Nanocomposite films with cerium oxide (CeO₂) nanoparticles as functional fillers and polystyrene (PS) as polymer matrix were prepared using solution casting method. Physical properties including both weak frequency dependence of dielectric permittivity and low dielectric loss were experimentally discovered in the CeO₂/PS nanocomposite films. To improve the dielectric properties of films further, the surface of CeO₂ nanoparticles was treated by H₂O₂ to increase the homogeneity of the nanocomposite film, which was confirmed by scanning electron microscopy (SEM) results. Furthermore, it was found that both the filler size and the filler volume fraction played a role on the dielectric properties of the nanocomposite films.

Moving rapidly and agilely in high-pressure environment is a challenge for existing miniature underwater robots, which limits deeply the ocean exploitation. Here, we present a spherical underwater robot with diameter of 7 cm, and it has merits of miniature structure without bulky and antihydropressure devices, 3-DOFs agile motion, and good adaptability for 25 MPa environment simultaneously. Four designed piezoelectric double-jet actuators are embedded directly in the spherical shell without transmission mechanism, which enables the robot with relatively fast motion speed by compared with the published robots. Six motion modes are implemented by the cooperation of actuators, including rising, hovering, and sinking motions in the vertical direction and straight driving, turning, and in-situ turning motions in the horizontal plane. A robot prototype was fabricated, and its performance was tested. Experimental results indicated that the rising, straight driving, and in-situ turning speed reached up to 95.2 mm/s (1.36 BL/s), 99.6 mm/s (1.42 BL/s), and 5 rad/s, respectively. Besides, the robot could also rapidly turn at 1.3 rad/s with the turning radius of 22.1 mm. The speed deviation within 10% under different water pressures was obtained. The obstacle avoidance was successfully fulfilled by controlling the robot to pass through the narrow gap with width of only 1.5 body length of robot. There excellent characteristics demonstrate agile mobility and give the robot ability to move in the confined area of deep sea.

A transient-state numerical simulation is conducted to investigate the cavitation flow in the ball valve of a common rail (CR) injector. The computational fluid dynamics (CFD) software, employing the RANS turbulence model, is employed for this purpose. The study aims to analyze the characteristics and underlying causes of the uneven distribution of cavitation in the ball valve. The results reveal a significant occurrence of cavitation, exhibiting an uneven distribution along the walls of both the ball and the valve seat. Notably, the initiation position of the intense cavitation region on the wall of the ball is observed to lag behind that on the wall of the valve seat. The intense cavitation region on the wall of the ball is found to reside behind the sealing surface of the ball valve. The intense cavitation region on the wall of the ball is located behind the sealing surface of the ball valve. This region experiences flow separation caused by main flow detour, resulting in the formation of vortices that entrapped the cavitation cloud, thus fostering the development of intense cavitation. Conversely, the intense cavitation region on the wall of the valve seat originates from the entrance of the ball valve. This can be attributed to the sudden change in geometry at the entrance, leading to a significant pressure drop and inducing cavitation based on geometric factors. Furthermore, the stagnation effect caused by the ball exacerbates the discrepancy in the distribution of the intense cavitation region between the ball and the valve seat.

To improve the high-precision directivity of the GyroWheel (GW) during torque output, a composite-structured adaptive compensating method is proposed in this article, which achieves high frequency tilting flutter suppression of GW rotor. The composite structure includes adaptive seeking compensator and feedforward compensator. First, the tilting flutter of the fundamental frequency and twice frequency are equivalent to the periodic disturbance torques. The adaptive seeking algorithm is adopted to generate compensation signals of the same frequency and phase to reduce the flutter. Variable step size seeking method with threshold function can improve the convergence rate of the algorithm. Then, in the range of small tilting angle, an auxiliary feedforward compensator is designed according to GW disturbance torque model, which can improve the suppression rate of the twice frequency and avoid the influence of sensor noise. Finally, both numerical simulations and experiments have verified the effectiveness of the active tilting flutter suppression scheme, improving the stable torque output performance of GW as an actuator.