Turbine Blade Vibration Research Articles

Cable connected active tuned mass dampers for control of in-plane vibrations of wind turbine blades

In-plane vibrations of wind turbine blades are of concern in modern multi-megawatt wind turbines. Today׳s turbines with capacities of up to 7.5MW have very large, flexible blades. As blades have grown longer the increasing flexibility has led to vibration problems. Vibration of blades can reduce the power produced by the turbine and decrease the fatigue life of the turbine. In this paper a new active control strategy is designed and implemented to control the in-plane vibration of large wind turbine blades which in general is not aerodynamically damped. A cable connected active tuned mass damper (CCATMD) system is proposed for the mitigation of in-plane blade vibration. An Euler–Lagrangian wind turbine model based on energy formulation has been developed for this purpose which considers the structural dynamics of the system and the interaction between in-plane and out-of-plane vibrations and also the interaction between the blades and the tower including the CCATMDs. The CCATMDs are located inside the blades and are controlled by an LQR controller. The turbine is subject to turbulent aerodynamic loading simulated using a modification to the classic Blade Element Momentum (BEM) theory with turbulence generated from rotationally sampled spectra. The turbine is also subject to gravity loading. The effect of centrifugal stiffening of the rotating blades has also been considered. Results show that the use of the proposed new active control scheme significantly reduces the in-plane vibration of large, flexible wind turbine blades.

Application of Active Damping Control Using Piezoelectric Material in Modeling of a Wind Turbine Blade

On the basic of passive damping control, we do modeling and simulating in another approach to improve the vibration alleviating effect, the piezoelectric layer damping (PLD), which is called active control. The piezoelectric damping patches are under control of PID controller (matlab simulating) in voltage defference. Here, we use the software PRO/ENGINEER to design and model a wind turbine blade before using COMSOL to simulate the dynamic motion of the wind turbine blade and its interaction with aerodynamic force of wind in finite element method. Some different models are built-- the original turbine blade and the turbine blade with damping patches on different location and quantity. Then, according to the simulation results, we compare the effects of passive and active damping control, also the effect of patches locations and quantities under different wind speed. This research can provide a direction for future study about ways to decrease vibration of turbine blades.

Wind turbine blade vibration at standstill conditions—the effect of imposing lag on the aerodynamic response of an elastically mounted airfoil

AbstractThe present study investigated physical phenomena related to stall‐induced vibrations potentially existing on wind turbine blades at standstill conditions. The study considered two‐dimensional airfoil sections while it omitted three‐dimensional effects. In the study, a new engineering‐type computational model for the aeroelastic response of an elastically mounted airfoil was used to investigate the influence of temporal lag in the aerodynamic response on the aeroelastic stability in deep stall. The study indicated that even a relatively low lag significantly increases the damping of the model. A comparison between the results from a model with lag imposed on all force components with the results from a model with lag imposed exclusively on the lift showed only marginal difference between the damping in the two cases. A parameter study involving positions of the elastic hinge point and the center of gravity indicated that the stability is relatively independent of these parameters. Another parameter study involving spring constants showed that the stability of each mode is dependent only on the spring constant acting in the direction of the leading motion of the mode. An investigation of the influence of the added mass terms showed that only the pitch‐rate and flapwise‐acceleration terms have any influence on the stability. An investigation of three different profiles showed that the stability is heavily dependent on the aerodynamic characteristics of the profiles—mainly on the lift. It was also shown that only the edgewise mode is unstable in deep stall. Moreover, independent of the amount of temporal lag in the aerodynamic response of the model, the inflow‐angle region in the vicinity of 180° remains unstable in the edgewise mode. Therefore, this inflow‐angle region may create stability problems in real life. The other type of vibrations potentially present at standstill conditions is vortex‐induced, being outside the scope of the present study. Copyright © 2014 John Wiley & Sons, Ltd.

Turbine Blade Vibration Measurement Methods for Turbocharges

This paper presents and compares the most important and often used methods to measure turbine blade vibrations: use of strain gauges and telemetry system which is an intrusive method or, on the other site. The Blade Tip Timing (BTT) method known as Non-Intrusive Stress Measurement (System) NSMS. Both methods have advantages and disadvantages which are described below. This paper focused on synchronous vibrations, which are more important in terms of turbine blades fatigue prediction and design optimization.

A trial wind turbine blade vibration measurement using 3dimensional motion analysis

A trial wind turbine blade vibration measurement using 3dimensional motion analysis

Wind turbine blade flapwise vibration control through input shaping

Wind turbine blade vibration is a serious problem not only because it will reduce the life of blade but also can it pass some unexpected frequencies to the tower, which will cause tower to vibrate. The aim of this paper is to develop a model for wind turbine flapwise vibration and reduce the pitch angle caused vibrations in flapwise direction. Lagrange's method is used to model the blade and input shaping method is used to reduce the residual vibrations caused by the change of pitch angle input. Effectiveness of designed input shaper is verified through comparison.

Dynamic characteristics of lag vibration of a wind turbine blade

Lagwise dynamic characteristics of a wind turbine blade subjected to unsteady aerodynamic loads are studied in this paper. The partial differential equations governing the coupled longitudinal-transverse vibration of the blade with large bending deflection are obtained by applying Hamilton's principle. The modal problem of the coupled vibration is handled by using the method of numerical integration of Green's function. Influences of the rotating speed, the pitch angle, the setting angle, and the aerodynamic loads on natural frequencies are discussed. Results show that: (1) Lagwise natural frequencies ascend with the increase of rotating speed; effects of the rotating speed on low-frequencies are dramatic while these effects on high-frequencies become less. (2) Influences of the pitch angle on natural frequencies are little; in the range of the normal rotating speed, the first frequency ascends with the increase of the absolute value of the pitch angle, while it is contrary to the second and third frequencies. (3) Effects of the setting angle on natural frequencies depend on the rotating speed; influences are not significant at low speed, while they are dramatic on the first frequency at high speed. (4) Effects of the aerodynamic loads on natural frequencies are very little; frequencies derived from the model considering aerodynamic loads are smaller than those from the model neglecting aerodynamic loads; relative errors of the results corresponding to two models ascend with the increase of the absolute value of the setting angle.

A mathematical model for horizontal axis wind turbine blades

A mathematical model describing the nonlinear vibration of horizontal axis wind turbine (HAWT) blades is proposed in this paper. The system consists of a rotating blade and four components of deformation including longitudinal vibration (named axial extension), out-of-plane bend (named flap), in-plane/edgewise bend (named lead/lag) and torsion (named feather). It is assumed that the center of mass, shear center and aerodynamic center of a cross section all lie on the chord line, and do not coincide with each other. The structural damping of the blade, which is brought about by materials and fillers is taken into account based on the Kelvin–Voigt theory of composite materials approximately. The equivalent viscosity factor can be determined from empirical data, theoretical computation and experimental test. Gravitational loading and aerodynamic loading are considered as distributed forces and moments acting on blade sections. A set of partial differential equations governing the coupled, nonlinear vibration is established by applying the generalized Hamiltonian principle, and the current model is verified by previous models. The solution of equations is discussed, and examples concerning the static deformation, aeroelastic stability and dynamics of the blade are given.

Guided Tuning of Turbine Blades: A Practical Method to Avoid Operating at Resonance

In gas turbine applications, forced vibrations of turbine blades under resonant—or nearly resonant—conditions are undesirable. Usually in airfoil design procedures, at least the first three blade modes are required to be free of excitation in the operating speed range. However, not uncommonly, a blade may experience resonance at other higher natural frequencies. In an attempt to avoid resonant oscillations, the structural frequencies are tuned away from the excitation frequencies by changing the geometry of the blade. The typical iterative design process—of adding and removing material through restacking the airfoil sections—is laborious and in no way assures an optimal design. In response to the need for an effective and fast methodology, the guided tuning of turbine blades method (GTTB) is developed and presented in this paper. A practical tuning technique, the GTTB method is based on structural perturbations to the mass and stiffness at critical locations, as determined by the methodology described herein. This shifts the excited natural frequency out of the operating speed range, while leaving the other structural frequencies largely undisturbed. The methodology is demonstrated here in the redesign of an actual turbine blade. The numerical results are experimentally validated using a laser vibrometer. The results indicate that the proposed method is not computationally intensive and renders effective results that jibe with experiments.

Active tuned mass dampers for control of in-plane vibrations of wind turbine blades

This paper investigates the use of active tuned mass dampers (ATMDs) for the mitigation of in-plane vibrations in rotating wind turbine blades. The rotating wind turbine blades with tower interaction represent time-varying dynamical systems with periodically varying mass, stiffness, and damping matrices. The aim of this paper is to determine whether ATMDs could be used to reduce in-plane blade vibrations in wind turbines with better performance than compared with their passive counterparts. A Euler–Lagrangian wind turbine mathematical model based on energy formulation was developed for this purpose, which considers the structural dynamics of the system and the interaction between in-plane and out-of-plane vibrations. Also, the interaction between the blades and the tower including the tuned mass dampers is considered. The wind turbine with tuned mass dampers was subjected to gravity, centrifugal, and turbulent aerodynamic loadings. Investigations show promising results for the use of ATMDs in the vibration control of wind turbine blades. Copyright © 2013 John Wiley & Sons, Ltd.

A Study on Coupled Bending and Torsional Vibrations of Wind Turbine Blades

A parametric study is developed to investigate the effect of geometry, material stiffness and the rotational motion on the coupled flapwise bending and torsional vibration modes of a wind turbine blade. The assumed modes method is used to discretize the derived kinetic and potential energy terms. Lagrange’s equations are used to derive the modal equations from the discretized terms, which are solved for the vibration frequencies. The parametric study utilizes dimensional analysis techniques to study the collective influence of the investigated parameters by combining them into few non-dimensional parameters, thus providing deeper insight to the physics of the dynamic response. Results would be useful in providing rules and guidelines to be used in blade design.

Modeling underplatform dampers for turbine blades: a refined approach in the frequency domain

Friction damping is one of the most exploited systems of passive control of the vibration of mechanical systems. In order to mitigate vibration of turbine blades, friction dampers are commonly included in the bladed disk design. A common type of blade-to-blade friction dampers are the so-called underplatform dampers (UPDs); these are metal devices placed under the blade platforms and held in contact with them by the centrifugal force acting during rotation. The effectiveness of UPDs to dissipate energy by friction and reduce vibration amplitude depends mostly on the damper geometry and material and on the static loads pressing the damper against the blade platforms. The common procedure used to estimate the static loads acting on UPDs consists in decoupling the static and the dynamic balance of the damper. A preliminary static analysis of the contact is performed in order to compute the static pressure distribution over the damper/blade interfaces, assuming that it does not change when vibration occurs. In this paper a coupled approach is proposed. The static and the dynamic displacements of blade and UPD are coupled together during the forced response calculation. Both the primary structure (the bladed disk) and the secondary structure (the damper) are modeled by finite elements and linked together by contact elements, allowing for stick, slip and lift off states, placed between each pair of contact nodes, by using a refined version of the state-of-the-art friction contact model. In order to model accurately the blade/damper contact with a large number of contact nodes without increasing proportionally the size of the set of nonlinear equations to be solved, damper and blade dynamics are modeled by linear superposition of a truncated series of normal modes. The proposed method is applied to a bladed disk under cyclic symmetric boundary conditions in order to show the capabilities of the method compared to the classical decoupled approaches.

830 風車のブレードとタワーの連成振動

830 風車のブレードとタワーの連成振動

Contactless Diagnostics of Turbine Blade Vibration and Damage

The study deals with the contactless diagnostic method used for the identification of steam turbine blade strain, vibration and damage. The tip-timing method based on the evaluation of time differences of blade passages in different rotor revolutions has been modified and improved to provide more precise and reliable results. A new approach to the analysis of the amplitude and time differences of impulse signals generated by a blade passage has been applied. Amplitudes and frequencies of vibrations and static position of blades ascertained by the diagnostic process are used to establish the state of blade damage. A contactless diagnostic system VDS-UT based on magneto-resistive sensors was developed in the Institute of Thermomechanics Academy of Sciences of the Czech Republic. The system provides on-line monitoring of vibration amplitudes and frequencies of all blades and notification of possible blade damage. Evaluation of the axial and circumferential components of the deflections by measuring the amplitude of blade impulse signals results in an overall improvement of the method. Using magneto-resistive sensors, blade elongation and untwisting can be determined as well.

Flexible and Vibration Characteristics Simulation for the Large Megawatt Size Wind Turbine Blades

In the development of new large megawatt size wind turbines, aerodynamic and structural reserch is interesting and important for study wind turbine performace and boost the development of wind power. In this paper, the aerodynamic and aeroelastic characteristic of blades is investigated and presented based on Blade Element Momentum and Hamilton theory. Then the flexible characteristics of balde is researched with the aerodynamic and aeroelastic model of the rotor. The flapwise and edgewise displacements, velocities and accelerations of blade tip are simulated and plotted to validate the model which is presented in this paper. The results have very important significance to investigate the vibration and fatigue lifetime of the wind turbine blades.

Vibration and flutter of wind turbine blade modeled as anisotropic thin-walled closed-section beam

Based on a variational asymptotic analytical model, vibration and aeroelastic stability of rotor blades modeled as anisotropic thin-walled closed-section beams are systematically addressed. The analysis is applied to a laminated composite construction of the circumferentially asymmetric stiffness (CAS) that produces bending-twist coupling. The vibration characteristics of composite beam are determined by the Extended Galerkin Method. The unsteady aerodynamic loads and centrifugal force are integrated with the classical aerodynamic model to deal with aeroelastic stability analysis. The influence of some related factors, ply angle, rotating velocity, and wind speed, is investigated. The paper gives methods of eigenvalue analysis and aeroelastic response, and gives the approaches to restrain classical flutter.

Влияние неоднородности температуры на упругие колебания лопаток газовой турбины

In the paper results of numerical simulation of elastic vibrations of gas turbine blades with non-uniform temperature distribution and cooling are presented. The results of analysis of natural frequencies of blade vibrations are demonstrated

Application of Elastic Wedge for Vibration Damping of Turbine Blade

Flexural waves traveling in an elastic wedge (plate whose thickness decreases towards zero following a power law function) are not reflected back and accumulate at the zero thickness edge what results in a very efficient damping. In practice reflection always occurs because manufacturing a zero thickness edge is not possible. To solve that problem Krylov proposed the addition of a small quantity of damping material on the thinner edge of the plate what results in very effective damping. In this paper, the application of elastic wedges to reduce the vibrations of turbine blades is investigated. The objectives of this research are to evaluate the damping effectiveness of elastic wedge theory in blades and second, to evaluate a non-polymeric material as vibration damping material. In this way, the vibration energy of the blade is dissipated by the damping material and, at the same time, high temperature and low strength problems characteristic of polymeric damping materials are prevented. First, a FEM modal analysis of a simplified blade model is performed to understand the effects that the elastic wedge has on the modal shapes and frequencies of the blade. Next, to evaluate the damping levels achieved, a frequency response of the simplified blade model with and without elastic wedge is evaluated with the added damping material. The results show that elastic wedge theory combined non-polymeric damping materials can be an efficient method to reduce vibrations of turbine blades or similar applications.

Fluid-structure interaction study of gas turbine blade vibrations

A recent research program has identified the possibility of using the analysis of casing wall pressures in the direct measurement of gas turbine rotor blade vibration amplitudes. Currently the dominant method of non-contact measurement of gas turbine blade vibrations employs the use of a number of proximity probes located around the engine periphery measuring the blade tip (arrival) time. Despite the increasing ability of this method there still exist some limitations, ie. the requirement of a large number of sensors for each engine stage, sensitivity to sensor location, difficulties in dealing with multiple excitation frequencies and sensors being located in the gas path. Analytical modelling of the casing wall pressures and reconstruction of rotor blade vibration amplitudes from the analysis of these simulated pressure signals has shown significant improvement over current non-contact rotor blade vibration measurement limitations by requiring only a limited number of sensors and providing robust rotor blade vibration amplitude estimates in the presence of simulated measurement noise. However, this modelling was conducted with some fundamental assumptions about the casing wall pressures being made. One of these assumptions presumed that during blade motion the pressure profile around the rotor blades follows the blade’s motion while it oscillates around its equilibrium position. This assumption is investigated in this paper through the numerical modelling of the fully coupled two-way rotor blade motion and fluid pressure interaction.

A model to study the reduction of turbine blade vibration using the snubbing mechanism

Blade vibration reduction is an important task in high performance turbo machinery for power generation, in order to avoid the risk of blade failure due to the overcoming of fatigue limit. A possible way to obtain this result is a contact related phenomenon, i.e. by physically limiting the vibration amplitude on the blade tip leaving a small gap between the shrouds of adjacent blades. When the relative displacement between adjacent blades exceeds the gap, in a certain vibration mode of the blade row, a contact occurs between the shrouds, the relative motion is restricted and energy is dissipated by friction and impact during the contact. This is called the snubbing mechanism.In this paper, an original simplified model of bladed disks, in which the snubbing mechanism can occur, is presented and numerical integration in time domain furnishes the time histories of the vibrations of the blades. The level of vibration reduction is then evaluated in some different modes that could be excited for instance by the fluid flow. It is also shown that unlucky combinations of system and excitation parameters can effect also a certain magnification instead of a reduction of the vibration amplitudes.Experimental results on single blade and blade groups of a steam turbine are used to tune the parameters of the system.