152 Scientific Journals 32(104) z. 2
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 Navigation70-500 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
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 navi-gation. 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 deci-sions 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.
The ship domain and methods of its determination
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 cir-cle, 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 in-cludes statistical methods. These consist in record-ing 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 intelli-gence, 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
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 .
Fig. 1. Ship trails determination at defined relative bearings at instant t
Fig. 2. Ship domain boundaries
The domain boundary is then determined by a set of points pDi (i = 1, 2, ..., n) at the preset rela-tive bearings i :
D D Di Dn
S p p p p
GD 1, 2,... ,..., (1)
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, re-spectively, 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 mete-orological 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 traf-fic zone, resulting in a variety of ship encounter situations. Also, this stretch of the fairway includes an area prohibited for navigation due to construc-tion work. The construcconstruc-tion 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
154 Scientific Journals 32(104) z. 2
models represent a wide spectrum of vessel types operated in the merchant marine. Table 1 contains basic parameters of the chosen ship models.
Table 1. Ship models
Ship model River-sea ship 1 LO-RO ship VLCC 1
Ship type Coaster LO-RO Tanker
Length overall (Lc) [m] 95.0 174.0 261.0
Breadth (B) [m] 13.0 23.0 48.0
Draft forward (DA) 3.7 7.5 5.8
Draft aft (DF) [m] 3.7 8.1 9.0
Moulded depth (A) [m] 11.1 24.2 37.6 Displacement (D) [t] 3510.0 19512.0 63430.0 Speed over water
(SOW) [w] 11.1/7.0 * 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.
Research
384 passages were conducted in total: 128 pas-sages for each ship type, including 32 paspas-sages following each of the scenarios. The simulations were executed in real time. The data from the pas-sages 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 deter-mine 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. Figure 3 shows example relative trajectories of a river-sea ship 1 for the scenario 4.
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.
a) b)
Fig. 3. Relative trajectories of the river-sea ships 1 for the scenario: 4; a) trajectories of the relative motion of computer-operated ships; b) trajectories of the relative motion of ships steered by navigators
Fig. 4. Trails of river-sea ship 1 for scenario 4
On this basis ship partial domains were deter-mined for each scenario k (k = 1, 2, 3, 4) on preset relative bearings i : (i = 1, 2, ..., n): domain, min-imum domain and maxmin-imum domain, described, respectively, by points pD ik, pDmin ik, pDmax ik (com-pare 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:
-1000 0 1000 -3000 -2000 -1000 0 1000 2000 3000 -1500 -1000 -500 0 500 1000 1500 -3000 -2000 -1000 0 1000 2000 3000 -1000 -500 0 500 1000 -3000 -2500 -2000 -1500 -1000 -500 0 500 1000 1500 2000 [m ] [m] [m] [m]
Zeszyty Naukowe 32(104) z. 2 155
DC DC DCi DCn
SC p p p p GD 1, 2,..., ,..., (2)
DC DC DC i DC n
SC p p p p GD min min 2 min 1 min min ..., , ..., , , (3)
DC DC DC i DC n
SC p p p p GD max max 2 max 1 max max ..., , ..., , , (4) The limits were such that for a given relative bearing i (i = 1, 2, ..., n)
; 1,2,3,4 min d k d ik D p i DC p (5)
; 1,2,3,4 min min min d k dpDC i pD ik (6)
; 1,2,3,4 min max max d k dpDC i pDC ik (7) wheredpDik – 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
the river-sea ship 1 for scenario 4 are presented in the figure 5.
Fig. 5. The partial domains of river-sea ship 1 for scenario 4
Figure 6 presents the total domains of the ships under analysis.
The analysis of the results
The research included an analysis of passing dis-tances between vessels accounting for their dimen-sions (ship contours). The program recording ship movement parameters was logging the position of GPS receiver antenna. For this reason it was
a) b) c)
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
-1000 0 1000 -3000 -2000 -1000 0 1000 2000 3000 y [m] x [m ] granica minimalna granica średnia -1000 0 1000 -3000 -2000 -1000 0 1000 2000 3000 y [m] x [m ] -1000 0 1000 -3000 -2000 -1000 0 1000 2000 3000 y [m] x [m ]
156 Scientific Journals 32(104) z. 2
necessary to determine the distances of characteris-tic points describing the ship contour in relation to the antenna position.
The determination of domain boundaries al-lowed to determine the lengths and widths of each domain for each type of ship. The results are listed in table 2.
Table 2. Domain boundary dimensions Types of domain
boundaries
Ship domain
River–sea ship 1 LO-RO ship VLCC 1 Minimum Length 1495 [m] 1200 [m] 2220 [m] Width 490 [m] 675 [m] 1135 [m] Mean Length 2320 [m] 1900 [m] 3790 [m] Width 600 [m] 955 [m] 1635 [m] Maximum Length 3440 [m] 3670 [m] 4900 [m] Width 845 [m] 1595 [m] 2168 [m]
Figures 7 and 8 graphically illustrate the param-eters of domain boundaries.
Fig. 7. A comparison of total domain lengths
Fig. 8. A comparison of total domain widths
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 signifi-cantly 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 tend-ed to maintain smaller domains than navigators handling larger vessels.
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.
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0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
River – sea ship 1 LO-RO ship VLCC 1
Do m ain len gh t [ m ]
Minimum Mean Maximum
0 500 1000 1500 2000 2500
River – sea ship 1 LO-RO ship VLCC 1
Do m ain w id th [ m ]
