This study considers the hydrodynamic characteristics of an AUV near uneven seabed. An improved hydrodynamic algorithm based on conformal mapping and boundary element method is proposed in this paper to improve the accuracy and efficiency of numerical computation. The proposed algorithm is validated by numerical examples. The effect of uneven seabed on the pressure distribution of hull surface is obtained. The improved algorithm is proved more efficient due to the avoidance of seabed boundary interception and dispersion.
Hydrodynamic performance of AUV plays an important role in AUV control and navigation, and has received interests of researchers in recent years (Kepler, et al. 2018; Abolvafaie, et al. 2018). The hydrodynamic model of AUV should be accurate enough to meet the requirement of motion simulation and control design. At present, the motion control design of AUV is normally based on the model in an unbounded water domain, which does not take the influence of boundary of the water domain into consideration. There is significant demand for AUVs working near seabed in military, scientific and industrial purposes, for example, underwater search and rescue (Sahoo, Dwivedy, and Robi, 2019), track oil-spill and gas leakage (Kimura, et al., 2013). There is a kind of AUV specially design for seabed application called Ocean Bottom Flying Nodes (OBFN) (Qin, 2018). Similarly, AUV missions in polar areas for scientific goals are widely reported (McPhail, 2019). Due to the complex flow around the AUV, the hydrodynamic characteristics of AUV near seabed (or ice shelf) has an obviously difference from that in unbound domains, which is an unfavorable factor for AUV stability, maneuvering control and positioning accuracy, limiting the development of subsea docking and recovery technology.
Many previous studies have investigated the hydrodynamic effect of vehicle moving near boundary of flow domain. Computational fluid dynamics is a popular approach for this problem. Du (2014) numerical simulated the hydrodynamics of an unmanned underwater vehicle (UUV) moving near flat seabed in by CFX. The lift force and pitching moment were solved in different distance and attack angle. Leong (2015) analyzed the hydrodynamic effect of an AUV operating near a submarine via CFD simulation. Mitra (2020) investigated the hydrodynamic characteristics of AUV over sloped channel-beds by Reynolds Stress Model (RSM) simulation and model experiments. Based on potential theory, Chen (2017) solved the added mass of an AUV near seabed by panel method.
