Performance investigations on service-class and observation-class marine robotic vehicles

Abstract

This thesis mainly investigates the performance characteristics of service-class and observation-class marine robotic underwater vehicles, a subset of in-situ marine platforms. The buoyancy-propelled vehicles such as underwater gliders and floats fall under mobile unmanned platforms. These vehicles have transoceanic range endurance at the expense of transit speeds creating large data samples. However, navigation of these unmanned platforms to a specific location is ineffective. This limitation was overcome by thruster propelled vehicles to execute various observation and complex maintenance operations. Nevertheless, complex intervention operations need overactuated UVs for better maneuverability and agility. They have better operational safety during subsystem failures than underactuated systems. However, they suffer from the underutilization of the active thrusters during a mission. Thus, each class of vehicles have their benefits and drawbacks. The existing platforms’ limitations evoke a research gap in developing sustainable vehicles considering each propulsion strategy’s advantages and limitations. The term ’sustainable’ in the present context refers to the vehicles which have the capacity to endure contradicting operational requirements, i.e., they do not compromise one operational requirement for the other. Here, a service-class underwater robot called Vectored Thruster Underwater Vehicle (VTUV) and an observation-class underwater robot called Hybrid Propulsion Underwater Robotic Vehicle (HPURV) are conceptualized with improved capabilities. They provide a strike-off between endurance, size, weight, thrust produced for better maneuverability. This thesis would help first understand and later address at least one of the issues, such as the vehicle design, propulsion, and control methodologies using existing sensor and power supply technologies to improve overall performance. Towards this direction, it is intended to explore the existing thruster configurations of underwater vehicles. The comparison studies on the fixed and vectored thruster configurations with actuator constraints shows the performance improvements of the latter. The vectored thrust layout with four thrusters was mathematically modeled to analyze the overall system performance at different operating conditions with focus on the hydrodynamic model parameters estimation and thruster dynamics. A suitable motion control scheme was derived for tracking, positioning, and various marine operations. Due to the reduced number of thrusters, a detailed study on the actuator active fault tolerance showed that an active fault accommodation control would help avoid vehicle loss. Finally, a functional prototype was developed to perform open-loop experiments and validate the mathematical model. The other part of this thesis deals with the investigations on the existing methods for observation-class applications. It attempts to understand the buoyancy propulsion limitations of the existing platforms and implements the same along with bioinspired propulsion for long term endurance. A mathematical model for multimodal operation was derived to understand the open-loop and closed-loop performance of the overall system using simulations, which requires a detailed hydrodynamic model parameters estimation and fin dynamics. Initially, the oscillating fin dynamics are derived using angle of attack theory. Later the buoyancy propulsion and moving mass models are overlayed for implementing the multiple operation modes. A detailed mechanical design was done to develop a functional prototype to perform qualitative experimental verification. The significant contributions of this thesis are mainly the conceptualization, simulation-based performance studies, and the development of two fully functional robotic vehicle systems at the Indian Institute of Technology Indore. Keywords: Underwater vehicle (UV), Hybrid propulsion, Bio-inspired propulsion, Ostraciiform, Boxfish, Buoyancy propulsion, Fin propulsion, Observation-class UV, Service-class UV, Thrust vectoring, Rotatable/tilting/pivoted thruster, Performance constraints, Actuator saturation, Actuator fault tolerance, Fault accommodation, Weighted pseudo-inverse, Backstepping control, Over-actuated system, Underactu ated system, Line of sight, Oceanic currents, Intervention-class AUV.