Variety Of Wave Conditions Research Articles

A numerical model for beach profile development

A time-dependent numerical model that calculates beach profile development due to offshore sediment transport is developed. The model allows variable wave conditions, water level fluctuations due to tide, arbitrary bathymetry, and sediment size. The accuracy of the model is tested by comparison of calculations with laboratory and with field data. The agreement between calculated and measured beach profiles is good. Key words: numerical model, beach profile, laboratory tests, field data.

ONSHORE-OFFSHORE SEDIMENT TRANSPORT NUMERICAL MODEL

A numerical model is presented for calculating beach profile development due to offshore sediment transport and tested with laboratory and field data. The model allows variable wave conditions, water level fluctuations due to tide and storm surge, arbitrary bathymetry, and arbitrary sediment size. The agreement between calculated and measured beach profile erosion is good.

FIELD INVESTIGATIONS OF SUSPENDED SEDIMENT TRANSPORT IN THE NEARSHORE ZONE

The suspended sediment distribution and longshore sediment transport characteristics at Leadbetter Beach, Santa Barbara, California were investigated using a series of miniature optical backseatter sensors which can measure particle concentrations as high as 180 gm/£ and have 10 Hz frequency response. Vertical arrays of sensors were maintained at up to four positions across the surf zone during 7-25 February 1980 and were operated concurrently with pressure sensors and current meters. Data were collected on a daily basis over 2-4 hour periods. The data were analyzed to reveal concentration profiles of suspended sediment, the average suspended sediment loads, and the longshore particle flux in relation to varying wave conditions. Results show that sediment transport occurs as individual suspension events related to incident wave motions and infragravity motion oscillations within the surf zone; suspended sediment concentration decreases approximately logarithimically away from the seabed; the maximum values of longshore transport rates occur in the mid-surf zone; and the measured suspended sediment longshore transport rate is equal to the total longshore transport rate as predicted by existing transport equations.

The design of dynamic ship positioning control systems using stochastic optimal control theory

AbstractThe design of dynamic ship positioning control systems and their associated wave filters is considered. The control problems and the basic components in the system are discussed first. The model of the vessel is then described, since this plays an important role in the design of the Kalman filter which is used to estimate the low frequency motions of the vessel. The model involves both high and low frequency subsystems. The total linearized model for the vessel is represented by state equations, and simulation results are given to illustrate the performance of the Kalman filter. A comparison with a notch filter is also presented.The design of the optimal control system using LQG stochastic control results is considered. The operation of the system under various operating conditions is illustrated. Schemes involving the extended Kalman filter are then described. These enable more realistic non‐linear models of the plant to be employed within the filter. This is shown to be unnecessary in the case of the low frequency ship model. However, the extended filter may be useful to track varying wave conditions (using parameter estimation) as represented in the high frequency model. Two extended filtering schemes are presented for this case.

On the relationship of radar backscatter to wind speed and fetch

The physics of the interaction of electromagnetic waves with the ocean surface has been an active area of research for a number of years. We present here the results of satellite and aircraft experiments to investigate the ability of active microwave radars to infer surface wind speeds remotely. Data obtained from the recent National Aeronautics and Space Administration (NASA) Skylab experiment are compared with surface wind speeds measured by low-flying aircraft and ships-of-opportunity and found to give useful estimates of the oceanic wind field. We also investigate the influence of varying wave height on radar measurements of wind speed by measuring the backscattering cross-section for constant wind speed but variable wave conditions. We conclude that this effect is of little importance.

Wave, longshore current, and beach profile records for Santa Margarita River Beach, Oceanside, California, 1949

The results of ten months of measurements of waves, longshore currents, and beach conditions for Santa Margarita River Beach are presented. Tables and graphs give the height, period, and steepness of the incident waves as measured by a subsurface, differential‐type pressure recorder; breaker heights as computed from these data; observed wave directions; longshore current measurements, both magnitude and direction, as obtained by tracing dye thrown into the water; and beach profiles measured along three ranges 500 ft apart from the berm to a depth of about 25 ft. It was found that the three sets of profiles were not consistent in regard to their relationship with varying wave conditions, and further that the type of beach profile (storm or ordinary) apparently did not bear the same relationship to the wave steepness as has been found in laboratory studies.