S A Sannasiraj

This study aims to explore the site-specific impact of coastal structures on the stability of the shoreline. For this study, the shoreline data were collected with higher-order accuracy along a few vulnerable stretches of the coast in the vicinity of hard structures such as Seawalls, Groyne, Breakwater, and Training walls along the southeast and southwest coasts of India. All the field collected shoreline data were analysed with statistical measures using DSAS (Digital Shoreline Analysis System) tool of ArcGIS software. The presence of shore connected coastal structures dictates the sedimentation process in its purlieu. The observed average rate of erosion and accretion in the adjoining coastlines are −5.7 m/yr and +4.92 m/yr, respectively. The field measurements from the present study would provide an effective base for the planning and implementation of coastal structures near the studied area, as well as to adopt a better methodology for coastal impact assessment. Most of the well-planned and executed hard engineering structures have yielded desirable results and benefit for the local coastal communities.

This chapter describes a coastal and marine data information system that can be used for Maritime Spatial Planning. The system takes advantage of Internet mapping and web services technology to publish data as maps. These maps are created dynamically and enable the visualization of a diverse and growing collection of environmental data. Capabilities of the system include (i) visualization of environmental parameters on 2D maps; (ii) visualization of location-specific depth profiles of selected parameters; (iii) time animation of grids of environmental parameters and (iv) preparation of digital elevation and cultural object data sets for 3D terrain visualization (Durairaju et al., 2003, 2010). The function and interaction between key components of the system are described to illustrate the working of the system. The use of a mature map publishing engine greatly eased the development of these capabilities into a web-based system.

The dynamics of multiple floating structures have been studied using the finite element method. The emphasis is on the hydrodynamic behaviour of multiple bodies under a multi-directional wave field. A two-dimensional numerical model has been adopted to evaluate hydrodynamic coefficients and forces in an oblique wave field. The responses in sway, heave and roll modes are reported. The linear filter technique is then used to extrapolate the responses under directional waves. The effect of mean wave direction and directional homogeneity on the hydrodynamic behaviour of the structure is studied. Based on the present study, it is found that the two-dimensional model is applicable to investigate the wave-structure interaction problems of the type herein considered. (C) 2000 Elsevier Science Ltd. All rights reserved.

The necessity to protect coastal regions from sea-level rise (SLR) and extreme events demands a rigorous assessment of coastal vulnerability. The intergovernmental panel for climate change (IPCC) predicts that climate change will severely impact the coastal region, river systems, and urban infrastructures. The changing climate is observed to be increasing the frequency and magnitude of extreme hydrometeorological conditions, such as storm surges that adversely affect coastal areas by flood inundation. This study emphasizes the need to use extreme events and socio-economic data to evaluate the Coastal Vulnerability Index (CVI) for planning and adaptation measures. Therefore, the present study utilizes spatially varying surge heights for improved estimation of the CVI, unlike the constant surge heights considered in the previous studies. For coastal adaptation measures, synthetic cyclones of different return periods, such as 20-, 50- and 100-year, are simulated using a hydrodynamic model to represent a range of risk and vulnerability in the estimated CVI. The proposed methodology for calculating the CVI is demonstrated by considering the Chennai coast in the state of Tamil Nadu, India. The use of spatial distribution of storm surges from hydrodynamic simulations makes the CVI more realistic. Such thorough assessments utilizing high-resolution CVI maps can help policymakers suggest appropriate measures for specific coastal zones, which are more devastatingly affected by shoreline erosion, SLR and storm surge. The vulnerability assessment indicates that great care is needed in the planning and adaptation of the coastal ecosystem to extreme events for the safety and well-being of coastal populations and infrastructures.

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 detailed data collection would pave the way for the interpretation of the morphological changes close to the real scenario, which is essential for an efficient and sustainable coastal protection planning and coastal zone management. This paper deals with shoreline on either side of the mouth of the Arasalar River draining into the Bay of Bengal with a year-long (March 2018 to February 2019) continuous shoreline assessment during which GAJA cyclone made its landfall on 16 November 2018 along the Karaikal coast of Union Territory of Puducherry located on the southeast coast of India. A pair of training walls effectively keeps the mouth from silting, thereby allowing free passage of vessels. This study aims to understand the seasonal variation coupled with the severe cyclonic impact on the southeast coast of India. Monthly spring shoreline and cross-shore profiles during low tide and high tide were collected, including post-cyclone field data. The results discuss the erosion and accretion pattern of the sediment processes adjacent to the training walls and cyclone effects.

This paper attempts to study the wave hind cast effects of cyclones of variable intensities in North Indian Ocean. Sensitivity of different input-dissipation formulations (packages) in the TOMAWAC model to simulate integrated parameter, significant wave height are investigated at deep and nearshore locations. Statistical estimates are used to analyze the performance of the input-dissipation formulations against buoy measurements. The analysis suggested that the simulation through a variant of WAM 4 cycle package [1] bestowed WAM 4 cycle [2] and WESTH [3] packages.

Significant wave height assessment in Bay of Bengal derived from third generation Wave Model (WAM cycle 4) has been improved by assimilating with continuous three hourly data from five moored buoys of National Institute of Ocean Technology using optimum interpolation technique. Covariance based weight function (gain) used in the study captures the model physics behind wind-wave process while distributing the errors at any buoy location. Gain composition at different buoy locations, due to assimilation of each buoy has been reported for both southwest (July) and northeast (November) monsoons, for year 2004. Qualitative and quantitative improvement in significant wave height due to buoy data assimilation during these two seasons are presented with reference to changing wind and wave characteristics. The order of improvement is found to be proportional to the magnitude of deviations found with respect to the measurements. Considerable model area has been influenced by assimilation.

We present an experimental study of reciprocating pipe flow with free-end effects, specifically, oscillations of a column of water trapped inside an open vertical cylinder under the action of regular linear waves. The aims were to identify parameters where an initial transition to non-linearity in reciprocating flow might occur and to quantify energy losses in the non-linear regime. Reciprocating flows are a subclass of oscillatory flows that are characterized by a zero-mean flux. The investigation may provide a deeper fundamental understanding of the characteristics of reciprocating flows, which differ significantly from the properties of well-studied unidirectional flows. From measured amplitudes of the incoming and excited oscillations inside the column, we draw the dependence of the amount of the absorbed kinetic power on the amplitude and frequency of the incident waves. Quantifications were made of the balance between the energy absorbed by the column and dissipated due to the radiation of waves and wall friction, which are usually considered linear, as well as non-linear losses of energy due to flow separation at the walls and vortex shedding and turbulence at the bottom free end of the cylinder. It is found that the non-linear effects become significant at incident wave amplitudes much smaller than expected, thus affecting the energy balance. We suggest that the initial transition from linear to non-linear behavior in reciprocating finite pipe flow has been identified and the critical oscillatory Reynolds number at which it occurs has been estimated as Reos = 4400 ± 1250.

A detailed three-dimensional laboratory investigation on hydrodynamic performance of an array of oscillating water column (OWC) devices, combined with offshore detached breakwater (ODBW) subjected to oblique wave incidence was studied. A Froude scale of 1:20 was chosen for integrating five similar devices of OWC to the ODBW (OWCBW) and a series of experiments was carried out in a shallow wave basin for angle of wave approaching between 90 0 and 70 0 with reference to the front face of the structure with an angular decrement of 10 0 . The hydrodynamic performance was studied in terms of front wall outside pressure, wave amplification, air pressure, capture width, and relative capture width. The convergence of water waves due to three-dimensional effects concentrates high amount of energy in front of the array of OWCs for normal wave incidence. It makes a system to absorb larger amount of wave power of about 1.12 times of the given input power at the natural frequency of the system. This confirms that the array of OWC devices, exhibits better performance than in isolation. The performance of the system reduces with angular decrement due to peak of the wave front reaches the line front of OWCBW in different time along with wave dissipation over the breakwater. The natural frequency of the system was found to be lying in the vicinity of d/L p of 0.12 and unaltered for different angles of wave incidence.

Off late, nontraditional structures and concepts are being explored for use in offshore industry. Experiments were carried out on a 1:45 non-ship shaped FPSO model. The main objective of the model test was to study the response of the vessel (heave and pitch) under regular and random waves. The vessel was tested for three different mooring configurations. Tests were also conducted on models with and without damping plates. In the present paper, the effect of mooring configurations in the heave response of the FPSO and the effect of damping plates in the heave and pitch responses of the FPSO under regular waves have been presented. Salient features of the details of the experiments carried out are also included. Copyright © 2008 by The International Society of Offshore and Polar Engineers.