Comparisons of Wave Force Model Effects on the Structural Responses and Fatigue Loads of a Semi-Submersible Floating Wind Turbine

The selection of wave force models will significantly impact the structural responses of floating wind turbines.In this study,comparisons of wave force model effects on the structural responses and fatigue loads of a semi-submersible floating wind turbine(SFWT)were conducted.Simulations were performed by employing the Morison equation(ME)with linear or second-order wave kinematics and potential flow theory(PFT)with first-or second-order wave forces.A comparison of regular waves,irregular waves,and coupled wind/waves analyses with the experimental data showed that many of the simulation results and experimental data are relatively consistent.However,notable discrepancies are found in the response amplitude operators for platform heave,tower base bending moment,and tension in mooring lines.PFT models give more satisfactory results of heave but more significant discrepan-cies in tower base bending moment than the ME models.In irregular wave analyses,low-frequency resonances were captured by PFT models with second-order difference-frequency terms,and high-frequency resonances were captured by the ME models or PFT models with second-order sum-frequency terms.These force models capture the response frequencies but do not reasonably predict the response amplitudes.The coupled wind/waves analyses showed more satisfactory results than the wave-only analyses.However,an important detail to note is that this satisfactory result is based on the overprediction of wind-induced responses.

Data-Driven Modeling for Wind Turbine Blade Loads Based on Deep Neural Network

Blades are essential components of wind turbines.Reducing their fatigue loads during operation helps to extend their lifespan,but it is difficult to quickly and accurately calculate the fatigue loads of blades.To solve this problem,this paper innovatively designs a data-driven blade load modeling method based on a deep learning framework through mechanism analysis,feature selection,and model construction.In the mechanism analysis part,the generation mechanism of blade loads and the load theoretical calculationmethod based on material damage theory are analyzed,and four measurable operating state parameters related to blade loads are screened;in the feature extraction part,15 characteristic indicators of each screened parameter are extracted in the time and frequency domain,and feature selection is completed through correlation analysis with blade loads to determine the input parameters of data-driven modeling;in the model construction part,a deep neural network based on feedforward and feedback propagation is designed to construct the nonlinear coupling relationship between the unit operating parameter characteristics and blade loads.The results show that the proposed method mines the wind turbine operating state characteristics highly correlated with the blade load,such as the standard deviation of wind speed.The model built using these characteristics has reasonable calculation and fitting capabilities for the blade load and shows a better fitting level for untrained out-of-sample data than the traditional scheme.Based on the mean absolute percentage error calculation,the modeling accuracy of the two blade loads can reach more than 90%and 80%,respectively,providing a good foundation for the subsequent optimization control to suppress the blade load.

Transient simulation of a pump-turbine with misaligned guide vanes during turbine model start-up

Experimental studies of a model pump-turbine S-curve characteristics and its improvement by misaligned guide vanes （MGV） were extended to prototype pump turbine through 3-D transient flow simulations. The unsteady Reynolds-averaged Navier-Stokes equations with the SST turbulence model were used to model the transient flow within the entire flow passage of a reversible pump-turbine with and without misaligned guide vanes during turbine model start-up. The unstable S-curve and its improvement by using misaligned guide vane were verified by model test and simulation. The transient flow calculations were used to clarify the variations of pressure pulse and internal flow behavior in the entire flow passage. The use of misaligned guide vanes can eliminate the S-curve characteristics of a pump-turbine, and can significantly increase the pressure pulse amplitude in the entire flow passage and the runner radial forces during start-up. The MGV only decreased the pulse amplitude on the guide vane suction side when the rotating speed was less than 50% rated speed. The hydraulic reason is that the MGV dramatically changed the flow patterns inside the entire flow passage, and destroyed the symmetry of the flow distribution inside the guide vane and runner.

A nonlinear model for aerodynamic configuration of wake behind horizontal-axis wind turbine

Determination of the aerodynamic configuration of wake is the key to analysis and evaluation of the rotor aerodynamic characteristics of a horizontal-axis wind turbine. According to the aerodynamic configuration, the real magnitude and direction of the onflow velocity at the rotor blade can be determined, and subsequently, the aerodynamic force on the rotor can be determined. The commonly employed wake aerodynamic models are of the cylindrical form instead of the actual expanding one. This is because the influence of the radial component of the induced velocity on the wake configuration is neglected. Therefore, this model should be called a "linear model". Using this model means that the induced velocities at the rotor blades and aerodynamic loads on them would be inexact. An approximately accurate approach is proposed in this paper to determine the so-called "nonlinear" wake aerodynamic configuration by means of the potential theory, where the influence of all three coordinate components of the induced velocity on wake aerodynamic configuration is taken into account to obtain a kind of expanding wake that approximately looks like an actual one. First, the rotor aerodynamic model composed of axial (central), bound, and trailing vortexes is established with the help of the finite aspect wing theory. Then, the Biot-Savart formula for the potential flow theory is used to derive a set of integral equations to evaluate the three components of the induced velocity at any point within the wake. The numerical solution to the integral equations is found, and the loci of all elementary trailing vortex filaments behind the rotor are determined thereafter. Finally, to formulate an actual wind turbine rotor, using the nonlinear wake model, the induced velocity everywhere in the wake, especially that at the rotor blade, is obtained in the case of various tip speed ratios and compared with the wake boundary in a neutral atmospheric boundary layer. Hereby, some useful and referential conclusions are offered for the aerodynamic computation and design of the rotor of the horizontal-axis wind turbine.

Modeling and Optimization of the Steam Turbine Network of an Ethylene Plant

In this paper,we developed a hybrid model for the steam turbines of a utility system,which combines an improved neural network model with the thermodynamic model.Then,a nonlinear programming(NLP) model of the steam turbine network is formulated by utilizing the developed steam turbine models to minimize the total steam cost for the whole steam turbine network.Finally,this model is applied to optimize the steam turbine network of an ethylene plant.The obtained results demonstrate that this hybrid model can accurately estimate and evaluate the performance of steam turbines,and the significant cost savings can be made by optimizing the steam turbine network operation at no capital cost.

Parametric Modeling System for Cooling Turbine Blade Based on Feature Design

Based on feature modeling and mathematical analysis methods,a process-oriented and modular parametric design system for advanced turbine cooling blade is developed with UG API,aiming at the structural complexity and high design difficulty of aero-engine cooling turbine blade.The relationship between the external and internal body features,the body attached feature is analyzed as viewed from the feature and parameter terms.The parametric design processes and design examples of the external body shape,tenon,platform and internal body shape,ribs,pin fins are introduced.The system improves the design efficiency of cooling turbine blade and establishes the foundation of multidisciplinary design optimization procedure for it.

Multiscale modelling and simulation of single crystal superalloy turbine blade casting during directional solidification process

As the key parts of an aero-engine,single crystal(SX)superalloy turbine blades have been the focus of much attention.However,casting defects often occur during the manufacturing process of the SX turbine blades.Modeling and simulation technology can help to optimize the manufacturing process of SX blades.Multiscale coupled models were proposed and used to simulate the physical phenomena occurring during the directional solidification(DS)process.Coupled with heat transfer(macroscale)and grain growth(meso-scale),3D dendritic grain growth was calculated to show the competitive grain growth at micro-scale.SX grain selection behavior was studied by the simulation and experiments.The results show that the geometrical structure and technical parameters had strong influences on the grain selection effectiveness.Based on the coupled models,heat transfer,grain growth and microstructure evolution of a complex hollow SX blade were simulated.Both the simulated and experimental results show that the stray grain occurred at the platform of the SX blade when a constant withdrawal rate was used in manufacturing process.In order to avoid the formation of the stray crystal,the multi-scale coupled models and the withdrawal rate optimized technique were applied to the same SX turbine blade.The modeling results indicated that the optimized variable withdrawal rate can achieve SX blade castings with no stray grains,which was also proved by the experiments.

Assessment of natural frequency of installed offshore wind turbines using nonlinear finite element model considering soil-monopile interaction

A nonlinear finite element model is developed to examine the lateral behaviors of monopiles, which support offshore wind turbines(OWTs) chosen from five different offshore wind farms in Europe. The simulation is using this model to accurately estimate the natural frequency of these slender structures, as a function of the interaction of the foundations with the subsoil. After a brief introduction to the wind power energy as a reliable alternative in comparison to fossil fuel, the paper focuses on concept of natural frequency as a primary indicator in designing the foundations of OWTs. Then the range of natural frequencies is provided for a safe design purpose. Next, an analytical expression of an OWT natural frequency is presented as a function of soil-monopile interaction through monopile head springs characterized by lateral stiffness KL, rotational stiffness KRand cross-coupling stiffness KLRof which the differences are discussed. The nonlinear pseudo three-dimensional finite element vertical slices model has been used to analyze the lateral behaviors of monopiles supporting the OWTs of different wind farm sites considered. Through the monopiles head movements(displacements and rotations), the values of KL, KRand KLRwere obtained and substituted in the analytical expression of natural frequency for comparison. The comparison results between computed and measured natural frequencies showed an excellent agreement for most cases. This confirms the convenience of the finite element model used for the accurate estimation of the monopile head stiffness.

Transient Model for Shafting Vibration of Hydro Turbine Generating Sets

The shafting vibration is closely related to the rotational angular speed.The angular speed of hydro turbine generating sets(HTGS)is rapidly change in fault transient,it maybe reduce the shafting damage.By means of energy analysis,the differential equation of shafting vibration for the HTGS is derived,in which include the equation of generator rotor and hydro turbine runner,it can be applied to transient analysis.Shafting model is transformed into first order differential equation groups,and is combined with the motion equation of HTGS to build integrated model.Various additional forces of shafting are taken as input inspire in proposed model,the generality of model is good.At last,the shafting vibration in emergency stop transient is simulated.

Double Multiple Streamtube Model and Numerical Analysis of Vertical Axis Wind Turbine

The present paper contributes to the modeling of unsteady flow analysis of vertical axis wind turbine (VAWT). Double multiple streamtube (DSMT) model was applied for the performance prediction of straight bladed fixed pitch VAWT using NACA0018 airfoil at low wind speed. A moving mesh technique was used to investigate two-dimensional unsteady flow around the same VAWT model with NACA0018 airfoil modified to be flexible at 150 from the main blade axis of the turbine at the trailing edge located about 70 % of the blade chord length using fluent solving Reynolds average Navier-strokes equation. The results obtained from DMST model and the simulation results were then compared. The result shows that the CFD simulation with airfoil modified has shown better performance at low tip speed ratios for the modeled turbine.

Local Scour Mechanisms and Prediction Methods Around Offshore Wind Turbine Foundations:Insights and Future Directions

Local scour around offshore wind turbine foundations presents a considerable challenge due to its potential influence on structural stability,driven by hydrodynamic forces.While research has made strides in comprehending scouring mechanisms,notable complexities persist,specifically with newer foundation types.Addressing these limitations is vital for advancing our understanding of scour mechanisms and for improving mitigation strategies in offshore wind energy development.This review synthesizes current findings on local scour across various offshore foundations,encompassing field observations,data-driven approaches,turbulence-sediment interactions,scour evolution processes,influencing factors,and numerical model advancements.The objective is to enrich our understanding of local scour mechanisms.In addition,future research directions are outlined,including the development of robust arti-ficial intelligence models for accurate predictions,the exploration of vortex structure characteristics,and the refinement of numerical models to strengthen prediction capabilities while minimizing computational efforts.

A general model for trailing edge serrations simulation on wind turbine airfoils

Trailing edge serrations(TESs)are capable of noticeably suppressing the turbulent trailing edge noise induced by rotating wind turbine blades and become an integral part of a blade.However,the challenges involved in the dimensional design of serration height 2 h,wavelengthλand flap angleϕare yet to be dealt with in a satisfactory manner.To address the problem,a general model for simulating the effects of serrations on the hydrodynamic and aeroacoustic performance is proposed due to its ease of use and relatively low requirements for user input.The solid serrations are replicated by momentum sources calculated by its aerodynamic forces.Then,a case relevant to wind turbine airfoil is examined,a hybrid improved delay detached eddy simulation(IDDES)method coupled with FW-H integration is deployed to obtain the flow features and far-field sound pressure level.It is found that the modeling method could reproduce the flow field and noise as serrated airfoil.

Platform motion minimization using model predictive control of a floating offshore wind turbine

Wind turbines are installed offshore with the assistance of a floating platform to help meet the world’s increasing energy needs.However,the incident wind and extra incident wave disturbances have an impact on the performance and operation of the floating offshore wind turbine(FOWT)in comparison to bottom-fixed wind turbines.In this paper,model predictive control(MPC)is utilized to overcome the limitation caused by platform motion.Due to the ease of control synthesis,the MPC is developed using a simplified model instead of high fidelity simulation model.The performance of the controller is verified in the presence of realistic wind and wave disturbances.The study demonstrates the effectiveness of MPC in reducing platform motions and rotor/generator speed regulation of FOWTs.

Comparison of Pile-Soil-Structure Interaction Modeling Techniques for A 10-MW Large-Scale Monopile Wind Turbine Model Under Wind and Wave Conditions

Considering the large diameter effect of piles,the influence of different pile-soil analysis methods on the design of monopile foundations for offshore wind turbines has become an urgent problem to be solved.Three different pile-soil models were used to study a large 10 MW monopile wind turbine.By modeling the three models in the SACS software,this paper analyzed the motion response of the overall structure under the conditions of wind and waves.According to the given working conditions,this paper concludes that under the condition of independent wind,the average value of the tower top x-displacement of the rigid connection method is the smalle st,and the standard deviation is the smallest under the condition of independent wave.The results obtained by the p-y curve method are the most conservative.

Modeling and Analyzing Dynamic Response for An Offshore Bottom-Fixed Wind Turbine with Individual Pitch Control

The asymmetric or periodically varying blade loads resulted by wind shear become more significant as the blade length is increased to capture more wind power.Additionally,compared with the onshore wind turbines,their offshore counterparts are subjected to additional wave loadings in addition to wind loadings within their lifetime.Therefore,vibration control and fatigue load mitigation are crucial for safe operation of large-scale offshore wind turbines.In view of this,a multi-body model of an offshore bottom-fixed wind turbine including a detailed drivetrain is established in this paper.Then,an individual pitch controller(IPC)is designed using disturbance accommodating control.State feedback is used to add damping in flexible modes of concern,and a state estimator is designed to predict unmeasured signals.Continued,a coupled aero-hydro-servo-elastic model is constructed.Based on this coupled model,the load reduction effect of IPC and the dynamic responses of the drivetrain are investigated.The results showed that the designed IPC can effectively reduce the structural loads of the wind turbine while stabilizing the turbine power out-put.Moreover,it is found that the drivetrain dynamic responses are improved under IPC.

Research on Fatigue Damage Behavior of Main Beam Sub-Structure of Composite Wind Turbine Blade

Given the difficulty in accurately evaluating the fatigue performance of large composite wind turbine blades(referred to as blades),this paper takes the main beam structure of the blade with a rectangular cross-sectionas the simulation object and establishes a composite laminate rectangular beam structure that simultaneouslyincludes the flange,web,and adhesive layer,referred to as the blade main beam sub-structure specimen,throughthe definition of blade sub-structures.This paper examines the progressive damage evolution law of the compositelaminate rectangular beam utilizing an improved 3D Hashin failure criterion,cohesive zone model,B-K failurecriterion,and computer simulation technology.Under static loading,the layup angle of the anti-shear web hasa close relationship with the static load-carrying capacity of the composite laminate rectangular beam;under fatigueloading,the fatigue damage will first occur in the lower flange adhesive area of the whole composite laminaterectangular beam and ultimately result in the fracture failure of the entire structure.These results provide a theoreticalreference and foundation for evaluating and predicting the fatigue performance of the blade main beamstructure and even the full-size blade.

Validation of the Actuator Line Model for Simulating Flows past Yawed Wind Turbine Rotors

The Actuator Line/Navier-Stokes model is validated against wind tunnel measurements for flows past the yawed MEXICO rotor and past the yawed NREL Phase VI rotor. The MEXICO rotor is operated at a rotational speed of 424 rpm, a pitch angle of ?2.3。, wind speeds of 10, 15, 24 m/s and yaw angles of 15。, 30。 and 45。. The computed loads as well as the velocity field behind the yawed MEXICO rotor are compared to the detailed pressure and PIV measurements which were carried out in the EU funded MEXICO project. For the NREL Phase VI rotor, computations were carried out at a rotational speed of 90.2 rpm, a pitch angle of 3。, a wind speed of 5 m/s and yaw angles of 10。and 30。. The computed loads are compared to the loads measured from pressure measurement.

Modeling Research on a Solar Tower Thermal Collection-natural Gas Turbine Power System

塔式太阳能-燃气轮机发电系统发电成本和研发风险都低于常规太阳能热发电系统，同时能克服太阳能随机性、波动性的缺点，可以推动太阳能热发电的商业化进程。为了研究塔式太阳能与燃气轮机发电系统的能量传递与热功转化规律，以及相关结构参数与运行参数对发电系统性能的影响，该文分别建立该系统中压气机、泡沫陶瓷吸热器、燃烧室、透平4部分的传热和热功转化模型，采用Matlab软件平台编程，进行了系统运行仿真模拟，并分析了压比、孔隙率、厚度、吸热器面积、进气温度等对系统性能的影响。研究结果可为系统的设计与运行提供参考。

Measurement system for wind turbine acoustic noise assessment based on IEC standard and Qin＇s model

A novel measurement system specially used in noise emission assessment and verification of wind turbine generator systems is presented that complies with specifications given in IEC 61400-11 to ensure the process consistency and accuracy. Theory elements of the calculation formula used for the sound power level of wind turbine have been discussed for the first time, and detailed calculation procedure of tonality and audibility integrating narrowband analysis and psychoacoustics is described. With a microphone and two PXI cards inserted into a PC, this system is designed in Qin′s model using VMIDS development system. Benefiting from the virtual instrument architecture, it′s the first time that all assessment process have been integrated into an organic whole, which gives full advantages of its efficiency, price, and facility. Mass experiments show that its assessment results accord with the ones given by MEASNET member.

THE PREDICTIONS OF CONVECTIVE HEAT TRANSFER ON TURBINE BLADE AIRFOIL BY USING LOW－REYNOLDS NUMBER TURBULENCE MODEL

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