Mauro Candeloro

Relative Velocity Control and Integral LOS for Path Following of Underactuated Surface Vessels

Abstract A control technique for path following applications of underactuated surface vessels in the presence of constant irrotational ocean currents is revisited and improved. It is shown that in steady state the presented guidance law paired with measurements of the absolute speed and the relative speed of the vessel yields to an estimation of the ocean current. The control strategy is based on a modified two-dimensional Line-of-Sight (LOS) guidance law with integral action and two feedback controllers. The integral effect in the LOS guidance is introduced to counteract slowly varying disturbances like wave drift, wind load and current. In particular the effect of sea current is studied and the chosen integration law is defined to reduce the risk of wind-up effects. Moreover, due to the irrotational nature of the ocean current, only relative velocities are used in the feedback loop. Compared to the approach based on absolute velocities, redefining the vessel model with relative velocities significantly simplifies the control system. Closed loop uniform local exponential stability is achieved for path following of straight-line paths. Finally, simulations are presented to support the theoretical results.

Relative velocity control and integral line of sight for path following of autonomous surface vessels: Merging intuition with theory

The integral line-of-sight guidance law for path following applications of autonomous surface vessels is presented in a unified manner, merging intuitive and theoretical aspects of this valuable control technique. Straight line path following scenarios of underactuated surface vessels in the presence of unknown constant irrotational ocean currents are considered. The integral line-of-sight guidance and two feedback controllers are combined into a cascaded configuration where the integral effect in the line-of-sight guidance is introduced to counteract the disturbance. The chosen integration law is defined to reduce the risk of wind-up effects, and it is shown that the integral action in the line-of-sight guidance law performs a vectorial sum between the vessel relative velocity and the unknown current velocity to compensate for the drift. Moreover, only relative velocities are used in the feedback loop since the ocean current is assumed constant and irrotational. Redefining the vessel model with relative velocities significantly simplifies the control system compared to the approach based on absolute velocities. Closed-loop uniform local exponential stability is achieved for path following of straight line paths. Furthermore, in steady state, the presented guidance law paired with measurements of the absolute speed and the relative speed of the vessel yields to an estimation of the ocean current. Simulations are presented to support the theoretical results.

Glowing in the dark: discriminating patterns of bioluminescence from different taxa during the Arctic polar night

Research since 2009 has shown that despite almost total darkness during the Arctic polar night, there is much more biological activity than previously assumed, both at the sea surface, water column and sea floor. Here, we describe in situ monitoring of the bioluminescent fraction of the zooplankton community (dinoflagellates, copepods, krill and ctenophores) as a function of time and space. In order to examine the relative contribution of each selected taxon and any diurnal patterns in the relative signals, a time series platform capable of detecting in situ bioluminescent flashes was established in Kongsfjord, Svalbard, during the polar night in January 2013. Combined with laboratory-controlled measurements of animals collected next to the time series platform, we present both taxon-specific and community characteristics of the bioluminescence signal from a location at 79°N and from the middle of the polar night. Based on this 51-h time series, we conclude that the bioluminescent fraction of the zooplankton does not maintain a diurnal signal. Rather, the frequency of bioluminescence flashes from the entire bioluminescent community remained steady throughout the sampling period. Furthermore, we conclude that bioluminescence flash kinetic characteristics have a strong potential for in situ taxa recognition of zooplankton.

HMD as a new tool for telepresence in underwater operations and closed-loop control of ROVs

With the recent development of computer graphics and video-gaming, 360° cameras and related technologies, Head Mounted Displays (HMDs) are becoming a popular tool to improve the users experience and efficiency. This trend is also connected to the computer technology improvements of the latest years and its price decrease: HMDs are now more performing and, at the same time, commercially accessible to the masses. In this paper a HMD is used to improve the telepresence experience, to increase the situational awareness during underwater operations, and to actively control a Remotely Operated Vehicle (ROV). Although HMDs are already used to actively control the point of view of the operator by moving the camera system of vehicles, in this paper they are used to control the vehicle itself, providing a hand-free Human-Machine Interface (HMI). In this way the operator has the possibility of controlling other devices (e.g. a manipulator attached to the ROV) while moving the ROV, highly increasing the efficiency of the underwater operations. Three control methods inspired by previous work developed for the classical joystick interface are presented, full-scale experiments and conclusions on the usability of the proposed solution for real off-shore operations are discussed.

Continuous Curvature Path Planning using Voronoi diagrams and Fermat's spirals

Abstract This paper presents a two-dimensional curvature-continuous path planning algorithm based on Voronoi diagrams and Fermats spiral segments. The map and the obstacles position are assumed to be known a-priori and static. Despite the disposition of the obstacles, the Voronoi diagram always presents at least one collision-free path, maximally distant from all the obstacles. If more than one flyable path is available, the shortest one is selected. The result is further refined to obtain a more practical path that is piecewise linear with discontinuous curvature and velocity. Fermats spirals are used to smooth the path and provide curvature-continuity. A maximum threshold for the curvature is set so that the result of the algorithm respects kinematics and dynamics constraints of the vehicle. Moreover a minimum clearance from the obstacles can be chosen to respect additional safety constraints. The final result of the algorithm is a simple and intuitive path composed only by straight lines and spiral segments.

Observers for Dynamic Positioning of ROVs with Experimental Results

Abstract This paper proposes a set of model-based observers included in the DP (Dynamic Positioning) system of the ROV Minerva operated by NTNU. In particular, the observers and the other main components of the DP control system are described. A linear Kalman Filter (LKF), an Extended Kalman Filter (EKF), an adaptive Kalman Filter and a passive nonlinear observer based on the ROV Minerva mathematical models with varying fidelity are proposed. The main aim is to compare different possibilities for the implementation of the observer in a DP control system for ROVs analyzing advantages and drawbacks. Finally, experimental results obtained during DP and tracking operations performed in the Trondheim Fjord are presented.

Analysis of a multi-objective observer for UUVs

Abstract UUVs (Unmanned Underwater Vehicles) were introduced in the past to perform various operations in the ocean environment such as marine biology mapping and monitoring, archaeology and oil and gas inspections and interventions. In this paper the operatively range of the UUVs is explored and the possibility of using it in the wave zone is analysed. Then a multi-objective control system that is able to operate into different model regimes could be designed. This aspect moves the main interest to the observer module, that should be able to produce good estimations of the system state regardless from the environment conditions or the mission characteristics. This paper addressed a switching observer for a multi-objective controller where simulation results based on a medium-sized ROV model are reported and discussed.

A 3D dynamic Voronoi diagram-based path-planning system for UUVs

This paper proposes a rapid path-planning and replanning system for Unmanned Underwater Vehicles (UUVs) that navigate in environments where subsea structures and other vehicles may be present. The proposed method is based on the Voronoi diagram, which is used to generate an initial set of connected waypoints (a roadmap) in the three-dimensional (3D) space, ensuring a certain clearance to avoid collisions with obstacles or grounding (e.g. collision with the ground). A 3D continuous path, composed by straight segments and circumference arcs, connects the aforementioned waypoints. If the vehicle encounters any moving or static obstacle and a collision risk is detected, the path is replanned online. In this context, an evaluation of the risk must be performed, and a list of traffic rules inspired by the International Regulations for Preventing Collisions at Sea (COLREGs, which are adopted for surface vessels), and by the Traffic and Collision Avoidance System (TCAS, which is adopted for aerial vehicles), is proposed for underwater vehicles. Those rules define the replanning procedure, so that an effective and safe collision avoidance maneuver can be performed whenever necessary. Simulations are performed on an subsea factory scenario, and results are presented to show the effectiveness of the proposed method.