  This paper proposes a novel design of liquid tank with built-in buoys for
wave energy harvesting, named the 'sloshing wave energy converter (S-WEC)'.
When the tank is oscillated by external loads (such as ocean waves), internal
liquid sloshing is activated, and the mechanical energy of sloshing waves can
be absorbed by the power take-off (PTO) system attached to these buoys. A
fully-nonlinear numerical model is established based on the boundary element
method for a systematic investigation on dynamic properties of the proposed
S-WEC. A motion decoupling algorithm based on auxiliary functions is developed
to solve the nonlinear interaction of sloshing waves and floating buoys in the
tank. An artificial damping model is introduced to reflect viscous effects of
the sloshing liquid. Physical experiments are carried out on a scaled S-WEC
model to validate the mathematical and numerical methodologies. Natural
frequencies of the S-WEC system are first investigated through spectrum
analyses on motion histories of the buoy and sloshing liquid. The viscous
damping strength is identified through comparisons with experimental
measurements. Effects of the PTO damping on power generation characteristics of
S-WEC is further explored. An optimal PTO damping can be found for each
excitation frequency, leading to the maximisation of both the power generation
and conversion efficiency of the buoy. To determine a constant PTO damping for
engineering design, a practical approach based on diagram analyses is proposed.
Effects of the buoy's geometry on power generation characteristics of the S-WEC
are also investigated. In engineering practice, the present design of S-WEC can
be a promising technical solution of ocean wave energy harvesting, based on its
comprehensive advantages on survivability enhancement, metal corrosion or
fouling organism inhibition, power generation stability and efficiency, and so
on.
