Dynamic Responses Analysis  of A 5MW NREL Wind Turbine Blade under Flap-Wise and Edge-Wise Vibrations

Abstract

A wind turbine is subjected to a regime of varying loads. For example, each rotor revolution causes a complete gravity stress reversal in the low-speed shaft, and there are varying stresses from the out-of-plane loading cycle due to fluctuating wind load. Consequently, wind turbine blade design is governed by fatigue rather than ultimate load considerations. Previous studies have adopted many different beam theories, using different techniques and codes, to model the National Renewable Energy Laboratory (NREL) 5 MW offshore wind turbine blade. There are differences, from study to study, in the free vibration results and the dynamic response. The contribution of this study is to apply the code written by the authors to the different beam theories used with the aim of comparing the different beam theories presented in the literature and that developed by the authors. This paper reports the investigation of the effects of deformation parameters on the dynamic characteristics of the NREL 5 MW offshore wind turbine blades predicted by the different beam theories. The investigation of free vibrations is a fundamental step in the analysis of structural dynamics, and this study cmpares different computational structural methods and investigates their effect on the predicted dynamic response. The modal characteristics of every model examined have been combined with strip theory to determine the dynamic response of the blade.

The Sensitivity of 5MW Wind Turbine Blade Sections to the Existence of Damage

“…Modal analysis can determine the modal characteristics of blade structure [20]. These characteristics represent the natural frequencies, mode shapes, and damping properties and reflect the healthy condition of the blade.…”

Study of Centrifugal Stiffening on the Free Vibrations and Dynamic Response of Offshore Wind Turbine Blades

“…where the first term is due to the flexural bending, the second term is for the kinetic energy resulting from the rotary inertia and the third is the result of adding the effects of pre-cone and pitch angles [30].…”

“…where the first term is the strain energy of the blade due to flexural bending and the second term is the potential energy due to the centrifugal and gravitational forces [17,30]. Applying Hamilton's principle:…”

“…To study the centrifugal stiffening effect on the modal features in the edge-wise direction, the governing Equation of motion for the Rayleigh theory in the edge-wise direction, including the effect of the control angle, can be obtained in terms of the forced edge-wise (in-plane) direction of the non-uniform beam as shown in [17,30]:…”

Damage identification in complex structures using vibration data

“…M, C, and K in the left hand side of the equation represent the local mass, local damping, and local stiffness matrices. The parameter r represents the radius at each certain section from 1 to n. The undamaged local modal matrices are composed of elements of[10]:…”