Autonomous Undersea Systems Institute

Abstract New robotic sensor platforms have computing resources that enable a rich set of tasks for adaptive monitoring of the environment. But to substantially augment the toolbox of environmental sensing, such platforms must be embedded with realistic statistical models and coherent methodologies for designing experiments and assimilating the data. In this article, we develop myopic and hybrid strategies for autonomous underwater vehicle sampling in space and time. These strategies are based on a stochastic advection‐diffusion Gaussian process model for the mine tailings concentration in a Norwegian fjord, and the goal is to monitor the excursion set (ES) of high concentrations. Closed form expressions for the expected misclassification probabilities of the ES enable real‐time operation on board the autonomous vehicle, and this is used to guide the spatio‐temporal sampling. Simulation studies show that the suggested strategies outperform other approaches that either (i) simplify the models for spatio‐temporal variation, or (ii) simplify the design criterion. A field test shows how autonomous underwater sampling is useful for refining an initial stochastic advection‐diffusion model. These experiments further show that the vehicle can adapt to focus on regions with intermediate concentrations where it is natural to improve the ES prediction.

Abstract We present a 2D high‐order and easily accessible immersed‐boundary adaptive harmonic polynomial cell (IB‐AHPC) method to solve fully nonlinear wave‐structure interaction problems in marine hydrodynamics using potential‐flow theory. To reduce the total number of cells without losing accuracy, adaptive quad‐tree cell refinements are employed close to the free‐surface and structure boundaries. The present method is simpler to implement than the existing IB‐HPC alternatives, in that it uses standard square cells both in the fluid domain and at the boundaries, thus without having to use the more complex and expensive overlapping grids or irregular cells. The spurious force oscillations on moving structures, which is a known issue for immersed boundary methods (IBMs), are eliminated in this study by solving a separate boundary value problem (BVP) for a Lagrangian acceleration potential. We also demonstrate that solving a similar BVP for the corresponding Eulerian acceleration potential is far less satisfactory due to the involved second derivatives of the velocity potential in the body‐boundary condition, which are very difficult to calculate accurately in an IBM‐based approach. In addition, we present, perhaps for the first time since the HPC method was developed, a linear matrix‐based stability analysis for the time‐domain IB‐AHPC method. The stability analysis is also used in this study as a general guide to design robust and stable numerical algorithms, in particular related to the treatment of boundary conditions close to the intersection between a Dirichlet and a Neumann boundary, which is essential in time‐domain wave‐structure interaction analyses using IBMs. We confirm theoretically through the stability analysis that square cells have the best stability properties. The present method has been verified and validated satisfactorily by various cases in marine hydrodynamics, including a moving structure in an infinite fluid, fully nonlinear wave generation and propagation, and fully nonlinear diffraction and radiation of a ship cross section.

The history of drone dates far back. Human in those days must have had a yearn for the sky. This article first gives an overview of the history of research and development of drone including fixed wing and rotary wing, followed by, in particular, the history of development of rotary wing drone with the following four periods: before 1990 when radio control is at its dawn period; 1990 to 2010 when drone is at its dawn period; 2010 to 2015 when hobby-use drone is at its spread period; and 2016 and after when industrial-use drone is at its dawn period to growth period. In addition, this article presents the Japanese government’s roadmap, followed by a five-stage class of drone in terms of flight level and autonomy. In particular, autonomy will be discussed from the points of view of guidance, navigation, and control. Then with reference to an ideal state of drone in future, the article will discuss importance of the guidance system by fault tolerant control and supervisor control with implementation of the AI technology and the like.

Public attention is frequently directed to visible macro-system impacts of events such as oil spills resulting in oil washing into estuaries, tar balls on beaches, and oiled megafauna. However oil and other types of accidental contaminants, such as radioactive particles, can have fundamental impacts on less-visible portions of delicate chemical and biological ecosystems. What happens to the contaminants after impact events? Where and how are the contaminants dispersed in the water column and over what distance? What long-term impacts do the contaminants have on chemical and biological ecosystems? These key questions need to be addressed over large spatial dimensions and over long time frames. This paper describes the initial steps of the development of an autonomous robotic sampling platform, deployable for long-term monitoring missions and capable of collecting samples to track contaminant dispersion.

The ocean covers about two-thirds of the earth and has a great effect on the future existence of all human beings. About 37% of the world's population lives within 100 km of the ocean. The ocean is generally overlooked as we focus our attention on land and atmospheric issues; we have not been able to explore the full depths of the ocean and its abundant living and non-living resources. For example, it is estimated that there are about 2,000 billion tons of manganese nodules on the floor of the Pacific Ocean near the Hawaiian Islands. We discovered, by using manned submersibles, that a large amount of carbon dioxide comes from the seafloor and extraordinary groups of organisms live in hydrothermal vent areas. Marine robots including unmanned surface vehicles and unmanned underwater vehicles can help us better understand marine and other environmental issues, protect the ocean resources of the earth from pollution, and efficiently utilize them for human welfare. This paper briefly presents some exemplary models of recent developments in marine robots in different application areas.

Unmanned Vehicles (UxVs) are now a key Intelligence Surveillance and Reconnaissance (ISR) resource for first-world defense organizations. But the barrier to entry for making unmanned systems has fallen, with terrorist groups and crime syndicates capable of creating sophisticated robots using Commercial Off-The-Shelf (COTS) components. With the explosive growth of unmanned systems in the air, on the water, and underwater, the threat from misuse of these technologies increases. Maritime Domain Awareness (MDA) for ports, harbors, and protection of cruise ship and military marine assets has largely focused on threats above the waterline from more conventional threats like suicide boaters, or unauthorized entry. MDA at and below the waterline presents severe but not insurmountable challenges. Effective risk mitigation from UxVs involves a probabilistic approach to disruptive scenarios that reverse-engineers the Concept of Operations (CONOPS) likely to be used, based on the capabilities of rogue UxVs, and the skill level of their operators. Consideration of oceanographie and meteorological data available to the public in real-time or near real-time from observing systems is part of the risk prediction. Technical countermeasures that exploit rogue UxV weaknesses, and training of personnel involved in MDA, are logical components to close the gap. Our group is developing approaches to reduce risks of successful UxV attack, and crafting appropriate responses to an unmanned systems disruption. We also are developing new tools and training measures that will be of use to waterside security personnel.

This paper reports on the development of an automatic thrust redistribution algorithm for a redundant autonomous underwater vehicle (AUV) in the case of thruster faults. Under favorable conditions, the transformation of the thruster force vector to the generalized body-fixed force vector can be computed in a least-squares manner, which provides the minimum norm solution. In the case of some type of thruster fault, the redundancy in the system allows for seamless redistribution of the thruster forces while maintaining the desired vehicle motion. An accurate, fault-detecting thrust estimator has been previously developed that is robust to changes in source power and propeller ventilation. Such an estimator is necessary in order to quantify the health of the thrusters, which can then be used to weigh the contribution of each thruster to the vehicle motion in a continuous manner. An example of the thruster health index in its simplest form is the approximated thrust divided by the reference thrust, passed through a moving average filter, and normalized over all thrusters. This index can effectively scale back the contribution of any faulty thruster to the body-fixed, vehicle force vector solution.

Tethered buoys have long served as a common gateway for communications between underwater, terrestrial, and air assets. Although common, tethered buoys lack the versatility envisioned with an anchorless buoy that can closely maintain a station or waypoint as long as needed and be remotely commanded to move to another waypoint. Indeed, an untethered gateway buoy would have multiple uses in the defense, commercial and scientific sectors. The predominant challenge to develop an untethered buoy is generating enough energy for the buoy to maintain a station for months in open ocean currents. Falmouth Scientific, Inc. and its partners have developed an untethered, station-keeping, gateway buoy, named Gatekeeper, under an SBIR contract with the U.S. Navy. A spar-shape buoy, Gatekeeper inherently offers superior stability to meet the requirement for a persistent radio and satellite link A bail winch system for dropping and raising an acoustic transducer provides a robust underwater acoustic link. The primary energy and power source for the Gatekeeper is a 35 kilowatt-hour patent-pending Salt Water Activated Power System (SWAPS?), which provides at least 200 Watts of power. The Gatekeeper's SWAPS? uses 55 pounds of an environmentally friendly metal alloy that reacts with saltwater to produce hydrogen for a fuel cell generator. SWAPS? is an order of magnitude better than any battery technology in terms of mass, volume and cost for the same amount of energy. A solar panel array serves as a renewable energy source for the Gatekeeper system in order to preserve the SWAPS? fuel, which is not renewable during deployment. A 2 kilowatt-hour battery is also used to store energy from the SWAPS? and solar panels when the Gatekeeper is idling. Gatekeeper demonstrated excellent navigational and station-keeping capability at speeds up to 2 knots during a SBIR Phase ? sea trial in the Fall of 2008 and operated solely from the SWAPS? and a solar array at speeds up to about 1.5 knots. Gatekeeper is projected to endure deployments that last several weeks with its configuration from the fall of 2008, which is a significant milestone. Improvements to Gatekeeper's endurance will be made in preparation for an at-sea endurance test that is planned for the early spring of 2010.

The solar powered AUV is a new system that provides very long endurance sampling capability. The SAUV II is the latest version of the solar powered AUV and has been evaluated in a series of tests during 2004. A number of in water tests were undertaken investigating communication and cooperation among multiple heterogeneous AUVs; these tests included experiments related to low-level underwater networking and high-level language protocols, and user interface issues inherent in multiple AUV mission planning, monitoring and control. These tests have shown that communications protocols can be designed and used successfully in the underwater acoustic environment with both gateway buoys and multiple AUVs. While more testing has to be accomplished to assess efficiency, timing, and to refine software, the tests were very positive. The testing verified that a network infrastructure can be put in place in the underwater environment and that the network will allow communication pathways to be broken and then reconfigured autonomously. Three different in water tests were completed. This paper will describe the results of the 2004 testing with the SAUV II system.

As hypoxic water masses increase worldwide in duration and extent due to coastal eutrophication, advanced technology water quality monitoring by autonomous vehicles can increase our capability to document and respond to these environmental perturbations. We evaluated the use of a long endurance autonomous underwater vehicle (AUV) to map dissolved oxygen levels to determine the extent of hypoxia in a small bay (Greenwich Bay, USA.) known to experience summertime hypoxic episodes that have resulted in massive fish kills. During a 7.5 hr nighttime/early morning period in September 2004, the AUV collected dissolved oxygen, conductivity, temperature and depth data along three transects in the Greenwich Bay. The AUV utilized was a new solar powered vehicle designed for continuous survey operations. This vehicle, referred to as the SAUV II, was recently developed for the US Office of Naval Research for long endurance missions requiring monitoring, surveillance, and/or station keeping with real-time bi-directional communications to shore. The vehicle was pre-programmed to transit to designated waypoints at various depths. Following each transect, the vehicle surfaced, maintained a watch circle, and transmitted data to shore via an RF link. The survey provided the participating scientists with near real-time access to the physical characteristics of the water column with improved spatial and temporal resolution over traditional sampling for dissolved oxygen concentrations. This pilot study served as a test of the SAUV II to collect high resolution, near real-time water quality data in a nearshore, shallow embayment. Water column temperature and conductivity was relatively uniform over the survey path (temperature varied from 22-23 /spl deg/C; conductivity varied from 43030-43981 /spl mu/S). The depth of the vehicle varied from near-surface to a maximum of 9.5 m. Depth and dissolved oxygen concentrations were correlated. Dissolved oxygen concentrations ranged from approximately 2.4 to 6.0 mg/L over the course of the survey; mildly hypoxic conditions were encountered. The lowest concentrations of dissolved oxygen occurred at the deeper depths (>6 m). As the pilot study was performed in September, the late stage of a hypoxic event was most likely observed. Using the SAUV II to increase spatial sampling of dissolved oxygen in Greenwich Bay and conducting more frequent SAUV II surveys during the summer months will improve our understanding of hypoxia in this complex coastal estuary.