scholarly journals BEACH CUSPS AND EDGE WAVES

1978 ◽  
Vol 1 (16) ◽  
pp. 81 ◽  
Author(s):  
D.A. Huntley ◽  
A.J. Bowen
Keyword(s):  
Incident Wave ◽  
Wave Motion ◽  
Field Measurements ◽  
Convincing Evidence ◽  
Edge Wave ◽  
Wave Frequency ◽  
Edge Waves ◽  
Wide Range ◽  
Beach Cusps ◽  
Resonant Waves

Beach cusps are very common, concave-seaward cuspate patterns at the shoreline of a beach, which tend to occur with a regular longshore spacing, but which can have a wide range of longshore wavelengths from a few centimeters to several kilometers or more. Edge waves, resonant waves trapped at the shoreline by refraction, have been suggested as the cause of beach cusps but it has proved difficult to establish a definitive link on natural beaches . This paper describes field measurements of nearshore velocities, in all three orthogonal directions, that show the presence of edge wave motion just before the formation of beach cusps of the corresponding wavelength, and thus provides convincing evidence that edge waves are responsible for beach cusps. The magnitude of the observed edge wave oscillatory and drift velocities are found to be large and apparently well able to form cusps of the observed size. The observed edge waves are at the subharmonic of the incident wave frequency and thus are the field equivalent of the laboratory observations of Guza and Inman (1975) and Guza and Bowen (1977). It is not clear, however, whether the developing cusp topography enhanced or suppressed the edge wave motion.

Experimental study of the instabilities of waves obliquely incident on a beach

1979 ◽  
Vol 95 (1) ◽  
pp. 199-208 ◽  
Author(s):  
R. T. Guza ◽  
D. C. Chapman
Keyword(s):  
Experimental Study ◽  
Boundary Conditions ◽  
Frequency Band ◽  
Edge Wave ◽  
Wave Frequency ◽  
Edge Waves ◽  
Additional Boundary Conditions ◽  
Obliquely Incident ◽  
Longshore Currents ◽  
Monochromatic Waves

Monochromatic waves obliquely incident on a plane beach, and strongly reflected there, are unstable to perturbations by edge waves. Theory suggests the possible width of the resonant edge wave frequency band. Experiments on beaches with absorbers at both ends show that the excited waves have frequencies at the centre of the band, as predicted by Guza & Bowen (1975). Advection by mean longshore currents must be taken into account. If reflectors are placed at the beach ends, the additional boundary conditions apparently lead to resonances scattered across the resonant band.

scholarly journals FIELD MEASUREMENTS OF NEARSHORE VELOCITIES

1974 ◽  
Vol 1 (14) ◽  
pp. 30
Author(s):  
David A. Huntley ◽  
Anthony J. Bowen
Keyword(s):  
Wave Motion ◽  
Field Measurements ◽  
Wave Form ◽  
Edge Waves ◽  
Free Standing ◽  
Frequency Wave ◽  
Storm Waves ◽  
Circulation Patterns ◽  
Two Component ◽  
Base Side

Two component electromagnetic flowmeters are being used as the basis of an apparatus to measure nearshore velocities on natural beaches. The flowmeters are mounted on free standing tripods, 1 m. base side and 0.3 m. high, to measure the two components of horizontal flow, and have been used in depths of up to 4 m. and up to 150 m. from the shoreline. The apparatus has proved both flexible and reliable on beaches ranging from steep shingle (slope ^ 0.13) to very shallow sand (slope'*' 0.01) and under a wide variety of wave conditions, including full storm waves on a beach of intermediate slope ( ^ 0.04). Results show that a single flowmeter can be used on a tidal beach to measure the variation of the flow field along a line perpendicular to the shoreline. In this way edge waves and steady nearshore circulation patterns have been detected. If several flowmeters are placed on a line perpendicular to the shoreline, the progress of individual waves can be followed as they pass over each flowmeter in turn, and hence propagation speeds, changes of wave form and the development of lower frequency wave motion close to the shoreline can be studied.

Subharmonic edge wave excitation by narrow-band, random incident waves

2019 ◽  
Vol 868 ◽  
Author(s):  
Giovanna Vittori ◽  
Paolo Blondeaux ◽  
Giovanni Coco ◽  
R. T. Guza
Keyword(s):  
Incident Wave ◽  
Narrow Band ◽  
Bottom Friction ◽  
Edge Wave ◽  
Random Waves ◽  
Wave Excitation ◽  
Edge Waves ◽  
Similar Time ◽  
Wave Phase ◽  
Incident Waves

A monochromatic, small amplitude, normally incident standing wave on a sloping beach is unstable to perturbation by subharmonic (half the frequency) edge waves. At equilibrium, edge wave shoreline amplitudes can exceed incident wave amplitudes. Here, the effect of incident wave randomness on subharmonic edge wave excitation is explored following a weakly nonlinear stability analysis under the assumption of narrow-band incident random waves. Edge waves respond to variations in both incident wave phase and amplitude, and the edge wave amplitudes and incident wave groups vary on similar time scales. When bottom friction is included, intermittent subharmonic edge wave excitation is predicted due to the combination of bottom friction and wave phase. Edge wave amplitude can be near zero for long times, but for short periods reaches relatively large values, similar to amplitudes with monochromatic incident waves and no friction.

scholarly journals ON PREDICTING INFRAGRAVITY ENERGY IN THE SURF ZONE

1984 ◽  
Vol 1 (19) ◽  
pp. 130
Author(s):  
Asbury H. Sallenger ◽  
Robert A. Holman
Keyword(s):  
Incident Wave ◽  
Surf Zone ◽  
Standing Waves ◽  
Wave Mode ◽  
Edge Wave ◽  
Flow Data ◽  
Edge Waves ◽  
Infragravity Waves ◽  
Synthetic Spectra ◽  
Wave Conditions

Flow data were obtained in the surf zone across a barred profile during a storm. RMS cross-shore velocities due to waves in the infragravity band (wave periods greater than 20 s) had maxima in excess of 0.5 m/s over the bar crest. For comparison to measured spectra, synthetic spectra of cross-shore flow were computed using measured nearshore profiles. The synthetic spectra were calculated assuming a white runup spectrum of mode-4 edge waves of unit amplitude, although the results would be essentially the same for standing waves or any edge-wave mode above 2. The structure, in the infragravity band, of these synthetic spectra corresponded reasonably well with the structure of the measured spectra. Total variances of measured cross-shore flow within the infragravity band were nondimensionalized by dividing by total infragravity variances of synthetic spectra. These nondimensional variances were independent of distance offshore and increased with the square of the breaker height. Thus, cross-shore flow due to infragravity waves can be estimated with knowledge of the nearshore profile and incident wave conditions.

scholarly journals IS SURF BEAT FORCED OR FREE?

1984 ◽  
Vol 1 (19) ◽  
pp. 59 ◽  
Author(s):  
David A. Huntley ◽  
Chang S. Kim
Keyword(s):  
Incident Wave ◽  
Wave Motion ◽  
Field Experiments ◽  
Beat Frequency ◽  
Low Frequency ◽  
Strongly Correlated ◽  
Edge Waves ◽  
Weakly Coupled ◽  
Dominant Feature ◽  
Incident Waves

Although many field experiments have shown that surf beat motion, with periods longer than incident wave periods, becomes the dominant feature of the nearshore velocity field as the shoreline is approached, the nature of this motion is still not fully understood. This paper describes a field experiment on a sheltered beach which was designed to distinguish between long wave motion directly forced by the incident wave envelope (as suggested by Longuet-Higgins and Stewart, 1962), and wave motion which is only weakly coupled to the local incident waves and therefore essentially free. The results for on/offshore flows show that low frequency surf beat (frequency less than 0.03 Hz) is strongly correlated with the wave envelope, suggesting the dominance of forced wave motion at these frequencies. In a higher frequency band, between 0.06 and 0.095 Hz, the correlation is generally much lower, suggesting that free wave motion, possibly subharmonic edge waves, is significant in this band. The longshore flows are much more weakly correlated to the envelope of either the longshore or on/offshore components of the orbital velocity. This is consistent with previous observations that edge wave motion dominates the longshore surf beat motion.

Caracteristiques morphologiques et conditions d'apparition de croissants de plage dans des environnements macrotidaux

2000 ◽  
Vol 171 (6) ◽  
pp. 649-656 ◽  
Author(s):  
Olivier Monfort ◽  
Franck Levoy ◽  
Claude Larsonneur
Keyword(s):  
Incident Wave ◽  
Sandy Beaches ◽  
Edge Waves ◽  
Tidal Zone ◽  
Wave Characteristics ◽  
Specific Direction ◽  
Wave Trains ◽  
Beach Cusps ◽  
First Time ◽  
Topographic Surveys

Abstract Beach cusps are sometimes present on the upper foreshore of sandy beaches along the northwest coast of France characterised by very large tidal ranges. These forms were observed on the high tidal zone of Luc-sur-Mer in the "baie de Seine" during morphodynamic surveys conducted between May and July 1996. Topographic surveys showed these cusps to be depositional features. The profile and incident wave characteristics do not favour the theory of cusp formation based on the presence of subharmonic edge waves, while the spacing between the horns is in disagreement with the theory of "self-organisation". The wave record on the lower beach shows, at the time of their appearance, two incident wave trains each with a specific direction and period. The observed beach cusps appear to be induced by the intersection of these two wave trains, thus confirming, for the first time in the field observations, experiments conducted in laboratory.

Formation and composition of training flax collection

2020 ◽  
pp. 61-71
Author(s):  
L.M. Kryvosheieva ◽  
V.I. Chuchvaha ◽  
N.M. Kandyba
Keyword(s):  
Plant Breeding ◽  
Gene Pool ◽  
Phenotypic Variability ◽  
Plant Genetic Resources ◽  
Field Measurements ◽  
Educational Process ◽  
Educational Institutions ◽  
Economic Traits ◽  
Wide Range ◽  
History Of

Aim. Based on the results of multi-year research into the flax gene pool, to form a flax training collection to provide breeding scientific organizations and educational institutions with collection samples as well as with information about the bast crop gene pool. Results and Discussion. The studies were conducted in the crop rotation fields for breeding and seed production of the Institute of Bast Crops of the NAAS (Hlukhiv, Sumska Oblast) in 1992-2018. The field measurements and laboratory analyses were carried out in accordance with conventional methods of field and laboratory studies of collection flax samples.The article presents the results on the formation of a training collection of flax at the Institute of Bast Crops of the NAAS, which has 117 accessions (11 botanical species and three varieties) from 22 countries. In addition to species diversity, the collection includes accessions with different levels of expression of valuable economic and biological characteristics. It also includes accessions selected by phenotypic variability of individual characters or their combinations. The multi-year research into the flax collection accessions resulted in identification of sources of highly-expressed valuable economic traits, which are of interest for the plant breeding course. The history of flax breeding in Ukraine is shown, where breeding varieties that are most widespread or were significant breeding achievements in solving certain problems, are presented. The collection can be used as a visual aid for the plant breeding course in educational programs; in addition, it can provide starting material for scientific and educational institutions. The collection is registered with the National Center for Plant Genetic Resources of Ukraine (certificate No. 00273 dated 04/11/2019). Conclusions. The studies of accessions from the national flax collection allowed us to build up a training collection and register it with the NCPGRU. The collection represents a wide range of biological and economic features of the gene pool of this crop. The collection can be used in the educational process of educational agricultural and biological institutions. The multi-year research into the national flax collection resulted in identification of sources of highly-expressed valuable economic traits, which are of interest to the plant breeding course. The history of flax breeding in Ukraine got covered, and breeding varieties that are most widespread or were significant breeding achievements in solving certain problems are presented.

Précis ofUnified theories of cognition

1992 ◽  
Vol 15 (3) ◽  
pp. 425-437 ◽  
Author(s):  
Allen Newell
Keyword(s):  
Cognitive Science ◽  
Full Range ◽  
Cognitive Architecture ◽  
Convincing Evidence ◽  
Syllogistic Reasoning ◽  
Human Cognition ◽  
Unified Theory ◽  
Theoretical Concepts ◽  
Wide Range ◽  
Unified Theories

AbstractThe book presents the case that cognitive science should turn its attention to developing theories of human cognition that cover the full range of human perceptual, cognitive, and action phenomena. Cognitive science has now produced a massive number of high-quality regularities with many microtheories that reveal important mechanisms. The need for integration is pressing and will continue to increase. Equally important, cognitive science now has the theoretical concepts and tools to support serious attempts at unified theories. The argument is made entirely by presenting an exemplar unified theory of cognition both to show what a real unified theory would be like and to provide convincing evidence that such theories are feasible. The exemplar is SOAR, a cognitive architecture, which is realized as a software system. After a detailed discussion of the architecture and its properties, with its relation to the constraints on cognition in the real world and to existing ideas in cognitive science, SOAR is used as theory for a wide range of cognitive phenomena: immediate responses (stimulus-response compatibility and the Sternberg phenomena); discrete motor skills (transcription typing); memory and learning (episodic memory and the acquisition of skill through practice); problem solving (cryptarithmetic puzzles and syllogistic reasoning); language (sentence verification and taking instructions); and development (transitions in the balance beam task). The treatments vary in depth and adequacy, but they clearly reveal a single, highly specific, operational theory that works over the entire range of human cognition, SOAR is presented as an exemplar unified theory, not as the sole candidate. Cognitive science is not ready yet for a single theory – there must be multiple attempts. But cognitive science must begin to work toward such unified theories.

The role of slow magnetostrophic waves in dipole formation in rapidly rotating dynamos

2021 ◽  
Author(s):  
Aditya Varma ◽  
Binod Sreenivasan
Keyword(s):  
Magnetic Field ◽  
Threshold Value ◽  
Dipole Field ◽  
Wave Frequency ◽  
Alfven Wave ◽  
Inertial Waves ◽  
Axial Dipole ◽  
Wide Range ◽  
The Magnetic Field

<p>It is known that the columnar structures in rapidly rotating convection are affected by the magnetic field in ways that enhance their helicity. This may explain the dominance of the axial dipole in rotating dynamos. Dynamo simulations starting from a small seed magnetic field have shown that the growth of the field is accompanied by the excitation of convection in the energy-containing length scales. Here, this process is studied by examining axial wave motions in the growth phase of the dynamo for a wide range of thermal forcing. In the early stages of evolution where the field is weak, fast inertial waves weakly modified by the magnetic field are abundantly present. As the field strength(measured by the ratio of the Alfven wave to the inertial wave frequency) exceeds a threshold value, slow magnetostrophic waves are spontaneously generated. The excitation of the slow waves coincides with the generation of helicity through columnar motion, and is followed by the formation of the axial dipole from a chaotic, multipolar state. In strongly driven convection, the slow wave frequency is attenuated, causing weakening of the axial dipole intensity. Kinematic dynamo simulations at the same parameters, where only fast inertial waves are present, fail to produce the axial dipole field. The dipole field in planetary dynamos may thus be supported by the helicity from slow magnetostrophic waves.</p>

Assessment of Certainty of Ventilation Processes Mathematical Modeling

2015 ◽  
Vol 725-726 ◽  
pp. 1255-1260
Author(s):  
Tamara Daciuk ◽  
Vera Ulyasheva
Keyword(s):  
Mathematical Modeling ◽  
Turbulent Flows ◽  
Turbulence Models ◽  
Field Measurements ◽  
Heat Emission ◽  
Emission Sources ◽  
Wide Range ◽  
Calculation Results ◽  
Definition Of ◽  
Semiempirical Models

Numerical experiment has been successfully used during recent 10-15 years to solve a wide range of thermal and hydrogasodynamic tasks. Application of mathematical modeling used to design the ventilation systems for production premises characterized by heat emission may be considered to be an effective method to obtain reasonable solutions. Results of calculation performed with numerical solution of ventilation tasks depend on turbulence model selection. Currently a large number of different turbulence models used to calculate turbulent flows are known. Testing and definition of applicability limits for semiempirical models of turbulence should be considered to be a preliminary stage of calculation. This article presents results of test calculations pertaining to thermal air process modeling in premises characterized by presence of heat emission sources performed with employment of different models of turbulence. Besides, analysis of calculation results and comparison with field measurements data are presented.

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