StudentShare
Contact Us
Sign In / Sign Up for FREE
Search
Go to advanced search...
Free

Significant of Edge Waves and Shear Waves - Essay Example

Cite this document
Summary
This essay "Significant of Edge Waves and Shear Waves " discusses velocity to pressure variance ratios indicating that shear waves contribute significantly (as much as 75%) to the total intracavity velocity variance in the region of strong seaward shear of the alongshore current profile…
Download full paper File format: .doc, available for editing
GRAB THE BEST PAPER98.5% of users find it useful
Significant of Edge Waves and Shear Waves
Read Text Preview

Extract of sample "Significant of Edge Waves and Shear Waves"

Order # 154744 Significant of Edge Waves and Shear Waves Introduction Waves are caused by wind, it changes the water's surface and made it into the ripples and then into waves. Waves travel effortlessly along the water's surface. This is made possible by small movements of the water molecules. As waves grow in height, the wind pushes them along faster and higher. Waves can become unexpectedly strong and destructive. As waves enter shallow water, they become taller and slow down, eventually breaking on the shore.There are several types of waves; among them are the edge wave and the shear wave. The paper will able to evaluate the significant of the edge wave and the shear wave. Edge Waves Edge waves or low frequency gravity motion waves are water waves that are trapped at the shoreline by refraction. It is produce by the variability of wave energy reaching shore. An edge-wave is a low frequency wave attached to the beach. The edge waves have periods of a minute, a long-shore wave-length of around a kilometer, and amplitude that decays exponentially offshore as shown in figure 1 (Cutchin and Smith, 1973).While they were originally considered to be a curiosity, these waves play a significant role in near shore hydrodynamics. (Eckart C., 1951). Figure 1 Computer-assisted sketch of an edge wave. Such waves exist in the breaker zone near the beach and on the continental shelf. From Cutchin and Smith (1973). The edge waves are modeled by creating incident waves that approach perpendicular to the direction of the constructed shoreline. The numerical modeling of edge waves was first described by Stokes equation in 1946. Eq.1 = standing edge wave height Ae = constant Ke = edge wave number X = distance from shore line = slope of beach A further numerical model is used to demonstrate the dispersion relation. It proposes for a given frequency that only mode of edge wave is able to be excited. Eq.2 Shear Wave Shear Wave is also known as the voticity wave. The stability of a steady alongshore current V(x) to small perturbations using a linear vorticity equation based on the shallow water equations and the rigid-lid approximation. They showed that in the region of strong seaward shear (d|V|/dx < 0), instabilities develop in the form of alongshore propagating velocity oscillations (shear waves). Ratios between variances of shear wave velocities and associated pressure fluctuations scale roughly as Whereas the velocity to pressure variance ratios of the individual u and components of gravity waves are sensitive to the edge-leaky wave mode mix the normalized ratio of total velocity to pressure variance R, is 1 (i.e., equi-partitioning of kinetic and potential energy) independent of the mode mix. For shear waves , R = O(gh/V2), that is, 1 for natural alongshore currents with typically small Froude numbers (e.g., Oltman-Shay et al. 1989). Hence, can be used to estimate the contributions of gravity waves and shear waves to the infragravity band. If the gravity and shear wave velocity fluctuations are assumed to be statistically independent, then the fraction of the infragravity velocity variance contributed by shear waves is approximately given by = 1 1/R.(17). The effects of Shear and Edge Wave in the Environment The shape of the land under sea determines the strength and direction of the wave toward the coastline, while above ground it determines the run-up. Since the generation of a wave is defined by transferance of energy, or force in simple mathematical terms, the decrease in sea floor depth has the proportional effect of focusing and speeding up the movement of the wave. Thus a wave generated from a large, deep body of water will produce larger waves than those produced from a shallower body of water. Beach coastlines. As shown by Adams & Lewis, (1979) offshore coastline has a modifying effect on the wave shape as it breaks on land. The most destructive waves are where the force of the wave is focused as it breaks on land. Beaches, with their concave sea floor relief are thus more susceptible are than promontories to damage from a tsunami of equal force, because the convex relief of the sea floor deflects the wave off centre and out to the side. Beach breaking waves have potentially more threat for two reasons. Land behind beaches tends to be lower than land behind promontories; therefore the penetration by a wave would be greater. Secondly, populations tend to congregate around beaches for reasons of leisure, and practicality of access for fishing vessels. Estuarine shorelines Low tides, where the water's edge recedes off shore due to lowering of the sea level have a mitigating effect of reducing the threat of tsunami. Combined with a high tide period where the sea level is higher and closer in shore, tsunamis pose more of threat. A tsunami hitting an estuarine environment will also have devastating effects for several important reasons. Since estuarine environments are not subject to normal wave action from the sea, only indirect tidal influences, the coastline topography can be quite different, particularly with large delta regions such as Zhujiang. Most of the land mass around the shorelines of a delta region is flat, and barely above the water line, and is somewhat static. In this type of environment, populations can and do congregate very close to shorelines, due to the lesser apparent wave threat (bearing in mind that people are thinking of ocean waves, not tsunamis), and also because of the easy access to plentiful food supplies. Most of these coastal communities have a lifestyle that revolves around water, fishing, boating, washing and irrigation are all activities associated with estuarine lifestyle. This familiarity with close proximity to water would lead people to have less fear of water, and hence possibly, less caution. Rivers Secondary to tsunami effects on coastlines, is the effect of the wave as it travels up rivers. Henry & Murty (1995) described the process of "resonance amplification", where the wave grows as it travels higher upstrem. Another effect is wave shear, where the river banks and their features are "scraped" by trapped "edge waves" as it travels upstream. This effect is almost identical in mechanics to tide surges and storm surges, and has been mentioned by Carrier in a paper on transverse waves travelling parallel to coastlines (Carrier, 1995) Sloped Shorelines Slopes cause a very destructive tsunami phenomenon known as run-up, where the wave will wash in over land, and the inertia will carry the water inland and push it up the slopes of a hill or mountain range, where it will then wash down, back into the sea. Historically, some absolutely incredible elevations have been reached by run-up. Classifying Waves Ways to classify waves: Disturbing force Free waves vs. forced waves Restoring force Wavelength Disturbing Force Wind waves: from wind energy - Seiche (really a function of shape of basin) - Tsunami: from seismic energy - Tides: gravitation attraction of moon and sun Free waves vs. forced waves Free waves moves without any further influence from the force that created them Forced waves movement is dependant upon the force that creates them Restoring Force The dominant force trying to return the water surface to flatness after a wave has formed If successful, energy would be transferred as heat not a wave Small waves (wavelengths < 1.73 cm) Surface tension Form capillary waves First waves to form when the wind blows Larger waves (wavelengths > 1.73 cm) Gravity Pulls crest down Wave moving forward, so crest becomes a trough Causes circular orbits of individual water molecules Can travel thousands of miles Wavelength Deep and Shallow water waves - Water depth a major control of wave characteristics - Water depth controls the shape of water orbits - Wave interact with bottom when water depth < wavelength - Below this depth orbits contain little energy - Called deep water waves Conclusion Estimates of velocity to pressure variance ratios indicate that shear waves contribute significantly (as much as 75%) to the total infragravity velocity variance in the region of strong seaward shear of the alongshore current profile. Both shoreward and seaward of this region the observed ratios are approximately equal to the gravity wave value g/h, indicating an infragravity spectrum composed primarily of gravity (edge and/or leaky) waves. Strong shear wave activity is consistently observed in the region of strong shear in the alongshore current, independent of large changes in the beach profile. This result is qualitatively consistent with numerical results of Dodd and Thornton (1990). The wave causes the tsunami which may cause a large destruction of the environment. It may be preempted by proper studying the location of the beaches as well as the present waves in this location. Thus a wave generated from a large, deep body of water will produce larger waves than those produced from a shallower body of water. Construction of buildings in this site maybe done according to the strength of the wave. People may be advised to stay away from these beaches to avoid incidents such as death and destruction due to tsunami. References: 1. Adams, W. M., Lewis, C. H., (1979) "Type Areas For Predicting Tsunami Inundation" Proceedings, Tsunami Symposium Canberra, December 1979, Griffith University and Intergovernmental Oceanographic Commission, p. 59-78 2. Carrier, G. F., (1995) "On-Shelf Tsunami Generation And Coastal Propagation" Tsunami: Progress in Prediction, Disaster Prevention and Warning. 1995 Kluwer Academic Publishers, Netherlands, p. 1 - 20 3. Cutchin D.L., and R.L. Smith. 1973. Continental shelf waves: Low-frequency variations in sea level and currents over the Oregon continental shelf. Journal of Physical Oceanography 3 (1): 73-82. 4. Dodd, N., and E. B. Thornton, 1990: Growth and energetics of shear waves in the nearshore. J. Geophys. Res., 95, 16075-16083 5. Henry, R.F. & Murty ,T.S. (1995) "Tsunami Amplification Due to Resonance in Alberni Inlet: Normal Modes" Tsunamis In The World: The Fifteenth International Tsunami Symposium, 1991. Kluwer Academic Publishers, Netherlands. p 117 6. Stewart, R. (2005), Chapter 17 Coastal Processes and Tides: http://oceanworld.tamu.edu/resources/ocng_textbook/chapter17/chapter17_01.htm 7. http://www.student.uwa.edu.au/cousem01/fm_edgewaves.htm 8. http://www.asian.gu.edu.au/tsunami/land.htm Read More
Cite this document
  • APA
  • MLA
  • CHICAGO
(“Significant of Edge Waves and Shear Waves Essay”, n.d.)
Significant of Edge Waves and Shear Waves Essay. Retrieved from https://studentshare.org/miscellaneous/1508887-significant-of-edge-waves-and-shear-waves
(Significant of Edge Waves and Shear Waves Essay)
Significant of Edge Waves and Shear Waves Essay. https://studentshare.org/miscellaneous/1508887-significant-of-edge-waves-and-shear-waves.
“Significant of Edge Waves and Shear Waves Essay”, n.d. https://studentshare.org/miscellaneous/1508887-significant-of-edge-waves-and-shear-waves.
  • Cited: 0 times

CHECK THESE SAMPLES OF Significant of Edge Waves and Shear Waves

Entering the Fourth Environmental Wave

In brief, the author (MacLean, 2009) began by defining that the world has been experiencing different periods of environmental alterations that occur in the form of waves.... Richard MacLean (2009) is the author of a significant article, “Entering the Fourth Environmental Wave” (MacLean, 2009) in which, author has done a remarkable job by defining and discussing specific issues of environmental management while providing some solutions and implications that seem practical and beneficial theoretically....
10 Pages (2500 words) Essay

Risks associated with ultrasound procedure

hellip; Ultrasonic imaging involves mechanical energy, in which pressure waves pass through tissue.... nbsp;It involves heating of tissues due to the absorption of ultrasonic waves by the tissues.... Tjie essay "Risks associated with ultrasound procedure" concerns the phenomenon of ultrasound and its impact....
7 Pages (1750 words) Essay

Blasts as Major Threat to Humanity

Explosives, which are usually thermobaric – commonly referred to as fuel-air explosives, are either finely divided particles mixed with gases/air, or droplets suspended in air.... Explosives… High explosives are extremely high reaction rate-chemical materials and their reaction is known as detonation....
10 Pages (2500 words) Essay

Gender Roles In The Second World War (UK)

An essay "Gender Roles In The Second World War (UK)" reports that femininity is about child-bearing, about motherhood, home keeping, sex life, inner and outer beauty.... nbsp; Our goal here is to sketch feminisms as they deviated from their traditional roles during WWII.... hellip; Many Writers construed feminism to mean differently....
12 Pages (3000 words) Essay

Interpretation of the Geophysical Data

Shear wave (The amplitudes of the elastic wave elastic waves amplitudes (Knight, 2010).... Seismic properties play a significant role in such understanding because they help remove the on-field constraints.... hellip; The measurement scale has significant impacts on the interpretation of geophysical data (Acosta-Colon, 2009)....
6 Pages (1500 words) Article

CAT Aircraft Make Use of Weather Radar

nbsp;… Radar is used to detect an object that specifically uses radio waves.... It is proved that strong wind shear can also create breaking waves such as those waves found on the water.... Due to the breakages of such waves, there is normally the creation of vortices in the air or turbulence which are associated with clear air.... As a normal happening, there's an occurrence of wind shear along the stream of the jet....
12 Pages (3000 words) Assignment

Structural Design Process

This is trailed by the investigation and processing of the inside terrible strengths of pushed, shear, bowing minutes, and turning minutes.... "Structural Design Process" paper argues that Designs and implementations should be stable with respect to daily use and operations that make up the functions of the object or product....
9 Pages (2250 words) Coursework

Aerodynamics of Supersonic Aircrafts

Supersonic Flight Theory and Shock waves Supersonic transport refers to aircraft designed to fly at speeds that are greater to that of sound (Mason, 2006).... To make cruising at supersonic speeds easy, various principles were developed in a bid to fight conflicting issues such as shock waves which served a major blow to supersonic plane control.... t supersonic speeds, the aircraft produces shock waves that reach the ground....
8 Pages (2000 words) Essay
sponsored ads
We use cookies to create the best experience for you. Keep on browsing if you are OK with that, or find out how to manage cookies.
Contact Us