Influence of soil–structure modelling techniques on offshore wind turbine monopile structural response

Abstract

The importance of appropriate offshore wind turbine (OWT) monopile structural modelling technique cannot be overstated in the successful design and installation of a new generation of larger and heavier structures to deliver the increasing capacity demand. The lack of clear design guidance and acceptable structural modelling techniques across the industry results in a range of conservative but expensive design and installation techniques. Most of the OWT monopile modelling efforts lie in the substructure (foundation) and interaction with the supporting soil which is highly nonlinear along the length of the embedment depth of the monopile structure. Typically, monopile offshore wind turbine structural modelling can be completed using, amongst others, one of the following techniques: 3D finite element modelling with mass soil foundation, API p-y curve soil springs, JeanJean soil springs, and the newly developed PISA modelling approach. The study presented in this paper considers the application of the 3D finite element modelling with mass soil, API p-y soil springs, and the JeanJean soil springs technique. By comparing the structural response, the 3D finite element modelling with mass soil results in an improved natural frequency and harmonic response. Furthermore, a reduced displacement was observed in the 3D finite element model with mass soil which will ultimately result in a corresponding improvement in the structure's useful operational design life. The application of the API p-y soil springs, JeanJean soil springs, and other modelling techniques requires extensive calibration to ensure the correct structural response and behaviour are achieved. This becomes a key factor as the boundaries of the size of the structure and turbine capacity are pushed even further for the new concept generation offshore wind turbines, which are required to deliver a higher capacity of 12 to 15 MW with the aim of achieving 20 MW, whilst achieving an efficient cost-effective engineering design and installation process.

Importance of higher modes for dynamic soil structure interaction of monopile‐supported offshore wind turbines

“…To ensure a robust correlation among the results given by different models, the determination of model parameters (standardization of models) is based on procedures widely accepted in engineering practice and uses the same mechanical material properties (input data) for each model. The input model parameters for the simplified foundation model are correlated with the mechanical properties of the material and are mentioned in various codes (API, 22 DNV 23,55 ) and technical papers (Løken and Kaynia, 8 Gazatas, 31 Sunday and Brennan 52 ). Although the simplified foundation models are widely accepted by researchers or practitioners for the calculation of the fundamental frequency of small‐capacity wind turbines, their capability of predicting higher vibration modes for modern OWT with real geometric configurations is not clear.…”

“…Its soil-structure interaction modeling techniques have been reviewed by many scholars and extensively used for the analysis and design of OWTs. 17,25,46,[49][50][51][52][53] Although different modeling techniques require different input parameters, the determination of parameters for each model is based on the procedures widely accepted in engineering practice to represent the same physical problem. Therefore, the common goal of each model is the same.…”

A Novel Reduced Column Approach for the Mitigation of Earthquake-Induced Vibrations of Wind Turbines

“…Table 1 reports the first 2 natural frequencies of the three wind turbine models. The "soft-stiff" design approach is maintained where the target natural frequency corresponds to a lower frequency than the rotor frequency (1P) equal to about 0.12 Hz [20] to avoid resonance which can lead to increase in fatigue damage and reduced operational life of wind turbines [24].…”

Influence of wave spreading on offshore wind turbine design: IEA 15-MW scenario

“…To conduct this study, we use our in-house aero-hydro-servo-elastic code [9] which has been verified against industry standard software such as OpenFAST and BLADED. This tool is based in on a multi-body formulation method that is fully coupled with 1-D finite elements, allowing accurate modelling of wind turbines in both operating and parked conditions [9]. Importantly, it enables modelling of the directional dependence of aerodynamic damping through explicitly capturing the aeroelastic behaviour.…”

“…The stochastic wind field is modelled using the Kaimal spectrum, as described in IEC 61400-3-1 [6]. Soil-structure interaction is modelled using a multi-surface plasticity approach capturing soil hysteretic behaviour along the full embedment depth, whereby hysteretic damping is explicitly captured within the mechanics of the model [9]. This being a key reason why we use this code over other software.…”