Abstract
Suction caisson foundations provide options for new foundation systems for offshore structures, particularly for wind turbine applications. During the foundation design process, it is necessary to make reliable predictions of the stiffness of the foundation, since this has an important influence on the dynamic performance of the overall support structure. The dynamic characteristics of the structure, in turn, influence its fatigue life. This paper describes a thermodynamically consistent Winkler model, called OxCaisson, that delivers computationally efficient estimates of foundation stiffness for caissons installed in homogeneous and non-homogeneous linear elastic soil, for general six degrees-of-freedom loading. OxCaisson is capable of delivering stiffness predictions that are comparable to those computed with three-dimensional finite-element analysis, but at a much lower computational cost. Therefore, the proposed model is suited to design applications where both speed and accuracy are essential, such as large-scale fatigue assessments of offshore wind farm structures. The paper demonstrates that the OxCaisson model can also be applied to short, rigid monopile foundations.
Highlights
There is increasing interest in employing suction caisson foundations for offshore wind turbine support structure applications, because of potential advantages such as quiet installation, faster installation and simpler decommissioning (Byrne & Houlsby, 2003) compared with other foundation options
This paper describes a new design model – ‘OxCaisson’ - to predict the stiffness of suction caisson foundations, especially for wind turbine support structure applications
It can be observed that there is some under-prediction for KM and KC
Summary
There is increasing interest in employing suction caisson foundations ( referred to as suction bucket foundations, see Fig. 1a) for offshore wind turbine support structure applications, because of potential advantages such as quiet installation (important for projects with noise restrictions), faster installation and simpler decommissioning (Byrne & Houlsby, 2003) compared with other foundation options. The design of suction caissons in this application relies on the availability of efficient procedures to predict foundation stiffness (relevant to dynamic analyses of the overall structure) and strength (to facilitate the analysis of storm loading events). The range of available design procedures for suction caissons in this application is rather more limited than is the case for monopile foundations, which are currently the dominant foundation system for offshore wind turbines in shallow waters. This paper describes a new design model – ‘OxCaisson’ - to predict the stiffness of suction caisson foundations, especially for wind turbine support structure applications. The design model is developed for full six degrees-of-freedom loading and is calibrated for homogeneous and non-homogeneous elastic soils for which the stiffness varies with depth. OxCaisson is fast to compute; it is well-suited to the design of offshore wind farms, which typically require a large number of computations to assess different foundation geometries and wind farm layouts to determine optimal configurations
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