Development of an electromechanical variable buoyancy system for shallow water operations

Autonomous Underwater Vehicles (AUVs) are widely used for marine survey, in both the coastal and deep sea areas and they are applicable to both civil and defense applications. They are pre-programmed and can operate without human intervention and this makes them attractive to many marine industries. A concern with AUVs is the high energy consumption required by their thrusters for depth control, buoyancy change and manoeuvrability and that adversely affects their performance and endurance. This paper presents the design and development of novel stand-alone variable buoyancy system for AUVs and investigates its performance through numerical and experimental investigations. The design idea is based upon the Pump Driven Variable Buoyancy System (PDVBS) and uses a hydraulic based method to control the buoyancy. The VBS is integrated into a medium sized AUV of 3 m length and the performance of the vehicle in vertical plane is investigated. The results are presented for a buoyancy change requirement of 5 kg and a diaphragm type positive displacement pump, with a buoyancy change rate of 5 kg/min, is utilized. Depth control performance of the AUV and its hovering capabilities, at a desired depth of 60 m using the Linear Quadratic Regulator (LQR) controller, are analysed in detail. Finally, the results indicate that the designed and developed VBS is effective in changing the buoyancy and controlling the heave velocity. These two features are expected to provide higher endurance and better performance in AUVs involved in rescue/attack operations.

Autonomous underwater vehicles (AUVs) have become main tools for underwater survey in scientific, military, and commercial applications. A significant amount of onboard power is needed to execute long-range missions; however, energy storage is limited in AUV. This paper presents a novel landing AUV that can land on the sea floor to perform long-term monitoring and measuring tasks and save onboard electric energy. The AUV has following characteristics. Firstly, a triangular structure of the AUV which is composed of three cabins is used to achieve stable bottom sitting. Secondly, the releasing mechanism is designed to eject and recover the AUV. Bottom sitting and recovering is verified by ocean trials. This paper provides guidance for design of similar AUVs.

Autonomous Underwater vehicles (AUV) with reconfigurable payloads are rapidly becoming common. Their dynamic characteristics are affected when payloads change. Typically, retuning of the controller is required to maintain good control performance. To address this situation, we develop a technique to enable rapid identification of AUV dynamics online. We demonstrate the technique with a fin-controlled single-thruster torpedo-shaped AUV. By decoupling the system according to planar and horizontal motion, mathematical models for yaw and pitch dynamics are developed. This results in a second-order transfer function with auxiliary steady state fin deflection. Identification of continuous-time model was performed to preserve the physical meaning of the parameters. Identification in continuous-time requires time-derivative terms which are reconstructed using the state variable filter (SVF). Then, recursive least-square (RLS) algorithm is used to identify the unknown parameters. The proposed identification method was validated through field deployments of our AUVs. The online estimates compare favorably with results obtained from offline identification methods requiring numerical optimization. We demonstrate how turning radius of the AUV can be estimated accurately from the identified parameters. We also show how a gain-scheduled controller, with better control performance than a constant-gain controller, can be designed using the estimated parameters.

Autonomous underwater vehicles (AUVs) allow us to survey and explore globally and freely in vast deep sea. We aim to develop long cruising range AUVs (LCAUVs) for researches of the global change, ocean-trench earthquake, and biodiversity and for exploring ocean resources. We have developed the first prototype of LCAUV, Urashima since 1998. The vehicle powered by a PEFC system marked the world record of cruising distance of 317 kilometers in 2005. The vehicle, 10 m long and 10 tons in weight, has the specifications: maximum depth ratings; 3500 m, maximum cruising speed; 3.2 knots, and endurance; 60 hours. This large vehicle has large user payload of a few hundreds kilograms. In 2007, research and development of the elemental technologies which will be utilizes for development of the second generation LCAUV started to expand cruising range to 3000 kilometers. For long range cruising, technology improvement of power sources, navigations, communications, and vehicle controlling are mainly important. Since endurance of the LCAUV becomes over 600 hours, during this cruising period the vehicle controller must autonomously deal with problems which may occur in any devices. If the vehicle controller does not recover a fatal problem, the controller appropriately leads status of the vehicle to quit an executing mission and ascend itself. We have improved the vehicle controller and plan sea-trials using the controller in January 2009. On the other hand, The AUV, MR-X1, 2.4 m long and 800 kg in weight, has been developed for scientific research and the test bed of the LCAUVs since 2000. This working AUV is also needed for installing or recovering observation equipment, tracking and sampling benthos or planktons, and doing simple repetitive works. The first sea-trial of MR-X1 was carried out in 2003. After that, the MR-X1 system is only used as a test bed of the developed devices in the LCAUV project. In this year, we have developed new items, a device installer on the sea-floor and mud core sampler for the MR-X1. In the technical report, a redundant controlling system for the LCAUV installed on the MR-X1 is described. And new items and their test results will be reported.

Autonomous underwater vehicles (AUVs) are becoming commonplace in the study of inshore coastal marine habitats. Combined with shipboard systems, scientists are able to make in-situ measurements of water column and benthic properties. In CSIRO, autonomous gliders are used to collect water column data, while surface vessels are used to collect bathymetry information through the use of swath mapping, bottom grabs, and towed video systems. Although these methods have provided good data coverage for coastal and deep waters beyond 50m, there has been an increasing need for autonomous in-situ sampling in waters less than 50m deep. In addition, the collection of benthic and water column data has been conducted separately, requiring extensive post-processing to combine data streams. As such, a new AUV was developed for in-situ observations of both benthic habitat and water column properties in shallow waters. This paper provides an overview of the Starbug X AUV system, its operational characteristics including vision-based navigation and oceanographic sensor integration.

Autonomous underwater vehicles (AUVs) have great advantages for activities in deep oceans, and are expected as the attractive tool for near future underwater development or investigation. However, AUVs have various problems which should be solved for motion control, acquisition of sensors' information, behavioral decision, navigation without collision, self-localization and so on. This paper proposes an adaptive biologically inspired neural controller for trajectory tracking of AUVs in nonstationary environment. The kinematic adaptive neuro-controller is an unsupervised neural network, which is termed Self-Organization Direction Mapping Network (SODMN). The network uses an associative learning system to generate transformations between spatial coordinates and coordinates of propellers' velocity. The neurobiological inspired control architecture requires no knowledge of the geometry of the robot or of the quality, number, or configuration of the robot's sensors. The SODMN proposed in this paper represents a simplified way to understand in part the mechanisms that allow the brain to collect sensory input to control adaptive behaviours of autonomous navigation of the animals. The efficiency of the proposed neurobiological inspired controller for autonomous intelligent navigation was implemented on an underwater vehicle capable of operating during large periods of time for observation and monitoring tasks.

Autonomous underwater vehicles (AUVs) have many, scientific, military, and commercial applications because of their potential capabilities and significant cost-performance improvements. Typical AUV development requires critical system design and many costly at-sea trials during which systems specifications can be validated. Modeling and simulation provides a cost-effective method for carrying out preliminary component or system (hardware and software) testing and verification. Due to the complexity of most AUV development and their tight schedules, the simulated systems often differ considerably from the actual embedded architecture, thereby reducing the fidelity of the entire simulation. We adopted a hardware-in-the-loop (HIL) simulation approach that includes some level of the system's hardware and software. As expected, an HIL simulation requires all components be run under hard real-time constraint. The paper presents our implementation and considerations on HIL simulation for single and multiple vehicles. A brief mention of sensor and environment modeling is also provided.

Autonomous underwater vehicles (AUVs), unmanned underwater vehicles, are cheaper to operate than remotely operated vehicles (ROVs), since an AUV does not require a trained human operator to control. As a result, in this paper, we propose the pipeline tracking algorithm using sequences of the forward-looking sonar (FLS) images installed on a preprogram AUV. The FLS is more suitable to be used in the subsurface environment than an optical camera due to the limited visibility and floating particles in the sub-sea surface environment. In our work we first employed the speckle noise reduction to the FLS images. Then, we applied the level-set method (LSM) to extract a pipeline boundary in each frame. Lastly, the post-processing step was designed to link the unconnected segments together to from a complete pipeline. Our algorithm can perform the segmentation and tracking with more than 85% accuracy.

This paper presents the design and analysis of the ‘Variable Buoyancy System (VBS)’ for depth control which is an essential operation for all underwater vehicles. We use the ‘Water Hydraulic Variable Buoyancy System (WHVBS)’ method to control the buoyancy and discuss details of the system design architecture of various components of VBS. The buoyancy capacity of the developed VBS is five kilograms and the performance of the VBS in standalone mode is analysed using numerical simulation. Presented VBS is operable to control the buoyancy up to sixty meters of depth and it can be directly installed to medium size UVs. Simulation results show that the developed VBS can reduce the energy consumption significantly and higher in each cycle (i.e. descending and ascending) of the same VBS in standalone mode being operated with either propeller or thruster for sixty meters depth of operation. Our results conclude and demonstrate that the designed VBS is effective in changing the buoyancy and controlling the heave velocity efficiently and this serves the purpose of higher endurance and better performances desired in rescue/attack operations related to the UVs both in civilian and defense domains.

Autonomous underwater vehicles (AUVs) are poised to become an indispensable tool for ocean exploration, underwater research and development, and military activities. One of the key elements of these vehicles is dependability; there must be some form of fault recovery/fault tolerance in the control system. In this work, we use an approach involving synthesis of motions in degrees of freedom (DOF) that are unactuated, by combining motions in DOF that are actuated. The objective is to determine the usefulness of the method for a typical streamlined vehicle which is controlled by control surfaces rather than thrusters. We find that the method has difficulties in its present form because of the righting moment designed into the vehicle, but it is functional on a modified model of the vehicle.

Autonomous underwater vehicles (AUVs) have come a long way in the last ten years or so with new battery technologies extending their endurance and programming development improving their reliability. This paper takes a look at the latest technologies that can be used to explore the world's oceans, which remain the last great unexplored wilderness.

Autonomous Underwater Vehicles have gained popularity for the last decades, especially a lot of AUVs were considered as the most suitable tool for the purpose of reducing risks of people in dangerous marine operations. This paper presents the preliminary results of the research on hardware design, the controller of an autonomous underwater vehicle model for the task of survey, search and rescue ... With a compact design, AUV can operate in limited spaces. Through a unique ducted propeller and rudder located at the aft, the AUV can perform horizontal motion. It can also control pitch angle and depth motion by an inside mass shifter mechanism (MSM) which changes the vehicle center of gravity. In addition, The AUV is integrated with powerful eletronic system, highprecision sensors helping it carries on missions from simple to complex. The use of Sliding Mode Control (SMC) to independently design the heading and depth controllers for AUV demonstrates the steady stability of the controllers with the nonlinear model, uncertainty parameters and disturbances. Finally, the simulation results show that the SMC controllers can control the AUV nonlinear model to track the desired steering angle and depth with high accuracy and stability.

Subsea pipeline leak inspection by autonomous underwater vehicle

This paper deals with the development of a pressure-tolerant autonomous underwater vehicle (AUV) for the deep sea, made without pressure hulls. Within the framework of a collaborative effort, a pressure-tolerant and hydrodynamically favorable formed test vessel is introduced. Moreover, individual systems, which are currently under construction, will be described in more detail. The vehicle is equipped with pressure-tolerant energy supply, various pressure-tolerant electric motors, a pressure-tolerant steering system, a pressure-tolerant jet propulsion system, a variable buoyancy system, a vehicle based navigational unit, as well as with two ultra-short baseline (USBL) modems. For the deployment of ocean engineering sensors, many variable payload sections exist. This paper will provide an overview of the contemporary development status of pressure-tolerant technology. Furthermore, an outlook for the entire project with the aim of doing test dives in the Atlantic Ocean is provided.

The vast and deep conditions of the ocean still contain many objects that have not been explored. Based on the type of autonomous underwater vehicle (AUV) device design, it consists of types that can drift, glide, and can propel itself in water. Types of AUV without propellers (nonpropelled, drifter). or glider), can float without thrusters or glide up and down the water by changing its buoyancy. This AUV uses little or no battery power compared to propeller-driven AUVs, but cannot perform as many maneuvers. Variable Buoyancy System used in different types of underwater craft, designed and built for specific rides and applications. Therefore, each system is completely different from the others. This research focuses on systems that raise and lower volume, using components such as diaphragms, bladders, and bellows. It is possible to use a diaphragm for a buoyancy engine to make the vehicle easier to fabricate. The aim of this research is to determine the magnitude of deformation of the diaphragm made from silicon rubber and EPDM (ethylene propylene diene monomer) with varying thickness of 0.5 mm; 1mm and 2mm. Through the Finite Element Method approach to obtain deformation analysis modeling, EPDM material provides higher deformation than using silicon material. However, for pressures of no more than 0.5 bar, using a rubber thickness of 0.5 mm is not suitable. So the appropriate application for Gliders is 1 mm thick.