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Behavior of Laterally‐Loaded Offshore Wind Turbine Monopiles under Storm Loading Conditions

TitleBehavior of Laterally‐Loaded Offshore Wind Turbine Monopiles under Storm Loading Conditions
Publication TypeConference Proceedings
Year of Publication2014
AuthorsCarswell W, Arwade SR, Degroot DJ
Conference NameEMI 2014: Engineering Mechanics Institute Conference
Date Published08/2014
PublisherEngineering Mechanics Institute
Conference LocationHamilton, Ontario
Keywordsfinite element model, Monopile, Offshore wind turbine
Abstract

The serviceability limit state for offshore wind turbine (OWT) monopiles is typically defined by a permanent accumulated tilt of the pile at the mudline, motivated by visual requirements and specifications by the wind turbine manufacturer. While OWT design guidelines (such as Det Norske Veritas) require designers to estimate accumulated tilt from representative loading conditions, no method is recommended. Due to the nonlinearity of soil behavior, the results of lateral soil-pile interaction models are highly dependent on modeling assumptions. Extreme loads can be modeled in several different ways: most simply, load maxima can be applied in a static analysis to determine pile head rotation; however, this method neglects dynamic effects which may not accurately reflect lateral pile behavior during and after storm loading. Alternatively, an idealized storm history may be applied in terms of load “parcels”, containing numbers of cycles at a given load amplitude; depending on the nonlinearity of the soil however, the sequence of load cycles may also influence lateral pile behavior. This study seeks to analyze the behavior of laterally-loaded monopile under storm loading conditions, comparing the results from different load modeling approaches. The soil-structure model will include a two-dimensional continuum finite element model of a 6 m-diameter pile for the National Renewable Energy Laboratory 5MW Reference Turbine assuming elastic-plastic, isotropic properties.