The mass of a magnetic coupler increases with the output of its wireless power transfer system, limiting broader application of this technology. It is imperative to solve this trade-off between output power and coupler mass. Here, we present a high-power-density wireless power transfer system designed for autonomous underwater vehicles (AUVs) based on a variable ring-shaped magnetic coupler. A lightweight design is achieved through the system topology and magnetic coupler structure, and the system parameters are optimized and analyzed. Our magnetic coupler can eliminate the gap between the AUV and the platform when charging and fix the posture of the AUV to improve the system power output and stabilize the transmission process. An 800 W prototype was built, and manipulation of the variable ring-shaped magnetic coupler maintained the DC-DC transmission efficiency of the system at 86.4% and increased the output power by 69.47 W, or 9.1%. With these improvements, the system power density reached 1.6 W/g after using the variable ring-shaped magnetic coupler, realizing an increase of 9.6%. Experimental results validate the theoretical analysis and simulation outcomes to prove the effectiveness of this new method.

Combining wireless power transfer (WPT) technology with an underwater inclusive charging platform is an effective method to solve the problem of energy replenishment for autonomous underwater vehicles (AUVs). To ensure a stable charging state of the AUV at arbitrary positions, an antirotation flexible magnetic coupler (FMC) is proposed in this article. The transmitter structure can follow the retractable cage changes of the charging platform. Through the optimization analysis, the FMC, composed of a single-layer transmitter coil and a double-layer receiver coil and rotated 45° between the two layers of receiver coils, has excellent antirotation capability under 360° rotations. Moreover, the magnetic field of the FMC is evenly distributed and concentrated between the magnetic cores of the transmitter and receiver, causing little effect on the equipment inside the AUV. To address the coupling parameter variations due to AUV rotation and the transmitter contraction during FMC operation, soft switching of the WPT system is achieved by pulse density modulation and slight detuning of the resonator. An experimental prototype was established to verify the antirotation characteristics of the FMC as well as the soft-switching attributes of the system, and the experimental results matched well with the simulations.

When autonomous underwater vehicles (AUVs) replenish energy through wireless power transfer (WPT) technology on the underwater charging platform, there are practical issues such as excessive transmission gaps and unstable positioning. Additionally, the fixed size of the charging platform leads to insufficient compatibility. This paper proposes a high compatibility WPT system based on a reconfigurable magnetic coupler (RMC) for AUVs replenishing underwater energy. The transmitter of the RMC is combined with the charging platform cage and can follow the charging platform cage in radial dimensions. RMC can provide better coupling performance, and its necessity and effectiveness have been verified through finite element simulation. When the proposed high-compatibility charging platform supplies energy to AUVs of different sizes, the RMC will reconfigure its structure, leading to changes in the transmitter's self-inductance. To address this issue, a switch-controlled capacitor (SCC) method was incorporated into the system to achieve dynamic tuning. Finally, an experimental prototype was built to test the functionality and performance of the proposed RMC structure and SCC method. Compared to existing methods, this approach significantly enhances the practical application capabilities of WPT technology in underwater charging platforms and positively contributes to the cluster deployment of AUVs.

BACKGROUND: Unmanned Aerial Vehicles (UAVs) have created safety problems for the publics. Assessments of the mental workload for UAV operations are essential to realize the causes of UAV accidents. OBJECTIVE: To test the following hypotheses: i. mission difficulty in UAV operation affects both subjective and objective measures of mental workload; ii. mission difficulty affects number of failures in UAV operation. METHODS: Fourteen male adults participated as UAV operators after attending a UAV training course. They performed four flight missions of different difficulty levels. During their flight missions, their heart rate and inter-beat interval (IBI) were collected. Upon completing each flight mission, the participants gave subjective ratings of mental workload using three commonly adopted assessment tools. The time of flight and number of failures in flight operations were also recorded. RESULTS: The results showed that mission difficulty affected the scores of all three assessment tools significantly. Mission difficulty also affected number of failures and IBI significantly. The scores of the three assessment tools were highly correlated (ρ= 0.7 to 0.83, p < 0.001) with one another. The results of the three subjective ratings were also consistent with that of the IBI data. CONCLUSIONS: High mental workload in UAV operation could lead to poor flight performance.

Hydraulic actuators play an important role in various industries. In the last decades, to improve system performance, some advanced control methods have been developed. Backstepping control, which can deal with the system nonlinearities, is widely used in hydraulic system motion control. This paper focuses on the high-frequency position servo control of hydraulic systems with proportional valves. In backstepping controllers, valve dynamics are usually ignored due to difficulty of controller implementation. In this paper, valve dynamics of the proportional valve were decoupled into phase delay and amplitude delay. The valve dynamics are compensated without increasing the system order. The phase delay is compensated by desired engine valve lifts transformation. For amplitude delay, the paper proposes a compensation strategy based on the integral flow error. By introducing the feedback of the integral flow error to the backstepping controller, the system has faster dynamic responses. Besides, the controller also synthesized proportional valve dead-zone and system uncertainties. The comparative experiment results show that the controller with integral flow compensation can improve engine valve lift tracking precision both in steady and transient conditions.