Monitoring of the water particle velocity field near the seabed under different wave and tidal scenarios: a real case

Monitoring of water particle velocity on the sea bed is crucial to study morphological shore changes in a coast at intermediate and shallow water depth under progressive surface waves and tidal flow current. Therefore, 3-D particle velocity was monitored continuously at the bottom of Santa Maria del Mar (SMM) beach (SW Spain) by means of a single point current meter during 3 weeks in 2007 since August 28. The current meter was placed at 0.45m above the seabed in order to acquire instantaneous velocity. Wave properties (height and period) were taken from the nearby wave buoy and tidal data were taken from a tidal gauge station. Wave-induced bottom particle velocities were obtained during spring and neap tides at a d/L (depth over wave length) parameter ranging from 0.06 to 0.3. Bottom water particle velocity near the seabed ranges from 0 to ± 0.5 m/sec of which about 82% does not exceed 0.2 m/sec during monitoring. Therefore, only 18% of the surveyed water particle velocities exceed the critical Shield parameter of the beach sand (d50 = 0.23mm) which is about 0.05-0.2 depending on Reynolds number. Results show that maximum horizontal speed is obviously lower during the slack tide (high or low tide) in comparison with flood tide and ebb tide. Moreover, speed is higher during ebb tide in comparison to adjacent flood tide, with steady wave climate. Finally and among other conclusions, the maximum real values of the bottom current surveyed in SMM, as well as the Shield parameter, substantially coincide with the theoretical estimates calculated for a given wave and tidal climate

Composite Seawall for Wave Energy Conversion

Detrimental impacts of fossil fuels and its foreseen scarcity are encouraging research for the development of the renewable energy as alternatives. A newly developed composite seawall concept could be a vitally important technique for wave energy conversion. A 3-D model of composite seawall has been simulated to comprehend its hydraulic performance. Composite seawall is a dual-purpose overtopping type of coastal shoreline device and wave energy conversion is considered as by-product of the seawall. Overtopped water generates hydraulic head convertible to electricity by means of low head hydro-power generator. A 3-D physical model of composite seawall has been developed and tested for both normal and oblique waves in this study. Fraude scale laws (geometric scale 1:50) are followed in the model scaling. Total 72 simulations are conducted, and overtopping and hydraulic power generated at the crest of the ramp of the composite seawall for each simulated wave parameters are recorded. Hydraulic performances are measured based on the input wave parameters and results. Wave breaker screen is also modeled and tested (by 12 simulations) to measure its suitability as outfall. Results show that maximum achievable hydraulic efficiency of the composite seawall is about 33.6 % and average hydraulic efficiencies are about 26.6%, 18.6%, 15.9% and 11.1% for the freeboard of 0.5 m, 1.0 m, 1.5 m and 2.0 m respectively. Hydraulic performance decreases for oblique wave approaches. Average hydraulic efficiency of a composite seawall (having 1.0 m freeboard) is about 20% in case of 1.0 m tidal variation. Composite seawall is not suitable option for high tidal variations and low wave heights. Wave breaker screen is a suitable outfall option but it decreases hydraulic head generated in the composite sea walls up to 12.5%. Composite sea walls for wave energy extraction could be suitable option in such a remote place such as Islands, where conventional energy supply would be highly expensive and rarely possible.Erasmus Mundus MSc CoMEMsection Hydraulic EngineeringCivil Engineering and Geoscience