Date of Award

2012

Document Type

Master Thesis

Degree Name

Master of Engineering (Research)

Department

Civil, Structural & Environmental Engineering

First Advisor

David Cadogan

Abstract

A brief description of the various offshore foundation systems currently available is provided in this report, including the advantages and disadvantages for each system and water depth in which they can be used. These foundation types include floating structures, jacket structures, gravity base structures and the monopile foundation, on which this research specifically focuses.

The monotonic lateral loading of the monopile structure is also examined and the reasons why monotonic testing is required are highlighted, along with the potential analysis that can be generated to improve the design of the monopile foundation. A review of previous test programmes for monopiles is carried out, where the piles have been modified with steel wings to increase the bearing capacity of the monopile in the weaker upper soil layers. The results of the analysis show that the modified monopile system does appear to increase the capacity of the monopile whilst reducing the total lateral displacement at the top of the pile. This validates the reason for attaching wings to such piles and indicates the necessity for the pile to be tested under cyclic load conditions.

The cyclic loading of a monopile system is investigated. The potential analysis of cyclic loading to improve the design process is examined. The different types of cyclic loading that may occur on a monopile are considered, such as zero based loading and full reversal loading, as well as how they would occur in real environmental conditions. An appraisal in regard to the validity of using a sine wave to model the environmental conditions is undertaken. Previous test data is analysed to show how other research programmes determined failure of the pile and how the wings should theoretically behave under cyclic loading. In addition recommendations are offered in regard to the proposed testing series to be undertaken as part of this project, including the frequency at which the load will be applied and the number of cycles for which the test is expected to be run.

A variety of relevant software packages -that will be utilised throughout the research are examined, including how the software packages will analyse the monopile system as a whole unit and how the results will be validated to ensure the accuracy in predicting the displacement and loads at a given number of cycles.

Finally, conclusions are presented in regard to what have been identified as possible foundation solutions for an offshore wind turbine. Recommendations are provided in terms of the constant parameters used in the test series and the software that will be used to analysis it, while a relevant Journal to which the final paper of the research can be submitted is discussed.

Access Level

info:eu-repo/semantics/openAccess

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