The JASON remotely operated vehicle system

The JASON remotely operated vehicle (ROV) system has been under development for the last decade. After a number of engineering test cruises, including the discovery of the R.M.S. Titanic and the German Battleship Bismarck, this ROV system is now being implemented in oceanographic investigations. This paper explains its development history and its unique ability to carry out a broad range of scientific research.Funding was provided by the Office of Naval Research under Contract No. NOOOI4-90-J-1912

DESIGN CONTROL OF SURFACE MARINE VEHICLE USING DISTURBANCE COMPENSATING MODEL PREDICTIVE CONTROL (DC-MPC)

This research studied ship motion control by considering four degrees of freedom (DoF): yaw, roll, sway, and surge in which comprehensive mathematical modeling forming a nonlinear differential equation. Furthermore, this research also investigated solutions for fundamental yet challenging steering problems of ship maneuvering using advanced control method: Disturbance Compensating Model Predictive Control (DC-MPC) method, which based on Model Predictive Control (MPC). The DC-MPC allows optimizing a compensated control then consider sea waves as the environmental disturbances. Those sea waves influence the control and also becomes one of the constraints for the system. The simulation compared the varying condition of Horizon Prediction (Np) and another method showing that the DC-MPC can manage well the given disturbances while maneuvering in certain Horizon Prediction. The results revealed that the ship is stable and follows the desired trajector

THE AUTOMATIC CONTROL OF LARGE SHIPS IN CONFINED WATERS

The design and evaluation of a control system, which can be utilised for the automatic guidance of large ships in confined or restricted waters, is investigated. The vessel is assumed to be a multivariable system and it is demonstrated that a non-linear, time-varying mathematical model most accurately describes the motion of the hull, particularly in tight manoeuvres. A discrete optimal controller has been designed to control simultaneously track, heading and forward velocity. The system is most effective whilst operating under a dual-mode policy. It is shown that feedback matrix adaption is necessary to deal with changes in forward velocity and a form of gain scheduling is proposed. Active disturbance control is employed to counteract effects of wind and tide. An inertial navigation system, together with an optimal controller and filter, is installed on-board a car ferry model. Free-sailing tests show that the performance characteristics of the system are in accordance with theoretical predictions. The feasibility of implementation on a full-size vessel is considered.University College, Londo

A DIGITAL FILTER/ESTIMATOR FOR THE CONTROL OF LARGE SHIPS IN CONFINED WATERS

Aeronautical and marine casualty statistics indicate that the human being, when under stress or at times of peak load, can be a poor co-ordinator of the information available to him, particularly when that information is from a number of different source:, as is often the case in modern ships. Integration and co-ordination of information and its useful application in a closed loop feedback system can reduce the probability of accident as has already been demonstrated in the case of automatic landing systems for aircraft. This thesis describes the development of a digital filter/estimator for use in conjunction with an optimal controller in the automatic guidance of large ships in the approaches to a port. A non-linear mathematical model of a ship is developed and validated by comparison with data from an actual ship. The model is then used in digital computer simulations of the passage of a twin screw car ferry into the Port of Plymouth. The simulations show that the control and guidance system is capable of safely navigating the vessel along the predetermined track through noisy measurements of position, course and speed, A reduced non-linear digital simulation model is then used in the design of a minimum variance filter suitable for installation in a physical model of the car ferry. Tests with this physical model confirm the earlier full scale digital computer simulations, showing that a minimum variance filter is capable of giving very good estimates of the measured states, even though the measurement subsystems are unable to give accurate information because of noise. In the event of a malfunction of one or more of these measurement systems it is shown that the filter continues to give good estimates of all the states

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

AN ADAPTABLE MATHEMATICAL MODEL FOR INTEGRATED NAVIGATION SYSTEMS

The project has been directed towards improving the accuracy and safety of marine navigation and ship handling, whilst contributing to reduced manning and improved fuel costs. Thus, the aim of the work was to investigate, design and develop an adaptable mathematical model that could be used in an integrated navigation system (INS) and an automatic collision avoidance system (ACAS) for use in marine vehicles. A general overview of automatic navigation is undertaken and consideration is given to the use of microprocessors on the bridge. Many of these systems now require the use of mathematical models to predict the vessels' manoeuvring characteristics: The different types and forms of models have been investigated and the derivation of their hydrodynamic coefficients is discussed in detail. The model required for an ACAS should be both accurate and adaptable, hence, extensive simulations were undertaken to evaluate the suitability of each model type. The modular model was found to have the most adaptable structure. All the modular components of this model were considered in detail to improve its adaptability, the number of non-linear terms in the hull module being reduced. A novel application, using the circulation theory to model the propeller forces and moments, allows the model to be more flexible compared to using traditional B-series four-quadrant propeller design charts. A new formula has been derived for predicting the sway and yaw components due to the propeller paddle wheel effect which gives a good degree of accuracy when comparing simulated and actual ship data, resulting in a mean positional error of less than 7%. As a consequence of this work, it is now possible for an ACAS to incorporate a ship mathematical model which produces realistic manoeuvring characteristics. Thus, the study will help to contribute to safety at sea.Kelvin Hughes Lt

A decision making aid for evaluating total ship system effectiveness.

The aim of this study was to contribute to the knowledge of Total Systems theory and methodologies, by developing an aid to decision making on the effectiveness of complex man-machine organisations. Sponsored by the Ministry of Defence (Navy) as a collaborative research project, the study was to be based on Royal Navy ships and also linked with certain MOD(N) projects working on related effectiveness problems. Initial pre-feasibility, then feasibility studies established a simple model of Effectiveness as the combination of Availability, Performance and Human Factors, which was followed by a more thorough examination of the Availability Function. The development of an Information System designed for the collection and analysis of reliability and maintainability data was central to this phase of the research. This culminates in a comprehensive description of the Phase I hardware, software requirements and information distribution network to be installed and operating commencing in 1983. The Human Factors research was linked to two additional Ministry of Defence (Navy) projects who made available the Human Factors data. This data, collected from five ships of the Type 42 Guided Weapons Destroyer Class, was concerned with the Operations Room organization. Using this data base, a subjective analysis resulted in key indicators being produced which were used with a rating scale technique to develop profiles. Following a systemic overview three interactive indicators - Variable Disjunction of Information, Knowledge and Information Processing were used as the basis of an Information Transfer Function conceptual model. This model, when combined with Systems Interaction Diagrams enabled a Methodology to be designed which was evaluated against a three man-function element within a total Operations Room complement of 33 men. On the premise that the Human Factors function could be transformed to metric data the framework of a Human Factors model was developed, based on an existing Total Ship Availability Model with the potential that these could be combined to produce an Effectiveness model. The information System, the proposed Methodology and the framework of a Ship Effectiveness Model were then incrementally and theoretically linked in order to develop the organisation of a decision making aid for evaluating the effectiveness of complex man-machine systens. The research was not intended to test or validate the decision making aid, as aspects of this will need to be approved by Ministry of Defence (Navy) authorities before proceeding to the next phase of implementing the results so far produced