The hydrodynamic performance of a novel hovering autonomous underwater vehicle, the autonomous underwater helicopter (AUH), with an original disk-shaped hull (HG1) and an improved fore–aft asymmetric hull (HG3), is investigated by means of computational fluid dynamics with the adoption of overlapping mesh method. The hydrodynamic performance of the two hull shapes in surge motion with variation of the angle of attack is compared. The results show that HG3 has less resistance and higher motion stability compared to HG1. With the angle of attack reaching 10 degrees, both HG1 and HG3 achieve the maximum lift-to-drag ratio, which is higher for HG3 compared to HG1. Furthermore, based on the numerical simulation of the plane motion mechanism test (PMM) and according to Routh’s stability criterion, the horizontal movement and vertical movement stability indexes of HG1 and HG3 (${\mathrm{G}}_{\mathrm{H}}^{\mathrm{HG}1}=1.0$, ${\mathrm{G}}_{\mathrm{V}}^{\mathrm{HG}1}=49.7$, ${\mathrm{G}}_{\mathrm{H}}^{\mathrm{HG}2}=1.0$,${\mathrm{G}}_{\mathrm{V}}^{\mathrm{HG}3}=2.1$) are obtained, which further show that the AUH has better vertical movement stability than the torpedo-shaped AUV. Furthermore, the scale model tail velocity experiment indirectly shows that HG3 has better hydrodynamic performance than HG1.

The artificially submerged cavitation water jet is effectively utilized by ejecting a high-pressure water stream into a low-pressure water stream through concentric nozzles and utilizing the cavitation phenomenon generated by the shear layer formed between the two streams. In this study, we investigated the cavitation characteristics of artificially submerged cavitation water jets by combining numerical simulations and erosion experiments. The results indicate that an appropriate standoff distance can generate more cavitation clouds on the workpiece surface, and the erosion characteristics of the artificially submerged cavitation water jet are most pronounced at a dimensionless standoff distance of S_D = 30. The shear effect formed between the two jets plays a crucial role in generating initial cavitation bubbles within the flow field of the artificially submerged cavitation water jet. Moreover, increasing the convergent angle between the two jets can significantly enhance the cavitation effect between them and lead to a more substantial cavitation effect. Simultaneously, increasing the pressure of the high-pressure inner nozzle also contributes to enhancing the cavitation effect of the artificially submerged cavitation water jet.

In this study, a sediment isobaric transfer device based on the principle of volume displacement was built, and the work process of the device was explained. A physical model was built in hydraulic analysis software AMESim to simulate the actual working conditions. The influences of pre-charge pressure and volume of accumulator, diameter, and length of the hydraulic pipeline and opening pressure of safety valve on the pressure fluctuation and pressure steady-time during transfer process were studied. The transfer system was optimally designed based on the results of parametric analysis. The sea trial verified that the system could transfer sediment with a pressure exceeding 90 MPa into a culture vessel with low-pressure fluctuating pressure.