Ship manoeuvring hydrodynamics in a new inland

Scientific Journals
Zeszyty Naukowe
Maritime University of Szczecin
Akademia Morska w Szczecinie
2014, 37(109) pp. 10–15
ISSN 1733-8670
2014, 37(109) s. 10–15
Ship manoeuvring hydrodynamics in a new inland
shiphandling simulator of SMU – InSim
Jaroslaw Artyszuk, Lucjan Gucma, Maciej Gucma
Maritime University of Szczecin, Faculty of Navigation
70-500 Szczecin, ul. Wały Chrobrego 1–2, e-mail: [email protected]
Key words: inland ship, hydrodynamics, manoeuvring, mathematical model
Abstract
The present paper describes the hydrodynamic modelling solutions, applied in the newly developed
shiphandling simulator at SMU (Szczecin Maritime University) for the inland navigation – called InSim.
The objective is to provide some guidance on the simulator capability and potential while conducting various
research and the crew training projects.
Introduction
mathematical model (the so-called dynamic model)
of the object’s motion. For a floating object, one
gets here a hydrodynamic model. The hydrodynamic model of a ship, based on differential equations in a moving frame, operates in a loop, where
for given instantaneous environment disturbances
and operator’s steering settings the particular forces
and moments are calculated. In the next step,
through equations integration, the resulting linear
and angular velocities, and corresponding displacements, are calculated and forwarded to the
simulator’s visual system responsible for displaying
the ship’s smooth movement.
The functional diagram of such simulator is presented in the figure 1, which also served as the
framework for developing hardware and software
of the latest, independent InSim simulator of SMU,
dedicated to inland navigation. The latter is a new
area of interest covered by SMU according to their
long-term experience and expansion policy. The
layout of InSim bridge is shown in the figure 2.
The major merits behind the computer simulation in general, and its application for evaluation
of vessel traffic safety in restricted waterways in
particular (like InSim), are among others today as
follows:
– high degree of conformity with reality;
– mathematical modelling flexibility ensuring
fast-built, simple, and adequate models accord-
The manoeuvring simulation models (simulators) of sea-going and inland ships, as used in
marine traffic engineering, belong to the following
two types:
– non-autonomous;
– autonomous.
The non-autonomous simulation model is an interactive model with a human (operator) input,
which mostly works in real time. The simulation
with such a model is very sensitive to the operator’s
knowledge and skills. Additionally, the obtained
results are essentially affected by the technical solutions used to simulate the informational (input)
environment – e.g. the bridge visual view, and/or
the bridge equipment display – and the control
(output) environment. The latter is connected with
the emulation of steering devices, for instance.
Nowadays, since the simulation almost entirely
has been run by the computers, where everything
must be mathematically (numerically) modelled
and programmed, the advantage of nonautonomous simulation is that we do not have to
mathematically model a very complex decision
process of a human. On the contrary, the human
modelling is absolutely required within the second
type of simulation – autonomous one. The key element of the computer simulation, if applied to
physical phenomena of motion, is the adopted
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Scientific Journals 37(109)
Ship manoeuvring hydrodynamics in a new inland shiphandling simulator of SMU – InSim
– time-effectiveness of data collection and processing;
– solutions can be tested and objectives met without the need to create a real system  non-
ing to research objectives, including the stochastic models;
– low financial effort in comparison to the physical simulation;
Fig. 1. The functional diagram of InSim simulator
Fig. 2. The photo of InSim simulator with presentation harbour of Szczecin – the neighbourhood of Wały Chrobrego
Zeszyty Naukowe 37(109)
11
Jaroslaw Artyszuk, Lucjan Gucma, Maciej Gucma
existing systems can be examined, e.g. a maximum ship for the safe operation of given waterways;
– virtual extreme loads can be applied on the investigated object, especially those destructive
ones.
The present study is devoted to hydrodynamic
modelling solutions applied in the InSim simulator.
They have direct and indirect effects on reliability
of simulation results and potential areas of the
simulator’s application.
The SMART library can be easily replaced with
another one, preserving the library functions calling
interface, since one of the key features of the InSim
simulator is open independent architecture, thus
allowing an extension of the simulator to meet
various, especially future training and/or research
the needs. The commercial simulators are mostly
prevented from doing even a small modernisation
by the user on his own that necessitates placing new
simulator upgrading orders to the same manufacturer.
Mathematical model description of InSim
The software of InSim
The differential equations of ship manoeuvring
motions in the usual moving frame of reference are
as follows:
All procedures for the ship manoeuvring computation are gathered in a self-contained MS Windows
DLL library developed using the C++ language.
This basic file “mm_model.dll” together with a ship
hydrodynamic database file (of .HDB extension)
for each ship model forms a package, referred to as
the “SMART DLL”. An additional nautical area
file (of .MAP extension), which brings a distribution map of various physical phenomena (wind,
current, wave, bank, fender, etc.), can also be
loaded. Appropriate programming interfaces to use
the dynamic-link library in C++ or Delphi programming environments are provided. The hydrodynamic database files can be supplied in encoded
or open format, as to allow in the latter case an
input from the authorized user by means of any text
editor. These ship specific data files comprise all
dimensional and nondimensional model parameters,
mostly of geometric or hydrodynamic nature, including among others sophisticated multidimensional lookup tables as representing functional relationships. Since the “SMART DLL” is a purely
mathematical library, the user is required to provide
a graphical interface within his application for acquiring steering commands.
The crucial procedure of the DLL library, called
“smm_inout (...)”, is basically a single recursive
advance of the ship motion state vector (but extended from the usual one as to combine also the
dynamics of steering devices). This is done through
a numerical integration of the aforementioned ship
motion differential equations. Various numerical
algorithms for ODE problems are available within
the package, but the Euler method is still here sufficient and mostly frequently used. If the
“smm_inout” procedure is run inside the PC timer
controlled loop, then a real-time mode is achieved.
Since the procedure is absolutely very fast, even
with large sizes of the accompanied ship model
HDB files, it is thus well suited also for fast-time
(offline) modes.

d v xg


m

m
 m  cm m22  v yg  z 

11
d
t


 m11  cm m22  v cy z  Fx

g
 m  m  d v y   m  m  v g  

22
11
x z
(1)
dt

c

 m11  m22  v x z  Fy

J  m  d  z  M
66
z
 z
dt


where:
vx, vy, z – surge, sway and yaw velocity;
t
– time;
m
– ship’s mass (displacement);
m11, m22, m66 – added (virtual) masses;
cm
– empirical (viscosity) reduction factor;
Fx, Fy, Mz – external physical excitations as resultant forces and moment;
g, c – superscripts denoting a ship’s ground
velocity vector components and the water
current velocity vector components.
The external excitations are modelled within the
modules below (the quoted symbols are also used
to distinguish particular components of the resultant
forces and moment):
H
– hull;
P
– propeller;
R
– rudder;
A
– wind (aerodynamics);
WV
– wave action (of 1st and 2nd order);
ICE
– ice interaction;
BE
– bank effect;
SS
– ship-to-ship;
LTU – lateral thruster unit;
FEND – fenders;
MOOR – moorings;
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Scientific Journals 37(109)
Ship manoeuvring hydrodynamics in a new inland shiphandling simulator of SMU – InSim
ANCH – anchors;
TUG – tugs.
Each of these excitation models consists of a
dimensional part (mostly being a product of certain
physical quantities leading to a proper unit, e.g. N
or NM) and a non-dimensional part, essentially
constituting a single non-dimensional coefficient,
being strictly a constant or a function of multiple
parameters. Sometimes, this non-dimensional coefficient (i.e. the multiple variable function underneath) is decomposed into a product or a sum of
simpler coefficients (functions) that gives much
comfort in storing, such relationships in lookup-tables. Latter can be easily handled if their dimensions are limited up to three, in which case we have
a three-variable functions. However, the two-dimensional lookup-tables are the best.
The above lookup-table approach is just fully
implemented in the SMART library in that any
analytical formulations for hydrodynamic coefficients, e.g. in the form of polynomial expansion, as
widely published in the literature, are strongly
avoided. The mentioned expansion sometimes
serves only as the background (initial guess) for
tuning the non-dimensional coefficients in accordance with the ship’s performance in sea trials.
The both parts of (semi-empirical) model for
given excitation, dimensional and non-dimensional
one, belong to the art of dynamic modelling. Both
required a lot of efforts to arrive at the adequate and
flexible solution, where all the essential effects /
relationships connected with particular excitation
are reflected up to the required level of accuracy.
For example, an improper choice of dimensional
part may significantly complicate the non-dimensional coefficient.
The dynamic model (1) has to be further supplemented with the known kinematical relationships – differential equations of the first order – for
the change of the heading angle and the ship’s
origin position.
Other details on model fitting procedures can be
found in [1].
Table 1. Basic data of “Luisa Lynn”
Length over all (L)
Breadth extreme
Draught extreme
Trim
Displacement (fresh water)
Main engine power/rpm
Gear
Propeller
Stern rudder
Bow thruster
a)
b)
Fig. 3. Selected views of “Luisa Lynn”; a) source: www.
marinetraffic.com, b) source: Rentrans Cargo Ltd. (Szczecin,
Poland) – the owner’s archive
propeller wake fraction and thrust deduction as
functions of forward speed and propeller loading.
Finally, the hull resistance coefficient in deep water, kept, however, constant against the speed, was
scaled accordingly (also for other non-zero drift and
dimensionless yaw values) to reach the known
maximum speed of “Luisa Lynn”, equal to abt.
10.9 km/h. The speed relevant to other settings
of the wheelhouse speed control knob is given in
the table 2.
Specific data on “Luisa Lynn”
The main particulars of “Luisa Lynn”, the first
ship being modelled for InSim simulator, are presented in the table 1.
The abovewater side view and the underwater
stern view are shown in the figure 3.
The values of thrust and torque coefficients of
the propeller, as functions of the advance coefficient and pitch ratio, were taken from available
published model tests on CPPs and preserved in the
mathematical model. The same was done with the
Zeszyty Naukowe 37(109)
78.8 m
8.0 m
2.12 m
–
1150 t
265 kW/340 rpm
none
CPP in half-nozzle, right-handed,
diameter 1.45 m, 3-bladed
underhung, dual-blade,
maximum angle 57
nominal thrust 0.5 t (estimated)
Table 2. Estimated speed of “Luisa Lynn”
Speed setting [%]
100
80
60
40
20
13
Speed [m/s]
3.03
2.58
2.26
1.69
1.07
Speed [kt]
5.89
5.02
4.39
3.29
2.08
Speed [km/h]
10.9
9.3
8.1
6.1
3.9
Jaroslaw Artyszuk, Lucjan Gucma, Maciej Gucma
lateral velocity
0
-0.1
0
100
200
300
400
4
-0.3
3
pomiar
trial
-0.4
pomiar
trial
2
sim.
symul.
-0.5
sim.
symul.
1
-0.6
60
forward velocity
5
-0.2
-0.7
vx[kt]
6
500
time[s]
time[s]
0
 vy[m/s]
0
drift angle
 []
100
30
40
20
300
10
30
time[s]
0
20
-10
10
400
heading
 []
40
50
200
0
100
200
300
400
-20
time[s]
0
-30
0
100
200
300
400
500
-40
forward velocity
2.5
Fig. 5. 20/20 zig-zag test (constant throttle)
vx[m/s]
2
Concerning the turning and yaw checking ability, determined by means of turning circle and zigzag tests, the combined trial and simulated charts
are presented in figures 4 and 5. The trial data, also
as a part of the InSim project, were obtained
through measurements at sea using a dedicated
hardware and software developed at SMU. The
simulated values refer to the model performance
after application of a special model fitting procedure, mostly connected with calibrating the hull
sway force and yaw moment coefficients (as functions of drift angle and dimensionless yaw velocity), and the rudder-hull interaction factors as well.
The displayed in the figure 4 turning circle trial
data, all except the yaw velocity z, have already
included an allowance for the existence of water
current at the trial site and refer to the midship position. The current set and drift, 170 (related to
ship’s initial heading) and 0.18 m/s accordingly,
were herein established on the principle of getting
during the data recalculation process a constant
drift angle at the steady phase of turning.
With regard to stopping ability the agreed sea
trial program only encompassed coasting stop tests,
i.e. with setting the propeller to zero pitch. For
a right-handed controllable pitch propeller this
leads to the well-known effect of ship’s turning
towards the starboard side. This phenomenon is
very clear for “Luisa Lynn” too. The figure 6 shows
the forward velocity and heading change for the
two conducted runs of such stopping. Though of the
same steering, they reveal some remarkable differences.
1.5
1
0.5
time[s]
0
0
100
200
300
 z[/min]
70
400
500
yaw velocity
60
50
40
30
20
10
time [s]
0
0
100
200
300
250
400
500
track
xO[m]
200
150
100
50
0
-150
-100
-50
0
50
yO[m]
Fig. 4. Turning circle test (rudder angle 57 PORT, constant
throttle)
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Scientific Journals 37(109)
Ship manoeuvring hydrodynamics in a new inland shiphandling simulator of SMU – InSim
vx[kt]
6
The reason for such strange behavior can be
hardly assessed at this stage of research. It should
be added that the water current effect has not been
analysed for the coasting stop tests.
The final manoeuvring mathematical model has
been essentially fitted against the trial No. 2 in the
figure 6 for speed decrease in that the wake fraction, thrust deduction, and the propeller thrust coefficient for zero pitch were tuned in the regions of
domain responsible for the coasting stop simulation. The yaw effect of the propeller zero pitch has
been however assumed in the middle of the both
records, since this has rather little influence on the
speed decrease rate, as in the case of “Luisa Lynn”.
The plots in the figure 7 demonstrate the
estimated performance (essentially based on the
adopted model test results of the CPP in concern)
during the crash stopping.
forward velocity
5
trial no.
1
pomiar
'ham1'
trial no.
2
pomiar
'ham2'
4
simul.
symul.
3
2
1
time[s]
0
0
100
200
300
400
500
heading
100
 []
80
60
40
20
time[s]
0
0
100
200
300
400
Final remarks
500
Fig. 6. Coasting stop performance
vx[kt]
6
The presented ship hydrodynamic model, despite the fact that only selected aspects of its have
been shown in this paper, is able to interact with
any inland waterway infrastructure. The other additional dynamic effects are also included in the
model. However, to perform simulation-based
safety studies in 3D visual environment provided
by InSim, concerning e.g. inland ship-bridge collisions and related bridge protection design (see [2]
for examples), we need a detailed graphical and
mechanical 3D model of inland waterway infrastructure. This is planned in the near future.
forward velocity
distance 168m (2.13 L)
time 110s
heading 62 to PORT
4
2
0
0
40
80
120
160
200
240
time[s]
-2
-4
0
0
40
80
-30
120
160
200
Acknowledgements
240
The work was carried out within the development
project of the Polish government: NCBIR –
R10002810, entitled Development and construction
of an integrated interactive simulator for inland ship
navigation and manoeuvring.
time[s]
-60
-90
-120
-150
-180
 []
References
heading
1. ARTYSZUK J.: Modelling and Simulation in Ship Manoeuvring Safety and Effectiveness Issues. Maritime University,
Szczecin 2013 (in Polish).
2. GUCMA L.: Risk Management in Ship Collision with
Waterway Bridges. Maritime University, Szczecin 2013
(in Polish).
Fig. 7. Estimated crash stop behaviour (FULL ASTERN)
Zeszyty Naukowe 37(109)
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