Nonlinear Oscillations: Exact Solutions and their Approximations

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...

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A new family of generalized distributions

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.

https://researchbank.swinburne.edu.au/file/bca43746-6f16-4ad2-a4b7-27f8d8d60fed/1/PDF (Published version).pdf

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

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.

Random seas and design of maritime structures

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.

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

OWC is reported to perform well when exposed to low frequency waves in narrow frequency band. On several occasions, the trough of the potential long wave might reach below the front lip wall of OWC, inducting air into the air chamber. To solve this problem, Boccotti (Boccotti, P. Ocean Engineering 34(5–6), 806–819 (2007a)) modified the conventional OWC concept by incorporating a duct in front of the opening with an intention was to capture the maximum magnitude of dynamic pressure available for oscillation inside the air chamber. This is widely referred to as U-OWC. The performance of U-OWC is explored in a laboratory wave flume. A Froude model scale of 1:20 was adopted to carry out a comprehensive experimental study to investigate the effect of water plane area on pneumatic damping with two aspect ratios (W/B, ratio of chamber width parallel to the wave crest to the width of the chamber in the wave direction) of 0.50 and 1.67 in the model geometry. To investigate the effect of dynamic pressure intensity variation with depth, three h/di of 0.15, 0.30, and 0.45 were considered in the study, where di is the water depth in the chamber. At each of the h/di, the effect of relative bottom opening (O/di) for better phase control and energy conversion was studied. The maximum impact of pressure excitation had occurred at h/di of 0.30 and b/B of 0.50. The performance of the U-OWC is found to be better over a relatively wider frequency bandwidth near the natural frequency of the system.

Hydrodynamic Performance Characteristics of U-OWC Devices

The time histories of wave elevation and the two horizontal in line and transverse velocity components measured in a groin field were subjected to time domain analysis. The variation of the wave and velocity characteristics with respect to the time of measurement at a particular location and its variation at different locations within the groin field at a particular instant of time are presented and discussed in detail in this paper. In addition, the validation of the linear theory in predicting the wave kinematics in the direction of the wave propagation from the measured wave elevations is examined on assumption that wave directional variability is small. Such investigations for the nearshore zone are scanty especially for a groin field.

Wave Kinematics in a Groin Field-Time Domain Analysis

Influence of cyclic load on model caisson seawalls embedded in marine clay

This work represents an attempt to provide an in-depth understanding of the three-dimensional flow physics related to the characterization of streaming flows due to the oscillating spherical body. The presence of any structure at sea will impact the local hydrodynamics of the site and therefore the local sediment dynamics. When a body oscillates while immersed in a quiescent fluid, the effects of their dynamic interaction are evident not only on the forces acting on the body but also on the flow field deformation by generating a non-zero mean flow. Thus, in many ocean engineering applications, it becomes necessary to understand not only the instantaneous events such as the wave-generated hydrodynamic forces acting on the structures but also the mean hydrodynamic pressure fields and fluid velocity fields. The non-linear streaming flows produced by an oscillating sphere driven in unidirectional simple harmonic motion in a quiescent fluid have been investigated. A comprehensive parametric study has been undertaken over a range of oscillatory Reynolds number and amplitude ratio and a quantitative assessment of the relation between the mean flows and the Lagrangian particle drift associated with the flow has been carried out. It is shown that while an inner mean viscous boundary layer flow is generated that is confined to a very small region near the sphere, a large mean outer vortex flow is generated that can extend a long way from the sphere along the axis of oscillation.

Numerical Investigation on the Mean Flow Fields Generated by an Oscillating Sphere

In the recent years, various geo-synthetic components find an extensive application in civil and coastal engineering practice. Commonly, geo-synthetics have a wide application for secondary or tertiary purposes, such as filtration, separation, barrier, reinforcement, whereas, they can be potentially exploited for various other applications in the coastal engineering practice. A sustainable seawall cross-section comprising different geo-synthetic products was proposed to be erected along the Pallana Beach ([Formula: see text] N and [Formula: see text] E), located in Alleppey district of Kerala along the south-west Indian coastline. Since the subsoil at the location is poorly graded, it was decided to replace the conventional materials like rock boulders and concrete armour units with geo-synthetic products. A comprehensive physical model study was conducted to assess the hydrodynamic performance (i.e. reflection, run-up, and pressure distribution) of the geo-synthetic seawall cross-section for a wide range of random wave characteristics and two water depth conditions. The relative overtopping rates for the seawall at varying water levels are computed conservatively from the guidelines prescribed by the EurOtop Manual and XGB Overtopping model.

Vallam Sundar

Papers

Hydrodynamic Performance Characteristics of U-OWC Devices

Wave Kinematics in a Groin Field-Time Domain Analysis

Influence of cyclic load on model caisson seawalls embedded in marine clay

Numerical Investigation on the Mean Flow Fields Generated by an Oscillating Sphere

Hydrodynamic Performance Assessment of a Geo-Synthetic Seawall