As terrestrial oil and gas resources continue to decline, deep-sea oil and gas development has become a strategic priority. A wide range of production equipment must be deployed on the seabed, among which subsea wet-mateable connectors are indispensable. To address the challenges of high pressure, low temperature, and corrosion in deep-sea environments, this study proposes a cooperative sealing strategy between the annular protrusion on the entry casing and a sliding sleeve. The leakage per single mate/demate cycle is quantified under varying insertion speeds and pressure differentials. By examining the effects of protrusion geometry, insertion speed, friction coefficient, and radial compression on sealing performance, the optimal parameters are identified: a friction coefficient of 0.15 and a trapezoidal-rib seal with 0.015 mm radial compression for dynamic sealing, yielding a contact pressure of 27.5 MPa and a mating/demating force of 197.26 N—satisfying the manipulation requirements of a remotely operated vehicle. Hydrostatic pressure tests demonstrate that the dynamic sealing design of the underwater connector achieves a balance between high reliability and low insertion resistance, and the prototype meets the operational requirements for deep-sea service.

The application fields of high-speed submersible permanent magnet synchronous motors (PMSM) are constantly expanding. Especially in high-risk and complex environments such as oil exploration, offshore oil exploitation, and deep well operation, the reliability, stability, and efficiency of motor drive systems are more and more prominent. The submersible motor is greatly affected by load disturbance, pressure change, and external oil flow, and the traditional method may not perform well in complex disturbance problems. Therefore, a three-order adaptive nonlinear extended state observer is proposed to collect the input and output information of the system in real time, and estimate the motor speed, position, and total disturbance. A linear feedback control law is designed to eliminate the disturbance. The superiority of the proposed algorithm under complex operating conditions is verified by the Simulink model and experiments, which provide a theoretical basis for the control of submersible motors.

Sentinel-3A and -3B satellite SAR altimeter wind speeds are routinely validated against moored buoys but increasingly benchmarked against ERA5 reanalysis when buoys are unavailable. We assess both reference choices over the Chinese nearshore seas using 14 months of matchups between satellite passes, moored meteorological buoys, and ERA5 wind fields. Against buoys, both altimeters show near-zero mean bias and a roughly flat error level across the wind-speed range. Against ERA5, the discrepancy grows strongly and monotonically with wind speed: the mean satellite-minus-ERA5 bias shifts from approximately −1.5 m/s in light wind to +1.4 m/s above Beaufort 6. Sentinel-3A tracks the buoy more closely than Sentinel-3B (r = 0.71 vs. 0.58), a gap that persists in the month-to-month RMSE record. Because the altimeter–buoy residual is flat, the wind-speed structure in the altimeter–ERA5 residual can be attributed to ERA5 rather than to the satellite retrieval. A compact quadratic fit to the altimeter–ERA5 residual, inverted to adjust ERA5 wind speed, removes essentially all of this wind-speed-dependent bias (per-bin mean bias reduced to within ±0.3 m/s), although the remaining scatter is set by representativeness differences that no bias model can remove. These results caution against uncorrected use of ERA5 as a stand-alone reference for altimeter evaluation in light-wind and extreme-wind regimes—over the semi-enclosed Chinese seas studied here, and more generally wherever sparse buoy coverage makes reanalysis the fallback reference for satellite wind validation.

The increasing demand for deep-sea drilling and the exploration of rock-hosted marine mineral resources has driven the development of seabed drilling systems with active control capabilities. A direct drive permanent magnet synchronous motor (PMSM) for seabed coring was designed to achieve low-speed high-torque operation, high efficiency, and low torque ripple. First, considering the limited installation space and operation requirements, six structural parameters, including stator slot depth, slot opening height, stator tooth width, air gap length, total effective core length, and pole arc coefficient, were selected as initial design variables. A fractional factorial design was employed to screen the significant design variables affecting motor efficiency and cogging torque. Subsequently, second-order response surface models were constructed to establish the nonlinear relationships between the design variables and optimization objectives. An NSGA-II algorithm with reference points is proposed to simultaneously maximize motor efficiency and minimize cogging torque. The optimization results demonstrate that the proposed method effectively improves the overall electromagnetic performance of the motor. Compared with the initial design, the motor efficiency was increased from 84.4583% to 86.7692%, while the cogging torque was reduced from 0.4952 N·m to 0.1711 N·m. A prototype motor was fabricated, and no-load, load, and torque ripple tests were performed to validate the optimized design.