Part I. The diffraction theory of sea waves and the shelter afforded by breakwaters

1952 ◽  
Vol 244 (882) ◽  
pp. 236-253 ◽  
Keyword(s):  
Diffraction Theory ◽  
Small Island ◽  
Sea Waves ◽  
Diffraction Of Light ◽  
Wave Patterns ◽  
Wave Heights ◽  
Optical Phenomena ◽  
The Waves

The diffraction of sea waves round the end of a long straight breakwater is investigated, use being made of the solutions of mathematically analogous problems in the diffraction of light. The wave patterns and wave heights are determined on both the leeward and windward sides of the breakwater, and for points quite close to the breakwater. This involves some extension of the calculations previously made for optical phenomena. The conditions obtaining in the lee of a small island are discussed. The penetration of waves through a single gap in a long breakwater is examined, and the result is shown to depend very much on whether the gap is small or not compared with the length of the waves. The investigation was suggested by problems arising in the construction of the Mulberry harbours.

scholarly journals GENERALIZED WAVE DIFFRACTION DIAGRAMS

2000 ◽  
Vol 1 (2) ◽  
pp. 2
Author(s):  
J. W. Johnson
Keyword(s):  
Wave Height ◽  
Wave Diffraction ◽  
Water Waves ◽  
Electromagnetic Waves ◽  
Wave Train ◽  
Diffraction Theory ◽  
Long Beach ◽  
Practical Application ◽  
Diffraction Of Light ◽  
Wave Heights

Wave diffraction is the phenomenon in which water waves are propagated into a sheltered region formed by a breakwater or similar barrier which interrupts a portion of a regular wave train (Fig. 1). The principles of diffraction have considerable practical application in connection with the design of breakwaters as discussed by Dunham (1951) at the Long Beach Conference. The phenomenon is analogous to the diffraction of light, sound, and electromagnetic waves. Two general types of diffraction problems usually are encountered: one, the passage of waves around the end of a semi-infinite impermeable breakwater (Putnam and Arthur, 1948), and, second, the passage of waves through a gap in a breakwater (Blue and Johnson, 1949t Carr and Stelzriede, 1951). In general, the theoretical solutions have been found to apply with conservative results, that is, the predicted wave heights in the lee of a breakwater are found to be slightly larger than the height of waves that may be expected under actual conditions. The use of the diffraction theory in breakwater design is made convenient when summarized in the form of diagrams with curves of equal values of diffraction coefficients on a coordinate system in which the origin of the Bystem is at the tip of a single breakwater (Figs. 2a-2b, and 3) or at the center of a gap (Figs. 2c, and 4-6). The diffraction coefficient in this instance is defined as the ratio of the diffracted wave height to the incident wave height and usually is designated by the symbol K». The procedure in preparing diffraction diagrams appears elsewhere (Johnson, 1950). The purpose of this paper is to present diffraction diagrams to supplement the material of Dunham (1951). For complete details on the application of diffraction diagrams to typical harbor problems the reader is referred to this latter paper.

scholarly journals EXPLORING SPATIO-TEMPORAL WAVE PATTERN USING UNSUPERVISED TECHNIQUE

2019 ◽  
Vol XLII-4/W16 ◽  
pp. 543-548
Author(s):  
N. A. Rohana ◽  
N. Yusof ◽  
M. N. Uti ◽  
A. H. M. Din
Keyword(s):  
Time Series ◽  
Wave Height ◽  
Coastal Areas ◽  
Sea Waves ◽  
Significant Wave ◽  
Early Action ◽  
Wave Patterns ◽  
Wave Heights ◽  
Significant Wave Heights ◽  
Spatio Temporal

Abstract. The sea waves are the up and down movements of water in the sea. The various heights of sea waves are known as significant wave heights. Each type of wave has their own characteristics based on their significant wave heights. The aim of this research is to explore spatio-temporal wave patterns and their effects on Tok Jembal coastal areas. For this study, the monthly wave data were obtained from the satellite altimeters that have been processed using Radar Altimeter Database System (RADS). The Self Organizing Map (SOM) method was used to extract the spatio-temporal wave height patterns from the monthly wave height data. From the clustering results, six number of clusters were extracted and then each of these clusters was categorized into specific type of wave heights. In addition, time series of Landsat satellite images were used to observe the coastal changes at Tok Jembal areas. Finally, we analyzed the effects of spatio-temporal wave patterns towards the occurrences of coastal erosion along the coastal areas. This study has discovered that the wave heights along the coastal areas fall in slight category and showed less effects on the erosion. From the visual interpretation of time- series images (10 years gap) also proved that the erosion can be considered as moderate. Overall, this study could benefit the coastal management especially for shoreline monitoring where early action can be taken when there are signs of erosion along the coast.

General Introduction

1952 ◽  
Vol 244 (882) ◽  
pp. 231-235 ◽  
Keyword(s):  
Diffraction Pattern ◽  
Gravity Waves ◽  
Sea Waves ◽  
General Introduction ◽  
The Third ◽  
Wave Patterns ◽  
The Waves

Five papers on various problems of gravity waves in perfect liquids are being published together; the first three papers are entirely theoretical, but the last two include a description of various experiments made to check and extend the mathematical investigations contained in the third paper. Part I, by Penney & Price, considers the diffraction pattern produced by a semi-infinite straight breakwater inclined at any angle to the direction of approaching parallel harmonic infinitesimal sea waves. The spread of the waves into the lea of the breakwater is particularly interesting. The wave patterns behind gaps, and other extensions of the theory, are also developed.

Wind speed data analysis for predictions of sea waves in Bitung Coastal Waters

2013 ◽  
pp. 35 ◽  
Author(s):  
Joanes E Koagouw ◽  
Gybert E Mamuaya ◽  
Adrie A Tarumingkeng ◽  
P A Angmalisang
Keyword(s):  
Data Analysis ◽  
Wind Speed ◽  
Coastal Waters ◽  
Transition Period ◽  
Marine Resources ◽  
Land Uses ◽  
Sea Waves ◽  
North West ◽  
North Sulawesi ◽  
The Waves

Coastal area of Bitung Municipality is one of the economical activities centers in North Sulawesi Province such as for land-uses and the exploitation of natural resources. Those activities are exaggerating day bay day and tended to be uncontrollable. The excess of those conditions, it has been recorded the change of waves in Bitung waters that has impacts to coastal areas and can affect the utilization of coastal and marine resources. This research was aimed to observe waves altitude variations in Bitung waters with Svedrup Munk and Bretchsneider (SMB) method that had been used to predict waves altitudes. The results showed that the wind speed during West Season was 0.33 m and were dominant to the East, while during East season was 0.91m from South-East to North-West, and then on transition period (March to May) was 1.08m from South-East to East. The results of those wind speed to the waves altitudes in Bitung waters is discussed in this paper© Pesisir pantai Kota Bitung merupakan salah satu pusat aktivitas ekonomi (misalnya pemanfaatan lahan dan eksploitasi sumberdaya) di Provinsi Sulawesi Utara. Aktivitas tersebut semakin hari semakin meningkat dan memiliki kecenderungan tidak terkontrol. Akibat dari keadaan tersebut, telah terjadi perubahan fenomena gelombang di perairan Bitung yang berdampak pada keberadaan daerah pesisir pantai di mana hal ini dapat mengganggu aktivitas pemanfaatan sumberdaya pesisir dan laut tersebut. Penelitian ini bertujuan untuk mengetahui variasi tinggi gelombang di perairan Bitung dengan menggunakan metode Svedrup Munk and Bretchsneider (SMB) yang biasa digunakan untuk peramalan tinggi gelombang signifikan. Hasil penelitian menunjukkan bahwa kecepatan angin pada Musim Barat sebesar 0,33 meter dan dominan ke arah Timur, sementara pada Musim Timur sebesar 0,91 meter dari arah Tenggara ke Barat Laut, serta pada Musim Peralihan (antara bulan Maret-Mei) adalah sebesar 1,08 meter dari arah Tenggara dan Timur. Pengaruh kecepatan angin tersebut terhadap gelombang laut di perairan Bitung dibahas dalam tulisan ini©

scholarly journals WAVES AT SEKONDI, GHANA

1966 ◽  
Vol 1 (10) ◽  
pp. 1 ◽  
Author(s):  
L. Draper
Keyword(s):  
Southern Hemisphere ◽  
Sea Waves ◽  
Severe Damage ◽  
Pressure Recording ◽  
Electric Wave ◽  
International Geophysical Year ◽  
Time Of Year ◽  
The Waves ◽  
Wave Recorder ◽  
International Geophysical

During the International Geophysical Year the National Institute of Oceanography in collaboration with Ghana IGY Committee and the Ghana Railway and Harbours Administration made recordings of sea waves at a point 2,300 feet off Sekondi point in a direction 156°. The instrument used was an N.I.O. piezo-electric wave recorder of the pressure recording type. Recordings started in June, 1958, and continued until the end of October that year when the cable suffered severe damage which could not easily be repaired. Because of the high cost of cable and the fact that a good series of records had already been obtained for a rough time of year, the instrument was recovered and used elsewhere. Records were taken every two hours and each has a useable length of twelve minutes. Most of the waves arriving at Sekondi are in the form of swell which has been generated by storms in the southern hemisphere; consequently wave conditions do not change very quickly, and it was found unnecessary to analyse every record except during rough conditions. The method of analysis used is that described in the associated paper "The Analysis and Presentation of Wave Data - a Plea for Uniformity".

scholarly journals MACH-REFLECTION AS A DIFFRACTION PROBLEM

1976 ◽  
Vol 1 (15) ◽  
pp. 45 ◽  
Author(s):  
Udo Berger ◽  
Soren Kohlhase
Keyword(s):  
Wave Height ◽  
Incident Wave ◽  
Water Waves ◽  
Gas Dynamics ◽  
Mach Reflection ◽  
Diffraction Problem ◽  
Vertical Wall ◽  
Oblique Wave ◽  
Wave Heights ◽  
The Waves

As under oblique wave approach water waves are reflected by a vertical wall, a wave branching effect (stem) develops normal to the reflecting wall. The waves progressing along the wall will steep up. The wave heights increase up to more than twice the incident wave height. The £jtudy has pointed out that this effect, which is usually called MACH-REFLECTION, is not to be taken as an analogy to gas dynamics, but should be interpreted as a diffraction problem.

scholarly journals WAVE RECORDING ON THE IJSSELMEER

2011 ◽  
Vol 1 (7) ◽  
pp. 3
Author(s):  
P. W. Roest
Keyword(s):  
Average Period ◽  
Recording Time ◽  
Ice Drift ◽  
Recording Station ◽  
Long Time ◽  
Wave Heights ◽  
Wave Research ◽  
The Difference ◽  
Hydraulics Laboratory ◽  
The Waves

The dimensions of the dikes in the Ijsselmeer are mainly determined by wave-attack. The dimensions of the waves as a result of the design gale are calculated with the diagram of the Hydraulics Laboratory at Delft (ref« 1). This diagram is based on data of Sverdrup for deep water and principally on laboratory studies for shallow water. For a long time there has been a need of wave recordings on the lake in order to verify the calculated wave heights. A problem is the impossibility of maintaining a permanent recording station on the lake due to ice-drift in wintertime. Otherwise the Ijsselmeer lends itself admirably to wave-research, because there are vast regions with only small variations in waterdepth. Another advantage is that frequently more or less stationary conditions will occur under the influence of winds of constant force and direction. When Dr. Dorrestein of the Royal Dutch Meteorological Institute introduced his new floating waverecorder, it was possible to take observations in every place of the lake. Soon it appeared that this recorder has many advantages. The equipment consists of an accelerometer mounted on a little raft of one meter each way, that follows the movement of the water surface. The signal of the accelerometer is transmitted by an electric cable to the ship, where it is double integrated and then recorded (ref. 3). During the last winter several observations have been carried out with an instrument of this type* As a result of initial troubles with the electronic equipment the number of observations during gale-conditions has been limited. The usual duration of each recording is about 15 minutes. The average period of the waves lies between three and a half and five seconds, so each diagram consists of 180 to 250 waves. Wave height is measured as the difference in height between a trough and the next crest. The average period is determined by dividing the total recording time by half the number of zerocrossings.

Neutron Optics

2020 ◽  
pp. 311-342
Author(s):  
Andrew T. Boothroyd
Keyword(s):  
Neutron Radiography ◽  
Scattering Length ◽  
Diffraction Theory ◽  
Neutron Imaging ◽  
Bragg Diffraction ◽  
Neutron Reflectivity ◽  
Neutron Optics ◽  
Coherent Wave ◽  
Optical Phenomena ◽  
Secondary Extinction

The description of neutron optical phenomena within the framework of dynamical diffraction theory is described. The coherent wave and optical potential are introduced, and an expression for the complex neutron refractive index in terms of the scattering length density and attenuation coefficient is obtained. The extension to magnetic media and polarized neutrons is covered. Neutron reflectivity is defined, and the wavevector dependence of the reflectivity profile is derived by a transfer matrix method and an optical method. Exact results are compared with the Born approximation. The technique of neutron imaging is described, including neutron radiography and computed tomography. Several optical phenomena that occur in Bragg diffraction from near-perfect crystals, including Pendellösung oscillations, and primary and secondary extinction.

A genesis of special relativity

2015 ◽  
Vol 24 (10) ◽  
pp. 1530024
Author(s):  
Valérie Messager ◽  
Christophe Letellier
Keyword(s):  
Special Relativity ◽  
19Th Century ◽  
Maxwell Equations ◽  
Light Propagation ◽  
Principle Of Relativity ◽  
Light Rays ◽  
Optical Phenomena ◽  
Light Particles ◽  
The 19Th Century ◽  
The Waves

The genesis of special relativity is intimately related to the development of the theory of light propagation. When optical phenomena were described, there are typically two kinds of theories: (i) One based on light rays and light particles and (ii) one considering the light as waves. When diffraction and refraction were experimentally discovered, light propagation became more often described in terms of waves. Nevertheless, when attempts were made to explain how light was propagated, it was nearly always in terms of a corpuscular theory combined with an ether, a subtle medium supporting the waves. Consequently, most of the theories from Newton's to those developed in the 19th century were dual and required the existence of an ether. We therefore used the ether as our Ariadne thread for explaining how the principle of relativity became generalized to the so-called Maxwell equations around the 1900's. Our aim is more to describe how the successive ideas were developed and interconnected than framing the context in which these ideas arose.

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