Event-triggered model predictive control for trajectory tracking of underwater gliders in currents

Annual net community production and carbon exports in the central Sargasso sea from autonomous underwater glider observations

Study on an on-line fault detection and diagnosis model of underwater gliders based on hidden Markov model

An important class of robotic applications involves multiple agents cooperating to provide state observations to plan joint actions. We study planning under uncertainty when more than one participant must proactively plan perception and/or communication acts, and decide whether the cost to obtain a state estimate is justified by the benefits accrued by the information thus obtained. The approach we introduce is suitable for settings where observations are of high quality and they—either alone or along with communication—recover the system’s joint state, but the costs incurred mean this happens only infrequently. We formulate the problem as a type of Markov decision process (mdp) to be solved over macro-actions, sidestepping the construction of the full joint belief space, a well-known source of intractability. We then give a suitable Bellman-like recurrence that immediately suggests a means of solution. In their most general form, policies for these problems simultaneously describe (1) low-level actions to be taken, (2) stages when system-wide state is recovered, and (3) commitments to future rescheduling acts. The formulation expresses multi-agency in a variety of distinct practical forms, including: one party assisting by providing observations of, or reference points for, another; several agents communicating sensor information to fuse data and recover joint state; multiple agents coordinating activities to arrive at states that make joint state simultaneously observable to all individuals. Though solved in centralized form over joint states, the mdp is structured to allow decentralized execution, under some assumptions of synchrony in activities. After providing small-scale simulation studies of the general formulation, we discuss a specific scenario motivated by underwater gliders. We report on a physical robot implementation mocked-up to respect these same constraints, showing that joint plans are found and executed effectively by individual robots after appropriate projection. On the basis of our experience with hardware, we examine enhancements to the model that address nonidealities we have identified in practice, including the assumptions regarding synchrony.

Underwater gliders are long-endurance vehicles that map the ocean using sawtooth trajectories, playing a key role in monitoring oceanic conditions. However, their limited manoeuvrability hinders performance in constrained environments and harsh conditions such as strong ocean currents and waves. Analysing their manoeuvring capabilities can help to unlock their full potential. Recent advancements in Computational Fluid Dynamics (CFD) have enabled a more comprehensive analysis of glider manoeuvrability beyond traditional mathematical models. This study investigates the manoeuvring performance of the Petrel-II glider using the Reynolds-Averaged Navier-Stokes (RANS) method. A computationally efficient numerical approach is developed to control ballasting and the linear and angular movements of the eccentric mass, allowing for adjustments to the glider’s pitch and roll angles to replicate real-time operations. The glider’s saw-tooth and spiral manoeuvres are analysed separately for descent and ascent scenarios using a moving domain method. Pitch angle, surge speed, yaw rate, turning radius, and depth per turn are identified as key parameters governing manoeuvrability. The results provide insights into the Petrel-II glider’s manoeuvrability within physical constraints, identifying optimal control inputs for different operating conditions. The proposed methodology demonstrates the ability to simulate manoeuvring trajectories of gliders with complex geometries and to account for various environmental loads.

Abstract. Underwater gliders equipped with current profilers and optical turbidity sensors offer a low-energy solution for high-resolution measurements of currents, suspended particle properties, and sediment transport in coastal waters. Because the spatial structure of hydrosedimentary processes often changes on short time scales (hours to weeks), especially in coastal areas, validating the distribution of glider observations is required to assess our capacity to represent hydrosedimentary processes. Here we propose to validate in a shelf tide-dominated environment, both (i) glider-based currents, and (ii) glider-based acoustic backscatters and optical turbidities in full resolution delayed mode, using in situ collocated and synchronous ancillary observations. The deployed glider system correctly measures the periodic pattern of the tidal current, with a RMSD of O(3 cm s−1), demonstrating the system's ability to accurately capture tidal variability. Glider optical turbidities highly correlate with the ancillary observations (R2 up to 0.83). They also correlate well with their glider acoustic counterpart for most of the campaign period (R2=0.76), allowing an estimation of suspended particulate matter concentrations from acoustic measurements. Hence, the glider could observe not only the presence of bottom nepheloid layers of several mg L−1 but also residual fluxes of the order of 1 gm-1s-1 on the shelf. These results highlight the potential of gliders for quantifying sediment fluxes and advancing our understanding of coastal hydrosedimentary processes.

Mesoscale eddies are the most striking feature in the global upper ocean with notable effects on the climate and marine ecosystem. However, acquiring three-dimensional structure of mesoscale eddies remains challenging as their scale is still beyond the resolution capacity of the current generation of global operational ocean observation system. In this study, we conducted an eddy-oriented survey targeting a cyclonic eddy in the Kuroshio Extension during September 2024. Compared to traditional ship-based observations, our survey is synchronized with the newly launched Surface Water and Ocean Topography (SWOT) mission, and complements shipboard measurements with those from 7 autonomous underwater gliders and 20 surface drifters, capturing the eddy's three-dimensional structure with spatially high-resolution and wide coverage. The resulting dataset holds significant value for facilitating the calibration and scientific utilization of the SWOT mission, estimating the eddy transport, and validating eddy-resolving ocean forecasting systems.

Abstract As a new type of underwater unmanned observation platform, autonomous underwater gliders (AUGs) play an important role in ocean exploration and marine environment monitoring. However, because of the dynamic and unpredictable marine environment, AUGs are often subjected to multiple disturbances, such as ocean currents, turbulence, and waves, which pose a substantial challenge to their precise attitude control. Therefore, research on a multisource disturbance rejection control algorithm for AUGs is crucial to improve their control accuracy. In this paper, first, based on the dynamic principle, a lightweight motion model of an AUG is established. Second, utilizing a multisource disturbance rejection control algorithm, a control scheme based on disturbance observer-based control (DOBC) and the $$H_{\infty}$$ H ∞ control law and a hybrid controller combining DOBC and the proportional-integral-derivative (PID) control algorithm are designed for the pitch angle control of AUG. The controllers are used to track the target attitude of the AUG, and the stability of the whole system is analyzed. Finally, the performance of the proposed algorithms is tested through simulation experiments, and their effectiveness and disturbance rejection performance are verified through comparison with the PID controller under the impact of various disturbances.

As a crucial force in marine scientific research, the underwater gliding unmanned system must perform tasks with high accuracy and efficiency. Due to the influence of rocket fuel, underwater gliders exhibit rapid response times, making it challenging to control their future attitude based solely on their current state. Therefore, accurate trajectory prediction is essential for ensuring effective and reliable control of the system. However, the complex underwater environment presents significant challenges for traditional dynamic model-based methods in accurately predicting the future trajectory of underwater gliders. Moreover, conventional prediction models struggle to maintain accuracy in the final stages of the trajectory, particularly in high-dynamic scenarios where fuel depletion leads to a rapid decline in speed. To address these issues, this paper proposes a Maformer(Marine-Informer) model for trajectory prediction in underwater gliding unmanned systems. Building upon the traditional Informer model, Maformer integrates velocity feature encoding and replaces the original convolutional layer with dilated convolution. Experimental results demonstrate that, compared to the traditional Informer model, Maformer achieves an average reduction of 52.82% in prediction error. The findings of this study offer a promising solution for trajectory prediction of multi-feature unmanned systems operating in high-speed, dynamically changing environments.

The Twin Hybrid Autonomous Underwater Vehicle (THAUV) is an underwater monitoring system consisting of a twin buoyant body and a fixed wing mounted between them. It is equipped with two propeller thrusters and a pair of elevators at the aft end. As a new type of underwater vehicle, it combines the long endurance of an underwater glider (UG), the high-speed maneuverability of an autonomous underwater vehicle (AUV), and the ability to carry larger payloads. In this paper, the motion equations of the THAUV are established, and its simulation model is developed using SIMULINK. Computational fluid dynamics (CFD) is further employed to identify hydrodynamic parameters under different elevator size conditions. A case study is conducted to analyze the effects of three different widths of elevators on glide performance, including gliding speed, pitching angle, and gliding trajectory. CFD results show that when the elevator deflection angle is zero, the hydrodynamic forces acting on the THAUV increase as the elevator width increases under identical angle of attack and velocity conditions. Under CFD conditions with fixed angle of attack and flow velocity, the sensitivity of the hydrodynamic characteristics to elevator deflection became significantly more pronounced. Increasing the elevator deflection angle led to substantial growth in the generated hydrodynamic forces. Motion simulations further show that increasing the elevator deflection angle enhances the THAUV’s gliding performance. Comparative results also reveal that glide performance improves with larger elevator width.

Phytoplankton blooms above the seamount Maud Rise in the Antarctic Ocean have been reported but their emerging mechanisms and their importance for the wider Southern Ocean are not well known. We use satellite data spanning over the last two decades and in-situ data collected from a ship, an underwater glider and Biogeochemical-Argo profiling floats to understand the processes involved in the formation of Maud Rise phytoplankton blooms. We find that the seamount generates upwelling of warm deep water that transports heat, and likely dissolved iron, to the surface via diapycnal mixing. This creates a recurring annular structure of chlorophyll concentration (or chlorophyll halo) in correspondence with the previously observed warm water and sea ice halo over Maud Rise. The in-situ observations reveal integrated chlorophyll-a concentrations of up to 100 mg·m−2, which suggests exceptionally high phytoplankton biomass within the Southern Ocean, thus making the seamount a regional phytoplankton hotspot.

Developing Ireland's ocean observatory network: feasibility and suitability of using a SoundTrap HF300 for passive acoustics from an underwater glider

A universal visualization method for promoting system representation and performance prediction of underwater gliders based on deep learning

Fixed-time trajectory tracking control for underwater glider: theory and experiment

Long-range straight-line path tracking for underwater gliders using reinforcement learning and ocean current forecasts

Energy consumption prediction and endurance optimization for underwater gliders based on data-model fusion

Cooperative coverage path planning of multiple underwater gliders considering sonar detection performance and energy efficiency

In the complex marine environment, the water entry process of air-droppable underwater gliders (ADUGs) faces numerous challenges. In particular, wave loads significantly affect the water entry characteristics and reduce the deployment success rate. This research builds a scaled-down ADUG model and a numerical wave tank through smoothed particle hydrodynamics - finite element method (SPH-FEM) to explore the water entry characteristics of ADUGs in waves. An improved recursive digital filtering algorithm is employed to calculate the shock response spectrum of the ADUG under wave conditions. The results show that the water entry impact acceleration varies with multiple parameters, including water entry point, wave height, water entry speed, and water entry angle. When the wave phase angle is π, the ADUG is more prone to exhibit the ‘ricochet’ behavior, which is most likely to happen when the wave height is 0.3 m. The inflection point in the impact response spectrum for water entry of the ADUG is mainly in the frequency band of 200 - 400 Hz. Under the same conditions, the angle of attack has little influence on the impact response spectrum. Tank experiments are performed based on a scaled-down model to investigate the water entry impact of ADUGs in waves. The experimental results show good consistency with the simulation results, with a maximum error of 13.58%. The research findings can guide the structural design and deployment planning of ADUGs and also offer theoretical references for the water entry research of other air-droppable equipment with complex geometries.

Digital twin-enabled structural real-time monitoring for blended-wing-body underwater gliders

Vibration and noise reduction of underwater gliders with a novel wing integrating flexible cladding and phononic crystals