Optimization of pile design for offshore wind turbine jacket foundations
The aim of this study is to use numerical methods of structural design optimization to design piles for offshore wind turbine jacket foundations. Pile mass is minimized with constraints on axial and lateral capacity. Results indicate that accurate knowledge about soil characteristics can translate into significant cost reductions. NOMENCLATURE d External diameter of the pile (m) di Internal diameter of the pile (m) l Length of the pile (m) t Thickness of pile wall (m) INTRODUCTION Foundation and substructure for offshore wind turbines can amount to more than 20 of the capital expenditure in a project. Pile anchoring a jacket foundation to the seabed requires to first perform a geological survey to map the soil characteristics and then design a pile with sufficient capacity to carry the loads from the substructure. Structural optimization [1] is the science of achieving the optimal load carrying structure. Given an objective such as compliance or cost, and some constraints such as limitations on the maximum stress or displacement, the optimal structure is defined as the one that minimizes the objective function while satisfying the constraints. A pile foundation is a slender hollow cylinder that is inserted into the soil. Anchoring by driven piles has been used extensively in the oil and gas industry, and in the last decade also for offshore wind turbines using either monopiles or piled jacket foundations. Pile foundation design is considered in this study according to the current state of practice for offshore foundations, see eg. [2] [3] Axial and lateral capacities are calculated based on shaft friction and end bearing resistance and lateral resistance respectively. The obtained ultimate loads formulate the design basis.