Abstract

Autonomous Underwater Vehicle (AUV) is an important tool for ocean exploration. However; due to the unstructured environment and difficulty in sensing; underwater missions of AUV always face various dangerous situations. Once an emergency accident occurs; AUV may bottom out and even be lost. Therefore; AUV security is an important topic. However; conventional AUV reliability analysis methods cannot well analyze the AUV autonomous system because of the complicated environment and working states. To this end; this paper establishes a set of security analysis framework using the System Theory Process Analysis (STPA) method for the AUV autonomous system. Taking the AUV bottom-following navigation as an example; the main steps include defining the research's purpose; establishing a control structure; identifying unsafe control behaviors; identifying cause scenarios; and forming security constraints. After identifying the cause scenarios; the linear-time temporal logic expressions were generated for security requirements by improving the conventional STPA causal scene analysis model. The AUV components failures were classified by combining the improved model with the classification of marine controller faults in the International Association of Classification Societies. Based on the emergency levels; final active emergency strategy actions include suspending the mission and waiting for recovery; stopping the mission to float up; stopping the mission; and load rejection to float up. Experiments were performed using real field test data; so the conclusion could be drawn that emergency response can be triggered in time when the AUV potential accidents were detected. The security and reliability of AUV can be improved through the STPA method and the active emergency strategy.

Introduction

Autonomous Underwater Vehicle (AUV) (Li and Tang; 2016) is a type of vehicle with a complex structure that can perform underwater missions. Nowadays; AUV is engaged in applications; such as hydrological data collection; seabed searching; rescuing; salvaging; subsea construction; and underwater structure inspection (Huang and Li; 2020). To make the AUV finish the mission satisfactorily and efficiently within the specified time; the AUV's security and reliability must be analyzed (Li; 2016) and scientifically evaluated.

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