provide essential insights into the specific regions where protective coatings should be applied, thereby extending the operational lifespan and enhancing overall resilience against sediment-induced wear. Full article

Dynamic wind-induced vibrations of structures will cause cyclic stresses in structural elements, potentially leading to fatigue damage accumulation or structural failure. Existing research on wind-induced fatigue mainly focuses on tower and large-span steel structures, such as chimneys, signal towers, transmission towers, long-span bridges, and wind turbines. However, existing studies on wind-induced fatigue damage in tall steel buildings remain limited. To determine whether and under what conditions wind-induced fatigue damage needs to be considered in tall steel structures, this study investigates wind-induced fatigue failure through wind tunnel tests and numerical simulations. Specifically, six real tall steel buildings were examined to assess their fatigue life under dynamic wind loads. First, wind tunnel tests using synchronous pressure models were conducted to obtain wind load time histories of these six buildings. Subsequently, time histories of wind-induced displacements and component stresses were calculated. The wind-induced fatigue life of each building was evaluated using the rain-flow counting method and the Palmgren–Miner rule, revealing that the fatigue life generally exceeds 400 years. The results demonstrate that tall steel structures designed according to current standards perform well in resisting wind-induced fatigue damage. Furthermore, when the ratio of the wind-induced root mean square (RMS) stress to the ultimate strength of a structural element reaches 0.125–0.164, the fatigue life of components may fall below the design life, indicating the necessity of considering potential fatigue damage. The RMS stress ratio can be preliminarily compared with the RMS stress ratio threshold proposed in this study to determine whether wind-induced fatigue damage needs to be considered in tall steel buildings. Finally, a simplified fatigue life prediction formula is established to provide approximate estimates for the fatigue life of tall steel buildings. Full article

IEA Wind Task 43 seeks to “unlock the full value of wind energy through digital transformation”. One mechanism to realize value is through enhanced data-driven decision-making and, while many areas in the wind sector can benefit from improved decision support, this case study focusses on a well-defined wind energy maintenance scenario involving blade inspection and repair. The solution concentrates on the specific damage category of blade leading edge erosion (LEE) and the optimum action to be taken for a given level of damage detected during periodic inspections. The key decision is whether to initiate repairs immediately or continue operating the turbine until the next inspection—and, if so, when that next inspection should take place. Even for such a specific damage type and decision option, the overall solution draws on multiple data types, ranging from damage classifications to cost drivers, and integrates a number of components including damage propagation, performance, and cost models. The core of the solution is a risk-based decision model using heuristic strategies, and Bayesian networks for optimized decision-making. This paper outlines the overall solution, expands on the data and modelling implementations, and discusses the results and conclusions arising from the investigation. Full article

The recent updates to the Single Day-Ahead Coupling (SDAC) framework in the European energy market, along with new rules for providing manual frequency restoration reserve (mFRR) products in the Nordic Energy Activation Market (EAM), have introduced a finer Market Time Unit (MTU) resolution. These developments underscore the growing importance of flexible assets, such as power-to-hydrogen (PtH) facilities, in delivering system flexibility. However, to successfully participate in such markets, well-designed and accurate bidding strategies are essential. To fulfill this aim, this paper proposes a Mixed Integer Linear Programming (MILP) model to determine the optimal bidding strategies for a typical PtH facility, accounting for both the technical characteristics of the involved technologies and the specific participation requirements of the mFRR EAM. The study also explores the economic viability of sourcing electricity from nearby wind turbines (WTs) under a Power Purchase Agreement (PPA). The simulation is conducted using a case study of a planned PtH facility at the Port of Hirtshals, Denmark. Results demonstrate that participation in the mFRR EAM, particularly through the provision of downward regulation, can yield significant economic benefits. Moreover, involvement in the mFRR market reduces power intake from the nearby WTs, as capacity must be reserved for downward services. Finally, the findings highlight the necessity of clearly defined business models for such facilities, considering both technical and economic aspects. Full article

Turbochargers operate under highly transient conditions, which impose significant mechanical and thermal loads on their rotating components. When supported by ball bearings combined with squeeze film dampers, the rotor system exhibits complex nonlinear dynamics that can critically affect bearing performance and service life. This study investigates the dynamic behaviour of ball-bearing-supported turbocharger rotors, focusing on lubrication conditions that reflect transient operating conditions. A high-fidelity computational model was developed to simulate multibody rotor dynamics, incorporating finite element-based flexible bodies and elastohydrodynamic lubrication (EHL) submodels to represent the contacts within the ball bearings. Validation of the simulation results against experimental data revealed that rotor vibrations significantly influence EHL contact, potentially leading to raceway damage. Additionally, differences in bearing loading between the inner and outer raceways, as well as between the compressor and turbine side bearings, were observed due to bearing clearance effects. Full article

To address the problems of local optima and insufficient convergence accuracy in parameter identification of primary frequency regulation (PFR) for steam turbines, this paper proposed a hybrid identification method that integrated an Improved Bayesian Optimization (IBO) algorithm and an Improved Whale Optimization Algorithm (IWOA). By initializing the Bayesian parameter population using Tent chaotic mapping and the reverse learning strategy, employing a radial basis kernel function hyperparameter training mechanism based on the Adam optimizer and optimizing the Expected Improvement (EI) function using the Limited-memory Broyden–Fletcher– Goldfarb–Shanno with Bounds (L-BFGS-B) method, IBO was proposed to obtain the optimal candidate set with the smallest objective function value. By introducing a nonlinear convergence factor and the adaptive Levy flight perturbation strategy, IWOA was proposed to obtain locally optimized optimal solutions. By using the reverse-guided optimization mechanism and employing a fitness-oriented selection strategy, the optimal solution was chosen to complete the closed-loop process of reverse learning feedback. Nine standard test functions and the Proportional Integral Derivative (PID) parameter identification of the electro-hydraulic servo system in a 330 MW steam turbine were presented as examples. Compared with Particle Swarm Optimization (PSO), Whale Optimization Algorithm (WOA), Bayesian Optimization (BO) and Particle Swarm Optimization-Grey Wolf Optimizer (PSO-GWO), the Improved Bayesian Optimization-Whale Optimization Algorithm (IBO-WOA) proposed in this paper has been validated to effectively avoid the problem of getting stuck in local optima during complex optimization and has high parameter recognition accuracy. Meanwhile, an Out-Of-Distribution (OOD) Test based on noise injection had demonstrated that IBO-WOA had good robustness. The time constant identification of the steam turbine were carried out using IBO-WOA under two experimental conditions, and the identification results were input into the PFR model. The simulated power curve can track the experimental measured curve well, proving that the parameter identification results obtained by IBO-WOA have high accuracy and can be used for the modeling and response characteristic analysis of the steam turbine PFR. Full article

A microgrid (MG) topology combines various kinds of resources like solar photovoltaic (PV) systems, wind turbines (WTs), energy storage systems, and the conventional utility grid. These different resources need to be coordinated in an optimal way to keep the power balanced, reduce the operational cost, and make the system resilient to any kind of failures. Therefore, an efficient energy management system (EMS) is essential in an MG system to provide suitable and reliable operation under different weather and demand load conditions. In this paper, a new EMS-based multi-objective Nizar Optimization Algorithm (NOA) is proposed. The suggested EMS aims to improve the power quality problem caused by the unpredictable nature of renewable energy sources and then minimize the grid power and battery degradation costs. By leveraging the adaptability of the NOA, the applied EMS method simply optimizes the allocation and energy sharing of the resources in a grid-connected MG. The proposed EMS was verified in simulation using MATLAB software. The performance of the proposed EMS was tested under different weather conditions, and the obtained results have been compared with those obtained in the existing methods. The obtained results indicate that the proposed EMS based on the NOA is capable of adjusting the multi-source energy allocation with minimal grid costs and the battery degradation issue. The proposed NOA indicates robust performance with total cost savings varying from USD 17 to USD 34 compared to other optimizers, as well as a great reduction in degradation cost, up to 27% improvement over the conventional methods. Finally, the proposed EMS offers several advantages over the conventional methods, including the improved dynamic system, faster convergence, lower operational costs, and higher energy efficiency. Full article

Few studies have addressed jack-up substructures with spudcans for offshore wind turbines targeting multi-layer seabed conditions, which are frequently found in the Korean seabed. This study analyzed existing guidelines to establish geotechnical design procedures for a newly proposed jack-up substructure supported by tubular legs with spudcans, as well as to present design cases for a target site. This jack-up spudcan was designed for seabed conditions representative of the Korean southwestern offshore seabed, consisting of a sand–clay–sand layer. Analytical procedures from ISO and InSafeJIP guidelines were adopted to estimate the vertical bearing capacity of the spudcan. The yield envelope was determined based on this estimation, and the spudcan size was selected using structural reaction forces. Predictions from theoretical equations were compared with results from centrifuge tests for verification and discussion. Theoretical vertical capacities according to ISO match well with centrifuge results in sand-over-clay layers, while InSafeJIP shows a similar trend in intermediate clay layers. For clay-over-sand layers, only the vertical capacity formula for a single-sand layer case is available in the guidelines, which tends to overestimate the actual capacity for the underlying sand. However, by applying appropriately selected strength reduction factors, the actual foundation behavior can be reasonably predicted for design, but it is still overestimated, requiring further study. Full article

Exergy efficiency is a measure of thermodynamic perfection. A device that operates reversibly has an exergy efficiency of 100 percent and is said to be thermodynamically perfect. A reversible process involves zero entropy generation and thus zero exergy destruction since X_destroyed = T₀S_gen. Exergy efficiency is generally defined as the ratio of exergy output to exergy input η_ex = X_output/X_input = 1 − (X_destroyed + X_loss)/X_input or the ratio of exergy recovered to exergy expended η_ex = X_recovered/X_expended = 1 − X_destroyed/X_expended. In this paper, exergy efficiency relations are obtained first for a general steady-flow system using both approaches. Then, explicit general relations are obtained for common steady-flow devices, such as turbines, compressors, pumps, nozzles, diffusers, valves and heat exchangers, as well as heat engines, refrigerators, and heat pumps. For power and refrigeration cycles, five different forms of exergy efficiency relations are developed, and their equivalence is demonstrated. With the unified approach presented here and the insights provided, the controversy and confusion associated with different exergy efficiency definitions are largely alleviated. Full article