Aeroelastic Instabilities of Large Offshore and Onshore Wind Turbines

Abstract

Offshore turbines are gaining attention as means to capture the immense and relatively calm wind resources available over deep waters. This paper examines the aeroelastic stability of a three-bladed 5MW conceptual wind turbine mounted atop a floating barge with catenary moorings. The barge platform was chosen from the possible floating platform concepts, because it is simple in design and easy to deploy. Aeroelastic instabilities are distinct from resonances and vibrations and are potentially more destructive. Future turbine designs will likely be stability-driven in contrast to the current loads-driven designs. Reasons include more flexible designs, especially the torsionally-flexible rotor blades, material and geometric couplings associated with smart structures, and hydrodynamic interactions brought on by the ocean currents and surface waves. Following a brief description of the stability concept and stability analysis approach, this paper presents results for both onshore and offshore configurations over a range of operating conditions. Results show that, unless special attention is paid, parked (idling) conditions can lead to instabilities involving side-to-side motion of the tower, edgewise motion of the rotor blades, and yawing of the platform.

Dynamics Modeling and Loads Analysis of an Offshore Floating Wind Turbine

“…Equation (2)(3)(4)(5)(6)(7)(8)(9)(10) for the incident-wave-excitation force is very similar to Eq. (2-9) for the incident-wave elevation-the only difference is the inclusion of the normalized wave-excitation force complex transfer function, .…”

“…2 These simulators are capable of predicting the coupled dynamic response and the extreme and fatigue loads of land-based horizontal-axis wind turbines (HAWTs). The U.S. wind industry relies on two primary design codes: (1) FAST (Fatigue, Aerodynamics, Structures, and Turbulence) [39] with AeroDyn [55,67] and (2) MSC.ADAMS ® (Automatic Dynamic Analysis of Mechanical Systems) with A2AD (ADAMS-to-AeroDyn) [20,54] and AeroDyn.…”

“…The forcing function, f i , depends nonlinearly on the set of system DOFs and their first time derivatives (q and q respectively), as well as the set of control inputs (u) and time (t), and is positive in the direction (2)(3)(4)(5)(6), in which it is implied that when the same subscript appears in multiple variables in a single term, there is a sum of all of the possible terms. In FAST, for example, subscripts i and j range from one to the total number of DOFs in the model (i.e., up to 22 for a two-bladed floating wind turbine or up to 24 for a three-bladed floating wind turbine).…”

“…To ensure, then, that the equations of motion were not implicit (i.e., I wanted to avoid f i depending on q ), the total external load acting on the support platform (other than those loads transmitted from the wind turbine and the weight of the support platform) was split into two components: an impulsive added-mass component summing with M ij and the rest of the load adding to f i . In other words, the total external load on the support platform, , was written as follows: (2)(3)(4)(5)(6). In Eq.…”

A computational simulation of the motion of floating wind turbine platforms

“…A summary of work using these models follows. Studies [13][14][15][16][17] that predicted the aeroelastic, hydrodynamic, and rigid body motion responses of floating wind turbines have been used to investigate various platform and mooring arrangements. References [8,18,19] summarize the development of simulation tools that include models of aerodynamic, gravitational, and inertial loading of the rotor, nacelle, and tower; elastic structural effects; wave loading; dynamic loading between the platform and turbine; and motions of the mooring cables.…”