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Determination of Moment of Inertia & Radius of Gyration of Flywheel (Part – II) 

Internal Flywheel Components

A typical system consists of rotor suspended by bearings inside a vacuum chamber to reduce friction, connected to a combination electric motor/electric generator. On larger systems, the bearings are magnetic. The rotors are generally made of steel on smaller systems but large systems use high-tensile-strength fibers (such as carbon fibers) embedded in epoxy resins, or some other high-strength composite material. Energy is stored by using an electric motor to increase the speed of the spinning flywheel. The system releases its energy by using the momentum of the flywheel to power the motor/generator.

Metal Flywheel Rotor

Energy is stored in the rotor in proportion to its momentum, but the square of the angular momentum. The kinetic energy stored in a rotating flywheel is:

where

ω is the angular velocity, and

I is the moment of inertia of the mass about the center of rotation.

• The moment of inertia for a solid-cylinder is ,


• for a thin-walled cylinder is ,


• and for a thick-walled cylinder is .

where m denotes mass, and r denotes a radius. More information can be found at list of moments of inertia

The amount of energy that can safely be stored in the rotor depends on the point at which the rotor will warp or shatter. The Hoop stress on the rotor is a major consideration in the design of a flywheel energy storage system.

where

σt is the tensile stress on the rim of the cylinder

ρ is the density of the cylinder

r is the radius of the cylinder, and

ω is the angular velocity of the cylinder.

Compiled by Samar Das