In permanent magnet synchronous machine(PMSM) drives, temperature information is critical to achieve reliable and high-performance control. The popular model-based estimation methods are based on extracting temperatur...In permanent magnet synchronous machine(PMSM) drives, temperature information is critical to achieve reliable and high-performance control. The popular model-based estimation methods are based on extracting temperature dependent terms from the voltages using the machine model. The estimation accuracy under low speed or load can be greatly affected by the model uncertainty and noise due to low signal-tonoise ratio. This paper presents a high frequency(HF) position offset injection-based winding and permanent magnet(PM) temperature decoupled estimation approach for PMSMs to achieve accurate and robust temperature estimation among a wide speed range especially under low-speed conditions. In the proposed approach, a small HF position offset is injected into the machine to construct a decoupled winding and PM temperature estimation model, in which the winding and PM temperatures are independently estimated from HF excitations. The temperature estimation is independent from the fundamental model and parameter variation, and it achieves high signal-tonoise ratio under low-speed conditions. Moreover, the temperature estimation is also not affected by magnetic saturation and inverter distortion, which can improve the accuracy and robustness of temperature estimation. The proposed approach is validated with experiments and comparisons on a laboratory machine under various operating conditions.展开更多
To ensure an uninterrupted power supply,mobile power sources(MPS)are widely deployed in power grids during emergencies.Comprising mobile emergency generators(MEGs)and mobile energy storage systems(MESS),MPS are capabl...To ensure an uninterrupted power supply,mobile power sources(MPS)are widely deployed in power grids during emergencies.Comprising mobile emergency generators(MEGs)and mobile energy storage systems(MESS),MPS are capable of supplying power to critical loads and serving as backup sources during grid contingencies,offering advantages such as flexibility and high resilience through electricity delivery via transportation networks.This paper proposes a design method for a 400 V–10 kV Dual-Winding Induction Generator(DWIG)intended for MEG applications,employing an improved particle swarmoptimization(PSO)algorithmbased on a back-propagation neural network(BPNN).A parameterized finite element(FE)model of the DWIG is established to derive constraints on its dimensional parameters,thereby simplifying the optimization space.Through sensitivity analysis between temperature rise and electromagnetic loss of the DWIG,the main factors influencing the machine’s temperature are identified,and electromagnetic loss is determined as the optimization objective.To obtain an accurate fitting function between electromagnetic loss and dimensional parameters,the BPNN is employed to predict the nonlinear relationship between the optimization objective and the parameters.The Latin hypercube sampling(LHS)method is used for random sampling in the FE model analysis for training,testing,and validation,which is then applied to compute the cost function in the PSO.Based on the relationships obtained by the BPNN,the PSO algorithm evaluates the fitness and cost functions to determine the optimal design point.The proposed optimization method is validated by comparing simulation results between the initial design and the optimized design.展开更多
Transition metal phosphides(TMPs)are recognized as such promising supercapacitor materials for the practical application,due to their superior electrical conductivity and excellent redox activity.Here,self-supported t...Transition metal phosphides(TMPs)are recognized as such promising supercapacitor materials for the practical application,due to their superior electrical conductivity and excellent redox activity.Here,self-supported three-dimensional NiCoP nanoparticles embedded in NiCoO2 nano wires(NiCoO2/NiCoP)electrode consisting of nickel cobalt phosphides(NiCoP)with high activity and nickel cobalt oxides(NiCoO2)with good stability were fabricated by a hydrothermal and phosphorization method.The electrode integrates the advantages of nanowire arrays for fast ion transport and foam Ni for effective charge transport and flexibility.Benefitting the proper composition control of the nanohybrid and unique structure design,the optimized NiCoO2/NiCoP-20 exhibits a high specific capacitance of 3204 F·g-1 at 1 A·g-1 in 3 mol·L-1 KOH aqueous electrolyte in a three-electrode system.Moreover,the asymmetric supercapacitor assembled with the prepared NiCoO2/NiCoP-20 and activated carbon achieves a specific capacitance of 116 F·g-1 with a high energy density of 40.32 Wh·kg-1 at the power density of 800.18 W·kg-1.The practical application is further demonstrated with all-solid-state winding supercapacitor devices,with decent flexibility,in series to light the Central South University(CSU)logo consisting of 21 red LED indicators.展开更多
Aiming at solving problems of low efficiency,low cable capacity in current 300m open-pit mine cable winding truck,a 900 m cable winding plan was proposed.In this paper,the mechanism of the thermal effect of the cable ...Aiming at solving problems of low efficiency,low cable capacity in current 300m open-pit mine cable winding truck,a 900 m cable winding plan was proposed.In this paper,the mechanism of the thermal effect of the cable was described,and a two-dimensional axisymmetric electromagnetic-fluid-temperature multiphysics coupling model of the cable reel was established regarding the 900m cable reel as independent system.Considering the structure of the drum,the number of cable winding layers,the factors of heat conduction,heat radiation and convective heat transfer in the actual working process,the steady state analysis of the multi-physical field coupling was carried out.The sum of the losses of each part of the cable was obtained through the calculation of electromagnetic field,which was used as a heat source to calculate and analyze the temperature distribution of different layers of cable winding,as well as the temperature distribution and heat dissipation characteristics of different structures of the drum.The results show that three layers of cable winding is the best design.The lowest temperature of closed cylindrical drum is 70℃after heat dissipation,which has obvious advantages compared with the lowest temperature of 85℃after heat dissipation of squirrel-cage cylindrical drum.The results provide a reliable theoretical basis for the research and development of a new type of mine cable winding truck with 900 m cable capacity.展开更多
In large-scale electric machines, unbalanced magnetic pull （UMP） caused by eccentricity usually results in stator-rotor rub, so it is necessary to investigate the amplitude and the influencing factors. This paper ta...In large-scale electric machines, unbalanced magnetic pull （UMP） caused by eccentricity usually results in stator-rotor rub, so it is necessary to investigate the amplitude and the influencing factors. This paper takes the squirrel-cage induction motor as an example. A magnetic loop model of an induction motor is established by an analytical method. The impact of stator winding setup （parallel branch and pole pairs） on each magnetomotive force （MMF） and unbalanced magnetic pull is analyzed. Using the finite element simulation method, the spatial and time distribution of flux density of the rotor outer circle under static eccentricity is obtained, and the unbalanced magnetic pull calculation caused by static eccentricity is completed. The conclusion of the influence of stator winding on the size of unbalanced magnetic pull provides reliable gist for motor noise and vibration analysis, and especially provides an important reference for large induction motor design.展开更多
A special winding machine with high accuracy has just been developed and applied to the construction of HT-7U Tokamak. It is one of the critical facilities for R & D of HT-7U construction. The machine mainly consi...A special winding machine with high accuracy has just been developed and applied to the construction of HT-7U Tokamak. It is one of the critical facilities for R & D of HT-7U construction. The machine mainly consists of five parts, including a CICC pay-off spool, a fourroller correcting assembly, a four-roller forming/bending assembly, a continuous winding structure and a CNC control system with three-axis AC servo motors. The facility is used for Cable in Conduit Conductor (CICC) magnet fabrication of HT-7U. The main requirements of the winding machine are: continuous winding to reduce joints inside the coils; pre-forming CICC conductor to avoid winding with tension; suitable for all TF & PF coils of various coil shapes and within the dimension limit; improving the configuration tolerance and the special flatness of the CICC conductor. This paper emphasizes on the design and fabrication of the special winding machine for HT-7U. Some analyses and techniques in winding process for trial D-shape coil are also presented.展开更多
This paper proposes the application of high-voltage stator-cable windings in superconducting machines,based on the characteristics of strong magnetic fields and large air gaps.Cross-linked polyethylene cable winding c...This paper proposes the application of high-voltage stator-cable windings in superconducting machines,based on the characteristics of strong magnetic fields and large air gaps.Cross-linked polyethylene cable winding can be employed to achieve a rated voltage of 35 kV in direct-current(DC)-field superconducting machines,thereby enabling a direct connection between the superconducting machine and the power grid,eliminating the need for transformers.We first,through finite element analysis,demonstrate that the proposed high-voltage high-temperature superconducting machine not only meets the requirement of a 35 kV-rated voltage,but also exhibits minimal flux leakage,torque fluctuation,and harmonic distortion.We then compare three candidate types to discuss the tradeoff between the multi-group superconducting field winding arrangement and machine performances.We propose inverted trapezoidal superconducting field winding as a promising candidate,because it has minimal superconductivity material usage,the largest safety margin for the superconducting coils(SCs),low thrust ripple,and low total harmonic distortion with the desired 35 kV-rated voltage.Finally,through large-scale design parameter sweeping,we show how we selected the optimal parameters for field winding and validated them by the finite element method.展开更多
Compared with the traditional three-phase star connection winding,the open-end winding permanent magnet synchronous motor(OW-PMSM)system with a common direct current(DC)bus has a zero-sequence circuit,which makes the ...Compared with the traditional three-phase star connection winding,the open-end winding permanent magnet synchronous motor(OW-PMSM)system with a common direct current(DC)bus has a zero-sequence circuit,which makes the common-mode voltage and the back electromotive force(EMF)harmonic generated by the inverters produce the zero-sequence current in the zero-sequence circuit,and the zero-sequence current has great influence on the operation efficiency and stability of the motor control system.A zero-sequence current suppression strategy is presented based on model predictive current control for OW-PMSM.Through the mathematical model of OW-PMSM to establish the predictive model and the zero-sequence circuit model,the common-mode voltage under different voltage vector combinations is fully considered during vector selection and action time calculation.Then zero-sequence loop constraints are established,so as to suppress the zero-sequence current.In the end,the control strategy proposed in this paper is verified by simulation experiments.展开更多
To investigate the wind⁃induced vibration re⁃sponse characteristics of multispan double⁃layer cable photo⁃voltaic(PV)support structures,wind tunnel tests using an aeroelastic model were carried out to obtain the wind⁃...To investigate the wind⁃induced vibration re⁃sponse characteristics of multispan double⁃layer cable photo⁃voltaic(PV)support structures,wind tunnel tests using an aeroelastic model were carried out to obtain the wind⁃induced vibration response data of a three⁃span four⁃row double⁃layer cable PV support system.The wind⁃induced vibration characteristics with different PV module tilt angles,wind speeds,and wind direction angles were analyzed.The results showed that the double⁃layer cable large⁃span flexible PV support can effectively control the wind⁃induced vibration response and prevent the occur⁃rence of flutter under strong wind conditions.The maxi⁃mum value of the wind⁃induced vibration displacement of the flexible PV support system occurs in the windward first row.The upstream module has a significant shading effect on the downstream module,with a maximum effect of 23%.The most unfavorable wind direction angles of the structure are 0°and 180°.The change of the wind direction angle in the range of 0°to 30°has little effect on the wind vi⁃bration response.The change in the tilt angle of the PV modules has a greater impact on the wind vibration in the downwind direction and a smaller impact in the upwind di⁃rection.Special attention should be paid to the structural wind⁃resistant design of such systems in the upwind side span.展开更多
With the development of high-frequency and highvoltagetraction machines(TM)incorporating hairpin windings(HW)and SiC inverters for electric vehicles(EV),both theinterturn voltage stress and temperature within HW are r...With the development of high-frequency and highvoltagetraction machines(TM)incorporating hairpin windings(HW)and SiC inverters for electric vehicles(EV),both theinterturn voltage stress and temperature within HW are rising,increasing the risk of partial discharge(PD),and presentingsignificant challenges to insulation safety.Therefore,this paperaddresses this issue and proposes potential solutions.Firstly,thepaper examines an 8-pole,48-slot,6-layer HW TM to highlightthe unique characteristics of this winding structure,and explainsthe uneven distribution of interturn voltage stress andtemperature.Subsequently,a high-frequency equivalent circuitmodel of the HW TM prototype is developed.The error ofsimulation and experiment is only 5.7%,which proves theaccuracy of the model.Then,an improved HW scheme isproposed to lower the maximum voltage stress by 29.3%.Furthermore,the temperature distribution of HW TM isanalyzed to facilitate a detailed examination of the impact oftemperature on insulation PD.Finally,the partial dischargeinception voltage(PDIV)of interturn insulation,consideringtemperature effects,is calculated and verified throughexperiment.The paper proposes a reliability-oriented designmethod and process for HW TM.It demonstrates that thereliability-oriented design can achieve PD-free performance inthe design stage of HW.展开更多
Research on the mechanical–electrical properties is crucial for designing and preparing high-temperature superconducting(HTS)cables.Various winding core structures can influence the mechanical–electrical behavior of...Research on the mechanical–electrical properties is crucial for designing and preparing high-temperature superconducting(HTS)cables.Various winding core structures can influence the mechanical–electrical behavior of cables,but the impact of alterations in the winding core structure on the mechanical–electrical behavior of superconducting cables remains unclear.This paper presents a 3D finite element model to predict the performance of three cables with different core structures when subjected to transverse compression and axial tension.The three cables analyzed are CORC(conductor-on-round-core),CORT(conductor-on-round-tube),and HFRC(conductor-on-spiral-tube).A parametric analysis is carried out by varying the core diameter and inner-to-outer diameter ratio.Results indicate that the CORT cable demonstrates better performance in transverse compression compared to the CORC cable,aligning with experimental data.Among the three cables,the HFRC cables exhibit the weakest resistance to transverse deformation.However,the HFRC cable demonstrates superior tensile deformation resistance compared to the CORT cable,provided that the transverse compression properties are maintained.Finite element results also show that the optimum inner-to-outer diameter ratios for achieving the best transverse compression performance are approximately 0.8 for CORT cables and 0.6 for HFRC cables.Meanwhile,the study explores the effect of structural changes in HTS cable winding cores on their electromagnetic properties.It recommends utilizing small tape gaps,lower frequencies,and spiral core construction to minimize eddy losses.The findings presented in this paper offer valuable insights for the commercialization and practical manufacturing of HTS cables.展开更多
This study employed a computational fluid dynamics model with an overset mesh technique to investigate the thrust and power of a floating offshore wind turbine(FOWT)under platform floating motion in the wind–rain fie...This study employed a computational fluid dynamics model with an overset mesh technique to investigate the thrust and power of a floating offshore wind turbine(FOWT)under platform floating motion in the wind–rain field.The impact of rainfall on aerodynamic performance was initially examined using a stationary turbine model in both wind and wind–rain conditions.Subsequently,the study compared the FOWT’s performance under various single degree-of-freedom(DOF)motions,including surge,pitch,heave,and yaw.Finally,the combined effects of wind–rain fields and platform motions involving two DOFs on the FOWT’s aerodynamics were analyzed and compared.The results demonstrate that rain negatively impacts the aerodynamic performance of both the stationary turbines and FOWTs.Pitch-dominated motions,whether involving single or multiple DOFs,caused significant fluctuations in the FOWT aerodynamics.The combination of surge and pitch motions created the most challenging operational environment for the FOWT in all tested scenarios.These findings highlighted the need for stronger construction materials and greater ultimate bearing capacity for FOWTs,as well as the importance of optimizing designs to mitigate excessive pitch and surge.展开更多
Unsteady aerodynamic characteristics at high angles of attack are of great importance to the design and development of advanced fighter aircraft, which are characterized by post-stall maneuverability with multiple Deg...Unsteady aerodynamic characteristics at high angles of attack are of great importance to the design and development of advanced fighter aircraft, which are characterized by post-stall maneuverability with multiple Degrees-of-Freedom(multi-DOF) and complex flow field structure.In this paper, a special kind of cable-driven parallel mechanism is firstly utilized as a new suspension method to conduct unsteady dynamic wind tunnel tests at high angles of attack, thereby providing experimental aerodynamic data. These tests include a wide range of multi-DOF coupled oscillatory motions with various amplitudes and frequencies. Then, for aerodynamic modeling and analysis, a novel data-driven Feature-Level Attention Recurrent neural network(FLAR) is proposed. This model incorporates a specially designed feature-level attention module that focuses on the state variables affecting the aerodynamic coefficients, thereby enhancing the physical interpretability of the aerodynamic model. Subsequently, spin maneuver simulations, using a mathematical model as the baseline, are conducted to validate the effectiveness of the FLAR. Finally, the results on wind tunnel data reveal that the FLAR accurately predicts aerodynamic coefficients, and observations through the visualization of attention scores identify the key state variables that affect the aerodynamic coefficients. It is concluded that the proposed FLAR enhances the interpretability of the aerodynamic model while achieving good prediction accuracy and generalization capability for multi-DOF coupling motion at high angles of attack.展开更多
In this study,ionosonde observations over Fuke(19.5°N,109.1°E),Wuhan(30.5°N,114.4°E),and Mohe(53.5°N,122.3°E)were analyzed to demonstrate the responses of the sporadic E()to the severe at...In this study,ionosonde observations over Fuke(19.5°N,109.1°E),Wuhan(30.5°N,114.4°E),and Mohe(53.5°N,122.3°E)were analyzed to demonstrate the responses of the sporadic E()to the severe atmospheric disturbances caused by the Tonga volcanic eruptions on January 15,2022.The most prominent signature was the disappearance of the layer after~10:00 UT over Wuhan and Fuke,which was attributed to the vertical drift caused by the eruptions.The occurred intermittently after 13:00 UT following the arrival of the tropospheric Lamb wave.To examine the causal mechanism for the intermittence,we also included data of horizontal winds in the mesosphere and lower thermosphere region recorded by the meteor radars at Wuhan and Mohe in this study.The wind disturbances with periods of~20 hours contributed to the formation of the layer in the nighttime on January 15.展开更多
A numerical method to predict the bursting strength of filament wound composite rocket motor case is proposed here.This method can evaluate the longitudinal stress evolution of each composite layer as impregnated fila...A numerical method to predict the bursting strength of filament wound composite rocket motor case is proposed here.This method can evaluate the longitudinal stress evolution of each composite layer as impregnated filaments with fiber tension are wound layer by layer,and consider the effects of accumulated stress and deformation during filament winding on the bursting strength of composite case.Taking∅520 mm composite cases as a case study,the filament-winding-process-induced stress and deformation as well as progressive damage behavior are numerically predicted,followed by a comparison with experimental results.The numerical results show that the predicted bursting pressures for composite cases manufactured on the mandrels with and without a flexible component are 14.20 MPa and 21.40 MPa,respectively.These values exhibit slight deviation from the measured pressures of 13.50 MPa and 21.57 MPa.Moreover,the predicted damage locations,situated respectively in the dome and cylinder,agree well with the experimental observation.These observations indicate that use of flexible component reduces the load-bearing capacity of the domes.Furthermore,it validates the reliability and accuracy of the proposed numerical method in predicting the bursting strength of composite cases.展开更多
Previous studies have indicated a global reversal of near-surface wind speeds from a declining trend to an increasing trend around 2010;however,it remains unclear whether upper-air wind speeds exhibit a similar revers...Previous studies have indicated a global reversal of near-surface wind speeds from a declining trend to an increasing trend around 2010;however,it remains unclear whether upper-air wind speeds exhibit a similar reversal.This study evaluates reanalysis products using surface and radiosonde observations to analyze upper-air wind speed variations in the Northern Hemisphere,focusing on their seasonal and latitudinal differences.Results demonstrate that JRA-55 effectively captures wind speed variations in the Northern Hemisphere.Notably,upper-air wind speeds over land experienced a reversal in winter 2010 with significant latitudinal differences.The trend reversal of upper wind speed between the midlatitudes and subtropics presents a dipole pattern.From 1990 to 2010,upper-air wind speeds in the midlatitudes(40°-70°N)significantly declined,while the subtropical zone(20°-40°N)displayed an opposite trend.However,during 2010-2020,wind speeds in the midlatitudes shifted to a significant positive trend,whereas the subtropics experienced a significant negative trend.The variations in Northern Hemisphere winter wind speeds can be attributed to changes in low-level baroclinicity driven by tropical diabatic heating and midlatitude transient eddy feedback.Enhanced diabatic heating and weakened eddy feedback during 1990-2010 contributed to reduced wind speeds in the midlatitudes and increased speeds in the subtropics,while reduced diabatic heating and strengthened eddy feedback during 2010-2020 resulted in increased wind speeds in the midlatitudes and decreased speeds in the subtropics.The reversal of upper-air wind speeds could affect surface wind speeds by downward momentum transfer,which could contribute to the reversal of surface wind speeds.展开更多
Aiming at the problems of large fluctuation of output active power and poor control performance in the process of frequency support of an energy-storage-type static-var-generator(ESVG),the adaptive adjustment control ...Aiming at the problems of large fluctuation of output active power and poor control performance in the process of frequency support of an energy-storage-type static-var-generator(ESVG),the adaptive adjustment control method for its active-loop parameters is used to realize thewind-farmfrequency support,which has become the current research hotspot.Taking the ESVG with a supercapacitor on the DC side as the research object,the influence trend of the change of virtual rotation inertia and virtual damping coefficient on its virtual angular velocity and power angle is analyzed.Then,the constraint relationship between the equivalent virtual inertia time constant of the supercapacitor and the virtual rotation inertia of the ESVG is clarified.Then,combined with the second-order response characteristics of the ESVG power control loop,the selection principles of the frequency modulation coefficient,the virtual rotation inertia,and the virtual damping coefficient are determined.An ESVG adjustment control method,considering the adaptive adjustment of the active loop parameters of the supercapacitor equivalent inertia,is proposed.While ensuring the frequency support capability of the ESVG,the fluctuation degree of its output active power and the virtual angular velocity are suppressed,and the proposed adjustment method also improves the stability of the ESVG control system and the frequency support capability for the wind farm.Finally,the simulation verifies the correctness of the theoretical analysis and the effectiveness of the proposed strategy.展开更多
Under the combination of currents and waves, seabed scour occurs around offshore wind turbine foundations, which affects the stability and safe operation of offshore wind turbines. In this study, physical model experi...Under the combination of currents and waves, seabed scour occurs around offshore wind turbine foundations, which affects the stability and safe operation of offshore wind turbines. In this study, physical model experiments under unidirectional flow, bidirectional flow, and wave-current interactions with different flow directions around the pile group foundation were first conducted to investigate the development of scour around the pile group foundation.Additionally, a three-dimensional scour numerical model was established via the open-source software REEF3D to simulate the flow field and scour around the prototype-scale foundation. The impact of flow on scour was discussed.Under unidirectional flow, scour equilibrium was reached more quickly, with the maximum scour depth reaching approximately 1.2 times the pile diameter and the extent of the scour hole spanning about 4.9 times the pile diameter.Compared with those under unidirectional flow, the scour depths under combinations of currents and waves, as well as bidirectional flow, were slightly smaller. However, the morphology of scour holes was more uniform and symmetrical. The numerical simulation results show good agreement with the experimental data, demonstrating the impact of varying flow directions on the velocity distribution around the foundation, the morphology of scour holes, and the location of the maximum scour depth.展开更多
This study investigates the characteristics of secondary eyewall formation(SEF)in idealized tropical cyclones embedded in vertical wind shear(VWS)at different heights.The results show that upper-layer VWS at a relativ...This study investigates the characteristics of secondary eyewall formation(SEF)in idealized tropical cyclones embedded in vertical wind shear(VWS)at different heights.The results show that upper-layer VWS at a relatively low shear height is more favorable for SEF than upper-layer VWS at a relatively high shear height and lowerlayer VWS.In the experiments with upper-layer VWS at a relatively low shear height,better-organized stratiform clouds are located in the downwind sector of outer rainbands.The low-level descending inflow associated with the stratiform sector is stronger in these experiments than in the experiments with upper-layer VWS at a relatively high shear height and lower-layer VWS.The enhanced descending inflow can trigger supergradient winds and convergence near the top of the boundary layer,close to three times the radius of the maximum wind,where convection is locally forced.The subsequent convection axisymmetrization leads to SEF.展开更多
A new piezoelectric energy harvester is proposed which employs the coupling effect between a piezoelectric beam and an elastic-supported sphere to capture wind energy from multiple directions.As wind flows across the ...A new piezoelectric energy harvester is proposed which employs the coupling effect between a piezoelectric beam and an elastic-supported sphere to capture wind energy from multiple directions.As wind flows across the sphere,it induces vortical vibrations that transfer to the piezoelectric beam,converting wind energy into electricity.A nonlinear coupled dynamic theoretical model based on the Euler-Lagrange equation is developed to study the interactions between the sphere and beam vibrations.The vortex-induced force acting on the sphere is determined,and the dynamic model of the coupled system is validated through experiments.The results show that in order to reach convergence,at least four modes are required in the Galerkin discretization.Moreover,the output performance of the energy harvester strongly depends on the frequency ratio between the sphere and the piezoelectric beam.We find that at a frequency ratio of approximately 1.34,the harvester achieves a maximum average power of 190μW at a wind speed of 3.90 m/s,with the lock-in region between 2.63 and 5.30 m/s.Subsequently,the impact of wind flow direction on the electrical performance of the energy harvester is investigated in a wind tunnel,by adjusting the angle between the harvester and incoming flows ranging from 0°to 360°.The findings indicate that the harvester maintains strong and consistent performance across variable wind flow directions and speeds.Particularly within the lock-in region,the output voltage fluctuations are below 5.5%,showcasing the robustness of the design.This result points to the potential utility of this novel harvester in complex environments.Our study also provides a theoretical basis for the development of small-scale offshore wind energy harvesting technologies.展开更多
基金supported by Shenzhen Science and Technology Program under Grant JCYJ20250604175412017the National Natural Science Foundation of China under Grant 62473387+1 种基金the Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai) under Grant SML2024SP007in part by the Department of Science and Technology of Guangdong Province under Grant. 2021QN020085。
文摘In permanent magnet synchronous machine(PMSM) drives, temperature information is critical to achieve reliable and high-performance control. The popular model-based estimation methods are based on extracting temperature dependent terms from the voltages using the machine model. The estimation accuracy under low speed or load can be greatly affected by the model uncertainty and noise due to low signal-tonoise ratio. This paper presents a high frequency(HF) position offset injection-based winding and permanent magnet(PM) temperature decoupled estimation approach for PMSMs to achieve accurate and robust temperature estimation among a wide speed range especially under low-speed conditions. In the proposed approach, a small HF position offset is injected into the machine to construct a decoupled winding and PM temperature estimation model, in which the winding and PM temperatures are independently estimated from HF excitations. The temperature estimation is independent from the fundamental model and parameter variation, and it achieves high signal-tonoise ratio under low-speed conditions. Moreover, the temperature estimation is also not affected by magnetic saturation and inverter distortion, which can improve the accuracy and robustness of temperature estimation. The proposed approach is validated with experiments and comparisons on a laboratory machine under various operating conditions.
基金funded by the Science and Technology Projects of State Grid Corporation of China(Project No.J2024136).
文摘To ensure an uninterrupted power supply,mobile power sources(MPS)are widely deployed in power grids during emergencies.Comprising mobile emergency generators(MEGs)and mobile energy storage systems(MESS),MPS are capable of supplying power to critical loads and serving as backup sources during grid contingencies,offering advantages such as flexibility and high resilience through electricity delivery via transportation networks.This paper proposes a design method for a 400 V–10 kV Dual-Winding Induction Generator(DWIG)intended for MEG applications,employing an improved particle swarmoptimization(PSO)algorithmbased on a back-propagation neural network(BPNN).A parameterized finite element(FE)model of the DWIG is established to derive constraints on its dimensional parameters,thereby simplifying the optimization space.Through sensitivity analysis between temperature rise and electromagnetic loss of the DWIG,the main factors influencing the machine’s temperature are identified,and electromagnetic loss is determined as the optimization objective.To obtain an accurate fitting function between electromagnetic loss and dimensional parameters,the BPNN is employed to predict the nonlinear relationship between the optimization objective and the parameters.The Latin hypercube sampling(LHS)method is used for random sampling in the FE model analysis for training,testing,and validation,which is then applied to compute the cost function in the PSO.Based on the relationships obtained by the BPNN,the PSO algorithm evaluates the fitness and cost functions to determine the optimal design point.The proposed optimization method is validated by comparing simulation results between the initial design and the optimized design.
基金financially supported by the National Key Research and Development Program of China(No.2018YFB0104200)。
文摘Transition metal phosphides(TMPs)are recognized as such promising supercapacitor materials for the practical application,due to their superior electrical conductivity and excellent redox activity.Here,self-supported three-dimensional NiCoP nanoparticles embedded in NiCoO2 nano wires(NiCoO2/NiCoP)electrode consisting of nickel cobalt phosphides(NiCoP)with high activity and nickel cobalt oxides(NiCoO2)with good stability were fabricated by a hydrothermal and phosphorization method.The electrode integrates the advantages of nanowire arrays for fast ion transport and foam Ni for effective charge transport and flexibility.Benefitting the proper composition control of the nanohybrid and unique structure design,the optimized NiCoO2/NiCoP-20 exhibits a high specific capacitance of 3204 F·g-1 at 1 A·g-1 in 3 mol·L-1 KOH aqueous electrolyte in a three-electrode system.Moreover,the asymmetric supercapacitor assembled with the prepared NiCoO2/NiCoP-20 and activated carbon achieves a specific capacitance of 116 F·g-1 with a high energy density of 40.32 Wh·kg-1 at the power density of 800.18 W·kg-1.The practical application is further demonstrated with all-solid-state winding supercapacitor devices,with decent flexibility,in series to light the Central South University(CSU)logo consisting of 21 red LED indicators.
基金This work was supported in part by 2019 Local Project of Science and Tech nology Research Service of Liaoning Provincial Department of Education(LJ2019FL003)by 2019 Science and Technology Research and Innovation Te am Project of Liaoning Provincial Department of Education(LT2019007)by 2020 Youth Science and Technology Talents"Nursery"Projects of Scient ific Research of Liaoning Province Education Department(LJ2020QNL019).
文摘Aiming at solving problems of low efficiency,low cable capacity in current 300m open-pit mine cable winding truck,a 900 m cable winding plan was proposed.In this paper,the mechanism of the thermal effect of the cable was described,and a two-dimensional axisymmetric electromagnetic-fluid-temperature multiphysics coupling model of the cable reel was established regarding the 900m cable reel as independent system.Considering the structure of the drum,the number of cable winding layers,the factors of heat conduction,heat radiation and convective heat transfer in the actual working process,the steady state analysis of the multi-physical field coupling was carried out.The sum of the losses of each part of the cable was obtained through the calculation of electromagnetic field,which was used as a heat source to calculate and analyze the temperature distribution of different layers of cable winding,as well as the temperature distribution and heat dissipation characteristics of different structures of the drum.The results show that three layers of cable winding is the best design.The lowest temperature of closed cylindrical drum is 70℃after heat dissipation,which has obvious advantages compared with the lowest temperature of 85℃after heat dissipation of squirrel-cage cylindrical drum.The results provide a reliable theoretical basis for the research and development of a new type of mine cable winding truck with 900 m cable capacity.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51677051 and 51377039)the Fund from the Anhui Province Key Laboratory of Large-scale Submersible Electric Pump and Accoutrements
文摘In large-scale electric machines, unbalanced magnetic pull （UMP） caused by eccentricity usually results in stator-rotor rub, so it is necessary to investigate the amplitude and the influencing factors. This paper takes the squirrel-cage induction motor as an example. A magnetic loop model of an induction motor is established by an analytical method. The impact of stator winding setup （parallel branch and pole pairs） on each magnetomotive force （MMF） and unbalanced magnetic pull is analyzed. Using the finite element simulation method, the spatial and time distribution of flux density of the rotor outer circle under static eccentricity is obtained, and the unbalanced magnetic pull calculation caused by static eccentricity is completed. The conclusion of the influence of stator winding on the size of unbalanced magnetic pull provides reliable gist for motor noise and vibration analysis, and especially provides an important reference for large induction motor design.
文摘A special winding machine with high accuracy has just been developed and applied to the construction of HT-7U Tokamak. It is one of the critical facilities for R & D of HT-7U construction. The machine mainly consists of five parts, including a CICC pay-off spool, a fourroller correcting assembly, a four-roller forming/bending assembly, a continuous winding structure and a CNC control system with three-axis AC servo motors. The facility is used for Cable in Conduit Conductor (CICC) magnet fabrication of HT-7U. The main requirements of the winding machine are: continuous winding to reduce joints inside the coils; pre-forming CICC conductor to avoid winding with tension; suitable for all TF & PF coils of various coil shapes and within the dimension limit; improving the configuration tolerance and the special flatness of the CICC conductor. This paper emphasizes on the design and fabrication of the special winding machine for HT-7U. Some analyses and techniques in winding process for trial D-shape coil are also presented.
基金State Grid Corporation of China R&D Project(No.5500-202319193A-1-1-ZN).
文摘This paper proposes the application of high-voltage stator-cable windings in superconducting machines,based on the characteristics of strong magnetic fields and large air gaps.Cross-linked polyethylene cable winding can be employed to achieve a rated voltage of 35 kV in direct-current(DC)-field superconducting machines,thereby enabling a direct connection between the superconducting machine and the power grid,eliminating the need for transformers.We first,through finite element analysis,demonstrate that the proposed high-voltage high-temperature superconducting machine not only meets the requirement of a 35 kV-rated voltage,but also exhibits minimal flux leakage,torque fluctuation,and harmonic distortion.We then compare three candidate types to discuss the tradeoff between the multi-group superconducting field winding arrangement and machine performances.We propose inverted trapezoidal superconducting field winding as a promising candidate,because it has minimal superconductivity material usage,the largest safety margin for the superconducting coils(SCs),low thrust ripple,and low total harmonic distortion with the desired 35 kV-rated voltage.Finally,through large-scale design parameter sweeping,we show how we selected the optimal parameters for field winding and validated them by the finite element method.
基金Fundamental Research Funds for the Central Universities,China(No.2232019D3-53)Initial Research Funds for Young Teachers of Donghua University,China(104070053029)Shanghai Rising-Star Program,China(No.19QA1400400)。
文摘Compared with the traditional three-phase star connection winding,the open-end winding permanent magnet synchronous motor(OW-PMSM)system with a common direct current(DC)bus has a zero-sequence circuit,which makes the common-mode voltage and the back electromotive force(EMF)harmonic generated by the inverters produce the zero-sequence current in the zero-sequence circuit,and the zero-sequence current has great influence on the operation efficiency and stability of the motor control system.A zero-sequence current suppression strategy is presented based on model predictive current control for OW-PMSM.Through the mathematical model of OW-PMSM to establish the predictive model and the zero-sequence circuit model,the common-mode voltage under different voltage vector combinations is fully considered during vector selection and action time calculation.Then zero-sequence loop constraints are established,so as to suppress the zero-sequence current.In the end,the control strategy proposed in this paper is verified by simulation experiments.
基金The National Natural Science Foundation of China(No.52338011).
文摘To investigate the wind⁃induced vibration re⁃sponse characteristics of multispan double⁃layer cable photo⁃voltaic(PV)support structures,wind tunnel tests using an aeroelastic model were carried out to obtain the wind⁃induced vibration response data of a three⁃span four⁃row double⁃layer cable PV support system.The wind⁃induced vibration characteristics with different PV module tilt angles,wind speeds,and wind direction angles were analyzed.The results showed that the double⁃layer cable large⁃span flexible PV support can effectively control the wind⁃induced vibration response and prevent the occur⁃rence of flutter under strong wind conditions.The maxi⁃mum value of the wind⁃induced vibration displacement of the flexible PV support system occurs in the windward first row.The upstream module has a significant shading effect on the downstream module,with a maximum effect of 23%.The most unfavorable wind direction angles of the structure are 0°and 180°.The change of the wind direction angle in the range of 0°to 30°has little effect on the wind vi⁃bration response.The change in the tilt angle of the PV modules has a greater impact on the wind vibration in the downwind direction and a smaller impact in the upwind di⁃rection.Special attention should be paid to the structural wind⁃resistant design of such systems in the upwind side span.
基金supported by the Project of National Natural Science Foundation of China under Grant 52407060 and 52422704supported by Liaoning Province science and technology plan doctoral project under Grant 2023-BSBA-255.
文摘With the development of high-frequency and highvoltagetraction machines(TM)incorporating hairpin windings(HW)and SiC inverters for electric vehicles(EV),both theinterturn voltage stress and temperature within HW are rising,increasing the risk of partial discharge(PD),and presentingsignificant challenges to insulation safety.Therefore,this paperaddresses this issue and proposes potential solutions.Firstly,thepaper examines an 8-pole,48-slot,6-layer HW TM to highlightthe unique characteristics of this winding structure,and explainsthe uneven distribution of interturn voltage stress andtemperature.Subsequently,a high-frequency equivalent circuitmodel of the HW TM prototype is developed.The error ofsimulation and experiment is only 5.7%,which proves theaccuracy of the model.Then,an improved HW scheme isproposed to lower the maximum voltage stress by 29.3%.Furthermore,the temperature distribution of HW TM isanalyzed to facilitate a detailed examination of the impact oftemperature on insulation PD.Finally,the partial dischargeinception voltage(PDIV)of interturn insulation,consideringtemperature effects,is calculated and verified throughexperiment.The paper proposes a reliability-oriented designmethod and process for HW TM.It demonstrates that thereliability-oriented design can achieve PD-free performance inthe design stage of HW.
基金supported by the National Natural Science Foundation of China(12072136).
文摘Research on the mechanical–electrical properties is crucial for designing and preparing high-temperature superconducting(HTS)cables.Various winding core structures can influence the mechanical–electrical behavior of cables,but the impact of alterations in the winding core structure on the mechanical–electrical behavior of superconducting cables remains unclear.This paper presents a 3D finite element model to predict the performance of three cables with different core structures when subjected to transverse compression and axial tension.The three cables analyzed are CORC(conductor-on-round-core),CORT(conductor-on-round-tube),and HFRC(conductor-on-spiral-tube).A parametric analysis is carried out by varying the core diameter and inner-to-outer diameter ratio.Results indicate that the CORT cable demonstrates better performance in transverse compression compared to the CORC cable,aligning with experimental data.Among the three cables,the HFRC cables exhibit the weakest resistance to transverse deformation.However,the HFRC cable demonstrates superior tensile deformation resistance compared to the CORT cable,provided that the transverse compression properties are maintained.Finite element results also show that the optimum inner-to-outer diameter ratios for achieving the best transverse compression performance are approximately 0.8 for CORT cables and 0.6 for HFRC cables.Meanwhile,the study explores the effect of structural changes in HTS cable winding cores on their electromagnetic properties.It recommends utilizing small tape gaps,lower frequencies,and spiral core construction to minimize eddy losses.The findings presented in this paper offer valuable insights for the commercialization and practical manufacturing of HTS cables.
基金Supported by the National Natural Science Foundation of China(51679080 and 51379073)the Fundamental Research Funds for the Central Universities(B230205020).
文摘This study employed a computational fluid dynamics model with an overset mesh technique to investigate the thrust and power of a floating offshore wind turbine(FOWT)under platform floating motion in the wind–rain field.The impact of rainfall on aerodynamic performance was initially examined using a stationary turbine model in both wind and wind–rain conditions.Subsequently,the study compared the FOWT’s performance under various single degree-of-freedom(DOF)motions,including surge,pitch,heave,and yaw.Finally,the combined effects of wind–rain fields and platform motions involving two DOFs on the FOWT’s aerodynamics were analyzed and compared.The results demonstrate that rain negatively impacts the aerodynamic performance of both the stationary turbines and FOWTs.Pitch-dominated motions,whether involving single or multiple DOFs,caused significant fluctuations in the FOWT aerodynamics.The combination of surge and pitch motions created the most challenging operational environment for the FOWT in all tested scenarios.These findings highlighted the need for stronger construction materials and greater ultimate bearing capacity for FOWTs,as well as the importance of optimizing designs to mitigate excessive pitch and surge.
基金supported by the National Natural Science Foundation of China(Nos.12172315,12072304,11702232)the Fujian Provincial Natural Science Foundation,China(No.2021J01050)the Aeronautical Science Foundation of China(No.20220013068002).
文摘Unsteady aerodynamic characteristics at high angles of attack are of great importance to the design and development of advanced fighter aircraft, which are characterized by post-stall maneuverability with multiple Degrees-of-Freedom(multi-DOF) and complex flow field structure.In this paper, a special kind of cable-driven parallel mechanism is firstly utilized as a new suspension method to conduct unsteady dynamic wind tunnel tests at high angles of attack, thereby providing experimental aerodynamic data. These tests include a wide range of multi-DOF coupled oscillatory motions with various amplitudes and frequencies. Then, for aerodynamic modeling and analysis, a novel data-driven Feature-Level Attention Recurrent neural network(FLAR) is proposed. This model incorporates a specially designed feature-level attention module that focuses on the state variables affecting the aerodynamic coefficients, thereby enhancing the physical interpretability of the aerodynamic model. Subsequently, spin maneuver simulations, using a mathematical model as the baseline, are conducted to validate the effectiveness of the FLAR. Finally, the results on wind tunnel data reveal that the FLAR accurately predicts aerodynamic coefficients, and observations through the visualization of attention scores identify the key state variables that affect the aerodynamic coefficients. It is concluded that the proposed FLAR enhances the interpretability of the aerodynamic model while achieving good prediction accuracy and generalization capability for multi-DOF coupling motion at high angles of attack.
基金the Funds of the National Natural Science Foundation of China(NSFC),grant numbers 42174211,42230207,and U2039205.
文摘In this study,ionosonde observations over Fuke(19.5°N,109.1°E),Wuhan(30.5°N,114.4°E),and Mohe(53.5°N,122.3°E)were analyzed to demonstrate the responses of the sporadic E()to the severe atmospheric disturbances caused by the Tonga volcanic eruptions on January 15,2022.The most prominent signature was the disappearance of the layer after~10:00 UT over Wuhan and Fuke,which was attributed to the vertical drift caused by the eruptions.The occurred intermittently after 13:00 UT following the arrival of the tropospheric Lamb wave.To examine the causal mechanism for the intermittence,we also included data of horizontal winds in the mesosphere and lower thermosphere region recorded by the meteor radars at Wuhan and Mohe in this study.The wind disturbances with periods of~20 hours contributed to the formation of the layer in the nighttime on January 15.
基金supported by the National Natural Science Foundation of China(No.11902231)the Major Program(JD)of Hubei Province,China(No.2023BAA004).
文摘A numerical method to predict the bursting strength of filament wound composite rocket motor case is proposed here.This method can evaluate the longitudinal stress evolution of each composite layer as impregnated filaments with fiber tension are wound layer by layer,and consider the effects of accumulated stress and deformation during filament winding on the bursting strength of composite case.Taking∅520 mm composite cases as a case study,the filament-winding-process-induced stress and deformation as well as progressive damage behavior are numerically predicted,followed by a comparison with experimental results.The numerical results show that the predicted bursting pressures for composite cases manufactured on the mandrels with and without a flexible component are 14.20 MPa and 21.40 MPa,respectively.These values exhibit slight deviation from the measured pressures of 13.50 MPa and 21.57 MPa.Moreover,the predicted damage locations,situated respectively in the dome and cylinder,agree well with the experimental observation.These observations indicate that use of flexible component reduces the load-bearing capacity of the domes.Furthermore,it validates the reliability and accuracy of the proposed numerical method in predicting the bursting strength of composite cases.
基金supported by the National Natural Science Foundation of China[grant numbers U2442207,42122034,42075043,and 42330609]the Youth Innovation Promotion Association[grant number 2021427]+2 种基金the West Light Foundation[grant number xbzgzdsys-202409]of the Chinese Academy of Sciencesthe Key Talent Projects in Gansu Provincethe Central Guidance Fund for Local Science and Technology Development Projects in Gansu Province[grant number 24ZYQA031].
文摘Previous studies have indicated a global reversal of near-surface wind speeds from a declining trend to an increasing trend around 2010;however,it remains unclear whether upper-air wind speeds exhibit a similar reversal.This study evaluates reanalysis products using surface and radiosonde observations to analyze upper-air wind speed variations in the Northern Hemisphere,focusing on their seasonal and latitudinal differences.Results demonstrate that JRA-55 effectively captures wind speed variations in the Northern Hemisphere.Notably,upper-air wind speeds over land experienced a reversal in winter 2010 with significant latitudinal differences.The trend reversal of upper wind speed between the midlatitudes and subtropics presents a dipole pattern.From 1990 to 2010,upper-air wind speeds in the midlatitudes(40°-70°N)significantly declined,while the subtropical zone(20°-40°N)displayed an opposite trend.However,during 2010-2020,wind speeds in the midlatitudes shifted to a significant positive trend,whereas the subtropics experienced a significant negative trend.The variations in Northern Hemisphere winter wind speeds can be attributed to changes in low-level baroclinicity driven by tropical diabatic heating and midlatitude transient eddy feedback.Enhanced diabatic heating and weakened eddy feedback during 1990-2010 contributed to reduced wind speeds in the midlatitudes and increased speeds in the subtropics,while reduced diabatic heating and strengthened eddy feedback during 2010-2020 resulted in increased wind speeds in the midlatitudes and decreased speeds in the subtropics.The reversal of upper-air wind speeds could affect surface wind speeds by downward momentum transfer,which could contribute to the reversal of surface wind speeds.
基金funded by the Science and Technology Project of State Grid Corporation,grant number 5500-202329500A-3-2-ZN,funding data 2023.10–2025.12.
文摘Aiming at the problems of large fluctuation of output active power and poor control performance in the process of frequency support of an energy-storage-type static-var-generator(ESVG),the adaptive adjustment control method for its active-loop parameters is used to realize thewind-farmfrequency support,which has become the current research hotspot.Taking the ESVG with a supercapacitor on the DC side as the research object,the influence trend of the change of virtual rotation inertia and virtual damping coefficient on its virtual angular velocity and power angle is analyzed.Then,the constraint relationship between the equivalent virtual inertia time constant of the supercapacitor and the virtual rotation inertia of the ESVG is clarified.Then,combined with the second-order response characteristics of the ESVG power control loop,the selection principles of the frequency modulation coefficient,the virtual rotation inertia,and the virtual damping coefficient are determined.An ESVG adjustment control method,considering the adaptive adjustment of the active loop parameters of the supercapacitor equivalent inertia,is proposed.While ensuring the frequency support capability of the ESVG,the fluctuation degree of its output active power and the virtual angular velocity are suppressed,and the proposed adjustment method also improves the stability of the ESVG control system and the frequency support capability for the wind farm.Finally,the simulation verifies the correctness of the theoretical analysis and the effectiveness of the proposed strategy.
基金financially supported by the National Key Research and Development Program of China (Grant No. 2021YFB2601100)the National Natural Science Foundation of China (Grant No. 51979190)。
文摘Under the combination of currents and waves, seabed scour occurs around offshore wind turbine foundations, which affects the stability and safe operation of offshore wind turbines. In this study, physical model experiments under unidirectional flow, bidirectional flow, and wave-current interactions with different flow directions around the pile group foundation were first conducted to investigate the development of scour around the pile group foundation.Additionally, a three-dimensional scour numerical model was established via the open-source software REEF3D to simulate the flow field and scour around the prototype-scale foundation. The impact of flow on scour was discussed.Under unidirectional flow, scour equilibrium was reached more quickly, with the maximum scour depth reaching approximately 1.2 times the pile diameter and the extent of the scour hole spanning about 4.9 times the pile diameter.Compared with those under unidirectional flow, the scour depths under combinations of currents and waves, as well as bidirectional flow, were slightly smaller. However, the morphology of scour holes was more uniform and symmetrical. The numerical simulation results show good agreement with the experimental data, demonstrating the impact of varying flow directions on the velocity distribution around the foundation, the morphology of scour holes, and the location of the maximum scour depth.
基金jointly supported by the National Natural Science Foundation of China[Grant Nos.U2342202 and 42175005]the Qing Lan Project[Grant No.R2023Q06]。
文摘This study investigates the characteristics of secondary eyewall formation(SEF)in idealized tropical cyclones embedded in vertical wind shear(VWS)at different heights.The results show that upper-layer VWS at a relatively low shear height is more favorable for SEF than upper-layer VWS at a relatively high shear height and lowerlayer VWS.In the experiments with upper-layer VWS at a relatively low shear height,better-organized stratiform clouds are located in the downwind sector of outer rainbands.The low-level descending inflow associated with the stratiform sector is stronger in these experiments than in the experiments with upper-layer VWS at a relatively high shear height and lower-layer VWS.The enhanced descending inflow can trigger supergradient winds and convergence near the top of the boundary layer,close to three times the radius of the maximum wind,where convection is locally forced.The subsequent convection axisymmetrization leads to SEF.
基金supported by the National Key R&D Program of China(No.2021YFF0501001)the National Natural Science Foundation of China(Nos.52308315,51922046,and 52192661)+4 种基金the Research Funds of Huazhong University of Science and Technology(No.2023JCYJ014)the China Postdoctoral Science Foundation(No.2023M731206)the Research Funds of China Railway Siyuan Survey and Design Group Co.,Ltd.(Nos.KY2023014S,KY2023126S,2021K085,2020K006,and 2020K172)the Research Fund of China Construction Science and Industry(No.CSCEC-PT-004-2022-KT-3.3)the Autonomous Innovation Fund of Hubei Province(No.5003242027),China.
文摘A new piezoelectric energy harvester is proposed which employs the coupling effect between a piezoelectric beam and an elastic-supported sphere to capture wind energy from multiple directions.As wind flows across the sphere,it induces vortical vibrations that transfer to the piezoelectric beam,converting wind energy into electricity.A nonlinear coupled dynamic theoretical model based on the Euler-Lagrange equation is developed to study the interactions between the sphere and beam vibrations.The vortex-induced force acting on the sphere is determined,and the dynamic model of the coupled system is validated through experiments.The results show that in order to reach convergence,at least four modes are required in the Galerkin discretization.Moreover,the output performance of the energy harvester strongly depends on the frequency ratio between the sphere and the piezoelectric beam.We find that at a frequency ratio of approximately 1.34,the harvester achieves a maximum average power of 190μW at a wind speed of 3.90 m/s,with the lock-in region between 2.63 and 5.30 m/s.Subsequently,the impact of wind flow direction on the electrical performance of the energy harvester is investigated in a wind tunnel,by adjusting the angle between the harvester and incoming flows ranging from 0°to 360°.The findings indicate that the harvester maintains strong and consistent performance across variable wind flow directions and speeds.Particularly within the lock-in region,the output voltage fluctuations are below 5.5%,showcasing the robustness of the design.This result points to the potential utility of this novel harvester in complex environments.Our study also provides a theoretical basis for the development of small-scale offshore wind energy harvesting technologies.
