Large-scale Wind Turbine Blade Research Articles

Uncertainty quantification of modal parameter estimates obtained from subspace identification: An experimental validation on a laboratory test of a large-scale wind turbine blade

The uncertainty afflicting modal parameter estimates stems from e.g., the finite data length, unknown, or partly measured inputs and the choice of the identification algorithm. Quantification of the related errors with the statistical Delta method is a recent tool, useful in many modern modal analysis applications e.g., damage diagnosis, reliability analysis, model calibration. In this paper, the Delta method-based uncertainty quantification methodology is validated for obtaining the uncertainty of the modal parameter and the modal indicator estimates in the context of several well-known subspace identification algorithms. The focus of this study is to validate the quality of each Delta method-based approximation with respect to the experimental Monte Carlo distributions of parameter estimates using a statistical distance measure. On top of that, the accuracy in obtaining the related confidence intervals is empirically assessed. The case study is based on data obtained from an extensive experimental campaign of a large scale wind turbine blade tested in a laboratory environment. The results confirm that the Delta method is, on average, adequate to characterize the distribution of the considered estimates solely based on the quantities obtained from one data set, validating the use of this statistical framework for uncertainty quantification in practice.

Depth detection of spar cap defects in large-scale wind turbine blades based on a 3D heat conduction model using step heating infrared thermography

The defects dispersed in a spar cap often lead to the failure of large-scale wind turbine blades. To predict the residual service life of the blade and make the repair, it is necessary to detect the depth of spar cap defects. Step-heating thermography (SHT) is a common infrared technique in this domain. However, the existing methods of SHT on defect depth detection are generally based on 1D models, which are unable to accurately detect the depth of spar cap defects due to ignoring material anisotropy and in-plane heat flow. To improve the depth detection accuracy of spar cap defects, a 3D model based on the theory of heat transfer is established by using the equivalent source method (ESM), and a defect depth criterion is proposed based on the analytical solution of the heat conduction equation. The modeling process is as follows. The heat conduction model of SHT was established by ESM. Then, coordinate transformation, variables separation, and Laplace transformation were utilized to solve the 3D heat conduction equation. A defect depth criterion was proposed based on emerging contrast Cr. A glass fiber reinforced plastic composite plate containing 12 square flat-bottom holes with different sizes and depths was manufactured to represent a spar cap with large thermal resistance defects, such as delamination and cracks. The experimental results demonstrate the validity of the 3D model. Then, the model was applied to an on-site SHT test of a 1.5 MW wind turbine blade. The test results prove that the depth detection accuracy of spar cap defects can be significantly improved by using the 3D model. In addition, by using an improved principle component analysis (PCA) method containing a contrast enhancement factor, artifacts can be reduced and the recognition time of defects can be shortened. The 3D model provides a tool for detecting the depth of deep-lying defects in a thick composite structure, and the SHT technology is optimized by improved PCA.

A Review on Modeling of Bionic Flow Control Methods for Large-Scale Wind Turbine Blades

Due to complicated working conditions, the normal operating large-scale wind turbine blades are often suffering from some inevitable problems, i.e., friction adhesion, flow separation and acoustic noise, which may significantly affect the aerodynamic performance of the blades and thus the wind turbine system. Therefore, effective measurements must be taken to solve these issues. Correspondingly, several novel bionic flow control methods by mimicking shark skin, whale fin and owl wing, i.e., riblet, leading-edge protuberance and trailing-edge serration, have been recently studied, and good progresses have been made in terms of effectiveness, analysis and mechanism. However, these potential techniques are unable to be widely applied within wind energy community due to the lack of reasonable modeling methods, clearly reflecting the effect of bionic structures on the flow field around, which results in incapability to carry out further optimal design of bionic blade. To this end, this review paper first concentrated on a summary of the control mechanisms of three bionic techniques. Based on this, some feasible ideas of model buildup were proposed. Finally, the flow analyses around the typical blade airfoils were chosen as case studies to verify the feasibility and accuracy of these simulation methods.

Multimobile Robot Cluster System for Robot Machining of Large-Scale Workpieces

In this article, a novel work pattern for large-scale workpiece machining, that is, multimobile robot cluster machining, is proposed. The key idea is to use distributed coordination control to link multiple robots as a cluster system. The coordination control law acts as a virtual constraint, and multiple robots move synchronously under a common leader. Two topological structures are introduced to describe the communication networks of the cluster system, namely, the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> -chain and close-loop topologies. The convergence rate and resistance index of different topological structures are analyzed, and the applications of different topologies in varied machining scenarios are discussed. Two experiments are conducted on the multimobile robot system. The cluster system with a close-loop topology is used for the collaborative handling task, where the relative distance of two mobile robots can be limited within 6 cm. The cluster system with an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> -chain topology is used for large-scale wind turbine blade machining. The cluster machining system requires little manual intervention and guarantees the synchronization performance of the machining system.

Design and static analysis of polymer composite wind turbine blade

Wind power is one of the world's fastest-growing energy sector and relatively mature technologies. Wind power is changing the wind energy into electricity, in which the blade plays a very important role. At present large-scale wind turbine blades are almost made of composite materials. Composite materials are a kind of new materials. Because of its high strength, stiffness, weight-lightness, resistance to fatigue, vibration, high temperature, easy-to-design, etc, the composite laminates plates have been widely used in the wind energy field. Therefore, blade vibration analysis, structural design technology and composite materials technology are closely linked. This is a paper on static analysis of polymer composite material for wind turbine blade. By an analysis using CATIA a better wind turbine profile is to be obtained with increased efficiency of energy generation and reduced damage due to vibration.

Research on advanced design technologies of large-scale wind turbine blades for use in complex terrain

In recent years, wind power has rapidly developed in China’s inland complex terrain. However, the level of core design technologies for related wind turbines is low. Therefore, on the basis of the achievements and experiences of the Institute of Engineering Thermophysics, the Chinese Academy of Sciences for the past 15 years, this study focuses on wind turbine blades, which are essential for the efficiency, reliability, and power cost of the wind power unit. In this study, the new generation of key technologies are researched (e.g., aerodynamic efficiency increase, passive coupling load reduction, and lightweight optimization under complex terrain conditions) to build an integrated optimization design technology system. This study fills the gaps in the domestic industry and strives to make the design level of large-scale Chinese wind turbine blades achieve the international advanced level. In addition, this study is essential for solving national energy security and environmental pollution problems.

Nonlinear Dynamics of a Rotary Energy Harvester With a Double Frequency Up-Conversion Mechanism

Abstract This paper develops a mathematical model of a two degree-of-freedom piezoelectric energy harvester (PEH) in which vibration is driven by disk swing motion. The proposed device converts slow mechanical rotation into piezoelectric vibration using gravity force and magnetic repelling force. The harvester consists of a disk and a piezoelectric cantilevered beam. The disk with an unbalanced mass swings on a rotating object (e.g., wind turbine blade) and two magnets attached to both the beam and the disk can transfer the kinetic energy of the disk to the beam without physical contact. The energy method is used to derive three coupled equations to model the motion of the disk, vibration of the beam, and the piezoelectric voltage output. The effect of harvester orientation on power generation performance is studied as the rotational speed changes, and the simulation results are experimentally verified. Possible application of this energy harvester to a power-sustainable sensor node for large-scale wind turbine blades monitoring is discussed.

Kinematic modeling and control of mobile robot for large-scale workpiece machining

Safety and reliability are significant in the sense of robotic machining for large-scale workpieces. In this article, a control scheme is proposed to ensure the safe motion of the mobile robot. Screw theory is used to analyze the motion of the mobile robot. The mobile platform with Mecanum wheels can be considered as a mechanism with four driven screws in series. An auxiliary reference position of the mobile platform is calculated based on the kinematic model, and the motion of the mobile platform and robot arm can be decoupled to handle its redundant degrees of freedom. Constant speed control is investigated to reduce the interaction force between the robot and platform. Experiments are conducted on the mobile robotic machining task for a large-scale wind turbine blade. The mobile robot moves steadily and smoothly owing to the constant speed control with an auxiliary target.

Comparative study of short-term extreme responses and fatigue damages of a floating wind turbine using two different blade models

In this work, two different blade structural models are used to estimate the blade deformations and the global structural responses of a 10MW floating offshore wind turbine (FOWT). One model is based on the Euler-Bernoulli beam theory and it is solved by the linear normal mode superposition method. The other model is based on the geometry exact beam theory (GEBT) which can consider the full geometric nonlinearity and large deformation. The control equations of GEBT are discretized by Legendre spectral finite elements. The aero-hydro-servo-elastic fully coupled numerical simulations are conducted in the open-source analysis tool OpenFAST to explore the feasibility of the two different structural models for modeling large scale wind turbine blades. Both the steady-state and dynamic results show that power generation and thrust on rotor are similar for the different blade models. There is a small difference in the results of the blade pitch angle and flapwise and edgewise blade root bending moment at high wind speeds due to the lack of torsion degree of freedom in the mode-based method. The difference between the two models is mainly reflected in the prediction of blade tip deformations. The one-hour short-term extreme blade root bending moments and the damage equivalent fatigue loads at blade root are both compared based on the two models. For edgewise bending moment, the extreme value of GEBT model is found at cut-out wind speed, whereas the linear beam model predicts the extreme value around rated wind speed. For the flapwise bending moment, the extreme value is captured around the rated wind speed for both of the two models, but GEBT model presents a larger value. As for fatigue loads, the short-term 1 Hz damage equivalent loads calculated based on the linear beam model are smaller than GEBT model at almost all load cases for both edgewise and flapwise root bending moment, which implies that the linear beam model may underestimate the life time fatigue damage at blade root.

An Acoustic Source Model for Applications in Low Mach Number Turbulent Flows, Such as a Large-Scale Wind Turbine Blade

Aerodynamic noise from wind turbine blades is one of the major hindrances for the widespread use of large-scale wind turbines generating green energy. In order to more accurately guide wind turbine blade manufacturers to optimize the blade geometry for aerodynamic noise reduction, an acoustic model that not only understands the relation between the behavior of the sound source and the sound generation, but also accounts for the compressibility effect, was derived by rearranging the continuity and Navier–Stokes equations as a wave equation with a lump of source terms, including the material derivative and square of the velocity divergence. Our acoustic model was applied to low Mach number, weakly compressible turbulent flows around NACA0012 airfoil. For the computation of flow fields, a large-eddy simulation (LES) with the dynamic Smagorinsky subgrid scale (SGS) model and the cubic interpolated pseudo particle (CIP)-combined unified numerical procedure method were conducted. The reproduced turbulent flow around NACA0012 airfoil was in good agreement with the experimental data. For the estimation of acoustic fields, our acoustic model and classical sound source models, such as Lighthill and Powell, were performed using our LES database. The investigation suggested that the derived material derivative of the velocity divergence plays a dominant role as sound source. The distribution of the sources in our acoustic model was consistent with that of the classical sound source models. The sound pressure level (SPL) predicted based on the above-mentioned LES and our newly derived acoustic model was in reasonable agreement with the experimental data. The influence of the increase of Mach number on the acoustic field was investigated. Our acoustic source model was verified to be capable of treating the influence of Mach numbers on the acoustic field.

Fabrication of continuous carbon fiber mesh for lightning protection of large-scale wind-turbine blade by electron beam cured printing

Wind-turbine blades are more vulnerable to lightning strikes as they lack a protection system for large-scale glass fiber reinforced polymer (GFRP) composite structures. A low-energy electron beam (EB) cured printing process for fabricating a continuous carbon fiber-reinforced thermoset resin as a non-metallic lightning protection mesh on a GFRP composite surface was carried out in this study. During the proposed process, a continuous carbon fiber mesh was printed through a Fused Filament Fabrication that integrates the rapid curing of an epoxy resin with low-energy EB irradiation. The printing process was analyzed and optimized by examining the correlation between the EB exposure dose and the printing height. Results from artificial lightning strikes showed that the printed carbon fiber mesh prevented damage, and the structure remained relatively intact with residual strength reaching 90.1 % at 100 kA maximum peak current. The protection mechanism was investigated using a high-speed camera, which revealed that the carbon fiber mesh spreads the striking current outside the laminate instead of penetrating inside.

Effect of morphed trailing-edge flap on aerodynamic load control for a wind turbine blade section

Application of Morphed Trailing-Edge Flap (MTEF) can significantly reduce the excessive loads that cause damage of blades and surrounding components in wind turbine. The present paper investigates the effect of MTEF on the aerodynamic load control of a large-scale wind turbine blade. Three design parameters that control MTEF kinematics, such as deflection length, amplitude and phase shift, are analyzed in detail by a validated Computational Fluid Dynamic (CFD) model, in which a specially-designed mesh update method is adopted. Results show that, compared with fully rigid airfoil, the morphed airfoil exhibits an excellent load control capability owing to the appropriate change of aft effective camber as deflection motion of MTEF, which significantly alters the pressure distribution and air flow. Furthermore, the performances are linearly improved with increasing MTEF deflection length, wherein every 0.1c increase in length results in the percentage variation of CL, min (+45%), CL, max (−3%), CD, max (−5%) and CL/CD (+30%). Whereas the improved performance due to the increase of deflection amplitude shows a reducing trend, and an oversize deflection amplitude (greater than βamp = 10°) leads to the depravation of aerodynamic efficiency. Moreover, the analysis of deflection phase shift suggests that a slight phase–lag is beneficial to stabilize the aerodynamic load exerted on wind turbine blade. Especially, the lift coefficient fluctuation (CL, max−CL, min) for the phase-lag case of φ = 1/8π has reduced by about 50% while the cycle-averaged lift coefficient has increased by 16.67% as compared to the fully rigid airfoil. The results of this paper will help guide future development and application of MTEF in practice.

Numerical Simulation and Modal Analysis of External Flow Field of Large Wind Turbine

Aiming at the problems of complex and slow optimization process of large-scale wind turbine blade design and the influence of wind turbine flutter, etc. The numerical simulation analysis and modal analysis of the external flow field of the wind turbine under the rated wind speed are carried out by the hybrid method. A fluid simulation model based on CFD was established. The method of rotating reference frame and SST k-omega turbulence model are used to simulate the external flow of fan wind turbine in FLUENT. The first 6 natural modes of the wind wheel are calculated in Hypermesh/Optistruct. The results show that the hybrid simulation method can quickly obtain the impeller flow field information, and the flow of the tip portion is extremely unstable. In each natural mode, the blade deformation position is basically from the maximum chord length to the tip position. The closer to the tip, the more obvious the blade vibration deformation is. At the same time, the first-order natural frequency of the wind wheel is 0.919Hz, which is greater than 0.382Hz when the rated speed is 12m/s, thus effectively avoiding resonance phenomenon.

Design of the parallel mechanism for a hybrid mobile robot in wind turbine blades polishing

Efficient and precise processing of large-scale parts is an uprising problem in industry. In this paper, a method to polish large-scale wind turbine blades using hybrid mobile robots is proposed. The robot combines an automated guided vehicle (AGV), a 2-DoF 3-parallelogram hybrid module and a 1T2R parallel module. This paper focuses on the design of the 1T2R parallel mechanism. In order to realize flexible A/B axis rotational capacity and efficient transmission of driving units, two 1T2R parallel mechanisms actuated by ball screw drives are derived under the guidance of a type synthesis approach based on Grassmann line geometry and a line-graph method. Under the description of Tilt and Torsion (T&T) angles, kinematics (especially the parasitic motion) of the proposed mechanisms is investigated. To carry out the dimension synthesis, performance evaluation indices including good transmission and constraint workspace, maximum orientation capacity, global transmission and constraint index and global average parasitic motion are defined. The performance atlases are plotted in the parameter design space. By comparing the parasitic motion and the motion/force transmission and constraint performance of the two mechanisms, 3-RCU mechanism is identified to develop the parallel module and its kinematic optimization is carried out. The CAD model with a set of optimal parameters is presented. The work in this paper lays the foundation for the development of the hybrid mobile robot, and the configuration design and parameter optimization in this paper can be further applied to the design of other parallel mechanisms.

Using a two-stage approach to improving accuracy of resonance fatigue tests for large-scale wind turbine blades

The increasing size and complexity of wind turbine blade designs challenge the ability of traditional fatigue testing methods to accurately and efficiently reproduce load distributions representative of real world conditions. A new two-stage approach is proposed. In the first stage, the blade is subjected to a dual-axis resonance test, where additional masses are mounted to the blade to control the bending moment distribution. In the second stage, part of the blade is removed, allowing it to be exercised at a higher frequency and for more damage to be applied to the root and transitional sections. The results of the proposed method were compared with those of traditional testing methods for 38 m and 60 m blades. The results indicate that the new methods have the potential to significantly improve accuracy, but the testing duration will increase.

Vibration analysis for large-scale wind turbine blade bearing fault detection with an empirical wavelet thresholding method

Blade bearings, also termed pitch bearings, are joint components of wind turbines, which can slowly pitch blades at desired angles to optimize electrical energy output. The failure of blade bearings can heavily reduce energy production, so blade bearing fault diagnosis is vitally important to prevent costly repair and unexpected failure. However, the main difficulties in diagnosing low-speed blade bearings are that the weak fault vibration signals are masked by many noise disturbances and the effective vibration data is very limited. To address these problems, this paper firstly deals with a naturally damaged large-scale and low-speed blade bearing which was in operation on a wind farm for over 15 years. Two case studies are conducted to collect the vibration data under the manual rotation condition and the motor driving condition. Then, a method called the empirical wavelet thresholding is applied to remove heavy noise and extract weak fault signals. The diagnostic results show that the proposed method can be an effective tool to diagnose naturally damaged large-scale wind turbine blade bearings.

Preliminary validation of ATOM: an aero-servo-elastic design tool for next generation wind turbines

Upscaling wind turbines has resulted in levelised cost of energy (LCoE) reductions. However, larger turbine diameters pose significant design challenges, often with conflicting requirements. For example, non-linear dynamics of aeroelastic tailored blades must be accurately predicted whilst, for the sake of efficient gradient-based design, it is also desirable to simplify the numerical definition of such blades—keeping design variables (DVs) to a minimum. This work presents and validates two features of the ATOM code (Aeroelastic Turbine Optimisation Methods), developed at the University of Bristol, that enable accurate and efficient modelling of large-scale wind turbine blades. Both an efficient parameterisation method and high-order beam elements illustrate the capacity for increasing the speed of gradient evaluations whilst accurately predicting blade dynamics—either by reducing DVs or simulation time. As a preliminary validation, aero-servo-elastic simulations from ATOM and an industry-standard software—DNV GL Bladed—are compared against field measurements gathered from an existing 7 MW turbine.

Predicting the Extreme Loads in Power Production of Large Wind Turbines Using an Improved PSO Algorithm

Predicting the extreme loads in power production for the preliminary-design of large-scale wind turbine blade is both important and time consuming. In this paper, a simplified method, called Particle Swarm Optimization-Extreme Load Prediction Model (PSO-ELPM), is developed to quickly assess the extreme loads. This method considers the extreme loads solution as an optimal problem. The rotor speed, wind speed, pitch angle, yaw angle, and azimuth angle are selected as design variables. The constraint conditions are obtained by considering the influence of the aeroelastic property and control system of the wind turbine. An improved PSO algorithm is applied. A 1.5 MW and a 2.0 MW wind turbine are chosen to validate the method. The results show that the extreme root load errors between PSO-ELPM and FOCUS are less than 10%, while PSO-ELPM needs much less computational cost than FOCUS. The distribution of flapwise bending moments are close to the results of FOCUS. By analyzing the loads, we find that the extreme flapwise bending moment of the blade root in chord coordinate (CMF_ROOT) is largely reduced because of the control system, with the extreme edgewise bending moment of the blade root in chord coordinate (CME_ROOT) almost unchanged. Furthermore, higher rotor speed and smaller pitch angle will generate larger extreme bending moments at the blade root.

Unsteady aerodynamic modeling and control of the wind turbine with trailing edge flap

Intense load fluctuations on large-scale wind turbine blades can cause significant damage over time. The needs for predicting the dynamic behavior of blades and extending the lifespan of wind turbines have become more important. Therefore, in this paper, a wind turbine model with trailing edge flap (TEF) based on the National Renewable Energy Laboratory 5-MW reference wind turbine is developed, and a TEF controller aimed at load alleviation and power-fluctuation suppression is proposed. The wind turbine model, established in MATLAB/Simulink, consists of a TEF actuator model, an unsteady aerodynamic model, a generator model, and a drivetrain model. The TEF controller, which adopts a feedback linearization-based control method, is employed to reduce the variability of the flapwise root moment of blade 1 (FRM1) and the generator output power. Then, a comparison of the present model and a simulation of wind turbine performance with TEF control are demonstrated. Consequently, the present model shows reliability both in unsteady aerodynamic performance and wind turbine performance. In normal turbulent model wind conditions, the standard deviations of FRM1 and the generator output power are reported with reductions of 33.0%–42.5% and 9.1%–16.1%, respectively; the power spectral density of FRM1 is also reported with reductions of 39.9%–47.7%.

Effect of main spar ply Parameters on performance of composite wind turbine blades

The change of layer parameters of composite material will affect the performance of wind turbine blades. In this paper, in order to study the regularity of the variation of the ply parameters of the main spar on the structural performance of the large-scale wind turbine blade, a 5 MW wind turbine blade was taken as the research object. By changing the angle of the main spar ply and the ply ratio at different ply angles, the different wind turbine blades were established which had different ply plans. The numerical simulation was conducted to get the pressure on the blade surface through FLUENT software at rated wind speed. After this, the static analysis and modal analysis were been performed to the blades which applied load. The results show that the maximum stress the blade bears is the smallest when the main spar layup angle of fibre was 0°, illustrating that 0° layup angle could withstand bending load better. So the angle 0° should be the main layup angle of the main spar. And the modal frequency and structural performance of blades is best when the angle 0° accounts for layup angle 49.333%.