Search Results (278)

With the development of inspection robot control technology, wheel-legged robots are increasingly used in complex underground space inspection. To address low stability during obstacle crossing in unstructured terrains, a motion control strategy integrating an improved CPG algorithm and a biological reflex mechanism is proposed. It introduces an adaptive coupling matrix, augmented with the Lyapunov function, and vestibular/stumbling reflex models for real-time motion feedback. Simulink–Adams virtual prototypes and single-wheeled leg experiments (on the left front leg) were used to verify the system. Results show that the robot’s turning oscillation was ≤±0.00593 m, the 10° tilt maintained a stable center of mass at 10.2° with roll angle fluctuations ≤±5°, gully-crossing fluctuations ≤±0.01 m, and pitch recovery ≤2 s. The experiments aligned with the simulations, proving that the strategy effectively suppresses vertical vibrations, ensuring stable and high-precision inspection. Full article

Mediterranean saline wetlands are significant ecological habitats defined by seasonal water availability and various biological communities, forming a unique ecotone that combines traits of both freshwater and marine environments. Moreover, they are regarded as notable natural and economic resources. Since the sustainable management of protected wetlands necessitates a multidisciplinary approach, the purpose of this study is to provide a comprehensive picture of the hydrological, hydrochemical, and ecological dynamics of a man-made groundwater dependent ecosystem (GDE) by combining remote sensing, hydrochemical data, geostatistical tools, and ecological indicators. The study area, called “Le Soglitelle”, is located in the Campania plain (Italy), which is close to the Domitian shoreline, covering a surface of 100 ha. The Normalized Difference Water Index (NDWI), a remote sensing-derived index sensitive to surface water presence, from Sentinel-2 was used to detect changes in the percentage of the wetland inundated area over time. Water samples were collected in four campaigns, and hydrochemical indexes were used to investigate the major hydrochemical seasonal processes occurring in the area. Geostatistical tools, such as principal component analysis (PCA) and independent component analysis (ICA), were used to identify the main hydrochemical processes. Moreover, faunal monitoring using waders was employed as an ecological indicator. Seasonal variation in the inundation area ranged from nearly 0% in summer to over 50% in winter, consistent with the severe climatic oscillations indicated by SPEI values. PCA and ICA explained over 78% of the total hydrochemical variability, confirming that the area’s geochemistry is mainly characterized by the saltwater sourced from the artesian wells that feed the wetland. The concentration of the major ions is regulated by two contrasting processes: evapoconcentration in summer and dilution and water mixing (between canals and ponds water) in winter. Cl⁻/Br⁻ molar ratio results corroborated this double seasonal trend. The base exchange index highlighted a salinization pathway for the wetland. Bird monitoring exhibited consistency with hydrochemical monitoring, as the seasonal distribution clearly reflects the dual behaviour of this area, which in turn augmented the biodiversity in this GDE. The integration of remote sensing data, multivariate geostatistical analysis, geochemical tools, and faunal indicators represents a novel interdisciplinary framework for assessing GDE seasonal dynamics, offering practical insights for wetland monitoring and management. Full article

Aiming to solve the difficult problem of the miniaturization of servo valves, this paper designs a subminiature two-dimensional (2D) electro-hydraulic servo valve, which realizes the integration of the pilot stage and the power stage and significantly improves the work-to-weight ratio. Meanwhile, a high-power-density brushless DC motor (BLDC) is adopted as the electro-mechanical converter to further reduce the volume and mass. Firstly, the structure and working principle of the two-dimensional (2D) servo valve are described, and the mathematical model of the electro-mechanical converter is established. Aiming at the special working condition of the electro-mechanical converter with high-frequency oscillation at a small turning angle, this paper designs a position–current double closed-loop PID control algorithm based on the framework of the vector control algorithm (FOC). At the same time, the current feedforward compensation technique is included to cope with the high-frequency nonlinear disturbance problem of the electro-mechanical converter. The stability conditions of the electro-mechanical converter and the main valve were established based on the Routh–Hurwitz criterion, and the effects of the control algorithm of the electro-mechanical converter and the main parameters of the main valve on the stability of the system were analyzed. The dynamic and static characteristics of the 2D valve were simulated and analyzed by establishing a joint simulation model in Matlab/Simulink and AMESim. The prototype was fabricated, and the experimental bench was built; the size of the experimental prototype was 31.7 mm × 29.3 mm × 31 mm, and its mass was 73 g. Under a system pressure of 7 MPa, the flow rate of this valve was 5 L/min; the hysteresis loop of the spool-displacement input–output curve was 4.8%, and the linearity was 2.54%, which indicated that it had the ability of high-precision control and that it was suitable for the precision fluid system. The step response time was 7.5 ms, with no overshoot; the frequency response amplitude bandwidth was about 90 Hz (−3 dB); the phase bandwidth was about 95 Hz (−90°); and the dynamic characterization experiment showed that it had a fast response characteristic, which can satisfy the demand of high-frequency and high-dynamic working conditions. Full article

Based on the cold-fluid hydrodynamic description, the interaction of a non-relativistic charged-particle beam with crossed magnetic fields is studied. This process results in the transfer of energy/momentum from the field to the beam, which, in turn, enhances the beam’s own electrostatic oscillations. This paper investigates the development features of such coupled axial and radial oscillations near resonant frequencies. The necessary conditions for the resonant amplification of this beam’s natural oscillations are identified. Such a process may be used for the creation of effective radiation sources. Full article

The damping groove structure of the port plate plays a crucial role in the pulsation suppression, vibration reduction, and noise optimization of the piston pump. Different damping groove structures have a significant impact on the flow distribution process during the normal operation of the port plate, affecting the pump outlet flow and pressure pulsations, which in turn influence the noise level of the piston pump. Therefore, the damping groove in the piston pump is one of the key structures influencing the pump’s pressure and cavitation behavior. To address the pressure shocks and oscillations caused by the distribution process in the piston pump, this study proposes a novel damping groove and performs CFD simulations on the non-damped groove. The analysis focuses on the pressure pulsation characteristics in the plunger chamber and the cavitation behavior of the pump. Additionally, an optimization analysis of the structural parameters of the new damping groove is conducted, which effectively reduces pressure shocks and cavitation in the swash plate axial piston pump. This study provides a theoretical foundation for improving the performance and lifespan of piston pumps. Full article

This study systematically investigates the temporal characteristics of a high-pressure CO₂ master oscillator power amplifier (MOPA) system under tunable spectral lines. Based on a continuously tunable CO₂ oscillator–amplifier system, we experimentally measured the variation in the laser pulse width before and after amplification at different spectral lines, with the oscillator and amplifier operating at pressures of 7 atm and 3 atm, respectively. The results indicate that, for most spectral lines, the laser pulse width remained nearly unchanged after amplification. However, at certain spectral lines, a distinct phenomenon was observed: pulse broadening for strong lines and pulse narrowing for weak lines. To explain this phenomenon, theoretical calculations were conducted based on a high-pressure CO₂ six-temperature model, and the experimental results were analyzed from the perspective of small-signal gain dynamics. This study reveals that variations in the laser pulse width primarily originated from differences in the gain build-up time across different spectral lines, which in turn influenced the amplification of both the pulse pedestal and the main pulse. For strong spectral lines, the amplifier gain built up rapidly, leading to more uniform amplification of the entire laser pulse and resulting in pulse broadening. Conversely, for weak spectral lines, the amplifier gain built up more slowly, with amplification primarily concentrated in the main pulse, causing a reduction in the pulse width. This finding has significant implications for optimizing narrow-pulse CO₂ lasers and provides crucial insights into the temporal characteristics of applications, such as laser isotope separation and extreme ultraviolet (EUV) light source generation. Full article

This paper presents an on–off power control technique for galvanically isolated dc–dc converters, which implements a feedback control loop for power regulation on the same isolation transformer used for power transfer. To this aim, the power oscillator is controlled with a PWM scheme, and the control signal is transmitted through the galvanic barrier by using an ASK modulation that acts on the secondary winding of the isolation transformer. The key building block of the proposed architecture is a PLL that allows the reconstruction of the PWM control signal when the power oscillator is turned off and data transmission is disabled. The effectiveness of the proposed power control architecture is validated by designing an isolated dc–dc converter based on a thick polyimide transformer. It complies with reinforced isolation while addressing the power requirements of applications such as low-power sensor interfaces, medical devices, and housekeeping power, e.g., gate drivers or controllers for power converters. At a 20 V output voltage, 110 mW isolated output power is delivered. The dc–dc converter also provides PWM power regulation against PVT variations. Full article

Changes in the flight attitude of plant protection unmanned aerial vehicles (UAVs) can lead to oscillations in the liquid level of their medicine tanks, which may affect operational accuracy and stability, and could even pose a threat to flight safety. To address this issue, this article presents the design of a flight attitude simulator for crop protection UAVs, constructed on a six-degree-of-freedom motion platform. This simulator can replicate the various flight attitudes, such as emergency stops, turns, and point rotations, of plant protection UAVs. This article initially outlines the determination and design process for the structural parameters and 3D model of the flight attitude simulator specific to plant protection UAVs. Subsequently, simulations were performed to analyze liquid sloshing in the pesticide tank under various liquid flushing ratios during flight conditions, including emergency stops, climbs, and circling maneuvers. Finally, the influence of liquid sloshing on the flight stability of the plant protection UAVs in different attitudes and with varying liquid flushing ratios is presented. These results serve as a cornerstone for optimizing the flight parameters of plant protection UAVs, analyzing the characteristics of pesticide application, and designing effective pesticide containers. Full article

To ensure the safe navigation of ships in rough seas while reducing steering gear energy consumption and losses, a steering control system with small rudder output angles, low steering frequency, and high control performance was designed. A third-order closed-loop gain-shaping algorithm was employed in the development of the controller, with the ultimate control strategy derived by embedding a nonlinear compound function between the proportional derivative (PD) controller and the second-order oscillation link to enhance control effectiveness. A nonlinear Nomoto model of the “Yupeng” ship was employed for simulation validation. The simulation results illustrated a 14.5% improvement in overall control performance achieved by the proposed controller compared to a nonlinear feedback controller. The controller’s robustness was additionally validated through the application of the Norrbin ship model. The proposed controller enhances the stability of ships in rough seas, effectively limiting the maximum rudder angle during turns and reducing the average rudder angle and steering frequency during navigation. This design aligns with practical requirements for maritime operations in heavy weather, contributing significantly to the economic, safe, and efficient navigation of ships. Full article

This paper presents a resonant wireless power transfer method that leverages a 90-degree voltage phase shift between the transmitting and receiving coils to enhance efficiency and maximize power transfer. When the resonant coupling is achieved, the secondary coil with an adjustable capacitor forms a tuned LC circuit. If the primary coil is driven at the resonant frequency of both the primary and secondary sides, the system can transmit 250W of power between the coils over a distance of 50 cm. Using a single power transmitting unit (PTU) board with multiple paralleled gallium nitride high-electron-mobility transistors (GaN HEMTs), the system achieves a maximum power transfer efficiency of 88%, highlighting the effectiveness of the design in high-efficiency, long-distance wireless power transmission. The key to the success of high-power, high-efficiency RWPT is in exhibiting the imaginary turn ratio presented on the air transformer. The imaginary turn ratio can realize the negative impedance conversion that converts the positive resistance on the power-receiving unit into a negative one, and thus, the damping of the resonance oscillation becomes negative and positively encourages more power to be delivered to the power-receiving unit (PRU) load. This paper derives the theory of the imaginary turn ratio and demonstrates the implementation of the RWPT system that exhibits the imaginary turn ratio effect. Full article

Based on a reduced model of a linear section of a steel gas pipeline between four supports and with a crack-like through defect, ANSYS FE software is used in this study to develop numerical approaches regarding three key parameters of a composite bandage in the form of a circular lining: the type of composite material and the length and thickness of the composite lining. The approach for assessing the static strength of a damaged section of a steel pipeline with a composite lining that is subjected to internal pressure allows for the determination of the optimal thickness of the composite lining itself, which is equal to the indicator “50.0% to 62.5%” of the pipe thickness. Furthermore, the approach for assessing the dynamic strength and analyzing the possible destruction of the reinforced damaged section of a pipeline experiencing an increase in internal pressure allows for the determination of the optimal length of the composite lining, which, in turn, should be at least 241.2 mm. This work also considers cases when there is no internal pressure and the steel pipeline is subjected to critical pressure. It is found that the frequency spectrum of pipeline oscillations without a composite lining is higher than that with a composite lining. The difference between the corresponding dynamic oscillations increases with the thickness or the length of the composite lining. In the absence of internal pressure, all frequencies of the steel pipeline with a crack closed by a composite lining are paired. This pairing is disrupted when the pipeline is subjected to critical internal pressure, and the difference between its oscillation frequency spectrum without and with a composite lining increases. In this case, the oscillation modes significantly differ from those of the same pipeline structure when unloaded. The results ensure the optimal stress distribution in the defect area of a steel pipeline wall and improve the reliability and safety of pipelines under seismic actions. The approach for increasing dynamic strength and eliminating defects can be applied to pipelines with a large diameter regardless of the causes and geometric dimensions of the defects. Moreover, this approach to increasing the strength can be used by various industries and/or institutes which work on the design of new, earthquake-resistant, reinforced pipelines. Full article

A bio-inspired vehicle with banded fin fluctuation as the propulsion mode is the research topic. However, this propulsion mode suffers from low efficiency and requires the urgent resolution of other issues. In this paper, the kinematic model of the banded fin surface and the numerical calculation model for its hydrodynamic performance are established based on the long dorsal fin propelled by MPF (Media and/or Paired Fin propulsion) mode. Through numerical simulation, the hydrodynamic performance of the banded fin under typical working conditions is explored and its propulsion mechanism is analyzed. By using a method of controlling variables, such as wave number, swing angle, and frequency, where only one independent variable is changed at a time while the others remain constant, the impact on thrust coefficient function and the obtained periodic variation laws governing hydrodynamic performance are studied. Oscillatory thrust is generated by the fin’s motion, where it first captures water through a ‘scoop’ motion and then expels it via a diagonal ‘push’ motion, producing thrust. Due to limitations in fin length and varying oscillation shapes, the effective water-pushing stroke differs, leading to variations in work and creating periodic oscillatory forces. When the variable is the oscillation frequency, the propulsion efficiency of the oscillating fins remains nearly constant when the oscillation frequency is less than or equal to 1 Hz. However, when the oscillation frequency exceeds 1 Hz, the propulsion efficiency decreases as the oscillation frequency increases, and the rate of decrease gradually slows down. The effect of leading-edge suction on hydrodynamic performance was studied by varying the oscillating fin’s angle of attack. The results showed that, compared to the unchamfered configuration, the forward chamfer better utilizes vortex energy, reducing input power and significantly improving propulsion efficiency. Guided by both numerical simulations and experimental results, we design and manufacture a prototype of an underwater banded fin bio-inspired propeller that encompasses shape modeling, mechanical structure design, and control mechanism design. We conduct real water tests to verify feasibility and reliability in terms of forward movement, backward movement, and turning ability, among others. Furthermore, we analyze how varying angle of attack or optimizing front/rear edge shapes can effectively enhance hydrodynamic performance. Full article

This research applies continuous wavelet analysis and seasonal correlation analysis to tree-ring data from Três Barras National Forest (FLONA Três Barras), revealing diverse influences on growth, including climate, solar activity, and external factors. The methodology involved tree-ring collection and subsequent wavelet and seasonal analyses to unveil the non-stationary characteristics of and multifaceted influences on growth. Key findings include the subtle effects of El Niño events on tree-ring development, the sensitivity of Araucaria angustifolia to temperature changes, the significant influence of precipitation during drought periods, and the intricate relationship between tree growth and solar cycles. The El Niño–Southern Oscillation (ENSO) emerges as a primary climatic driver during specific intervals, with external factors (precipitation, temperature, and solar cycle–solar irradiance) influencing tree response between 1936 and 1989. Additionally, the seasonal correlation analysis highlighted the importance of sub-annual climate variability, capturing specific intervals, such as a 3-month season ending in March of the previous year, that significantly impacted tree-ring growth. The study underscores the importance of protecting the endangered Araucaria angustifolia for climatic studies and local communities. Historically, in Brazil, Araucaria angustifolia seeds played a vital role in sustaining indigenous populations, which in turn helped to disperse and propagate forests, creating anthropogenic landscapes that highlight the interconnected relationship between humans and the preservation of these forests. Full article

In this work, the preindustrial control (piControl) and Historical experiments results from climatic Earth system models participating in the sixth phase of the Coupled Model Intercomparison Project (CMIP6) are analyzed for their ability to predict the El Niño–Southern Oscillation (ENSO). Using the principal component method, it is shown that the Global Atmospheric Oscillation (GAO), of which the ENSO is an element, is the main mode of interannual variability of planetary anomalies of surface air temperature (SAT) and atmospheric sea level pressure (SLP) in the ensemble of 50 CMIP6 models. It turns out that the CMIP6 ensemble of models reproduces the planetary structure of the GAO and its west–east dynamics with a period of approximately 3.7 years. The models showed that the GAO combines ENSO teleconnections with the tropics of the Indian and Atlantic Oceans, and with temperate and high latitudes. To predict strong El Niño and La Niña events, we used a predictor index (PGAO) obtained earlier from observation data and reanalyses. The predictive ability of the PGAO is based on the west–east propagation of planetary structures of SAT and SLP anomalies characteristic of the GAO. Those CMIP6 models have been found that reproduce well the west–east spread of the GAO, with El Niño and La Niña being phases of this process. Thanks to this, these events can be predicted with approximately a year’s lead time, thereby overcoming the so-called spring predictability barrier (SPB) of the ENSO. Thus, the influence of global anomalies of SAT and SLP on the ENSO is shown, taking into account that it may increase the reliability of the early forecast of El Niño and La Niña events. Full article

The article presents an analytical and experimental method for determining the dynamic coefficients of cutting tools, with particular emphasis on turning tools. The method involves aligning the acceleration profile obtained from empirical investigations with a mathematical model describing the oscillations of the cutting tool tip. The stiffness (k) and damping (c) coefficients determined using this approach enable the design of tools with desired dynamic characteristics, tailored to specific machining processes, such as machining with long overhangs. From the perspective of mechanical dynamics, selecting appropriate stiffness and damping values allows for the design of tools with optimal dynamic properties. High stiffness reduces the occurrence of deformations under external forces, while adequate damping facilitates the rapid attenuation of vibrations, thereby minimising their adverse effects on the machining process. The developed method could serve as a practical tool for identifying the dynamic parameters applicable to a wide variety of cutting tools. The analysis includes three types of turning tools: one with a steel shank, another with a carbide-core steel shank, and a third with a carbon fibre-core steel shank. The results of the tests indicate that the E-A20Q SDUCL 11 tool is best suited for operations requiring high stability and minimal vibration, owing to its favourable damping and stiffness properties. Full article