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Method for estimation of icebreaker propulsion performance in ice
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Polar Mechanics 2018
IOP Conf. Series: Earth and Environmental Science 193 (2018) 012027 IOP Publishing
doi:10.1088/1755-1315/193/1/012027
1
Method for estimation of icebreaker propulsion performance
in ice
G I Kanevsky 1, A M Klubnichkin 1, A V Ryzhkov2 and K E Sazonov1
1 Ice laborotary, Krylov State Research Centre, St.Petersburg, Russia
2 Central Design Bureau «Iceberg», St.Petersburg, Russia
E-mail: K_Sazonov@ksrc.ru
Abstract. Classical methods of ship propulsion estimations based on the traditionally applied
system of hull and propeller interaction coefficients are not suitable for prediction of icebreaker
performance in ice. This is because the wake fraction tends to assume negative values in
operating conditions typical of navigation in ice. This paper suggests an alternative system of
hull/propeller interaction coefficients to overcome the problem. The alternative system
comprises the thrust deduction factor t and the factors allowing for hull effect on thrust iTB and
hull effect on torque iQB. An alternative method of ship propulsion performance estimations is
developed based on this system of coefficients to take into account all characteristics of
icebreaker sailing in ice. The method was used to analyze the full-scale data obtained from sea
trials of the icebreakers Vladivostok and Novorosiisk. The initial data inputs for the analysis
were ship speed in ice and consumed power measured during the sea trials. The number of
propeller revolutions and ice resistance were calculated. The estimated propeller revolutions
were compared with the full-scale data gathered during the sea trials in ice. The ice resistance
was compared with the predictions based on model tests in ice basin. It is shown that at slow
speeds in ice, ranging from 0.5 to 5.0 knots, the predicted number of propeller revolutions is
in good agreement with the data measured during the sea trials. Propulsion performance of the
Vladivostok icebreaker in 1.5-m thick ice was estimated
1. Introduction
In view of the modern developments in Arctic shipping it is required to increase the operational
efficiency of icebreakers and ice-going vessels and, in this connection, to drastically raise the accuracy
of predictions regarding the propulsion performance of ships in ice. The propulsion performance in ice
has two components: ice resistance and thrust of propulsion system. Recently the most vivid progress
has been achieved in development of experimental [1, 2] and computational [3–7] methods for ice
resistance evaluations. All these references as well as many other studies provide for ice resistance
predictions with acceptable accuracy for design purposes, in particular for the cases of close-to-limit
ice conditions.
A vast majority of studies on icebreaker propulsion systems have focused only on the interaction
between ice and propellers or propulsion pods with an emphasis on strength considerations [8-12].
However, little attention has been paid to the hydrodynamic aspects of icebreaker propulsions. Only
one reference can be cited [13] where some specific hydrodynamic issues of icebreaker propulsors
have been addressed, e.g. cavitation phenomena.
Traditional approaches used today enable us to confidently predict only the limit ice-going
capability of icebreakers and vessels, i.e. the maximum thickness of ice field where the ship is able to
Polar Mechanics 2018
IOP Conf. Series: Earth and Environmental Science 193 (2018) 012027 IOP Publishing
doi:10.1088/1755-1315/193/1/012027
2
sail without stopping at a given power of main engines. However, it is impossible to predict the thrust,
torque, speed of revolutions and efficiency of icebreaker propulsors in a broader range of ice
navigation conditions, which is necessary for optimizing operation of icebreakers and ice-class
vessels. In this context it appears that prediction of ship propulsion in ice for the entire spectrum of
operating conditions is very much relevant today.
2. Traditional and “bollard pull” system of hull/propeller interaction coefficients
The traditional system of hull/propeller interaction coefficients is made up of three factors: t – thrust
deduction coefficient, w – wake fraction and iQ – factor allowing for non-uniform wake effect on
torque. The values of these coefficients and their dependence on propeller load are determined
experimentally by self-propelled model tests, comparing propeller curves obtained in open water and
behind model hull. This comparison is done at equal thrust coefficients in open water
0T
K
and behind
model hull
T
K
. Figure 1 gives a typical curve of wake fraction versus effective thrust of propulsors
KDE, showing that the wake fraction turns negative at KDE variations in the range from 0 to 1.0, which
is typical for ice sailing. The traditional approach to propulsion performance prediction in this case is
no longer applicable because of negative wave fraction values.
0,0 1,0 2,0 3,0
0,00
0,05
0,10
0,15
KDE
t
nb=12.5 rps, nc=13.2 rps:
t
t
-0,5
0,0
nb=12.5 rps, nc=13.2 rps:
WT, iQ
- starboard
- portboard
- central
wTB
wT_Un_C
wTSB
wTPB
wT_Un_C
Figure 1. Typical results obtained using
traditional hull/propeller interaction
coefficients
The alternative system of interaction coefficients is based on the data traditionally obtained
from towing tank experiments [14]. Coefficients are determined at a given constant advance ratio of
propeller
J
. For this purpose the test data plots are used to pick up the values of thrust and torque in
open water
00 ,QT KK
and behind model hull
QT KK ,
, as well as effective thrust coefficient
E
K
. The
interaction coefficients are defined by the following equations:
Polar Mechanics 2018
IOP Conf. Series: Earth and Environmental Science 193 (2018) 012027 IOP Publishing
doi:10.1088/1755-1315/193/1/012027
3
- factor allowing for hull effect on thrust
( )
( )
JK
JK
iT
T
T0
=
- factor allowing for hull effect on torque
( )
( )
JK
JK
iQ
Q
Q0
=
- thrust deduction factor
( )
( )
JK
JK
tT
E
−= 1
.
The thrust deduction factor is estimated in the same way as it is done under the traditional
approach.
A specific feature of the “bollard pull” approach is that flow velocities in open water and behind
model hull are equal, hence the advance ratios are also equal, however, the propeller thrusts in this
case are different. The propulsive efficiency
in the “bollard pull” approach is defined as:
( )
Q
T
sh i
ti −
=1
0
where
sh
- shafting efficiency,
0
- propeller efficiency in open water.
Figure 2 shows values of alternative interaction coefficients for a four-shaft icebreaker sailing
ahead.
0,0 0,2 0,4 0,6 0,8 1,0
0,9
1,0
1,1
1,2
1,3
1,4
1,5
iT- central propeller
iQ- central propeller
iT- board propellers
iQ- board propellers
iQ, iT
KDE
Hull/propeller interaction coefficients for icebreker project 22220.
Moving ahead. Deep water.
0,0
0,1
0,2
0,3
0,4
0,5
0,6
t
t
Figure 2. Alternative interaction coefficients versus load coefficient Kde for icebreaker.
3. Propulsion performance estimations for icebreaker
Introduction of the “bollard pull” coefficients system enabled us to work out a method for estimation
of icebreaker propulsion performance in ice environment. The main assumption is that the
hull/propeller interaction coefficients estimated based the “bollard pull” approach can be extended to
the icebreaker operation mode in ice. It is a quite conventional assumption that was used before to
study ship sailing in ice. The efforts to develop a new method required certain correction of the
traditional performance prediction technique as well as generalization of results to the case of a multi-
Polar Mechanics 2018
IOP Conf. Series: Earth and Environmental Science 193 (2018) 012027 IOP Publishing
doi:10.1088/1755-1315/193/1/012027
4
shaft vessel whose propulsion system comprises different type propulsive units, e.g. conventional
screw propellers and podded thrusters.
The new approach makes it possible to estimate the revolutions and thrust of propulsors. Figure 3
shows a diagram relating all main characteristics of icebreaker performance in ice: speed, thrust and
number of revolutions.
Figure 3. Propulsion performance diagram for icebreaker Pr.21900m
4. Application of results
The new method is applicable to a range of practical tasks in the design of icebreakers. The main
advantages are new opportunities in the analysis of full-scale data from icebreaker sea trials, insights
into the ice influence on hydrodynamic characteristics of icebreakers, more accurate test in ice basins
with self-propelled models of icebreakers.
Sea trials. As it is seen from the diagram of Figure 3 it is possible to find the pulling thrust
developed by propulsors based on the power and speed of the icebreaker measured in sea trials. The
number of propulsor revolutions also determined from the above diagram serves as an indicator to
confirm the procedure correctness.
If we pick the records of ship speed, power and propeller revolutions at the sections where
propellers do not show any significant interaction with ice, it is possible to estimate the thrust of
propulsion system and, therefore, ice resistance for these sections. Actually, the suggested method
makes it possible to estimate the ice resistance in full scale conditions. With this capability of
estimating full-scale ice resistance one can address a range of issues. In the analysis of full-scale data
the information about ship ice resistance enables us, first, to make full use of the measurements taken
at partial power outputs of ship power plant. Secondly, the ice resistance data enable extrapolation of
full-scale test results to different ice strength and thickness values using well-known correction
techniques employed in model experiments. Figure 4 illustrates results of full-scale data processing. It
shows the speed of Vladivostok icebreaker versus ice thickness referred to a standard ice bending
strength of 500 kPa, as per full-scale trial data [15]. Squares on the graph refer to the results obtained
0 1 2 3 4 5 6 7 8 9 10 11 12
6
7
8
9
10
11
12
13
14
15
16
17
18
100 110
120
130
140
600
800
1000
1200
1400
1600
PS, MW
VS, kn
TE = 1700 kN
n=150rpm
Polar Mechanics 2018
IOP Conf. Series: Earth and Environmental Science 193 (2018) 012027 IOP Publishing
doi:10.1088/1755-1315/193/1/012027
5
by traditional processing method with extrapolation of power and speed data. Circles refer to the
results of ice resistance extrapolations by formulas used in model experiments. The results are in good
agreement.
0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0
0
2
4
6
8
10
12
14
16
18
obtained by traditional method
obtained by proposed method
Ship speed, knots
Ice thickness, m
Figure 4. Speed vs ice thickness obtained by different methods for the Vladivostok icebreaker
Investigation of interaction coefficients in ice conditions. Investigation of hull/propeller interaction
coefficients for a ship sailing in ice is a very challenging task that has not been resolved yet. One of
the reasons is negative wake fractions mentioned above. However, our alternative system of
interaction coefficients brings us closer to the solution of this problem. The new system enables us to
examine ice effects on the interaction coefficients both in model experiments and in the analysis of
full-scale trials.
The values of interaction coefficients under the alternative method can be obtained by testing self-
propelled ship models towed in ice basin by towing carriage at constant speed in ice field. During
these tests the frequency of propeller revolutions is varied to change KDE. Model experiments in ice
field with variation of model speed at constant frequency of propeller revolutions cannot be used for
evaluation of hull/propeller interaction coefficients because in this case ice pieces adjacent to the
underwater hull change their size [16]. Obviously, it may have significant influence on the coefficient
values. The functions
( )
JfKT=
and
( )
JfKQ=
obtained from ice tests can be used to determine the
alternative system coefficients. Then their comparison with the coefficients obtained in open water
enables us to judge the ice effect.
Sea trial data can also provide information about hull/propeller interaction coefficients in ice. If
propeller revolutions measured in full scale are different from predictions, e.g. based on the diagram of
Figure 3, then it is always possible to choose an appropriate correction factor to adjust the assumed
coefficient values and remove discrepancies in the frequency of propeller revolutions. With
accumulation of statistical data from full-scale trials of various ships it would be possible to generalize
the results and derive empirical relationships for interaction coefficients in ice.
Calculation of propulsion performance in ice for model conditions (with stock propellers) make it
possible to set the frequency of propeller revolutions more accurately in model tests to better simulate
real conditions. This selection of propeller revolutions is most important when slipstreams of
Polar Mechanics 2018
IOP Conf. Series: Earth and Environmental Science 193 (2018) 012027 IOP Publishing
doi:10.1088/1755-1315/193/1/012027
6
propellers may have effect on the ice on the underwater hull of model (sailing astern, bow propellers,
etc.)
5. Conclusions
The alternative system of hull/propeller interaction coefficients is helpful in addressing a broad range
of issues related to ship propulsion performance in ice. In addition to estimation of critical icebreaker
parameters in ice: power, propeller revolutions and pulling thrust, the proposed system of coefficients
paves the way for systematic studies on hull/propeller interaction coefficients in ice, providing
requisite “initial conditions” for this purpose.
The alternative system of interaction coefficients enables rather accurate predictions of ice
resistance for full-scale sea trials, increasing the efficiency of such trials. Also, the ice resistance
calculations may well be used by designers of ship engines for their improvement.
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IOP Conf. Series: Earth and Environmental Science 193 (2018) 012027 IOP Publishing
doi:10.1088/1755-1315/193/1/012027
7
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