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• W1592369566 abstract "To provide a vehicle with the ability to hold position in a coastal environment requires a significant amount of onboard power. This power requirement either forces the vehicle size to increase to allow for suitable mission duration or reduces the amount of time the vehicle has to conduct its mission. To relax the power requirement, we propose to develop vehicles that can employ a bottom-sitting or soft grounding behavior. To obtain this behavior requires vehicles that have the capability to selfballast. By optimally positioning itself and sitting on the bottom, the AUV can be placed in a sleep mode, with only monitoring sensors awake, thereby conserving power. In this paper we present the preliminary work conducted in the areas of simulation, design and testing of a Variable Buoyancy System (VBS) for an Autonomous Underwater Vehicle (AUV). This buoyancy system will be integrated into the new NPS AUV which is currently under construction, to support the upcoming joint operations with the University of Lisbon's MARIUS vehicle. We will discuss the tradeoffs and analysis that went into the design of the system, as well as the challenges associated with the integration of such a behavior and system into the vehicle. INTRODUCTION Energy storage is limited in AUV’s. To assist with energy management, data gathering missions have been proposed where the vehicle should sit on the bottom and gather acoustic/video/chemical data over extended periods of time. In this grounding scenario, thrusters may be used. However, there are two disadvantages for this method: high energy consumption and restricted use close to the ocean bottom. The motivation for this paper is to study a low cost, simple soft grounding capability for a submersible vehicle using controllable ballast. For simplicity, water ballast is considered. The design of the control system is based on the NPS Phoenix AUV. The ballast system is designed to control the weight addition into or out of the two ballast tanks. Ballast control of vehicles is not a new subject and we can find many examples beginning in the 1900’s, the non-rigid airships are very good examples of ballast control. One of the most important elements of a non-rigid airship is the ballonet-system. A ballonet as seen in Figure 1 is an airbag (one or two of them) inside the envelope, which is provided with air from a blower or directly from the engine unit. The air could be removed from the ballonet through the valves. If the airship has a front and aft ballonet then the height and pitch of the airship can be steered. For example, if the aft bag is filled with more air, then the airship will become heavier in the rear part of the envelope and the ship will incline increasing the altitude of the ship by using the engines. As Figure 1 depicted, the airship can also be statically trimmed [1]. Control was manual. For most underwater vehicles, the depth / pitch control is normally provided by hydroplanes. As an example, consider the NPS Phoenix AUV, the MIT Odyssey and the WHOI Remus. At low speed however, the control surfaces provide reduced control authority and the ballast control problem is very complex due to nonlinear, time-varying, uncertain hydrodynamics. Inherent lags arising from the integration of ballast water flow rate commands into weight change makes the control difficult to stabilize. There are some designs that used a bang-bang control system [2]. The ARPA’s Unmanned Undersea Vehicle (UUV) employed a fuzzy logic ballast controller which was claimed to be comparable with the performance that can be obtained from standard control techniques, but does not require traditional linear or nonlinear design methods. Figure 1. Sectional elevation of the Parseval-Airship PL VI, 1910. Report Documentation Page Form Approved OMB No. 0704-0188 Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. 1. REPORT DATE 2005 2. REPORT TYPE 3. DATES COVERED 4. TITLE AND SUBTITLE Design and Development of Low Cost Variable Buoyancy System for the Soft Grounding of Autonomous Underwater Vehicles 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER 5e. TASK NUMBER 5f. WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) Naval Postgraduate School,Center for AUV Research,Monterey,CA,93943-5000 8. PERFORMING ORGANIZATION REPORT NUMBER 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR’S ACRONYM(S) 11. SPONSOR/MONITOR’S REPORT NUMBER(S) 12. DISTRIBUTION/AVAILABILITY STATEMENT Approved for public release; distribution unlimited 13. SUPPLEMENTARY NOTES The original document contains color images. 14. ABSTRACT To provide a vehicle with the ability to hold position in a coastal environment requires a significant amount of onboard power. This power requirement either forces the vehicle size to increase to allow for suitable mission duration or reduces the amount of time the vehicle has to conduct its mission. To relax the power requirement, we propose to develop vehicles that can employ a bottom-sitting or soft grounding behavior. To obtain this behavior requires vehicles that have the capability to selfballast. By optimally positioning itself and sitting on the bottom, the AUV can be placed in a sleep mode, with only monitoring sensors awake, thereby conserving power. In this paper we present the preliminary work conducted in the areas of simulation, design and testing of a Variable Buoyancy System (VBS) for an Autonomous Underwater Vehicle (AUV). This buoyancy system will be integrated into the new NPS AUV which is currently under construction, to support the upcoming joint operations with the University of Lisbon’s MARIUS vehicle. We will discuss the tradeoffs and analysis that went into the design of the system, as well as the challenges associated with the integration of such a behavior and system into the vehicle. 15. SUBJECT TERMS 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT 18. NUMBER OF PAGES 12 19a. NAME OF RESPONSIBLE PERSON a. REPORT unclassified b. ABSTRACT unclassified c. THIS PAGE unclassified Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std Z39-18 2 In another fuzzy logic control model, a 15 state Kalman filter was developed to provide estimates of the motion variables and the applied lift and torque acting on the UUV. The control law decided between three possible control actions; pump water in both tanks, pump water out of both tanks and turn both pumps off. The fuzzy input state space was composed of depth error and depth rate, and each is divided into partitions. The fuzzy controller interpolated between the partitions allowing the control to vary smoothly as the states move from one partition to another. These movements of states were provided by on and off of ballast pumps [3]. In this paper we outline the development of a depth controller using sliding mode control techniques for a neutrally buoyant vehicle. The sliding mode controller is designed on the basis of the simplified four degrees of freedom vertical plane equations of motion. A linear quadratic regulator (LQR) proportional approach is then utilized for the design of the ballast controller, which produces flow rate commands, allowing the vehicle to have a soft grounding behavior. These two controllers use a logic based depth regulator to provide realistic simulation of the vehicle’s flight and grounding operations in a single mission. VEHICLE MODELING AND EQUATIONS OF MOTION We will deal with only vertical plane variables; i.e., heave, pitch, and surge. The vertical plane stability analysis involves heave and pitch motions. However, the surge equation couples into pitch and heave through the offset, zG. This is a dynamic coupling, and could be eliminated by redefining hydrodynamic coefficients with respect to the ship’s center of gravity instead of its geometric center. Restricting the motions of the vehicle to the vertical (dive) plane, the only significant motions that must be incorporated to model the vehicle in the dive plane are, the surge velocity (u), the heave velocity (w), the pitch velocity (q), the pitch angle (θ ) and the global depth position (Z). q = θ& θ θ ρ δ α δ δ sin ) ( cos ) ( ) ( ) ( 2 1 ) ( ) ( ) ( ) ( 3 2 B z W z B x W x xdx xq w xq w x b C M M U Uw M wq mz Uq mx M q M I w M mx" @default.
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• W1592369566 title "Design and Development of Low Cost Variable Buoyancy System for the Soft Grounding of Autonomous Underwater Vehicles Proceedings of 11th International Symposium on Unmanned Untethered Submersible Technology (UUST'99), August 22-25, 1999" @default.
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