Constrained multi-objective optimization of a hydraulic flywheel accumulator

Improving energy storage technology is an important means of addressing concerns over fossil fuel scarcity and energy independence. Traditional hydraulic accumulator energy storage, though favorable in power density, durability, cost, and environmental impact, suffers from relatively low energy density and a pressure-dependent state of charge. The hydraulic flywheel accumulator concept utilizes both pneumatic and kinetic energy domains by employing a rotating pressure vessel. This paper describes a mathematical model of the hydraulic flywheel accumulator and presents the results of a multi-objective optimization of the associated design parameters. The two optimization objectives are to minimize the total system mass and minimize the total energy converted between the pneumatic and kinetic domains during operation. These objectives are pursued by varying five design parameters: accumulator radius, wall thickness, and length; end cap length; and maximum angular velocity. Constraints on combinations of these design parameters are imposed by material stress, as well as the energy capacity required to complete a specified drive cycle. This optimization approach can be used to guide the design of a hydraulic flywheel accumulator for a variety of different applications.