Ocean waves represent a significant source of renewable energy.
However, accessing and converting this energy requires working at the boundary of several physics domains: hydrodynamics, mechanics, electrical, and control.
This project explores the development of a multiphysics unifying modeling framework based on equivalent electrical circuits.
The two-body Reference Model 3 (RM3) wave energy converter (WEC) model is the initial working system, although future work will generalize the framework for any WEC.
The equations of motion for the RM3 are formulated in all 6 DOF and include the following forces: wave excitation, mooring, radiation damping, added mass, and hydrostatic stiffness.
Electrical circuits schematics are graphical language representing equalities and constraints on voltage, current, and power and can be used for linear and non-linear systems.
There are two options for modeling mechanical physics as an equivalent circuit: voltage as force and current as velocity; and voltage as velocity and current as a force.
For example, using current as force, a mass is represented as a capacitor, a spring as an inductor, and a damping force is represented as an admittance (i.e., reciprocal of resistance.
Non-linear damping effects can be represented by diodes; their native exponential relationship to voltage and current provide a natural basis function upon which to approximate other functions.
Other circuit elements, such as varistors, play an important role. Once the hydrodynamics, mechanics, electronics, and control can be represented as equivalent circuits, standard techniques such as Thevenin equivalents can collect and simplify the physics to enable better modeling and control. Since the wave energy used to have a dominant frequency, which has the prominent energy density presented in, for instance, the JONSWAP spectrum, matching the resonant frequency of the circuit will greatly increase the efficiency of the energy absorption on WEC. Once the resonant of the equivalent circuit representation is determined as controllable as changing the control technique in terms of the generator, the WEC can be optimized to harvest more energy.
This presentation will include an overview of the modeling framework and results compared to WEC-Sim.