CFD approach to modelling, hydrodynamic analysis and motion characteristics of a laboratory underwater glider with experimental results

Underwater gliders are buoyancy propelled vehicle which make use of buoyancy for vertical movement and wings to propel the glider in forward direction. Autonomous underwater gliders are a patented technology and are manufactured and marketed by corporations. In this study, we validate the experimental lift and drag characteristics of a glider from the literature using Computational fluid dynamics (CFD) approach. This approach is then used for the assessment of the steady state characteristics of a laboratory glider designed at Indian Institute of Technology (IIT) Madras. Flow behaviour and lift and drag force distribution at different angles of attack are studied for Reynolds numbers varying from 10(5) to 10(6) for NACA0012 wing configurations. The state variables of the glider are the velocity, gliding angle and angle of attack which are simulated by making use of the hydrodynamic drag and lift coefficients obtained from CFD. The effect of the variable buoyancy is examined in terms of the gliding angle, velocity and angle of attack. Laboratory model of glider is developed from the final design asserted by CFD. This model is used for determination of static and dynamic properties of an underwater glider which were validated against an equivalent CAD model and simulation results obtained from equations of motion of glider in vertical plane respectively. In the literature, only empirical approach has been adopted to estimate the hydrodynamic coefficients of the AUG that are required for its trajectory simulation. In this work, a CFD approach has been proposed to estimate the hydrodynamic coefficients and validated with experimental data. A two-mass variable buoyancy engine has been designed and implemented. The equations of motion for this two-mass engine have been obtained by modifying the single mass version of the equations described in the literature. The objectives of the present study are to understand the glider dynamics adopting a CFD approach, fabricate the glider and its variable buoyancy engine and test its trajectory in water and compare it with numerically obtained trajectory in the vertical plane. (C) 2017 Shanghai Jiaotong University. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license

Open-source Simulation of Underwater Gliders

Autonomous underwater gliders (AUGs) are currently deployed in oceans throughout the globe and are recording real-time, in-situ data. Simulating AUGs is rendered particularly difficult by the identification of the underlying dynamic model, as these vehicles embed several internal movable components. Acausal simulators can significantly improve the possibility to study and understand the dynamics of this class of vehicles and can in turn support the design of more robust control systems. In this paper, an open-source simulator architecture designed in OpenModelica is proposed to simulate underwater gliders. The validation is carried out using two different AUGs models, a ROGUE and a Seawing. The vehicle dynamics is firstly compared with analytical results and, following, with values obtained by means of another simulator. Further steps will entail comparing the dynamics of a simulated Seaglider with real deployment data publicly available. In this work, some of the main hydrodynamic and geometrical properties of a Seaglider are identified, computed through Computational Fluid Dynamics (CFD) analyses and retrieved from the mission ballast sheet. Overall, the developed model is expected to enhance gliders’ control strategies, thus improving their performance and mitigating incidents such as being carried away by undesired ocean currents

Hovering-mode control of the glider-type unmanned underwater vehicle

Thesis (Master)--Izmir Institute of Technology, Mechanical Engineering, Izmir, 2011Includes bibliographical references (leaves: 104-107)Text in English; Abstract: Turkish and Englishxiii, 109 leavesResearch on the underwater robotics has attracted the interest of many researchers over the years. The primary reasons are the need to perform underwater intervention tasks that are dangerous for a diver and the need to perform underwater survey tasks that last for longer periods of time. Unmanned underwater vehicles can be divided into two categories. Most of the systems, today, that require a certain level of precision and dexterity are built as Remotely Operated Vehicles (ROV). On the other hand, the systems that perform repetitive tasks are configured as Autonomous Underwater Vehicles (AUV). The objective of the thesis is to design a novel, cost-efficient, and fault-tolerant ROV that can hover and be used for shallow water investigation. In order to reduce the cost, the numbers of thrusters are minimized and internal actuators are used for steering the vehicle and stability in hovering mode. Also, the design is planned to be open for modification for further improvements that will enable the use of the vehicle for intervention tasks and studies. In this work, previously developed unmanned underwater vehicles are reviewed. Following this, the conceptual designs are created for the underwater vehicle and internal actuator designs are developed. Designed mechanisms are modeled in SolidWorks© and transferred to MATLAB© Simulink for hovering-mode control studies. Afterwards, to verify the simulation results, experiments are conducted with a seesaw mechanism by using LabVIEW© programming. Finally, results are given, discussed and future works are addressed

A GAIN-SCHEDULED CONTROL SCHEME FOR IMPROVED MANEUVERABILITY AND POWER EFFICIENCY OF UNDERWATER GLIDERS

Underwater gliders are a relatively new type of low-power, long duration underwater vehicle that use changes in buoyancy to propel themselves forward. They are widely used today for oceanographic research, and a number of theoretical control schemes have been derived over the years. However, despite their nonlinear dynamics that evolve as a function of their environment and operating conditions, most fielded gliders use linear control methods, such as static-gain proportional-integral (PI) or proportional-integral-derivative (PID) compensators for motion control, which can significantly limit vehicle performance. This thesis develops an alternative approach to underwater glider control that employs control system gain-scheduling to improve vehicle performance and efficiency over a wider range of operating conditions as compared to static or fixed-gain approaches. The primary contribution of this thesis is the development of a practical gain-scheduling procedure using linearized models of the decoupled pitch and yaw dynamics of the vehicle. This methodology improves on the current fixed-gain topologies used on fielded gliders today, while being straightforward and cost-effective to implement. In this thesis, the development of a nonlinear dynamical model of a Slocum glider using computer-aided design (CAD) and computational fluid dynamics (CFD) simulations was also carried out to support the high-fidelity characterization of the controller topologies. A nonlinear numerical simulation of the Slocum glider was developed in Matlab and was used to assess the performance improvements and the increased robustness of the gain-scheduled PID method to a standard fixed-gain PID approach

Persistent gliding waterframe: the waterframe conceptual project

Underwater gliders are autonomous vehicles that profile vertically by controlling buoyancy and move horizontally due to its wings.[14,17] At the top of a bounce, the glider decreases its buoyancy, which causes it to begin to sink. As the glider sinks, the hydrodynamic shape of the exterior (waterframe design) produces horizontal motion. The gilder uses a method of control to adjust pitch and roll as it continues forward. At the bottom of a bounce, the glider becomes more buoyant, which causes it to begin an upward path. Again, horizontal motion is produced by the shape of the waterframe and mainly by wings. When the glider reaches the surface, it will communicate with a ground station, sending out the data it collected during the dive and receiving instructions for its next trajectory.[5] This type of vehicles can operate over long ranges and are relatively low cost [2] ocean research vehicles, making them the ideal choice for locate potential areas in the ocean that would be suitable for sea farming. The PGW will be equipped with sensors that will monitoring the underwater environment. The data collected from the PGW will help researchers monitor the fish population and even implement sea farming. The driving customer requirements for the PGW include a four-month continuous operational runtime, the ability to produce a lower cost system than the current competitors, a two-year useful life before refitting, the ability to launch and recover the PGW from a boat or a dock, the ability to reach a maximum depth of 300 meters, the ability to navigate within 1000 meters of the PGW’s intended course, and all fluids contained in the PGW must be biodegradable. This thesis presents the development of the waterframe for small (75 Kg, 2,00m long) autonomous underwater vehicle with operating speeds about and ranges up to 3000 Km . A half scale prototype was built and performance tests need to be done to evaluate waterframe's performance.Os planadores subaquáticos são veículos autónomos que se deslocam verticalmente controlando a sua flutuabilidade e se movem horizontalmente devido à presença de asas.[14,17] Quando se encontram à superfície, o planador diminui a sua flutuabilidade, o que faz com que comece a afundar. Enquanto o veículo afunda, a sua forma exterior produz movimento horizontal. O veículo usa um controlo para ajustar o ângulo de picada e de rolamento para se continuar a deslocar na trajectória correcta. Quando o planador atinge o ponto de profundidade máxima, começa a ficar menos denso que a água que o rodeia e mais uma vez a sua forma exterior e principalmente as asas, fazem com que se desloque horizontalmente. Quando regressa à superfície, o planador subaquático pode comunicar com a estação de controlo enviando os dados recolhidos durante o mergulho anterior e receber informações para o próximo mergulho.[5] Os planadores subaquáticos podem operar durante longos períodos de tempo tendo por isso um grande alcance e um custo de operação relativamente baixo [2], fazendo com que sejam a escolha ideal para identificar, nos oceanos, potenciais locais para aquacultura. O veículo será equipado com sensores que monitorizarão o ambiente subaquático. Os dados recolhidos pelo planador ajudarão os investigadores a monitorizar os cardumes e a implementar a aquacultura. Os requisitos do cliente para o PGW incluem 4 meses de operação contínua, a capacidade de produzir o veículo a um custo inferior ao dos concorrentes, a capacidade de operar em oceanos, 2 anos de vida útil antes de manutenção, a capacidade de poder ser depositado na água através de um barco ou de uma doca, a capacidade de chegar aos de profundidade, a capacidade de navegar com um erro 1000m máximo de em relação à trajectória definida previamente e ainda o facto de todos os fluidos contidos no PGW terem de ser obrigatoriamente biodegradáveis. Esta dissertação apresenta o desenvolvimento de uma plataforma para um veículo subaquático autónomo, pequeno ( 75 kg, 2,00 m de comprimento) com velocidades de operação de cerca 0,4 m/s de e alcance de cerca de 3000 km. Foi ainda construído um protótipo a metade da escala e é necessário efectuar testes para avaliar a performance da plataforma desenvolvida

Hydrodynamic Modelling for a Transportation System of Two Unmanned Underwater Vehicles: Semi-Empirical, Numerical and Experimental Analyses

Underwater transportation is an essential approach for scientific exploration, maritime construction and military operations. Determining the hydrodynamic coefficients for a complex underwater transportation system comprising multiple vehicles is challenging. Here, the suitability of a quick and less costly semi-empirical approach to obtain the hydrodynamic coefficients for a complex transportation system comprising two Unmanned Underwater Vehicles (UUVs) is investigated, where the interaction effects between UUVs are assumed to be negligible. The drag results were verified by Computational Fluid Dynamics (CFD) analysis at the steady state. The semi-empirical results agree with CFD in heave and sway; however, they were overpredicted in surge due to ignoring the wake effects. Furthermore, experiments were performed for the validation of the time-domain motion simulations with semi-empirical and CFD results. The simulations which were performed with the CFD drags were close to the experiments. The semi-empirical approach could be relied on once a correction parameter is included to account for the interactive effect between multiple UUVs. Overall, this work makes a contribution by deriving a semi-empirical approach for the dynamic and controlling system of dual UUVs, with CFD and experiments applied to ascertain its accuracy and potential improvement

Developing the next generation of Autonomous Underwater Gliders

Submitted in partial fulfillment of the requirements for the degree of Master of Science in Mechanical Engineering at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2022.This thesis presents a novel, hybrid Autonomous Underwater Glider (AUG) architecture developed for improved performance in shallow, high-current environments while maintaining all capabilities inherent to a deep, 1000m-rated AUG. Numerous regions of scientific interest, such as the marginal ice zone (MIZ) and continental shelf breaks present significant challenges to conventional AUG operations due to a combination of changing ocean currents and depths. AUGs are traditionally optimized for performance in shallow (less than 200m) or deep water (200m to 1000m) environments. The design of a buoyancy drive on a deep-rated AUG does not support the pump rate required for fast inflections in narrow depth bands. Contained within this thesis is the framework to expand the operational envelope of a Teledyne Webb Research (TWR) G3 Slocum glider through substantial modification of the glider’s hardware components backed by rigorous hydrodynamic analysis and computational fluid dynamics (CFD) modelling. Since AUGs are limited in both speed and maneuverability, the goal of this thesis is to improve and modify the glider’s flight characteristics, specifically the glider’s speed through water, its inflection rate, and its efficiency. These performance improvements are accomplished through the introduction of a high-power thruster, modified wings, and aft fin surfaces. The modified glider’s efficacy is evaluated through various laboratory experiments and field data obtained in Buzzards Bay and the Caribbean Sea. Design concepts for a future, more advanced glider are also discussed.Support for this research was provided through grants from the National Science Foundation (NSF) Navigating the New Arctic Grant (NNA #1839063) and the National Ocean Partnership Program (NOPP) Enhanced Propulsion Integrated Capability - Deep Autonomous Underwater Glider (EPIC-DAUG) grant (NA19OAR0110408)

Open-source simulation of underwater gliders

Autonomous underwater gliders (AUGs) are currently deployed in oceans throughout the globe and are recording real-time, in-situ data. Simulating AUGs is rendered particularly difficult by the identification of the underlying dynamic model, as these vehicles embed several internal movable components. Acausal simulators can significantly improve the possibility to study and understand the dynamics of this class of vehicles and can in turn support the design of more robust control systems. In this paper, an open-source simulator architecture designed in OpenModelica is proposed to simulate underwater gliders. The validation is carried out using two different AUGs models, a ROGUE and a Seawing. The vehicle dynamics is firstly compared with analytical results and, following, with values obtained by means of another simulator. Further steps will entail comparing the dynamics of a simulated Seaglider with real deployment data publicly available. In this work, some of the main hydrodynamic and geometrical properties of a Seaglider are identified, computed through Computational Fluid Dynamics (CFD) analyses and retrieved from the mission ballast sheet. Overall, the developed model is expected to enhance gliders’ control strategies, thus improving their performance and mitigating incidents such as being carried away by undesired ocean currents