STUDY ON THE MANUEVERABILITY OF AN UNDERWATER GLIDER WITH APPENDAGES

This paper presents the hydrodynamic analysis with the aim of determining the underwater glider with appendage maneuverability performance. The external appendage would affect the behaviour of the underwater glider. Computer Aided Design (CAD) is used to deal with the geometric variation of the underwater glider. Based on the design model, a simulation system using Computational Fluid Dynamics (CFD) for the underwater glider is established. The different velocities are simulated to analyse the hydrodynamics of the underwater glider. In order to evaluate the influences of appendage on the maneuverability performance of the underwater glider, simulations of underwater glider with and without appendage are performed and compared. The results demonstrate that the underwater glider with appendage shows higher drag force, high pressure coefficient and high velocity zone where the ability to maintain its gliding path is unsymmetrical, resulting in poor turning performance

Modular Dynamic Modeling and Development of Micro Autonomous Underwater Vehicle: Lancelet

Ph.DDOCTOR OF PHILOSOPH

Improving Swimming Performance and Flow Sensing by Incorporating Passive Mechanisms

As water makes up approximately 70% of the Earth\u27s surface, humans have expanded operations into aquatic environments out of both necessity and a desire to gain potential innate benefits. This expansion into aquatic environments has consequently developed a need for cost-effective and safe underwater monitoring, surveillance, and inspection, which are missions that autonomous underwater vehicles are particularly well suited for. Current autonomous underwater vehicles vastly underperform when compared to biological swimmers, which has prompted researchers to develop robots inspired by natural swimmers. One such robot is designed, built, tested, and numerically simulated in this thesis to gain insight into the benefits of passive mechanisms and the development of reduced-order models. Using a bio-inspired robot with multiple passive tails I demonstrate herein the relationship between maneuverability and passive appendages. I found that the allowable rotation angle, relative to the main body, of the passive tails corresponds to an increase in maneuverability. Using panel method simulations I determined that the increase in maneuverability was directly related to the change in hydrodynamic moment caused by modulating the circulation sign and location of the shed vortex wake. The identification of this hydrodynamic benefit generalizes the results and applies to a wide range of robots that utilize vortex shedding through tail flapping or body undulations to produce locomotion. Passive appendages are a form of embodied control, which manipulates the fluid-robot interaction and analogously such interaction can be sensed from the dynamics of the body. Body manipulation is a direct result of pressure fluctuations inherent in the surrounding fluid flow. These pressure fluctuations are unique to specific flow conditions, which may produce distinguishable time series kinematics of the appendage. Using a bio-inspired foil tethered in a water tunnel I classified different vortex wakes with the foil\u27s kinematic data. This form of embodied feedback could be used for the development of control algorithms dedicated to obstacle avoidance, tracking, and station holding. Mathematical models of autonomous vehicles are necessary to implement advanced control algorithms such as path planning. Models that accurately and efficiently simulate the coupled fluid-body interaction in freely swimming aquatic robots are difficult to determine due, in part, to the complex nature of fluids. My colleagues and I approach this problem by relating the swimming robot to a terrestrial vehicle known as the Chaplygin sleigh. Using our novel technique we determined an analogous Chaplygin sleigh model that accurately represents the steady-state dynamics of our swimming robot. We additionally used the subsequent model for heading and velocity control in panel method simulations. This work was inspired by the similarities in constraints and velocity space limit cycles of the swimmer and the Chaplygin sleigh, which makes this technique universal enough to be extended to other bio-inspired robots

Advanced Techniques for Design and Manufacturing in Marine Engineering

Modern engineering design processes are driven by the extensive use of numerical simulations; naval architecture and ocean engineering are no exception. Computational power has been improved over the last few decades; therefore, the integration of different tools such as CAD, FEM, CFD, and CAM has enabled complex modeling and manufacturing problems to be solved in a more feasible way. Classical naval design methodology can take advantage of this integration, giving rise to more robust designs in terms of shape, structural and hydrodynamic performances, and the manufacturing process.This Special Issue invites researchers and engineers from both academia and the industry to publish the latest progress in design and manufacturing techniques in marine engineering and to debate the current issues and future perspectives in this research area. Suitable topics for this issue include, but are not limited to, the following:CAD-based approaches for designing the hull and appendages of sailing and engine-powered boats and comparisons with traditional techniques;Finite element method applications to predict the structural performance of the whole boat or of a portion of it, with particular attention to the modeling of the material used;Embedded measurement systems for structural health monitoring;Determination of hydrodynamic efficiency using experimental, numerical, or semi-empiric methods for displacement and planning hulls;Topology optimization techniques to overcome traditional scantling criteria based on international standards;Applications of additive manufacturing to derive innovative shapes for internal reinforcements or sandwich hull structures

EFFECT OF HYDROPLANE PROFILE ON HYDRODYNAMIC COEFFICIENTS OF AN AUTONOMOUS UNDERWATER VEHICLE

AUVs are the most suitable tool for conduction survey concerning with global environmental problems. AUVs maneuverability should be carefully checked so as to improve energy efficiency of the vehicle and avoid unexpected motion. Oblique towing test (OTT) is simulated virtually in a computational fluid dynamic (CFD) environment to obtain hydrodynamic damping coefficients of a full-scale autonomous underwater vehicle. Simulations are performed for bare hull and hull equipped with four different hydroplanes. The hydrodynamic forces and moment are obtained to calculate hydrodynamic coefficients. Nonlinear damping coefficients are also obtained by using suitable curve fitting. Experiments of resistance and OTT are carried out in specific condition, for validation purpose. Following the extracting numerical results a mathematical model is developed to calculate hydrodynamic force for different sail type in order to predict autonomous underwater vehicle (AUV) maneuverability. The results shows good agreement between theory and experiment

Modeling of an Autonomous Underwater Vehicle

Autonomous Underwater Vehicles (AUV) have multiple applications for military, commercial and research purposes. The main advantage of this technology is its independence. Since these vehicles operate autonomously, the need for a dedicated support vessel and human supervision is dismissed. However, the autonomous nature of AUVs also presents a complex challenge for the guidance, navigation and control system(s). The design of motion controllers for AUVs is model-based i.e. a dynamic model is used for the design of the control system. The dynamic model can also be used for simulation and performance analysis. In this context, the purpose of this thesis is to provide a dynamic model for a double-body research AUV being developed at CEiiA. This model is to be subsequently used for the design of the control system. Since the purpose is the design of the control system and, in the scope of providing multiple design approaches, the appropriate lateral and longitudinal subsystems are devised. These subsystems are subsequently validated by comparing simulation results for the subsystems with simulation results for the complete model. The AUV is modeled using Fossen’s dynamic model. The model is divided into kinematics and kinetics. Kinematics addresses the geometrical aspects of motion. For this purpose, both Euler angles and quaternions are used. Kinetics focuses on the relationship between motion and force. This model identifies four distinct forces that act on the underwater vehicle: rigid-body forces; hydrostatic forces; hydrosynamic damping (or drag) and added-mass. The estimation of model parameters is performed using analytical and computational methods. A detailed 3D CAD model, developed by CEiiA, proved helpful for estimating mass and inertia parameters as well as hydrostatic forces. Hydrodynamic damping estimation was performed by adapting CFD analysis, also developed by CEiiA, to satisfy model parameters. Added mass parameters were estimated using proven analytical methods. Due to limitations inherent to current modeling methods, simplifications were unavoidable. These, when analyzed considering the requirements of typical control systems, did not pose an impediment to the use of the dynamic model for this purpose. Regarding the dynamics of this AUV, the hydrodynamic analysis suggests that this AUV is unstable in the presence of angles of attack and side-slip. However the AUV’s motors should be capable of controlling such instabilities.Os veículos subaquáticos autónomos (Autonomous Underwater Vehicles – AUV’s) têm múltiplas aplicações militares, comerciais e para investigação científica. A grande vantagem destes veículos advém da sua independência, sendo que operam sem a necessidade de supervisão humana. No entanto esta capacidade implica que os sistemas de navegação, guia e controlo sejam completamente responsáveis pelo governo do veículo. O sistema de controlo destes veículos é tipicamente projetado tendo como base um modelo dinâmico do mesmo. Este modelo pode ser também usado para simulação e análise de desempenho. O propósito deste trabalho é desenvolver um modelo dinâmico para um AUV de investigação de duplo-corpo, a ser desenvolvido no CEiiA. Dado que o objetivo principal do modelo é projetar controladores e, de modo a fornecer várias abordagens para o efeito, os respetivos modelos (subsistemas) lateral e longitudinal são deduzidos. Estes modelos são posteriormente validados através da comparação de resultados de simulação para os subsistemas com os resultados de simulação para o modelo completo. A modelação deste veículo é efetuada usando o modelo dinâmico de Fossen. Este modelo pode ser dividido em cinemática e cinética. Cinemática aborda os aspetos geométricos do movimento. As equações de cinemática são fornecidas tanto para ângulos de Euler como para quaterniões. As equações de cinética centram-se na relação entre movimento e força. O modelo de Fossen identifica quatro forças distintas que influenciam a dinâmica dos veículos subaquáticos: forças de corpo rígido; forças hidrostáticas; amortecimento (atrito) hidrodinâmico e added mass. Estas forças são modeladas através de métodos analíticos e computacionais. O modelo CAD do veículo, desenvolvido pelo CEiiA, foi usado para estimar os parâmetros de massa e inércia, bem como forças hidrostáticas. O amortecimento hidrodinâmico foi estimado através da adaptação de análises CFD, também efetuadas pelo CEiiA, para satisfazer os parâmetros do modelo. Os parâmetros added mass foram estimados usando métodos analíticos comprovados. Devido a limitações inerentes aos métodos de modelação atuais, simplificações foram inevitáveis. As mesmas, quando analisadas tendo em conta os requisitos de sistemas de controlo típicos não provaram ser impeditivas da aplicação deste modelo para o desenvolvimento dos mesmos. No que diz respeito à dinâmica deste AUV, a análise hidrodinâmica sugere que este AUV é instável quando na presença de ângulos de ataque e derrapagem. No entanto os motores do AUV deverão ser capazes de corrigir tais instabilidades