Francis turbines deployed in sediment-laden flow conditions undergo intensive hydro-abrasive erosion, which triggers efficiency deterioration and structural property degradation. Conventional design approaches typically address hydraulic performance or material durability separately, neglecting their synergistic effects. This study proposes a novel hydraulic-structural coordinated optimization methodology for Francis turbines, integrating a coupled CFD-DPM-FEA framework to simultaneously enhance erosion resistance, preserve hydraulic efficiency, and ensure structural integrity. The discrete phase model (DPM) is employed to predict sediment erosion patterns, while nonlinear finite element analysis (FEA) assesses stress distributions and modal characteristics. The blade wrap angles, setting angles, and crown/band gap geometries are optimized, with constraints on efficiency loss, power output, and structural safety. Results show that the optimized runner reduces erosion in critical regions (blade pressure side, crown, and band gaps) by 42% to 48% compared to the original design, without compromising efficiency or inducing excessive stress. The natural frequencies of the optimized runner are separated from the dominant RSI hydraulic excitation frequencies by margins exceeding 79%, eliminating resonance risks. Static and dynamic stresses are maintained within safe allowable limits despite slight increases, meeting industrial design standards. The proposed methodology provides a holistic design paradigm for erosion-resistant turbines in high-sediment regions, with demonstrated applicability to the 10 MW Francis turbine unit studied.

Large-diameter monopiles are widely used as foundations for offshore wind turbines. In marine environments, hydrodynamic flow around monopiles intensifies local bed shear stress, driving scour and the loss of scour protection materials. This study employs a numerical model, based on large eddy simulation (LES) and sediment transport theory, to simulate scour evolution and bed shear stress distribution around monopiles under combined wave-current conditions. The model is validated against physical model test data and a modified method for predicting equilibrium scour depth around large-diameter piles. Results show that the amplification factor of bed shear stress (M = z/z0, where z and z0 are the amplified and undisturbed bed shear stress, respectively) expands laterally with increasing current-wave ratio (Ucw = Uc/(Uc + Uwm), where Uc and Uwm are the current velocity and wave-induced oscillatory velocity, respectively), leading to wider scour. Lower Ucw causes contraction of downstream low-M regions, resulting in more uniform scour shapes. The spatial distribution of M determines scour morphology, and a method based on M distribution predicts scour width within 25% error. Additionally, under wave-dominant conditions, scour slows with increasing Ucw, while it accelerates under current-dominant conditions. These insights provide a theoretical basis for the assessment of scour and the optimization of protective measures under different hydrodynamic conditions.

With the expansion of offshore wind energy into deeper waters, Tension Leg Platforms (TLPs) have emerged as a promising substructure solution for large-scale Floating Offshore Wind Turbines (FOWT) due to their inherent motion stability. This study presents a comprehensive dynamic response analysis of a conceptual TLP designed to support the 15 MW IEA reference wind turbine. The primary objective of this study is to systematically evaluate the performance of the proposed platform under a comprehensive set of environmental conditions. A high-fidelity, fully coupled aero-hydro-servo-elastic numerical model of the Tension Leg Platforms Floating Offshore Wind Turbine (TLP FOWT) system was developed with OrcaFlex. A comprehensive set of intact load cases, considering various co-directional wind, wave, and current approach angles, were simulated to characterize the platform’s dynamic behavior. Key performance indicators, including 6-DOF platform motions, nacelle accelerations, dynamic air gap, and tendon tensions, were statistically analyzed. Furthermore, an Accidental Limit State (ALS) analysis was conducted by simulating the sudden failure of a primary tendon under a severe storm condition to assess the system’s residual strength and stability. The analyses performed in this study confirm that the proposed TLP design is a viable and robust solution for supporting a 15 MW wind turbine. The platform complies with the primary performance, safety criteria of relevant design standards under both intact and damaged conditions, demonstrating its suitability for deep-water applications.

[Objective]As China gradually phases out its subsidy policy for offshore wind power(OWP),the industry has entered a decisive cost reduction and efficiency enhancement stage.Unlike onshore wind projects,OWP projects still face substantially higher construction and operating costs,which makes competitiveness under grid-parity conditions highly challenging.However,the theoretical framework for managing the smart lifecycle of OWP projects remains underdeveloped,with incomplete asset management and evaluation methods.The smart lifecycle management of OWP projects is in its nascent stage,with fragmented data systems and poor integration across planning,construction,and operations.Consequently,there is an urgent need for an innovative,lifecycle-oriented management approach to support the OWP industry's high-quality and sustainable development.[Methods]This study proposes a closed-loop smart management mechanism for OWP projects,focusing on four key dimensions:perception,analysis,real-time control,and optimization.This study summarizes the digital transformation and smart management pathways of OWP assets throughout their lifecycle,from feasibility to construction,operation,and final decommissioning.This study classifies management elements into cost,efficiency,and risk,creating a closed-loop evaluation model for OWP assets.This model enables a dynamic representation of each asset's status in terms of cost,efficiency,and risk levels at any moment.Furthermore,this study identifies and analyzes key smart management technologies relevant to various phases of the lifecycle.Accordingly,a smart lifecycle management platform has been designed with a five-layer architecture:data acquisition,data management,modular functional applications,decision support,and interactive visualization.A prototype system was developed to address project development and design,smart construction,and smart operation and maintenance.The system was applied in a large offshore wind farm in Jiangsu Province,China,and the asset conditions were compared before and after its implementation.[Results]A comparative analysis based on actual operational data showed significant improvements:(1)Effective cost control was achieved during the construction period,along with rational planning for operation and maintenance,reduced downtime,and improved generation efficiency.Thus,the lifecycle levelized cost of energy decreased from 0.92 yuan/(kW·h)to 0.76 yuan/(kW·h),which was approximately 17.4％.(2)When evaluated against three key efficiency indicators-compliance rate of power generation,effective operation time assurance rate,and average failure rate-the poorly performing turbines(#3,#10,and#16)showed significant improvements after rectification,with lower osculating values.(3)Comprehensive risk assessment identified anomalies in the transmission and blade systems as primary concerns,which allowed for targeted maintenance interventions,improved equipment availability,and reduced unplanned maintenance requirements.[Conclusions]The proposed closed-loop smart lifecycle management system offers a new technical solution for reducing costs and improving efficiency in OWP projects.Practical application shows that the system can enhance project planning and design,reduce development and operational costs,improve asset equipment reliability,extend the power generation lifecycle,and ensure ongoing value creation throughout the lifecycle.The study findings offer valuable guidance for smart management in similar offshore renewable energy projects,thereby contributing to the sustainable development of the wind power industry through digital transformation.

Battery balancing plays a crucial role in improving the overall performance and lifespan of battery packs. However, most balancing strategies only pursue balancing speed and don't consider temperature difference among cells, which leads to a large temperature difference at the end of balancing. Uneven temperature distribution can have adverse effects on the safety, lifespan, and power stability of battery packs. To address this issue, a novel active balancing strategy considering temperature is proposed. Firstly, a distributed bidirectional flyback transformer balancing topology is designed based on the LTC3300 series chips, which enables energy transfer between individual cells and modules. Based on this topology, the balancing strategy that takes temperature into consideration is proposed. This strategy takes state of charge (SOC) difference and temperature difference as the optimization objective. Surrogate optimization algorithm is proposed to solve the optimization problem. Finally, a series of simulation experiments were conducted to validate the superiority of the proposed strategy. The results demonstrate that the proposed strategy can improve SOC and temperature inconsistency. Compared to the maximum difference strategy, although the balancing speed has slightly decreased, the maximum temperature difference at the end of balancing process is reduced by around 35 %-50 %.

With the rapid development of modern wind power generation technology, wind energy has become the most promising renewable energy in the world. At present, wind power development has transformed from land-based to offshore and is committed to further expanding to offshore deep-water areas. Floating offshore wind turbines (FOWTs) are currently the most promising new technology for developing offshore deep-water wind energy and have become a research hotspot in the offshore wind power field globally. Based on the working characteristics of large-scale FOWTs and in combination with the design experience of FOWTs, this study proposes a barge-type floating platform and mooring system suitable for a 60 m water depth to support the Technical University of Denmark (DTU) 10 MW wind turbine. The platform features a four-monopod structure paired. The barge-type floating platform has the advantages of having a simple structure, convenient manufacturing and a better response related to the stability (hydrostatics) of the platform under operational and extreme conditions. The hydrodynamic characteristics and coupled motion response under various wind and wave conditions of the structure were analyzed and verified by physical model tests. Key findings include the effectiveness of geometric and Froude similarity laws in model design, the critical role of low-Reynolds-number blade modifications in achieving aerodynamic thrust similarity, and the alignment of motion responses with DNV standards under extreme conditions. This research provides a robust experimental framework and practical insights for optimizing barge-type FOWT designs.

Large-diameter offshore monopiles are frequently subjected to scour hazards, necessitating the implementation of scour protection measures to mitigate soil erosion around the pile foundation. Riprap, the most widely used scour protection, has been extensively studied with respect to particle size design in armor and filter layers; however, the subsequent edge scour process – particularly its impact on the long-term protection stability and pile bearing capacity – remains poorly understood. In the present study, a series of tests were carried out to investigate the effects of key protection parameters (flow intensity, protection width, thickness, and stone size) on equilibrium edge scour depth and morphological characteristics. A predictive model for maximum edge scour depth is developed based on experimental observations from both this study and that of Petersen et al. (2015a), which has an overall model inaccuracy within ±25%. Furthermore, 3D finite element analysis of pile-seabed interaction incorporating the edge scour effects reveals that riprap installation effectively compensates for scour-induced reductions in lateral pile capacity, with its protection width exhibiting a greater influence than thickness. These findings provide valuable references for riprap design in offshore engineering applications.

With the rapid development of offshore wind power toward deep-sea areas and larger capacities, corrosion of foundation structures in complex marine environments has emerged as a critical bottleneck affecting economic viability and safety. This study systematically investigates corrosion mechanisms, protection technologies, and repair methods for offshore wind power foundations under multi-factor coupled marine corrosion conditions (e.g., salt spray erosion, microbial adhesion, and wet-dry cycles). A corrosion control technology system spanning the entire lifecycle—from design to monitoring and repair—is established. At the corrosion mechanism level, the synergistic mechanism between Cl- diffusion dynamics and sulfate-reducing bacteria (SRB) metabolism is revealed, and a temperature-salinity-flow velocity coupled model for splash zone corrosion rates is developed. For protection technologies, innovative solutions including nano-composite coatings (graphene/TiO2-enhanced epoxy resin) and self-healing microcapsule coatings are proposed, with optimized current distribution in cathodic protection systems through boundary element method (BEM). In repair technologies, the principles of in-situ superhydrophobic coating spraying via remotely operated vehicles (ROVs) and microbial-induced calcium carbonate precipitation (MICP) for crack repair are elucidated. Through a case study of a wind farm in Rudong, Jiangsu, the detection and evaluation results of sacrificial anodes are analyzed.

This paper encapsulates the advancements in marine renewables utilization technologies globally, analyzed through the lenses of research emphasis and variations in device mechanisms. The multi-energy complementarity and the integration of marine renewable energy systems with aquaculture technologies are discussed, and the engineering applications are introduced. Tidal energy and offshore wind energy technologies have achieved mature commercial operation, while tidal current energy and wave energy technologies are undergoing full-scale prototype testing. Temperature-difference energy technology has reached the full-scale prototype testing phase, whereas salinity-gradient energy technology remains in the laboratory verification stage. In recent years, many researchers have conducted engineering measurements, and further breakthroughs are needed in critical enabling technologies and safety measures. From the standpoint of geographical integration, the realization of aquaculture with offshore wind energy and wave energy or tidal current energy is simpler. The integration of aquaculture with marine renewable energy technologies represents a promising avenue for the future development and global utilization of marine energy resources.

Artificial reefs (ARs) are man-made structures deployed on the seabed to enhance benthic marine ecosystems. Their presence significantly dampens local flow dynamics, making them a potential solution for scour protection of offshore wind monopiles. Although the concept appears feasible, the underlying flow-sediment interaction processes remain highly complex and have not yet been systematically investigated. To address this gap, fixed-bed flume experiments were conducted to reveal the hydrodynamics of two AR shapes (cubic and hemispherical) arranged in a tightly packed 3 x 3 configuration around a monopile. In parallel, live-bed tests were performed to evaluate the efficacy of ARs in scour protection. Results indicate that cubic ARs nearly eliminate downward flow on the monopile's upstream side and reduces wake flow velocities by 50 %-80 %. Hemispherical ARs similarly attenuated wake flows but induced descending flow patterns upstream of the monopile. While cubic ARs reduced scour depths by up to 100% upstream and downstream, edge scour development displaces the ARs, thereby compromising long-term protection. Hemispherical ARs provided moderate scour reduction but exhibited greater stability against edge scour. These findings suggested an optimized AR layout balancing scour protection and structural resilience.

Scour around a circular monopile in coastal regions has been investigated extensively over the past decades, but the time development of scour depth around an offshore-wind monopile under large current-wave ratio still lacks a predictive model. By considering the conservation of sand volume and adopting the conventional exponential law for temporal variation, a semi-empirical model, which has three parameters, i.e., an equilibrium scour depth, a shape coefficient and a scour characteristic time scale, is developed for predicting the time development of scour depth around a monopile under live-bed conditions of combined wave–current flows. A series of laboratory experiments was conducted in current-only and wave–current flows to obtain data for model calibration and validation. Experimental results indicate that adding weak waves on current accelerates scour development, which is successfully captured by the proposed model through using the far-field bottom shear stress as a key model input. The overall model inaccuracy is within 25%, and the model’s applicability is further confirmed by field measurements from an offshore wind farm in east China. This model can help to determine the timing of installing scour protection around offshore monopiles, especially for the circumstances with very strong local sediment transport (live-bed).

The dynamic behavior of hydro-turbine rotor system is a complex multi-field and nonlinear problem, which has been studied by many researchers. The analysis of the rotor system dynamic characteristics is usually carried out based on the behavior analysis of bearings, hydraulics, electromagnetics, etc., while the thermo-elasto-hydrodynamic characteristics of bearings are extremely important to numerical accuracy. Therefore, this paper first summarizes the research progress in bearing lubrication performance, and further summarizes the research on hydro-turbine rotor system dynamic characteristics, including the modal characteristics and dynamic response characteristics. Finally, this paper summarizes the main research progress of the hydro-turbine rotor system and proposes possible directions in future research. Literature review shows that the hydro-turbine runners and bearings have achieved multi-field coupling analysis of three-dimensional (3D) models, and some work on multi-field coupling of rotor systems has been carried out. The transition of 3D multi-field coupling from single component to rotor system is significant to accurately predict the rotor system dynamic characteristics and the solution of engineering problems, which requires further in-depth research on the multi-field coupling theory, numerical methods, 3D model integrity, simulation software, etc., and the spatiotemporal synergy between multi-fields should be fully considered.

Abstract It is known that when choosing water as a substitution of liquid hydrogen and liquid oxygen for cavitation investigations, the influence of thermodynamic effect should not be ignored. However, due to the lack of systematic experiments, most existing simulating studies use the average dynamic characteristics obtained earlier in 1970s for simulation validation, which may not be effectively accurate. In this paper, the unsteady experimental observations of cavitating flow on flat plate hydrofoil are presented in detail with the help of the advanced water tunnel in Tsinghua University, which is conducted in 2020s. Then the effectiveness of the numerical method considering the influence of thermodynamic effect is further verified with these dynamic observations. Results show that the method is effective and reliable, capturing the main features of the cavitating flow. And it can be used to simulate the cavitating flow considering the influence of thermal effect in the future.

Composite sandwich structure, as the largest part of wind turbine blades, often experiences complex failure phenomena during full-scale blade testing and wind farm operation. In order to better understand failure behaviors and reveal the failure mechanism of sandwich structures for wind turbine blades, composite sandwich samples were designed, fabricated, and tested in consideration of the real laminate and core machining configuration, manufacturing process, and dominating load of wind turbine blades, In-plane compressive strength and failure behaviors were investigated by experimental and theoretic methods. It was found that the grooved with perforations and cut (GPC) machining configuration can improve in-plane compressive strength of sandwich samples more than that of the double grooved with perforations (DGP) configuration due to higher core shear modulus, the failure mode of sandwich samples shifted from global buckling for Plain configuration to a combination of core shearing and skin/core debonding at both sides for DGP configuration, and finally to skin/core debonding at the shallow groove core side for GPC configuration. The failure mode of sandwich samples with DGP core mainly transferred from global buckling to a combination of core shearing and skin/core debonding at both sides, and further to skin/core debonding at both sides alone with increasing foam density. All samples with GPC core exhibited skin/core debonding at the shallow groove side after slight buckling, which was driven by the asymmetric structure of the GPC core. Classical methods can reasonably predict failure loads of sandwich samples with Plain and DGP cores, but overestimate that of sandwich samples with GPC core.

The impacting-freezing behaviors of supercooled water droplets on superhydrophobic spheres are investigated. A numerical model using the VOF (Volume of Fluid) method and enthalpy–porosity technology is established and validated by comparing the droplet profiles and spreading area factors by simulations and experiments. The effects of Weber number, supercooling degree and sphere-to-droplet diameter ratio (D*) on the impacting-freezing dynamics, including the droplet profile, spreading area factor and final rebound/adhesion, are studied. The results indicate that the supercooling rarely influences the spreading stage but significantly affects the receding stage with a larger stable spreading area factor obtained at a greater supercooling degree. With the decreasing of diameter ratio, the droplet generates a larger maximum spreading arc angle, a higher receding speed and thus a shorter contact time. The maximum spreading area factor greatly increases with reducing diameter ratio for D*<10 but it remains almost unchanged for D*≥10. Three different final morphologies of full rebound, partial rebound and adhesion are obtained, revealing the competition between the fluid flow and phase change in the droplet impacting-freezing process. The morphology map of rebound and adhesion indicates that the boundaries for droplet rebound and adhesion initially move to a smaller supercooling degree and then revert to the previous value as the diameter ratio becomes smaller. The findings in this research may deepen our understanding of the mechanism of supercooled water droplet impacting and freezing on a superhydrophobic curved surface, and contribute to the design of anti-icing/frosting surface.

The dynamic behavior of the pump-turbine thrust bearing is important to the safety operation of the unit. This paper analyzed the lubrication and energy dissipation mechanism of pump-turbine thrust bearing during load-rejection based on the thermo-hydrodynamic model. The results show that the variation of the axial force and the maximum pad surface pressure is basically consistent with that of the inclination of the pad surface. The change of the friction loss is consistent with the change of rotational speed, while the change of pad surface temperature is affected by the combination of pad inclination and rotational speed. The chaotic flow in the oil tank is accompanied by different forms of vortices, such as Taylor vortices, vortex pairs, and Karman vortices, and results in a significant asymmetry in the pressure distribution. The flow in the bearing pad groove has an effect on the energy dissipation in the oil film. This paper provides a theoretical basis for the design and optimization of thrust bearings, and provides a reference for solving the problems of wear, oil mist, and other related problems of thrust bearings in engineering.

Abstract When the hydro-turbine operates under part-load conditions, a large-scale vortex flow will form in the draft tube. This vortex can cause low-frequency pressure pulsations that endanger the safe operation of the hydro-turbine. By injecting air into the draft tube, the structure of the vortex can be effectively disrupted, reducing the amplitude of the pressure pulsations. In this paper, a propeller hydro-turbine was studied, and the SST k-ω turbulence model based on the Reynolds averaged Navier-Stokes equations (RANS) was utilized to perform a full-channel unsteady numerical simulation on a part-load condition with the guide vane opening (GVO) of 35°. Then, the fast Fourier transform (FFT) was applied to analyze the pressure fluctuations at monitoring points on the draft tube wall, the head cover, and the nose of the spiral casing. The results indicated that injecting air with an appropriate flow rate into the draft tube through short pipes can reduce the pressure fluctuations on the draft tube wall by 51.4% to 72.5% and decrease the pressure fluctuations on the head cover and the nose of the spiral casing by approximately 40% to 42%. This study proposes a new air admission structure that can enhance the operating stability of the propeller hydro-turbine under part-load conditions.

For the traditional polyethylene and nylon nets, lots of studies have been carried out to study their hydrodynamic characteristics in waves and currents. However, the studies of the metal nets which also have wide application prospect in marine aquaculture are rare, especially on their performance in waves. In this study, a series of laboratory experiments are conducted to investigate the hydrodynamic characteristics of the chain-link type aluminum alloy nets. Two net panels of identical dimensions are placed in the ocean basin. They are parallel to each other, with a certain length of gap. The wave forces on the net panels under different wave heights, wave periods and immersion depths are measured. The wave elevations at different downstream positions of the nets and the wave forces on both upstream and downstream net panels are measured to investigate the shielding effects. The wave transmission coefficient and shielding coefficient of the horizontal wave force are therefore derived. The experimental results show that both two coefficients are around 1 under different wave conditions which indicates that the shielding effects of the chain-link type aluminum alloy nets can be ignored. Thereby, in the calculation of wave loads on upstream and downstream fish nets, it is reasonable to neglect the wave attenuation inside the nets.