Blade Displacement Research Articles

A Keyphasor-Free Traveling Waves Analysis Method Based on Blade Tip Timing and Experimental Validation

Abstract Blade Tip Timing (BTT) emerges as a non-intrusive, promising method for assessing blade vibration. Despite its potential, BTT's inherent measurement limitations often result in the under-sampling of individual blade data. Assuming that the bladed-disk assembly vibrates in nodal diameter modes, traveling wave analysis (TWA) can overcome the limitations of under-sampling and identify the nodal diameter modes. Traditional TWA methods rely on a keyphasor or once-per-revolution (OPR) sensor to provide shaft reference signals. However, such a sensor could be damaged during operation or challenging to install due to limited space. In this paper, a new keyphasor-free TWA (KF-TWA) method is introduced, which is capable of measuring the order and nodal diameter of nodal diameter vibrations with as few as two sensors. Theoretical derivations reveal the method's resilience to the steady-state displacement of blades. The feasibility and effectiveness of the KF-TWA method are validated through numerical experiments and compressor tests. In the numerical experiments, blade detuning and nodal diameter vibration responses are simulated, leading to the development of a criterion for identifying nodal diameter vibrations. A compressor test rig, equipped with a 64-keyphasor disk and a sufficient number of circumferentially distributed sensors, is designed to provide blade vibration benchmark. In the experiments, the KF-TWA method successfully identified nodal diameter vibrations with amplitudes as low as 0.014 mm, consistently yielding identical results across multiple sensor pairs, which demonstrates a higher robustness compared to the traditional TWA method.

Improved non-contact vibration measurement via acceleration-based blade tip timing

The conventional displacement-blade tip timing (D-BTT) measurements often rely on Once-Per-Revolution (OPR) sensors to compute expected or theoretical time of arrival (TOA) based on rotational speed. However, integrating OPR sensors within the confined space of aero-engines presents challenges, and estimating theoretical TOA introduces computational errors, particularly for low-amplitude, high-frequency blade vibrations. This paper presents the Acceleration-based Blade Tip Timing (A-BTT) method as a solution. Building upon A-BTT, the acquisition of blade tip vibration acceleration serves not only to capture rapid changes in vibration but also to offer richer data for precise measurement of high-frequency blade vibrations. With only three blade tip timing sensors recording actual TOA without an OPR sensor, A-BTT eliminates the need for estimating expected TOA, thus mitigating calculation errors. Furthermore, by analyzing the relationship between maximum blade tip vibration acceleration and displacement during synchronous blade vibration, vibration parameters, such as natural frequency, can be directly identified without prior information such as engine orders. Simulation and experimental results validate the efficacy of the A-BTT method, demonstrating its successful application to specific aero-engine compressor rotor blades.

Optimization of classifying accurate and misarticulated speech sounds for use in a gamified real-time ultrasound biofeedback system

Integrating ultrasound biofeedback therapy (UBT) into a real-time, gamified interface to provide articulatory feedback for speech remediation promotes an external focus of attention, thereby reducing the complex cognitive demands required for standard UBT. Previous studies have shown that accuracy of American English rhotic /r/ can be predicted by a single parameter, the difference between tongue dorsum and blade displacements measured by ultrasound imaging during speech production. This parameter has classified speech productions of rhotic syllables as correct versus misarticulated with a classification accuracy up to 85%. However, implementation of this classification approach into real-time gamified UBT, including both measurement timing and establishment of difficulty levels for progressive therapy, would benefit from optimization using a larger dataset. 2,450 productions of 10 distinct rhotic syllables (including prevocalic and postvocalic contexts) from 50 children, with and without misarticulations, were analyzed. For each production, ultrasound image sequences were processed by TonguePART software to acquire tongue displacement trajectories, and accuracy was judged by trained listeners using a visual analog scale. Analyses were conducted to optimize selection of the image frame for classification, determine parameter thresholds appropriate for real-time prediction of /r/ production accuracy, and integrate these thresholds into a difficulty level design for gamified UBT.

Finite element analysis of the effect of residual lateral wall volume on postoperative stability in intertrochanteric fractures

BackgroundLateral wall fractures represent crucial risk factors for postoperative internal fixation failure in intertrochanteric femoral fractures. However, no consensus exists on the type of lateral wall fracture requiring interventional management. This study aimed to investigate the effect of residual lateral wall volume on the postoperative stability of intertrochanteric femur fractures with associated lateral wall fractures, providing valuable reference for the clinical management of the lateral wall.MethodsEleven bone defect models of intertrochanteric femur fractures with varying residual lateral wall volumes were constructed using finite element analysis. These models were fixed with proximal femoral nail antirotation (PFNA). Simulations of von Mises stress and displacement distribution of the PFNA and femur during normal walking were conducted. Statistical analysis was performed to assess the correlation between volume and the maximum von Mises stresses and displacements of the PFNA and femur.ResultsIn all 11 models, the maximum von Mises stress and displacement of the helical blade, intramedullary nail, and femur occurred at the same locations. As residual lateral wall volume increased, the maximum von Mises stress and displacement of the helical blade, intramedullary nail, and maximum femoral displacement gradually decreased. However, the overall trend of the maximum femoral von Mises stress gradually decreased. At 70% retention of the residual lateral wall volume, there was a more pronounced change in the value of the maximum stress change of the helical blade and the intramedullary nail. Statistical analysis, including the Shapiro–Wilk test and Pearson correlation analysis, demonstrated a significant negative correlation between volume and the maximum von Mises stress and displacement of the helical blade, intramedullary nail, and femur. Linear regression analysis further confirmed this significant negative correlation.ConclusionFinite element analysis of the residual lateral wall revealed a significant correlation between volume and the postoperative stability of intertrochanteric femur fractures. A volume of 70% may serve as the threshold for stabilizing the residual lateral wall. Volume emerges as a novel index for evaluating the strength of the residual lateral walls.

Structural Integrity of Turbine Stator Blades Using Different Super Alloys with Internal Cooling at Fluid Temperature Range of 600 K – 700 K

The importance of turbines in power generation cannot be overstated. While the failure in stationary plants can lead to downtime and high repair costs, its failure in mobile plants like the jet engines can be catastrophic with attendant loss of lives. Hence, by all possible means, the prevention of turbine failure is a necessity, and a very good means of doing this is with the use of super-alloys. Super-alloys are tailored to withstand the demands of turbine operations especially stress and elevated temperature and pressure. The blades are thus, manufactured from super-alloys, and of prominence are the Nickel-based super-alloys. The performance of five different super-alloys: (DS) GTD 111, Ti-6Al-4V, Inconel 718, CMSX-4, and Nimonic 80A was simulated using COMSOL MultiPhysics 5.5 at cooling air temperature range of 600 K – 700 K. The mode of cooling employed in the study is only internal cooling. With the developed stress percentage of the yield stress value and the stator blade displacement at the operating conditions as the criteria of performance, super-alloy Ti-6Al-4V faired as the best material for the stator blade.

Smart optimized structural control of onshore wind turbines with MR dampers

This paper presents an effective control approach for structural vibration of onshore wind turbines in the edgewise direction. Huge multi mega-watt wind turbines are currently developed to harvest large amounts of energy from the wind. Such designs require the construction of huge slender blades and towers which consequently lead to undesirable structural deformations that hinder the power production and reduce life span of the wind turbine. Many researchers have worked on structural control of wind turbines. However, these efforts neither have resulted in an effective reliable mitigation for deformation of structural elements, nor they have achieved an economical solution in terms of actuators exploitation. The work presented in this paper, however, introduces a particle swarm optimisation-based semi-active controller which exploits magnetorheological dampers to mitigate edgewise blade displacements. Dampers are modelled using neural networks for they are capable of predicting future forces and eliminating control lag. The developed controller is tested at several configurations of actuators placement on a benchmark 5-MW wind turbine. The proposed approach, indeed, showed a significant reduction of over 80% in the peak responses and about 77% of peak-to-peak response of blades against uncontrolled and passive systems which leads to promoting longevity of wind turbines.

Flutter analysis of compressor blades under travelling wave modes using an efficient fluid–structure interaction method

Flutter is a self-sustained vibration which could create serious damage to compressor blades. Improving the efficiency and accuracy of Fluid-Structure Interaction (FSI) method is crucial to flutter analysis. An efficient FSI method which combines a fast mesh deformation technology and Double-Passage Shape Correction (DPSC) method is proposed to predict blades flutter under traveling wave modes. Firstly, regarding the fluid domain as a pseudo elastic solid, the flow mesh deformation and blade vibration response can be quickly obtained by solving the governing equations of the holistic system composed of blade and pseudo elastic solid. Then, by storing and updating the Fourier coefficients on the circumferential boundary, the phase-lagged boundary condition is introduced into the computational domain. Finally, the aerodynamic stability for the blades of an axial compressor under various Inter-Blade Phase Angle (IBPA) is analyzed. The results show that the proposed method can effectively predict the characteristics of aerodynamic damping, aerodynamic force and blade displacement. And a conceptual model is proposed to describe the motion behavior of the shock wave. Compared with the multi-passage method, the proposed method obtains almost the same unstable IBPA interval and the blade displacement error is less than 3.4%. But the calculation time is significantly shortened especially in small IBPA cases.

Effect of Adjacent Blade Oscillation on the Forces on A Blade of a Compressor Cascade

The current trend of aircraft engines is one towards attaining high isentropic efficiency while minimizing its weight. This leads to a state where the blades are highly loaded and consequently susceptible to vibrations. High cycle fatigue caused as a result of such self-excited flutter or forced vibration due to defects in the air stream are detrimental to the engine. An understanding of the onset of instabilities is essential to predict their occurrences to avoid a catastrophic failure during operation or costly redesign during the development phase. The critical parameters in turbomachine aeroelasticity are the reduced frequency and the interblade phase angle. The damping of the system is known to be a function of the phase difference between the blade forces and the blade motion. In the present study, a linear cascade of five blades is considered to understand the effect of harmonically varying boundary conditions. The second and fourth blades of the cascade are subjected to torsional oscillation by an external mechanism. The third blade, considered as the reference, is stationary and instrumented. The unsteady pressure along the reference blade surface is measured simultaneously with the loads acting on the blade. The unsteady pressures are measured using a multi-sensor pressure scanner by multiplexing and the loads are measured using a five-channel strain gage balance. The blade displacement is determined from the integrated accelerometer signal mounted on an oscillating blade. The experiments are conducted at a low-subsonic speed and multiple oscillation frequencies. The cascade is set at zero incidence and four stagger angles. The effect of inter-blade phase angle is included as the oscillation of the walls adjacent to the reference blade. The phase difference between the harmonic motion of the neighboring walls and the pressure and load signals on the reference blade is related to the damping characteristics of the reference blade. The variation in damping is studied for the range of blade motion phase difference angles and reduced frequencies. The effect of the phase difference between the oscillating blades is seen to strongly affect the damping characteristics of the reference airfoil.

GE 1.5 XLE Wind Turbine Blade Analysis with Computational Methods for Various Composite Materials

The purpose of this paper is to investigate various composite materials that have been applied in wind turbine blades.Α computational study on a GE 1.5 XLE wind turbine blade with different composite materials was performed. The computational evaluations from the fluent analysis have been used in order to calculate the equivalent (Von-Mises) stress, shear stress, and displacements of a wind turbine blade. The proposed study results in useful and interesting conclusions for the stress and displacement fields that arise in blades with different materials and under different loading conditions.

Quantification of swallowing movements by ultrasound imaging in normal and disordered subjects

Ultrasound imaging may be useful for tracking oral-pharyngeal structures of the vocal tract critical for effective swallowing, but use of this technology has been hampered by a lack of validation against standard clinical measures derived from x-ray video fluoroscopy (Modified Barium Swallow Studies or MBSS). Here, we compare quantitative tracking of hyoid bone and tongue motion from ultrasound imaging and simultaneously measured MBSS from a range of participants with disordered and healthy swallowing behavior. The proximal edge of the hyoid bone in MBSS and ultrasound recordings is tracked using CASM (Computational Analysis of Swallowing Mechanics) software, while tongue motion is tracked using TonguePART software, originally developed for analysis of speech. Hyoid trajectories and velocities measured from synchronized ultrasound and MBSS recordings are compared and standard deviations of differences between the two measurements are evaluated. Tongue motion during swallowing is characterized by analysis of root, dorsum, and blade displacement, velocity, and timingas well as tongue base retraction in the pharynx. Preliminary findings show quantitatively similar patterns in ultrasound and MBSS, suggesting that ultrasound has potential utility as an accessible tool for bedside diagnosis and biofeedback. Characteristic patterns separating normal from healthy swallowing, as well as potential therapeutic targets for biofeedback treatment of dysphagia, will be discussed.

Investigation of the Mechanical Behavior of a New Generation Wind Turbine Blade Technology

Wind turbine blades are one of the largest parts of wind power systems. It is a handicap that these large parts of numerous wind turbines will become scrap in the near future. To prevent this handicap, newly produced blades should be recyclable. In this study, a turbine blade, known as the new generation of turbine blade, was manufactured with reinforced carbon beams and recycled, low-density polyethylene materials. The manufacturing addressed in this study reveals two novelties: (1) it produces a heterogeneous turbine blade; and (2) it produces a recyclable blade. In addition, this study also covers mechanical tests using a digital image correlation (DIC) system and modeling investigations of the new generation blade. For the mechanical tests, displacement and strain data of both new generation and conventional commercial blades were measured by the DIC method. Instead of dealing with the modeling difficulty of the new generation blade’s heterogeneity we modeled the blade structural system as a whole using the moment–curvature method as part of the finite element method. Then, the behavior of both the new generation and commercial blades at varying wind speeds and different angles of attack were compared. Consequently, the data reveal that the new generation blades performed sufficiently well compared with commercial blades regarding their stiffness.

Dynamic response of turbine blade considering a droplet-wall interaction in wet steam region

The high-speed impact of liquid droplets on blades in wet steam region seriously affects the safe operation of steam turbine. For blade stability and response characteristics, most studies utilized ideal gas as working medium and few studies focused on the role of droplets in the flow field. In this study, both the distribution information of droplet particles in the flow field and the impact of droplet particles on blades were comprehensively considered. First, the droplet distribution at the last stage inlet was calculated, and then the droplet-wall interaction model was determined and loaded into calculation process. The pressure distribution on blade surface, blade force variation, mechanical properties, and further dynamic response characteristics of blade were analyzed with ideal gas and wet steam models, respectively, by using one-/two-way fluid-structure interaction. Results show that the blade displacement of leading and trailing edges under wet steam model reaches the maximum at near 80% blade height, and there is a low frequency amplitude corresponding to 460 Hz–470 Hz with the peak value in the range of 22Pa–26Pa. The variations of the maximum displacement and maximum equivalent stress of the blade with time are more intense under wet steam model compared with those under ideal gas model.

Vibration Control of Large Wind Turbine Blades with Unidirectional Cable Pendulum Damper

A unidirectional cable pendulum damper is proposed to mitigate vibration responses of large-scale wind turbine blades in the edgewise direction, and the effectiveness of the proposed device for vibration response control is investigated. First, the configuration and working principles of the vibration damper are introduced. Second, the Euler–Lagrange equation of the single blade vibration damping system with the vibration damper is derived based on the Hamilton’s principle. At last, considering the effect of blade rotation, the wind load that applied on the blade was calculated using the rotating sample spectrum. The dynamic responses of blades are also calculated using the MATLAB/Simulink platform. The peak value and standard deviation of blade responses were taken as evaluation indexes to evaluate the vibration control efficiency of the device with varying the parameters such as the mass ball pendulum length, the fixed pulley block installation position, the stiffness and the pre-stress of the flexible cable. The optimal parameters of the vibration damper are investigated and obtained based on the assumption that no pounding happens between the mass ball of the vibration damper and the inner wall of the blade. Results show that the length of the mass ball pendulum and the installation position of the fixed pulley block, the values of which are within a reasonable range, can ensure the optimal performance of the vibration damper. The displacement of the mass sphere can be effectively reduced by increasing the stiffness of the flexible cable, and the pre-stress shows marginal beneficial effect on the damping performance and the displacement control of the mass sphere. Using the optimum parameters, the vibration damper can keep the mass ball within a safe running distance. The reduction of the peak value and the standard deviation of the blade displacement can reach 89.36% and 89.83%, respectively. The proposed device space can effectively reduce the blade tip response of the wind turbine by occupying less space. Moreover, the size of the device installation space can be changed by adjusting the weight ball swing length, which is suitable for the vibration control of the wind turbine blade edgewise direction.

The Effect of Trailing Edge Profile Modifications to Fluid-Structure Interactions of a Vertical Axis Tidal Turbine Blade

Renewable energy has become an essential energy alternative since the continual depletion of non-renewable energy resources and increasing environmental issues. Tidal energy is a promising future renewable resource which can be extracted using a vertical axis tidal turbine. Since it was proposed, a tidal turbine performance requires improvements which can be obtained by a blade’s trailing edge modification. Modifying the blade’s trailing edge profile is confirmed to be one way to improve a turbine’s work. However, the influence of a trailing edge modifications on a vertical axis tidal turbine blade’s interaction with fluid has not been fully understood, thus the fluid induced vibration as the fluid behaviour working on a vertical axis tidal turbine blade has not been completely discovered. In this paper, 2D fluid-structure interactions of modified vertical axis tidal turbine blades are examined and modelled using OpenFOAM. Three different modified blade profiles are proposed: sharp, rounded, and blunt. The modified profiles are employed to an original NACA 0012 blade and their influences on a vertical axis tidal turbine blade interaction are observed. The result discovers the fluid behaviour and fluid-induced vibrations at all positions (represented by 12 positions) over one turbine’s cycle. The results demonstrate the frequency domain blade velocities and time domain blade displacements for all modified blades. The fluid behaviour around the blade is confirmed by pressure distribution plots over the blade’s upper and lower surfaces. The results show that the blunt profile provides less frequent vibrations due to a reducing vorticity in the downstream fluid regime. However, the vibration amplitude that occurs on the blunt blade is higher than those of rounded and sharp profiles. Based on this research, the blunt trailing edge profile appears to be more favourable to be applied and used for vertical axis tidal turbine blades.

Output Power Control and Load Mitigation of a Horizontal Axis Wind Turbine with a Fully Coupled Aeroelastic Model: Novel Sliding Mode Perspective

The power control of horizontal axis wind turbines can affect significantly the vibration loads and fatigue life of the tower and the blades. In this paper, we both consider the power control and vibration load mitigation of the tower fore-aft vibration. For this purpose, at first, we developed a fully coupled model of the NREL 5MW turbine. This model considers the full aeroelastic behaviour of the blades and tower and is validated by experiment results, comparing the time history data with the FAST (Fatigue, Aerodynamics, Structures, and Turbulence) code which is developed by NREL (National Renewable Energy Lab in the United States). In the next, novel sensorless control algorithms are developed based on the supper twisting sliding mode control theory and sliding mode observer for disturbance rejection. In region II (the wind speed is between the cut-in and rated wind velocity), the novel sensorless control algorithm increased the power coefficient in comparison to the conventional indirect speed control (ISC) method (the conventional method in the industry). In region III (the wind speed is between the rated and cut-out speed), an adaptive neural fuzzy inference system (ANFIS) is developed to estimate pitch sensitivity. The rotor speed, pitch angle, and effective wind velocity are inputs, and pitch sensitivity is the output. The designed novel pitch control performance is compared with the gain scheduled PI (GPI) method (the conventional approach in this region). The simulation results demonstrate that the flapwise blade displacement is reduced significantly. Finally, to reduce the fore-aft vibration of the tower, a tuned mass damper (TMD) was designed by using the genetic algorithm and the fully coupled model. In comparison to the literature body, we demonstrate that the fully coupled model provides much better accuracy in comparison to the uncoupled model to estimate the vibration loads.

Deformation Measurements of Helicopter Rotor Blades Using a Photogrammetric System

As an important part of the helicopter, the rotor directly affects flight safety and flight quality. Knowledge of the rotor dynamic behaviors is significant for validating and optimizing the performance of the helicopter rotor system. In this study, a photogrammetric system, based on 3D point tracking and stereo photogrammetry technology, is presented to solve the full-field dynamic motion and deformation parameters of rotating blades by identifying the retro-reflective targets arranged on the rotor. The photogrammetric system is demonstrated in the wind tunnel tests of a 2 m-diameter model rotor, conducted at the 5.5 m × 4 m Aeroacoustic Wind Tunnel of the China Aerodynamics Research and Development Center (CARDC). With the targets attached on the special hat installed directly over the rotor hub, a unified rotor coordinate system, that was stationary with respect to the rotor, could be established at any measuring instant. Therefore, by transforming the 3D coordinates of all measured targets to the rotor coordinate system, the blade displacements and deformations at different test conditions could be calculated consistently. Experimental results from current study were compared to simulation results calculated by the comprehensive analytical model of rotorcraft aerodynamics and dynamics (CAMRAD), which shows quite good agreements.

Numerical investigation into fluid-solid coupling characteristics of blade leading edge vortex cooling under different rotation numbers

In this paper, the fluid-solid coupling analysis is carried out on the vortex cooling. Under rotation conditions, the process of high-temperature gas scouring the blade and the vortex coolant cooling the blade is numerically calculated. At the same time, five rotation numbers of 0, 0.183, 0.339, 0.457 and 0.512 are selected. In addition, this paper proposes a method to improve vortex cooling performance under rotation conditions. The results show that at high rotation numbers, the centrifugal force drives coolant to flow downstream of vortex chamber. The downstream chamber accumulates a large amount of coolant to derive centrifugal buoyancy, which causes the back flow of coolant and makes the upstream heat transfer effect poor. As the rotation number increased from 0 to 0.512, the average Nusselt number on the target wall decreased by 35.49%. For the blade solid region, the effect of thermal load plays a major role on blade stress and displacement characteristics. Insufficient cooling performance in the chamber upstream leads to a higher temperature of the blade root, and a higher thermal stress concentration is generated because the blade root is constrained. In addition, by improving the intake chamber into a convergent structure, the coolant flow into the vortex chamber can be promoted, and the effect of back flow can be reduced, thereby obtaining a better vortex cooling performance. The target wall average Nusselt number of the convergent intake chamber structure is 977.17, which is 23.63% higher than that of the original rectangular intake chamber structure.

Simultaneous Pressure and Displacement Measurement on Helicopter Rotor Blades Using a Binocular Stereophotogrammetry PSP System

A simultaneous surface pressure and displacement measurement method that integrates pressure-sensitive paint (PSP) and binocular stereophotogrammetry is proposed. The assays were completed on the Φ4 m rotor test stand at China Aerodynamic Research and Development Center (CARDC). A single-shot lifetime approach was utilized to acquire the instantaneous pressure field on a rotor blade coated with PSP. At the same time, the PSP feature points were used to obtain the 3D coordinates of stereo cameras, which yielded the blade displacement field. The experimental results showed that the displacement measuring accuracy was better than 0.2 mm, and the pressure measurement accuracy was not affected, with Standard Deviation (STD) values below 700 Pa. The advantages of the proposed system are its simple structure, low cost, high accuracy and high test efficiency, which will offer a practical solution for the exploration of fluid–structure interplay. Hence, such a system is a prospective for the wind tunnel tests of helicopter rotor blades.

Structural Design of Wind Turbine Blades with an Additively Manufactured Graded Lattice Core using Topology Optimisation

Conventional wind turbine blade manufacture relies on large, expensive moulds. Instead, using additive manufacturing to print the internal structure of blades, upon which it would be possible to lay composite plies, could significantly reduce manufacturing costs and, as one could “3D print” topologically optimal designs, improve structural efficiency. In general, topology optimisation integrates well with additive manufacturing. There are, however, two main challenges associated with the adoption of topology optimisation in wind blade design, i.e. accounting for: (i) the aeroelastic response of blades; and (ii) the variety of different materials that would be employed, in the composite laminates as well as the printed structure. To address these challenges, the present paper proposes a new multi-step design and optimisation framework relying on the combination of three software. First, a conventional aero-servo-elastic model is used to evaluate blade loads and displacements. Next, a topology optimisation software is used to optimise the blade laminates and core structure. Third, a lattice generator is used to convert the topological optimised “grey” design into an equivalent cellular design that can be printed using additive manufacturing. The full methodology of this design framework and an initial proof-of-concept topology optimisation solution are presented in this paper.

Investigation on the Effect of the Baseline Control System on Dynamic and Fatigue Characteristics of Modern Wind Turbines

In order to investigate the effect of a baseline control system (BCS) on dynamic and fatigue characteristics of modern wind turbines, the simulation results of a 5-MW wind turbine subjected to wind loading without and with considering BCS (No. 1 and No. 2, respectively) were compared. The displacement and moment of tower and blades were compared, and the rainflow counting algorithm was used to analyze the fatigue load expressed in damage equivalent load (DEL). The results indicate that the mean and maximum values of structural dynamic responses in No. 2 have a great reduction with wind speed exceeding the rated speed comparing to No. 1; the 3P (3-times the frequency of rotor speed) of the wind turbine rotor speed will be close to the tower fore-aft (FA) natural frequency with the wind velocity around the cut-in speed in No. 2, which caused larger dynamic responses, number of load cycles, and DELs for the tower compared with No. 1; when wind velocity exceeds the rated wind speed, the BCS caused higher fluctuation of loads, increasing the related DELs. It is concluded that when analyzing the dynamic responses and designing wind turbine tower and blades, taking the BCS into account during analysis is significant.