# Research on the Influence of Turbulent Flow Induced by Dunes on AUVs
## 4 Conclusions  
AUVs play an increasingly significant role in marine exploration. However, existing assessments of AUV maneuverability and navigation design often neglect unsteady hydrodynamic disturbances caused by the seafloor. In this study, an analysis of the hydrodynamic performance of AUVs in turbulent flow fields generated by underwater dunes was conducted. The AUV was placed about 3 m from the crest of the dune. Using the  
Figure 23: Comparison between the average pressures on the upper and lower sides in the longitudinal section of the AUV in the center plane at different near-seafloor distances; \(u=1.5\) m/s: (**a**) \(H/D=1.5\); (**b**) \(H/D=2.5\); (**c**) \(H/D=3.5\); (**d**) \(H/D=4.5\); and (**e**) \(H/D=5.5\).  
LES method, the hydrodynamic characteristics of the AUV and flow field variations were investigated under different flow velocities and near-seafloor distances. The results of this study include the following. In turbulent flow fields, the hydrodynamic coefficients of the AUV present fluctuations within a certain range, which become more pronounced with increasing flow velocity. In the range studied in this paper, the amplitude of the curve fluctuation in the hydrodynamic coefficient can reach about 2-8 times its mean value. Among these coefficients, the variation in the pressure resistance coefficient predominantly affects the total resistance coefficient. The friction resistance coefficient of the AUV presents relatively minor fluctuations under different flow velocities and is less affected by turbulent flow fields. The lift coefficient and pitch moment coefficient are more sensitive to variations in the turbulent flow field, with higher flow velocities resulting in more pronounced changes. As the distance between the AUV and the seafloor increases, the fluctuations in the hydrodynamic coefficients gradually diminish, particularly for the resistance coefficient. Overall, when \(H/D>5.5\), the AUV moves away from the region of the flow field where turbulence is significant, and the influence of turbulence on the hydrodynamic performance of the AUV becomes negligible. Regarding the frictional drag, it remains relatively stable when \(H/D>1.5\). Additionally, when \(H/D<1.5\), the AUV hampers the formation of vortices below it.  
In summary, the hydrodynamic performance of AUVs in turbulent flow fields caused by the underwater dune is influenced by the constantly changing flow field structure. This effect is particularly pronounced in high flow velocity conditions and when the AUV is situated closer to the seafloor. While this study provides an exploration of the hydrodynamic performance of AUVs in underwater dune terrain, further experimental validation and engineering applications are required. Future research can combine real-world scenarios to optimize AUV design and control strategies, adapting them to complex seafloor environments.  
Conceptualization, Y.G. and P.L.; methodology, Y.G. and P.L.; validation, Y.G.; formal analysis, Y.G. and P.L.; investigation, Y.G. and P.L.; resources, H.Q.; data curation, Y.G.; writing--original draft preparation, Y.G.; writing--review and editing, Y.G. and P.L.; visualization, Y.G., Z.L. and J.G.; funding acquisition, P.L. All authors have read and agreed to the published version of the manuscript.  
This work was funded by the National Natural Science Foundation of China, grant number 52231011), the Research Fund from Stable Supporting Fund of Science and Technology on Underwater Vehicle Technology, grant number JCKYS2022 SXJQR-11, and the \"Chunhui Project\" Cooperative Scientific Research Foundation of Ministry of Education of China, grant number 202200288.  
Not applicable.  
Data available in a publicly accessible repository.  
The authors declare no conflict of interest.