The contact mechanics model of the metal lens-type sealing gasket is established on the basis of Hertz theory on the macroscopical scale in this paper. The relationship among sealing width, contact pressure, and preload is solved. Based on the structural characteristics of the subsea collet connector, the self-locking characteristics are analyzed to determine the gain coefficient of the sealing structure for the loading thrust. On the microscopic scale, the contact characteristics of the turning lens-type sealing gasket and the hub structure are analyzed by the equivalent replacement of the peak cut coefficient of the one-dimensional sinusoidal wave. The influence of different leakage forms on sealing performance is discussed from both radial and circumferential leakage, and the leakage rate of the lens-type sealing structure is calculated. The hydrostatic pressure experiment of the subsea collet connector with lens-type sealing gasket is carried out, and the correctness of the theoretical analysis is verified from the results of the pressure maintaining, sealing width measurement, and preload conversion.

The mathematical model of the contact stress is established based on the theory of Hertz contact with the assumption that the contact of a seal gasket and hubs of collet connectors is cylindrical. The mechanical models of the seal are established separately by sealing theory in the preloading and operating modes, and the relationships between the preload, the contact stress, and the sealing width are obtained. The relationships of structural parameters and the preload are analyzed and verified with finite element simulation and experiments. An experimental system has been designed and experiments have been conducted to verify the analytical models. Finite element simulation results and experimental results agree with analytical ones very well and the differences of the preload and sealing width are acceptable.

In this study, an annular jet pump optimization method is proposed based on an RBF(Radial Basis Function) neural network model and NSGA-II(Non-Dominated Sorting Genetic Algorithm) optimization algorithm to improve the hydraulic performance of the annular jet pump applied in submarine trenching and dredging. Suction angle, diffusion angle, area ratio and flow ratio were selected as design variables. The computational fluid dynamics (CFD) model was used for numerical simulation to obtain the corresponding performance, and an accurate RBF neural network approximate model was established. Finally, the NSGA-II algorithm was selected to carry out multi-objective optimization and obtain the optimal design variable combination. The results show that the determination coefficient R2 of the two objective functions (jet pump efficiency and head ratio) of the approximate model of the RBF neural network were greater than 0.97. Compared with the original model, the optimized model's suction angle increased, and the diffusion angle, flow ratio and area ratio decreased. In terms of performance, the head ratio increased by 30.46% after the optimization of the jet pump, and efficiency increased slightly. The proposed jet pump performance optimization method provides a reference for improving the performance of other pumps.

Underwater oil and gas pipelines are prone to alignment differences and angle offsets during docking, and the spherical flange connector can address this problem. Its main function is to enable compensation of the different angles of the pipeline during docking and to apply a non-standard spherical sealing structure using O-rings to the connection. In this paper, the study of a spherical sealing structure using O-rings was based on a spherical structural model of the connector. The Mooney–Rivlin constitutive equation and material parameters of the O-ring were determined according to nonlinear theory. The structure of the non-standard spherical sealing groove was designed and analysed with reference to the standard sealing groove, the calculation expression of the spherical groove specific size was deduced, and the width and depth of the groove were determined. A finite element analysis of the non-standard O-ring sealing structure was carried out using ANSYS Workbench software; the effects of different pressures and compression ratios on the O-ring sealing performance were analysed and studied in terms of von Mises stress, contact pressure and contact width of different contact surfaces so as to determine a more reasonable compression ratio in the sealing structure. Finally, the theoretical analysis of the non-standard spherical sealing structure using O-rings was validated by testing, and it was proven that it could maintain a good seal under high pressure.

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