Geotechnical aspects of offshore wind turbine dynamics from 3D non-linear soil-structure simulations

Abstract

The massive development of the offshore wind industry is motivating substantial research efforts worldwide, where offshore wind turbines (OWTs) of increasing size are being installed in deeper water depths. Foundation design is a major factor affecting the structural performance of OWTs, with most installations founded to date on large-diameter monopiles.This work promotes advanced 3D finite element (FE) modelling for the dynamic analysis of OWT-monopile-soil systems. A detailed FE model of a state-of-the-art 8 MW OWT is analysed by accounting for dynamic soil-monopile interaction in presence of pore pressure effects. For this purpose, the critical-state, bounding surface SANISAND model is adopted to reproduce the hydro-mechanical cyclic response of the sand deposit. The response to realistic environmental loading histories (10 minutes duration) are simulated, then followed by numerical rotor-stop tests for global damping estimation.While linking to existing literature, all FE results are critically inspected to gain insight relevant to geotechnical design. The modelling tools adopted (i) support the robustness of 'soft-stiff' foundation design with respect to natural frequency shifts, even during severe storm events; (ii) provide values of foundation damping in line with field measurements; (iii) suggest that pore pressure effects may more likely affect soil-monopile interaction under weak-tomoderate environmental loading.

Decoupled Modelling Approaches for Environmental Interactions with Monopile-Based Offshore Wind Support Structures

“…To the authors' knowledge, such a comprehensive attempt has not taken place yet. Existing studies focus either on the modelling of one of the media, be it in the realm of academia or engineering [34][35][36][37][38], or on the dynamic description of the controlled offshore wind turbine [14,39,40]. The latter case is referred to as the integrated modelling approach, albeit that the full coupling with the surrounding media is not accounted for in full.…”

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

“…A few studies have separately considered the effect of pile diameter on the kinematic interaction forces 18 . More recently, advanced constitutive models 19–22 have been used for response of different types of piles in liquefiable soil 23,24 …”

“…18 More recently, advanced constitutive models [19][20][21][22] have been used for response of different types of piles in liquefiable soil. 23,24 Interest in renewable energy in 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.…”

Memory-Enhanced Plasticity Modeling of Sand Behavior under Undrained Cyclic Loading

“…Among these, the PM4Sand model (Boulanger and Ziotopoulou 2013;Ziotopoulou and Boulanger 2016) possesses remarkable capabilities to reproduce undrained cyclic behaviour, including the simulation of pore pressure build-up, liquefaction triggering and, in medium-dense/dense sands, 'cyclic mobility' (Elgamal 2 Liu et al, July 14, et al 2003) -in turn associated with transient regains in shear resistance, and gradual shear strain accumulation at vanishing confinement. Cyclic mobility is relevant to the serviceability of earth structures and foundations under prolonged cyclic loading (Ziotopoulou and Boulanger 2016;Kementzetzidis et al 2019), as well as to seismic site response (Roten et al 2013).…”