Effect of kinematic interaction on seismic response of offshore wind turbines on monopiles

Abstract

Interest in renewable energy over the past decade has motivated a remarkable research on offshore wind energy. Due to the environmental loading conditions in the early developments of offshore wind farms, the focus of the research and engineering has been on aerodynamic and hydrodynamic subjects. However, earthquake has turned out to be a major design concern in seismic areas such as East Asia, Southern Europe, and United States. The topics include, among others, nonlinear response of foundations, soil liquefaction, and their impacts on foundation performance. An important topic in seismic soil‐structure interaction (SSI) analysis is the kinematic seismic response of foundations. This information is crucial for analyses based on the substructuring approach where both kinematic response and foundation impedances are key parameters. While considerable research has been spent on the latter topic, very little has been reported on the kinematic interaction. Large monopoles with low aspect ratios tend to rotate much more than regular piles in pile group foundations due to seismic waves. The rotation leads to additional load on the tower and the turbine. This article uses a rigorous numerical model for monopole‐soil interaction in layered soil and computes both rotational and horizontal responses at the pile head (seabed) as functions of frequency. A suite of generic homogeneous and heterogeneous soil profiles with shear moduli representative of clay (generally linear) and sand (generally parabolic) are considered in these analyses. Through representative analyses, both in frequency domain and time domain, it is illustrated how the kinematic interaction influences the earthquake loads imparted to an offshore wind turbine (OWT).

Seismic excitation of offshore wind turbines and transition piece response

“…44 Given the complexity of the grouted connection model and the associated high computational cost, the selection of a limited number of relevant earthquake motions was essential. As such, two earthquake records were selected for this study, enabling direct comparison with published work on offshore turbines under seismic loads 17,18,45 : (i) Kobe, Japan, Nishi-Akashi, January 17, 1995, and (ii) Chi-Chi Taiwan-03, CHY082, September 20, 1999. These were also selected because of their significantly contrasting characteristics, enabling further insight into the dynamic behaviour of the structure under varying seismic loads:…”

“…Research of the structural behaviour of offshore wind turbines under dynamic loads is increasing. De Risi et al 14 Vacareanu et al 15 and Kaynia 16,17 showed high sensitivity of OWT structures to historical seismic events, accounting for the combination of seismic and environmental (wind/wave) loading. Sensitivity to the operational conditions (e.g.…”

“…Vacareanu et al 15 . and Kaynia 16,17 showed high sensitivity of OWT structures to historical seismic events, accounting for the combination of seismic and environmental (wind/wave) loading. Sensitivity to the operational conditions (e.g.…”

Offshore wind turbine subjected to supershear earthquake ruptures

“…Zhao et al, (2020) used a response spectrum method to evaluate the OWT's pile-water and pile-soil interactions, also pointed out that pile-water interaction significantly affects the structural displacement. In recent work, Kaynia, (2020) presented the effect of kinematic interaction through the numerical of monopole OWT. Higher kinetic interaction is noted for the stiff soil and medium-to-high frequency content.…”

Investigation of pile‐induced filtering of seismic ground motion considering embedment effect

“…[13][14][15] The filtering of seismic ground motion due to soil-pile interaction has been established using several closed form analytical solutions, 11,[16][17][18][19][20] boundary element formulations 21,22 as well as numerical models. [23][24][25][26][27][28][29][30] Studies by Gazetas and Dobry 19 and Kaynia and Kausel 20 showed that the filtering of the free-field motion was stronger in inhomogeneous soil profiles when compared to homogeneous profiles. Simplified expressions for the kinematic interaction factor for single piles have also been proposed in past studies.…”