  A fully-coupled-fluid-structure-piezoelectric model is presented based on the
finite element method that is capable of modeling piezoelectric harvesters in
the presence of free-surface flow and floating lightweight harvesters with
arbitrary movements. The Navier-Stokes equations and the phase-field method are
employed to describe the free-surface waves. Equations of the conservation of
linear momentum in company with the piezoelectric constitutive relations in the
strain-charge form are utilized to obtain solid deformation and the electric
field intensity. According to the results, attaching mass to the tip of the
beam leads to 13.5% rise in the output voltage compared to the state without
the attached mass. Another studied factor was the influence of the load
resistance on voltage and the output power. The generated voltage grows along
with the load resistance until it reaches a constant value. However, the power
has an optimum load resistance that is 2.61 times higher than the reference
state. The beam's inclination is significant in effectively exploiting water
waves due to raising the root mean square (RMS) value of the voltage by 89.53%
at an angle of 40 degrees relative to the vertical state. By altering the
thickness of the beam from 1 mm to the value of 1.5 mm, the RMS voltage
exhibits a considerable upward change of 66%. By increasing the length of the
cantilever beam connected to the buoyant structure, and therefore, the
indentation of the beam in the water, the output voltage grows, such that a
beam with the length of 25 cm shows a 2.92 times increase in the output voltage
relative to the beam with a length of 15 cm.
