MARINE APPLICATIONS OF FLAPPING FOILS/PLATES TO THE STATIONKEEPING SYSTEM

Abstract

Flapping motion is very common in nature. It’s basically used for propulsion and maneuvering by birds, fish and many other species in air and water. Also, studies proved that the flapping motion has the capability of producing high instantaneous forces. In the ocean, when a hydrofoil placed horizontally close to the free surface, the hydrofoil can flap and generate thrust forces against the wave propagation using wave energy, famously called “wave devouring propulsion”. However, the exact estimation of forces generated by flapping remains a challenge for the researchers. Therefore, the uses of flapping are not so common in man-made structures. In this study, an elastic plate was used that was fixed at one end and attached to the leading edge of the hydrofoil or flat plate from another end. This setup minimizes the complexity of the flapping in water such as no phase lag between heave and pitch motions of the hydrofoil. The passive flapping foil/plate experiments were carried out for various wave conditions in a wave flume at Widetank, UOU. The aim of the experiment was to use the flapping foil/plate to the stationkeeping system therefore, the model was flapping at a set location and the generated thrust forces were recorded using a load cell. Further, empirical formulas are derived for the thrust estimation of flapping foil and flapping plate using dimensional and regression analysis based on experimentally recorded data. The effects of the elastic plate on thrust generation and the resultant thrust force generated by a group of flapping foils are also experimentally recorded and reported in this thesis. The experimentally recorded data were validated with the fluid-structure interaction (FSI) numerical simulation using ANSYS Workbench 19.2. It was a challenge to deal with 2-way FSI simulation with multiphase flow due to its complexity in defining geometries, the interaction between a fluid and solid and requirements of computational resources. Results confirmed that the passive mode flapping wasn’t effective for stationkeeping in short waves. Therefore, the active flapping foil was modeled and thrust generated by it in short waves using numerical simulation was reported. Finally, the effects of azimuth angles of flapping foil on the thrust force in the passive mode were reported in the thesis.