Ship domain in the restricted area – simulation research

Ship domain in the restricted area – simulation research

Scientific Journals
Zeszyty Naukowe
Maritime University of Szczecin
Akademia Morska w Szczecinie
2012, 32(104) z. 2 pp. 152–156
2012, 32(104) z. 2 s. 152–156
Ship domain in the restricted area – simulation research
Zbigniew Pietrzykowski, Mirosław Wielgosz, Marek Siemianowicz
Maritime University of Szczecin, Faculty of Navigation
70-500 Szczecin, ul. Wały Chrobrego 1–2, e-mail: {z.pietrzykowski; m.wielgosz}@am.szczecin.pl
Key words: navigational safety, encounter situations, passing distance
Abstract
The ship domain – the area around the ship that should be clear of other vessels or objects – depends on many
factors. In this paper authors present results of simulation research on ship domain determination. The
influence of ship size on domain shape and dimensions in the restricted area have been analyzed. The method
of determining ship domain is characterized. The results have been presented. The domains of ships of
different sizes have been compared and conclusions formulated.
Introduction
The ship domain and methods of its
determination
One of the main tasks of navigation is to ensure
ship's safety during its voyage at sea. Navigational
equipment and systems installed on board are an
important source of information for the navigator
during decision making. The use of up to date
information technologies enables the integration of
information (integrated bridge) and its automatic
processing. This is of particular importance in the
case of information referring to navigational safety,
such as a radar report (ARPA, ECDIS) including
the parameters known as CPA and TCPA. The CPA
as a safety criterion is very useful in open sea navigation. Its use in restricted waters, such as narrow
channels and fairways, in most cases is difficult to
implement. The reason is that a ship has no free
choice of the route. Therefore, a lot of attention is
paid on developing methods and tools for the
determination of an area around the ship that should
be clear of other vessels or objects – ship domain
[1, 2, 3, 4, 5, 7, 8, 9, 10]. This approach is due to
the fact that the concept of domain is intuitively
accepted by the human and enables an analysis and
assessment of the situation and working out decisions on manoeuvring in open and restricted areas.
The concept of domain is applicable on ships, as
well as in land-based vessel traffic centres.
The shape and size of ship domain depend on
many factors, which makes it difficult to define it.
The ship size is one of these factors.
Domains proposed by various authors can be
divided into two- and three-dimensional ones. The
former describe an area around the ship. Typical
shapes of two-dimensional domains include a circle, rectangle, ellipsis, polygon and more complex
planar shapes.
The determination of ship domain requires that
its boundary is identified. There are three groups
of methods of ship domain determination. One includes statistical methods. These consist in recording trajectories of ships' movements to get data for
identifying the area around the ship that navigators
keep clear of other navigational objects [2, 3].
Analytical methods, in turn, are based on the
analytical description of domain area. The domain
boundaries in these methods may be defined on the
basis of the closest point of approach (CPA) and
time to closest point of approach (TCPA), as well
as formulas describing ship's manoeuvrability,
hydrological and meteorological conditions and
relations applicable to ship in motion in a given
area [8, 9].
The application of methods and tools of
knowledge engineering, including artificial intelligence, enables acquiring, representing and using
the procedural and declarative knowledge of expert
navigators for the identification of ship domain.
Examples are provided by artificial neural networks
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Ship domain in the restricted area – simulation research
used for defining the level of navigational safety,
the basis for outlining the ship domain [6, 7, 11].
Chronologically, statistical methods were first
proposed methods to be used for ship domain
determination [2, 3]. The domain was determined
from registered ship trails indicated by radar. In
restricted areas the ship size has to be taken into
consideration. Using the equipment and systems
used presently on ships’ board and in land-based
centres, capable of registering ship position with
greater accuracy, it can determine ship’s trails that
depend on the ship dimensions (contours).
To determine the domain boundary these
authors adopted the method proposed in [2], based
on the density analysis of ships’ trails around the
central ship. The ships’ trails were assumed to be
the points of waterplane (waterline) of another ship
at preset relative bearings, the nearest to the centre
of the central ship (Fig. 1). Besides, it was assumed
that ship trails would be recorded at fixed time
intervals t at n relative bearings i (i = 1, ..., n) in
the 000÷359 [o] and the discretization step .
The domain boundary is then determined by
a set of points pDi (i = 1, 2, ..., n) at the preset relative bearings i :
GDS  pD1, pD 2 , ... pDi ,..., pDn 
such that for a given relative bearing i the trail
density at point pDi, lying at a distance dpDi from the
centre of the central ship is maximum.
Additionally, it can determine the minimum and
maximum boundary of the domain, described, respectively, by points with minimum and maximum
distances of ships’ trails (Fig. 2).
The scope of research
The research aimed at the determination of
domains of various size ships in a restricted area
and an analysis of how encountering ships’ sizes
affect the shape and size of the domain.
The primary method used was that of non-autonomous simulations with the participation
of expert navigators, who worked on the ECDIS
simulator at the Maritime University of Szczecin.
The navigators, of varying sea service period, were
trainees attending an ECDIS operation course run
at the same university. The research consisted in
simulated passages of ships conducted according to
pre-determined ship encounter scenarios.
The scenarios assumed good weather conditions
to exclude the influence of hydrological and meteorological factors. The passages, then, took place
at daylight, good weather and visibility, with no
current or wind effects.
The Singapore Strait was the area chosen for
tests. This major trading route in South-East Asia is
65.7 Nm long and about 8.6 Nm wide. The strait is
situated between Singapore Island and the Riau
Archipelago. The route traffic intensity is one of the
densest in the world. The beginning of the fairway
leading to the Port of Singapore was selected for
simulations. The port is situated southeast of Jurong
Island, where the fairway neighbours offshore traffic zone, resulting in a variety of ship encounter
situations. Also, this stretch of the fairway includes
an area prohibited for navigation due to construction work. The construction work area restricts the
fairway on the port side, and the offshore traffic
on the starboard side, which limits the choice of
manoeuvres.
The Navi-Trainer Professional 4000 simulator
offers a selection of 118 ship models for simulation
tests, of which 18 can be handled by the operator.
Having considered all the ship models available,
authors chose three types of ships with various size
for planning the simulated passages. The chosen
Fig. 1. Ship trails determination at defined relative bearings at
instant t
Fig. 2. Ship domain boundaries
Zeszyty Naukowe 32(104) z. 2
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153
Zbigniew Pietrzykowski, Mirosław Wielgosz, Marek Siemianowicz
models represent a wide spectrum of vessel types
operated in the merchant marine. Table 1 contains
basic parameters of the chosen ship models.
The method described in Chapter The ship
domain... was used for the determination of ship
domain limits. To this end the trails of ships located
around the central ship (the one operated by the
computer) were determined. The positions of GPS
antennas on each ship were taken into account. The
ships’ contours were approximated to polygon
shapes.
The ships’ trails recorded at the time interval
t = 5 [s] were analyzed for the relative bearing
discretization  = 5 . Figure 4 illustrates the
analyzed trails of river-sea ship 1 for scenario 4.
Table 1. Ship models
Ship model
Ship type
Length overall (Lc) [m]
Breadth (B) [m]
Draft forward (DA)
Draft aft (DF) [m]
Moulded depth (A) [m]
Displacement (D) [t]
Speed over water
(SOW) [w]
River-sea
ship 1
Coaster
95.0
13.0
3.7
3.7
11.1
3510.0
11.1/7.0 *
LO-RO
ship
LO-RO
174.0
23.0
7.5
8.1
24.2
19512.0
VLCC 1
Tanker
261.0
48.0
5.8
9.0
37.6
63430.0
a)
16.3/9.0* 16.3/11.0*
* Speed of the slower ship in scenario 4 (overtaking).
Encounter situations of two ships of the same
type on collision courses were considered, where
one ship was steered by the operator, the other was
automatically handled by a computer. Four basic
scenarios of encounters were developed:
1) encounter of ships on opposite courses;
2) encounter of ships on crossing courses, where
the ship steered by the navigator had the right of
way;
3) encounter of ships on crossing courses, where
the ship steered by the navigator had no right of
way;
4) overtaking situation, where the ship steered by
the navigator was overtaking the other ship, with
no right of way.
3000
2000
2000
1000
1000
0
0
-1000
-1000
-2000
-2000
-3000
-1000
0
1000
-3000
-1500 -1000 -500
0
500
1000 1500
Fig. 3. Relative trajectories of the river-sea ships 1 for the
scenario: 4; a) trajectories of the relative motion of computeroperated ships; b) trajectories of the relative motion of ships
steered by navigators
Research
-1000
[m]
-500
[m]
384 passages were conducted in total: 128 passages for each ship type, including 32 passages
following each of the scenarios. The simulations
were executed in real time. The data from the passages were recorded at the preset discretization step
t = 1 [s].
The ships’ trajectories had to be calculated to
get the relative motion parameters in order to verify
the passing distances between ships and to determine their domains. The ship’s relative motion was
considered for two cases:
a) the navigator-steered ship motion was displayed
relative to the motion of the computer-operated
ship;
b) the ship operated by the computer was shown
relative to the one handled by the navigator.
b)
3000
0
500
1000
-3000
-2500
-2000
-1500
-1000
-500
[m]
0
500
1000
1500
2000
[m]
Fig. 4. Trails of river-sea ship 1 for scenario 4
On this basis ship partial domains were determined for each scenario k (k = 1, 2, 3, 4) on preset
relative bearings i : (i = 1, 2, ..., n): domain, minimum domain and maximum domain, described,
respectively, by points pD ik, pDmin ik, pDmax ik (compare chapter The ship domain..., Fig. 2).
On the basis of the partial domains determined
for each scenario (four scenarios in the case under
consideration), the limits of total domains GDSC,
GDSCmin and GDSCmax were defined:
Figure 3 shows example relative trajectories of
a river-sea ship 1 for the scenario 4.
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Scientific Journals 32(104) z. 2
Ship domain in the restricted area – simulation research
GDSC

 pDC 1 , pDC 2 , ..., pDC i , ..., pDC n

GDSC min 

 pDC min 1 , pDC min 2 , ..., pDC min i , ..., pDC min n
 (3)
GDSC max 

the river-sea ship 1 for scenario 4 are presented in
the figure 5.
(2)
 pDC max 1 , pDC max 2 , ..., pDC max i , ..., pDC max n
 (4)
The limits were such that for a given relative
bearing i (i = 1, 2, ..., n)


d p DC i  min d p D ik ; k  1, 2, 3, 4

 mind
(5)

; k  1, 2, 3, 4
d pDC min i  min d pDmin ik ; k  1, 2, 3, 4
(6)
d pDC max i
(7)
pDC max ik
where
dpDik – distance from the centre of the central
ship to the limit of the partial domain on
the relative bearing i for the scenario k;
dpD min ik – distance from the centre of the central
ship to the limit of the minimum partial
domain on the relative bearing i for the
scenario k;
dpD max ik – distance from the centre of the central
ship to the limit of the maximum partial
domain on the relative bearing i for the
scenario k.
As an example the determined partial domain
boundaries – minimum, mean and maximum – for
Figure 6 presents the total domains of the ships
under analysis.
The analysis of the results
The research included an analysis of passing distances between vessels accounting for their dimensions (ship contours). The program recording ship
movement parameters was logging the position
of GPS receiver antenna. For this reason it was
b)
c)
3000
3000
2000
2000
2000
1000
1000
1000
0
x [m]
3000
x [m]
x [m]
a)
Fig. 5. The partial domains of river-sea ship 1 for scenario 4
0
0
-1000
-1000
-1000
-2000
-2000
-2000
-3000
-1000
0
y [m]
1000
-3000
-1000
0
y [m]
1000
-3000
-1000
0
y [m]
1000
Fig. 6. Total ship domains(minimum, mean and maximum) for ships of different size: a) river-sea ship 1; b) LO-RO ship; c) VLCC1
Zeszyty Naukowe 32(104) z. 2
155
Zbigniew Pietrzykowski, Mirosław Wielgosz, Marek Siemianowicz
necessary to determine the distances of characteristic points describing the ship contour in relation to
the antenna position.
The determination of domain boundaries allowed to determine the lengths and widths of each
domain for each type of ship. The results are listed
in table 2.
The analysis of data has shown that domain
shapes are similar. It has been also found that the
domain boundaries are irregular at some places.
The shapes of minimum and mean domains significantly differ from the expected ones. This is due to
a large number of manoeuvres where the starboard
side of the central ship was being passed at a short
distance. It seems purposeful to undertake further
research.
As expected, large differences were observed in
length and width of domains depending on ship
type. Navigators steering the smallest vessels tended to maintain smaller domains than navigators
handling larger vessels.
Table 2. Domain boundary dimensions
Types of domain
boundaries
Length
Minimum
Width
Length
Mean
Width
Length
Maximum
Width
Ship domain
River–sea ship 1 LO-RO ship
1495 [m]
1200 [m]
490 [m]
675 [m]
2320 [m]
1900 [m]
600 [m]
955 [m]
3440 [m]
3670 [m]
845 [m]
1595 [m]
VLCC 1
2220 [m]
1135 [m]
3790 [m]
1635 [m]
4900 [m]
2168 [m]
Conclusions
The influence of ship size on domain shape and
dimensions in the restricted area has been analyzed.
Based on the simulation tests participated by expert
navigators domains of various size ships were
determined. The results confirmed a significant
influence of ship size on the shape and dimensions of
the domain. Further research is needed in reference
to the method of domain determination as well as the
analysis of other factors determining the ship domain
area in a restricted area, such as the area parameters
and hydrological and meteorological conditions.
Figures 7 and 8 graphically illustrate the parameters of domain boundaries.
5000
4500
Domain lenght [m]
4000
3500
3000
2500
References
2000
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1500
1000
500
0
River – sea ship 1
Minimum
LO-RO ship
Mean
VLCC 1
Maximum
Fig. 7. A comparison of total domain lengths
Domain width [m]
2500
2000
1500
1000
500
0
River – sea ship 1
Minimum
LO-RO ship
Mean
VLCC 1
Maximum
Fig. 8. A comparison of total domain widths
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