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This work focuses on the hydrodynamic performance analyses of three different types of flapping hydrofoils, in this case the pitch-heave (PH), left-swing (LS), and right-swing (RS) types, in their power extraction regimes via two dimensional CFD simulations. The power extraction performance is presented in an isocontour parametric map and is investigated from a comparison of the kinematics parameters and the development of unsteady vortices among the three types. It is found from the parametric analysis and comparison that the LS-type of flapping hydrofoil outperforms the PH and RS-types due to relatively high forces as well as the good synchronization of the forces and moment with the translational velocity and pitch angular rate, respectively upon the different aspects of the vortex development. Consequently, the power extraction performance improves from the LS to the PH and then to the RS-types. It is also recognized from another isocontour parametric map that the maximum power-extraction efficiency is achieved at a similar maximum effective angle of attack, at the maximum effective angle of attack rate, and at the maximum pitch angle rate for the LS and RS types, while the range of the maximum effective angle of attack rate is lower in the PH-type hydrofoil.

In recent years, nonlinear dynamic models have been developed for flapping-type energy harvesting systems with a rigid wing, but not for those with a flexible wing. Thus, in this study, flexible wing designs of NACA0012 section are proposed and measurements of the forces of rigid cambered wings, which are used to estimate the performance of the designed wings, are conducted. Polar curves from the measured lift and drag coefficients show that JavaFoil estimation is much closer to the measured values than Eppler over the entire given range of angles of attack. As the camber of the rigid cambered wings is increased, both the lift and drag coefficients increase, in turn increasing the resultant forces. Moreover, the maximum resultant forces for all rigid cambered wings are achieved at the same angle of attack as the maximum lift coefficient, meaning that the lift coefficient is dominant in representations of the wing characteristics. Keywords: Flapping-type energy harvesting system, Flexible wing, Cambered rigid wing, Wing characteristics, NACA0012

This paper describes the control design of the oscillation motion of hydroplane in dual system of lab-scale flapping type tidal energy harvester (FT-TEH).In dual system, two identical single systems of lab-scale FT-TEH are arranged cascade in the distance of a chord length of the hydroplane, wherein the flapping arm of each system is facing inward to each other. However, the pitch noses of hydroplanes are facing the same direction against the water flow. The controller is designed to control the motion of hydroplane such that each system is moving in synchronized motion to each other. Here, the system is using automatic gain controller with PID as the control feedback. Simulation and experiment results indicate that the controller of pitch oscillation for dual system of lab-scale FT-TEH is well implemented.

A lab-scale flapping-type turbine with a semi-passive activation mode has been designed and implemented. A non-linear dynamic model, developed in our previous work, is validated by a series of experiments along with computational fluid dynamics (CFD) simulations. Previously, the dynamic model was used only to estimate the dynamic response of a flapping-type turbine. In this work, the applicability of the dynamic model is extended to estimate the hydrodynamic forces, extracted power, and efficiency. It was demonstrated from a comparison of the CFD results and measured values that the dynamic model based on a quasi-steady approach estimates the aforementioned performance parameters of measurements well in cases particularly with a low effective angle of attack, thus demonstrating the usefulness of the dynamic model for a flapping-type turbine at an early stage.

This paper presents a mathematical model to predict the dynamic response of a lab-scale flapping-type tidal energy harvester. In the model, the forces produced by the hydroplane were derived based on a quasi-steady-state assumption, and no approximation was applied to the terms of the force equation. Therefore, the equation of motion becomes nonlinear; it was solved using the Runge–Kutta method. The mathematical dynamic model was validated through a series of experiments. Thereafter, the flapping speed of the system was estimated and compared with the measured speed. The comparison proved that the dynamic model reasonably estimates the flapping response, flapping speed, and generated forces. The dynamic model can be used for performance prediction of the lab-scale flapping tidal energy harvester and optimization of the scaled-up model in the future.

In this work, a dual flapping tidal current generator is developed and then validated in indoor and in-situ experiments. It is recognized from the indoor experiments that the dual flapping generation system is optimal at the reduced frequency, 0.125 in terms of power extraction. In the consecutive in-situ experiments, system power, 6.4kW and system efficiency 36.5 % are obtained. The dual power transmission, which is also developed for transferring the swing motion of the flappers to the rotational output shaft, is validated in the both experiments and amended into a simple and different arrangement.

We conducted a comprehensive study to investigate the aerodynamic characteristics and force generation of the elytra of a beetle, Allomyrina dichotoma. Our analysis included wind tunnel experiments and three-dimensional computational fluid dynamics simulations using ANSYS-CFX software. Our first approach was a quasi-static study that considered the effect of induced flapping flow due to the flapping motion of the fore-wings (elytra) at a frequency of around 30 Hz to 40 Hz. The dihedral angle was varied to represent flapping motion during the upstroke and downstroke. We found that an elytron produces positive lift at 0° geometric angle of attack, negative lift during the upstroke, and always produces drag during both the upstroke and downstroke. We also found that the lift coefficient of an elytron does not drop even at a very high geometric angle of attack. For a beetle with a body weight of 5 g, based on the quasi-static method, the fore-wings (elytra) can produce lift of less than 1% of its body weight.

In present, there are increasing interests in the research on mechanical and control system of underwater vehicles. These ongoing research efforts are motivated by more pervasive applications of such vehicles including seabed oil and gas explorations, scientific deep ocean surveys, military purposes, ecological and water environmental studies, and also entertainments. However, the performance of underwater vehicles with screw type propellers is not prospective in terms of its efficiency and maneuverability. The main weaknesses of this kind of propellers are the production of vortices and sudden generation of thrust forces which make the control of the position and motion difficult. On the other hand, fishes and other aquatic animals are efficient swimmers, posses high maneuverability, are able to follow trajectories, can efficiently stabilize themselves in currents and surges, create less wakes than currently used underwater vehicle, and also have a noiseless propulsion. The fish’s locomotion mechanism is mainly controlled by its caudal fin and paired pectoral fins. They are classified into Body and/or Caudal Fin (BCF) and Median and/or paired Pectoral Fins (MPF). The study of highly efficient swimming mechanisms of fish can inspire a better underwater vehicles thruster design and its mechanism. There are few studies on underwater vehicles or fish robots using paired pectoral fins as thruster. The work presented in this paper represents a contribution in this area covering study, design and implementation of locomotion mechanisms of paired pectoral fins in a fish robot. The performance and viability of the biomimetic method for underwater vehicles are highlighted through in-water experiment of a robotic fish.

In this study, we conduct experimental and consecutive numerical analyses of a flapping tidal current generator with a mirror-type dual configuration with front-swing and rear-swing flappers. An experimental analysis of a small-scale prototype is conducted in a towing tank, and a numerical analysis is conducted by means of two-dimensional computational fluid dynamics simulations with an in-house code. An experimental study with a controller to determine the target arm angle shows that the resultant arm angle is dependent on the input arm angle, the frequency, and the applied load, while a high pitch is obtained simply with a high input arm angle. Through a parametric analysis conducted while varying these factors, a high applied load and a high input arm angle were found to be advantageous. Moreover, the optimal reduced frequency was found to be 0.125 in terms of the power extraction. In consecutive numerical investigations with the kinematics selected from the experiments, it was found that a rear-swing flapper contributes to the total amount of power more than a front-swing flapper with a distance of two times the chord length and with a 90° phase difference between the two. The high contribution stems from the high power generated by the rear-swing flapper, which mimics the tail fin movement of a dolphin along a flow, compared to a plunge system or a front-swing system, which mimics the tail fin movement of a dolphin against a flow. It is also due to the fact that the shed vorticities of the front-swing flapper slightly affect negatively or even positively the power performance of the rear-swing system at a given distance and phase angle.

A flapping-type turbine extracts power from the kinetic energy of water stream by heaving up and down. A nose-up pitch angle will create an upstroke motion of the flapping arm and vice versa for nose-down pitch. These upstroke and downstroke motion will then be converted into a continuous rotary motion of an output shaft by a transmission system. In this work, we describe our current progress on the development of design and prototype implementation of a flapping-type tidal energy harvester and introduce the dynamic model and its experimental validation together with power and efficiency.