Chongwei Zhang

Analytical Study on an Oscillating Buoy Wave Energy Converter Integrated into a Fixed Box-Type Breakwater

An oscillating buoy wave energy converter (WEC) integrated to an existing box-type breakwater is introduced in this study. The buoy is installed on the existing breakwater and designed to be much smaller than the breakwater in scale, aiming to reduce the construction cost of the WEC. The oscillating buoy works as a heave-type WEC in front of the breakwater towards the incident waves. A power take-off (PTO) system is installed on the topside of the breakwater to harvest the kinetic energy (in heave mode) of the floating buoy. The hydrodynamic performance of this system is studied analytically based on linear potential-flow theory. Effects of the geometrical parameters on the reflection and transmission coefficients and the capture width ratio (CWR) of the system are investigated. Results show that the maximum efficiency of the energy extraction can reach 80% or even higher. Compared with the isolated box-type breakwater, the reflection coefficient can be effectively decreased by using this oscillating buoy WEC, with unchanged transmission coefficient. Thus, the possibility of capturing the wave energy with the oscillating buoy WEC integrated into breakwaters is shown.

Analytical Study on a Concentric Cylindrical OWC Wave Energy Converter

A novel cylindrical-shape oscillating water column (OWC) wave energy converter with dual-chamber is proposed to harvest wave energy effectively in deep water. The analytical model is developed to investigate its hydrodynamics based on linear potential flow theory and eigenfunction expansion technique. The computational domain is divided into six sub-domains. The unknowns are solved by matching the continuous conditions of fluid velocity and velocity potential between neighboring sub-domains. A pneumatic model is adopted to describe the relationship between air pressure in the chamber and turbine characteristics. The comparison between the results of the single- and dual-chamber OWCs shows that the effective frequency bandwidth of the dual-chamber OWC is broader than that of the single-chamber OWC.

Numerical modelling of nonlinear extreme waves in the presence of wind

A numerical wave flume with fully nonlinear free surface boundary conditions is adopted to investigate the temporal characteristics of extreme waves in the presence of wind at various speeds. Incident wave trains are numerically generated by a piston-type wave maker, and the wind-excited pressure is introduced into dynamic boundary conditions using a pressure distribution over steep crests, as defined by Jeffreys’ sheltering mechanism. A boundary value problem is solved by a higher-order boundary element method (HOBEM) and a mixed Eulerian-Lagrangian time marching scheme. The proposed model is validated through comparison with published experimental data from a focused wave group. The influence of wind on extreme wave properties, including maximum extreme wave crest, focal position shift, and spectrum evolution, is also studied. To consider the effects of the wind-driven currents on a wave evolution, the simulations assume a uniform current over varying water depth. The results show that wind causes weak increases in the extreme wave crest, and makes the nonlinear energy transfer non-reversible in the focusing and defocusing processes. The numerical results also provide a comparison to demonstrate the shifts at focal points, considering the combined effects of the winds and the wind-driven currents.

Hydrodynamic performance of an oscillating wave surge converter in regular and irregular waves: an experimental study

A series of physical experiments are carried out to investigate the hydrodynamic performance of a bottom-hinged flap-type oscillating wave surge converter (OWSC). The power take-off (PTO) system in ...

Analytical Study of Transient Coupling between Vessel Motion and Liquid Sloshing in Multiple Tanks

AbstractThe transient coupling between the vessel motion and liquid sloshing in multiple tanks is investigated. External disturbance factors (e.g.,xa0spring constraint or force field) that might affect the oscillation characters of the coupling system are not involved so that the vessel motion is only excited by the liquid sloshing in tanks. The analytical solution for this coupling problem has been derived based on the potential flow theory, which converts the problem to a linear system of ordinary differential equations. The approach to determine natural frequencies of the coupling system is also given. The vessel with one or more rectangular tanks is considered for cases studies. Effects of factors, such as vessel mass, number of tanks, tank configuration and free-surface deformation on the vessel motion, liquid sloshing, and mechanical-energy components of the system are studied systematically.