WAVE
คลื่น คลื่นคืออะไร พลังงาน ตัวกลาง
คำจำกัดความ The wavelength, λ, is the horizontal distance (in metres) between two successive crests. The period, T, is the time interval (in seconds) between the passage of successive crests passed a fixed point. The frequency, f, is the number of crests which pass a fixed point in 1 second. It is usually measured in numbers per second (Hertz) and is the same as 1/T. The amplitude, a, is the magnitude of the maximum displacement from mean sea-level. This is usually indicated in metres (or feet). The wave height, H, is the difference in surface elevation between the wave crest and the previous wave trough. For a simple sinusoidal wave H = 2a. The rate of propagation, c, is the speed at which the wave profile travels, i.e. the speed at which the crest and trough of the wave advance. It is commonly referred to as wave speed or phase speed. The steepness of a wave is the ratio of the height to the length (H/λ).
การแบ่งคลื่นออกเป็นชนิดต่างๆ
ชนิดของคลื่น เราอาจแบ่งคลื่นมหาสมุทรออกเป็นชนิดต่างๆโดยอาศัยคาบคลื่นเป็นตัวแบ่งได้ดังนี้ คลื่นลม (wind-generated waves) น้ำขึ้นน้ำลง (Tides) คลื่น Seiches ซึนามิ (Tsunami)
“Wind Wave Initial wind stress on the water surface causes what are known as capillary waves - wavelength of less than 1.73 cm The force that tries to restore them to equilibrium is the cohesion of the individual molecules. Capillary waves are important in starting the process of energy transfer from the air to the water. Most wind-generated waves are referred to as gravity waves Wind is extremely important in the marine environment Accurate marine wind analyses and forecasts are each critical to marine forecast problems
Wind speed or strength relative to wave speed- Fetch Width of area affected by fetch Wind Duration - the time over which the wind has blown over a given area Water depth
Tides Tides are produced by the gravitational attraction of the moon and the sun and by the inertial or centrifugal force produced by the earth rotating with these bodies. The tidal effect of the moon is about twice that of the sun Because a body of water can be easily deformed, the side of the earth facing the moon experiences a high tide as the moon’s gravity pulls on the water creating a bulge in the sea level.
TIDES
TIDES Semi Diurnal Diurnal Mixed
TIDES
SEICHE A seiche is a standing wave that oscillates back and forth within a water body. Seiches are generated by a disturbance such as an earthquake, landslide, wave interaction, changes in air pressure, or changes of wind. The rise and fall of a seiche can be from a few centimeters to more than three meters in extreme cases. Most often, a seiche is generated by a persistent strong wind blowing down the long axis of a large water body. When the wind subsides, the water is released as a seiche wave. An atmospheric pressure gradient along the lake can contribute to the water level change, but this is a second-order factor in seiche development.
TSUNAMI
TSUNAMI
TSUNAMI Tsunami are a series of long-period waves (on the order of tens of minutes) that are usually generated by an impulsive disturbance that displaces massive amounts of water, such as an earthquake occurring on or near the sea floor. Underwater volcanic eruptions and landslides can also cause tsunami. While traveling in the deep oceans, tsunami have extremely long wavelengths, often exceeding 100 km (60 miles), with small amplitudes (a few tens of centimeters) and negligible wave steepness, which in the open ocean would cause nothing more then a gentle rise and fall for most vessels, and possibly go unnoticed.
Tsunami travel at very high speeds, sometimes in excess of 700 km per hour As tsunami reach the shallow waters near the coast, they begin to slow down while gradually growing steeper, reaching sometimes more than 10 m height. Large tsunami have been known to rise to over 30 meters
Pressure Induced rare type develop as a pressure perturbation moves over the water surface