Soil Interaction and Grout Behavior for the NREL Reference Monopile Offshore Wind Turbine

Abstract

Monopiles for offshore wind are the most used foundations by farm operators due to their low production costs, when compared to other bottom-fixed or floating foundations. In this research, a monopile foundation for offshore wind power was evaluated for its soil interaction and grout behavior, and an appropriate numerical model for the structural analysis of the foundation and tower was developed. FAST 8, an aero-hydro-servo-elastic numerical code developed by NREL, was used to obtain the loads applied on the supporting structures. These loads were pre-processed before they were inputted on the finite element model, developed using the finite element software ANSYS. The considered conical grout connection, which connects the monopile to the transition piece through friction, was modeled under a changing-status nonlinearity condition. To model the soil–pile interaction, a p-y model was applied using the ANSYS APDL commands. Static, modal, and transient structural analyses were produced to study the structure suitability for its use on offshore environments. Different soil interactions were modeled, and their results were then compared within the transient and modal analysis, indicating that the angle of the grout connection strongly affects the loading conditions on the grout. Moreover, scouring affects the dynamic behavior of the overall supporting structures, thus protection against this phenomenon is suggested.

Variable Natural Frequency Damper for Minimizing Response of Offshore Wind Turbine: Effect on Dynamic Response According to Inner Water Level

“…Therefore, the DS method was used to economize the analysis process. The DS method was applied through the nonlinear spring element (COMBIN39) [43] for both lateral and vertical directions, as illustrated in Figure 4. COMBIN39 is capable of describing the nonlinear relationship between compression and tension stiffness (force-displacement) for transversal or torsional directions.…”

Seismic excitation of offshore wind turbines and transition piece response

“…Dynamic analyses were performed using implicit-explicit switching, with an initial implicit analysis to preload the structure, followed by dynamic excitation using the explicit solver, and finally followed by an implicit analysis to obtain the post-earthquake monotonic response. This numerical modelling scheme was chosen following work by Asnaashari et al 22 and Vieira et al 23 who demonstrated the effectiveness of 3D FE analysis to model grouted connections under static loads. Natural frequencies and modeshapes were determined using the Block Shift and Invert Lanczos method.…”

Damage detection of nonlinear structures using probability density ratio estimation

“…Figure 8 shows the spring stiffness curves for the undamaged state. In other words, the pile is supported by a series of nonlinear elastic springs, which simulate soil reactions, and the unloading occurs along the same loading curve (Carswell et al., 2015; Vieira et al., 2020). The considered damage was scouring (Devriendt et al., 2014; Prendergast et al., 2015), that is, erosion of the mudline near the foundation.…”