Vallam Sundar

Bio: Vallam Sundar is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Wind wave & Shore. The author has an hindex of 24, co-authored 195 publications receiving 1778 citations. Previous affiliations of Vallam Sundar include Indian Institutes of Technology.

Effects of Power Take-Off Damping and Model Scaling on the Hydrodynamic Performance of Oscillating Water Column Device

Abstract: A systematic numerical investigation on the hydrodynamic performance of an oscillating water column (OWC) system for different damping values from the power take-off (PTO) device and at different model scales has been studied. Further, an experimental programme was devised with a Froude model scale of 1:12 in a shallow wave flume by representing PTO damping by varying the air orifice ratio, a/A [ratio of air orifice area (a) to plan area (A)]. In the case of numerical investigation, simulation was carried out in the computational fluid dynamics (CFD) model, REEF3D. Herein, the equivalent PTO damping on the OWC chamber is represented by the porous media flow relation. First, the numerical results are validated by comparing with the laboratory measurements for five different PTO damping. Second, following the validation stage, the open-source numerical model is used to evaluate model scale effects on the hydrodynamic performance of the OWC by comparing hydrodynamic parameters of four different model scales from 1:12 to full scale. In this paper, the influence of PTO damping and model scales on the variation of pressure behind the lip wall, air pressure, and hydrodynamic efficiency is studied. The results are reported for different relative water depths. Since the air is modelled as incompressible, the effect of scaling on the hydrodynamic performance of OWC is found with negligible variation.

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.

Very severe cyclonic storm impacts to shoreline and beach profiles along the Karaikal coast of India

Abstract: Shorelines experience significant changes near a coastal structure and around the confluence of a river and the sea. Field investigation and site data collection by the latest technologies for the ...

Influence of Harbour Wall on Pressure Variation in an Oscillating Water Column

Abstract: In the midst of a variety of wave energy converters (WECs), the oscillating water column (OWC) device that exploits ocean waves for its energy is an important class. It is a partially submerged structure with an opening to the sea below the water line that traps the air above the water column. Owing to the wave motion, the rise and fall of water level in a closed chamber pump the air thus causing its oscillation to drive a turbine coupled to electric generators. The objective of the present study is to analyse the influence of harbour walls on the pressure variation between the inside and front of the lip wall of a bottom mounted OWC. In contemplation of enumerating the influence of the harbour walls, a two-dimensional physical model study was conducted with a model scale of 1:20 in a 72.5 m long, 2 m wide and 2.5 m deep wave flume. The study was carried out with different configurations of harbour walls by changing its projecting length to examine the response of OWC. The dimensions of OWC have been chosen in such a way that the device can absorb more energy for a particular relative water depth (d/L). The model was exposed to the action of regular waves in order to evaluate the hydrodynamic performance characteristics of the device mainly the effect of the harbour walls. The details of test set-up, testing facility, parameters of models, harbour wall configurations, test procedure, analysis of results and discussion are reported in this paper.

A new family of generalized distributions

Abstract: Kumaraswamy [Generalized probability density-function for double-bounded random-processes, J. Hydrol. 462 (1980), pp. 79–88] introduced a distribution for double-bounded random processes with hydrological applications. For the first time, based on this distribution, we describe a new family of generalized distributions (denoted with the prefix ‘Kw’) to extend the normal, Weibull, gamma, Gumbel, inverse Gaussian distributions, among several well-known distributions. Some special distributions in the new family such as the Kw-normal, Kw-Weibull, Kw-gamma, Kw-Gumbel and Kw-inverse Gaussian distribution are discussed. We express the ordinary moments of any Kw generalized distribution as linear functions of probability weighted moments (PWMs) of the parent distribution. We also obtain the ordinary moments of order statistics as functions of PWMs of the baseline distribution. We use the method of maximum likelihood to fit the distributions in the new class and illustrate the potentiality of the new model with a...

Global trends in wind speed and wave height over the past 25 years

Abstract: Wind speeds over the world’s oceans have increased over the past two decades, as have wave heights. Studies of climate change typically consider measurements or predictions of temperature over extended periods of time. Climate, however, is much more than temperature. Over the oceans, changes in wind speed and the surface gravity waves generated by such winds play an important role. We used a 23-year database of calibrated and validated satellite altimeter measurements to investigate global changes in oceanic wind speed and wave height over this period. We find a general global trend of increasing values of wind speed and, to a lesser degree, wave height, over this period. The rate of increase is greater for extreme events as compared to the mean condition.

Random seas and design of maritime structures

Abstract: Evolution of Design Method Against Random Waves Statistical Properties and Spectral of Sea Waves Transformation and Deformation of Random Sea Waves Design of Breakwaters Design of Coastal Dikes and Seawalls Probabilistic Design of Harbor Facilities Harbor Tranquility and Vessel Mooring Hydraulic Model Tests with Random Waves Theoretical Description of Random Sea Waves Statistical Theory of Irregular Waves Techniques of Random Wave Analysis 2D Computation of Wave Transformation with Random Breaking and Nearshore Currents Statistical Analysis of Extreme Waves Prediction and Control of Beach Deformation Processes.

Multiple Scattering: Interaction of Time-Harmonic Waves with N Obstacles

Abstract: The interaction of waves with obstacles is an everyday phenomenon in science and engineering, arising for example in acoustics, electromagnetism, seismology and hydrodynamics. The mathematical theory and technology needed to understand the phenomenon is known as multiple scattering, and this book is the first devoted to the subject. The author covers a variety of techniques, describing first the single-obstacle methods and then extending them to the multiple-obstacle case. A key ingredient in many of these extensions is an appropriate addition theorem: a coherent, thorough exposition of these theorems is given, and computational and numerical issues around them are explored. The application of these methods to different types of problems is also explained; in particular, sound waves, electromagnetic radiation, waves in solids and water waves. A comprehensive bibliography of some 1400 items rounds off the book, which will be an essential reference on the topic for applied mathematicians, physicists and engineers.