National Institute Of Ocean Technology Research Articles

Evaluation of radiative fluxes over the north Indian Ocean

Radiative fluxes are a key component of the surface heat budget of the oceans. Yet, observations over oceanic region are sparse due to the complexity of radiation measurements; moreover, certain oceanic regions are substantially under-sampled, such as the north Indian Ocean. The National Institute of Ocean Technology, Chennai, India, under its Ocean Observation Program has deployed an Ocean Moored Network for the Northern Indian Ocean (OMNI) both in the Arabian Sea and the Bay of Bengal. These buoys are equipped with sensors to measure radiation and rainfall, in addition to other basic meteorological parameters. They are also equipped with sensors to measure sub-surface currents, temperature, and conductivity from the surface up to a depth of 500 m. Observations from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor onboard the National Aeronautics and Space Administration (NASA) AQUA and TERRA satellites have been used to infer surface radiation over the north Indian Ocean. In this study, we focus only on the shortwave (SW↓) fluxes. The evaluations of the MODIS-based SW↓ fluxes against the RAMA observing network have shown a very good agreement between them, and therefore, we use the MODIS-derived fluxes as a reference for the evaluation of the OMNI observations. In an early deployment of the OMNI buoys, the radiation sensors were placed at 2 m above the sea surface; subsequently, the height of the sensors was raised to 3 m. In this study, we show that there was a substantial improvement in the agreement between the buoy observations and the satellite estimates, once the sensors were raised to higher levels. The correlation coefficient increased from 0.87 to 0.93, and both the bias and standard deviations decreased substantially.

Marine Biofouling on Moored Buoys and Sensors in the Northern Indian Ocean

AbstractEquipment and structures deployed in seawater and other marine environments are susceptible to marine growth. This marine biofouling is one of the critical factors that affects the measurement of continuous real-time data from the oceanographic sensors deployed for long-term observations. To understand the characteristics of biofouling on marine sensors, an investigation was conducted on sensors deployed in a moored buoy network deployed and maintained by the National Institute of Ocean Technology (NIOT) in the Arabian Sea and Bay of Bengal regions. The present paper attempts to elucidate the characteristics of biofouling on sensor components deployed at seven locations in the Bay of Bengal and five locations in the Arabian Sea, at varying depths ranging from the surface to 500-m depth. Biofouling on bare sensor surfaces and surfaces with various antifouling measures has been studied for 2 consecutive years (2015 and 2016), and the effect of antifouling measures is discussed in this paper. Among the locations studied, buoys deployed in the Arabian Sea exhibited a higher biofouling load compared to the buoys deployed in the Bay of Bengal. The study showed that the pedunculate barnacles Lepas anatifera Linnaeus, 1758, was the predominant biofouling species on these sensors. Furthermore, observations show that the use of copper- and zinc-based antifouling methods reduced the incidence of biofouling by 59% on average.

Energy extraction from ocean currents using straight bladed cross-flow hydrokinetic turbine

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.

Interlaboratory Comparisons of Hydrophone Calibration in the 3–500 kHz Frequency Range

A method and results are described for international interlaboratory comparisons of hydroacoustic measurement reference standards. The comparison was organized by the National Institute of Ocean Technology, India, with the participation of reference standards from Germany and Russia. Data are presented on the reference standard installations of the comparison participants and the measurement methods used, and the impact of water temperature on comparison results during calibration is discussed.

An approach to operational risk modeling and estimation of safety levels for deep water work class remotely operated vehicle—A case study with reference to ROSUB 6000

This paper presents a quantitative approach to operational risk modeling and estimation of safety integrity levels, required for the deep water electric work class remotely operated vehicle with reference to ROSUB6000 developed by the National Institute of Ocean Technology, India. ROSUB6000 is used for carrying out bathymetric surveys, gas hydrate surveys, poly-metallic nodule exploration, salvage operations, and meeting emergency response situations. The system is expected to be in operation for a period of 300h per year, and has to be extremely safe and reliable. Methods and models for the quantitative assessment of operational safety and estimation of safety integrity levels for ROV are seldom available in the deep water intervention industry. The safety instrumented functions implemented in the ROV should be able to meet the SIL requirements of specific mission. This study indicates that the required safety factors are implemented into the design of the state-of-the-art ROV ROSUB 6000, considering IEC 61508/61511 recommendations on Health, Safety and Environment and it is found that the system is able to meet the required SIL for seven identified functions. This paper gives the design and safety engineers in the ROV industry, an overview of the numerical operational risk assessment methods and safety-centered ROV engineering.

Two decades of operating the Indian moored buoy network: significance and impact

ABSTRACTOcean–atmosphere interactions in the North Indian Ocean play a vital role in the onset, progression and withdrawal of the Indian monsoon. This paper describes the Ocean Observation System (OOS), an operational observational programme of the Earth System Science Organization and the National Institute of Ocean Technology (ESSO-NIOT) under India’s Ministry of Earth Sciences (MoES). Since 1997 it has provided oceanographic and surface meteorological data in real time for weather forecasting, climate research and several other applications. The programme focuses on understanding the phenomenon of the mean seasonal cycle of the Indian monsoon, the intra-seasonal to intra-decadal oscillations of air–sea interactions, trends that are related to tropical cyclones and the annual cycle balance in the exchange of waters between the two limbs of North Indian Ocean, i.e. the Arabian Sea and the Bay of Bengal. In situ observations are also used to develop, initialise and validate regional forecast models that provide high resolution data. There is also a growing need to understand the spatial phenomenon of oceans using satellite observations, wherein the quality of data needs to be validated and verified carefully. This paper also provides an overview of the scientific and societal impact of the Indian moored buoy network over two decades of operation.

Initial set of oceanographic data from Bay of Bengal using an underwater glider as mobile sensor node

Underwater gliders measure high-resolution spatiotemporal oceanographic data. However, glider operations have not been carried out in the Indian Ocean region so far. In September 2013, the National Institute of Ocean Technology, Chennai introduced a mobile sensor node, the underwater glider ‘Barathi’, for observation in the Bay of Bengal (BoB). Herein we address ballasting procedure of the glider operated in highly variable density waters of the BoB. The temperature and conductivity data collected by us are strongly correlated with commercially available instrument with coefficient of determination R2 > 0.97. This article reports results from a long-duration (127 days) mission in 2014. The variation of temperature, salinity, density, sound velocity, mixed layer depth, sonic layer depth and lower cutoff frequency of surface duct along 13°N lat. and between 80.76°E and 86.28°E long. are also presented. The results show a trace of the East Indian Coastal Current. The glider operations demonstrate a novel in situ observation platform in the BoB.

Estimation of Significant Wave Heights Using Numerical and Neural Techniques and Comparison with Buoy and Satellite Observations

Short term significant wave heights have been evaluated using the numerical WAM model and the results are compared with satellite (Jason-2) and moored buoy measurements. Additionally artificial neural network (ANN) is used to predict significant wave heights over a future time step and such predictions are also compared with corresponding satellite and buoy measurements. The observations from moored buoys monitored by India's National Institute of Ocean Technology for a period of about four and a half years at three locations in the Arabian Sea and three in Bay of Bengal covering the west as well as east coast of India are involved. The buoy recorded largest waves during the cyclonic condition, and this was confirmed at a location code named: BD11 by the satellite measurements as well as the WAM and ANN based evaluations. The evaluation accuracy reflected in the coefficient of correlation is found to be high in the Arabian Sea than the Bay of Bengal.

Validation of in situ wave spectrum with JONSWAP in the Indian Ocean

The moored data buoys deployed by the National Institute of Ocean Technology (NIOT) are floating platforms designed to carry a specific suit of sensors to measure wave parameters. Waves are measured by the Motion Reference Unit (MRU), which outputs roll, pitch, compass, and heave. These data are recorded at a rate of 1 Hz for 17 minutes every three hours. For this study, wave measurements were carried out at two locations (deep and shallow water) over the same period. The wave spectra were generated from the hard disk data (roll, pitch, heave, and compass) of the moored buoys. A Matrix Laboratory (MATLAB) program was developed for generating the wave spectrum using the hard disk data. The spectrum exhibits significant features for deep- and shallow-water buoys. In a single peak spectrum the dominant peaks are observed at 0.08 and 0.1 Hz and the multi-peak spectrum energy is distributed over a wide range, from 0.05 to 0.25 Hz. The buoy spectra were compared to the Joint North Sea Wave Project (JONSWAP) spectrum in deep- and shallow-water locations in the Bay of Bengal, and also the deep-water buoy spectrum was compared to the wave model (WAM) output spectrum in the Arabian Sea. The JONSWAP spectrum mostly conforms to the buoy spectrum in regard to marine wind conditions.

A Study of the Algorithms for the Detection of Tsunami Using an Ocean Bottom Pressure Recorder

AbstractThe National Institute of Ocean Technology (NIOT), an autonomous organization under the Ministry of Earth Sciences, government of India, is engaged in developing and installing systems for tsunami detection and reporting. This involves high-precision bottom pressure recorders (BPRs) installed on the ocean floor, which can detect water level changes in the order of a few centimeters. Data are logged and recorded subsea by instruments located close to the BPRs. The detection of abnormal changes in the water level is required for detecting a tsunami event. This paper describes algorithms incorporated in most BPRs for detecting a tsunami by predictive methods such as Newton’s Extrapolation and Kalman predictor techniques. The most widely used tsunami detection algorithm is based on Newton’s extrapolation. The tsunami detection technique based on the Kalman prediction algorithm developed by NIOT can be an alternative for the existing technique. This paper describes both the algorithms and analyzes their effectiveness during tsunami event detection using MATLAB software. It is found that the Kalman algorithm has a better detection performance over the Newton extrapolation technique for tsunami wave amplitudes up to 300 mm. The Newton extrapolation technique has a better detection performance for tsunami wave duration of less than 10 min. For tsunami wave durations greater than 10 min, the Kalman algorithm has a better detection performance. As the wave durations of most of the recorded tsunamis are greater than 10 min, the Kalman algorithm could be a viable substitute for tsunami detection.

2 kHz high power smart transducer for acoustic sub-bottom profiling applications

In this study, a 2 kHz Tonpilz projector was designed using a Terfenol-D and modeled in ATILA. For the purpose of modeling studies, it has been determined that a radiating head mass exhibits better transmitting current response (TCR) at 136 mm diameter, where the resonance occurs at 2.4 kHz and the peak value of 118 dB re 1 μPa/A at 1 m occurs at 12 kHz. Also bolt at a 46 mm distance from the center of the head mass offers resonance at 2.4 kHz, and the peak value of 115.3 dB re 1 μPa/A at 1m occurs at 11.5 kHz. This optimized design is fabricated and molded with polyurethane of 3 mm thickness. The prototype was tested at the Acoustic Test Facility (ATF) of National Institute of Ocean Technology (NIOT) for its underwater performances. Based on the result, the fundamental resonance was determined to be 2.18 kHz and the peak value of TCR of 182 dB re 1 μPa/A at 1m occurs at 14 kHz. The maximum value of the RS was found to be −190 dB re 1V/μPa at 1m at a frequency of 2.1 kHz.

Reliability-Centered Development of Deep Water ROV ROSUB 6000

AbstractThis paper presents the reliability-centered development of a deep water Remotely Operable Vehicle (ROV) ROSUB 6000 by the National Institute of Ocean Technology (NIOT), India. ROV operations are required during deep water interventions, such as well head operations, emergency response situations, bathymetric surveys, gas hydrate surveys, poly-metallic nodule exploration, and salvage operations. As per our requirements, the system needs to be capable of deep water operation for a period of 300 h/year and to be extremely reliable. Methodologies applied during the development and enhancement phases of electrical and control systems, taking into consideration the cost, space, and time constraints to attain the best possible reliability are detailed. Reliability, availability, and maintainability (RAM) studies are carried out to identify possible failure cases. It is found that ROV-Tether Management System (TMS) docking failure could be detrimental to the ROV system, and manipulator system failure could be detrimental to subsea operations. It has been calculated and found that the improved design has a mean time between failure (MTBF) of 4.9 and 6.2 years for ROV-TMS docking and manipulator system operations, respectively. The importance of monitoring tether cable healthiness during normal and winding operations and the systems implemented for effectively monitoring and maintaining the tether cable operational and functional healthiness, using the tether cable pay-out, vehicle heading, electric insulation, and optical performance sensors with the aid of a sea battery, are discussed. Maintenance decision support tables, which detail the operational personnel for the upkeep of the systems during the indicated interval so that the highest possible reliability is maintained during the mission period, are also presented.

Application of Soft Computing Tools for Wave Prediction at Specific Locations in the Arabian Sea Using Moored Buoy Observations

The knowledge of design and operational values of significant wave heights is perhaps the single most important input needed in ocean engineering studies. Conventionally such information is obtained using classical statistical analysis and stochastic methods. As the causative variables are innumerable and underlying physics is too complicated, the results obtained from the numerical models may not always be very satisfactory. Soft computing tools like Artificial Neural Network (ANN) and Adaptive Network based Fuzzy Inference System (ANFIS) may therefore be useful to predict significant wave heights in some situations. The study is aimed at forecasting of significant wave height values in real time over a period of 24hrs at certain locations in Indian seas using the models of ANN and ANFIS. The data for the work were collected by National Institute of Ocean Technology, Chennai. It was found that the predictions of wave heights can be done by both methods with equal efficiency and satisfaction.

A finite element approach to renew underwater shell plate of a dumb barge sans dry docking: an innovative and cost-effective model

Sagar Shakti, a million litre/day desalination dumb barge belonging to the National Institute of Ocean Technology (NIOT), was damaged on its underwater hull during deployment of a mooring buoy at 1000 m depth. The shell plate had several perceptible wide punctures leading to rapid seepage of sea water into void spaces. Shipyards on the east coast of India expressed inability to renew the shell plate and insisted on dry docking as the only possible way. Owing to financial and time constraints combined with severe monsoon conditions, the barge could not be towed. A suitable water-tight chamber was designed and fabricated to use it as a cofferdam with ceramic back strip welding. Finite element analysis on the water-tight chamber showed that the design was optimum. Welding was done inside the hull; molten metal fills the gap between two plates of butt joint, thereby eliminating external welding. Non-destructive tests including radiography showed the perfection of the weld joint. It was a successful work after which the barge was put into operation to demonstrate a desalination plant. This kind of underwater shell plate renewal without dry docking was done for the first time in India under class approval, thereby saving the huge cost of dry docking, and provided an innovative idea to the industry.

Salient features of Andhra Pradesh cyclonic storm in the Bay of Bengal during September 1997

During 23–30 September 1997, a rare cyclonic storm has developed close to the Andhra coast, and it has later travelled parallel to coastline northward and finally crossed the land at Chittagong (22°N, 91°E) on 27 September. While translating along the east coast of India, it has produced heavy to very heavy rainfall on the coastal stations causing devastating floods. In this study, we made an attempt to understand the salient causes of this unique cyclone movement. We have analyzed daily fields of wind and relative humidity for 850, 700, 500 hPa and mean daily OLR data to understand the plausible reasons for its movement. The buoy data deployed by National Institute of Ocean Technology, Chennai, Viz. DS5 (15°N, 81°E), DS4 (19°N, 88°E) and SW7 (20°N, 86°E) were analyzed to understand the ocean–atmosphere interaction processes in the west Bay of Bengal during formation of the system. Analysis of OLR over the cyclonic storm region has revealed that the heavy rainfall areas coincide with low OLR (120–180 W m−2). The persistent southward movement of 500 hPa ridge on the eastern wedge of the system along with the steering current at 200 hPa has helped in maintaining the movement of the system parallel to the east coast of India during its life cycle.

Derivation of wave spectrum using data driven methods

The current techniques of derivation of a wave spectrum from given values of design wave parameters, like significant wave height and average wave period, are fraught with considerable uncertainties. This leaves scope for alternative approaches. The reported work proposes potential applications of two recent data driven methods, namely support vector regression (SVR) and model tree (MT), to obtain the wave spectra. In the present study the above tools were used to estimate wave spectra at two locations: no. 44008 maintained by National Data Buoy Centre (NDBC) in the Gulf of Maine, USA and ‘DS5’ monitored by National Institute of Ocean Technology (NIOT) in Bay of Bengal, India. The choice of these two locations facilitated the comparison of model performances in different geographical areas. The SVR and MT models were developed in order to estimate the wave surface spectral density over a wide range of wave frequencies out of average wave parameters of significant wave height and average zero-cross wave period. The models were trained and tested using randomly selected sea states. Both MT and SVR were able to derive the spectral shapes satisfactorily as reflected in high values of the correlation coefficients and low values of root mean square error and mean square error.

Low Temperature Thermal Desalination (LTTD): new sustainable desalination process

Water is a scarce resource, and new collection and production facilities are predicted as necessary in the coming years. Sea water desalination shall be a key technology for the production of fresh water in many areas of the world, and great efforts are now in progress to increase the reliability of the desalination processes and to reduce the relevant investment and operation costs. In this effort, new conceptual desalination process and schemes have been implemented with remarkable innovative content by desalination engineers worldwide. This paper is focused on a quite innovative and inexpensive new process. This process was originally tested by the former SOWIT in Italy and is now redesigned on independent parameters by the National Institute of Ocean Technology (NIOT) in India, for the same specific installations on islands of the Indian Ocean.

Wave hindcast for the Indian Ocean region covering the period of ARMEX-I (June-August 2002)

Wave hindcast has been carried out for the Indian Ocean (30°-120° E, 30° S - 30° N) region covering ARMEX, PHASE-I observational programme (June-August 2002). The analysed wind fields at six hourly intervals provided by National Centre for Medium Range Weather Forecast (NCMRWF), New Delhi is used to drive the third generation wave model “WAM” (1.5° × 1.5° resolution). The primary objectives of this hindcast, is to provide the sea-state information for the period of ARMEX which would help in research applications and to implement WAM operationally for the Indian Ocean to meet various requirements in future. The model was earlier validated using the Ship Borne Wave Recorder (SBWR) data collected onboard INS Sagardhwani, the visual estimates reported in the Indian Daily Weather Report (IDWR) published by the India Meteorological Department (IMD) and time-series buoy measurements of National Institute of Ocean Technology (NIOT). The model outputs are compared with the available buoy data of NIOT. The comparisons between the hindcast wave parameters and measurements reveal that the model could predict wave heights with errors ranging from ±12% to ±20%.

Advanced Magnetostrictive Materials for Sonar Applications

Piezoelectric or magnetostrictive materials can be utilised as active materials for electroacoustic underwater transducers. Piezoceramic materials gained edge over the conventional magnetostrictive materials during 1940s due to their unique electro-acoustic properties. At present, inspite of passive sonars there is a need of low-frequency high-power active sonars for the Navy. This led toresearch for new activematerials with competing characteristics to that of the existing piezo transducers. The discovery of a giant magnetostrictive material, commercially known as Terfenol-D, led to a breakthrough in the development of a new generation of sonar transducers. Now, the materials (including composites) as well as sensors are commercially available. A new generation of transducers have emerged in ocean-related areas like acoustic tomography, longrange underwater communication, geophysical exploration, oil well exploration, etc. Indian Institute of Technology Madras, Chennai, has also developed the basic material technology a few years back. At present, in India, National Institute of Ocean Technology, Chennai, is developing underwater transducers utilising giant magnetostrictive materials as well as piezoelectric materials for marine applications like sub-bottom profiling (seafloor mapping) and long-range underwater communications. A prototype of a portable, low-frequency medium power transmitter operating over a wide-frequency range has been developed. The main advantage of this transducer is its simplicity in design. In this paper, (he recent developments in material processes, importance of device-oriented material characterisation, and transducer design aspects have been emphasised. Some results on the underwater performance of a wide-band transducer have also been presented. These materials also have ultrasonic applications, capable of revolutionising the processing industry.

The Indian 1 MW Demonstration OTEC Plant and the Pre-Commissioning Tests

Ocean Thermal Energy Conversion (OTEC) utilizes the thermal gradient available in the ocean to operate a heat engine to produce work output. Even though the concept is simple and old for almost one century, recently it has gained momentum due to worldwide search for clean continuous energy sources to replace the fossil fuels. There are technological hurdles to overcome to tap the immense potential of OTEC. But still the technology is mature enough to establish commercial power plants. National Institute of Ocean Technology was involved in the design, development and demonstration of a 1 MW OTEC floating plant-the largest of its kind-in the Indian waters. This is to be commissioned 60 km south east of Tuticorin, South India where an ocean depth of 1200m available. The site surveys, computer analysis, model studies were done in 1999. The basic power cycle design Was completed within 4 months. The plant was integrated and stage qualification tests were carried out in 2000-02. The project is to be commissioned in January 2003. This paper is projecting the technological and economical aspects of the OTEC with an overview of the various pre-commissioning activities of the project.