System Identification and the Modeling of Sailing Yachts

This research represents an exploration of sailing yacht dynamics with full-scale sailing motion data, physics-based models, and system identification techniques. The goal is to provide a method of obtaining and validating suitable physics-based dynamics models for use in control system design on autonomous sailing platforms, which have the capacity to serve as mobile, long range, high endurance autonomous ocean sensing platforms. The primary contributions of this study to the state-of-the-art are the formulation of a five degree-of-freedom (DOF) linear multi-input multi-output (MIMO) state space model of sailing yacht dynamics, the process for identification of this model from full-scale data, a description of the maneuvers performed during on-water tests, and an analysis method to validate estimated models. The techniques and results described herein can be directly applied to and tested on existing autonomous sailing platforms. A full-scale experiment on a 23ft monohull sailing yacht is developed to collect motion data for physics-based model identification. Measurements include 3 axes of accelerations, velocities, angular rates, and attitude angles in addition to apparent wind speed and direction. The sailing yacht herein is treated as a dynamic system with two control inputs, the rudder angle, dR, and the mainsail angle, dB, which are also measured. Over 20 hours of full scale sailing motion data is collected, representing three sail configurations corresponding to a range of wind speeds: the Full Main and Genoa (abbrev. Genoa) for lower wind speeds, the Full Main and Jib (abbrev. Jib) for mid-range wind speeds, and the Reefed Main and Jib (abbrev. Reef) for the highest wind speeds. The data also covers true wind angles from upwind through a beam reach. A physics-based non-linear model to describe sailing yacht motion is outlined, including descriptions of methods to model the aerodynamics and hydrodynamics of a sailing yacht in surge, sway, roll, and yaw. Existing aerodynamic models for sailing yachts are unsuitable for control system design as they do not include a physical description of the sails' dynamic effect on the system. A new aerodynamic model is developed and validated using the full-scale sailing data which includes sail deflection as a control input to the system. The Maximum Likelihood Estimation (MLE) algorithm is used with non-linear simulation data to successfully estimate a set of hydrodynamic derivatives for a sailing yacht. As there exists a large quantify of control algorithms which may be applied to systems described by a linear model, the non-linear model is simplified to a 5DOF MIMO state space model with a state vector including surge velocity, sway velocity, roll rate, yaw rate, and roll angle: , and a control vector: . Over 100 singlet and doublet maneuvers specifically designed to identify linear model dynamic responses are included in the full-scale data. The one-shot least squares (OSLS) technique offered a simple and fast means to estimate many linear models from this large sub-set of the full-scale data. As no sailing yacht linear dynamic model exists, especially for the test yacht, the only way to evaluate the fidelity of estimated models is to evaluate their predictive capability. This is accomplished through two separate criteria, Theil inequality coefficient UT and R2 > 0.75 0.75, which are shown to provide sufficient quality models to enable control system design. Each linear model is estimated from only 3 maneuvers, one rudder singlet, one rudder doublet, and one sail singlet, and validated with a similar set of independently collected maneuvers. In total, 102 linear models are estimated in the Jib configuration, 17 linear models in the Genoa configuration, and 1 linear model in the Reef configuration. The dynamic modes of the models estimated from the full-scale data are investigated using the eigenvectors and eigenvalues of the linear state space model A matrix. First, the estimated models are characterized by the number of first and second order modes observed for each given model, and are referred to herein as Type A or Type B models. Type A models exhibit two second order modes, and one first order mode, whereas the Type B models exhibit one second order mode and three first order modes. The modes are then separated by natural frequency. A subset of models from the Jib configuration which exhibit an ,R2 > 0.88 0.88 are analyzed via eigenvector modal analysis. It is shown that all sailing yacht models will contain a second order mode (referred to herein as Mode 1A.S or 4B.S) which is dependent upon trimmed roll angle. For the test yacht it is concluded that for this mode when the trimmed roll angle is , roll rate and roll angle are the dominant motion variables, and for surge velocity and yaw rate dominate. This second order mode is dynamically stable for . It transitions from stability in the higher values of to instability in the region defined by . These conclusions align with other work which has also found roll angle to be a driving factor in the dynamic behavior of a tall-ship (Johnson, Miles, Lasher, & Womack, 2009). It is also shown that all linear models also contain a first order mode, (referred to herein as Mode 3A.F or 1B.F), which lies very close to the origin of the complex plane indicating a long time constant. Measured models have indicated this mode can be stable or unstable. The eigenvector analysis reveals that the mode is stable if the surge contribution is 20%. The small set of maneuvers necessary for model identification, quick OSLS estimation method, and detailed modal analysis of estimated models outlined in this work are immediately applicable to existing autonomous mono-hull sailing yachts, and could readily be adapted for use with other wind-powered vessel configurations such as wing-sails, catamarans, and tri-marans

Generalized Predictive Control of Ship Coupling Motions Using Active Flume Tanks

This dissertation uses the Generalized Predictive Control (GPC) approach to design a control system for a ship rolling motion coupled with the sway and yaw using an activated flume tank. GPC is a strategy based on system output prediction over finite horizon known as the prediction horizon. GPC controller is designed from the coefficients of the Autoregressive model with exogenous input (ARX) that are computed directly from input and output data. It computes the future control input based on the cost function with weighted input and output. System identification approach is implemented on the system to find the ARX coefficients parameters. A mathematical model of the anti-rolling flume tank and the ship coupling model are derived to be in the state space form. The time domain model of the ship motions has been extended to predict the coupling motions of sway, yaw and roll. Also, the disturbance model is generated as irregular waves. Analyses for the ship rolling and coupling models, with and without the anti-rolling flume tank, are presented. A numerical simulation using the MATLAB program is implemented. The numerical simulation indicates that there are three factors that affect the ship motions: sea state conditions, wave attack angle and ship control system. The simulation result shows that the passive control system using an anti-rolling flume tank is able to reduce the ship rolling angle up to fifty percent. In comparison, simulation result of the actively controlled system using GPC shows that the ship rolling angle can be mitigated up to eighty percents. The GPC approach is tested on the ship model in different weather conditions. The numerical simulation is implemented to evaluate the controller performance and investigate the benefit of the GPC in the ship coupling motions. The numerical results show that the coupling model of roll, sway and yaw can affect each other simultaneously. The roll motion can be affected by the sway force more than yaw moment. The effect and performance of the GPC in controlling the ship roll motion in different wave\u27s disturbances and sea state conditions are discussed

Adaptive Control of Joystick Steering in Recreational Boats

This thesis addresses the challenge of commissioning recreational boats with joystick control when the boat’s physical parameters are not known. The research was conducted by following a model-based, systems engineering approach which leveraged MATLAB simulations and scale-model physical testing. The outcome of the research is a working methodology using L1 Adaptive Control which provides fast adaption in a way that could reduce the cost of commissioning recreational boats with joystick control, improve the robustness of the final design, and potentially expand the accessible market to new boat types

A Mathematical Model To Simulate Small Boat Behaviour

The use of mathematical models and associated computer simulation is a well established technique for predicting the behaviour of large marine vessels. For a variety of reasons, mainly related to effects of scale, existing models are unable to adequately predict the manoeuvring characteristics of smaller vessels. The accuracy with which the performance of a boat under autopilot control can be predicted leaves much to be desired. The thesis provides a mathematical model to simulate small boat behaviour and so can assist with the design and testing of marine autopilots. The boat model is presented in six degrees-of-freedom, which, with suitable wave disturbance terms, allows motions such as broaching to be analysed. Instabilities in the performance of an autopilot arising from such sea induced yaw motions can be assessed with a view to improving the control algorithms and methodology. The traditional "regressional" style models used for large ships are not suitable for a small boat model since there exist numerous small boat types and diverse hull shapes. Instead, a modular approach has been adopted where individual forces and moments are categorised in separate sections of the model. This approach is still in its infancy in the field of marine simulation. The modular concept demands a clearer understanding of the physical hydrodynamic processes involved in the boat system, and the formulation of equations which do not rely solely upon approximations to, or multiple regression of, data from sea trials. Although many hydrodynamic coefficients have been introduced into the model, a multi-variable Taylor series expansion of the states about some equilibrium condition has been avoided, since this would infer an approximation to have been made, and the higher order terms rapidly become abstract in their nature and difficult to relate to the real world. The research rectifies the glaring omission of a small boat mathematical model, the framework of which could be expanded to encompass other marine vehicles. Additional forces and moments can be appended to the model in new modules, or existing modules modified to suit new applications. Much more work, covering a greater range and fidelity, is required in order to provide equations which accurately describe the true physical situation

Modelling and control of a UAV-USV collaboration scheme for fluvial operations

This thesis focuses on a Model Based Design approach to the dynamic modelling and control design of a multi-robot solution based on a collab- oration scheme between a UAV and USV. The purpose of the system is to provide a suitable platform to autonomously perform limnology related surveys. The dynamic models of both platforms are derived from a Newton- Euler formalism and implemented through block oriented modelling us- ing the Simscape Multibody toolset within Simulink. The implementation of both the simulation architecture and the control architecture are de- scribed and explained. This control architecture is based on PID feedback loops that are used for achieving control of the UAV and USV dynamics. Finally, the built simulator is used to asses the performance and relia- bility of the designed controllers and the dynamic modelling approaches selectedIngeniería en Tecnologías Industriale

CONTROL TECHNIQUES APPLIED TO INTEGRATED SHIP MOTION CONTROL

Fins stabilisers are devices which are fitted to the hull of a ship and utilised to ameliorate its rolling motions. They apply a regulated moment about the ship's axis of roll in order to oppose the sea induced disturbances. Recognising their unsurpassed performance, the Royal Navy, since the 1950's, equips all its vessels with fin stabilisers. It can be shown that the rudders, in vessels of appropriate size, also have the potential to be harnessed as roll stabilisers Rudder Roll Stabilisation (RRS) without degrading the ship's course-keeping. Thus creating a more stable platform for the human operators and equipment. The reported success of RRS imparted an impetus to the Royal Navy to initiate this study. The objectives are to ascertain whether RRS is possible without rudder modifications and to establish whether enhanced levels of stabilisation would accrue if the fins and RRS were operated in congress. The advantages in this novel approach being: avoidance of redesign and refit of rudders, three modes of operation (fins alone, RRS alone and combined RRS and fins), reduced fin activity and by implication self-generated noise, and amenability to be retrofitted by simple alteration of any existing ship's autopilot software. The study initially examined the mathematical models of the ship dynamics, defining deficiencies and evaluating sources of uncertainty. It was postulated that the dual purpose of the rudder can be separated into non-interacting frequency channels for controller design purposes. An integrated design methodology is adopted to the roll stabilisation problem. Investigating the capabilities of the rudder servomechanism, a new scheme, the Anti-Saturation Algorithm (ASA) was proposed which can eliminate slew rate saturation. Application of the ASA is generic to any servomechanism. The effects of lateral accelerations of the ship on human operators was examined. This resulted in an unique contribution to the Lateral Force Estimator problem in terms of generating time domain models and defining the limitations of the applicability of a control design strategy. Linear Quadratic Guassian and two types of classical controllers were constructed for the RRS and fins. A novel application of linear robust control theory to the ship roll stabilisation problem resulted in H . controllers whose performance was superior to the other design methods. This required the development of weight functions and the identification and quantification of possible sources of uncertainty. The structured singular value utilised this information to give comparable measures of robustness. The sea trials conducted represent the first experience of the integrated ship roll stabilisation approach. Experimental results are detailed. These afforded an invaluable opportunity to validate the software employed to predict ship motion. The data generated from the sea trials concurs with the simulations data in predicting that enhanced levels of roll stabilisation are possible without any modification to the rudder system. They also confirm that when the RRS is acting in congress with the fin stabilisers the activity of both actuators diminishes

High performance path following for marine vehicles using azimuthing podded propulsion

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006.Includes bibliographical references (p. 101-102).Podded propulsion systems offer greater maneuvering possibilities for marine vehicles than conventional shaft and rudder systems. As the propulsion unit rotates about its vertical axis to a specified azimuth angle, the entire thrust of the propeller contributes to the steering moment without relying on lift generation by a control surface such as a rudder. However, the larger sideforce and moment cause the ship to enter the nonlinear realm sooner than a ruddered vessel. Furthermore if the rudder or azimuthing propulsor is aft of the vessel's center of gravity then the system is non-minimum phase; during a turn the ship center initially moves in the direction opposite the turn. For these reasons it is necessary to design a robust maneuvering control system to set the azimuth angle of the propulsor in an intelligent and stable manner. This thesis focuses on the path following performance of a vessel with podded propulsion. The enhanced maneuvering abilities of such vessels allow the time constant of cross-track error response to be greatly reduced. Additionally these vessels can follow course changes and waypoints more precisely than ruddered vessels.(cont.) A simple path following algorithm was developed to achieve this performance; the algorithm uses simulation-based feedforward terms to anticipate the sliding motion of the vessel during a turn. The stability and performance analysis was performed in three domains: linear theory, a nonlinear simulation, and experiments with a 12-foot autonomous surface vessel. Experiments confirmed that path following performance was vastly improved using the feedforward algorithm for waypoints at which the course change angle was large.by Matthew B. Greytak.S.M

Adaptive Interval Type-2 Fuzzy Logic Control of Marine Vessels

Ph.DDOCTOR OF PHILOSOPH