gliders the autonomous under water vehicles

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  • 1.Gliders - The Autonomous Underwater vehicles Unmanned submarine glidersNasiha. J Mar ine I nst r ument at ion Dept of Ocean Engineer ing I I T Madr as

2. Outline Problem/Motivation Underwater Gliders How it works? Instrumentation Specifications Type Examples Applications conclusion 3. Problem / Motivation Manual Ocean Sampling labor, limited spacial and temporal variations, highly affected by bad weather conditions, resource, and time intensive Objectives/Sensing Oceanographic profiling Feature Tracking Boundary Monitoring Mapping Autonomous Distributed Agents both reduce over costs, improve accuracy, and reduce uncertainty in the observed data 4. Underwater Gliders Autonomous marine sensing equipment that profile vertically by controlling buoyancy and move horizontally on wings Developed for measuring oceanographic properties in the coastal and open ocean at low costs Unmanned robotic vehicle with a sensor suite to collect oceanographic parameters of interest Low power and slow moving but very efficient glide patterns to increase life times Represent a rapidly maturing technology 5. Why Gliders? Gliders are truly transformational, not dead weights Low Power Buoyancy changes drive vehicle up / down Wings provide lift to drive forward Hence, long endurance per small size Autonomous Proven command, control and navigation even in bad weather through GPS, Iridium link through antenna Small Two-person deployable Platform independent 6. How it works? No propeller is required. A change in volume (generated by filling an external oil bladder or moving a piston) creates positive and negative buoyancy Buoyancy engine to change their weight in water Generation of hydrodynamic lift and drag forces Slightly heavy at the surface, the glider dives. Once at a maximum depth, the ballast system allows the glider to become slightly lighter and to navigate back to the surface Generally maneuver at the speed of half a knot (~0.257m/s) How deep a glider can dive depends on the model, but ranges between 200 and 1500 meters 7. Closed loop control of attitude and depth- performed by an on-board computer that executes a pre-programmed mission while submerged Antennaes are integrated into the gliders Glider collects data from their scientific sensors Communication at the surface using an IRIDIUM satellite connection Besides CTD sensors, they even carry PAR sensors and Fluorometers 8. Glider structureGlider Major Systems/Subsystems Buoyancy Engine (BE) Pitch/Roll System Control System Communications System (in EB) Power System 9. Types i. Multi stroke Reciprocating (multi-stroke) pumps are smaller and lighter than singlestroke pumps. Ex. Seaglider, Spray This capability is important, particularly at large maximum operating pressures A disadvantage of small reciprocating pumps is sensitivity to vapour lock, which occurs when the pump cylinder fills with gas and the compression ratio of the pump is insufficient to raise the pressure of the compressed gas to the ambient pressure. If this happens to all cylinders of a reciprocating pump, pumping ceasesii. Single-stroke Single stroke pumps, are more robust, do not need the valving that reciprocating pumps use to provide bi-directional buoyancy control, and are effectively immune to vapour lock. Ex. Slocum gliders Slocum is optimized for shallow and coastal operation where rapid maneuverability is important and, consequently, uses a more powerful motor than the other gliders for rapid buoyancy control. 10. Gliders and specifications 1. Spray 2. Slocum 3. Seaglider 11. Spray glider Deep ocean explorer, maximum operating depth 1500m Multistroke pumps are used Sensors used include: CTD; Sea Point Optical Backscatter Sensor; Sea Point Chlorophyll Fluorometer; Tritech PA200 acoustic altimeter for bottom avoidance; and Sontek Argonaut-SGP 750-kHz Acoustic Doppler Current Profiler 12. Slocum glider Coastal ocean explorer, depth range: 4 200 m Single stroke pumping Needs higher energy to work at larger depths, not like SPRAY and seaglider Sensor Package: conductivity, temperature, depth 13. Seaglider Open ocean explorer, depth Range: 4 200 m Compound hull with flooded fibreglass and Aluminium interior Sensor Package: Sea-Bird temperature-conductivitydissolved oxygen, Wet Labs fluorometer-optical backscatter 14. Advantages Traditionally, oceanographic data is collected by scientists aboard seagoing vessels. Unfortunately, this method results in a very low rate of data acquisition compared to what it costs to obtain the data. The use of gliders is more advantageous. They provide subsurface data on a larger scale and higher frequency than traditional shipboard techniques at a fraction of the cost, and their ability to gather data is not affected by rough weather. Gathering ocean data in real-time becomes very cost effective High performance glider that can provide continuous efficient ocean monitoring Lower speed (below 0.5 m/s) and higher endurance (typically 1-2 months) The long endurance enables the glider to explore the oceans, acquiring data over large areas, with a deep vertical profile When it surfaces, it sends collected data ashore and receives new mission commands via the Iridium Satellite Network. The operator uses a webbased interface to stay in contact with surfaced gliders and to monitor glider history. Thus data acquisition and control over the device becomes easier. 15. Applications Oceanographic data collection Temperature, salinity, turbidity, chlorophyll, nuetrients, magnetic field variations and other parameters being monitored by the gliders Different set of sensors carried in the payload Volume of the payload differs for various glider design according to their application. 16. Oceanographic sensorsRINKO-II Hypoxia sensors 17. Oceanographic sensors 18. Oceanographic sensors 19. Conclusion Autonomous underwater vehicles, and in particular autonomous underwater gliders represent a maturing technology with a large cost saving potential over current ocean sampling technologies for sustained real time measurements. 20. References 1.2. 3. 4. 5.6. 7.APL (2008). Applied Research Laboratory, Seaglider Fabrication Center, University of Washington, Seattle,WA. Retrieved on 11 September 2008, Autonomous Underwater Gliders, Wood, Stephen Florida Institute of Technology, United States of America Underwater Gliders for Ocean Research, Daniel L. Rudnick et al., Marine Technology Society Journal Stommel, H. 1989. The Slocum mission, Oceanography. 2:22-25 Wilcox, J. S., J. G. Bellingham, Y. Zhang and A. B. Baggeroer. 2001. Performance metrics for oceanographic surveys with autonomous underwater vehicles. IEEE J Oceanic Eng. 26:711-725 21. Thank you