# Research on the Influence of Turbulent Flow Induced by Dunes on AUVs
###### Abstract  
The demand for oceanic resource exploration and development is increasing, and autonomous underwater vehicles (AUVs) have emerged as potential tools for ocean exploration. To meet specific operational requirements, AUVs are required to operate in close proximity to the seafloor. However, complex and changeable seafloor terrains have complex spatiotemporal characteristics, which produce unsteady hydrodynamic interference on AUVs, affecting their safety and stability. In order to investigate the hydrodynamic characteristics of AUVs in turbulent flow fields near seafloor terrains, this study selects a typical dune terrain. Based on the computational fluid dynamics (CFD) method, the flow field around an AUV near the seafloor is simulated, and the flow field is solved using the large eddy simulation (LES) method, calculating the AUV's hydrodynamic instantaneous and average characteristics, as well as flow field characteristics at different inflow velocities and distances from the seafloor. The results indicate that when the AUV is situated within the turbulent flow field caused by the terrain, its drag, lift, and pitch moment performance present significant fluctuations. Variations in total resistance are primarily caused by variations in pressure resistance. Variations in lift and pitch moment are more sensitive to variations in the flow field structure. The AUV also affects the development of the turbulent flow field near the terrain. When the AUV is in close proximity to the seafloor, it hampers the development of vortices below it. These results will offer guidance for the maneuverability and control of AUVs in practical engineering applications. A 2023 13 10273 10.3390/10/2023 1  
sensitive to them. Research by [PERSON] et al. [6] used computational fluid dynamics (CFD) to simulate submarine near-seafloor towing experiments, which revealed changes in submarine hydrodynamics and established linear relationships between certain hydrodynamic parameters and the ratio of submarine diameter to distance from the seafloor (\(D/H\)) and attack angle. They suggest that unmanned underwater vehicles (UUVs) traveling with small positive attack angles could counteract some of the seafloor suction effects. Building on this, [PERSON] et al. [7] studied the water dynamics of a submarine model (SUBOFF) near the seafloor and concluded that certain hydrodynamic components of submarine motion present good linear relationships with the square of the inverse dimensionless distance from the seafloor (\(D/H\))\({}^{2}\). Similarly, [PERSON] et al. [8] analyzed the impact of the seafloor on unmanned underwater vehicles (UUVs) and obtained a critical distance from the seafloor where UUVs are less affected by seafloor interference. [PERSON] et al. [3] extended these results by determining the distance from the wall where maximum resistance occurs and noting that in the limit of small wall distances, boundary layer flow induces a decrease in velocity and frictional resistance. [PERSON] et al. [9] conducted underwater vehicle zero-angle-of-attack towing experiments at different distances from the seafloor and concluded that interference from the seafloor can be neglected when the distance is greater than a quarter of the vehicle length. [PERSON] et al. [10] calculated additional mass for underwater helicopters near the seafloor using the panel method and established a linear relationship between additional mass and distance from the seafloor. [PERSON] et al. [11] analyzed the unsteady hydrodynamic interference between an underwater self-propelled AUV and the seafloor using the CFD method and reported the critical conditions under which the AUV was affected. In the above studies, the seafloor boundary is regarded as a flat wall, and the phenomena of increasing resistance and negative lift of underwater vehicles near the flat seafloor are mainly analyzed, as well as linear relationships between hydrodynamic parameters and cruising height and attack angle.