Mooring lines analysis and design for wave energy converters

Student thesis: Doctoral Thesis

Abstract

Soon, wave energy converters will be anchored in several offshore locations for extended periods of time, where high wave energy exist. These devices moored in such areas experience continuous dynamic loads exerted mainly by colliding waves. Therefore, their mooring system is a fundamental component, which inuences overall performance characteristics through its dynamic behaviour.The mooring component of wave power devices has been typically analysed and designed by using a simplified static and quasistatic based approach and thus independent from the design of the oating structure dynamics. Given the peculiarities of mooring system design and analysis for wave energy devices, no particular available tools are suitable for analysing and design the mooring component as an integral active part of the entire moored system. All commercial software and codes available are in fact developed by having in mind different mooring requirements.Through this project, opportunities to improve entire moored system design were investigated. This study aimed to consider the potential option of designing mooring component as an integral dynamic part of the whole wave energy converter system. An overview of relevant existing studies is delineated, and a generic methodology, aiming at analysis and design moored wave energy system based on a fully dynamic approach, is proposed.For showing on how this can be applied, a particular focus on an Earth-reacting type of wave energy devices is made. Thus, a numerical code capable of analysing the dynamics, and predict performances of specific single tethered Earth-reacting wave energy converters, was developed. Through this code moored devices of any shape under regular or irregular seas' loads can be analysed.Both frequency-domain and time-domain mathematical formulations of the system considered are resolved by the proposed method. By using the comparison of numerical predictions with experimental data, the numerical code was validated for the specific cases of both, a half submerged and a fully submerged, spherical oaters. The accuracy of the proposed method was quantified.Results showed that the numerical method proposed is accurate, computationally efficient and well validated by the extensive experimental data, which was beside acquired during this project. Following the validation of the numerical tool, this last was used in two case studies. The outcome of these studies indicated that by using the proposed method, the trade-off between oater's immersion depth and mooring load peaks could be examined so that the optimal system design can be identified.The main advantage of the developed tool, compared to existing codes, is that this is tailored to the specific case of analysis and design for Earth-reacting wave energy converters. The new generic methodology proposed showed to be useful and suitable for analysing and design wave energy converters by including the mooring system as an integral component.
Date of Award1 May 2016
LanguageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsUniversity of Strathclyde
SupervisorAlexander Day (Supervisor) & (Supervisor)

Cite this