Deep sea water (DSW) is a globally utilized source of renewable energy and other resources. To understand the characteristics of DSW resources in the South China Sea, in July 2022, the Guangzhou Marine Geological Survey (GMGS) investigated temperature, salinity, pH, dissolved oxygen (DO), inorganic salts (DIN, PO₄³⁻-P, and SiO3-Si), heavy metals (Hg, Pb, As, and Cd), trace elements (Cu, Zn, Fe, Mn, Ni, Se, and Mo), and other related indicators. The results of this investigation elucidate the horizontal and vertical changes in the physical and chemical properties of deep sea water in the Xisha Sea. The surface seawater quality in Xisha was found to be excellent and to meet first-class seawater survey standards. However, the concentrations of various nutrient salts in the surface layer were relatively low. As the seawater depth increased, different trace elements and heavy metals exhibited variations, and the concentrations of various nutrients also gradually increased.

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.