Maritime University of Szczecin
Akademia Morska w Szczecinie
2010, 20(92) pp. 146–152 2010, 20(92) s. 146–152
Models of DP systems in full mission ship simulator
Modele systemów dynamicznego pozycjonowania
w wielozadaniowym symulatorze statku
Paweł Zalewski
Maritime University of Szczecin, Faculty of Navigation, Institut of Marine Traffic Engineering Akademia Morska w Szczecinie, Wydział Nawigacyjny, Centrum Inżynierii Ruchu Morskiego 70-500 Szczecin, ul. Wały Chrobrego 1–2, e-mail: p.zalewski@am.szczecin.pl
Key words: ship’s simulator, DP systems, Kalman filtering, systems modelling Abstract
The paper presents modelling principles of DP systems integrated into the modernized full mission ship simulator of Kongsberg Polaris® type at Maritime University of Szczecin. Comparisons to real systems and research possibilities are given. Basing on the effects and conclusions obtained from scientific-research works performed by marine traffic engineering staff until now, the advantages of modernization of “full mission simulator” have been shown.
Słowa kluczowe: symulator statku, systemy DP, filtracja Kalmana, modelowanie systemów Abstrakt
W artykule przedstawiono modele systemów dynamicznego pozycjonowania (DP) w wielozadaniowym sy-mulatorze statku typu Kongsberg Polaris® w Akademii Morskiej w Szczecinie. Zaprezentowano porównania z rzeczywistymi systemami i możliwości badawcze. Na podstawie rezultatów dotychczasowych prac nauko-wo-badawczych realizowanych w Instytucie Inżynierii Ruchu Morskiego AM w Szczecinie przedstawiono zalety modernizacji wielozadaniowego symulatora manewrowo-nawigacyjnego statku.
Introduction
The Maritime University of Szczecin started the project of the Navigational Technologies Centre (NTC) comprising DP systems integration into Full Mission Ship Simulator and building of research laboratories with ship’s integrated bridge systems and network and mobile technologies of navigation data transfer. The NTC project is co-financed from EU funds in the Innovative Economy Operational Programme (IEOP – POIG). The realistic hardware and open software environment of the Full Mission Simulator give new possibilities of ship hydro-dynamics and DP systems modelling and human factor analysis including:
– visual evaluation in manoeuvring and close approach, platform support, berthing and un-berthing;
– realistic tandem loading and offshore operations; – ship handling in narrow waters, i.e. cruise liners approach to passenger terminals and operation in small harbours and narrow channels;
– emergency manoeuvre to avoid collision etc.; – manoeuvring safety analysis.
DP systems at full mission ship simulator
Hardware and software of a DP Class 2 System integrated into Full Mission Kongsberg Polaris Simulator for Maritime University of Szczecin were specified in compliance or exceeding the regulations set forward in:
– STCW’95,
– IMO Resolution MSC / Circ. 645,
– IMO Resolution MSC / Circ. 738 ref. IMCA M 117.
The open structure of modelled vessels allows for hydrodynamic tuning, thrusters and rudders allocation research essential in DP systems.
Generally a seagoing vessel is subjected to forces from wind, waves and currents as well as from forces generated by the propulsion system. The vessel’s response to these forces, i.e. its changes in position, heading and speed, is measured by the position-reference systems, the gyrocompass and the vertical reference sensors. Wind speed and direction are measured by the wind sensors. The DP system calculates the deviation between the measured (actual) position of the vessel and the required position, and then calculates the forces that the thrusters must produce in order to make the deviation as small as possible. In addition, the system calculates the forces of wind, wave and water current which act upon the vessel and the thrust required to counteract them. The system controls the vessel’s motion in three horizontal degrees of freedom – surge, sway and yaw. The DP system is designed to keep the vessel within specified position and heading limits, and to minimise fuel consumption and wear and tear on the propulsion equipment. In addition, the DP system tolerates transient errors in the measurement systems and acts appropriately if an error occurs in
the propulsion units. Figure 2 presents block diagram of DP system or DP simulator. The kernel of this system is the vessel model which hydro-dynamics are actually supplemented by extended Kalman filter algorithm similar to the one presented in [1]. The algorithm calculates values of vessel’s state vector (position, heading and motion) by measurements filtration and then it changes resulting force demand – thrusters allocation to meet position, heading and motion settings.
Kalman filtering
A discrete random dynamic system is described by two equations in the Kalman filter:
– state equation (structural model of the process):
k k k
k
A
x
w
x
1
1
(1)– measurement equation (measurement model):
k k k
k
H
x
v
z
(2)where: x – nth dimension state vector, w – rth dimension state disturbance vector, z – mth dimension measurement vector, v – pth dimension state disturbance vector (measurement noise), A –
n × n dimension transition matrix, H – m × n
dimension measurement matrix, r ≤ n, p ≤ m.
Fig. 1. Full Mission Ship Simulator with DP systems Rys. 1. Wielozadaniowy symulator statku z systemami DP
Besides, it is assumed for disturbance vectors w and
v that they are Gaussian noise of normal
distribution, of zero mean vector and are mutually
not correlated. The state equation describes the trend of the vector concerned, and the measurement model gives the functional dependence of the
Fig. 2. Block diagram of DP system / simulator based on [2] Rys. 2. Schemat blokowy systemu / symulatora DP na podstawie [2]
measurement on this vector. The solution to the equation system (1), (2), taking into consideration the limitations imposed on disturbance vectors, is in the Kalman filter.
The estimation of the state vector in the filter can be presented by the equations below:
– state vector forecast: 1 ˆ ˆk Akxk x (3) where: n k x
ˆ − forecast or a-priori estimated value of the state vector at k-moment, n
k
x
ˆ −
a-posteriori estimated value of the state vector, – covariance value of the forecast of state vector:
k T k k k k A P A Q P 1 (4)
where: Q is the matrix of the covariance of the state disturbance (of vector w), index T means matrix transposing,
– filter amplification matrix:
1 T k k k k T k k k P H H P H R K (5)where R is the covariance matrix of measurement disturbance (of vector v),
– estimate of the state vector from filtration after making measurement zk:
k k k k k k x K z H x xˆ ˆ ˆ (6)– covariance matrix of the estimated state vector:
k k k k I K H P P (7)where I is the identity matrix.
In DP systems controlling vessel’s position with fixed heading in two dimensions generally the following values are to be estimated: position coordinates (ϕ, λ), projections of the speed vector in relation to the bottom onto the meridian and the parallel (VN, VE), acceleration vector projections
onto the meridian and the parallel (aN, aE) and the
projections of acceleration vector derivatives in relation to the bottom onto the meridian and the parallel (a’N, a’E). In this case the state vector will
have the following elements:
T E N E N E N kV
V
a
a
a
a
x
,
,
,
,
,
,
,'
'
(8) The measured values will be: position coordi-nates of the positioning system used (ϕPS, λPS),speed components in relation to the meridian and the parallel from DR navigation performed by the positioning system used (position changes deriva-tives VN, VE), acceleration components in relation to
the meridian and the parallel from an inertial transformer (aN, aE). So the measurement vector
will have the following elements:
T E N E N PS PS kV
V
a
a
z
,
,
,
,
,
(9)The matrixes in equations (1)–(7) containing the above mentioned elements are build similarly to ones presented in [1]. Some assumptions like values of variance and covariance for particular measurements have to be done, for instance: DGPS system − σϕ = 1.0 m; σλ = 1.0 m; coordinates not
correlated; speed components − σV = 0.1 m/s;
acceleration components − σa = 0.01 m/s2.
Instructor role
The instructor station can access all exercise and environmental conditions, introduce failures and situations where the operator must take corrective actions [3]. The instructor can initiate loss of thrusters and generators and create noise in sensor readings and position reference systems. The instructor has the same range of information in “feedback” from the DP operators. Faults and errors introduced, will force the trainee to e.g. find another thrusters allocation, start emergency generators and other systems, or selecting another sensor or position reference system. A full set of sensor systems, fully interfaced to the DP system, are available with instructor controlled faults, noise and interference.
Fig. 3. Instructor station at Full Mission Ship Simulator with DP systems
Rys. 3. Stanowisko instruktorskie w wielozadaniowym symu-latorze statku z systemami DP
Sensors
The following sensors are simulated: – gyrocompass,
– wind sensors,
– Vertical Reference Sensors, – speed sensor (log).
The Gyro sheet at instructor station [3] allows for monitoring of the Gyro compasses and for controlling and monitoring the Gyro correction (due to latitude and speed) panel on the active Ownship bridge.
The Air sheet at instructor station allows for monitoring of the wind parameters and for controlling of the wind sensors (wind direction and speed uniform with gusts or from chart database with shadows emulated). The wind sensor location can be changed inside ship model (see Fig. 4).
Fig. 4. Advantages and disadvantages of wind sensor location Rys. 4. Zalety i wady rozmieszczenia czujników przepływu powietrza (anemometrów)
The Vertical Reference Sensors comprising VRS, VRU and MRU are used for measuring pitch, roll and heave of real vessel. In the ship simulator environment that kind of data can be obtained from ship hydrodynamical model with emulation of any warnings, alarms and messages as in real sensors. The Waves and Sea sheets at instructor station allow for generation and controlling of external water forces.
The speed sensor can be either Doppler or electromagnetic type.
Acoustic Position Reference
The Acoustic Positioning Operator System (APOS) is operated as normal Kongsberg HiPAP / HPR system where a simulator replaces transceiver and the transponders [3]. A typical Long Base Line (LBL) and Super-Short Base Line (SSBL) operator presentation is shown in the figure 4. The vessel is positioned in the LBL array with the locations 1, 2, 3 and 4, and the SSBL transponder B27 is positioned relative to the vessel.
The APOS has following features:
– defined with one HiPAP and one HPR 400 receiver,
– sound velocity ray-trace calculation with dis-playing of deflection based on velocity profile input,
– SSBL positioning of transponders,
– telemetry communications with transponders, – calibration of LBL arrays,
– examining the expected accuracy when posi-tioning in different arrays,
– data output for testing telegram interfaces to external computers (standard HiPAP / HPR telegrams).
Fig. 5. LBL and SSBL operator presentation
Rys. 5. Interfejs operatora systemu APOS w konfiguracji LBL i SSBL
Artemis Position Reference
Fig. 6. Parameters measured and calculated by Artemis Rys. 6. Prametry mierzone i wyliczane przez system Artemis
The Artemis panel allows for microwave positioning of the range – bearing type. It outputs range and bearing from the fixed antenna to the ship’s antenna. Lost of signal, DIP zones and surface reflections impact the simulated measure-ment error. WINDSENSORSLOCATED INPOSITIONS1AND2 WILLGIVEINPUT DISTORTEDBY TURBULENCE FROM STRUCTURE LOCATIONS3AND4 AREBETTERBUTINPUT MAYNEEDTOBESCALED DOWNDUETOALTITUDE EXAGGERATINGTHE WINDSTRENGTH 1 2 3 4 WINDSENSORLOCATION North FIX Azimuth MOB Distance North Azimuth
Relative Mobile Antenna Bearing North
Heading
Heading = Azimuth + 180° - Relative Mobile Antenna Bearing
Windsensors located in positions 1 and 2 will give input distorted by turbulence from structure locations 3 and 4 are better but input may need to be scaled down due to altitude exaggerating the wind strength
North
Azimuth Distance
Relative Mobile Antenna Bearing Azimuth
Heading
Heading = Azimuth + 180 − Relative Mobile Antenna Bearing North
Satellite Position Reference
The Satellite Positioning Systems are operated via typical receiver interfaces or DP consoles as other position reference systems. The GPS has simulated default accuracy of 15 m (95%), DGPS of 3.3 m (95%), D(GPS + GLONASS) of 0.7 m (95%) and GALILEO of 4.0 m (95%). The accuracy of satellite position reference can be changed via instructor station.
Radius Position Reference
The Radius panel allows for similar radar positioning as Artemis. Because transponders have no moving parts their angle of operation is limited (max. 90) and depends on transponder location on the vessel (changeable in the ship model).
Fanbeam Position Reference
The Fanbeam panel allows for laser based positioning. The probability of the system locking on other reflecting objects and blocking of the signal is determined at the instructor station. The range depends on the simulated weather. It outputs ranges and bearings to the reflecting prisms (their positions defined inside models used in the scenario).
Thrusters
Thruster and propulsion systems are ship-model dependent and can be chosen among:
– main propellers and rudders: • single or twin screw, • with or without nozzle, • variable pitch and fixed RPM, • fixed pitch and variable RPM, • variable pitch and RPM, • single or twin rudder, • rudder active or inactive; – azimuth thrusters;
– tunnel thrusters; – water jet;
– voith-Schneider thruster.
The “Fail-safe” mode for controllable pitch propellers in DP vessels is the “zero pitch” point, however several possible failure modes can cause pitch freeze (fail-as-set), full pitch, failure to zero pitch, failure to any pitch setting.
DP integrated consoles
Dual redundant DP Operator Consoles (K-Pos Class 2) that will be installed at Maritime University of Szczecin Full Mission Ship Simulator allow for manual joystick operation and automatic station-keeping including:
– position and heading change, – Autopilot,
– Auto Track.
Various system faults can be simulated via instructor station. Figure 7 presents block diagram of DP system integration into ship simulator,
Fig. 7. Block diagram of DP Class 2 System integrated into ship simulator system [2]
Rys. 7. Schemat blokowy systemu DP klasy 2 zintegrowanego z symulatorem wielozadaniowym statku [2]
Wind Gyro VRS External force Other sensors Thurster-feedback Thurster-setpoint Pos. ref. Power
abbreviations stand for: OS – operator station, DPC-2 – dynamic positioning controller with dual controllers (class required redundancy).
Conclusions
DP models implemented into Kongsberg-Polaris Full Mission Simulator enable not only advanced training in all aspects of ship-handling and navigation but also allow for in-depth scientific studies because of their customizable open structure. By following conclusions – the systems presented in chapter 2 – for DP models utilization in research can be quite straightforward:
1. DP capability analysis for various vessels and external conditions (weather conditions) can be performed either in the on-line or off-line mode. Figure 8 shows, by means of a schematic radar-plot outline, an example of capability radar-plot presenting operational margins with respect to the environmental conditions (wind speed vector) and possible system failures. Symbols at the top mean from the left clockwise: waves direction, wind direction, sea-current direction, EBL direction for detailed readout.
2. Studies in ship motion modelling, identification of ship motion and ship’s steering conducted on
very realistic hardware can lead to more accurate ship models, modification of their parameters and equations.
3. Data analysis leading to autonomous models of track steering as presented in [4] can be developed further.
4. New software interfaces based on human-factor analysis can be designed with methodology similar to PNS [5].
5. Human factor on contemporary ship bridge with navigation equipment customised to any ship and / or emergency scenario can be thoroughly analysed.
6. Finally the navigation safety analysis of offshore DP vessels can be performed including the complex risk criterion [5] (Fig. 9).
Fig. 9. Manoeuvring area obtained during navigation safety analysis
Rys. 9. Obszar manewrowy uzyskany w wyniku analizy bez-pieczeństwa nawigacji
References
1. BANACHOWICZ A.: Variants of Structural and Mesurement
Models of Integrated Navigational Systems. Sekcja Nawi-gacji Komitetu Geodezji PAN, Polskie Forum Nawiga-cyjne, Gdynia 2001, Annual of Navigation 2001, 3, 5–12. 2. Operator and Maintenance Manual – Kongsberg K-Pos DP,
Basic and Advanced Trainer Szczecin. Doc. no.: 1129220, Kongsberg Maritime AS, Horten 2010.
3. Technical Manual Section 5a – Instructor’s Manual POLARIS Ship’s Bridge Simulator. Doc. no.: SO-0612-O, Kongsberg Maritime AS, Horten 2007.
4. ZALEWSKI P.: Fuzzy Fast Time Simulation Model of Ship’s
Manoeuvring. In 8th International Symposium on Marine
Navigation and Safety of Sea Transportation TransNav 2009, Gdynia, A.A. Balkema Publishers, Rotterdam, Netherlands 2009.
5. GUCMA S.,GUCMA L.,ZALEWSKI P.: Symulacyjne metody
badań w inżynierii ruchu morskiego. Wyd. Naukowe AM, Szczecin 2008.
Fig. 8. Example of DP capability plot for various wind speeds and directions
Rys. 8. Przykładowy wykres ograniczeń utrzymania statku na pozycji systemem DP dla różnych prędkości wiatru
