Showing papers by "Vallam Sundar published in 2012"

Performance of flexible emergent vegetation in staggered configuration as a mitigation measure for extreme coastal disasters

Abstract: The performance characteristics of emergent greenbelt vegetation has received considerable attention in the recent years, post-Great Indian Ocean Tsunami (26 December 2004). In the present work, a comprehensive laboratory study on the hydraulic resistance characteristics due to a group of slender cylindrical members representing flexible plantation has been carried out in a laboratory open channel. The model stem groups comprised of individual members of different sizes and concentrations in staggered configuration. The sizes and concentrations were chosen in such a way that they would fall into the practical ranges of vegetations in coastal forestry. The results indicate that the flow resistance varies with stem concentration, stem diameter and elastic properties of the individual members and the flow velocity. Based on the results, the Darcy friction factor, f, for various flow and vegetative parameters was derived. A new empirical equation is proposed for evaluating f for partially submerged vegetation in staggered configuration for a wide range of depths of flow in relation to un-deflected plant heights. It is expected that the f thus determined will be useful in modelling the shallow flows using shallow water equations.

Role of vegetation on beach run-up due to regular and cnoidal waves.

Abstract: The effectiveness of measures in protecting the coast against natural hazards depends on the extent of run-up by ocean waves, which is an essential parameter in their planning and design. Although, several formulae have been derived in the past for estimation of run-up in laboratory studies for a variety of wave front structures, certain uncertainties still remain pertaining to flat slopes and long waves. To understand the performance characteristics of vegetation in attenuating run-up, a comprehensive experimental investigation was taken up. The studies were carried out with regular and cnoidal waves propagating over a plane slope of 1 ∶ 30 in the presence and absence of vegetation of different characteristics. The results on the variation of dimensionless run-up as a function of wave and vegetal parameters are presented and discussed in this paper.

Review of the research on emerged and submerged semicircular breakwaters

Abstract: Scientists and researchers are currently focusing considerable attention on the hydrodynamic characteristics of semicircular breakwaters worldwide, particularly in Japan and the People’s Republic o...

Performance of a perforated submerged semicircular breakwater due to non-breaking waves

Abstract: The present experimental research work focused on how a semicircular breakwater performs hydrodynamically under submerged conditions. In the field, a submerged semicircular breakwater may be preferred in front of the vertical breakwater to mitigate the wave forces and to minimize coastal erosion on its lee side. Various parameters affect the hydrodynamic performance of a semicircular breakwater such as the reflection and transmission characteristics, the dimensionless pressures, the horizontal forces and the vertical forces, and these are considered in the present study. Experiments were performed for three different perforations, namely 7%, 11% and 17%, of the exposed surface area with perforations on its sea side (sea-side perforated) and on both sides (fully perforated) owing to regular and random waves. The effect of the water depth was also studied in addition to the effect of perforation. All the hydrodynamic characteristics considered for the present study on the semicircular caisson are presented ...

The effects of flexible vegetation on forces with a Keulegan-Carpenter number in relation to structures due to long waves

Abstract: Extreme coastal events require careful prediction of wave forces. Recent tsunamis have resulted in extensive damage of coastal structures. Such scenarios are the result of the action of long waves on structures. In this paper, the efficiency of vegetation as a buffer system in attenuating the incident ocean waves was studied through a well controlled experimental program. The study focused on the measurement of forces resulting from cnoidal waves on a model building mounted over a slope in the presence and absence of vegetation. The vegetative parameters, along with the width of the green belt, its position from the reference line, the diameter of the individual stems as well as the spacing between them, and their rigidity are varied so as to obtain a holistic view of the wave-vegetation interaction problem. The effect of vegetation on variations of dimensional forces with a Keulegan-Carpenter number (KC) was discussed in this paper. It has been shown that when vegetal patches are present in front of structure, the forces could be limited to within F*≤1, by a percentile of 92%, 90%, 55%, and 96%, respectively for gap ratios of 0.0, 0.5, 1.0, and 1.5. The force is at its maximum for the gap ratio of 1.0 and beyond which the forces start to diminish.

Empirical Equation for the Prediction of Run-Up Due to Random Waves on Beaches Fronted by Vegetation

Abstract: The run-up due to ocean waves on an open coast and over coastal structures is an essential parameter in their planning, design and effectiveness in protecting the shore against natural hazards. Most of the formulae derived in the past for run-up through laboratory studies are for sloping walls exposed to the action of regular and random waves. The presence of vegetation, however, is expected to alter the flow field, thereby resulting in an uncertainty in the application of the existing formulae. A well-controlled experimental program to investigate the effect of vegetation on the run-up due to regular, random and cnoidal waves has been carried out. The details of the parameters adopted for the waves and vegetation, test set-up, experimental procedure, analysis of the results and discussion are reported in this paper.