Journal of
Marine Science
and Engineering
Article
Collision Avoidance Algorithm Based on COLREGs for
Unmanned Surface Vehicle
Hyo-Gon Kim 1 , Sung-Jo Yun 1 , Young-Ho Choi 1 , Jae-Kwan Ryu 2 and Jin-Ho Suh 3, *
1
2
3
*
Intelligent Robotics R&D Division, Korea Institute of Robotics and Technology Convergence,
Pohang 37666, Korea; hgkim@kiro.re.kr (H.-G.K.); yunsj@kiro.re.kr (S.-J.Y.); rockboy@kiro.re.kr (Y.-H.C.)
Unmanned/Intelligent Robotic Systems R&D, LIG Nex1, Seongnam 13488, Korea; jaek-wan.ryu@lignex1.com
Department of Mechanical System Engineering, Pukyoung National University, Busan 48513, Korea
Correspondence: suhgang@pknu.ac.kr; Tel.: +82-51-629-6189
Abstract: Recently, unmanned surface vehicles (USV) are being actively developed. For USVs to be
put to practical use, it is necessary to secure safety by preventing collisions with general ships. To this
end, USVs must avoid opposing vessels based on international regulations for preventing collisions at
sea (COLREGs, 1972). This paper proposes an algorithm for USVs to avoid collisions with opposing
vessels based on COLREG rules. The proposed algorithm predicts dangerous situations based on
distance to closest point of approach (DCPA) and time to closest point of approach (TCPA). It allows
USVs to avoid opponent ships based on the dynamic window approach (DWA). The DWA has been
improved to comply with COLREGs, and we implemented a simulation and compared the standard
DWA with the COLREG-compliant DWA (CCDWA) proposed in this paper. The results confirm that
the CCDWA complies with COLREGs.
Keywords: unmanned surface vehicle; autonomous navigation; dynamic window approach;
COLREGs
Citation: Kim, H.-G.; Yun, S.-J.; Choi,
Y.-H.; Ryu, J.-K.; Suh, J.-H. Collision
Avoidance Algorithm Based on
1. Introduction
COLREGs for Unmanned Surface
An unmanned surface vehicle (USV) refers to a surface vehicle that can be remotely
controlled or operated autonomously. There is growing demand for USVs to replace
manned vessels in hazardous areas such as conflict or disaster zones. In particular, the
necessity of developing USVs for military use has been greatly emphasized, and LIG
Nex10 s sea sword was developed in Korea. Spartan Scout USV, ASW USV, and UISS of the
US, C-Sweep of the UK, Mk2 of France, Dolphin of Canada, and Protector of Israel were
also developed [1,2].
USVs must be able to recognize their current position, control the thrusters to move
autonomously to the destination, and recognize and avoid static and dynamic obstacles
during movement [3–6].
For USVs to autonomously navigate safely to their destinations while avoiding static
and dynamic obstacles, it is necessary to first plan a path from current location to destination. The path plan can be divided into global and local path plans. The global path plan
involves the entire travel route to the destination based on the environment map given before the USV departs for the destination; the local path plan involves safe avoidance paths
that do not greatly deviate from the global path plan, allowing USVs to avoid unexpected
obstacles [7]. The A* algorithm and rapidly-exploring Random Tree (RRT) algorithm are
representative global path planning algorithms; the virtual force field (VFF) and vector
field histogram (VFH) algorithms are local path planning algorithms.
The dynamic window approach (DWA) is used for local route planning and is a
destination tracking algorithm that can avoid collisions by reflecting the dynamic state of
the USV. The DWA can be applied via fusion with the global path control algorithm [8,9].
DWA is an algorithm that, by deriving the optimal linear velocity and angular velocity
and evaluating the direction, velocity, and distance to the obstacle based on the object
Vehicle. J. Mar. Sci. Eng. 2021, 9, 863.
https://doi.org/10.3390/jmse9080863
Academic Editor: Alessandro Ridolfi
Received: 30 June 2021
Accepted: 2 August 2021
Published: 11 August 2021
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with regard to jurisdictional claims in
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Copyright: © 2021 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
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4.0/).
J. Mar. Sci. Eng. 2021, 9, 863. https://doi.org/10.3390/jmse9080863
https://www.mdpi.com/journal/jmse
J. Mar. Sci. Eng. 2021, 9, x FOR PEER REVIEW
J. Mar. Sci. Eng. 2021, 9, 863
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DWA is an algorithm that, by deriving the optimal linear velocity and angular veloc2 of 10
ity and evaluating the direction, velocity, and distance to the obstacle based on the object
function allows the USV to avoid obstacles and arrive at the destination. In addition, the
DWA is a flexible local path control technique that can derive the desired result by adding
an
optimal
condition
to thetoobject
Through
previous
the path
trackfunction
allows
the USV
avoidfunction.
obstacles
and arrive
at thestudies,
destination.
Inline
addition,
ing
performance
was
confirmed
by
adding
a
term
for
tracking
the
path
line
to
the
object
the DWA is a flexible local path control technique that can derive the desired result by
function
[9].
However,
standard
DWAs
dofunction.
not take Through
into account
the COLREG
rules,
so
adding an
optimal
condition
to the
object
previous
studies, the
path
using
DWAs
to
avoid
obstacles
can
create
dangerous
situations.
line tracking performance was confirmed by adding a term for tracking the path line to the
this paper,
we propose
a supplemented
DWA
comply
with COLREG
objectInfunction
[9]. However,
standard
DWAs do not
takethat
intocan
account
the COLREG
rules,
rules.
This
papertofirst
describes
thecan
standard
DWA and situations.
then the proposes the COLREGso using
DWAs
avoid
obstacles
create dangerous
compliant
implementing DWA
a simulation,
was
In thisDWA
paper,(CCDWA).
we proposeBy
a supplemented
that cancomparison
comply withverification
COLREG rules.
performed
between
the standard
DWA
andand
the then
CCDWA.
This paper first
describes
the standard
DWA
the proposes the COLREG-compliant
DWA (CCDWA). By implementing a simulation, comparison verification was performed
2.
Dynamic
between
theWindow
standard Approach
DWA and the CCDWA.
We applied the DWA as a local pass plan to avoid opposing vessels. The DWA cre2. Dynamic
Window
Approach
ates
a dynamic
window
representing the range of linear and angular velocities that can
We
applied
the
DWA
a local
pass plan
vessels.
Thepairs
DWAofcreates
be output from the currentasship’s
velocity
for to
theavoid
next opposing
time. Then,
from the
linear
a
dynamic
window
representing
the
range
of
linear
and
angular
velocities
canthe
be
velocity (v) and angular velocity (ω) in the dynamic window, the algorithmthat
selects
output
from
the
current
ship’s
velocity
for
the
next
time.
Then,
from
the
pairs
of
linear
pair that maximizes the value of the object function.
velocity
and angular
velocity
(ω)expressed
in the dynamic
window,
the algorithm
selects
the pair
The(v)
dynamic
window
can be
as shown
in Figure
1 [8,9]. The
vertical
and
that
maximizes
the
value
of
the
object
function.
horizontal axes represent the linear and angular velocities. Vs indicates the range of linear
The dynamic
window
can
be expressed
in Figure 1 [8,9]. The vertical and
d is the area from the minimum velocity
and angular
velocity
that the
ship
can output.asVshown
horizontal
axes
represent
the
linear
and
angular
velocities.
Vsnext
indicates
of linear
to the maximum velocity that the ship can output until the
time; the
it isrange
expressed
by
and
angular
velocity
that
the
ship
can
output.
V
is
the
area
from
the
minimum
velocity
d
Equation (1). The maximum acceleration and deceleration
specifications of the vessel
can
to the
maximum
that
the ship
be
reflected
in thevelocity
algorithm
through
Vdcan
[8,9].output until the next time; it is expressed by
Equation (1). The maximum acceleration and deceleration specifications of the vessel can
𝑣, ω | 𝑣 ∈
+ 𝑣 ∆t,
𝑣+𝑣
∆t ,
𝑉 =through
be reflected in the algorithm
Vd 𝑣[8,9].
(1)
∆t,
.
. ω
.
ω∈ ω+
ω + ω . ∆t
Vd = v, ω v ∈ v + vmin ∆t, v + vmax ∆t , ω ∈ ω + ω min ∆t, ω + ω max ∆t
(1)
Figure 1. Dynamic
window
(The window
composition
meaning and
of the
picture of
arethe
similar
to are
[8,9]).
Figure
1. Dynamic
(Theand
composition
meaning
picture
similar to [8,9]).
Vrr isisthe
thearea
areaexcluding
excludingthe
thearea
areacolliding
collidingwith
withthe
theobstacle
obstacleininthe
theVV
This
area
V
d area.
This
area
is
d area.
is the
input
range
velocitycontrol
controlthat
thatallows
allowssafe
safemovement
movementin
inaa range
range in which the
the
input
range
forforvelocity
vehicle can
can accelerate
accelerate and
vehicle
and decelerate
decelerate from
from the
the current
current velocity
velocity [8,9].
[8,9].
Vr 𝑉==Vs𝑉∩∩V𝑉
a ∩∩V𝑉
d
(2)
The
DWA is
is written
written as
as Equation
Equation (3).
(3).
The objective
objective function
function of
of the
the standard
standard DWA
G (v, ω ) = α × heading(v, ω ) + β × distance(v, ω ) + γ × velocity(v, ω )
where v and ω represent the linear and angular velocity within the dynamic window.
(3)
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α, β, and γ are weighting factors. By adjusting these parameters, we can tune the
propensity of the USV to head to the GOAL, avoid obstacles, and run quickly.
The velocity (v, ω) term is the vessel’s speed, the heading (v, ω) term is the heading to
the target after ∆t time, and the distance (v, ω) term is the distance from the ship’s position
to the obstacle after ∆t time.
By substituting the v, ω pair in the dynamic window into the objective function, the v,
ω pair with the largest objective function value is selected as the control input value [8,9].
For the velocity term, the highest value is selected within the velocity range of the dynamic
window, as in Equation (1).
At positions x, y, θ, when the ship moves with v, ω, the positions x0 , y0 , θ 0 after ∆t time
can be defined as Equation (4) [9].
 0  
 
 

x
xc + ωv sin(θ + ω ·∆t)
x
− ωv sin θ + ωv sin(θ + ω ·∆t)
 y0  =  yc − v cos(θ + ω ·∆t) =  y  +  v cos θ − v cos(θ + ω ·∆t) 
(4)
ω
ω
ω
θ0
θ + ω ·∆t
θ
ω ·∆t
When the angular velocity is 0, the position of the ship according to the linear velocity
is defined as Equation (5) [9].
 
 

x0
x
v·∆t·cosθ
 y0  =  y  +  v·∆t·sinθ 
θ0
θ
0

(5)
At positions x0 , y0 , θ 0 , the heading (v, ω) and distance (v, ω) terms of the objective
function are calculated. The distance from position x0 , y0 to position xob , yob of the other
ship can be expressed as Equation (6) in consideration of the safety distance r [9].
distance(v, ω ) =
q
( xob − x 0 )2 + (yob − y0 )2 − r
(6)
In this way, the standard DWA selects linear and angular velocities at which collision
avoidance is possible based on the relationship between the position of our own vessel and
the position of the other vessel.
3. COLREG-Compliant DWA (CCDWA)
For the USV to be put to practical use, it is necessary to secure safety by preventing
collisions with general ships. To this end, USVs are required to evade opposing vessels
under the COLREG rules and to avoid creating danger to other vessels.
Figure 2 shows the four main scenarios of COLREGs. The first scenario is a head-on
situation. When two power-driven vessels meet on reciprocal or nearly reciprocal courses,
each shall alter her course to starboard so that each shall pass on the port side of the other
(Rule 14).
The second and third scenarios are crossing situations. When two power-driven
vessels cross, the vessel that has the other on her own starboard side shall keep out of the
way and shall, if the circumstances of the case admit, avoid crossing ahead of the other
vessel (Rule 15). In other words, the USV shall give way in crossing when a dynamic
obstacle approaches from the starboard side (second scenario). In addition, the USV shall
keep course and speed in crossing when the dynamic obstacle approaches from the port
side (third scenario).
The fourth scenario is an overtaking situation. Any vessel overtaking any other shall
keep out of the way of the vessel being overtaken (Rule 13) [10,11].
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. Mar. Sci. Eng. 2021, 9, x FOR PEER REVIEW
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Figure 2. Main COLREG scenarios (the keywords in [10] was used; the composition and meaning
of the picture are similar to [11,12]).
The second and third scenarios are crossing situations. When two power-driven vessels cross, the vessel that has the other on her own starboard side shall keep out of the
way and shall, if the circumstances of the case admit, avoid crossing ahead of the other
vessel (Rule 15). In other words, the USV shall give way in crossing when a dynamic obstacle approaches from the starboard side (second scenario). In addition, the USV shall
keep course and speed in crossing when the dynamic obstacle approaches from the port
side (third scenario).
fourth
scenario
is an overtaking
situation.
Anywas
vessel
overtaking
any otherand
shall
2.The
Main
COLREG
(the
keywords
[10]
used;
the
meaning
Figure 2. Main COLREGFigure
scenarios
(the
keywords
in [10]scenarios
was used; the
composition
andin
meaning
of the
picture
arecomposition
similar to [11,12]).
keep out of the way of the vessel being overtaken (Rule 13) [10,11].
of the picture are similar to [11,12]).
To
To apply
apply COLREGs,
COLREGs, it
it is
is necessary
necessary to
to know
know where
where the
the other
other ship
ship is
is located
located in
in relation
relation
to
to our
our own
own ship.
ship. Figure
Figure 33 provides
provides aa diagram
diagram that
that shows
shows the
the position
position of
of the
the other
other ship
ship
The second
and third
scenarios areto
crossing
situations.
When two power-driven
vesrelative
relative to
to our
our own
own ship
ship [12].
[12]. According
According to the
the locations
locations of
of head-on,
head-on, starboard,
starboard, port,
port, and
and
sels stern,
cross,situations
the vessel
that
has the
other oncrossing
her own
starboard
side shall
keep
out of the
can
from
stern, situations
can correspond
correspond to
to head-on,
head-on, crossing
from the
the right,
right,crossing
crossing from
from the
theleft,
left,
wayand
and
shall, if scenarios
the
circumstances
the case
admit, respectively.
avoid
crossing ahead of the other
overtaking
of
COLREGs
scenarios,
and
overtaking
scenarios
of the
the main
main of
COLREGs
scenarios,
respectively.
vessel (Rule 15). In other words, the USV shall give way in crossing when a dynamic obstacle approaches from the starboard side (second scenario). In addition, the USV shall
keep course and speed in crossing when the dynamic obstacle approaches from the port
side (third scenario).
The fourth scenario is an overtaking situation. Any vessel overtaking any other shall
keep out of the way of the vessel being overtaken (Rule 13) [10,11].
To apply COLREGs, it is necessary to know where the other ship is located in relation
to our own ship. Figure 3 provides a diagram that shows the position of the other ship
relative to our own ship [12]. According to the locations of head-on, starboard, port, and
stern, situations can correspond to head-on, crossing from the right, crossing from the left
and overtaking scenarios of the main COLREGs scenarios, respectively.
Figure 3. Diagram showing position of other ship relative to our own ship.
Figure 3. Diagram showing position of other ship relative to our own ship.
In the typical vessel interaction, shown in Figure 4, TCPA and DCPA for the position of
our own ship (xo , yo ) and the position of the other ship (xt , yt ) are expressed by Equations (7)
and (8), respectively [13]. If TCPA is positive, ships are approaching. In addition, if DCPA
is less than the safe distance, the ships are in a dangerous situation.
.
. .
. − (yt − yo ) yt − yo + ( xt − xo ) x t − x o
TCPA =
(7)
.
. 2
.
. 2
yt − yo + x t − x o
q
DCPA =
2 2
.
. .
. (yt − yo ) + yt − yo × TCPA + ( xt − xo ) + x t − x o × TCPA
(8)
DCPA =
J. Mar. Sci. Eng. 2021, 9, 863
(𝑦 − 𝑦 ) + (𝑦 − 𝑦 ) × 𝑇𝐶𝑃𝐴
+ (𝑥 − 𝑥 ) + (𝑥 − 𝑥 ) × 𝑇𝐶𝑃𝐴
(8)
At this point, Figure 3 is referenced to determine which COLREG scenario is appro5 of 10
priate for the situation, and our own ship must get out of the dangerous situation by following COLREGs through obstacle avoidance control.
Figure
Typical vessel
The
composition
of similar.to
the picture[13].
are similar.to [13].
Figure 4. Typical
vessel4.interaction.
Theinteraction.
composition
and
meaning ofand
the meaning
picture are
At
point,
Figure 3 issituation,
referenced
to determine
whichships
COLREG
scenarioaway
is appropriIn this
a vessel
avoidance
if TCPA
is negative,
are moving
and are
ate
for
the
situation,
and
our
own
ship
must
get
out
of
the
dangerous
situation
by
out of danger, so the vessel should stop its avoidance movements and continuefollowing
the existCOLREGs
through
obstacle
avoidance
control.
ing voyage.
The flow
chart of
USV control,
including the above process, is shown in Figure
In a vessel avoidance situation, if TCPA is negative, ships are moving away and are
5.
out of danger, so the vessel should stop its avoidance movements and continue the
existing
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11
In this paper, the DWA is selected for obstacle avoidance control. To6 of
apply
the
voyage. The flow chart of USV control, including the above process, is shown in Figure 5.
COLREG rules to the DWA, we propose to divide the dynamic window into two regions,
left and right, as shown in Figure 6a. To change the course of our own ship to starboard,
we deactivate the left area of the dynamic window. On the other hand, to change the
course of our own ship to port, the right area of the dynamic window is deactivated.
5. Flowchart
of USV control.
Figure 5. Figure
Flowchart
of USV control.
In this paper, the DWA is selected for obstacle avoidance control. To apply the
COLREG rules to the DWA, we propose to divide the dynamic window into two regions,
left and right, as shown in Figure 6a. To change the course of our own ship to starboard, we
deactivate the left area of the dynamic window. On the other hand, to change the course of
our own ship to port, the right area of the dynamic window is deactivated.
J. Mar. Sci. Eng. 2021, 9, 863
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Figure 5. Flowchart of USV control.
(a) Normal dynamic window
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(b) Disable the left area of the dynamic window
(c) Disable the right area of the dynamic window
Figure 6. window.
Modified dynamic window.
Figure 6. Modified dynamic
In the
dynamic
window
region,
the vthe
and
ω values
that cause
the objective
Inactive
the active
dynamic
window
region,
v and
ω values
that cause
the objective
function to reach its highest value are derived. In this way, an avoidance movement that
function to reach its highest value are derived. In this way, an avoidance movement that
satisfies the COLREG rules is made using the derived v and ω. For example, in ahead-on
satisfies
COLREG
rules
is made
derived
and ω. For
example,
in ahead-on
situation,
ourthe
own
ship must
turn
to theusing
right the
to avoid
thev obstacle
ship.
Therefore,
the
situation,
our own
turn
the rightwindow,
to avoidasthe
obstacle
ship. Therefore,
CCDWA
deactivates
theship
left must
area of
thetodynamic
shown
in Figure
6b. Our the
leftthe
area
of the
dynamic
window,
as shown
inactive
Figure
6b. Our
own CCDWA
ship turnsdeactivates
to the rightthe
using
v and
ω derived
through
the DWA
in the
right
ship turns
to theOn
right
v and
ω our
derived
through
themove
DWA
area own
of dynamic
window.
theusing
other the
hand,
when
own ship
has to
toin
thethe
leftactive
to avoid
ship, the CCDWA
rightwhen
area our
of the
dynamic
window,
rightobstacle
area of dynamic
window. deactivates
On the otherthe
hand,
own
ship has
to moveasto the
shown
leftintoFigure
avoid 6c.
obstacle ship, the CCDWA deactivates the right area of the dynamic window,
as shown in Figure 6c.
4. Simulation and Analysis
Simulation was performed to compare the CCDWA proposed in this paper and the
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4. Simulation and Analysis
Simulation was performed to compare the CCDWA proposed in this paper and the
standard DWA, and to verify the performance of the CCDWA. The standard DWA, the
CCDWA, and the simulation environment were implemented in C# programming language.
Table 1 shows the parameters of the standard DWA and the CCDWA. The weighting factors
α, β, and γ were set to 0.25, 0.5, and 0.25 values. By substituting the v, ω pair in the
dynamic window defined by Table 1 into the objective function including the weighting
factor, the v, ω pair with the largest objective function value is selected as the control
input value. The selected v and ω do not exceed the maximum velocity value. The ship’s
position x0 , y0 after ∆t time according to the speed was calculated and updated through
Equations (4) and (5). In addition, the algorithm operation pattern according to the passage
of time was confirmed.
Table 1. Parameters for DWA and CCDWA.
Parameter
Value
Maximum linear velocity
10 m/s
Minimum linear velocity
0 m/s
Maximum linear acceleration
±2 m/s2
Maximum angular velocity
±25 deg/s
Maximum angular acceleration
±5 deg/s2
α
0.25
β
0.5
γ
0.25
Figures 7 and 8 show the progress of the simulation and represent chronological order
from left to right. The position of our own ship is marked with an orange dot; the direction
of the ship’s progress is marked with a red arrow. The path passed by our own ship (O)
is indicated by a blue solid line. The ship obstacle (T1) is indicated by a green dot, and
the trajectory is indicated by a light blue solid line. The outside of the arc represented by
the virtual position of the vessel is defined by the velocity pair in the dynamic window
is marked with a green dot. It can be seen that the arc is distorted by obstacles. The
purple dotted line indicates the path of our own ship. CPA (closest point of approach)
was displayed in the simulation to express the dangerous situation between our own ship
and the obstacle ship. The CPA of our own ship and the CPA of the obstacle ship can be
expressed by Equations (9) and (10), respectively.
CPAo ( TCPA) =
CPAt ( TCPA) =
.
xo + x o × TCPA
.
yo + yo × TCPA
.
xt + x t × TCPA
.
yt + yt × TCPA
(9)
(10)
The CPA of our own ship (CPAo ) and the CPA of the obstacle ship (CPAt ), which
change in real time according to the movement of our own ship, are expressed with red
and blue dots, respectively. DCPA can be checked through the distance between CPAo and
CPAt shown in the figure. The simulation time is indicated in the upper right of the figures.
In addition, the grid was drawn at 100m intervals on the horizontal and vertical axes of
the figures.
First, the standard DWA and the CCDWA were compared through simulation in a
head-on situation with a dynamic obstacle. As an initial setting, our own ship was set to
move in the right direction at a speed of 10 m/s, and the obstacle ship was set to move at
J. Mar. Sci. Eng. 2021, 9, 863
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a speed of 10 m/s in the front direction of our own ship at a distance of 600 m from our
own ship.
Figure 7a shows the simulation results when applying the standard DWA in a head-on
situation with a dynamic obstacle. In the first figure, TCPA of our own ship and obstacle
ship is 25 s and the DCPA is 34 m. That is, they get closer to 34 m after 25 s. In the second
figure, since the obstacle ship (T1) is approaching from the slightly right side in front of our
own ship (O), the velocity pair located on the left side of the dynamic window is selected
as the input value by the objective function. Accordingly, our own ship turned to the left to
avoid the obstacle ship. The DCPA at this moment is 102 m. In the third picture, TCPA is
negative and ships are moving away and are out of danger. However, it was confirmed
that the standard DWA does not follow the COLREG rules in a head-on situation.
Figure 7b shows the simulation results when applying the CCDWA in a head-on
situation with a dynamic obstacle. In the first figure, TCPA of our own ship and the
obstacle ship is 29.5 s and the DCPA is 34 m. At this time, TCPA is positive, and DCPA
is less than the safe distance (100 m); the ships are in a dangerous situation. Referring to
Figure 3, it is a head-on situation. In the second figure, the CCDWA deactivates the left
area of the dynamic window. Accordingly, our own ship turned to the right to avoid the
obstacle ship. In the third picture, TCPA is negative and DCPA is greater than the safe
distance; ships are moving away and are out of danger. As a result, when applying the
CCDWA, our own ship turned to the right to avoid the obstacle ship. It was confirmed9 that
J. Mar. Sci. Eng. 2021, 9, x FOR PEER REVIEW
of 11
the CCDWA complies with the COLREG rules in a head-on situation.
(a) Standard DWA
(b) CCDWA
Figure 7.
7. Simulation
head-on situation
dynamic obstacle:
dot is
is the
the
Figure
Simulation in
in aa head-on
situation with
with aa dynamic
obstacle: an
an orange
orange dot
dot is
is our
our own
own ship,
ship, aa green
green dot
obstacle
ship,
a
blue
line
is
our
own
ship’s
trajectory,
a
light
blue
is
the
obstacle’s
trajectory.
obstacle ship, a blue line is our own ship’s trajectory, a light blue is the obstacle’s trajectory.
Second, we compared the standard DWA with the CCDWA through simulation in
the intersection situation with dynamic obstacles. As an initial setting, our own ship was
set to move in the right direction at a speed of 10 m/s, and the obstacle ship was set to
move in a direction to the right side of our own ship at a distance of 500 m from our own
ship at a speed of 10 m/s.
Figure 8a shows the simulation results when applying the standard DWA in the in-
J. Mar. Sci. Eng. 2021, 9, 863
J. Mar. Sci. Eng. 2021, 9, x FOR PEER REVIEW
9 of 10
10 of 11
(a) Standard DWA
(b) CCDWA
Figure 8.
8. Simulation
Simulation in
in crossing
crossing situation
situation with
with dynamic
dynamic obstacles: an orange dot is our
our own
own ship,
ship, aa green
green dot
dot is
is the
the obstacle
obstacle
ship,
a
blue
line
is
our
own
ship’s
trajectory,
and
a
light
blue
is
the
obstacle’s
trajectory.
ship, a blue line is our own ship’s trajectory, and a light blue is the obstacle’s trajectory.
5. Conclusions
Second, we compared the standard DWA with the CCDWA through simulation in the
intersection
situation
with dynamic
As an
initial setting,
our own
ship
to
USVs need
to secure
safety byobstacles.
preventing
collisions
with other
ships.
Towas
do set
this,
move
in
the
right
direction
at
a
speed
of
10
m/s,
and
the
obstacle
ship
was
set
to
move
in
USVs must avoid opposing vessels in collision-hazardous situations according to thea
direction torules.
the right
side
of ourwe
own
ship at aa distance
of 500 m
own to
ship
at a
COLREGs
In this
paper,
proposed
USV algorithm
to from
allowour
vessels
avoid
speed
of
10
m/s.
collisions with opposing vessels based on the COLREG rules. First, we define the main
Figure
shows the
simulationand
results
when
applying
standard
DWA
in the
collision
risk8a
situations
of COLREGs
propose
a method
to the
improve
DWA
to comply
intersection
situation
with
dynamic
obstacles.
In
the
first
figure,
the
TCPA
of
our
own
ship
with the COLREG rules according to collision risk situations. In addition, we implement
and
the
obstacle
ship
is
33
s
and
the
DCPA
is
70
m.
Therefore,
they
get
closer
to
33
m
after
the simulation and compare the standard DWA with the CCDWA proposed in this paper.
70 s.
In the second
figure, our
turned
in the direction
of the obstacle ship. At this
As
a result,
it is confirmed
thatown
the ship
CCDWA
complies
with COLREG.
time, the DCPA was 18 m, which made the situation more dangerous than the situation in
In future works, the proposed assistance technique will be integrated into the operthe first figure. In the end, it was confirmed that the ships collided in the third figure.
ating system of USVs. Then, the validity of the proposed CCDWA will be verified by conFigure 8b shows the simulation results when applying the CCDWA in the intersection
ducting a sea operation experiment on the USVs.
situation with dynamic obstacles. In the first figure, the TCPA of our own ship and the
obstacleContributions:
ship is 32 s and
the DCPA is 76 m.
At this
time,
the TCPA
is positive
and the
DCPA
Author
Conceptualization,
H.-G.K.
and
Y.-H.C.;
methodology,
H.-G.K.;
software,
is
less
than
the
safe
distance
(100
m);
the
ships
are
in
a
dangerous
situation.
Referring
S.-J.Y. and H.-G.K.; validation, H.-G.K.; formal analysis, H.-G.K.; investigation, H.-G.K. and J.-K.R.;
to FigureY.-H.C.
3, it is and
a situation
crossing
from
the right.
In thewriting—original
second figure, draft
the CCDWA
resources,
J.-K.R.; data
curation,
H.-G.K.
and S.-J.Y.;
preparadeactivates
the
left
area
of
the
dynamic
window.
Accordingly,
our
own
ship
turned
to the
tion, H.-G.K.; writing—review and editing, H.-G.K. and J.-H.S.; visualization, S.-J.Y. and H.-G.K.;
right
to
avoid
crossing
ahead
of
the
other.
In
the
third
picture,
the
TCPA
is
negative
and
supervision, J.-H.S. All authors have read and agreed to the published version of the manuscript.
the DCPA is greater than the safe distance; the ships are moving away from each other
Funding: This research was financially supported by the Institute of Civil Military Technology Coand are out of danger. As a result, it was confirmed that the CCDWA complies with the
operation funded by the Defense Acquisition Program Administration and Ministry of Trade, InCOLREG
inofthe
intersection
situation
with
dynamic obstacles.
dustry
and rules
Energy
Korean
government
for USV
Development
for Coast Surveillance and Rapid
Response; in addition, this work was supported by the Promotion of Innovative Businesses for Regulation-Free Special Zones funded by the Ministry of SMEs and Startups (MSS, Korea).
Data Availability Statement: Data are contained within the article.
Conflicts of Interest: The authors declare no conflict of interest.
J. Mar. Sci. Eng. 2021, 9, 863
10 of 10
5. Conclusions
USVs need to secure safety by preventing collisions with other ships. To do this, USVs
must avoid opposing vessels in collision-hazardous situations according to the COLREGs
rules. In this paper, we proposed a USV algorithm to allow vessels to avoid collisions
with opposing vessels based on the COLREG rules. First, we define the main collision
risk situations of COLREGs and propose a method to improve DWA to comply with
the COLREG rules according to collision risk situations. In addition, we implement the
simulation and compare the standard DWA with the CCDWA proposed in this paper. As a
result, it is confirmed that the CCDWA complies with COLREG.
In future works, the proposed assistance technique will be integrated into the operating system of USVs. Then, the validity of the proposed CCDWA will be verified by
conducting a sea operation experiment on the USVs.
Author Contributions: Conceptualization, H.-G.K. and Y.-H.C.; methodology, H.-G.K.; software,
S.-J.Y. and H.-G.K.; validation, H.-G.K.; formal analysis, H.-G.K.; investigation, H.-G.K. and J.-K.R.;
resources, Y.-H.C. and J.-K.R.; data curation, H.-G.K. and S.-J.Y.; writing—original draft preparation, H.-G.K.; writing—review and editing, H.-G.K. and J.-H.S.; visualization, S.-J.Y. and H.-G.K.;
supervision, J.-H.S. All authors have read and agreed to the published version of the manuscript.
Funding: This research was financially supported by the Institute of Civil Military Technology
Cooperation funded by the Defense Acquisition Program Administration and Ministry of Trade,
Industry and Energy of Korean government for USV Development for Coast Surveillance and Rapid
Response; in addition, this work was supported by the Promotion of Innovative Businesses for
Regulation-Free Special Zones funded by the Ministry of SMEs and Startups (MSS, Korea).
Data Availability Statement: Data are contained within the article.
Conflicts of Interest: The authors declare no conflict of interest.
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