Modeling of an Autonomous Underwater Vehicle

• Autor(a) principal: Bentes, Cristiano Alves
• Data de Publicação: 2016
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10400.6/6359
• topic: Dinâmica; Duplo-Corpo; Estimação; Lateral; Longitudinal; Modelo de Fossen; Simulação; Veículo Subaquático Autónomo; Domínio/Área Científica::Engenharia e Tecnologia::Outras Engenharias e Tecnologias

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.