Underwater glider is a low-energy and buoyancy-driven exploration robot that is used in long-term ocean exploration tasks, such as anticyclonic eddy observations, marine noise detection, and biogeochemical analyses. To enhance its overall performance, multidisciplinary optimization during the design and application phases is crucial. An effective method for enhancing hydrodynamic performance involves optimizing the surface micromorphology of underwater vehicles. Drawing inspiration from this micromorphology design concept, this paper conducts a multiobjective design optimization of the riblet parameters on the wing surface of an underwater glider to enhance its overall performance.

This study begins with the "Petrel-Ⅱ" underwater glider prototype, proposing an initial riblet design scheme based on the movement characteristics of the underwater glider. Subsequently, a computational fluid dynamics simulation model of the entire glider was developed. An optimized Latin hypercube experimental design was used to obtain sample riblet parameters and attack angles, followed by computational fluid dynamics simulations under various operating conditions. Hydrodynamic equations, including riblet parameters, were established through polynomial fitting and computational fluid dynamics results. These hydrodynamic equations were integrated into the dynamic model of the glider, allowing for a comprehensive dynamic analysis that includes riblet effects. Using the entire vehicle dynamic model, a theoretical derivation of the underwater glider's speed, static stability, and energy consumption evaluation was achieved, enabling a quantitative and comprehensive performance analysis. A surrogate model for performance evaluation was established using optimized Latin hypercube experimental designs, dynamic simulations, and performance models, considerably improving computational efficiency. The optimization objective function for the riblet parameters of the wing surface was determined. Riblet spacing, depth, and direction were selected as optimization design variables. The surrogate model and second-generation nondominated sorting genetic algorithm were used for optimization calculations. The optimization aimed to simultaneously improve the horizontal speed, vertical speed, energy efficiency, and static stability of the underwater glider. As a result, four single-objective optimal solutions and one multiobjective compromise solution were obtained, leading to the final riblet design scheme.

Numerical examples demonstrate that the smaller direction and the larger depth of the riblet can effectively and simultaneously improve the glider's speed, static stability, and energy efficiency. The effect of riblet spacing on the glider's performance indicators shows certain contradictory and nonlinear characteristics. Compared with the performance analysis result of the glider without riblet on the wing surface, the optimization result considerably enhances the glider's overall performance, proving the effectiveness of the proposed design method. In addition, 3D printing technology was used to produce a prototype of the wing. The surface of the obtained wing prototype is smooth, with the clear and undeformed riblet profile, which confirms the machinability of the riblet-enhanced surface.

The riblet on the wing surface can effectively improve the underwater glider's overall performance, and the proposed optimization method can make the above improvement more significant. This research provides theoretical guidance and a reference for the actual optimization design of underwater gliders. The next step is to consider improving the micromorphology of the hull's surface to further enhance the glider's overall performance and carrying out the corresponding parameter optimization.