Energy Efficiency Analysis of Multi-Type Floating Bodies for a Novel Heaving Point Absorber with Application to Low-Power Unmanned Ocean Device

Abstract

Long-term energy supplies hinder the application of the low-power unmanned ocean devices to the deep sea. Ocean wave energy is a renewable resource with amount stores of enormous and high density. The wave energy converter (WEC) could be miniaturized so that it can be integrated into the devices to make up the power module. In this paper, a small novel heaving point absorber of energy supply for low-power unmanned ocean devices is developed based on the counter-rotating self-adaptive mechanism. The floating body as an important part of the heaving point absorber, the geometric parameters is optimized to increase the efficiency of power production. Through constructing the constitutive relation between the geometric parameters, the wave force, the motion displacement, the motion velocity, and the capture width ratio of the floating body, the energy efficiency characteristics of the multi-type floating bodies are calculated, and the optimal shape is selected. On the other hand, in the calculation process of the wave force, the Froude-Krylov method is an effective method to accurately calculate the wave excitation force. Meanwhile, nonlinear static and dynamic Froude-Krylov force effectively overcomes the inaccuracy of the linear models and reduces the time consumed to simulate. Finally, the wave force, heaving velocity, heaving displacement, and capture width ratio of the three floating bodies are compared and analyzed, and the results show that the cylindrical floater that is vertically placed on the wave surface is more suitable for the novel heaving wave energy point absorber.

Using Flexible Blades to Improve the Performance of Novel Small-Scale Counter-Rotating Self-Adaptable Wave Energy Converter for Unmanned Marine Equipment

“…Among them, η ext is an important characteristic parameter of WEC surface buoy, which has been studied in detail by our research group [33]. Generator is a standardized industrial product with mature technology, and its performance characteristics were fully studied.…”

“…The surface buoy is in direct contact with the sea surface waves and is affected by the wave radiation-diffraction effect. Based on the existing research basis [33], the energy conversion characteristics of surface buoy are preliminarily studied and evaluated.…”

“…Assuming that the water around the surface buoy is non-viscous, irrotational and incompressible, and considering the interaction of wave motion and surface buoy, the dynamic equation of the surface buoy can be expressed as [33,36]:…”

“…The research group also conducted a theoretical study on the effects of different types of surface buoys on WEC performance characteristics. The constitutive relations of wave forces, motion and geometric parameters of surface buoys with different geometric shapes were constructed, and the capture efficiency of wave energy of various types of surface buoys was investigated [33]. In the verification experiments, we found that the rigid blade WEC could adapt well to the wave motion, drive the upper and lower absorbers to generate electric energy.…”

Boussinesq Model and CFD Simulations of Non-Linear Wave Diffraction by a Floating Vertical Cylinder

“…Using a fully non-linear numerical method and potential flow, the results of wave scattering by a vertical cylinder were compared with experiments and low-order perturbation results in [20]. A small heaving point absorber for low-power ocean devices was developed [21] based on the counter-rotating self-adaptive mechanism and numerical simulation to study the vertical force, heaving displacement and velocity, and width ratio of the multi-floating bodies. A numerical study of wave run-up on fixed cylinder using OpenFOAM was also performed [22].…”