Search Results (29)

The wave glider is an unmanned marine observation platform propelled by wave energy. Accurate prediction of its motion performance is crucial for structural design and motion control. This paper presents a four-degree-of-freedom nonlinear coupled dynamic model for wave gliders in complex marine environments, developed using a separated-body modeling approach. The model incorporates the torsional properties of the umbilical cable and includes coupled environmental forces that account for wave–current interactions. Simulation results demonstrate that the proposed model agrees well with existing studies. Based on the model, experimental analyses were conducted to investigate the turning and heading tracking performance under various operational conditions. The findings reveal that the rudder angle determines the radius and direction. The significant wave height influences the longitudinal velocity and turning rate; the average longitudinal velocity increases from $0.15\mathrm{m}/\mathrm{s}$ (at $0.5\mathrm{m}$ wave height) to $0.3\mathrm{m}/\mathrm{s}$ (at $1.25\mathrm{m}$ wave height), leading to a notable increase in turning cycles per unit time. Current disturbances cause trajectory drift, the pattern of which depends on the wave–current angle, exhibiting a distinct $\eta$-direction offset under ${90}^{\circ }$ conditions. A conventional PID controller fails to achieve precise heading maintenance under second-order wave forces. The surface float exhibits more pronounced oscillations than the submerged glider, and the heading deviation becomes more severe at a wave height of $1.25\mathrm{m}$. Full article

Marine magnetic surveys are vast and time-consuming, and researchers have long been seeking an economical mode for large-area data acquisition. A towed magnetic measurement system was developed based on the motion characteristics of the wave glider. By modifying the SeaSPY2 magnetometer, a twin-body towed configuration was developed, in which an S-shaped towing cable mitigates motion-induced impacts from the platform, and a high-precision GNSS positioning module was integrated into the system. Sea trials were conducted in the coastal waters near Qingdao. The results indicated that the system achieved an average cruising speed of 0.56 m/s, with the towed body’s pitch and roll angles controlled within ±5° and ±1°, respectively. The dynamic noise was measured at 0.0639 nT (Level 1), and the internal consistency for repeated survey lines and cross lines was 1.832 nT and 1.956 nT, respectively, meeting the requirements of marine magnetic survey standards. The system offers unmanned operation, zero carbon emissions, and a minimal environmental footprint, and long endurance, supporting applications such as nearshore exploration, mapping in sensitive marine areas, and underwater magnetic target detection. The research provides a novel unmanned technological solution for deep-sea magnetic surveys and lays the foundation for low-cost, cluster-based operations. Full article

Wave gliders’ power system shafts face complex conditions. To enhance their operational stability, it is crucial to study PTFE, a polymer material that could replace traditional metals. This study added carbon fiber (CF), titanium carbide (Ti-C), and both to a PTFE matrix. The impact of seawater immersion on water absorption and the mechanical properties was examined, as well as friction and wear characteristics under constant amplitude cyclic (CAC) loading and seawater lubrication. The results indicated that while Ti-C boosts PTFE matrix hardness, its poor binding with the PTFE matrix leads to high water absorption in Ti-C/PTFE (PTFE-3), causing a significant decrease in the mechanical properties post-immersion and poor friction and wear performance. In contrast, CFs and the PTFE matrix have good interfacial bonding and greatly improve the resistance of the PTFE matrix to cyclic loading and seawater immersion. Therefore, CF/PTFE (PTFE-2) shows good mechanical and tribological properties. Moreover, incorporating a certain amount of CFs into Ti-C enhances its adhesion to the PTFE matrix, reducing the occurrence three-body wear and allowing Ti-C to fully utilize its high hardness. Thus, the combination of Ti-C and CFs markedly improves PTFE’s mechanical and tribological properties under cyclic loading and in seawater. Full article

This paper conducts wear tests of rotating shafts and bearings, and collects the wear amount, surface morphology, and friction force signals to study its tribological behaviors using the fractal and chaotic analysis. The rotation shaft surface fractal dimension were calculated to characterize the self-similarity and smoothness, the signals’ phase trajectories were constructed, and its correlation dimension and phase-point saturation were calculated to reveal the dynamic evolution of the system. The results show that the surface fractal dimension increases from low to high. The phase trajectory fluctuates and then maintains in a finite space, and the correlation dimension increases and stabilizes near the larger value while the phase-point saturation has the opposite evolution. The changes in surface fractal dimension, phase trajectories, correlation dimension, and phase-point saturation are similar to the wear rate, exhibiting a transition from instability to stability, which is more objective and sensitive than traditional representation methods. According to the fractal and chaotic characterization results of the worn surface and friction force signal, the material of CrNiMoN has better friction and wear properties than GCr15. The results reveal the tribological behaviors and wear mechanisms of the rotating shaft and provide guidance for material selection and designing, along with a basis for characterizing the wear status of the rotating shaft of wave glider wing. Full article

Uncrewed Wave Gliders (UWGs) are capable of harnessing energy from ocean waves and photovoltaic sources to enable long-duration voyages. Since the float’s yaw motion relies on the rudder of the submersible for control, this introduces many unknown nonlinear and time-delay factors into the control system. Moreover, the susceptibility of UWGs to waves influences results in limited maneuverability and necessitates energy efficiency considerations, complicating the task of following a designated path to a specific point for observations. To address these challenges, this paper first introduces a differential model-free adaptive control (DMFAC) approach for managing the float’s heading control, along with a proof of its stability. Furthermore, an improved attractive force line-of-sight (IAFLOS) guidance strategy for overall mooring control is proposed. The integration of the DMFAC heading controller and the IAFLOS strategy forms a comprehensive mooring control system, which is validated through simulation studies in typical maritime conditions. This control system ensures that, while considering energy conservation strategies, the distance between the wave glider and the mooring point remains within 20 m during mooring. Full article

This paper deals with the neural network identification-based model predictive heading control problem in a wave glider. First, based on a kinematic model of the wave glider subjected to external disturbance and system uncertainty, a state space model of the wave glider is established. Then, a neural network identification-based model predictive heading controller (NNI-MPHC) is designed for the wave glider. The heading controller mainly includes three components: a model predictive controller, a neural network-based model identifier, and a linear reduced-order extended state observer. Third, a design algorithm of the NNI-MPHC is presented. The algorithm is demonstrated through simulation, where the results show the following: (i) The designed NNI-MPHC is remarkably capable of guaranteeing the tracing effects of the wave glider. (ii) Comparing the NNI-MPHC and existing heading controllers, the former is better than the latter in terms of tracking accuracy and rapidity and robustness to model uncertainty and/or external disturbances. Full article

Objectives: The article’s aim is to test if rotary or reciprocating glide path influences the overall performance of WaveOne Gold in S-shaped canals. Methods: Sixty endo training blocks with an S-shape curvature were divided into three groups based on the glide path method used: no glide path; glide path preparation with ProGlider; glide path preparation with WaveOne Gold Glider. All blocks were then shaped with WaveOne Gold Primary. The time for shaping, the incidence in reaching working length and the number of pecking motions were recorded. ANOVA with Turkey’s test was used, and the p-value was set to 0.05. Results: WaveOne Gold Primary reached working length faster in the control group when comparing total working times. No significant differences in the ability of the WaveOne Gold Primary to reach working length in all groups (p > 0.05). The mean number of pecking motions was higher in the control group compared to other groups. Conclusions: No significant differences in the time needed to achieve a glide path between Proglider and WaveOne Gold Glider. WaveOne Gold Primary can shape a double curved canal faster if a glide path is present but takes less time to reach length if it is the only file used. No difference in the ability to reach working length. Full article

A wave glider is an ocean observation platform that utilizes wave energy to drive and solar energy to power. Its metal structure will generate related electromagnetic fields due to corrosion and underwater motion. In the detection of weak electromagnetic field signals underwater, its own electromagnetic field characteristics will have an impact on signal detection. To study the applicability of electric field sensors and magnetic field sensors on wave glider platforms, the structural characteristics of the wave glider were analyzed, and the installation positions of electric field sensors and magnetic field sensors were designed based on the different motion states of the water surface mother body and underwater towing body. The measured electromagnetic field data of the wave glider platform were measured, and the measured data were analyzed. It was determined that the interference electric field energy under typical working conditions of the wave glider was mainly concentrated within 1 Hz, which decreased with increasing frequency, and the magnitude was mV/m. The magnitude of the interference magnetic field is several tens of nT, indicating that the electromagnetic field interference is significant during the working state of the wave glider. Installing an electric field sensor directly at the bottom of the wave glider will cause significant noise interference, while installing the magnetic field sensor directly at the bottom of the tractor will affect the servo and the shaking-induced magnetic field. Moreover, wave gliders should not use electric field signals below 1 Hz as signal sources, but they can utilize axial frequency electromagnetic fields to detect weak electromagnetic signals underwater. Full article

Enhanced turbulence triggered by near-inertial wave (NIW) trapping by a mesoscale anticyclone and typhoon “Kompasu” was observed in the northern South China Sea. The observations provide evidence for the trapping of NIW packets of amplitude ~0.2 m/s near the base of an anticyclonic eddy, and of ~0.3 m/s after the passage of typhoon “Kompasu”. The wave energy was amplified in a layer located near the base of the anticyclonic eddy, between 150 and 300 m, while stronger NIWs triggered by the typhoon extended to depths > 500 m. Diffusivity was calculated by a fine-scale parameterization. A diffusivity elevated by one order of magnitude, the occurrence of high near-inertial velocity shears, and the low (≤1) Richardson numbers were consistent with turbulence production and mixing from the base of the anticyclonic eddy and following the passage of the typhoon, and were associated with the trapped NIWs. This study showed that, by serving as a bridge between mesoscale eddies and small-scale motion, NIWs are an important pathway for ocean energy transmission. Mesoscale-NIW interactions represent a significant source of NIWs as well as a sink of mesoscale energy. Full article

Rotary instrumentation has been proposed in undergraduate teaching. The aim of this study was to evaluate student’s performance, through the obturation quality and treatment time, in a sequential range of L-simulated root canals. A senior undergraduate dental student sequentially prepared randomly numbered canals from 1 to 40, with the WaveOne Gold glider and primary file, according to the manufacturer instructions. A gutta-percha cone matched with the finishing instrument and epoxy resin-based sealer (AH Plus) was selected for the obturation. Three independent observers evaluated the obturation quality according to both density and length. Active, total instrumentation and obturation times were also measured. Statistical analysis was obtained by Mann–Whitney and Kruskal–Wallis tests with a significance level of p < 0.05. The quality of the obturation was independent of the number of prepared canals with adequate length and density in 87.5% of the prepared canals. Both active and total instrumentation, as well as obturation times, reduced significantly as the number of the prepared canals by the student increased (p ˂ 0.05). The use of WaveOne Gold instrumentation and matched cone obturation by an inexperienced operator provided an adequate obturation quality in most of the curved simulated canals. The working time was significantly reduced through a short learning curve. Full article

We performed oceanic and atmospheric observations in the region off the Sanriku coast, Japan, from May 11 to 5 July 2022, using a wave-propelled unmanned surface vehicle, a Wave Glider (WG). Despite the severe weather conditions of atmospheric low-pressure system crossings, we successfully measured wind, air temperature, humidity, and sea surface temperature over the course of 55 days to calculate the turbulent heat flux. The WG observed that the atmosphere became more humid due to the southerly wind along the northwestern rim of the North Pacific subtropical high. The warm Kuroshio water expanded to the southeast of Hokkaido as a result of the northward shedding of an anticyclonic mesoscale ($~100$ km) eddy, called a warm-core ring, from the Kuroshio Extension. The WG traversed smaller (sub-mesoscale) water regions that were warmer and saltier than the surrounding Kuroshio water. The observations indicate that cold, dry air masses advected by northerly winds following the passage of atmospheric low-pressure systems generate a substantial upward turbulent heat flux over sub-mesoscale warm water regions, contrasting to no heat flux in the surrounding Kuroshio water region. Full article

Glider-type autonomous underwater vehicles are today one of the most promising areas of marine robotics. This is confirmed by the frequent and remarkable results of various research missions and projects. The cumulative group application of underwater and no less innovative wave gliders can significantly reduce the time of obtaining oceanographic data. Together with wave gliders, one group of such robotic objects can significantly increase the efficiency, time and volume of obtaining oceanographic data. There is big interest in increasing the functionality of such a group. This article presents one of the possible alternatives to increase the functionality of a group of underwater and waveguide hang gliders. We present the process of upgrading the existing design, control algorithms and software of the SHADOW underwater glider, which was developed by the teams of the St. Petersburg State Marine Technical University (SMTU) and Okeanos JSC in order to jointly study the monitoring of underwater potentially dangerous objects with the St. Petersburg State Fire Service EMERCOM of Russia. A structural-functional approach to the group application of underwater and waveguides is also proposed, which is capable of providing oceanographic, meteorological and environmental monitoring data online, based on the developed multilayer system for planning the trajectories of group movement of objects. The results of full-scale sea trials and the developed algorithms are demonstrated. Full article

The wave glider is an ocean-wave-propelled autonomous marine vehicle with unique dual-body architecture, which can converse the energy obtained from the ocean wave into the forward thrust. In this paper, the dynamic models of the submerged glider based on dynamic characteristics of tandem hydrofoils and the surface float were separately established. The pitching angles of the hydrofoils and the submerged glider and the angle of attack between hydrofoils and relative current were considered for dynamic models and hydrodynamic coefficients. The translational hydrodynamic coefficient term for high-angle-of-attack passive motion of the submerged glider was calculated from static test simulations by using Computational Fluid Dynamics (CFD). Moreover, the rotational damping coefficients and added mass coefficients varying with the pitching angle of hydrofoils were analyzed by the simulation of the vertical planar motion mechanism (VPMM) tests. Furthermore, the numerical simulation of longitudinal motion with the computed hydrodynamic coefficients was performed, and the simulation results were compared with the sea trial data. The analysis was performed, and conclusions were drawn, which would provide a theoretical reference for the design of the wave glider. Full article

Both underwater and wave gliders are known as autonomous unmanned energy-saving vehicles which have recently found applications for monitoring the world ocean. The paper under consideration discusses simplified mathematical models of these platforms enabling the straightforward parametric investigation into relationships between their parameters and performance. In its first part the paper discusses equations describing the motion of an underwater glider (UG) in a vertical plane as a basis for derivations relating geometric, kinematic and hydrodynamic characteristics of UG and its lifting system with relative differential buoyancy and pitch angle. Obtained therewith are formulae for the estimation of the UG glide path speed, lift-to-drag ratio, range of navigation and endurance. The approach is exemplified for typical cases of the UG conceived as winged bodies of revolution and flying wings. The calculated results feature dependencies of the UG speed on its configuration and volume as well as on the angle of attack for different magnitudes of relative buoyancy. Also considered is an optimal mode of operation, based on the maximization of the lift-to-drag ratio. The second part of the paper is dedicated to the estimation of the thrust and speed of a wave glider (WG), comprising a surface module (float) and underwater module represented by a wing, with the use of a simplified mathematical modeling intended to clarify the influence of the parameters upon the performance of the WG. The derivations led to an equation of forced oscillations of the vehicle accounting for the interaction of the upper and lower modules, connected by a rigid umbilical. The exciting impact of progressive waves of a given length and amplitude is found through the calculation of the variation of a buoyancy force in accordance with the Froude–Krylov hypothesis. The derivatives of time-varying lift with respect to kinematic parameters, entering the equation of vertical motion of the WG, as well as coefficients of instantaneous and time-averaged thrust force, are found by resorting to the oscillating hydrofoil theory. The derivation of the available thrust and the approximate calculation of the drag of the vehicle with account of wave and viscous components enable the evaluation of the speed of the WG for the prescribed geometry of the craft and wave motion parameters. Full article

A wave glider can convert vertical wave motion into its forward propulsion. There are many factors affecting the propulsion performance of a wave glider. The swing amplitude of hydrofoil can affect the efficiency of hydrofoil to capture wave energy, and the pull direction of an umbilical cable can affect the transmission efficiency of wave energy. In this paper, an optimized hydrofoil mechanism with a self-adjusting lower limit (SALL) was proposed by analyzing the un- synchronized movement between the submerged glider and the surface float. This mechanism was able to transfer the movement of umbilical cable to the hydrofoil swing mechanism through the linkage to control the lower limit of hydrofoil swing (maximum swing angle of hydrofoil in a counterclockwise direction). Firstly, the user-defined function (UDF) was written to control the motion of hydrofoil in the fluid domain. The lower limit swing angle and the heave direction of the hydrofoil were both set in the UDF, and the forward thrust generated by the passive swing of the hydrofoil in the fluid domain was able to be obtained by the simulation. Secondly, the prototype was designed by introducing a parallelogram mechanism on a conventional submerged glider, and a wave simulation test platform was built to verify the propulsive performance of the prototype. The results showed that, in comparison with the conventional submerged glider, the forward thrust of the SALL submerged glider was able to be improved by 1.50%, 17.78%, 7.42%, and 20.70% under the stiffness coefficients of torsion spring set to K = 2, K = 4, K = 6, and K = 8 in the simulation experiment, respectively. The forward thrust of the SALL submerged glider was able to be elevated by 9.99% with torsion spring K = 8 in the tank experiment. The advantage of the SALL mechanism was verified by comparing the results of the simulation and the tank experiment. Finally, the feasibility of the SALL submerged glider was verified in actual sea conditions by a sea trial. Full article