## Linear Machines

Electrical machines are almost exclusively of a rotary configuration, primarily due to their application. Notable exceptions to this, where some research has been performed, are for transportation purposes (levitating high speed trains, 'Maglev'), projectile launchers or small biomedical actuators [60]. These are all high speed operations, with the electrical machine acting as an actuator / motor. For marine renewable applications, as demonstrated in previous chapters, the concept of a linear machine offers the opportunity to simplify the mechanics of the system if it can be used as a slow speed generator. The guiding principles for rotary and linear machines are identical, simply in a different plane of motion. As such, all equations describing a rotary machine are equally applicable to a linear machine, with the slight modification of some terms, such as torque to force. Conceptually, a linear machine can be thought of as the circumference of its rotary counterpart flattened out. Figure 3.1 shows the basic form of a linear machine being derived from its rotary counterpart.

Figure 3.1: Imaginary process of unrolling rotational machine to obtain linear counterpart

The power absorbed by a linear machine is equal to the product of the reactive force it can deliver and the velocity at which it is displaced. In order to develop greater power for a given velocity, therefore, it is necessary to be able to exert a greater force. It follows that the specific shear stress, the force per unit area of the active airgap, provides a valid basis on which to asses machine topologies.

All the machines in this chapter consist of a stationary part, referred to as the stator, and a moving part, referred to either as the translator, or as with its rotary counterpart, the rotor.

## Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

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