Wind Turbine Tower Failure Modes under Seismic and Wind Loads

Abstract

The main objective of this paper is to study the structural response and the failure modes of a typical wind turbine tower under different strong ground motions and wind loading based on a detailed finite element model of the tower. The ground motions were selected to match the design response spectrum with different design characteristic periods (Tg) in order to explore the influence of the frequency content of the earthquake on the response. The wind loads were generated from tropical cyclone scenarios. Nonlinear dynamic time-history analyses were conducted and the structural performance under wind load as well as short-and long-period ground motions was compared. A modal pushover was applied to further clarify the failure related to structural modes. It is observed that under strong wind loads the collapse of the wind turbine is driven by the formation of a plastic hinge at its bottom part, which is attributed to the contribution of the first (long-period) vibration modes of the structure activated by the wind loads. Under earthquake excitations the bottom region is also critical in most cases but in some of them the upper part of the tower triggers the collapse. The latter occurs because of the contribution of high-order vibration modes in the earthquakes dominated by short periods, characteristic of rocky ground conditions. In addition, it is found that long-period ground motions tend to magnify the response of the structure in the elastic range and have associated a higher probability of failure for the same peak ground acceleration. It is concluded that the response of the wind turbine under extreme dynamic actions is strongly dependent on the relationship between the frequency content of the excitation and the structural response.

Seismic vulnerability of offshore wind turbines to pulse and non‐pulse records

“…The damage pattern 1 is consequential to the stress concentration due to the thickness difference between the transition piece (60 mm) and the main tower (30 mm). This agrees with, where the change in thickness led to the formation of plastic hinge at the tower base of a 1.5MW onshore wind turbine, which could spread towards the top and cause failure under extreme earthquake intensities ( PGA = 2 to 3 g). Thus, the damage pattern 1 may be avoided in OWTs that are to experience the near‐field crustal records with weak vertical components, by controlling the thickness between the substructure and the main tower in the design phase.…”

A Simplified Blade Model for Reliable Seismic Assessments of Wind Turbines

“…However, the local blades details, such as airfoil shape, twist angle, and material distribution, are not only challenging to find but are also numerically complicated and computationally expensive. As a result, it is a common practice to either assume these details [5][6][7]10] and/or use the lumped mass approach to represent the RNA in finite element models (FEM) of wind turbines [1,11].…”

“…Several studies have reported the design and optimisation of composite blades using complex FE shell or solid element models to evaluate their strength and modal response [12][13][14][15]. Such high-fidelity FE models are difficult to implement with reasonable computational efficiency in earthquake engineering problems, particularly when a large number of numerical analyses of the whole rotor-towerfoundation-system is needed under a representative set of earthquake records [1,7,10,11].…”

A Novel Tripod Concept for Onshore Wind Turbine Towers

“…The structural design of such towers has attracted the attention of many researchers (i.e., references [11][12][13][14][15][16]). Prevailing failure modes that dictate the design and determine the required cross-sections are the buckling of the tubular shells [17][18][19], fatigue of the connections [20][21][22] and avoidance of resonance between the tower's fundamental frequencies and the rotor and blade-passing frequencies, denoted as 1P and 3P, respectively [10,23].…”