Oral Defense of Doctoral Dissertation – Computational Sciences and Informatics – Gautami D. Erukulla – Coupled Dynamic Analysis of Moored Wave Energy Converters in Waves

Notice and Invitation
Oral Defense of Doctoral Dissertation
Doctor of Philosophy in Computational Sciences and Informatics
Department of Computational and Data Sciences
College of Science
George Mason University

Gautami D. Erukulla
Bachelor of Science, Osmania University, 2003
Master of Science, Jawaharlal Nehru Technical University College of Engineering, 2006
Master of Science, George Mason University, 2010

Coupled Dynamic Analysis of Moored Wave
Energy Converters in Waves

Tuesday, April 10, 2018, 1:30 p.m.
Research Hall, Room 162

All are invited to attend.

Committee
Chi Yang, Dissertation Director
Rainald Löhner
Juan Cebral
Dhafer Marzougui

Abstract:

Waves have the potential to provide a clean and sustainable source of energy that can be captured and converted into electricity by the Wave Energy Converters (WECs). These devices are restrained by a mooring system and there exists a strong coupling between the dynamic response of the WEC and the mooring system. An accurate study of moored wave energy converter (WEC) requires a coupled analysis that considers the dynamics of the mooring system when computing the dynamics of the WEC. However, the conventional methods of marine design do not fully address the coupling effects of the moored WECs. Therefore, there is a need for a further development of coupled analysis methods. The aim of this research is to develop a coupled model to investigate the motion response of moored WEC in waves.

This dissertation work is divided into three stages. In stage one, a computational tool for static and dynamic analysis of mooring cable is developed. The mooring cable considered in this research is treated as an inextensible elastic slender rod, and the Slender Rod Theory is thus used to derive the governing equations for the mooring cable dynamics. The finite element method is chosen to solve the governing equations. Validation studies are performed for various mooring systems. The numerical solutions obtained using the developed mooring program show a good agreement compared to analytical solutions, experimental data, and MAPS mooring program.

In the second stage, a numerical wave tank is developed and fluid structure interaction simulations are performed, using open source CFD solver OpenFOAM extended with wave generation tool box waves2Foam. Numerical results of the wave tank simulations show a fairly good agreement with those evaluated by the second-order Stokes wave theory. Validation studies of green water impact on a fixed 3D body with and without a vertical wall on the deck are performed to ensure that waves2Foam can simulate highly nonlinear waves. The computed results are compared with the experimental measurements, and the agreements are satisfactory.

Finally, in stage three, a coupled model is developed by integrating the mooring program to the CFD solver OpenFOAM.  Several coupled analyses of a point absorbing WEC in regular and irregular waves are performed. The results show that the hydrodynamic characteristics of the WEC in regular waves are accurately predicted.  The numerical results of mooring cable tension time history demonstrate the good accuracy and stability of the mooring program. Numerical results show that the present coupled model is able to perform the coupled dynamic analysis in the resonance region effectively, where the device undergoes the largest motion and transfers maximum energy. In addition, the coupled analysis of WEC subjected to bichromatic wave train and JONSWAP wave spectrum have been conducted and reliable results have been obtained. The developed coupled model is employed to study of motion response of WEC in a regular wave with varying mooring cable pretensions. 2D/3D analysis of WEC in regular wave, restrained with two catenary mooring cables is investigated using the coupled model. Thus, it can be stated that the coupled model developed in this study can successfully simulate the dynamics of the moored WEC in waves, which is of practical importance to the study of the mooring cable effects and the design of the effective and efficient WEC.

A copy of Gautami’s dissertation is available for examination from Karen Underwood, Department of Computational and Data Sciences, 227 Research Hall. The dissertation is available to read only within the Department and cannot be taken out of the Department or copied.