Explore the vast range of titles available.

This study examines data collected with an autonomous underwater glider during a period of vigorous radiatively driven convection (RDC) and low winds in deep, unstratified Lake Superior. Conductivity, temperature and depth (CTD) measurements reveal distinct convective plumes of warm downwelling water with temperature anomalies of ∼0.1° ${\\sim} 0.1{}^{\\circ}$C and width scales on the order of 10−100 $10-100$ m, consistent with theoretical scalings for the unstratified convective regime. Shear and temperature microstructure measurements indicate turbulent kinetic energy (TKE) dissipation (ε) $(\\varepsilon )$ and temperature variance dissipation rates χT $\\left({\\chi }_{T}\\right)$ orders of magnitude greater in thermal plumes than laterally adjacent waters. Decay timescales of ε $\\varepsilon $ indicate highly efficient mixing is sustained throughout the night. Energetics, mixing efficiency, and constraints on convective plume scales are also discussed. These observations demonstrate that RDC can dominate vertical mixing dynamics even in deep ice‐free systems, and these systems can serve as a real‐scale laboratory for investigation of convective dynamics.

The Gulf Stream transports heat from the tropics poleward and is an integral part of how the planet redistributes heat. Studies of the variability of the Gulf Stream have suggested that the seasonal cycle of ocean mixed layer heat content in the Gulf Stream may be driven by the local net atmospheric heat flux or by oceanic advection of heat in the strong western boundary current. Here we use sustained underwater glider observations of the Gulf Stream from 80°^{\\circ}$ W to 67°^{\\circ}$ W during 2015–2023 to show that oceanic advection heats the ocean mixed layer in spring when the upper ocean switches from cooling to warming. Estimated terms of the mixed layer temperature budget demonstrate that the net atmospheric heat flux cools the upper ocean in all seasons except summer and that mixed layer warming in spring is due to ocean advection of heat from farther south. Plain Language Summary Over the North Atlantic Ocean, the seasonal cycle of upper ocean temperature is influenced by seasonal variations in heating from the sun. However, the seasonal variation of upper ocean temperature in the Gulf Stream may also depend on the amount of heat transported in the fast‐moving, warm, ocean current. Using an estimate of the seasonal cycle of the upper ocean of the Gulf Stream and estimates of the heat exchanged with the atmosphere, we demonstrate that heat carried by the ocean current warms the Gulf Stream at the start of spring. The ocean heat transport is an important component of how the Gulf Stream's upper ocean temperature evolves seasonally. Key Points Observations collected by underwater gliders in 2015–2023 were used to estimate the seasonal cycle of the Gulf Stream Ocean advection is responsible for warming the Gulf Stream mixed layer during the spring The net air‐sea heat flux moves heat into the atmosphere over the Gulf Stream for all seasons except summer

Buoyancy-driven underwater gliders are highly efficient winged underwater vehicles driven by modifying the net buoyancy and internal shape. Many advantages, such as wide cruise range, less power consumption, low noise, and no pollution, make the underwater glider an important platform for marine environment observation and ocean resource exploration. For the wide cruise range, attitude control of underwater glider becomes the core technology. In this paper, the underwater glider named OUC-III has been developed for marine observation. To control the attitude of glider, the kinematic and dynamic models of it have been calculated by mathematical analysis. Furthermore, a novel control algorithm is proposed to control the attitude of glider. The algorithm is combined reinforcement learning with Active Disturbance Rejection Control (ADRC) and compared with classical ADRC by simulation based on the dynamic model of OUC-III. The simulation experimental results indicate that the proposed algorithm compensates well for the ocean current disturbances on OUC-III attitude control mission and it obtains high-precision and high-adaptive control ability.

Mesoscale eddies are important for transporting oceanic energy and matter. We investigated the three-dimensional structure of an irregularly shaped warm eddy using three Chinese underwater gliders and satellite data during May 2015 in the northern South China Sea. The warm eddy lasted for 2 months, remained quasi-steady, and had a mean radius of ~ 70 km from May 10 to May 31. The heat contents observed along the two glider tracks differed markedly, by 2 × 10 9 J/m 2 , which reflected an imbalance in the geostrophic and tangential velocity distributions of the eddy. The geostrophic/tangential velocity decreased/increased with depth within the warm eddy. The maximum tangential velocities calculated using the datasets from the two gliders were 0.8 and 0.25 m/s, respectively, confirming that the shape of the warm eddy was horizontally asymmetrical. Large errors can arise when the heat, energy, and matter transport for an irregularly shaped eddy are estimated using a regular circular model. We suggest that more intersecting glider tracks should be used to retrieve the three-dimensional eddy structure, and that those tracks should be better designed. The irregular shape of the warm eddy was likely induced by oceanic currents such as the wind-induced Ekman current. Further study is needed to elucidate the eddy–current interactions and the mechanisms thereof.

The underwater glider is a kind of novel invention that has been proven to be perfect for long-duration, wide-range marine environmental monitoring tasks. It is controlled by changing the buoyancy and adjusting the posture. For precise control of the underwater glider’s trajectory, a fuzzy adaptive linear active disturbance rejection control (LADRC) is designed in this paper. This controller allows the glider to dive to a predetermined depth precisely and float at a specific depth. In addition, the controller takes some important factors into account, such as model uncertainty, environmental disturbances, and the limited dynamic output of the actual mechanical actuator. Finally, simulation results show the superiority of this fuzzy adaptive LADRC control method. Particularly, when the underwater glider was controlled to dive 100 m at a predetermined attitude angle θ = −1 rad, the maximum overshoot of FLADRC is reduced by 75.1%, 56.6% relative to PID, LADRC, respectively.

Underwater gliders (UGs) play a prominent role in collecting data within a specific underwater depth range. Due to the unmanned nature of these vehicles, the path-following control significantly influences their other systems and energy consumption. In this study, the performance of the path-following control was improved under hydrodynamic coefficient uncertainties using the adaptive control structure. The main control system, using the adaption law, autonomously updates itself to mitigate the adverse effects of uncertainties. The stability of the control law was proven through the utilization of a Lyapunov-function candidate. In the study, we take into account uncertainties in hydrodynamic coefficients, actuators, and position and orientation estimation. The impact of uncertainties on performance was investigated using the Monte Carlo simulation technique, which stochastically selected parameters. The results ultimately demonstrate that the uncertainties adversely affect the control of states. However, the adaptive structure exhibits robust performance compared to traditional controllers such as PID and LQR controllers with fixed gains. The adaptive path-following control structure reduced actuator usage, leading to decreased power consumption by the controller. Furthermore, the proposed structure was involved in an experimental case study, which was tested in a pool to validate its performance.

Underwater gliders have emerged as effective tools for long-term ocean exploration. Employing aircraft for launching underwater gliders could significantly expand their application. Compared to slender underwater vehicles, the distinctive wing structure of underwater gliders may endure huge impact forces when entering water, leading to more intricate impact load characteristics and potential wing damage. This paper employs a computational fluid dynamics approach to analyze the water entry event of an airdropped underwater glider and its impact load behavior. The results indicate that the glider impact load is enhanced prominently by the wing, and that the extent of enhancement is influenced by the entry attitude. At an entry angle of 80°, the glider exhibits the maximum impact load during different water entry angles. In addition, a larger attack angle indicates a higher glider impact load. Our present study holds significant importance for both the hydrodynamic shape design and water entry strategy control of airdropped underwater gliders.

Hybrid underwater gliders (HUGs) combine buoyancy-driven gliding with propeller-assisted propulsion, offering extended endurance and enhanced mobility for complex underwater missions. However, precise depth control remains challenging due to system uncertainties, environmental disturbances, and inadequate adaptability of conventional control methods. This study proposes a novel optimized line-of-sight active disturbance rejection control (OLOS-ADRC) strategy for HUG depth tracking in the vertical plane. First, an Optimized Line-of-Sight (OLOS) guidance dynamically adjusts the look-ahead distance based on real-time cross-track error and velocity, mitigating error accumulation during path following. Second, a Tangent Sigmoid-based Tracking Differentiator (TSTD) enhances the disturbance estimation capability of the Extended State Observer (ESO) within the Active Disturbance Rejection Control (ADRC) framework, improving robustness against unmodeled dynamics and ocean currents. As a critical step before costly sea trials, this study establishes a high-fidelity simulation environment to validate the proposed method. The comparative experiments under gliding and hybrid propulsion modes demonstrated that OLOS-ADRC has significant advantages: the root mean square error (RMSE) for depth tracking was reduced by 83% compared to traditional ADRC, the root mean square error for pitch angle was decreased by 32%, and the stabilization time was shortened by 14%. This method effectively handles ocean current interference through real-time disturbance compensation, providing a reliable solution for high-precision HUG motion control. The simulation results provide a convincing foundation for future field validation in oceanic environments. Despite these improvements, the study is limited to vertical plane control and simulations; future work will involve full ocean trials and 3D path tracking.

A disc-type underwater glider (DTUG) is characterized by full-wing body shape, omnidirectional characteristics, and high maneuverability. To further reveal the differences between DTUGs and hybrid-driven underwater gliders (HUGs), the vertical motion of a DTUG with zero pitch angle is simulated. Based on the structural characteristics of DTUGs, the motion control equations with control inputs are derived and solved by the fourth-order Runge–Kutta method. The DTUG’s vertical velocity, fixed-depth motion, vertical motion with external disturbance, and stability are mainly analyzed and compared with those of an HUG. The results show that the DTUG’s full-wing body shape increases its vertical resistance so that the vertical steady motion velocity is low, which is advantageous for vertical depth control but disadvantageous for fast vertical motion; furthermore, fixed-depth motion control can be easily realized in limited space. The DTUG’s vertical motion with external disturbances can quickly return to a stable state within a smaller vertical distance than that of the HUG, which is beneficial for assisting the DTUG in returning to the target position and will improve its movement efficiency in a small body of water with limited depth. The stability analysis shows the DTUG can remain stable within the range of control parameter.

Energy management is a critical and challenging factor required for efficient and safe operation of underwater gliders (UGs), and the energy consumption model (ECM) is indispensable. In this paper, a more complete ECM of UGs is established, which considers ocean currents, seawater density variation, deformation of the pressure hull, and asymmetry of gliding motion during descending and ascending. Sea trial data are used to make a comparison between ECMs with and without the consideration of ocean currents, and the results prove that the ECM that considers the currents has a significantly higher accuracy. Then, the relationship between energy consumption and multiple parameters, including gliding velocity relative to the current, absolute gliding angle, and diving depth, is revealed. Finally, a simple example is considered to illustrate the effects of the depth-averaged current on the energy consumption.