P. Chandramohan

Longshore sediment transport rate-measurement and estimation, central west coast of India

Abstract Measurements of the longshore sediment transport rate (LSTR) along the surf zone at a 4-km-long beach on the central west coast of India were made over a 4-month period. During the study, both the lateral and vertical distributions of the sediment transport rate were measured with traps deployed on a line spanning the surf zone. Sediment transport in the swash zone was not considered in the present study. The longshore current was measured at each trap location. The breaking wave parameters were calculated from a directional wave buoy at 16-m water depth. The measured values were compared with those calculated from three selected empirical formulas. The standard coefficient values in the empirical formulas were used without calibration to the data sets. The measured average gross transport was 726 m 3 /day and that calculated were 1108, 1017, and 781 m 3 /day based on CERC, Walton and Bruno, and Van Rijn formula. During the data collection 69% of the time, the transport was direct towards north, and in the remaining period, it was direct towards south. The correlation coefficient between the longshore sediment transport rates measured and those calculated by CERC, Walton and Bruno, and Van Rijn formula were 0.38, 0.71, and 0.74, respectively. The average RMS error between the measured and the calculated longshore sediment transport rate based on CERC, Walton and Bruno, and Van Rijn formula were 0.91, 0.57, and 0.47.

Estimation of wave directional spreading in shallow water

Abstract This paper describes wave directional spreading in shallow water. Waves were measured for a period of 2 months using the Datawell directional waverider buoy at 15 m water depth on the east coast of India in the Bay of Bengal. The study also showed that in shallow water wave directional spreading was narrowest at peak frequency and widened towards lower and higher frequencies. The wind direction was found to deviate from the wave direction during most of the time. The unidirectional spectrum was found to be satisfactorily represented by Scott spectra.

ESTIMATION OF ADDED-MASS AND DAMPING COEFFICIENTS OF A TETHERED SPHERICAL FLOAT USING POTENTIAL FLOW THEORY

Abstract Added-mass (α) and damping coefficients (β) of a tethered spherical float, undergoing oscillatory motion in sinusoidal waves, have been derived from the motion generated velocity potential for one degree-of-freedom (surge) using potential flow theory. Variations of added-mass and damping coefficients with respect to water depth, wave period and float size have been obtained. Variations of added-mass and damping coefficients with wave period show that these hydrodynamic coefficients are frequently dependent, and this is because motion generated velocity potential is associated with the generation of surface gravity waves by the oscillating float. The added-mass and damping coefficients are unaffected by water depth, but increase with size of the float. Natural and resonant frequencies of the tethered float are computed for a wide range of wave periods using α and β values. Theoretical values of natural period of sscillation of the float agree closely with the experimental values.