Chapter 8 Waves and Water Dynamics Most waves are wind driven most waves are generated by storms Waves travel without breaking 3 types of waves are longitudinal transverse and orbital interface waves waves on the ocean surface parts of the wave are the crest trough wave height H wave length L Orbital waves particles move in an orbital path these waves transmit energy along in terface between two fluids of different density liquids or gasses Orbital waves are seen in the ocean Origin of waves Waves transport energy not mass Boundary between and within fluids with different densities air ocean interface air air water water ocean waves atmospheric waves internal waves Types of waves surface waves internal waves happen between low density water on top and high density water deeper water Most of energy is in wind waves Lots of energy in tides Individual tsunamis are power ful but they are rare Relative to wind waves little energy is collectively found in tsunamis Other types of waves splash waves caused by coastal landslides seismic sea wave tsunami caused by sea floor movement tides caused by gravitational attraction among moon sun and earth wakes caused by ships Wave Motion Particles in ocean waves move in orbital paths Circular orbital motion particles move in a circle movement is up and down and back and forth rubber duck example Wave Characteristics wavelength L distance from crest to crest or trough to trough wave period T time between passing crests inverse of frequency Frequency per second 1 T number of crests passing fixed point over time Wave height H height from trough to crest Wave steepness H L if 1 7 wave breaks because of gravity Wave speed S wavelength L wave period T Diameter of orbital motion decreases with the depth of water Wave Base 1 2L There are 3 types of waves 1 Deep water waves The water depth is greater than the wave base or equal to 1 2L Wave speed celerity is proportional to the wavelength Long wave length moves faster Speed is calculated easily 2 Shallow water waves When water depth is or equal to L 20 wave orbits are squashed into ellipses Celerity proportional to depth of water Waves all move at the same speed Don t move up and down as much as forward and backwards Speed is dependents on the depth of the ocean wavelength does not matter 3 Transitional waves Characteristics of both deep and shallow water waves Celerity depends on both water depth and wavelength Happens between1 20 wavelength or equal to depth or equal to 1 2 Wind Generated Wave Development Capillary waves ripples formed first rounded crests very small wavelengths Gravity waves increasing wave energy symmetrical waves with longer wavelength Trochoidal waveforms increased energy pointed crests crests pointed troughs rounded greater wave heights 3 Factors control wave energy wind speed wind duration and fetch the distance over which wind blows Wave height is directly related to wave energy wave heights usually less than 2 me ters 6 6 feet Breakers called white caps form when the wave reaches critical steepness Beaufort wind scale describes appearance of the sea Maximum wave height for a long time thought to be 60 ft Reliable measurement by USS Rampo in 1933 wave height 34 m or 112 feet Fully developed Sea Maximum wave height wavelength for particular fetch speed and duration of the winds at equilibrium conditions Swell Uniform symmetrical waves that travel outward from storm area long crests transport energy long distances Longer wavelength travels faster and outdistances other waves Sorting of waves by their wavelength is wave dispersion Wave train is a group of waves with similar characteristics wave train speed is 1 2 the speed of an individual wave when one wave dies out another wave picks up start with 4 waves will continue to have 4 waves entire time Wave interference patterns when different swells come together Constructive interference in phase wave trains with about the same wave lengths This is how we get large waves further out in the sea energy s meet and build up Destructive interference same wave length but are at different phases they cancel each other out and create a flat sea Mixed interference different wave lengths and are at different phases you get two small waves and one big wave in the middle between the two MOST COMMON 1 2 3 large waves then smaller ones Waves in Surf Zone Surf zone is the zone of breaking waves near shore Shoaling water is when water becomes gradually shallower When deep water waves encounter shoaling water less than 1 2 their wavelength they become transitional waves Waves approach shore come in as deep water swell waves shoal become transitional waves then shallow water waves wave speed decreases wave length decreases wave height increases wave steepness increases then waves break and period remains constant Breakers in the surf zone top of the wave topples over base because of decrease in wave speed due to friction with sea floor Wave form is not sustained Different types of breakers associated with different slope of sea floor There are three types 1 Spilling breakers gently sloping sea floor wave energy expended over longer distance water slides down front of wave 2 Plunging breakers moderately steep sea floor wave energy is expended over shorter distance better for surfers curling wave crest 3 Surging Breakers steepest sea floor energy spread over shortest dis tance best for body surfing waves break on the shore Wave Refraction waves approach the shore they bend so that wave crests are parallel to shore Wave speed is proportional to the depth of the water shallow water wave Different segments of wave crest travel at different speeds Wave refraction gradually erodes headlands and sediment accumulates in bays creating beaches Wave energy distribution at shoreline energy focused on headland headland eroded because wave is continuously hitting it Energy is dissipated in the bay bay is then filled up with sediment Wave reflection happens when the waves hit something solid a barrier and bounce back A reflected wave can interfere with the next incoming wave Standing Wave happens when two waves with the same wavelength moving in opposite directions the water particles move horizontally and vertically water sloshes back and forth bathtub Internal Waves are associated with pycnocline they are larger than surface waves and are caused by tides turbidity currents winds and ships Internal waves are possible hazards for submarines Internal waves have
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