State-Dependent Model of a Hydraulic Power Takeoff for an Inverse Pendulum Wave Energy Converter
Authors: Zhang Dahai , Huang Haocai , Chen Ying , Zhao Haitao , Li Wei 
Published: October 2015

AbstractThis article reports on a state-dependent model of a hydraulic power takeoff (PTO) for an inverse pendulum wave energy converter. The PTO influences the energy conversion performance by its efficiency and by the damping force exerted, which affects the motion of the
body. The state-dependent model presented gives a description of the damping force and the internal dynamics of the hydraulic PTO system. Different values of the parameters of the accumulator and the motor torque are analyzed in order to improve the dynamic performance of the converter. The
simulation results prove that it is possible to achieve a great enhancement of the power output with the implementation of optimization parameters of the hydraulic PTO and that a possible combination of some of them might be beneficial for improved efficiency of the system. <def-list>Nomenclature<def-item><term>A
:</term><def>pipe cross-section area</def></def-item><def-item><term>B :</term><def>rotational friction coefficient</def></def-item><def-item><term>Dh :</term><def>pipe
hydraulic diameter</def></def-item><def-item><term>Fy :</term><def>damping force</def></def-item><def-item><term>L :</term><def>angular momentum of the motor</def></def-item><def-item><term>Leq
:</term><def>equivalent length of local resistances</def></def-item><def-item><term>Lg :</term><def>pipe geometrical length</def></def-item><def-item><term>J :</term><def>inertia
momentum</def></def-item><def-item><term>kl :</term><def>motor leakage coefficient</def></def-item><def-item><term>kS :</term><def>pipe cross-section shape factor</def></def-item><def-item><term>pa
:</term><def>accumulator pressure</def></def-item><def-item><term>pd :</term><def>pressure drop along the pipe</def></def-item><def-item><term>pp :</term><def>oil
pressure</def></def-item><def-item><term>ppr :</term><def>precharged pressure of accumulator</def></def-item><def-item><term>qa :</term><def>accumulator flow</def></def-item><def-item><term>qleak
:</term><def>leakage flow from motor</def></def-item><def-item><term>qm :</term><def>motor flow</def></def-item><def-item><term>qp :</term><def>oil flow</def></def-item><def-item><term>Re
:</term><def>Reynolds number</def></def-item><def-item><term>R :</term><def>set point for damping force</def></def-item><def-item><term>S :</term><def>piston cylinder cross-section
area</def></def-item><def-item><term>Tf :</term><def>losses due to rotational friction</def></def-item><def-item><term>TG :</term><def>generator torque</def></def-item><def-item><term>Tm
:</term><def>motor torque</def></def-item><def-item><term>Ts :</term><def>losses due to rotational momentum</def></def-item><def-item><term>V :</term><def>oil volume</def></def-item><def-item><term>VA
:</term><def>accumulator volume</def></def-item><def-item><term>V :</term><def>piston velocity</def></def-item><def-item><term>ηm :</term><def>mechanical efficiency
of the motor</def></def-item><def-item><term>ωm :</term><def>angular velocity of the motor</def></def-item><def-item><term>ρ :</term><def>oil density</def></def-item></def-list>