On the evaluation of wind loads for wind turbines' foundation design: Experimental and numerical investigations

Abstract

Summary In the past two decades, wind farms have been enjoying renewed interest as means for clean and renewable energy production. Larger and taller wind turbines are used for harvesting wind energy. In this paper, a boundary‐layer wind tunnel experiment was carried out on a model of the 5‐MW National Renewable Energy Laboratory (NREL) wind turbine, to evaluate overall wind‐induced base loadings in a parked condition. While mean and background base loadings were measured experimentally, a posttest dynamic analysis framework is developed to assess inertial loads analytically. The analytical analysis is carried out under both rigid and flexible tower‐foundation assumptions. Whenever applicable, the wind tunnel measurements are compared with NREL results, which were obtained by using the Fatigue, Aerodynamics, Structures, and Turbulence (FAST) software. The comparison shows a good agreement between the proposed approach and the available FAST results. In addition, the study indicates that the flexibility of the foundation may result in a reduced overall wind loads, due to base isolation effects. However, the assumption of a rigid foundation results in a slightly conservative base loads. This said, depending on the available foundation system, the methodology followed in the current paper remains in force and the base stiffness can be updated to permit the estimation of actual foundation loadings.

Vibration control in wind turbines to achieve desired system-level performance under single and multiple hazard loadings

“…The system was defined based on the properties of the wind turbine in parked position excited by a filtered band limited Gaussian white noise. The filter was designed such that the excitation force following the experimental originated data of a wind turbine in a parked position . Figure shows the measured wind load spectrum extracted from Abdelkader et al and the spectrum of a filtered white noise excitation.…”

“…The filter was designed such that the excitation force following the experimental originated data of a wind turbine in a parked position . Figure shows the measured wind load spectrum extracted from Abdelkader et al and the spectrum of a filtered white noise excitation. An appropriate bandpass IIR Butterworth digital filter has been used to filter the band‐limited Gaussian white noise inputs and make it to follow the experimental spectrum.…”

Dynamic Performance of Monopile-Supported Wind Turbines (MWTs) under Different Operating and Ground Conditions

“…Using a numerical model, Abhinav and Saha [26] studied the effects of soil stiffness and pile parameters on the natural frequency and amplitude of the response. Abdelkader et al [27] showed that the existence of a foundation may reduce wind loads, and they assumed that a fixed foundation leads to a conservative design. Thus, ground conditions impact the natural frequency and damping ratio of MWTs, which further affect structural responses.…”

Long-Term Variability of Wind Speed and Direction in the Mediterranean Basin

“…Moreover, the variability in wind direction also affects the fetch length and therefore, the wave propagation schemes and sea-state intensity [42], as well as the estimation of wind and/or wave design values [43,44]. The probabilistic modeling of wind direction seems to be increasingly important for wind farm design and micro-siting, both onshore and offshore [45][46][47], for structural stability and reliability [48][49][50] and long-term economic gains from such applications [51].…”