Stiffness and Damping of monopile foundations in sand刚度和阻尼的单桩基础在砂.pptVIP

Monopiles in SandStiffness and Damping Christian LeBlanc Thilsted, DONG Energy RenewablesNiels Jacob Tarp-Johansen, DONG Energy Renewables EWEA 2011, 14-17 March, Brussels Introduction, soil stiffness and damping Impact on design Experience Soil damping Overview of soil damping Theoretical derivation of damping due to pore pressure dissipation Conclusions On-going and future work Full-scale measurements * Outline Wind-wave misalignment cause the resonant response to be governed by soil damping Damping (excl. aerodynamic damping) become a design driver  Consequence of underestimation soil damping: increased use of steel higher costs * Soil damping Increasing water depths and larger turbines reduces the 1st natural frequency Soil stiffness become a major design driver Consequence of underestimating soil stiffness : increased use of steel higher costs applicable range of monopile foundations limited to water depths less than ~30 m. Soil stiffness Impact on design Damping presently used for design calculations is based on a theoretical reconstruction of damping contributions * Soil damping - theoretical 20 m 20 m 80 m D=4.7 m Source 1st mode ? (%) Remark Soil ~3-5 Visco-elastic Hydrodynamic ~0.75 Radiation only Steel tower + pile ~1.2 Disregarding grout Tower damper Typically 2 Turbine dependent Aerodynamic ~1 Inherent in BEM 0.3 Hz Table adapted from: Niels Jacob Tarp-Johansen et al. Comparing Sources of Damping of cross-wind Motion, European Offshore Wind 2009, Stockholm (? modal = Modal log. decr., ? ? 2??, ? = damping ratio) * Soil damping - measurements Emergency stops, i.e. no aerodynamic damping Horns Rev 1 Offshore Wind Farm Burbo Offshore Wind Farm Measurements show more damping (excl. aerodynamic damping) than assumed in present design calculations Current design = Theoretical approach: ? modal = 8 % Measurements: ? modal 10 % Soil stiffness - theoretical The p–y curves for piles in sand described by Reese et al. (1974) and O’Nei