Harvesting marine renewable energy remains to be a prime focus of researchers across the globe both in environmental and in commercial perspectives. India is blessed with a long coastline, and the seas around Indian peninsula offer ample potential to tap various ocean energy forms. National Institute of Ocean Technology carries out research and various ocean energy technologies, out of which harnessing kinetic energy in seawater currents is one. This article presents the open sea trials recently carried out on National Institute of Ocean Technology’s cross-flow hydrokinetic ocean current turbine in South Andaman. The turbine was designed to generate 100 W electricity at 1.2 m/s current speed and was built in-house. The turbine was initially tested in a seawater channel and then was deployed in Macpherson Strait in Andaman. It was fitted below a floating platform designed especially for this purpose, and the performance of the turbine was continuously logged inside an on-board data acquisition system. The trials were successful and in line with computations.
Oscillating water column wave energy harvesting system uses pneumatic power to run a turbine and generate power. Both reaction (mainly Wells turbine) and impulse type turbines are tested in oscillating water column system and the performances are investigated. Reaction turbines are easy to install, and the operating range is narrow and possesses higher peak efficiency. On the contrary, impulse turbines have the wider operating range and lower peak efficiency. Some of the key parameters for Wells turbine are solidity, tip clearance, and the hub-to-tip ratio. Significant performance improvement is possible by redesigning the turbines using optimization techniques. Till date, surrogate modeling and an automated optimization library OPAL are commonly used in optimization of oscillating water column air turbines. In this article, various types of oscillating water column turbines are reviewed, and optimization techniques applied to such turbines are discussed. The Wells turbine with guide vane has the maximum efficiency, whereas the axial-impulse turbine with pitch-controlled guide vane has the widest operating range. Turbines with optimized geometry have better overall performance than other turbines.
Tidal inlets get disconnected depending on the seasons due to the formation of sand bars near its mouth are termed as “seasonally open tidal inlets.” These inlets are usually small of width of about 100 m and occur in micro-tide (tidal range not exceeding 1 m). Since the east coast of India experiences a net littoral drift of up to about 0.8 Mm 3 /annum, which is one of the largest in magnitudes that needs to be considered in the analysis of modeling of the sand bar formation and the associated phenomena. Kondurpalem inlet situated along the South east coast of India is considered as a case study. A frequency domain wave model (STeady-state spectral WAVE) has been used to compute the nearshore wave climate. The wave-induced currents have been obtained, and the longshore sediment transport rate is obtained through empirical relations. The tidal prism is found from measured depth and tidal velocity by solving shallow water equations. The stability of the inlet is investigated by applying the criteria developed by Bruun (1986). The effect of a pair of training walls on maintaining the stability of the mouth is reassessed over the periods.
The history of ocean renewable energy developments in Australia is reviewed. A layperson’s description of the physical operating principle is given for the main classes of technology that have been tested in Australian waters. The Australian marine domain possesses among the world’s most energetic wave-energy resources, driven by powerful mid-latitude westerly winds. The northern coast of Western Australia has tidal ranges significant on a global scale, and some geographical features around the continent have local tidal resonances. The East Australian Current, one of the world’s major western boundary currents, runs along the eastern Australian seaboard, offering potential for ocean-current energy. Sea-water temperatures in the tropical north-east of Australia may permit ocean thermal energy conversion. While this abundance of resources makes Australia an ideal location for technology development, the population is highly concentrated in a few large cities, and transmission infrastructure has developed over a century to supply cities from traditional power plants. Several wave-power developments have resulted in demonstration of deployments in Australian waters, three of which have been grid connected. Trials of tidal devices have also occurred, while other classes of ocean renewable energy have not yet been trialled. The prospects for marine renewable energy in Australia are discussed including non-traditional applications such as coastal protection and energy export.
We present an analysis of turbulent kinetic energy dissipation rates in the upper ocean using in situ measurements collected by a coherent Doppler sonar in the Labrador Sea during summer 2004. The sonar recorded horizontal velocity fluctuations of the upper 2 m with an uncommonly small spatial resolution of 0.8 cm, allowing direct calculations of wavenumber spectra and the application of Kolmogorov theory to obtain turbulent kinetic energy dissipation rates for the first time in this area. The project presented a unique opportunity for the study of air–sea exchange during a phytoplankton bloom, being the first time a specialized air–sea interaction spar buoy was deployed during such particular event. An additional uniqueness of this experiment resulted from being the first turbulent kinetic energy dissipation rate observations obtained at higher latitudes, coincidentally in a well-known region of dense water formation, with a fundamental role in both global circulation and forecasting studies of global climate change. Focusing on the relationship between turbulent kinetic energy dissipation rates and wave phase in the upper 2 m, we estimated O[Formula: see text] turbulent kinetic energy dissipation rates, consistent with previous estimates obtained through similar devices and methods. A T-test between dissipation rates calculated at the crest and at the trough of waves showed no dependency of turbulent kinetic energy dissipation rates on the wave phase at 2 m depth, coinciding with many of the earlier findings available. a comparison with previous research showing conflicting results with our values is also discussed here linking them to the relative roles of experimental design variations, diverse dynamical frames, and particular environmental conditions.
Indian Space Research Organization had launched Oceansat-2 on 23 September 2009, and the scatterometer onboard was a space-borne sensor capable of providing ocean surface winds (both speed and direction) over the globe for a mission life of 5 years. The observations of ocean surface winds from such a space-borne sensor are the potential source of data covering the global oceans and useful for driving the state-of-the-art numerical models for simulating ocean state if assimilated/blended with weather prediction model products. In this study, an efficient interpolation technique of inverse distance and time is demonstrated using the Oceansat-2 wind measurements alone for a selected month of June 2010 to generate gridded outputs. As the data are available only along the satellite tracks and there are obvious data gaps due to various other reasons, Oceansat-2 winds were subjected to spatio-temporal interpolation, and 6-hour global wind fields for the global oceans were generated over 1 × 1 degree grid resolution. Such interpolated wind fields can be used to drive the state-of-the-art numerical models to predict/hindcast ocean-state so as to experiment and test the utility/performance of satellite measurements alone in the absence of blended fields. The technique can be tested for other satellites, which provide wind speed as well as direction data. However, the accuracy of input winds is obviously expected to have a perceptible influence on the predicted ocean-state parameters. Here, some attempts are also made to compare the interpolated Oceansat-2 winds with available buoy measurements and it was found that they are reasonably in good agreement with a correlation coefficient of R > 0.8 and mean deviation 1.04 m/s and 25° for wind speed and direction, respectively.
The effect of seawall on the adjacent beaches and coastal dynamics has not been well documented in literature. The purpose and function of coastal structures, especially seawalls, have often been misunderstood, as in some cases, seawalls lead to coastal erosion, contrary to protecting the shoreline for which they are generally constructed. Seawalls have been reportedly causing changes in the near-shore process, specifically the sediment dynamics by affecting the onshore/offshore and, to some extent, the longshore sand transport. Therefore, it becomes imperative to understand the effect of seawalls on the adjoining beach to make sure more informed decisions are made on their installation. This article discusses the effects of seawall construction along the coast of Fansa, South Gujarat, India. A numerical model has been used to estimate the wave parameters along the selected coast, the results of which are subsequently utilized in an analytical model (parabolic shape model) to predict the end-wall effect. Independently, remote sensing datasets of CARTOSAT 1 with spatial resolution of 2.5 m are used to understand the shoreline change dynamics in this region, post-construction of this seawall. It is found empirically that the net longshore sediment transport rate is approximately 1.9 Mm 3 per year along the coast. The results of the analytical model predict a maximum landward erosion of about 20 m and an alongshore erosion of 200 m on the down-drift side of the seawall. These estimations agree with those obtained by the remote sensing–based analysis, which estimates an erosion of approximately 40 m by the year 2014.
Oceans have significant renewable energy options to provide environmental friendly and clean energy. Technology for ocean energy systems and the feasibility for extraction of the same is an important area on which research is being focused worldwide. This article covers a detailed review of available tidal energy conversion technologies and case studies, with specific focus on tidal power potential in India. The proven option for tidal energy conversion is barraging. Recently, open-type turbine (usually known as tidal stream turbines) has been studied by several researchers and pilot demonstrations have been made. While conventional turbines of 10–20 MW rating are used in barrages, the application of tidal stream turbines of 0.5–2.0 MW has been demonstrated in water depths between 40 and 60 m. A new scale is proposed for categorizing the tidal energy potential in terms of tidal velocity and tidal range which could be used to categorize the potential sites and their ranking. A new systematic approach proposed for the assessment of tidal energy conversion potential can facilitate the suitability of either tidal stream energy or tidal barrage for a location. Within this, one could also decide the site could be developed as a major project or minor project. Therefore, the present work will be useful for engineers and decision makers in technology selection investment potential identification.
The 26 December 2004 Tsunami generated by the submarine earthquake in Andaman Sea with the magnitude of 9.2 Richter scale triggered the worst destruction, widespread inundation and extensive damage in terms of life and property along the Tamil Nadu coast and Andaman Nicobar Group of Islands. The shoreline features like dunes, vegetation and steepness of beaches played vital role in attenuating the impact of Tsunami from destruction. While the low-level Marina beach experienced minimum inundation, the coast between Adyar and Cooum was inundated heavily. As the present generation of India was not aware of Tsunami, the emergency plan and preparedness were zero and so the loss of human life was huge. In this article, the authors describe the Tsunami occurred in India on 26 December 2004 and its impacts on morphology. The appropriate Emergency Preparedness plan and the Disaster Management Plan in case of reoccurrence of such natural disaster are discussed.
Assessment of coastal erosion is of high significance given the fact that the coastal communities are densely populated areas and have an influence on the food cycle directly and indirectly. Continuous monitoring is essential part of the work for any intervention to be carried out owing to the seasonal and inter-annual variability. The article discusses the measurement criteria and stages in an operational plan for a monitoring exercise, preparation and execution. Erosion can be due to a variety of natural and anthropogenic causes in general. The topic draws attention of both researchers and coastal communities equally. This article explains the need for operational strategies for an optimal monitoring of coastal erosion. Demonstration of such methodology was presented with a case study at a micro-tidal sandy beach located in Tamil Nadu. A generic set up for a plan boundary to measure met-ocean parameters over a time and spatial extent covering the beach and near-shore sediment regime, shore face and surf zone hydrodynamics is discussed. For a detailed understanding, numerical models are set up against the measurements to have a feel of the spatial variability. Validation was taken up extensively and the predictions were used to enhance the measurements in spatial and temporal scales, advantages with such setup.
Mangroves thrive in the intertidal areas (interface between land and sea) of tropical and sub-tropical belt and play an important role in overall attenuation of nearshore waves. Multiple interactions of waves with mangrove trunks and roots and bottom friction are the two primary mechanisms responsible for wave attenuation in mangrove forests. Earlier studies, comprising both analytical and experimental, reported an exponential decay in wave height for waves propagating over vegetation with idealized bottom topography and a few on sloping bottom. But hardly studies have attempted to characterize the wave attenuation by vegetation over varying seabed slopes since mangroves generally grow luxuriantly on gradual topography having large tidal amplitudes. Nowadays, several studies are being carried out on development of artificial mangroves to reduce the coastal hazard risks; thenceforth, there is an imperative requirement to study the wave damping characteristics of mangroves on varying seabed slopes. Consequently, this study performs sensitivity experiments to analyze the wave attenuation over mangroves with different sea-bottom slopes using a third-generation wave model. The study exposes sensitivity of wave attenuation characteristics to different beach slopes in the presence of mangroves and aims at understanding how the wave attenuation characteristics by mangroves differ with varying bottom slopes. The total percentage energy reduction for waves reaching the shoreline after propagating through mangroves on mild slope (1:80, 1:40) is observed to be 93%–98%, nearly 84% for 1:20 slope, and 67% for steep slope (1:10). The study reveals that the wave height decays exponentially for the mild slope and found to be consistent with the earlier studies, but as the degree of bottom steepness increases, the wave height reduction becomes gradual, and this can be attributed to the water depth variation, shoaling, breaking, and reflection characteristics associated with different slopes, in the presence of mangroves.
A finite difference–based three-dimensional modeling has been conducted to evaluate tidal power density at different locations along the Gulf of Khambhat, India. The model uses the Navier–Stokes transport equation in three-dimensional plane under the assumption of shallow water and Boussinesq. The model results were validated with observed water levels and currents available in the literature. The Gulf has strong and varying currents and associated circulation patterns, especially in the northern region, due to complex bathymetry. The current velocities and corresponding power densities were computed for different vertical layers of the entire model domain. The maximum tidal current velocities are found in the northern region along the narrowing part of the Gulf. The estimated values are 2.6 and 1.5 m/s during spring and neap tidal cycles, respectively. Then, the energy flux approximation method has been used to estimate the tidal power densities along the gulf spatially and temporally. The estimated maximum available potential is about 3 and 0.7 kW/m 2 during spring and neap at two arbitrary point locations, respectively.
Marine renewable energy has the potential to solve both the energy-security and coastal-protection problems affecting coastal societies. In this article, the potential benefits arising from the combination of marine renewable energy technologies with infrastructural needs for coastal protection and other local needs are analysed. Classifications of technologies are developed to inform future coastal planning. Explanations of the resources and technologies are presented in layperson’s term. The threat of coastal inundation under climate-change scenarios is a major global issue. The investment in new infrastructure demanded by cities, ports and communities at risk of inundation could very substantially reduce the levelised cost of electricity from renewable sources, provided the infrastructure is designed with the dual purpose of power generation and coastal protection. Correspondingly, the sale of electricity from such infrastructure could defray the long-term cost of installing coastal protection. Furthermore, many marine renewable energy technologies provide a platform on which other forms of renewable energy generation could be mounted. It is noted that the complex geophysical and engineering issues arising from this opportunity must be assessed considering socio-economic factors.
Determining the bathymetry of ocean is important for many aspects such as generating navigational charts, to study changes in the seafloor profile, sea level rise, and beach erosion. Traditionally, the bathymetry of ocean was determined by a hydrographic ship carrying an echo sounder instrument which was cost effective but time consuming and also often inaccessible in shallow water regions. The alternate solution to infer the bathymetry of ocean is remote sensing technology. The multispectral satellite platform such as Ikonos and WorldView images are commercially available, whereas the Landsat-8 imagery is freely accessible and therefore the Landsat-8 imagery is used. In this study, the first objective was to evolve a procedure to determine the bathymetry of ocean using the ratio transform algorithm. The second objective was to find the effectiveness of improving the spatial resolution of Landsat-8 imagery to estimate the bathymetry of ocean, and the results of both before and after improving the spatial resolution are compared. The statistical indices, root mean square error and mean absolute error, are computed between the algorithm results and the reference hydrographic chart values, and it was found that the improved spatial resolution of Landsat-8 imagery provided better estimation up to 10 m depth.
The Indian Tsunami Early Warning System situated at Indian National Center for Ocean Information Services, Hyderabad, India, monitors real-time earthquake activity throughout the Indian Ocean to evaluate potential tsunamigenic earthquakes. The functions of the Indian Tsunami Early Warning System earthquake monitoring system include detection, location and determination of the magnitude of potentially tsunamigenic earthquakes occurring in the Indian Ocean. The real-time seismic monitoring network comprises 17 broadband Indian seismic stations transmitting real-time earthquake data through VSAT communication to the central receiving stations located at the Indian Meteorological Department, New Delhi, and the Indian National Center for Ocean Information Services, Hyderabad, simultaneously for processing and interpretation. In addition to this, earthquake data from around 300 global seismic stations are also received at the Indian National Center for Ocean Information Services in near-real-time. Most of these data are provided by IRIS Global Seismographic Network and GEOFON Extended Virtual Network through Internet. The Indian National Center for Ocean Information Services uses SeisComP3 software for auto-location of earthquake parameters (location, magnitude, focal depth and origin time). All earthquakes of Mw >5.0 are auto-located within 5–10 minutes of the occurrence of the earthquake. Since its inception in October 2007 to date, the warning centre has monitored and reported 55 tsunamigenic earthquakes (under-sea and near coast earthquakes of magnitude ⩾6.5) in the Indian Ocean region. Comparison of the earthquake parameters (elapsed time, magnitude, focal depth and location) estimated by the Indian Tsunami Early Warning System with the US Geological Survey suggests that the Indian Tsunami Early Warning System is performing well and has achieved the target set up by the Intergovernmental Oceanographic Commission.
The Mousuni Island in West Bengal, India is wide-open to Bay of Bengal. This island by virtue of its location is exposed to river flow as well as wave action. It is thus subjected to severe erosion along its south-western coastal stretch and also significantly affecting agriculture due to seawater inundation. This is due to the lower level of bund crest elevation combined with high water levels during coastal flooding. The most suitable method to arrest the shore erosion and salt water intrusion is to divert the flow gradually toward the deeper section of the channel. To meet this requirement, after carrying out a comprehensive profiling of the existing bund, bank connected series of spurs with locally available construction materials and unskilled labor are proposed. In order to design these spurs, the magnitude and direction of sediment movement along the stretch is estimated. The layout of protection measures is proposed based on a detailed analysis of site conditions and the environmental conditions. The tranquility inside the proposed coastal protecting structure is substantiated with a two-dimensional horizontal flow model. Furthermore, the behavior of the shorelines has been studied numerically with the proposed coastal protection measure. The detailed analysis of the results from the numerical model and the protection measure are discussed in this article.
This article describes the first Indian arctic multi-sensor mooring (IndARC) observatory in Kongsfjorden of Arctic waters. The Ministry of Earth Sciences evolved a unique moored observatory ‘IndARC’ with suite of sensors for physico-chemical and oceanographic in situ long-term data collection. The Arctic Ocean plays an important role in governing the earth’s climate and also faithfully records its past climatic history and represents a significant gap in ocean observations. This indigenously designed and installed observatory IndARC, for the first time, collected various parameters from July 2014 to July 2015. The uniqueness of this system, the challenges faced and results from data collected are presented in this article.
This work investigates the strength of artificial neural network that is trained by an optimization technique called particle swarm optimization in the task of time series prediction of weekly and monthly significant wave heights. The suggested approach has been implemented at the location of New Mangalore Port in India. Three years of wave data measured during 2005–2007 are analyzed. It is found that the network trained with the help of the particle swarm optimization produces more accurate predictions of the significant wave heights and further with lesser amount of data than the traditionally trained feed-forward back-propagation network.
The behaviour of arrays of 12 heaving point absorbers in concentric arrangements is numerically assessed in a frequency domain model. The floaters are attached to a central cylindrical bottom-mounted structure. Each point absorber is restricted to the heave mode and is assumed to have its own linear power take-off system consisting of an external damping coefficient enabling power extraction and a supplementary mass coefficient tuning the point absorber to the incoming waves. The external damping and supplementary mass coefficients are optimized to maximize the power absorption by each floater in the array, with a restriction on the total control force that can be applied on the floaters. Various concentric arrangements with different radii and number of concentric circles are analysed to determine the most efficient among them. Moreover, the influence of the presence of a central bottom-mounted pillar and the effect of change in its dimension and shape on the power absorption are also studied.
