Print Email Facebook Twitter Method for extracting an equivalent Winkler model of the 3D dynamic soil-structure interaction of large-diameter offshore monopile foundations Title Method for extracting an equivalent Winkler model of the 3D dynamic soil-structure interaction of large-diameter offshore monopile foundations Author Versteijlen, W.G. De Oliveira Barbosa, J.M. Van Dalen, K.N. Metrikine, A. Faculty Civil Engineering and Geosciences Department Hydraulic Engineering Date 2015-12-31 Abstract The motivation for this work stems from the offshore wind industry, where designers are faced with a discrepancy between the available design methods and the typical dimensions of the offshore wind foundations that call for other design approaches. Throughout the years, much valuable work has been performed in the prediction of long, slender, flexible piles which are most often applied in the field. For the large-diameter rigidly behaving ‘caisson’ foundations, less methods are available. These two types of piles (flexible and rigid) interact in a fundamentally different way with the soil. The fact that the observed fundamental frequencies of installed offshore wind structures are higher than designed for, is believed to confirm the underestimation of stiffness associated with the often used ‘p-y’ design method. For the damping related part, being it a more complex mechanism, there is even more uncertainty. As a result, conservative low damping ratios are assumed during design. Though it is less straightforward to measure the damping ratios of installed turbines, the published values range from a factor of 1 to 4 with respect to the value used in design. Like for stiffness, empirical relations were derived to estimate damping in the 1970s and 80s based on more advanced 2D and 3D models in combination with field tests and the previously mentioned p-y curves. Again, these relations are restricted to flexible piles, where the pile tip is assumed to be fixed. To capture the interaction for the currently applied pile dimensions, it is necessary to simulate the 3D interaction between the pile and the soil, and perform full scale tests. The latter are not yet available, but results of a few campaigns are expected in the near future. Advanced 3D numerical models are available, and for the purpose of physical insight and for engineering applications, it is useful to extract a 1D equivalent model that can mimic the 3D simulation. In this work, a linear elastic dynamic 3D FE model of a pile-soil system is used to extract the static and the frequency dependent displacements. The FE domain is surrounded with perfectly matched layers (PMLs) that absorb the propagating waves at the boundaries for the relevant frequencies of excitation. The soil properties of a design location are used, which have been identified using seismic measurements. A method for the derivation of a 1D equivalent dynamic stiffness (i.e., a Winkler model with distributed springs and dashpots) is derived thereafter. The results obtained with the 1D model for the static response and for a dynamic case are compared to the response of the 3D FE analysis. To reference this document use: http://resolver.tudelft.nl/uuid:7cff7e1c-060c-424d-b55e-322e708e1cb5 Publisher Institute for Problems in Mechanical Engineering of RAS, IPME RAS Source Proceedings of 43th International Summer School-Conference Advanced Problems in Mechanics (APM), St. Petersburg, Russia, 22-27 June 2015 Part of collection Institutional Repository Document type conference paper Rights (c) 2015 The Author(s) Files PDF 326350.pdf 967.08 KB Close viewer /islandora/object/uuid:7cff7e1c-060c-424d-b55e-322e708e1cb5/datastream/OBJ/view