Tata Sudhakar

Design and development of non- rotary propulsion for autonomous underwater vehicles

Autonomous underwater vehicles that are propelled by altering buoyancy have been in demand in recent years as they have the ability to operate at sea for long periods. The buoyancy of an object in a fluid can be varied by two methods. One method changes the buoyancy of the vehicle by changing the mass without changing the volume and the other varies the buoyancy of the vehicle by changing its volume without altering the mass. The non-rotary propulsion system (Variable Buoyancy Engine) is the key component in the efficient design of autonomous underwater vehicles which enables it to ascend and descend through the water column by varying the buoyancy of the vehicle by changing its volume. The variable buoyancy system is capable of operating at a maximum depth of 500 m. The system consists of micro hydraulic pump, DC electric motor, internal reservoir, external rubber bladder, oil level sensor and valves. The design uses a micro hydraulic pump to increase buoyancy by transferring fluid from oil reservoir to an external bladder. Subsequently, a proportional control valve and the internal vacuum of the housing used for achieving negative buoyancy by decreasing the volume of the external bladder.

Adaptive filtering based on least mean square algorithm

In this paper, an adaptive filter based on Least Mean Square (LMS) algorithm is implemented. The paper discusses the system configuration, filter structure and the implementation of the Adaptive LMS algorithm. The convergence and stability of the filter which ensures stable adaptation behavior is also discussed. The performance of the designed adaptive filter is comparable to the in-built Matlab LMS filter. The performance of the designed filter is evaluated based on the bit error rates by varying the additive white gaussian noise levels in the system. The performance of the designed adaptive filter is found to be satisfactory and is viable to be applied in underwater acoustic communication.

Case study of Tsunami warning system using RTK GPS method

A reliable Tsunami detection system is vital importance in protecting mankind from disasters. Real Time Kinematic-Global Positioning System (RTK-GPS) is considered to be the promising GPS techniques due to its reliability and accuracy to minimize complexity in establish and maintenance with existing BPR. In the present study we have used RTK-GPS to find the sea water elevation difference in the detection of tsunami. Comparison is done between tsunami height data obtained from coastal tidal stations/offshore wave stations by using greens law with data obtained from RTK-GPS system and tsunami frequency spectrum are separated from actual tidal wave observation Another added advantage of this method is that it also produces a reliable estimate of the destructive potential of a tsunami within minutes of detection before tsunami reaches the coastal areas. By developing a global tsunami warning system utilizing an expanded network of coastal GPS stations may be effective in detection of tsunamis.

Indigenous drifting buoys for the Indian Ocean observations

Drifting buoys are widely deployed to measure near surface ocean currents and temperature. The Global Ocean Observation System program designed a global array of 1250 drifter buoys to cover oceans at resolution of one per 5 ° × 5 ° grids spatially. The National Institute of Ocean Technology, India indigenized drifting buoy in 2012 with geostationary satellite communication to have near real-time data at every hour. The drifting buoy technology is applied for intellectual property right and transferred to Industries. The measurement scheme in the drifting buoys is capable to measure fluctuations in sea surface temperature and smaller surface eddies. This article describes case studies of indigenous drifting buoys in the Indian Ocean from 2012 onwards. The sea surface temperature and drifting speed measured with indigenous drifting buoy is compared with market available drifting buoy (Marlin-Yug), moored data buoy (BD11) and remote sensed data. We also report results from a drifting buoy with General Packet Radio Service (GPRS) telemetry in the coastal region.

Shape optimization of vertical profiler using computational fluid dynamics

Autonomous underwater vertical profiler is a free-drifting profiling drifter that measures the temperature and salinity of the upper 2000 m of the ocean depth and is used to continuously monitor the climatic state of the ocean. The main objective is to determine the hull resistance for a given boundary conditions using computational fluid dynamics techniques. The hull resistance is an important factor in determining the speed of the system. In the present work, the numerical simulation of flow past the vertical profiler has been performed by using ANSYS Fluent 14.5 with Reynolds-Averaged Navier-Stokes based k-epsilon turbulence model. The turbulent flow has been simulated to investigate the drag force coefficient, the velocity vector and the vortex formation over the vertical profiler for its ascending and descending motions in ocean for its present shape. The flow simulation without stability disc has been carried out to see how the stability disc affects the flow and the drag. Then the work deals with the shape optimization of the vertical profiler under the limitation of manufacturing feasibility, without altering the weight and volume. The bladder cover and the stability disc have been modified to reduce the drag coefficient for the descending and ascending motion of the vertical profiler.

Development of an autonomous catamaran based observatory system for collecting meteorological and oceanographic parameters at Gulf of Khambhat-Gujarat

An instrumented, self-orienting catamaran based observatory system has been developed successfully by National Institute of Ocean Technology (NIOT) to measure the physical properties above and below sea surface[1]. The autonomous observatory has the capabilities of measuring currents of depth up to 40m. The above development work has been undertaken to meet the requirement of establishing met-ocean observatory system in different locations in Gulf of Khambhat (GoK), in Gujarat state for the construction of dam in the Gulf of Khambhat under Kalpasar project. The prime objective of the establishment of network of observatories is to collect time series measurements of met-ocean data sets which are necessary for the understanding, conceptual design and modeling. The observatory systems are categorized in to three types depending on sensor configuration on each type. This paper describes on the developmental work carried out for the establishment of catamaran based observatory system which is suitable for high current [2]. This development work has been successful with the CPU interfaced to the required set of sensors on the catamaran based observatory platform.

Mach-Zehnder Interferometer based high sensitive water salinity sensor for oceanographic applications

A high sensitive Mach-Zehnder Interferometer (MZI) based fiber optic sensor for the measurement of sea water salinity has been demonstrated in this research. At first, femtosecond laser is used as the source and its performance in sensing salinity of sea water is analyzed. Secondly, a Carbon monoxide (CO) laser operating in the spectrum of 4.8 to 8.3 pm is used to excite the arms of MZI. It has been observed that wavelength shifts related to attenuation dips are highly sensitive to salinity of sea water when CO laser is used as the source. Using simple and robust schematic design, sensitivity of 0.01pm/ppt is achieved for salinity range of 31 to 37 ppt at a constant temperature of 27°C. The all-optical MZI salinity sensor indicated here is easy to fabricate, low cost, highly sensitive and finds application in the field of oceanography.

Mechanical system design of automatic sub-surface floating fish cage

The culture of fish in cages has become a practical and successful method in oceans to get good yield in fish production without going to deep sea. Our system contains a fish cage and an electronic system which makes the cage system submerge to a desired depth to protect fish during adverse weather condition. An automatic sub-surface floating fish cage has been developed for deployment in the coastal waters to safeguard the cage during bad weather condition. The prototype fish cage system consists of a rigid HDPE pipe assembly, net cage, variable ballast tank, submersible pump, air control system, floats, mooring ropes, anchors, and control station. The variable ballast tank is used to change the buoyancy of the system so that the fish cage can either be surfaced or submerged. The cage is free to move vertically in a water column by adjusting the weight and the buoyancy with an automatic control system. The system was tested in a test tank facility and sea trail was conducted off Chennai in Bay of Bengal to verify the operability of the fish cage.

Glider operations in the Bay of Bengal

Indian Ocean has an important role in regional and global climate due to its geography. Presently, variety of ocean observation instruments are employed to measure time and space variability of the large ocean that extends to two closed bays at higher latitudes. Underwater gliders are recently considered to be a vital platform for ocean observation. The revolutionary new underwater glider (“Barathi”), as a mobile sensor node was steered remotely and carried out highly spatial and temporal resolution measurement in Bay of Bengal (BoB) on April-August 2014 is presented in this paper.

Validation methods implemented to ascertain the positional data uncertainty of an indigenously developed drifter buoy-Pradyu

A systematic approach in implementing a suitable validation method which evaluates a newly developed product is highly necessary to ensure its continuous reliability and consistency of its quality[1] performances. More specifically any sensor or instrument developed for the real time data collection and measurement of ocean parameters need to be prejudged and evaluated for its data product quality before its being suggested to use for the practical applications particularly for study and modeling of any physical phenomenon. NIOT has successfully implemented a high accuracy smart sensor GPS receiver module in its drifter buoy which acquires positional (Latitude & Longitude) information and transmits using INSAT modems. NIOT named this drifter buoy indigenization as Pradyu. Performed land based triangulation test method and deployment & comparison of drifters using the imported drifter from Marlin-Yug, Ukraine is carried out in Bay of Bengal. The above validation methods[2] carried out confirms the drifters ability to follow and track the surface mixed layer current[5] with a positional accuracy of ±10m. In this paper, the recent outcome of different methods implemented for validating the drifter is presented.