196 Scientific Journals 36(108) z. 2
Scientific Journals
Zeszyty Naukowe
Maritime University of Szczecin
Akademia Morska w Szczecinie
2013, 36(108) z. 2 pp. 196–199 2013, 36(108) z. 2 s. 196–199
ISSN 1733-8670
Analysis of a real vessel and its simulation model behavior
Piotr Zwolan, Krzysztof Czaplewski
Polish Naval Academy
81-103 Gdynia, ul. Śmidowicza 69, e-mail: krzysztof@czaplewski.pl
Key words: manoeuvring, parameters, ship’s behaviour, navigation simulator, real conditions Abstract
The paper describes a mean of using vessel’s manoeuvring parameters recorded in real conditions for the purpose of analysing the environment influence on ship’s behaviour. This information has also been used to conduct a comparative analysis of a real vessel and its simulation model in the data base of a navigation-manoeuvring simulator. The measurements were taken on an unrestricted sea area so as to eliminate the impact of developed sites on wind field. The research was conducted in the region of the North Sea and Baltic Sea.
Introduction
Navigation-manoeuvring simulators are manda-tory equipment of maritime academies and training centres for marine personnel. The possibility of using them in the teaching process is largely de-pendent on the library of the structures in the data base of simulation software. This refers particularly to data bases of own vessels. The quality of teach-ing and of the experiments conducted with the use of the simulator depends first and foremost on the accurate mapping of the behaviour of vessel’s simulation model in comparison with its real coun-terpart. Another element providing software’s qual-ity is the model of the environment impacting ships and other floating objects. From the point of view of the software’s operator, it is not possible to inter-fere with the model of external environment im-plemented in the simulator. However, thanks to additional components it is possible to edit vessels’ mathematical models. One of the ways of assessing virtual models is by doing tests in real conditions. At the Institute of Navigation and Hydrography there have been a series of measurement sessions on a real vessel in order to determine the compati-bility degree of one of the ships featured in the data base of the Transas simulator. In the first stage, the recording of manoeuvring parameters was limited to determining the impact of wind and wave on
a vessel adrift. The research works included the use of a measurement platform made by the Institute’s employees. The structure enables data collection from particular navigation devices and data trans-mission via a wireless network, RS 232 port or USB port.
The paper is a part of a project which aims at formulating a methodology of verifying simulation models. It includes a method of assessing such a model, using as an example the data collected during measurement sessions. Due to the large amount of recorded information, only an example record has been described. In the latter stages the author intends to conduct tests enabling vessels’ motion analysis at 6 degrees of freedom, with par-ticular emphasis laid on the activity of wind and waves. Subsequently, all of the collected data will be used to edit the ship’s mathematical model using the Virtual Shipyard application, one of the simula-tor’s components responsible for creating mathe-matical models of vessels.
Tests in real conditoins
Tests aiming at recording vessel’s manoeuvring parameters were conducted in the North Sea and Baltic Sea. The location was chosen in view of the possibility of running simulation trials including a weather model and a wind wave model prepared
Analysis of a real vessel and its simulation model behavior
Zeszyty Naukowe 36(108) z. 2 197
for the North Sea. The trials involved collecting information from particular navigation devices to obtain knowledge about the motion of vessel adrift, influenced by wind and wind wave [1]. The record-ed data was usrecord-ed in a simulation experiment lead-ing to determinlead-ing the differences between the activity of the real ship and its virtual model. To achieve the research goal, a measurement platform was constructed. Its main elements are:
– Weather station; – Inertial system; – AIS; – GNSS receiver; – NMEA multiplexer; – Wi-Fi router; – Data logger.
Presented below is a test bench placed on board a ship. The measurement platform was placed in a RACK-type casing, under the platform there is a recording device. Instead of a central unit one can use a Windows tablet in order to minimise the sizes and to enhance mobility.
Apart from the above-mentioned navigation de-vices, there is a possibility of connecting systems on the vessel. Data transmission is possible via
Fig. 1. Measurement platform (1) with a recording device (2)
RS 232, USB port and wireless network [2]. One advantage of using such a structure is the possibil-ity of integrating a few navigation devices via an NMEA multiplexer [3]. This enables data transfers to the data logger in a single message. If installing additional devices is not feasible, the platform may be integrated with the vessels’ ECDIS and thanks to the NMEA OUTPUT, it is possible to record data transmitted form particular navigation devices [4]. In the configuration presented below, the test-bench enabled
recording information from:
– the weather station (direction and speed of real and relative wind, position, air temperature, at-mospheric pressure, compass course thanks to in-built compass);
– the GNSS receiver;
– the ship’s ECDIS system (gyrocompass course, position, speed, direction, wind speed);
– manoeuvring parameters from the inertial sys-tem.
Presented below is a selected data-log later used during simulation tests. Due to limitations for data presentation, the paper includes only some of the
Fig. 2. Test bench installed on ship 1
2
Table 1. Ship’s manoeuvring parameters Time [s] [°]φ [°]λ Heading [°] COG [°] SOG [knots]
True wind direction
[°] True wind speed [knots] 00 55.70151750 003.88307367 076.9 137.6 0.46 340 7.15 10 55.70147906 003.88312874 077.4 141.8 0.51 334 7.45 20 55.70144318 003.88318468 077.9 151 0.51 329 8.64 30 55.70141194 003.88324677 079.0 152.2 0.53 331 9.05 40 55.70138321 003.88329440 079.0 153.3 0.61 337 6.99 50 55.70135897 003.88334750 079.4 153.4 0.59 341 6.27 60 55.70132765 003.88340188 080.2 153.7 0.57 345 5.89 70 55.70127900 003.88345446 080.2 154.1 0.58 342 6.46 80 55.70123780 003.88348938 081.6 154.2 0.61 336 7.21 90 55.70118699 003.88354227 081.7 154.2 0.61 335 7.30 100 55.70114392 003.88359121 082.2 154.3 0.60 338 7.46 110 55.70109031 003.88363245 082.1 154.3 0.56 341 6.84 120 55.70105165 003.88368172 082.3 154.4 0.57 342 7.02
Piotr Zwolan, Krzysztof Czaplewski
198 Scientific Journals 36(108) z. 2
collected parameters. The table includes only in-formation enabling the execution of the goal set by the article which was to assess the vessel’s drift and drift angle. The results of the measurements are presented in the form of a 120-second course. The measurement device recorded data at second inter-vals, whereas the use of the inertial system enabled collecting information at the frequency of 100 Hz [5].
Simulation tests
The simulation experiment was to recreate the course of real manoeuvring trials in simulated con-ditions. It assumed a scenario where a vessel is placed in a given position and exposed to external conditions recorded during real tests. Assessed were the ship’s motion parameters in mind the drift and drift angle. The computer-generated weather zone included changes in the speed and direction of the wind at particular time intervals. The simulator allows for corrections at second intervals. Presented
below are the results of a comparative analysis of three of the recorded parameters.
Difference between the real vessel and the simulation model’s heading
Based on the analysis of ship’s heading shown on the graph (Fig. 3) it has been concluded that the real vessel gradually changed its course to star-board. Such activity resulted from the larger wind area in the vessel’s bow section, whereas the simu-lation model at the initial stage drifts changing course to port. It subsequently steadies its course at 075º. The analysis of the above-mentioned test reveals a balance construction of the simulation model. The surface wind area was evenly arranged on its entire virtual model length.
Difference between the real vessel and the simulation model’s SOG
From the comparative analysis of speed over ground of both vessels (Fig. 4) one can observe that
0 10 20 30 40 50 60 70 80 90 100 110 120 SHIP 76.90 77.40 77.90 79 79 79.4 80.2 80.2 81.6 81.7 82.2 82.1 82.30 SIMULATOR 76.9 76.893 76.816 76.6 76.287 75.995 75.78 75.661 75.61 75.567 75.518 75.497 75.538 74.00 75.00 76.00 77.00 78.00 79.00 80.00 81.00 82.00 83.00 84.00 H ea di ng [º ]
Fig. 3. Comparison of heading
0 10 20 30 40 50 60 70 80 90 100 110 120 SHIP 0.46 0.51 0.51 0.53 0.61 0.59 0.57 0.58 0.61 0.61 0.6 0.56 0.57 SYMULATOR 0.13 0.17 0.21 0.25 0.29 0.29 0.29 0.23 0.3 0.32 0.33 0.33 0.34 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 S O G [ kno ts ]
Analysis of a real vessel and its simulation model behavior
Zeszyty Naukowe 36(108) z. 2 199
the simulation model exhibits lower leeway speed by approximately 0.2 knot at the moment when the vessels steadies itself. This can be accounted for by a too small total wind surface area of the simulation model. This discrepancy could also have been caused by difficulties in estimating the speed of sea current on the given sea area. The above assump-tion of an incorrect estimate of wind surface area is confirmed by an analysis of manoeuvring tests not included in the article. The tests were recorded on sea area with minimal current values and the afore-mentioned disproportion is also visible.
Difference between the real vessel and the simulation model’s COG
On the basis of the collected data on course over ground (Fig. 5) one can notice a significant differ-ence in the motion of the two vessels. At the first stage the real vessel turns to starboard, which is in line with the analysis conducted in Difference
be-tween the real vessel and the simulation model's heading. The change in COG could stem from the
fact that the GPS antenna is placed not in the ves-sel’s pivot point, but closer to the bow. This trig-gers vessel’s initial circular movement up until leeway steadies. However, the simulation model drifts at the established angle. The virtual vessel’s motion corresponds to the above-described tests.
Conclusions
A measurement platform used in the research process enables logging all of the vessel’s indispen-sable manoeuvring parameters for the assessment of wind’s and wind wave’s impact on vessel’s ac-tivity.
Data recorded during trial runs could be used for comparative purposes and to assess whether the ship’s virtual model was properly designed.
Data collected from the inertial system enable an analysis of the impact of hydro-meteorological conditions for the analysis of vessel’s motion at 6 degrees of freedom.
A comparative analysis of the real ship with the simulation model gives a possibility of editing and correcting its mathematical model thanks to the use of the simulator’s additional components responsi-ble for creating virtual models of vessels.
References
1. Guide for vessel manoeuvrabilit, American Bureau of Shipping, Houston 2006, USA.
2. NMEA 0183 Standard for Interfacing Marine Electronic Devices. National Marine Electronics Association, 2002. 3. SPITZER S.: NMEA 2000 Past, Present and Future. RTCM
Annual Conference, 2009.
4. Navi-Sailor 4100 user manual. Transas Marine, Sankt Pe-tersburg 2011.
5. MONTEWKA J., GUCMA M.: Podstawy morskiej nawigacji
inercyjnej. Akademia Morska w Szczecinie, Szczecin 2006. 0 10 20 30 40 50 60 70 80 90 100 110 120 SHIP 137.60 141.80 151.00 152.2 153.3 153.4 153.7 154.1 154.2 154.2 154.3 154.3 154.40 SYMULATOR 165.8 165.7 165.4 164.9 164.8 164.9 164.9 165 164.9 164.8 164.7 164.6 164.6 137.00 142.00 147.00 152.00 157.00 162.00 167.00 C O G ( °)
