Due to the challenges regarding the limits of their endurance and autonomous capabilities, underwater docking for autonomous underwater vehicles (AUVs) has become a topic of interest for many academic and commercial applications. Herein, we take on the problem of relative navigation for the generalized version of the docking operation, which we address as proximity operations. Proximity operations typically involve only two actors, a chaser and a target. We leverage the similarities to proximity operations (prox-ops) from spacecraft robotic missions to frame the diverse docking scenarios with a set of phases the chaser undergoes on the way to its target. We emphasize the versatility on the use of factor graphs as a generalized representation to model the underlying simultaneous trajectory estimation and relative navigation problem that arises with any prox-ops scenario, regardless of the sensor suite or the agents’ dynamic constraints. To emphasize the flexibility of factor graphs as the modeling foundation for arbitrary underwater prox-ops, we compile a list of state-of-the-art research in the field and represent the different scenario using the same factor graph representation. We detail the procedure required to model, design, and implement factor graph-based estimators by addressing a long-distance acoustic homing scenario of an AUV to a moving mothership using data sets from simulated and real-world deployments; an analysis of these results is provided to shed light on the flexibility and limitations of the dynamic assumptions of the moving target. A description of our front- and back-end is also presented together with a timing breakdown of all processes to show its potential deployment on a real-time system.

Open data are scarce in underwater robotics, making it more difficult for researchers to develop new methods that address real-world problems. In this work, we present the experimental design, execution, and curation of three datasets that represent different conditions in a realistic underwater dynamic proximity operation. The raw datasets gathered during the deployments are post-processed to improve consistency. We detail and use a joint batch optimization technique that uses a probabilistic approach to iteratively search for the set of optimal agent trajectories that are in best agreement with the relative measurements provided by a USBL positioning system and optical pose measurements from a fiducial light array. Error analysis of the relative measurements with respect to the baseline and optimized trajectories validate our results, effectively providing ground-truth trajectories of the agents. The resulting datasets, together with their documentation, are publicly available at github.com/aldoteran/asko_2024_datasets

Good knowledge of the atmospheric boundary layer in open seas is crucial for the development of wind-propelled and wind-assisted ships. Still, very little data is available away from the shores, and one needs to rely on modelling to estimate the wind conditions at sea. This paper presents experimental measurements of the vertical wind profile over the North-Atlantic ocean made on board a cargo ship during its normal operation. The study focuses on two aspects: the estimation of the “undisturbed” atmospheric boundary layer profile and the influence of the hull on the flow. One of the methods often used to describe the evolution of wind speed with height is by using a power law, with a typical value for the exponent of 1/7 (≃0.14). The results of this study however show a significantly smaller value, around 0.035, to be representative of the predominant conditions, and highlight that the 1/7 exponent overestimates by 50% the amount of kinetic energy compared to the predominant conditions. The results also show the very large variability of the power law exponent. At the same time, the flow disturbance is clearly visible above the deck up to one or two times the hull height, with a strong dependency on the apparent wind angle, which can lead to wind speed variations up to 20% compared to the power law profile and direction changes of more than 10 degrees compared to the undisturbed wind.

This paper discusses the impact of scaling effects in the performance of a standalone wing sail, comparing experiments and numerical simulations. The experimental data of a standalone wing sail with a NACA0015 section, tested in the R.J. Mitchell wind tunnel at the University of Southampton, are compared with wind tunnel tests run at KTH Royal Institute of Technology, where the L2000 wind tunnel and wing sail had a smaller scale, and with Computational Fluid Dynamics simulations of three different cases. For the numerical simulations, first the model scale Southampton wind tunnel was simulated. Then, keeping the same scale, the wind tunnel domain was substituted with a larger domain to simulate an open-field condition, and analyse the presence of blockage effects. Finally, full-scale simulations were achieved keeping the same scale of the model scale open-field simulations, and reaching the full-scale Reynolds number by varying the viscosity of the fluid. The flow in the numerical simulations is modelled with the RANS equations and the k − ω SST turbulence model, knowing about its limitations in simulating stall conditions, but judged to be satisfactory for a preliminary study about scale effects. The range of model scale Reynolds numbers covered by both experimental campaigns spans from 2.2x105 to 6.7x105, while the full-scale Reynolds number is equal to 7.9x106, covering a range representative of most wind propulsion technologies. The main conclusions are that the simulations capture well the shape of the lift curve up to an angle before stall, after which the simulations diverge from the experiments. In full-scale, higher lift coefficients are reached, and the lift curve shows a different behaviour than in model scale, with a longer linear region and a more abrupt stall.

International regulations on greenhouse gas (GHG) emissions as well as strong market demand for zero-emission transport calls for a radical change in the shipping industry. Measures such as hull form optimization, use of alternative fuels and efficient machinery systems, new coatings, and smart routing have already improved the energy efficiency of the world fleet. However, it is far from enough. To effectively respond to the climate challenges, we must turn to emission-free energy sources. One such promising and well-proven zero-emission propulsion system for shipping is wind propulsion. Using wind to power cargo vessels re-started on a commercial scale about a decade ago and there are today more than 50 wind-assisted vessels in commercial trade or under construction. They are equipped with a variety of wind propulsion technologies like Flettner rotors, wing sails and kites, which may give fuel and emission reductions of up to about 20%. With the goal of demonstrating that even higher energy and emission reduction is feasible, 11 representatives of the European maritime industry and research community have recently joined forces in the large-scale EU-funded project Orcelle, led by Wallenius Wilhelmsen Ocean. The present paper outlines the project’s ambition, scope of work and expected outcome.

To further improve the design and operation of modern sailing cargo vessels, additional knowledge of the interaction between multiple sails in combination with the hull is needed. This study investigates the aerodynamic performance of a fully sailing car carrier through an experimental test campaign with a large, fully instrumented model of the complete ship at the Volvo Cars Wind Tunnel in Gothenburg. The ship design is based on the latest version of the Orcelle vessel deigned by Wallenius Marine,which is a 217 m long car-carrier, equipped with six two element wingsails. The campaign focuses on evaluating multiple sail trims under varying apparent wind angles and different hull configurations. All tests are done at a chord based Reynolds number of approximately 0.9 × 10⁶. The evaluation involves measuring the aerodynamic forces through individual force measurements for each wingsail, combined with the overall force generated by the integrated hull and wingsail system, all measured in six degrees of freedom. The results highlight the importance of the sail trim and demonstrate how hull design influences wingsail performance. For apparent wind angles below 30°, reduced flap angles, a slender bridge, and trimming strategies that maximize forward thrust while minimizing yaw moment are favorable. At apparent wind angles closer to 90°, larger flap angles are preferred, bridge design becomes less critical, and maximizing forward thrust remains the primary trimming objective.

Autonomous underwater docking is of the utmost importance for expanding the capabilities of Autonomous Underwater Vehicles (AUVs). Due to a historical focus on underwater docking to only static targets, the research gap in underwater docking to dynamically active targets has been left relatively untouched. We address the state estimation problem that arises when trying to rendezvous a chaser AUV with a dynamic target by modeling the scenario as a factor graph optimization-based Simultaneous Localization and Mapping problem. We present a set of boundary factors that aid the inference process by seamlessly transitioning the target’s state between the different observability stages, intrinsic to any dynamic docking scenario. We benchmark the performance of our approach using the Stonefish simulated environment.

Uncrewed aerial vehicles (UAVs) are frequently used in glaciological applications, among other things, for photogrammetric assessments of calving dynamics at glacier termini. However, UAVs are often limited by battery endurance and weight constraints on the scientific payload that can be added. At Sálajiegna, the largest freshwater calving glacier in Sweden, we explored the combined use of a versatile maritime robot (uncrewed surface vehicle, USV) and a UAV to characterise Sálajiegna's short-term and seasonal calving front dynamics and mass loss. For this, a photogrammetric payload suite was integrated into the USV. Consecutive USV surveys of Sálajiegna's front, followed by point cloud based calving detection and surface-reconstruction based volume quantification, allowed for a detailed description of calving-induced terminus changes and is hence suggested as a viable alternative to the differencing of digital elevation models. By combining USV and UAV measurements, we identify sectors of high and low calving activity, a calving front retreat of up to 56 m and a thinning rate in the terminus region of 5.4 cm d−1 during the summer of 2022.

Terminal docking is an important step towards long-term underwater residency of Autonomous Underwater Vehicles (AUVs). An important part is to correctly estimate the relative position between the AUV and the docking station. While there are many solutions to this problem, it is unclear how they perform with respect to each other in terms of accuracy and computational performance. We propose a side by side comparison of a Rao-Blackwellized particle filter (RBPF) with a Maximum-A-Posteriori (MAP) method in a vision-based terminal homing scenario. Both methods are evaluated in a simulation study based on performance under different uncertainties. Subsequently, they are validated using real-world data from field tests. The comparison shows that in the simulation study, the smoothing performs more accurate than the RBPF, whereas on the experimental data, they perform equally. However, the smoothing requires less computational power compared to the RBPF.

Tell-tales are used by sailors on boats of any size, from a small dinghy up to ocean racing mega yachts. They give information to the trimmer about the local flow conditions on the sails and hence enable optimal trimming. With the development of wind powered commercial vessels, the process of sail trimming however needs to be automated, and new sensing techniques need to be found to allow this. In this paper, we present a preliminary study of an optical computer-vision algorithm detecting the state of the tell-tales on the 7 meters long Oceanbird demonstrator developed at KTH Royal Institute of Technology. 8 cameras were recording all sides of the 4 symmetric rigid wings while sailing. In post-processing, the time series relating the state (attached or detached flow) of the 88 tell-tales (11 per side on each wing) were extracted. During the experiments, different types of manoeuvres were performed with the wings to ensure a variety of conditions where different flow characteristics are expected. The preliminary study focuses on the feasibility of the method, therefore the videos were not treated in real time and used for trimming. Results show that even with a very simple detection scheme, the method is a promising tool to understanding the flow characteristics and a potentially useful target for wing trimming in some conditions.