Drag forces on vegetation due to waves and currents

The research focused on the variation trend of drag coefficient with Keulegan-Carpenter number in vegetation mimics in pure wave and combined current-wave flow conditions. Experiments were carried out in the Environmental Fluid Mechanics Laboratory at Delft university of Technology. Completion of this thesis was only made possible with the help of many people who graciously shared their time, expertise and encouragement. First, I would like to extend great thanks to the faculty supervisor and committee chair, Prof. Dr. Ir. Uijttewaal W.S.J, who provided invaluable supervison and support in terms of expertise and access to the laboratory facilities. Secondly, I sincerely appreciate the supervision and evaluation made by other committee members: Ir. Zitman T.J. and Mr. Hu Zhan. Moreover, I would like to extend my thanks to all of the laboratory stuff at TU Delft, most notably Mr. Sander de Vree for helping me daily with experimental issues. In addition, I acknowledge Dr. Tjeerd Bouma for offering force sensors. In addition, I would like to thank Mr. Hu Zhan and Ms. Mirjam Flierman and Ir. Lorraine Buckman in providing the help in experimental data collection and processing. Finally, from the bottom of my heart, I would like to express my thanks to my parents and friends. Great thanks are extended for my parents who gave me full support both financially and mentally during my pursuing this master degree. Moreover, the tremendous encouragement from my friends helps me a lot in living through the tough time. Thank you very much! ii iii Summary Vegetation in coastal areas plays an important role in its environment. In addition, vegetation can also be utilized for coastal protection. Incoming wave energy could be effectively attenuated by the upstanding vegetation plants. The reduced wave energy results in stabilized seabed and harmonious environment in coastal zones. Nowadays, an increasing number of projects have been carried out to apply vegetation as a soft measure for coastal protection. Wave energy dissipation by vegetation is primarily induced by the work done by drag force acting on the vegetation. A drag coefficient (C D) is introduced to characterize the flow resistance from the plant stems. Knowledge of C D is of great importance for understanding and predicting the wave dissipation process. In previous studies, relations between C D and Reynolds number (Re) have been proposed in pure current or pure wave. In addition, relations between C D and the Keulegan-Carpenter number (abbreviated …