194 research outputs found
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
Modular Dynamic Modeling and Development of Micro Autonomous Underwater Vehicle: Lancelet
Ph.DDOCTOR OF PHILOSOPH
Heading control of an underwater vehicle
In this thesis an overview of Autonomous Underwater Vehicles (AUV) is presented which covers the state of art in AUV technology, different components such as sensors and actuators of AUV and the applications of AUVs. This thesis describes the development and verification of six degree of freedom, non-linear simulation model. In this model, external forces and moments are defined in terms of vehicle coefficients. A nonlinear model of AUV is obtained through kinematics and dynamics equations which are linearized about an operating point to get a linearized horizontal plane model. The objective of the AUV control here is heading control i.e. to generate appropriate rudder angle position and thrust so that the desired heading is achieved.
For the above heading control we develop a controller that consists of two loops, one is controlled by a PD controller and the other loop by a P control action. The first and second order Nomoto model of the vehicle is formulated and studied for simpler qualitative analysis of complicated ship model.
Simulation studies were undertaken also for yaw control of a single AUV. The above controller is designed for effective tracking of desired trajectory of the AUV in horizontal plane. All the simulations were performed using both MATLAB and SIMULINK.
The results obtained for heading and yaw control of the AUV studied are presented and discussed in this thesis
Design of a Mobile Underwater Charging System
Autonomous Underwater Vehicles (AUVs) are extremely capable vehicles for numerous ocean related missions. AUVs are energy limited, resulting in short mission endurance on the scale of hours to days. Underwater Gliders (UGs) are able to operate on the order of months to years by using nontraditional propulsion methods. UGs, however, are unable to perform missions requiring high speed or direct forward motion due to the nature of their buoyancy driven motion. This work reviews the current state of the art in recharging AUVs and offers an underwater recharging network concept at a significantly reduced cost to traditional methods. The solution includes the design of a UG capable of serving as charge carrying agent that couples with and charges AUVs autonomously. The vehicle design is built on the work done previously at the Nonlinear and Autonomous Systems Lab on the development of ROUGHIE (Research Oriented Underwater Glider for Hands-on Investigative Engineering). The ROUGHIE2 design is a rethinking of the original ROUGHIE capabilities to serve as a mobile charger by increasing depth rating, endurance, and payload capacity. The recharging concept presented will be easy to adapt to many different AUVs and UGs making this technology universal to small AUVs
ISME trends: Autonomous surface and underwater vehicles for geoseismic survey
The paper presents the recent and ongoing activities of the Italian Center named ISME on the use of Autonomous Surface Crafts (ASCs) and Autonomous Underwater Vehicles (AUVs) for geoseismic survey. In particular, the paper will focus on the technologies and the algorithms developed in the framework of the H2020 European Project WiMUST
Wave Excited Mass-Spring-Damper System for a Self-recharging Autonomous Underwater Vehicle
Autonomous underwater vehicles\u27 (AUVs) endurance is constrained by the lifetime of their batteries and the distance that tether wires can traverse. Solving the endurance problem of AUV using the enormous potential of ocean wave energy is the motivation behind this thesis. The objective of this research is to model a mass-spring-damper system to emulate the permanent magnet linear generator (PMLG) of a self-recharging AUV and identify its energy absorption capability through numerical simulation and experimental testing. The research activities started with modeling and fabricating a 1:5 scale model. The scaling was done by comparing the most common AUV size of 1.5m. The preliminary dry testing result confirmed the inadequate damping of the devised prototype. After detailed wave tank testing with a fixed PTO, the vertical orientation of the converter was chosen for the second stage research. A modified 1:3 large-scale prototype was developed in the next phase. The model showed strong oscillating mass motion in the dry test rig. Comparison with numerical simulation showed that for lower wave frequency, the damping coefficient of the model matches well with the experimental result. But the prototype damping behavior is much more complex for a higher wave frequency. The tank testing confirmed that the prototype pitch amplitude in the wave needs to be enhanced for higher energy absorption
Simulation Study on a New Hybrid Autonomous Underwater Vehicle with Elevators
This study aims to design a new hybrid twin autonomous underwater vehicle (HTAUV) consisting of dual cylinder hulls and analyze its pitching motion. The kinematic model for the HTAUV is established, followed by the execution of hydrodynamic simulation CFD of the HTAUV using Ansys Fluent. These simulations are conducted to obtain the hydrodynamic force equation of the HTAUV, which relates to the deflection angle of the elevator. Through the motion simulation of the HTAUV, under the same net buoyancy condition, notable differences emerge when the elevator is deflected. Specifically, parameters such as gliding speed, gliding angle, and pitch angle of the HTAUV are larger when the elevator is deflected, as compared to cases where no deflection is applied
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