Solitary and cnoidal wave scattering by a submerged horizontal plate in shallow water

Solitary and cnoidal wave transformation over a submerged, fixed, horizontal rigid plate is studied by use of the nonlinear, shallow-water Level I Green-Naghdi (GN) equations. Reflection and transmission coefficients are defined for cnoidal and solitary waves to quantify the nonlinear wave scattering. Results of the GN equations are compared with the laboratory experiments and other theoretical solutions for linear and nonlinear waves in intermediate and deep waters. The GN equations are then used to study the nonlinear wave scattering by a plate in shallow water. It is shown that in deep and intermediate depths, the wave-scattering varies nonlinearly by both the wavelength over the plate length ratio, and the submergence depth. In shallow water, however, and for long-waves, only the submergence depth appear to play a significant role on wave scattering. It is possible to define the plate submergence depth and length such that certain wave conditions are optimized above, below, or downwave of the plate for different applications. A submerged plate in shallow water can be used as a means to attenuate energy, such as in wave breakers, or used for energy focusing, and in wave energy devices

Ocean wave spectra off Cochin, west coast of India

106-112Spectra of waves off Cochin are generally multipeaked and wide-banded with high frequency sides showing similar slopes. The slope is milder than that proposed by Phillips (1958) for fully developed sea conditions. Examination of weather maps relating to the period of study explains the multipeakedness in the spectra to be due to the presence of sea waves and swells. The observed spectra are closer to those of Scott and Scott-Wiegel with the latter fitting the peak better. An average spectrum defined in terms of only wave heights is proposed for the location studied

Co-operation and the urban environment: An exploration

Many urban environmental problems (such as littering of streets) arise from the open access character of the resource concerned and can be analysed in the framework of co-operation. Studies in the context of rural commons have indicated that though seeming to be violating a narrow definition of rationality, people do cooperate. This paper attempts to explore some issues in the context of the urban environment, focusing on solid waste management in Madras, India, and a co-operation based institution called Exnora. A number of hypotheses on the conditions affecting co-operation are examined. While group size may be relevant for costs, it does not have any impact on co-operation. The management style of committees and economies of scope seem to be important.