Waves In Coastal Waters Research Articles

Numerical experiments on the generation of long ocean waves in coastal waters of the Buenos Aires province, Argentina

A numerical model (two horizontal dimensions, vertically integrated) is used to investigate the generation of long ocean waves, ranging from 20 min to almost 2 h, at Buenos Aires continental shelf. The domain includes the Río de la Plata estuary and the continental shelf together and extends from 33.5° to 40.5°S latitude, and from 51° to 63°W longitude. Sea-level oscillations are modeled by forcing with passage of atmospheric cold fronts and atmospheric gravity waves. Both forcing mechanisms, which have been present during high activity lapses of long ocean waves, are mathematically implemented. After several numerical simulations, it is concluded that the pressure and wind fields associated to cold fronts do not generate long ocean waves in the area, though they do produce disturbances with periods longer than the tidal ones. On the other hand, it is so concluded that atmospheric gravity waves are an effective mechanism to force long ocean waves. Results obtained show that generation of long ocean waves is highly sensitive depending on the propagation direction and the phase speed of the atmospheric gravity waves. The long ocean wave event detected during the large-amplitude gravity-wave event of 13 October 1985 is successfully simulated. Finally, all our results suggest that atmospheric gravity waves are a highly effective mechanism forcing for the generation of long ocean waves in Buenos Aires coastal waters.

Improved coastal boundary condition for surface water waves

Surface water waves in coastal waters are commonly modeled using the mild slope equation. One of the parameters in the coastal boundary condition for this equation is the direction at which waves approach a coast. Three published methods of estimating this direction are examined, and it is demonstrated that the wave fields obtained using these estimates deviate significantly from the corresponding analytic solution. A new method of estimating the direction of approaching waves is presented and it is shown that this method correctly reproduces the analytic solution. The ability of these methods to simulate waves in a rectangular harbor is examined.

Monitoring surface waves in coastal waters by integrating HF radar measurement and modelling

A new scheme for retrieval of wave spectra in coastal seas from HF radar data has been developed which is capable of measuring directional wave spectra even from the data of the single antenna array. It does this by making use of a wave propagation model to link wave spectra, and therefore also HF radar Doppler spectra at different points in space. The resulting scheme processes all HF radar data within the area covered by the system simultaneously. In coastal applications, the method offers increased flexibility in the radar configuration and improved coverage. Tests are reported on simulated HF radar data, and a first application to HF radar data collected near Holderness on the English east coast is reported.

Observation of Short Wind Waves in Coastal Waters*

Abstract Observations of wind-generated gravity–capillary waves have been made during two recent field programs in coastal environments. The results of wave slope spectra on clean water show a well-defined correlation with the wind friction velocity. However, spectral values at higher wavenumbers (above 200 rad m−1) are significantly higher than previous laboratory results. In the presence of surface films wave spectra may decrease by more than one order of magnitude at lower wind stresses. The dispersion characteristics of short waves vary markedly depending on the wavenumber, the wind stress, and the surface chemical condition. Some results in the presence of surface films at intermediate winds show much higher apparent phase speeds than the theoretical dispersion relation. This may be because of an enhanced near-surface current or because of the relative increase of wave energy that is phase-locked to longer steep gravity waves.

Current measurements over the western continental shelf of India

Current meter observations obtained from a site off Goa (15°08′N, 73°16′E) over the western continental shelf of India are presented. Data were collected from the site during three different months in a water column of depth about 100 m. The nature of flows are described by means of visual display, linear regression and spectral analysis. The flows are a result of the superimposition of oscillations of wide-ranging frequencies over a weak mean flow. The mean flow was towards south during May and March and towards north during November. The spectral analysis indicates that the inertial and semidiurnal frequency motions are the major contributors to the current structure. The inertial currents were concentrated near the surface with a rapid decay towards the bottom. The analysis also indicates that the diurnal and semidiurnal motions are mainly due to baroclinic internal tides rather than due to barotropic surface tides. Above the semidiurnal frequencies the currents were composed mainly of high-frequency oscillations of comparatively low magnitudes. These motions are strongly time-dependent and they may be related to internal waves in coastal waters.

On the radiation damping of finite-amplitude progressive edge waves

Using small-amplitude expansions, it is demonstrated that weakly nonlinear periodic edge waves, travelling along the shoreline of a beach, can be attenuated owing to radiation of oblique waves out to sea. A few beach profiles, for which edge-wave dispersion relations are known in closed form, are discussed, and necessary conditions are determined for such radiation to occur due to nonlinear self-interactions. In particular, it is shown that quadratic nonlinear interactions cause the second edge-wave mode on a uniformly sloping beach of slope α to radiate when 1/18π < α < ⅙π; a detailed derivation to find the amplitude of the radiated wave and the attendant decay rate of the edge wave is presented, using the full water-wave theory. Also, it is pointed out that a concomitant nonlinear mechanism can transfer energy from incoming oblique waves to subharmonic edge waves – a plausible mechanism for the generation of travelling edge waves in coastal waters – and the details of this process are discussed within the framework of a shallow-water model.

Waves in coastal waters off Mangalore Pt. I: Distribution of wave characteristics

Wave records obtained from the pressure recorder for measuring sea waves, installed off Mangalore have been analysed and wave parameters like period, height etc. have been obtained for the period June 1968 to May 1969. Frequency distribution of wave heights and periods during various months have been drawn. Energy spectra obtained from the data are presented. From the study of the distributions of wave parameters it has been found that period follows normal distribution and the height follows Rayleigh distribution. The energy spectra .are composite In nature giving the average condition for a month when the record for the whole month 18 considered as a single record.

Observations of the Directional Characteristics of Sea Waves

Summary Simultaneous records of orbital velocity and pressure disturbance in wind generated waves have been analysed by power spectral methods, to obtain the first five angular harmonics of the directional spectrum. The observations were made at a coastal site, offshore from a gently sloping beach, where the bottom topography was sufficiently simple to permit corrections for the effects of refraction. The orbital velocities were measured by an electromagnetic flowmeter and the pressure disturbance by an N.I.O. pressure recorder. A capacitance probe was also available for recording the surface elevation. A computer program has been developed which computes the auto and cross-spectra of the pressure and velocity components, the angular harmonics and a smoothed estimate of the directional spectrum directly from data which were recorded digitally on punched paper tape. Estimates of the mean direction and the width of the directional spectrum and its skewness, have been obtained for a wide range of frequencies and related to wind conditions in the generating area. After correction for refraction, the mean direction of the waves was found to correspond well to the mean wind direction. For waves generated by a reasonably constant wind field, the spectrum width exhibits a general tendency to increase with frequency. At low frequencies the spectrum width corrected for refraction is not inconsistent with the resonance angle given by Phillips’ theory, while at frequencies just above the transition frequency defined by the combined Miles-Phillips theory, the spectrum is appreciably narrower than the resonance angle. The smoothed directional spectrum estimate based on five harmonics gives no indication of bimodality in the spectrum. A method of obtaining improved angular resolution using an array of three flowmeters to obtain four additional harmonics was only partially successful on account of turbulent interference generated by the pier structure to which the sea units were attached. The surface power spectrum was found to fit the equilibrium power law at high frequencies under saturation conditions. A spectrum obtained under conditions very similar to those in the SWOP project has been compared with the SWOP spectrum. Marked differences between the two suggest that bottom friction is a major influence on waves in coastal waters. The attenuation of the waves in depth was determined from the ratios of the surface elevation and pressure spectra. No significant departure

Sea waves in coastal waters of the British Isles : Darbyshire, M., 1962. Deutsch. Hydrogr. Z., 15 (6): 256–264

Sea waves in coastal waters of the British Isles : Darbyshire, M., 1962. Deutsch. Hydrogr. Z., 15 (6): 256–264

Sea waves in coastal waters of the British isles

Wave records obtained from the Smith's Knoll and Morecambe Bay light vessels are used to obtain relationships between wind speed and wave height and period in shallow water conditions for various lengths of fetch. Spectra obtained from data from the Smith's Knoll, Morecambe Bay and Seven Stones light vessels are presented. The spectrum formula for shallow water is found to be identical with that for deep water, found previously, with the same modifications for short fetch conditions.