Shake table testing and numerical simulation of a utility‐scale wind turbine including operational effects

Abstract

Shake table tests were undertaken on an actual wind turbine (65 kW rated power, 22.6 m hub height and a 16 m rotor diameter) using the Network for Earthquake Engineering Simulation Large High Performance Outdoor Shake Table at the University of California, San Diego. Each base shaking event was imparted in two states, whereas the turbine rotor was still (parked), and while it was spinning (operational). Each state was tested in two orientations of shaking direction, one parallel (fore-aft) and another perpendicular (side-to-side) to the axis of rotation of the rotor. Structural response characteristics are presented for motions imparted in both configurations and both operational states. Modal parameters (natural frequencies, damping ratios and mode shapes) were estimated throughout the testing program. It is found that shaking imparted in the fore-aft direction while spinning is the only observed situation where operational effects appear significant, with reductions up to 33% in seismic bending moment demand near the tower base. Using modifications developed by the research team to the FAST code, experimental results are compared with corresponding simulations to show that dynamic characteristics, acceleration time histories and trends in tower bending seismic demand can be numerically approximated. This experimental evidence and associated numerical simulations suggest that modeling of combined wind and earthquake loading with existing turbine specific codes produce meaningful results. Discrepancies between experimental and numerical results support that further refinement of simulation codes can improve accuracy beyond the current state.

Seismic analysis of offshore wind turbines on bottom-fixed support structures

“…The same observation can be made based on the acceleration profile in the y-direction. The activation of the second FA and SS support structure modes is confirmed by the fact that the acceleration profiles exhibit significant values at approximately 2/3 of the support structure height, and this result is consistent with analogous results for land-based HAWTs under earthquake loading [11].…”

Some Results on the Vulnerability Assessment of HAWTs Subjected to Wind and Seismic Actions

“…In particular, comparative analyses in the time domain between the results obtained by fully-coupled simulation performed in GH BLADED [27] and those obtained by linear combination of separate wind and earthquake responses, the latter computed by adding different levels of aerodynamic damping, are carried out. The results show that errors in bending moment and shear forces are within engineering margins, which is encouraging for the use of the uncoupling approach, and confirm that a value of 4% for the aerodynamic damping, recommended by ASCE-AWEA RP2011 [17] and in previous studies [6][7][8][9][10][11][12][13][14][15][16][17][18], can reasonably also be used in time-domain uncoupled analyses.…”

“…Then, Prowell et al [8] conducted experimental work on a 65 kW Nordtank wind turbine, applying earthquake motions in two horizontal directions, and concluding that the importance of considering seismic demand increases as the turbine grows in capacity. Again, Prowell et al [9,10] showed that earthquakes can produce, in the NREL 5 MW HAWT, a bending-moment demand at the tower base well above the one from extreme wind events in operational, emergency shutdown and parked simulations.…”

Seismic Fragility Analysis of Monopile Offshore Wind Turbines under Different Operational Conditions

“…Many attempts to study the seismic dynamic responses [6][7][8][9], structural safety [4,5,[10][11][12] and analytical methods [4,13] of wind turbines have been conducted. Most studies focused on onshore wind turbines, which are shorter in the cantilever length than their offshore counterparts.…”