Waves Transferring energy in the ocean

Waves Essential Questions What forces cause waves? What forces cause the ocean to return to its original level after a wave has occurred? How does the depth of the water determine if a wave is a deep-water or shallow water waves? Can all waves be both deep-water and shallow-water waves? How does the speed of a shallow water wave differ from that of a deep-water wave? What occurs as a wave train moves toward shore? When will a wave break? What are the three types of breakers? What occurs when a wave line approaches the shore at an angle? What occurs when waves reach an obstacle? What occurs when waves hit a barrier? What occurs when waves meet? What causes a tsunami? What type of wave is a tsunami? What destruction can be reached by a tsunami? How can wave energy be harnessed? Is harnessing energy from waves practical? A wave is the transmission of energy through matter. Key word is “through.” When energy moves through matter as a wave, matter moves, but overall doesn’t shift forward or backward. It transmits the energy to adjacent matter, allowing the energy to continue. NOAA Ocean Explorer

Wave vocabulary breaker crest deep water wave diffraction disturbing force interference plunging breaker reflection refraction restoring force seiche shallow water wave spilling breaker surging breaker trough tsunami wave wave frequency wave height wave length wave period wave train

WHAT ARE THEY? Waves …

What is a wave? A wave can be described as a disturbance that travels through a medium from one location to another location. It’s ENERGY!

Types of waves There are three types of progressive waves: 1.Longitudinal waves ‒ move through all states of matter and ‒ occur when energy moves in the same direction that the energy travels. 2.Transverse waves ‒ only transmit through solids. ‒ They occur when the energy motion is perpendicular to the travel direction. 3.Orbital waves ‒ only transmit through fluids. ‒ They occur when the energy moves the fluid in a circular motion as it passes.

Types of waves Longitudinal Wave Video Transverse Wave Video Orbital Wave VideoOrbital Wave Video 12:32 Introduction to WavesIntroduction to Waves (11:51)

OCEAN WAVES Different types of …

What generates waves? Energy that causes ocean waves to form is called a disturbing force. These forces include: –wind (wind waves), –changes in atmospheric pressure (seiches) –storm surges, –faulting of the seafloor, volcanic eruptions and landslides (tsunami) and, –gravitational attraction and the rotation of the Earth (tides). The ocean’s surface is returned to its original level by either surface tension or gravity. These are called restoring forces.

Wind waves Wind waves or, more precisely, wind- generated waves are surface waves that occur on the free surface of oceans, seas, lakes, rivers, and canals or even on small puddles and ponds. They usually result from the wind blowing over a vast enough stretch of fluid surface. Waves in the oceans can travel thousands of miles before reaching land. Wind waves range in size from small ripples to huge waves over 30 m high.

Wind wave formation Five factors influence the formation of wind waves: –Wind speed or strength relative to wave speed- the wind must be moving faster than the wave crest for energy transfer –The uninterrupted distance of open water over which the wind blows without significant change in direction (called the fetch) –Width of area affected by fetch –Wind duration - the time over which the wind has blown over a given area –Water depth

Seiches A seiche (from a French word meaning “to sway back and forth”) is a standing wave in an enclosed or partially enclosed body of water. Seiches and seiche-related phenomena have been observed on lakes, reservoirs, swimming pools, bays, harbours and seas. The key requirement for formation of a seiche is that the body of water be at least partially bounded, allowing the formation of the standing wave.

Storm surges A storm surge is a temporary offshore rise of water level associated with a low pressure weather system, typically tropical cyclones and strong extratropical cyclones. Storm surges are caused primarily by high winds pushing on the ocean's surface. Sometimes called “storm set-up”, “wind set-up”, “storm-induced rise”, or “storm rise.” NOAA Storm Surge Page

Tsunamis A tsunami is a series of water waves caused by the displacement of a large volume of a body of water, generally an ocean or a large lake. Caused by: –earthquakes, –volcanic eruptions and other underwater explosions (including detonations of underwater nuclear devices), –landslides, –glacier calvings, –meteorite impacts and other disturbances above or below water. Tsunami waves do not resemble normal sea waves, because their wavelength is far longer. A tsunami may initially resemble a rapidly rising tide, and for this reason they are often referred to as tidal waves. DART Buoy National Geographic – Japan 2011 Tsunami

Tides Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon and the Sun and the rotation of the Earth.

PARTS OF A WAVE Wave anatomy …

Wave vocabulary - static Crest – highest point above average water level. Trough – lowest point below average water level. Height – vertical measurement from trough to crest. Wavelength – horizontal distance between the identical point of two waves. Often shown as lambda (λ)

Wave vocabulary - dynamic Period – time it takes for the same spot on two waves to pass a single point (seconds). Frequency – the number of waves that pass a fixed point in one second (1/period – Hz or cycles/second). Speed – distance/time → wavelength/period –The speed of a deep-water wave can be calculated with the equation v (m/s) =1.56T where T is the period (Note: doesn’t depend on water depth) –The speed of a shallow-water wave is given by v (m/s) = √gh = 3.13√h (Note: does depend on water depth) –Also called the wave celerity As a matter of convenience, longer and slower waves, such as ocean surface waves, tend to be described by wave period rather than frequency. Frequency/period video Wave Speed video

Shallow and Deep Water Waves If the depth of the water is greater that ½ the wavelength, the wave is a deep-water wave. –Only wind waves can be deep water waves If the depth of the water is less than 1/20 (some say 1/25) the wavelength, the wave is a shallow water wave. If the depth of the water is between ½ and 1/20 the wavelength, the wave is an intermediate or transitional wave.

BREAKERS - REFRACTION, DIFFRACTION & REFLECTION Waves approaching the shore …

When waves form In deep water, as a wave train moves toward shore, the depth will reach less than ½ the wavelength. The circular motion near the bottom is interrupted, packing the wave’s energy into less water depth; so the wave crest becomes peaked. Wavelength decreases, but the period remains unchanged. A wave breaks when its height exceeds one-seventh of its wavelength (i.e., H:L ratio exceeds 1:7). –Due to drag from the seafloor, the bottom of the wave slows so that the top of the wave is traveling faster than the bottom. This, and exceeding the 1:7 ratio, makes the wave break, toppling the upper part of the wave forward. SurfSurf 8:10

The Science of Big Waves

Surf and Breaking Waves There are three basic types of wave breaks: 1.Spilling breakers are characterized by the top of the wave tumbling and sliding down the front of the wave as it decelerates slowly. They occur on beaches with a gentle slope. 2.Plunging breakers are characterized by a curl as the top of the wave pitches through the air before splashing into the bottom. They occur on moderately steep beaches. 3.Surging breakers occur on very steep beaches that are almost like walls. Because they do not slow, they surge virtually unbroken and can be very destructive.

Shallow water waves Spilling Plunging Surging

Bending and Bouncing Waves Waves rarely hit the shore squarely. Refraction, diffraction, and reflection affect wave behavior. –On an irregular shoreline, refraction concentrates wave energy toward protrusions because the side of the wave nearest to the protrusion slows first, turning the wave toward it. –Wave diffraction occurs when waves hit an obstacle, such as a jetty. Energy shifts within the wave, allowing a new wave pattern to form past the obstacle or through an opening. –Reflection occurs when waves hit an abrupt obstacle that is nearly perpendicular in the water, such as a sea wall. Reflected wave energy can bounce around the sides of an enclosed area, creating complex wave patterns. Reflection can cause a standing wave. This wave is a vertical oscillation in which water rocks back and forth, rising and falling at the ends, but relatively motionless near the center.

Diffraction

Refraction

Reflection Lecture on Refraction and Reflection (9:20) Video of wave reflection (3:00)

Constructive and Destructive Interference When waves meet, constructive or destructive interference occurs. Constructive = builds, adds to Destructive = tears down, lessens In phase = together Out of phase = opposite

GENERATING ENERGY FROM WAVES Waves doing work …

Harnessing wave energy Wave energy can be harnessed in three ways: –using the changing level of the water to lift an object; –using the orbital motion of the water particles to rock an object and; –using the rising water to compress air in a chamber or pump water.

Changing levels Green Ocean Energy will be designing two innovative devices – Ocean Treader and Wave Treader, which will float on the surface of ocean while the motion of waves activate the attached floating arms to move up and down, in order to power onboard generators. Each of the devices can generate an output of around 500 KW (transferable through underwater cables), which is enough to power 125 homes.

Orbital motion OysterOyster is a mammoth contraption designed for utilizing the power of ocean waves and converting them into electricity. Installed off the Atlantic shores of the Orkney Islands, the oscillators inside this gigantic device are fitted with pistons. Once these pistons become impelled by the wave movement, they start to pump high-pressure water through a underwater sea pipeline to the shore. The high pressure water is then converted to electricity by conventional hydroelectric generators. The whole system being deployed at near-shore water depths of 12 to 16 meters, takes advantage of more precise directional spread of the waves in this edge of the sea.

Pumping water The buoys move harmonically when passed over by the waves of water. The unit starts operating when the height of the wave is at least one metre. The motion of the buoys increases the water pressure. The high-pressure water, carried to shore via a pipeline, is used to drive hydroelectric turbines to produce renewable power with zero emissions. The water carried to the shore can further be used to drive the pumps of water desalination plants, such as reverse osmosis plants. Carnegie Wave Energy’s CETO System

Compressing air As the water waves flow into the bottom opening of the device, air is compressed inside the chamber, once the pressure is great enough the air begins to turn the turbine.