Matthew Burns

Date of Award

8-2013

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Civil Engineering

Advisor

Melissa Landon Maynard

Second Committee Member

William Davids

Third Committee Member

Thomas Sandford

Abstract

The Department of Energy has specified that offshore wind become an important component of the U.S. energy portfolio in the near future. Floating substructures are the most cost effective option for offshore wind turbine development in deeper water. In order to address the need for efficient and cost effective anchoring of floating offshore wind, a novel solution by which a single anchor is used to anchor multiple floating wind platforms is proposed. Within such a system, a network of interconnected foundations mooring multiple devices has the potential to reduce cost by reducing the number of site investigation and foundation locations.

The research aims to investigate the design and performance of multi-line loaded suction caisson foundations for floating offshore wind turbine platforms. Suction caissons are large diameter cylinders that are closed at the top and open at the bottom that are installed into the seabed by penetration of the open end into the seafloor first under self weight. Water is then pumped out from inside the caisson, creating a pressure differential allowing for complete installation. Installed, a suction caisson resists lateral and axial loading as does a pile. The added resistance due to the development of passive suction, in addition to reduced installation costs makes suction caissons an attractive option for foundation systems.

Research is conducted through numerical modeling using the finite element software ABAQUS to predict capacity and deformation behavior of a suction caisson under orthogonal multi-line loading. The numerical model is validated against published data for single line loading and is then modified to include double line simulations. The robust model predicts caisson capacity under multi-line loading for comparison to multi- line centrifuge testing obtained in conjunction with the research project. Parametric models are developed to investigate the effects of varying load inclination angle for each line, combinations of monotonic and sustained loading, pad-eye location, and circumferential pad-eye distribution. A simplified method to implement cyclic degradation within the ABAQUS framework is presented and compared with published results.

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