An Overview of the\ NREL/SNL Flexible Turbine Characterization Pttgject (original) (raw)

An overview of the NREL/SNL flexible turbine characterization project

1998

There has been a desire to increase the generating capacity of the latest generation of wind turbine designs. In order to achieve these larger capacities, the dimensions of the turbine rotors are also increasing significantly. These larger structures are often much more flexible than their smaller predecessors. This higher degree of structural flexibility has placed increased demands on available analytical models to accurately predict the dynamic response to turbulence excitation. In this paper we present an overview and our progress to date of a joint effort of the National Renewable Energy Laboratory (NREL) and the Sandia National Laboratory (SNL). In this paper we present an overview and status of an ongoing program to characterize and analytically model the dynamics associated with the operation of one of the most flexible turbine designs currently available, the Cannon Wind Eagle 300 (CWE-300). The effort includes extensive measurements involving a detailed inventory of the turbine's physical properties, establishing the turbine component and full-system vibrational modes, and documenting the dynamic deformations of the rotor system and support tower while in operation.

A Progress Report on the Characterization and Modeling of a Very Flexible Wind Turbine Design

1998

Printed on paper containing at least 50% wastepaper, including 20% postconsumer waste ABSTRACT The combination of increasing turbine rotor diameters and the desire to achieve long lifetimes has placed increased emphasis on understanding the response of flexible turbine structures in a turbulent inflow environment. One approach to increase fatigue lifetimes has been to design structures that can either shed or adequately absorb turbulent loads through the use of flexible rotors and support towers, and hubs and nacelles that exhibit multiple degrees of angular freedom. The inevitable result in such designs is a substantial increase in dynamic complexity. In order to develop a sufficient knowledge of such concepts, extensive measurements coupled with detailed analytical simulations of a flexible turbine design are required. The Wind Eagle 300 turbine, with its lightweight flexible rotor and hub, meets these criteria and is currently being investigated.

Structural dynamic modeling of wind turbine blades

A 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.

IJERT-Dynamic Characteristics of Wind Turbine Blade

International Journal of Engineering Research and Technology (IJERT), 2014

https://www.ijert.org/dynamic-characteristics-of-wind-turbine-blade https://www.ijert.org/research/dynamic-characteristics-of-wind-turbine-blade-IJERTV3IS080113.pdf this paper presents a review on the dynamic characteristics of Wind Turbine. One of the most important sources of renewable energy is Wind Power. Wind-turbines extract kinetic energy from the wind. The design of a wind turbine structure involves many considerations such as strength, stability, cost and vibration. To design a commercial flexible system, comprehensive understanding of the dynamic characteristics is essential. Reduction of vibration is a good measure for a successful, safe design of the blade structure. Hence to find out the natural frequency of the turbine blade the two different techniques are used, one is Frobenius Method and another is Finite Element Method. It may promote other important design goals, such as low cost and high stability level. A good design for reducing vibration is to separate the natural frequencies of the structure from the harmonics of rotor speed. This would avoid resonance where large amplitudes of vibration could severely damage the structure. Influences of the rotating speed, the pitch angle, the setting angle, and the aerodynamic loads on natural frequencies are discussed in this paper.

Seismic Analysis of Wind Turbines

Earthquake Spectra, 2013

An analytical model of an operating wind turbine to obtain the seismic response due to three base accelerations is presented. The model considers the flexibility of the blades in the flapping direction and the flexibility of the tower in bending and twisting. Blade aerodynamics and gyroscopic moments are included. A Vestas-V82 turbine is selected to demonstrate the methodology. The results show that only the first two tower modes in each direction (fore-aft and lateral) are mostly excited. It is found that the lateral motion of the wind turbine is more susceptible to experiencing large displacements since the aerodynamic effects are negligible in this direction. The stresses due to combined operational and seismic loads and due to extreme wind loads are less than the allowable stresses. The stresses calculated at the tower top section due to combined operational and seismic loads are larger than those due to extreme wind loads.

A Framework for Dynamic and Aeroelastic Analysis of Horizontal Axis Wind Turbines

ASME 2002 Wind Energy Symposium, 2002

This paper presents a framework for the dynamic and aeroelastic analysis of a horizontal axis wind turbine modeled as a multi-flexible-body system. The multi-rigid-body portions of the system, composed of the nacelle and hub, are modeled as a system of interconnected rigid bodies using Kane's equations. The flexible portions, composed of the the blades and tower, are represented using nonlinear beam finite elements, taken from a mixed formulation for the dynamics of moving beams. Each analysis leads to a set of symbolic equations that can be coupled symbolically to represent the dynamic behavior of the wind turbine. A solution procedure is implemented to assess the dynamic stability of the system. Here the solution is divided into two parts: a set of nonlinear ordinary differential equations governing the periodic steady-state operating condition, and a set of equations that are linearized about the steady-state operating condition governing the transient dynamics. The harmonic balance method is used for the nonlinear periodic steady-state solution, and the finite element in time method is proposed as an alternative method. Linearization of the equations about the steady-state operating condition yields system equations with periodic coefficients which are solved by Floquet approach to extract the modal parameters. For the aeroelastic analysis, aerodynamic loads from an aerodynamic model to be selected in the future will be inserted into the present framework. Then, the framework can produce a symbolic system matrix, potentially useful for control design. Numerical results are presented for the dynamic characteristic of HAWT's with flexible tower and blades.

Aeroelastic coupling analysis of the flexible blade of a wind turbine

a b s t r a c t This paper presents an aeroelastic coupling analysis of the flexible blade of a large scale HAWT (horizontal axis wind turbine). To model the flexibility of the blade more accurately, 'SE' (super-element) is introduced to the blade dynamics model. The flexible blade is discretized into a MBS (multi-body system) using a limited number of SEs. The blade bending vibration and torsional deflection are both considered when calculating the aerodynamic loads; thus, the BEM (blade element momentum) theory used in this study is modified. In addition, the BeL (BeddoeseLeishman) dynamic stall model is integrated into the BEM-modified model to investigate the airfoil dynamic stall characteristics. The nonlinear governing equations of the constrained blade MBS are derived based on the theory of MBS dynamics coupling with the blade aerodynamics model. The time domain aeroelastic responses of the United States NREL (National Renewable Energy Laboratory) offshore 5-MW wind turbine blade are obtained. The simulation results indicate that blade vibration and deformation have significant effects on the aerodynamic loads, and the dynamic stall can cause more violent fluctuation for the blade aerodynamic loads compared with the steady aerodynamic model, which can considerably affect the blade fatigue load spectrum analysis and the fatigue life design. Energy xxx (2015) 1e9 Please cite this article in press as: Mo W, et al., Aeroelastic coupling analysis of the flexible blade of a wind turbine, Energy (2015), http:// dx.

MODELING THE STRUCTURAL DYNAMICS OF CHOSEN COMPONENTS OF THE HORIZONTAL AXIS WIND TURBINE

As the horizontal axis wind turbines are getting larger, their dynamic behaviour is becoming more important. Dynamic analysis gives knowledge how to improve efficiency and safety also in small wind turbines. This article describes numerical models of chosen components of upwind, three-bladed wind turbine. Geometry of each component is generated separately and then assembled together by transformation matrices. Material of the blades is composite, the hub is assumed to be made of steel and material of the planet carrier is casted iron. These mentioned components are modelled by shell elements. The numerical model of the hub takes into account aerodynamic and gravity loads of blades, inertia forces due to rotation of the rotor and aerodynamic damping. The aerodynamic loads, calculated according to the modified Blade Element Momentum theory, are attached to aerodynamic centres. Wind conditions were assumed for I-class wind turbine according to Germanischer Lloyd. Stress Reserve Factors were calculated for DLC 6.1 load case according to Germanischer Lloyd, too. As a first step, numerical strength analysis with using AnSYS software was performed with maximum values of principal stresses as an output. Then, based on FEM analysis results, Stress Reserve Factors were calculated. SRF values show that analyzed hub and planet carrier have sufficient strength for extreme loads. Methodology of safety margin evaluation presented in this paper allows assessing if the object fulfils relevant standards demanding.

Multi-flexible-body Dynamic Analysis of Horizontal Axis Wind Turbines

Wind Energy, 2002

A dynamic stability analysis is presented for a horizontal-axis wind turbine modeled as a multi-body system with both rigid-and flexible-body subsystems. The rigid-body subsystems are modeled as an interconnected set of rigid bodies using Kane's method, which can lead to equations of motion that are more compact than they would be using other methods. The flexible-body subsystems are modeled using nonlinear beam finite elements, derived from a mixed variational formulation for the dynamics of moving beams. The equations for the rigid and flexible subsystems are coupled to obtain a unified framework that models the dynamic behavior of the complete system. Linearization of the dynamic equations about the steady-state solution yields system equations with periodic coefficients that must be solved by Floquet theory to extract the dynamic characteristics. Numerical studies are presented to investigate the natural frequencies and mode shapes for a wind turbine with flexible blades. The presented results demonstrate the performance of the present methodology to aid in understanding of the dynamic characteristics of the wind turbine.