Edin Omerdic

Adaptive fuzzy ship autopilot for track-keeping

An adaptive fuzzy gain autopilot for ship track-keeping is developed. This autopilot is composed of Sugeno fuzzy type autopilot in an ordinary feedback loop and adjustable scaling factors mechanism in an additional feedback loop. The adjustment mechanism represents a fuzzy controller that changes scaling factors of the base fuzzy autopilot. The control system for the track-keeping is completely described. For the track-keeping problem, the maneuver of way-point turning and ship guiding through a complex path (trajectory) are presented. The influence of sea current and wave disturbances on track-keeping performance was also considered. Simulation results obtained by the Sugeno fuzzy type autopilot are first presented. Then, those results are compared with ones obtained by an adaptive fuzzy autopilot.

Improved Fuzzy Autopilot for Track-Keeping

Abstract Improved 2-input fuzzy autopilot for ship course control and 3-input fuzzy autopilot for track-keeping are proposed. Nonlinear model of a ship and a steering subsystem is used. The 3-input fuzzy autopilot uses heading signal, yaw rate signal and lateral offset from the nominal track to produce a command rudder angle. Input variable fuzzyfication, fuzzy associative memory rules and output set defuzzyfication are described. Obtaining of FAM rules for 3-input fuzzy is described. Dynamical behavior of 2 and 3-input fuzzy autopilot is compared. The influence of wave disturbance, sea current and external disturbance from a passing ship on track-keeping performance was analyzed.

Precision navigation sensors facilitate full auto pilot control of Smart ROV for ocean energy applications

A Smart Remotely Operated Vehicle, ROV Latis designed as a prototype test bed for operation such as the challenging role of ocean engineering support in wave and tidal energy development is presented in this paper. With state of the art navigation sensors/instruments the vehicle can achieve precision navigation and positioning sub sea and this capability has been utilised within automatic control functionality and autopilot control systems developed and trialed on ROV Latis and not available in commercial ocean ROV technology. This paper describes the vehicles many novel design features: sensor and control systems, autopilot systems, station keeping, fully automatic way point navigation, rapid auto tuning when ROV configuration or payload is changed, fully automatic fault tolerant thruster control with redundancy. The paper also introduces the transparent ocean immersive augmented reality pilot control environment.

Implementation and application of a real-time sidescan sonar simulator

This paper describes the functional theory and design of a modular simulator to generate, in real-time, physically representative spatiotemporal sidescan sonar echo data. The seafloor topography is generated using fractal theory and the resulting terrain is tesselated into triangular facets. Propagation of the acoustic fan beam is determined by a ray theory solution of the governing wave equation while the contribution of each facet to the recorded intensity at the sonar transducer is resolved by applying Jacksons seafloor scattering model. The computational bottleneck inherent in the discovery of illuminated facets at each ping is significantly reduced by the implementation of an optimised mesh refinement scheme intended for interactive rendering of large-scale complex surfaces described by polygonal meshes. The resulting performance increases enabled the successful integration of the sonar simulator with an existing AUV simulator. Synthetic images and the performance measures of the sidescan simulator image generation are presented.

Extension of feasible region of control allocation for open-frame underwater vehicles

Abstract Standard pseudoinverse method for solution of the control allocation problem for overactuated open-frame underwater vehicles is able to find a feasible solution only on a subset of the attainable command set. This subset is called the feasible region for pseudoinverse. Some other methods, like direct control allocation or fixed-point iteration method, are able to find the feasible solution on the entire attainable command set. A novel, hybrid approach for control allocation, proposed in this paper, is based on integration of the pseudoinverse and the fixed-point iteration method. It is implemented as a two-step process. The pseudoinverse solution is found in the first step. Then the feasibility of the solution is examined analysing its individual components. If violation of actuator constraint(s) is detected, the fixed-point iteration method is activated in the second step. In this way, the hybrid approach is able to allocate the exact solution, optimal in the l 2 sense, inside the entire attainable command set. This solution minimises a control energy cost function, the most suitable criteria for underwater applications.

Fault Detection and Accommodation for ROVs

Abstract A new approach for fault detection and accommodation for remotely operated underwater vehicles is proposed in this paper. The proposed Fault Detection and Accommodation System (FDAS) consists of two subsystems: Fault Detection Subsystem (FDS) and Fault Accommodation Subsystem (FAS), The FDS uses fault detector units (FDU), associated with each thruster, to monitor their healthy state. Robust and reliable fault detection units are based on integration of self-organising maps and fuzzy logic clustering methods. These units are able to detect internal and external faulty states of a thruster. The FAS uses information provided by the FDS to accommodate faults and perform an appropriate reconfiguration, A control energy cost function is used as the optimisation criteria. In fault-free and faulty cases the FAS finds the optimal solution, which minimise this criteria. The proposed FDS is evaluated with data obtained during test trials.

Design of an advanced AUV for deployment close to the seabed and other hazards

High-resolution (acoustic & video) seabed survey requires deployment of sensors on platforms close to the seabed. The unstructured, harsh and hazardous nature of the ocean environment and close proximity to the seabed and other hazards produces serious problems for autonomous underwater vehicle (AUV) during the mission. The Mobile & Marine Robotics Research Group at the University of Limerick is developing a highly manoeuvrable AUV/ROV platform to address the challenges of high-resolution seabed survey in both shallow and deep water. The overall system integrates state-of-the-art survey equipment, a multi-thruster open-frame AUV Tethra and an advanced control system. This paper gives a short overview of the overall system including simulation results.

A fuzzy track-keeping autopilot for ship steering

In this paper a non-linear fuzzy autopilot for ship track-keeping is presented. The proposed autopilot has four inputs (actual and desired heading, rate of change of heading and offset from the desired path) and one output (command rudder angle). The track-keeping problem is decomposed into two subtasks: (i) follow the desired heading, and (ii) bring the ship onto the desired path and keep tracking. Internally, the autopilot consists of two autopilots that fulfil these tasks simultaneously. The proposed control scheme has been verified using a non-linear model of a Mariner-class vessel and steering mechanism under the influence of wave and current disturbances. Results presented show how such a control strategy enables improved tracking performance.

A Flexible Multi-Mode of Operation Survey Platform for Surface and Underwater Operations

Abstract This paper describes a novel vehicle designed for operation flexibility in high-resolution near seabed survey from shallow inshore waters out to the continental shelf edge. The vehicle can be operated in surface tow or as a thrusted pontoon. With buoyancy module release the vehicle becomes neutrally buoyant and is operated as a survey class remotely operated vehicle (ROV) depth rated to 1,000m. Special features of the system include: deployment interoperability for small inshore boats and larger research vessel; fault tolerant thruster control; novel high frequency short range sonar; onboard computer control enabling real-time disturbance reaction; topside augmented reality system support etc.

Assistive tools for system integration, deployment, monitoring, and maintenance of ocean energy devices

This paper describes a set of assistive tools and technologies for system integration, deployment, monitoring, and maintenance of ocean energy devices. The flexible design of these tools enables their use as separate standalone modules, as well as their integration into a unique integrated system. A major component of the system is a smart remotely operated vehicle ROVLATIS — a novel, multi-mode of operation marine robotics vehicle designed for flexibility in near seabed operations from shallow inshore waters out to the continental shelf edge. Ocean energy technologies play an important part in meeting the Irish governments energy strategy, which targets 33 per cent of Irish electricity to be generated from renewable sources by 2020. The assistive tools, proposed in this paper, will help developers of ocean energy devices in meeting this target during different stages of design, deployment, and operation.