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

An Artificial Potential Field Model for the Risk Assessment of Icebreaker Escort Operations
2

Jiru Han1,2, Di Zhang2,3, Da Wu1,2,3, Wengang Mao4Intelligent Transportation Systems Research Center, Wuhan University of Technology, Wuhan, China
National Engineering Research Center for Water Transport Safety, Wuhan University of Technology, Wuhan, China
3
Inland Port and Shipping Industry Research Co., Ltd. of Guangdong Province, Guangdong, China
4
Department of Mechanics and Maritime Sciences, Chalmers University of Technology, Gothenburg, Sweden
1ABSTRACTThe artificial potential field (APF) was first proposed by (Khatib, 1985),
which is widely used in the study of robot obstacle avoidance becauseof perceptual intuition and easy-to-understand. The method is also
commonly used for vehicle collision avoidance studies. In the APF
theory, the risk factors around the target can be regarded as different
potential energy fields, which will affect target states and behaviors.
(Xue et al., 2011) proposed an algorithm based on APF for routefinding and collision avoidance of ships in possible collision situations.
(Lu et al., 2018) presented a real-time and deterministic route planning
for autonomous ships based on APF and the International Regulations
for Preventing Collisions at Sea (COLREGs). (Wang et al., 2016)
proposed the driving safety field to represent the influences of thedriver-vehicle-road factors on driving safety and proved the feasibilityof using APF for risk assessment.

The icebreaker escort operations are typical navigation models in
Arctic shipping. The current studies mainly focus on analyzing andquantifying the ship navigation risk for icebreaker escort operations
concerning ship-to-ship collision avoidance. However, scenarios ofship stuck in sea ice are also interested and lacking study. To this end,
we proposed a risk assessment model based on the artificial potential
field theory, including two parts: a) the icebreaker risk field and b) thesea ice risk field. The icebreaker risk field describes the ship-to-ship
collision risk, while the sea ice risk field describes the risk of ships
stuck in sea ice. The proposed model can determine fleet members’
minimum and maximum safety distances to enhance the safety ofArctic fleet shipping.

This paper focuses on the risk assessment of ship-to-ship collision, andthe ship stuck in sea ice under icebreaker escort operations. We
proposed a new model based on APF theory, i.e., the ship navigation
risk field model, to analyze and quantify the ship, sea ice, and theirinteractions in the fleet system. Furthermore, a method based on theproposed model is developed to obtain the safety distance illustrating
the ship following behavior under icebreaker assistance.

KEY WORDS: artificial potential field, polar navigation, icebreakerescort operations, navigation risk, safey distance

INTRODUCTION
Recently, navigation in Arctic waters is gradually improved along with
the increased melting of the sea ice. Ships that navigate in Arctic waters
can greatly shorten the voyage distance and reduce costs. Nevertheless,
Arctic shipping is still full of challenges and risks with harshenvironments, such as remoteness, complex ice condition, low visibility,and low air temperature (Fu et al., 2018). Because of this, low ice-classships mainly rely on icebreaker escort and convoy operations in icecovered waters and form a fleet system for security and economy.
Icebreaker escort opertaions are that the icebreaker breaks a channel,
and one assisted ship follow it at a certain safety distance. Icebreakerconvoy operations are similar to icebreaker escort operations but withseveral assisted ships following the icebreaker(Goerlandt et al., 2017).

THE SHIP NAVIGATION RISK FIELD
This section proposes a new concept of the ship navigation risk field for
icebreaker escort operations based on the APF theory to describe thepotential navigation risk in actual scenarios due to risk influence factors(RIFs). Each RIF generates a risk field to denotes the influence of it onnavigation safety. The ship navigation risk field for icebreaker escort
operations is shown in Fig. 1. The x-axis in the figure is the position of
the ship and sea ice. The y-axis is the risk field strength. The shaded
areas are potential energies of the assisted ship. The icebreaker risk
field and sea ice risk field connsist the ship navigation risk field.

The main risks of icebreaker escort and convoy operations are theuncertainty of safety speed and distance between ships, resulting inaccidents. Recently, many scholars employed ship-following theory(Zhang et al., 2017, 2018, 2019) to study the safety distance and speed
between ships under icebreaker assistance. Most researches focus on
the safety distance to avoid the ship-to-ship collision (Zhang et al.,2017, 2018, 2019, Khan et al., 2019). However, there is a lack of studyon the accident scenarios of the ship stuck in sea ice.

The icebreaker risk field denotes the influence of the icebreaker on theassisted ship navigation safety. The icebreaker attributes determine themagnitude and direction of its field strength. The sea ice risk field
denotes the influence of the sea ice on the navigation safety. The sea ice
concertation determines the magnitude and direction of its fieldstrength.

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