How do ocean waves transfer energy?

Answer 1

Note: This discussion is about the transfer of energy from waves in water. Light waves, sound waves etc. are not discussed. Let's begin at the beginning: Ocean waves are an example of a mechanical wave where in the energy of the wave is carried by the water. The source, whatever it is, acts in a way to transfer energy into the water. It applies a force on or to the water, and the water "accepts" the energy and it is carried out away from the source by or in the form of a wave. The force displaces the water in some way, and this transfers energy into the water. Without beating up the issue, let's do a simple experiment. You walk out onto a dock that is low to the very calm water of a pond. You have a bottle and a clipboard. You kneel down at the end of the dock, and, grasping the bottle by the neck, lower it onto the surface of the water. Then you push gently down on it and pull up the same amount in a gentle "pumping" action. You'll generate a wave with each "pump" by displacing the water. Set the bottle aside and pick up the clipboard. By grasping it at the top and holding it upright, you can lower the bottom edge into the water. Slip it in a couple of inches. Now "sweep" the clipboard out and back gently. If you can imagine the clipboard as a paintbrush, you're "painting" the water with that out-and-back motion. You'll be displacing water with each "stroke" and this will generate the wave. The direction the force acts is different in each case, but the result is the same. The application of force to a fluid acts to displace it, and this transfers mechanical energy into the medium. The mechanical energy is expressed (or "carried" or "transferred") as a mechanical wave in the fluid. The energy in waves results from wind on water. This makes wave energy a derivative of wind energy.

The transfer of energy from waves can be looked at in two ways - impact of waves on surfaces standing in the waves (dykes, sea-walls etc) and secondly the transfer of energy to collection devices in "Wave Farms" 1. Kinetic Impact of Waves

In a wave one of the motions of the water is a forward motion of the water. This is caused by the effect of wind on the water making a moving mound of water. When this mound of water runs into an obstacle it is similar to any object running into an object. The kinetic energy is transferred to the object, which, if stationary, reflects it back into the wave. After repeated wave strikes the object may became increasing less stable and eventually move away from the wave.

A special case of this type of wave is the Tidal Wave caused by an earthquake. The initial source of energy is different but the physics are the same as regards the wave.

2. Transformation of Wave Energy in Wave Farms

Waves also have an up and down motion. Any time there is this cyclic type of motion it is possible to harness it for energy production.

In the simplest case there are floats on the surface of the water. The lifting and falling of the floats activates a subsurface crank through a chain. The rotating crank turns a generator creating electric power which is sent to shore by standard cables.

In a slightly more complex case the waves activate pumps in the same manner as they activate the generators. The pumps send water to a reservoir on shore which is constructed at some height. Water is drained from the reservoir to turn turbines which produce electricity. This is connected to the electricity grid and becomes part of the normal supply.

3. Related Energy Recovery

A specific type of wave, a tidal bore, occurs when the tides enter a narrow estuary such as Canada's Bay of Fundy. Since tides are created by the gravitational force of the moon this is a conversion of gravitational energy to electricity. The water can be trapped by creating dams that allow this water's entrance but not egress. The water is drained from the up stream side of the dyke during low tide through a generator to produce energy.