Keywords: Actuators, thrusters, propulsion systems, and sensors in marine systems, Surface and underwater vehicles, Information systems and methods in marine applications
Abstract: This paper presents an adaptive approximation-based scheme for learning a partially known ship power propulsion plant under various environmental conditions. Considering the effect of water depth on the engine power, a dynamic model is defined comprised of the engine dynamics and the 1-DoF ship manoeuvring dynamics. The modelling challenge is the determination of ship resistance. To meet this challenge analytical modelling of ship resistance is combined with an error-filtering online learning (EFOL) scheme for computing an approximation of the unmodeled part of ship resistance related to wind and air. After simulations under multiple weather conditions, the trained model was demonstrated to efficiently estimate the unmodelled part of the ship resistance for an inland vessel.

Keywords: Adaptive and robust control in marine systems, Intelligence and autonomy in marine systems and operations
Abstract: Underwater Unmanned Vehicles (UUVs) have to constantly compensate for the external disturbing forces acting on their body. Adaptive Control theory is commonly used there to grant the control law some flexibility in its response to process variation. Today, learning-based (LB) adaptive methods are leading the field where model-based control structures are combined with deep model-free learning algorithms. This work proposes experiments and metrics to empirically study the stability of such a controller. We perform this stability analysis on a LB adaptive control system whose adaptive parameters are determined using a Cross-Entropy Deep Learning method.

Keywords: Adaptive and robust control in marine systems, Guidance, navigation and control (GNC) of unmanned marine vehicles (surface and underwater), Maritime robotics (underwater, surface, aerial)
Abstract: A robust design of a trajectory tracker for an unmanned underwater vehicle under the influence of disturbances is addressed in this article. The controller policy is formulated upon an adaptive sliding mode approach, where a manifold of a non-singular terminal sliding mode ensures the tracking errors to converge to a locality close to zero in practical finite-time. Moreover, the adaptation dynamics allow no overestimation of control gains, reducing chattering as well as the control efforts, and maintain robustness against external perturbations with unknown boundaries. Simulation results conducted in a full mathematical model of the craft showcase the performance and feasibility of the suggested method to track the desired references, even with the vehicle subject to water currents.

Keywords: Guidance, navigation and control (GNC) of unmanned marine vehicles (surface and underwater), Adaptive and robust control in marine systems, Autonomous and remotely operated (surface and underwater) marine vessels
Abstract: This paper presents a prescribed performance guidance line-of-sight (LOS) law derived from the traditional LOS algorithm. At the initial stage, the proposed guidance law can be regarded as a proportional LOS guidance law. Then, by the merit of LOS algorithm, the cross-track error will exponentially converges to zero. Subsequently, once the error converges to a threshold so that the performance inequalities is satised, the guidance law smoothly switches to a prescribed performance guidance law, which ensures that the cross-track error is conned to the predened constraints. The asymptotic stability of closed-loop system is established via Lyapunov theory. Moreover, preliminary model basin and lake experiments are carried out to validate the eective of proposed guidance law.

Keywords: Autonomous and remotely operated (surface and underwater) marine vessels, Adaptive and robust control in marine systems
Abstract: Motivated by the needs of long-endurance autonomous underwater vehicles, we seek to better understand trade-offs associated with control systems that seek to reduce energy consumption. In this paper we demonstrate a technique for controller design for an autonomous underwater vehicle (AUV). We examine the well-known design requirements, such as reference tracking performance and agility (e.g, step-response characteristics) in the context of energy required by control surface servos. The results of our analysis are used to inform an H-infinity controller synthesis problem with the objective of balancing these tradeoffs while reducing energy consumption.

Keywords: Autonomous and remotely operated (surface and underwater) marine vessels, Guidance, navigation and control (GNC) of unmanned marine vehicles (surface and underwater), Actuators, thrusters, propulsion systems, and sensors in marine systems
Abstract: The planning of safe trajectories that are also time and energy efficient is an important part of automated ships. During trajectory planning, the expected motion of other traffic participants as well as the dynamic capabilities of the own vessel need to be considered. This paper presents a variation of the path-velocity decomposition (PVD) approach that builds upon a predefined reference trajectory instead of a reference path. By solving a shortest-path problem, collisions with dynamic obstacles are avoided. Collisions with static obstacles are inherently ruled out by selecting a suitable reference trajectory. The proposed method ensures dynamic feasibility and energy efficiency of the optimized trajectory using a detailed powertrain model. In addition, the collision detection is divided into a broad and narrow phase to reduce calculation time. As a concrete application, the trajectory planning is designed for a double-ended river ferry with four cycloidal propellers. The proposed method is tested within an exemplary traffic scenario with three dynamic obstacles using a high-fidelity vessel simulator. The results show the ability of the presented approach to generate collision-free and energy efficient trajectories that can safely be calculated within the required cycle time of 5 s. Using multiple reference trajectories in parallel and a velocity-dependent ship orientation offers potential for improvement for future research.

Keywords: Autonomous and remotely operated (surface and underwater) marine vessels, Guidance, navigation and control (GNC) of unmanned marine vehicles (surface and underwater)
Abstract: A velocity obstacle (VO) based collision avoidance method for autonomous surface vessels operating in restricted and unstructured environments with traffic is considered. We propose a novel VO for enforcing maneuvering compliance with rules 13-15 and 17 in the International Regulations for Preventing Collisions at Sea (COLREGs), where the vessel-to-vessel encounter is first classified w.r.t. the COLREGs, then an encounter-specific domain is assigned to the opposing vessel, and finally a VO for that domain is formulated. The maneuvers of the opposing vessel throughout the encounter is considered when evaluating which side is appropriate to pass the vessel on. This increases robustness to non-compliant behaviour by the opposing vessel. The domain size is determined based on a measure for the available space to maneuver, which ensures an appropriate separation of the vessels in both confined spaces and open waters. Furthermore, collision avoidance with static obstacles from electronic charts is included, where a convex set that is free of static obstacles is constructed to simplify complex geometries, and the boundary of the set is enforced by VOs. The performance of the proposed collision avoidance method is demonstrated through numerical simulation, where it show compliance with COLREGs rules 13-15 and 17. Furthermore, the novel VO shows improved COLREGs compliance compared to another popular COLREGs-specific VO.

Keywords: Autonomous and remotely operated (surface and underwater) marine vessels, Dynamic positioning & position mooring systems for ships & platforms, Modeling, identification, simulation, and control of marine systems
Abstract: In difficult whether conditions the complexity of docking maneuvers of autonomous surface vessels (ASVs) increases. Docking maneuvers take place in proximity to piers and other vessels. The slow speed at which the maneuvers take place decreases the maneuverability of the vessel and environmental disturbances such as wind and waves increase in effect. In these scenarios ropes can be utilized to support the maneuver and compensate for the compromised actuation capabilities. The modeling of the modified mechanics plays a center role. It has been shown in previous work that this setup, connecting the vessel to the pier with a constant distance (e.g. with a rod) can be modeled using the concept of differential-algebraic equations (DAEs). With the adapted vessel dynamics a trajectory generation problem can be solved using optimal control theory. Here, a direct numerical method, in this case a full discretization of the optimal control problem (OCP), is used. The contribution in this paper allows for slackness in the rope. This is done by using a smooth penalty function, as well as solving a complementary problem. Both methods lead to feasible solutions. The penalty function shows are more smooth behavior but suffers from numerical robustness in comparison to the linear complementary solution.

Keywords: Dynamic positioning & position mooring systems for ships & platforms, Nonlinear and optimal control in marine systems
Abstract: Docking operations for autonomous surface vehicles (ASVs) involve challenges related to low-speed maneuvering in confined harbour spaces while handling environmental forces and traffic. Recently, optimization-based docking approaches have demonstrated promising results in unobstructed convex harbor areas, however they are still limited in dealing with static obstacles, which adds the significant challenge of non-convex constraints. In this paper, we present two hybrid methods that addresses the problem of docking while avoiding both static and dynamic obstacles that obstruct the direct path to the quay. The first phase involves the utilization of computational geometry for partitioning the non-convex harbor area into convex polygons. Then, a search algorithm computes the optimal sequence of convex polygons that connect the starting pose to the docking pose in an obstacle-free manner. Finally, trajectory planning is achieved via numerical optimal control. In this way, the proposed methods helps avoiding local minima and preserves the benefits of optimization-based approaches with respect to vehicle kinematics and dynamics, as well as actuator and spatial constraints.

Keywords: Guidance, navigation and control (GNC) of marine vessels, Actuators, thrusters, propulsion systems, and sensors in marine systems
Abstract: The berthing of vessels is a safety critical operation due to tight requirements for precise navigation in the constrained harbor area. This study proposes a novel guidance and motion control algorithm to achieve the automated berthing operation of a twin-waterjet propelled vessel. A three phases guidance algorithm is devised that enables the smooth operation of the vessel between the transition and docking phase. The superior manoeuvrability offered by the twin-waterjet propulsion system provides high precision control of the vessel also at low speed, and the possibility of performing complex manoeuvres in limited space. A sliding mode manoeuvring controller and a two stage trust allocation scheme translate the computed speed and heading set-points into actual control actions. A simulation case study is utilized to verify the feasibility of the proposed berthing strategy.

Keywords: Autonomous and remotely operated (surface and underwater) marine vessels, Automation of ship’s systems, Adaptive and robust control in marine systems
Abstract: For autonomy in the maritime domain, object detection is a very important task, as one needs to perceive the surroundings to take appropriate action decisions. A large issue in maritime object detection and classification is the shortage of thorough datasets. In this work, our aim is to reduce this problem by introducing a pipeline for the generation of simulated data that matches the target domain, thereby achieving a more reliable and robust performance of our object detector. This data generation pipeline is easily modifiable and allows for varying setups that would be hard or dangerous to collect in real life. Furthermore, it enables the introduction of new classes without issue.

Keywords: Autonomous and remotely operated (surface and underwater) marine vessels, Decision support and safe operation, Modeling, identification, simulation, and control of marine systems
Abstract: This work presents the use of particle swarm optimization (PSO) for dynamic risk-aware path following, or waypoint re-planning during autonomous surface navigation in a maritime environment with polygonal grounding obstacles. Although recent research on control and local or global path planning for maritime autonomous surface ships (MASS) is considerable, few deal with the concept of risk during dynamic path following along a pre-planned path. The proposed method introduces risk-based terms in the PSO fitness function for dynamic (online) adjustment or re-planning of intermediate waypoints during path following of a pre-planned route, where the control of the vessel in this work is left to a standard line-of-sight PID controller. Moreover, the results are compared to the performance of an analogous implementation of risk-aware model predictive control (MPC) using a gradient-based solver. The suggested method yields adequate performance similar to that of the MPC algorithm. Ultimately, the PSO approach may in future works allow for more complex and dynamic risk-aware behavior related to e.g. weather conditions implemented through lookup tables, or discrete machinery modes that are non-smooth.

Keywords: Maritime safety and security for ports and ships, Autonomous and remotely operated (surface and underwater) marine vessels, Guidance, navigation and control (GNC) of marine vessels
Abstract: This paper describes a method of using fiducial markers to aid Unmanned Surface Vehicles (USVs) as an additional positioning source during auto-docking. Vision-based techniques allow USVs to localize themselves relative to their surroundings without relying on external communication. This paper shows and evaluates a vision-based strategy to localize USVs to a pier. We used the Global Navigation Satellite System (GNSS) with Real-Time kinematic (RTK) and Inertial Navigation System (INS) with a base station on the pier to validate the vision-based position estimates. The experiment shows that traditional computer vision techniques using fiducial markers can give accurate outdoor position estimates in good conditions. We also highlight some adverse conditions where the performance decreased considerably.

Keywords: Surface and underwater vehicles, Subsea construction and operation, Autonomous and remotely operated (surface and underwater) marine vessels
Abstract: Marine growth on offshore underwater structures is a problem as it reduces the lifespan. The structures are cleaned annually by manually operated ROVs. Automation of these ROVs can improve the removal efficiency, and thereby reduce the cleaning campaign time and cost, as it is challenging for the operators to manually stabilize the ROVs under the harsh offshore conditions. Waves, ocean currents, the attached tether and the cleaning tool all generate external forces to the ROVs acting as substantial disturbances which can be rejected by a controller. This study examines the operating range of a standard compact ROV subject to external disturbances. To analyze the cleaning performance a normalized performance parameter is defined which weight the relative distance of the water jet with the most efficient distance. The results show that the waves has a larger effect on the cleaning performance compared to the ocean current. This paper examines the operating range of a reconfigured BlueROV2. For Hs less than or equal to 1.4 m it is possible to clean in the entire operating range. To clean at all the considered sea states Hs less than or equal to 3m and ocean currents of 0.1 - 0.5 meter per second the ROV needs to be below 13 m.

Keywords: Guidance, navigation and control (GNC) of unmanned marine vehicles (surface and underwater), Cooperative navigation and control, Autonomous and remotely operated (surface and underwater) marine vessels
Abstract: Autonomous underwater vehicles (AUVs) rely on surface support for communication with operators and position fixes to bound inertial navigation errors. By installing an acoustic modem on an autonomous surface vehicle (ASV), the ASV can carry out these tasks, replacing more expensive and less flexible manned research vessels. This paper proposes a hybrid tracking controller for an ASV providing mission support for an AUV. The proposed controller keeps the ASV in a donut-shaped safety domain about the AUV defined by the risk of collision (inner boundary) and the risk of communication loss (outer boundary). At the same time, the hybrid controller reduces power consumption and acoustic signal noise by going into standby mode when it is within the safety domain. Results from a simulation study and field trials are presented to demonstrate and validate the controller's performance. The results show that the controller performed well in the tested cases.

Keywords: Virtual reality in marine applications, Human-machine interaction in marine systems, Marine cyber-physical systems
Abstract: Man's admiration of the underwater world has been recorded ever since ancient times and to this day, it does not cease to amaze large sections of modern society. Whether for recreational or sport purposes, commercial activities or strategic military operations, the underwater environment plays an amusing yet inhospitable host to its many explorers. Knowledge and respect for our oceans are keys for a sustainable and safe relationship between humans and the underwater. People have often used their ingenuity for adaptation to various environments and the technology for allowing divers to reach extreme places in a safe manner is developing rapidly. This paper will investigate benefits of using robots as diving buddies for aiding underwater navigation. In a typical dive mission scenario, a diver is given relative distance and bearings to an underwater target as he tries to overcome environmental influences to navigate to that target using customary diving equipment; a compass and diving computer/watch. Diving robots can introduce sensors capable of achieving advanced navigation and guiding divers even in low visibility conditions. The experiment in this paper compares these two approaches and validates the results in a simulation environment on 26 participants. The success rate in finding and reaching the targets are compared in terms of time and distance travelled. Finally, the simulation tools are evaluated by participants as well as its potential in developing algorithms and user training using a NASA-TLX workload estimation scale.

Keywords: Biomimetics in marine robotics, Guidance, navigation and control (GNC) of unmanned marine vehicles (surface and underwater), Maritime robotics (underwater, surface, aerial)
Abstract: The paper investigates the application of a bio-inspired control paradigm encompassing nonlinear function approximation and adaptive learning to design a manoeuvring controller for a remotely operated vehicle. The bio-inspired learning controller is adopted to overcome limitations introduced by unknown nonlinear dynamics as well as by environmental disturbances. The bio-inspired manoeuvring controller is compared against a traditional adaptive controller with respect to tracking performance and control effort. Simulation results show that the bio-inspired controller displays better tracking performance when the structure of the system dynamics is unknown. Further, the paper shows that offline training of the functional approximator helps in delivering a smoother control effort, and that a bio-inspired integral action fulfils the disturbance rejection.

Keywords: Cooperative navigation and control, Maritime robotics (underwater, surface, aerial), Autonomous and remotely operated (surface and underwater) marine vessels
Abstract: Cooperative control of autonomous underwater robots can provide capabilities that exceed those of any single marine robot. In this paper, the cooperation between two different underwater vehicle-manipulator systems is considered. Cooperation is enabled through a control scheme which generates state-dependent reference signals to achieve synchronization of the end-effector positions of the robots. These references are tracked by the individual control systems, which consist of decoupled kinematic and dynamic controllers. Consequently, the control systems do not constrain the choice of cooperation scheme. Due to the kinematic redundancy of the robots, a task-priority inverse kinematics controller is used for velocity-level redundancy resolution, and several tasks are defined for each robot. Furthermore, the dynamics of the robots are controlled by a higher-order sliding mode controller, namely the generalized super-twisting algorithm with adaptive gains. The dynamic control approach provides robustness to model uncertainties and unknown disturbances. The effectiveness of the methods is verified in a simulation study on a heterogeneous pair of UVMSs.

Keywords: Autonomous and remotely operated (surface and underwater) marine vessels, Guidance, navigation and control (GNC) of unmanned marine vehicles (surface and underwater), Maritime robotics (underwater, surface, aerial)
Abstract: Remotely operated vehicles (ROVs) are the main driver in inspection, maintenance, and repair (IMR) of underwater structures. The commercial use of ROVs in industrial applications dates to the 1980s, however, the control and operation of work class ROVs for performing IMR interventions still carried out by the team of minimum two expert ROV pilots, despite the immense efforts to automate the operation of ROVs in the last decades. This paper provides a new approach to automation of ROV operation by considering the needs of the ROV pilots. To this end, a new controller is presented enabling the subsea IMR operations with a presence of a single pilot. The result are tested using a residential work class ROVs in Snorre B (SNB) oilfield by an expert Pilot.

Keywords: Intelligence and autonomy in marine systems and operations, Information systems and methods in marine applications, Decision support and safe operation
Abstract: We apply non-myopic informative path planning in a simulated case study with several constraints on our agent. A cost valley philosophy is proposed to guide the agent through the field. Among others, we employ RRT*, a variant of RRT (rapidly-exploring random trees), as the path planner to determine the least cost trajectory between locations. The distance budget from start to end destination, the obstacle constraint and the directional filtering are desired penalty fields, whereas the expected integrated Bernoulli variance and the variance reduction are the two reward fields. The cost valley is then computed by superimposing those five fields. The simulation results demonstrate the efficiency of such a strategy. They show that the suggested approach balances exploitation and exploration while bearing in mind the go-home constraint.

Keywords: Marine cyber-physical systems, Maritime robotics (underwater, surface, aerial), Aquaculture
Abstract: Cooperation of a lightweight autonomous aerial vehicle (LAAR) and an autonomous surface vehicle (ASV) in prolonged robotic inspections missions in mariculture requires a landing platform (LP) with a docking system mounted onto the ASV. The autonomous surface and aerial vehicles developed in the scope of HEKTOR (Heterogeneous Autonomous Robotic System in Viticulture and Mariculture) project are presented herein. Furthermore, mechanical and electrical design of the LP, the control scheme and communication protocol of the LP with the ASV, and LP-ROS interface for future high-level mission control are described. The ASV autonomy test results show that it can work for 10-11h. Laboratory and field trials of the LP show that the chosen concept works in various settings.

Keywords: Control applications in marine renewable energy, Ocean renewable energy, Offshore systems modeling and control
Abstract: Marine renewable energy (MRE) is a label that embraces a range of technologies used to harness ocean energy, including wave, tidal stream, tidal barrage, ocean thermal energy conversion (OTEC) and salinity gradient, as well as offshore wind (floating and fixed). For the current analysis, floating solar is omitted from the MRE set. With an increasing drive towards zero-carbon energy provision, and the need for complementarity with increasing penetration of wind and solar, the need to tap the vast available MRE resources has never been greater. Ultimately, the adoption of MRE energy harnessing technology is contingent on the cost of MRE being competitive with other renewable, and conventional, energy sources, in terms of Levelised Cost of Energy (LCoE). The value of appropriate control systems, which can maximise the energy conversion capability of MRE and give added value to the capital investment, has been identified as an important modulator of LCoE. This paper examines the range of control problems within the gamut of MRE technologies and documents commonality and contrasts, as well as the emergence of control problems that are unique to aspects of MRE.

Keywords: Control applications in marine renewable energy, Ocean renewable energy
Abstract: Tidal stream turbine (TST) has the potential to become a key enabling technology for sustainable electricity supply in remote islands and coastal communities. This type of turbines are typically employed under water and subject to various external disturbances. These external disturbances make the development of control system for TST very challenging. A comprehensive continuous sliding-mode (CSM) control approach has been developed in this work for high-performance control of TST. First, a continuous twisting algorithm (CTA) is applied for robust regulation of the rotational speed under various marine current disturbances. Then, a multi-variable generalized super twisting controller is applied for current regulation that takes into account the cross-coupling effect in the current dynamics. Through numerical simulation, the performance of the proposed comprehensive CSM control technique is tested over the active disturbance rejection controller (ADRC).

Keywords: Ocean renewable energy, Control applications in marine renewable energy, Modeling, identification, simulation, and control of marine systems
Abstract: Tidal barrages have been used as a source of renewable energy since Medieval times, though the commercial utilisation of tidal barrages for electricity production began in 1966. In the intervening time, a number of techniques have been used to optimise the operation of tidal barrages, in order to maximise their utility, against set criteria, usually including maximisation of converted energy. This paper examines what can be learned from a sister renewable energy application, wave energy, in terms of the energy-maximising control schemes employed. Specifically, comparisons are made in terms of the characteristics of the primary energy excitation, the set of control protocols available, and the mathematical models used to describe each system. In order to provide a preliminary assessment of the potential for the use of wave energy control concepts, a sample case study is undertaken, where a popular wave energy control philosophy is used to optimise the operation of a tidal barrage.

Keywords: Ocean renewable energy
Abstract: Reverse electrodialysis (RED), an emerging electrochemical technology that uses ion-selective membranes to directly draw electricity out from salinity differences between two solutions, i.e., salinity gradient energy (SGE), has the potential to be a clean and steady renewable source to reach a sustainable water and energy supply portfolio. Although RED has made notable advances, full-scale RED progress demands more techno-economic and environmental assessments that consider full process design and operational decision space from module- to system-level. This work presents an optimization model formulated as a Generalized Disjunctive Programming (GDP) problem to define the cost-optimal RED process design for different deployment scenarios. We use a predictive model of the RED stack developed and validated in our research group to fully capture the behavior of the system. The problem addressed is to determine the RED plant’s topology and the working conditions for a given design of each RED stack which renders the cost-optimal design for the defined problem and scenario. Our results show that, compared with simulation-based approaches, mathematical programming techniques are an efficient and systematic approach to provide decision-making support in early-stage applied research and to obtain design and operation guidelines for full-scale RED implementation in real scenarios.

Keywords: Offshore systems modeling and control, Modeling, identification, simulation, and control of marine systems, Fault tolerant control and fault handling for marine vessels
Abstract: This paper presents a fault-tolerant control design for an offshore ocean thermal energy conversion (OTEC) system with constraints. We use a distributed parameter system (DPS) to model the OTEC system, which is described by a set of partial differential equations (PDEs) and ordinary differential equations (ODEs). Moreover, a boundary fault-tolerant control scheme is proposed to solve actuator failures, while suppressing system vibration and achieving system stability. Two controllers are designed to deal with actuator faults while considering the output nonlinearity of the OTEC system. In addition, the uniform bounded stability of the OTEC system based on barrier Lyapunov function (BLF) is proven numerical simulation verifies the effectiveness of the proposed fault-tolerant control method, which can effectively improve the performance and safety of ocean thermal energy conversion in the OTEC system.

Keywords: Offshore systems modeling and control, Control applications in marine renewable energy, Ocean renewable energy
Abstract: Increasingly large floating wind turbines (FWTs) are being introduced to access the offshore wind resource over deep water at lower cost. In connection with designing a 25 MW semi-submersible wind turbine, we examine the scaling trends associated with the dynamic performance of the generator torque and blade pitch controllers and highlight the challenges that may be encountered for such devices. The increased rotor inertia, reduced blade pitch rates, longer platform pitch and surge natural periods, and flexible modes of the tower, platform, and rotor all affect the ability of the controller to track the desired rotor speed. The effects of control design and tuning choices on the FWT behavior in representative wind and wave conditions are shown.

Keywords: Autonomous and remotely operated (surface and underwater) marine vessels, Guidance, navigation and control (GNC) of marine vessels, Systems for integrated operation
Abstract: Autonomous sailing is seen as one of the possible solutions to cope with the decrease in qualified officers, to minimise the risk to humans and ships at challenging conditions, and to decrease the environmental impact of the transport sector. Autonomous sailing is not limited to moving the vessel safely through the seas, but it also includes docking the vessel. Docking is considered a difficult and critical manoeuvre in autonomous sailing.

The objective of this work is to construct a trajectory including its time derivatives for our newly designed 71m long underactuated feeder vessel to approach a dock. The trajectory can be used by a feedback controller to steer the vessel to the dock, and the time derivatives can be used to construct a feed forward signal to improve the tracking performance.

An optimal control problem is formulated to answer i) what the best pose is to start an approach to the dock, and ii) what trajectory is optimal from an arbitrary initial pose. The resulting trajectory gives an optimal minimal-time solution, but the computational time was too large to employ real-time. A second trajectory was constructed based on bez curves. The computational load of this trajectory is negligible. The trajectory can be used for a subset of initial states. It does provide a smooth trajectory with all the derivatives, and is seen as a good option when the vessel starts the docking manoeuvre from a not too challenging pose.

Keywords: Autonomous and remotely operated (surface and underwater) marine vessels, Guidance, navigation and control (GNC) of unmanned marine vehicles (surface and underwater), Maritime robotics (underwater, surface, aerial)
Abstract: Hydrothermal vent areas are unique ecosystems with high productivity and high biodiversity that are subject to ongoing research. Hydrothermal vents form in areas with increased magmatic activity where superheated, mineral rich water leaks from the seafloor. Due to the rapid cooling of the water the metal sulfides precipitate and form a black or white plume that can be sensed several hundred meters away from the vent source. Finding and reliably following such plumes with autonomous underwater vehicles (AUVs) is a challenging task since the plume does not have a smooth concentration gradient but lots of local patches due to the turbulent particle flow. This paper presents an algorithm that combines biology inspired chemotaxis with Unscented Kalman filter (UKF) based extremum seeking control (ESC). The effectiveness is demonstrated by a simulation of a physics-based AUV model in a turbulent 3D Plume model.

Keywords: Autonomous and remotely operated (surface and underwater) marine vessels, Maritime robotics (underwater, surface, aerial), Guidance, navigation and control (GNC) of unmanned marine vehicles (surface and underwater)
Abstract: Autonomous Surface Vehicles (ASVs) can be employed as platforms to study Autonomous Underwater Vehicles (AUVs) navigation. Navigation systems are commonly constituted by combining data from multiple on-board sensors in order to optimize position and orientation estimates, improving its accuracy, performance, and stability. Sensory fusion techniques are responsible for performing the combination of data from on-board sensors in the vehicle. Among the available techniques, the Kalman filter is the most used. In this work, a trimaran type ASV is presented, and its application in the field of AUV navigation is discussed.

Keywords: Autonomous and remotely operated (surface and underwater) marine vessels, Intelligence and autonomy in marine systems and operations, Maritime robotics (underwater, surface, aerial)
Abstract: A key challenge in autonomous vehicles is the high-level decision-making required to be reactive to significant changes in the environment. Timeline-based planning is a paradigm for temporal (time-aware) task planning that can provide such high-level decisions. We present an algorithm for incrementally translating a timeline-based planning problem into satisfiability modulo theories (SMT). Compared to existing SMT translations, our approach uses unsatisfiable cores to build the SMT formula in a conflict-directed way, typically producing smaller SMT problems that can be solved faster. Our system shows promising performance on several benchmark problems. Our planning software was developed as part of research projects on inspection operations for subsea installations and for mobile robots on marine installations.

Keywords: Guidance, navigation and control (GNC) of unmanned marine vehicles (surface and underwater), Intelligence and autonomy in marine systems and operations, Maritime robotics (underwater, surface, aerial)
Abstract: Maritime autonomous surface ships (MASS) have become a topic of intensive research in academia and industry, with focus areas such as path following and tracking, low-level control, collision avoidance, situational awareness, and others. However, high-level mission planning has received less attention in the literature, although it constitutes an important aspect of autonomy. This paper takes a step towards closing this gap by developing a basic mission planning system, which can generate a feasible and efficient sequence of high-level actions (plans) that are subsequently executed by the control system. The mission planner is based on the Graphplan algorithm, and considers actions related to, for example, entering docking mode, visiting a specific location, or starting (un)loading of containers, which are then to be executed by appropriate control systems. In addition, we couple the mission planner with the ship's guidance, navigation and control system, which has path planning, path following and fuzzy logic-based collision avoidance capabilities. To assess the performance of the proposed method, we present a set of simulations of a MASS navigating in a realistic marine environment including static obstacles and other ships.

Keywords: Intelligence and autonomy in marine systems and operations, Marine swarms of heterogeneous agents, Autonomous and remotely operated (surface and underwater) marine vessels
Abstract: Reinforcement learning is being broadly studied as a solution for many real-world problems. Reinforcement learning algorithms outperform humans in games such as Go and chess. On the other hand, reinforcement learning still can not achieve human-level in most real-world tasks. When reinforcement learning agents perform similar to humans, they will replace humans in many areas. Many real-world tasks need cooperation, and multi-agent reinforcement learning appears as a solution. However, multi-agent reinforcement learning algorithms are not yet being applied because of the challenge of high-dimensional data, computational complexity, and credit assignment. Meanwhile, people can manage to adapt to a new group without understanding the global goal of the group he or she belongs to. This is because people moderately imitate senior workers. Our work aims to test if the imitation strategy can be applied to a reinforcement learning agent. To validate the proposed methodology, we design a problem named Convoy problem and evaluate our new algorithm on the convoy problem.