Thesis (Master of Engineering in Mechanical Engineering)--Cape Peninsula University of Technology, 2018. / Underwater glider wings are the lifting surfaces of unmanned underwater vehicles UUVs depending on the chosen aerofoil sections. The efficiency as well as the performance of an underwater glider mostly depends on the hydrodynamic characteristics such as lift, drag, lift to drag ratio, etc of the wings. Among other factors, the geometric properties of the glider wing are also crucial to underwater glider performance. This study presents an opportunity for the numerical investigation to improve the hydrodynamic performance by incorporating curvature at the trailing edge of a wing as oppose to the standard straight or sharp trailing edge. A CAD model with straight leading edge and trailing edge was prepared with NACA 0016 using SolidWorks 2017. The operating conditions were setup such that the inlet speed varies from 0.1 to 0.5 m/s representing a Reynolds number 27.8 x 10ᵌ and 53 x 10ᵌ. The static pressure at different angles of attack (AOA) which varies from 2 to 16degrees at the increment of 2degrees for three turbulent models (K-Ԑ-standard, K-Ԑ-RNG and K-Ԑ-Realizable), was computed for upper and lower surfaces of the modified wing model using ANSYS Fluent 18.1. Thereafter the static pressure distribution, lift coefficient, drag coefficient, lift to drag ratio and pressure coefficient for both upper and lower surfaces were analysed. The findings showed that the lift and drag coefficient are influenced by the AOA and the inlet speed. If these parameters change the performance of the underwater glider changes as depicted by figure 5.6 and figure 5.7. The hydrodynamics of the underwater glider wing is optimized using the Cʟ/Cᴅ ratio as function of the operating conditions (AOA and the inlet speed). The investigation showed that the optimal design point of the AOA of 12 degrees and a corresponding inlet speed of 0.26m/s. The critical AOA matched with the optimal design point AOA of 12 degrees. It was also observed that Cp varies across the wing span. The results showed the Cp is higher closer to the fuselage while decreasing towards the mid-span and at the tip of the wing. This showed that the wing experiences more stress close to the fuselage than the rest of the wing span which implies that a higher structural rigidity is required close to the fuselage. The results of the drag and lift curves correspond to the wing characteristics typical observed for this type of aerofoil.

The use of autonomous underwater vehicles (AUVs) for oceanic observation and research is becoming more common. Underwater gliders are a specific class of AUV that do not use conventional propulsion. Instead they change their buoyancy and center of mass location to control attitude and trajectory. The vehicles spend most of their time in long, steady glides, so even minor improvements in glide range can be magnified over multiple dives. This dissertation presents a rigid-body dynamic system for a generic vehicle operating in a moving fluid (ocean current or wind). The model is then reduced to apply to underwater gliders. A reduced-order point-mass model is analyzed for optimal gliding in the presence of a current. Different numerical method solutions are compared while attempting to achieve maximum glide range. The result, although approximate, provides good insight into how the vehicles may be operated more effectively. At the end of each dive, the gliders must change their buoyancy and pitch to transition to a climb. Improper scheduling of the buoyancy and pitch change may cause the vehicle to stall and lose directional stability. Optimal control theory is applied to the buoyancy and angle of attack scheduling of a point-mass model. A rigid-body model is analyzed on a singular arc steady glide. An analytical solution for the control required to stay on the arc is calculated. The model is linearized to calculate possible perturbation directions while remaining on the arc. The nonlinear model is then propagated in forward and reverse time with the perturbations and analyzed. Lastly, one of the numerical solutions is analyzed using the singular arc equations for verification. This work received support from the Office of Naval Research under Grant Number N00014-08-1-0012. / Ph. D.

Nowadays underwater gliders have become to play a vital role in ocean exploration and allow to obtain the valuable information about underwater environment. The traditional approach to the development of such vehicles requires a thorough design of each subsystem and conducting a number of expensive full scale tests for validation the accuracy of connections between these subsystems. However, present requirements to cost-effective development of underwater vehicles need the development of a reliable sampling and testing platform that allows the conducting a preliminary design of components and systems (hardware and software) of the vehicle, its simulation and finally testing and verification of missions. This paper describes the development of the HIL test bench for underwater applications. Paper discuses some advantages of HIL methodology provides a brief overview of buoyancy variation systems. In this paper we focused on hydraulic part of the developed test bench and its architecture, environment and tools. Some obtained results of several buoyancy variation systems testing are described in this paper. These results have allowed us to estimate the most efficient design of the buoyancy variation system. The main contribution of this work is to present a powerful tool for engineers to find hidden errors in underwater gliders development process and to improve the integration between glider’s subsystems by gaining insights into their operation and dynamics.

Orientador: Prof. Dr. Marat Rafikov / Dissertação (mestrado) - Universidade Federal do ABC, Programa de Pós-Graduação em Engenharia Mecânica, 2016. / O objetivo desta dissertação é o controle de trajetória e navegação de um robô móvel autônomo subaquático. O robô abordado nesta dissertação faz parte de uma nova classe de AUV¿s (Autonomous Underwater Vehicles) chamados de planadores subaquáticos. Os planadores subaquáticos se destacam por substituírem os propulsores por um mecanismo de translação e rotação de massas internas e variação de flutuabilidade, para se locomoverem. Essa nova classe de veículos visa superar o problema de autonomia, encontrado em outros tipos de AUV¿s, devido à limitada duração das baterias. O controle de posicionamento é realizado através da linearização do modelo não ¿linear e aplicada a estratégia de controle ótimo conhecida por LQR (Regulador Linear Quadrático). Essa estratégia é aplicada ao problema de regulação do robô a uma referência e a eficácia do método de controle do robô é verificada através de simulações numéricas. Nas simulações verificou ¿ se que o controle LQR foi capaz de fazer com que o veículo convergisse para a trajetória de referência desejada, demonstrando assim que a aplicação de um controlador linear para o modelo não ¿ linear do veículo é uma opção de aplicação em missões reais. / Within the structures optimization study area, one of the extensively explored methods is the TO objetivo desta dissertação é o controle de trajetória e navegação de um robô móvel autônomo subaquático. O robô abordado nesta dissertação faz parte de uma nova classe de AUV¿s (Autonomous Underwater Vehicles) chamados de planadores subaquáticos. Os planadores subaquáticos se destacam por substituírem os propulsores por um mecanismo de translação e rotação de massas internas e variação de flutuabilidade, para se locomoverem. Essa nova classe de veículos visa superar o problema de autonomia, encontrado em outros tipos de AUV¿s, devido à limitada duração das baterias. O controle de posicionamento é realizado através da linearização do modelo não ¿linear e aplicada a estratégia de controle ótimo conhecida por LQR (Regulador Linear Quadrático). Essa estratégia é aplicada ao problema de regulação do robô a uma referência e a eficácia do método de controle do robô é verificada através de simulações numéricas. Nas simulações verificou ¿ se que o controle LQR foi capaz de fazer com que o veículo convergisse para a trajetória de referência desejada, demonstrando assim que a aplicação de um controlador linear para o modelo não ¿ linear do veículo é uma opção de aplicação em missões reais.

Nowadays underwater gliders have become to play a vital role in ocean exploration and allow to obtain the valuable information about underwater environment. The traditional approach to the development of such vehicles requires a thorough design of each subsystem and conducting a number of expensive full scale tests for validation the accuracy of connections between these subsystems. However, present requirements to cost-effective development of underwater vehicles need the development of a reliable sampling and testing platform that allows the conducting a preliminary design of components and systems (hardware and software) of the vehicle, its simulation and finally testing and verification of missions. This paper describes the development of the HIL test bench for underwater applications. Paper discuses some advantages of HIL methodology provides a brief overview of buoyancy variation systems. In this paper we focused on hydraulic part of the developed test bench and its architecture, environment and tools. Some obtained results of several buoyancy variation systems testing are described in this paper. These results have allowed us to estimate the most efficient design of the buoyancy variation system. The main contribution of this work is to present a powerful tool for engineers to find hidden errors in underwater gliders development process and to improve the integration between glider’s subsystems by gaining insights into their operation and dynamics.

A long-baseline (LBL) underwater acoustic communication and localization system was developed for the Virginia Tech Underwater Glider (VTUG). Autonomous underwater vehicles, much like terrestrial and aerial robots require an effective positioning system, like GPS to perform a wide variety of guidance, navigation and control operations. Sea and freshwater attenuate electromagnetic waves (sea water is worse due to higher conductivity) within very few meters of striking the water surface. Since radio frequency communications are unavailable, many undersea systems use acoustic communications instead. Underwater acoustic communication is the technique of sending and receiving data below water. Underwater acoustic positioning is the technique of locating an underwater object. Among the various types of acoustic positioning systems, the LBL acoustic positioning method offers the highest accuracy for underwater vehicle navigation. A system consisting of three acoustic 'beacons which are placed on the surface of the water at known locations was developed. Using an acoustic modem to excite an acoustic transducer to send sound waves from an underwater glider, the range measurements to each of the beacons was calculated. These range measurements along with data from the attitude heading and reference system (AHRS) on board the glider were used to estimate the position of the underwater vehicle. Static and dynamic estimators were implemented. The system also allowed for underwater acoustic communication in the form of heartbeat messages from the glider, which were used to monitor the health of the vehicle. / Master of Science