scholarly journals EXCITATION OF LOW FREQUENCY TRAPPED WAVES

1978 ◽  
Vol 1 (16) ◽  
pp. 25
Author(s):  
Robert King ◽  
Ronald Smith
Keyword(s):  
Incident Wave ◽  
Standing Waves ◽  
Low Frequency ◽  
Nonlinear Interactions ◽  
Edge Waves ◽  
Constant Depth ◽  
Side Band ◽  
Rectangular Basin ◽  
Trapped Wave ◽  
Narrow Wave

Weak nonlinear interactions in water of non-constant depth between an incident wave, a side-band incident wave and a relatively low frequency trapped wave are shown to lead to the generation of the trapped wave. Three situations are considered in detail: edge waves in a wide rectangular basin, progressive edge waves on a straight beach, and standing waves in a narrow wave tank.

Seiche Excitation in Port San Juan, British Columbia

1979 ◽  
Vol 36 (10) ◽  
pp. 1223-1227
Author(s):  
D. D. Lemon ◽  
P. H. LeBlond ◽  
T. R. Osborn
Keyword(s):  
British Columbia ◽  
Water Waves ◽  
Pressure Gauge ◽  
Low Frequency ◽  
San Juan ◽  
External Forcing ◽  
Edge Waves ◽  
Rectangular Basin ◽  
Juan De Fuca ◽  
Juan De Fuca Strait

Seiche motions observed in San Juan Harbour with a bottom-mounted pressure gauge have been Fourier-analyzed and interpreted in terms of a theoretical model of oscillations in a rectangular basin with an exponential depth profile. Two of the observed periods (at 14.6 and 38.5 min) are identified with resonances of the basin; two other significant low frequency peaks (at 21 and 55 min) do not coincide with resonant periods of the basin and must be due to strong external forcing. Higher frequency fluctuations (20–160 s) are attributed to swell and to its subharmonic interactions with edge waves. Key words: water waves, seiches, mathematical model, Juan de Fuca Strait, British Columbia

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.

Vibronic side bands of Sm2+ in alkali halides

1969 ◽  
Vol 47 (17) ◽  
pp. 1757-1767 ◽  
Author(s):  
M. Buchanan ◽  
E. J. Woll Jr.
Keyword(s):  
Low Frequency ◽  
Alkali Halides ◽  
Frequency Region ◽  
Defects In Crystals ◽  
Side Band

The calculation of vibronic side bands of defects in crystals is discussed. A model for the deformation of the lattice about a Sm2+ defect in alkali halides and side-band calculations on this model for KBr and KCl containing Sm2+ are compared with experimentally observed side bands. Improvements, particularly in the low frequency region, are found over the calculations assuming no deformation.

scholarly journals Trapped Planetary (Rossby) Waves Observed in the Indian Ocean by Satellite Borne Altimeters

2017 ◽  
Author(s):  
Yair De-Leon ◽  
Nathan Paldor
Keyword(s):  
Indian Ocean ◽  
Rossby Waves ◽  
Low Frequency ◽  
Propagation Speed ◽  
Wave Theory ◽  
Planetary Waves ◽  
Sea Surface ◽  
Trapped Wave ◽  
The Indian Ocean ◽  
Frequency Variations

Abstract. Using 20 years of accurately calibrated, high resolution, observations of Sea Surface Height Anomalies (SSHA) by satellite ‎borne altimeters we show that in the Indian Ocean south of the Australian coast the low frequency variations of SSHA are ‎dominated by westward propagating, trapped, i.e. non-harmonic, planetary waves. Our results demonstrate that the ‎meridional-dependent amplitudes of the SSHA are large only within a few degrees of latitude next to the South-Australian ‎coast while farther in the ocean they are uniformly small. This meridional variation of the SSHA signal is typical of the ‎amplitude structure in the trapped wave theory. The westward propagation speed of the SSHA signals is analyzed by ‎employing three different methods of estimation. Each one of these methods yields speed estimates that can vary widely ‎between adjacent latitudes but the combination of at least two of the three methods yields much smoother variation. The ‎estimates obtained in this manner show that the observed phase speeds at different latitudes exceed the phase speeds of ‎harmonic Rossby (Planetary) waves by 140 % to 200 %. In contrast, the theory of trapped Rossby (Planetary) waves in a ‎domain bounded by a wall on its equatorward side yields phase speeds that approximate more closely the observed phase ‎speeds.‎

scholarly journals GROIN LENGTH AND THE GENERATION OF EDGE WAVES

1976 ◽  
Vol 1 (15) ◽  
pp. 85 ◽  
Author(s):  
Michael K. Gaughan ◽  
Paul D. Komar
Keyword(s):  
Incident Wave ◽  
Wave Length ◽  
Critical Length ◽  
Beach Erosion ◽  
Rip Currents ◽  
Edge Waves ◽  
Normal Waves ◽  
Wave Basin ◽  
Incident Waves ◽  
Selection Of

A series of wave basin experiments were undertaken to better understand the selection of groin spacings and lengths. Rather than obtaining edge waves with the same period as the normal incident waves, subharmonic edge waves were produced with a period twice that of the incoming waves and a wave length equal to the groin spacing. Rip currents were therefore not formed by the interactions of the synchronous edge waves and normal waves as proposed by Bowen and Inman (1969). Rips were present in the wave basin but their origin is uncertain and they were never strong enough to cause beach erosion. The generation of strong subharmonic edge waves conforms with the work of Guza and Davis (1974) and Guza and Inman (1975). The subharmonic edge waves interacted with the incoming waves to give an alternating sequence of surging and collapsing breakers along the beach. Their effects on the swash were sufficient to erode the beach in some places and cause deposition in other places. Thus major rearrangements of the sand were produced between the groins, but significant erosion did not occur as had been anticipated when the study began. By progressively decreasing the length of the submerged portions of the groins, it was found that the strength (amplitude) of the edge waves decreases. A critical submerged groin length was determined whereby the normally incident wave field could not generate resonant subharmonic edge waves of mode zero with a wavelength equal to the groin spacing. The ratio of this critical length to the spacing of the groins was found in the experiments to be approximately 0.15 to 0.20, and did not vary with the steepness of the normal incident waves.

Effect of Coriolis force on edge waves (I) Investigation of the normal modes

2020 ◽  
Vol 78 (4) ◽  
pp. 229-261
Author(s):  
Robert O. Reid
Keyword(s):  
Coriolis Force ◽  
Wind Stress ◽  
Formal Solution ◽  
Wave Length ◽  
Normal Modes ◽  
Low Frequency ◽  
Phase Speed ◽  
Free Edge ◽  
Edge Wave ◽  
Edge Waves

Essentially two classes of free edge waves can exist on a sloping continental shelf in the presence of Coriolis force. For small longshore wave length, fundamental waves of the first class behave like Stokes edge waves. However, for great wave lengths (of several hundred kilometers or more) the characteristics of the first class are significantly altered. In the northern hemisphere the phase speed for waves moving to the right (facing shore from the sea) exceeds the speed for waves which move to the left. Also, the group velocity for a given edge wave mode has a finite upper limit. Waves of the second class are essentially quasigeostrophic boundary waves with very low frequency and, like Kelvin waves, move only to the left (again facing shore from the sea). Unlike Stokes edge waves, those of the quasigeostrophic class are associated with large vorticity. Examination of the formal solution for forced edge waves indicates that those of the second class may be excited significantly by a wind stress vortex. Also, in contrast to the conclusion of Greenspan (1956), it is proposed that a hurricane can effectively excite the higher order edge wave modes in addition to the fundamental if wind stress is considered.

scholarly journals High-frequency homogenization for periodic media

2010 ◽  
Vol 466 (2120) ◽  
pp. 2341-2362 ◽  
Author(s):  
R. V. Craster ◽  
J. Kaplunov ◽  
A. V. Pichugin
Keyword(s):  
High Frequency ◽  
Wave Equations ◽  
Standing Waves ◽  
Low Frequency ◽  
Homogenization Theory ◽  
Periodic Media ◽  
Mode Spectrum ◽  
Bloch Mode ◽  
Long Wavelength Asymptotics ◽  
Model Equations

An asymptotic procedure based upon a two-scale approach is developed for wave propagation in a doubly periodic inhomogeneous medium with a characteristic length scale of microstructure far less than that of the macrostructure. In periodic media, there are frequencies for which standing waves, periodic with the period or double period of the cell, on the microscale emerge. These frequencies do not belong to the low-frequency range of validity covered by the classical homogenization theory, which motivates our use of the term ‘high-frequency homogenization’ when perturbing about these standing waves. The resulting long-wave equations are deduced only explicitly dependent upon the macroscale, with the microscale represented by integral quantities. These equations accurately reproduce the behaviour of the Bloch mode spectrum near the edges of the Brillouin zone, hence yielding an explicit way for homogenizing periodic media in the vicinity of ‘cell resonances’. The similarity of such model equations to high-frequency long wavelength asymptotics, for homogeneous acoustic and elastic waveguides, valid in the vicinities of thickness resonances is emphasized. Several illustrative examples are considered and show the efficacy of the developed techniques.

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