Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

Numerical Computation on Hydrodynamic Characteristic of AUV Near Uneven Seabed Based on
Schwarz-Christoffel Mapping
Zhiyuan Jiang1, Peng Li*,1,2, Hongde Qin1,2 and Yu Guo1
1. State Key Laboratory of Autonomous Underwater Vehicle, Harbin Engineering UniversityHarbin, Heilongjiang, China
2. Yantai Research Institute and Graduate School, Harbin Engineering UniversityYantai. Shandong, China

ABSTRACTThis 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 thispaper to improve the accuracy and efficiency of numerical computation.
The proposed algorithm is validated by numerical examples. The effectof uneven seabed on the pressure distribution of hull surface is obtained.
The improved algorithm is proved more efficient due to the avoidanceof seabed boundary interception and dispersion.

KEY WORDS: hydrodynamics; AUV; uneven seabed; conformalmapping; boundary element method.

INTRODUCTION
Hydrodynamic performance of AUV plays an important role in AUV
control and navigation, and has received interests of researchers inrecent years (Kepler, et al. 2018; Abolvafaie, et al. 2018). The
hydrodynamic model of AUV should be accurate enough to meet therequirement of motion simulation and control design. At present, themotion control design of AUV is normally based on the model in an
unbounded water domain, which does not take the influence ofboundary of the water domain into consideration. There is significant
demand for AUVs working near seabed in military, scientific andindustrial purposes, for example, underwater search and rescue (Sahoo,Dwivedy, and Robi, 2019), track oil-spill and gas leakage (Kimura, etal., 2013). There is a kind of AUV specially design for seabedapplication called Ocean Bottom Flying Nodes (OBFN) (Qin, 2018).
Similarly, AUV missions in polar areas for scientific goals are widelyreported (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 anunfavorable factor for AUV stability, maneuvering control andpositioning accuracy, limiting the development of subsea docking andrecovery technology.

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Many previous studies have investigated the hydrodynamic effect ofvehicle moving near boundary of flow domain. Computational fluid
dynamics is a popular approach for this problem. Du (2014) numericalsimulated 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 asubmarine via CFD simulation. Mitra (2020) investigated thehydrodynamic characteristics of AUV over sloped channel-beds byReynolds 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.
Bank effects of ships moving near a bank or in shallow water is aclassic problem. Relevant researches have reference value for theproblem on AUV. In regard to this problem, early researches aremainly based on experiments. Norrbin (1974) firstly carried out a seriesof model test on ships moving near side wall of a channel, and thelateral force and yawing moment were measured. Lataire (2009)
proposed a regression model for predicting bank effects based on theentire test program, and the regression model was extended to bank ofarbitrary shape (Lataire, et.al, 2018). A recent numerical researchdeveloped by Huang (2020) carried out a fast algorithm based on
potential flow theory for hydrodynamic computing of a shipmaneuvering in restricted waters and the sinkage and trim of the ship
are investigated through iteratively solving. It is notable that this able tointegrated in onboard computer systems for real-time computing.
However, there are a few research on the hydrodynamic characteristicof underwater near uneven seabed with complex shape. This problem
needs a further study.
This paper presents an improved numerical algorithm forhydrodynamic computation of an AUV moving near uneven seabed.
The proposed algorithm is validated by comparing with conventionalboundary element method (BEM) in test examples of unboundeddomain, flat seabed and step seabed. The influence of uneven seabed on
the pressure distribution of AUV surface is analyzed.