Achieving the highest possible efficiency from a propeller is needed to minimize
fuel. However, this is limited by the occurrence of cavitation, vibration, noise and
material strength possessed by propellers. Thus it is necessary to do a new
breakthrough in designing or modifying the shape of the propeller to achieve
maximum performance. One modification that can be done is to change the skew
angle. Propeller B-Series is a propeller that is often used and has a fairly complete
geometry data. Cavitation is something that must be considered because it will
manifest into noise, vibration and erosion in the propeller blade. The modification of
the skew angle will be analyzed using the CFD (Computational Fluid Dynamics)
method of how the relationship between performance and cavitation results from the
various variations that have been made. So that later it can be known that skew angles
produce maximum performance and low cavitation. From the simulation results it can
be concluded that the greater the skew angle, the value of the thrust and torque
2. The Effect of Variation Skew Angle B-Series Propeller on Performance and Cavitation
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decrease, but this is inversely proportional to the value of efficiency that has an
upward trendline with the greater angle of skew. Increasing the skew angle can
reduce the potential of cavitation at certain skew angles. The skew angle which has a
thrust value, torque, and efficiency that is quite high and has a fairly low cavitation
potential is at the skew angle 0⁰.
Keywords: Skew angle, B-series propeller, Cavitation, Computational fluid dynamics.
Cite this Article: Edi Jadmiko, Raja Oloan Saut Gurning, M. Badrus Zaman,
Setyo Leksono, Semin, Miskli Iska Nanda, The Effect of Variation Skew Angle B-
Series Propeller on Performance and Cavitation, International Journal of Mechanical
Engineering and Technology 10(5), 2019, pp. 219-234.
http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=10&IType=5
1. INTRODUCTION
Marine technology has progressed very rapidly. The progress was marked by the discovery of
theories and equipment that supported the operation of the ship. In addition, the development
that can be done is to modify it, one of the examples that can be modified is propeller in a ship
propulsion system. This certainly attracts the interest of scientists, experts and students on the
importance of innovation in a certain field that is expected to be better. The discovery of
theory and innovation originated from an observation of a particular object that is considered
to have characteristic values needed to complement the shortcomings of previous innovations.
Propulsion system is a system that functions to move the ship. The design of this
propulsion must be able to overcome all obstacles that occur on the ship in accordance with a
predetermined speed. A loss that is obtained when a propulsion system does not work
properly can result in inefficient fuel consumption. For this reason, further development
studies on the propulsion system are needed to minimize these losses. The propulsion system
on the ship consists of three components, namely the main engine, transmission system, and
propulsor. The resources obtained from the main engine will drive shafts and propellers that
will move the ship. The power received by the propeller will be reduced from the source
power because of the transmission process. The received power will drive the propeller which
can finally move the ship at a certain speed.
Reduced energy from the main power can occur due to mandatory transmission processes
and loses that occur in the propeller. Many studies have acknowledged that the modification
of the geometry of the propeller can increase or decrease the performance of the propeller [1].
Thus a new breakthrough is needed to design or modify the shape of a propeller. One
modification that can be done is to change the skew angle. This skew angle is the angle
formed between the propeller shaft center line and the blade tip [2]. Skew can also function as
a pressure drop on the propeller when breaking a fluid and minimize cavitation. [3] [4] [5]
Achieving the highest possible efficiency from a propeller is needed to minimize fuel.
However, this is limited by the occurrence of cavitation, vibration, noise and material strength
possessed by the propeller to continue to rotate continuously mechanically. Therefore some of
these things will be minimized as soon as possible in designing and modifying propellers. The
pressure distribution on the blade surface is very important for designing a blade by
considering the emphasis on cavitation. This emphasis on cavitation can later be seen from the
pressure coefficient (Cp) [6].
Propeller B-Series is a propeller that is often used and has a fairly complete geometry
data. However, to modify this propeller, it should be noted that the limits set so that the data
used such as graphs and diagrams can be appropriate. Previous studies have analyzed the
effect of skew angle variations on performance, but for effects that occur because these
3. Edi Jadmiko, Raja Oloan Saut Gurning, M. Badrus Zaman, Setyo Leksono, Semin, Miskli Iska Nanda
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changes such as cavitation, vibration, and noise have not been analyzed on a B-Series
propeller. The propeller performance can be in the form of thrust, torque and efficiency.
2. METHOD
In this chapter discuss the calculations performed at the preliminary design stage and analyze
the results of CFD simulation. The calculation on the design preliminary will determine the
propeller that will be used as a model. After determining the main size of the propeller
obtained, the model will then be made [7] and skew varied according to the one described in
the chapter. All models will be simulated CFD using numeca fine marine software. The
simulation results to be sought are performance results in the form of thrust, torque, efficiency
and cavitation. In the final stage, the relationship between performance and cavitation will be
analyzed due to the effect of skew angle variations on the B-Series propeller.
2.1. Preliminary Design
In this stage there are several calculations, namely: ship resistance, selection of B-Series
propeller type by making a graph using the polynomial method, and calculating cavitation
predictions with burril diagram [8]. In this study using the Moeri Container Ship (KCS) test
ship.The following is the main data size of the test vessel used in this study.
Lwl = 232.5 m
Lpp = 230.0 m
B = 32.2 m
D = 19.0 m
T = 10.8 m
Vsea = 24.0 knots
Cb = 0.651
Cm = 0.985
LCB = -1.48m
Fn = 0.26
2.1.1. Calculation of Ship Resistance
The calculation of the total resistance of this vessel uses the Holtrop Method which is
processed in the Maxsurf Resistance software. Data used for processing shaped surfaces (.igs)
obtained from sources. From the results of calculations on MaxSurf software, it can be seen
that the resistance at the ship's speed of 24 knots is 1333.5 kN.
2.1.2. Making KT Design Curve, KT, KQ, and Propeller Efficiency Using the Polynomial
Method
The making of KT-KQ-J curves on certain AE / AO consists of several KT curves and
propeller efficiency whose amount depends on the number of P / D variations, and one design
KT curve [9]. Where efficiency and KT are the ordinate axes and J is the abscissa axis.
Following are the calculation steps and what must be done so that it becomes a curve. there
are several steps of calculation and some formulas for making graphs.
J =
D.n
Va
(1)
KT = 42
.Dρ.n
T
[ Nm ] (2)
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KQ = 52
.Dρ.n
Q
[ Nm ] (3)
By substituting the formula n, it is obtained:
KTdesign = T . J2
/ ρ . Va2 .
D2
(4)
The KT curve of this design varies depending on the variable diameter of the propeller.
Below is a discussion of the design KT that matches the vessel resistance used along with
variations in advance coefficient (J) from 0.00 to 1.70 with 0.05 intervals as shown in the
table 1.
Table 1 Kt Design
J Kt Design J Kt Design
0.00 0.0000000 0.90 0.2817449
0.05 0.0008696 0.95 0.3139195
0.10 0.0034783 1.00 0.3478332
0.15 0.0078262 1.05 0.3834861
0.20 0.0139133 1.10 0.4208782
0.25 0.0217396 1.15 0.4600095
0.30 0.0313050 1.20 0.5008799
0.35 0.0426096 1.25 0.5434894
0.40 0.0556533 1.30 0.5878382
0.45 0.0704362 1.35 0.6339261
0.50 0.0869583 1.40 0.6817531
0.55 0.1052196 1.45 0.7313194
0.60 0.1252200 1.50 0.7826248
0.65 0.1469595 1.55 0.8356693
0.70 0.1704383 1.60 0.8904531
0.75 0.1956562 1.65 0.9469760
0.80 0.2226133 1.70 1.0052381
0.85 0.2513095
This calculation varies 4 B-Series propeller blades, namely leaves 3, 4, 5, and 6. This
calculation is also classified based on the price of AE / AO and P / D. KT curve and
efficiency are forms of variations in price of AE / AO and P / D. So in one price variation AE
/ AO there are 12 variations in the price of P / D. The following is the B-Series Polynomial
Wageningen which is used to determine the price of ΔKT and ΔKQ.
KT = d
c
O
E
b
a
abcd .Z
A
A
..
D
P
..JAΣ
(5)
KQ = d
c
O
E
b
a
abcd .Z
A
A
..
D
P
..JBΣ
(6)
The ΔKT and ΔKQ value is the exponential total number of the KT formula in the same
input. Efficiency Propeller can be calculated by formula:
η = KT . J / (2π . KQ)
KQ = KT . J / (2π . η)
(7)
Table 2 express an example of the performance results of KT; KQ, and Efficiency of B-
Series 6 propeller blades at Ae / Ao 50 in various P / D 0,5.
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Table 2 Example of Calculation Result B6-50
P/D = 0.50 Varition = 1
J Kt 1 10 Kq Eff 1
0 0.224507 0.202654 0
0.05 0.210639 0.193584 0.086588
0.1 0.195423 0.18416 0.168889
0.15 0.1789 0.174214 0.245153
0.2 0.161105 0.163578 0.313499
0.25 0.142079 0.152084 0.371712
0.3 0.121858 0.139566 0.416886
0.35 0.100481 0.125855 0.444735
0.4 0.077986 0.110784 0.448142
0.45 0.05441 0.094186 0.413735
0.5 0.029792 0.075893 0.312381
0.55 0.00417 0.055737 0.065483
0.6 -0.02242 0.033552 -0.63807
0.65 -0.04994 0.009168 -5.63446
0.7 -0.07834 -0.01758 4.96466
0.75 -0.1076 -0.04686 2.74083
0.8 -0.13767 -0.07884 2.223307
0.85 -0.16852 -0.11369 2.005247
0.9 -0.20011 -0.15158 1.891034
0.95 -0.2324 -0.19266 1.823786
1 -0.26534 -0.23712 1.78099
1.05 -0.29892 -0.28512 1.752022
1.1 -0.33308 -0.33682 1.731262
1.15 -0.36778 -0.39239 1.715501
1.2 -0.403 -0.452 1.702796
1.25 -0.43869 -0.51583 1.691926
1.3 -0.47481 -0.58402 1.682099
1.35 -0.51133 -0.65676 1.672794
1.4 -0.5482 -0.73422 1.663661
1.45 -0.5854 -0.81654 1.654467
1.5 -0.62287 -0.90392 1.645057
1.55 -0.66059 -0.99651 1.635329
1.6 -0.69852 -1.09448 1.625219
1.65 -0.73661 -1.19799 1.614688
1.7 -0.77484 -1.30723 1.603716
From the table 1 and table 2, Kt-J graph and efficiency with the following price variations
are obtained:
Variation in price pitch ratio (P / D), namely: 0.5 to 1.4
Variation of AE / A0 according to the book Principle of Naval Architecture Volume II Page
186
Price of variation J between 0.00 - 0.17 with an interval of 0.05
Blade propeller (Z) is taken 4 blade, namely 3, 4, 5, and 6.
J is used as the axis (x)
Kt and efficiency are used as ordinate axis (y)
After all the polynomial calculations are completed, then the graphs of KT, KQ, and
Efficiency are carried out which intersect with KT design.
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Figure 1 Graph of B6-50
2.1.3. Propeller Cavitation Check
This calculation is done to check that a propeller has cavitation or not [8]. The following
calculation must be done by Burril Diagram method:
Developed Area:
AD = 2
O
E
D..0.25.
A
A
.
[m2
] (8)
Projected Area Ratio:
D
P
A
A
= 1.067 – 0.229 P/D (9)
Projecred Area:
AP = D.
A
A
D
P
[m2
] (10)
Relative Velocity:
VR= 22
...7.0 DnVa
(11)
Mean thrust loading iin blade
τC‘ = 2
R
P
.1025.V0,5
T/A (12)
Local Cavitacion Number at 0,7 radius
(13)222
836.4
'62.192.188
0,7R
DnV
h
A
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This value of σ0.7R is used to find out the value of cavitation numbers on burrill diagrams
cut by the curve of the merchant ship propeller. If Tc burrils> Tc count (cavitation).
Reference in selecting B-Series propeller types by choosing a propeller that has maximum
efficiency and does not experience cavitation. The thrust produced by the propeller must also
be greater than the thrust of the ship. So that in this study choose a B-Series B6-80 type
propeller.
2.2. Calculation of the Main Size of Foil Propeller
2.2.1. Propeller Main Data
The main data from the propeller is known after the selection of the B-Series propeller type.
The following main propeller data is the initial data that will be used to calculate the
coordinates of each foil and draw a propeller projection. Below is the main data propeller:
D : diameter propeller = 7.56 m
AE/A0 : expanded area ratio = 0.80
Z : number of blade = 6
P/D : pitch ratio = 1.2
2.2.2. Calculation of Maximum Length and Thickness of Each Propeller Blade Foil
This calculation is based on "table 14-Values of V1" and "table 15-Values of V2" in the book
"Principle of Naval Architecture" Chapter VI page 188 [8]. V1 and V2 function as constants
in the calculation of Yface and Yback. The length of the foil is divided into two parts, namely
the front of the maximal thickness until the leading edge and the back are maximal thickness
to the trailing edge. Each part is divided into the same number of pieces (usually 10 parts)
according to the needs written based on the percentage of the length of each part with the
tmax position as the neutral axis. At the front of the max price the percentage is positive and
the + P symbol ends at the end of the leading edge, while the rear part of tmax is negative and
ends with a -P symbol at the end of the trailing edge. P is the maximum length of the two
parts. At these points the Yface and Yback coordinates are calculated. Here is the formula for
Yface and Yback in both parts:
P > 0 = Yface = V1 ( tmax - t l.e )
Yback = ( V1 + V2 ) ( tmax - t l.e ) + t l.e
(14)
P ≤ 0 = Yface = V1 ( tmax - t t.e )
Yback = ( V1 + V2 ) ( tmax - t t.e ) + t t.e
The making of the propeller model must be solid so that later it can be simulated using
computational fluid dynamics, namely software Numeca [10]. Depiction of these coordinates
can be done using CAD software or PropCad. Furthermore, making surfaces on Rhino
software and solidifying the propeller blade are stored in parasolid form (* x_t) using rhino or
solidwork software which is then checked on numeca. The variation model made in this Final
Project is to modify the skew propeller angle to 0⁰, 14⁰(Original), 30⁰, 45⁰, and 60⁰.
Figure 2 shows the solid check body. CFD simulation is performed using Numeca Fine
Marine software through the C-Wizard menu for Open Water Test at propeller B6-80. CFD
simulation data is divided into thrust, torque, and cavitation values. Validation is done so that
the data processed and analyzed can maintain accuracy. The validation of the final assignment
model this time is done by the original B-series skew which is by skew angle 14 which is
done by simulating CFD compared to the results of the calculations that have been done at the
design preliminary stage. The value used for comparison is thrust or thrust. The thrust results
in the original B-Series blade CFD simulation amounted to 1802,028 kN while the thrust
count results obtained at the design preliminary stage for the selection of propellers were
1630.54. So the error margin is because the comparison of the two methods is 171,769 kN.
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Figure 2 Solid Check Body
One of the absolute requirements for a form to be simulated on a CFD is a solid form file
and can be checked on hexpress numeca software. If the Software has informed "selected
bodies are clean" then the file is ready and can be done in the meshing stage. In the meshing
step there are 5 steps that must be successfully passed so that a domain can be created
(simulated area boundary) simulated or running. The standard size of the domain by
propellers with cylindrical shapes is the length of 8D, radius 6D, and 3D for the location of
the propeller from the inlet. Then there are 5 stages of meshing, namely initial mesh, adapt to
geometry, snap to geometry, optimize and viscous layer to optimize the number of cells to the
shape to be simulated.
Figure 3 Meshing Stage
In addition to being used to check geometric errors that cannot be meshed as shown in
Figure 3. The meshing manipulation stage is done to adjust the cell to be made according to
the capabilities of the computer being used. In the next stage, the original skew modeling
process with skew angle variations is then carried out then the model simulation is done using
Numeca Fine Marine software. Process The CFD simulation uses the Cfx solver to find out
the results.
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2.3. Cavitation
Cavitation is a phenomenon that is found in propellers that are very loaded, where outside a
certain critical revolution, there is a progressive disturbance in the flow and consequently loss
of impulse. In its extreme form, it can prevent the ship from reaching the desired speed.
However, before this stage is reached, it manifests itself with noise, vibration and erosion in
the propeller, support and steering [8].
Many things can cause cavitation. An example in everyday life is boiling water. In boiling
water the vapor pressure will rise due to the increase in water temperature. In hydrodynamics
cavitation is generally caused by flow. Such cavitation flow is a two-phase flow consisting of
liquid and water vapor, and the phase transition is caused by changes in pressure. Figure 4
shows the mechanism for cavitation. An air leaf or foil cross section is placed at a certain
angle in 2-dimensional flow without thickness.
Figure 4 Air pressure and flow in foil [8]
Which in figure 5 the pressure at point A should not exceed, if it exceeds cavitation will
occur.
Figure 5 Pressure difference [8]
use the formula [8]:
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Or
(15)
Where p0 and V, pressure and velocity of fluid. Whereas the pressure and velocity pa and
Va at the position at point A. To find out the pressure in the water so using Bernoulli
Equation:
Or
(16)
Substituting between the equations is generated:
Or
Where σ is a cavitation number and Cp is a pressure coefficient, as
(17)
And
Where po is the depth pressure plus atmospheric pressure, namely:
(18)
with ph = ρ g h
Because σ cavitation number is constant with the change in each Cp, cavitation will occur
with the following equation:
Cavitation will occur if
Cavitation will not occur if the equation is as follows:
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3. RESULT AND DISCUSSION
3.1. Thrust and Torque Simulation Results
Simulation results can be seen at the start of the monitor in the software and examples can be
seen in the picture below:
Figure 6 Thrust simulation results at the skew angle 0⁰
Figure 7 Torque simulation results at the skew angle 0⁰
3.1.1. Obtain Thrust Simulation Results and Torque Data
From the thrust and torque results obtained from the simulation, it can be obtained Kt and Kq
values which will be needed to find efficiency values using the Open Water Test equation,
namely Kt, Kq, and Efficiency on each skew variation on propeller B6-80 at J = 0.833 . The
following table results from the calculation of Kt, Kq, and Efficiency.
Table 3 Result Calculation of Kt, Kq, Efficiency
From the data processing that has been done, then it will be displayed in graphical form to
analyze the characteristics of each model variation and be analyzed. The analysis is divided
into thrust analysis, torque, and efficiency on the angle of the propeller skew.
Skew
Angle
Thrust Torque Kt 10Kq
Effi-
ciency
0⁰ 1937.82 2728.79 0.342 0.637 0.712
14⁰ 1802.028 2618.00 0.267 0.513 0.690
30⁰ 1778.031 2563.01 0.263 0.502 0.696
45⁰ 1557.966 2238.47 0.230 0.438 0.698
60⁰ 1501.437 2153.56 0.222 0.422 0.699
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3.1.2. Thrust Analysis of Skew Angle Propeller B6-80
Graph 1 Thrust Against the Skew Angle Propeller
From the graph above it can be seen that there is an influence due to the increase in skew
angle to thrust. Thrust value decreases in every addition of skew angle from 0⁰ to skew 60⁰. At
the skew angle of 30⁰ to 45⁰ there was a significant decrease in thrust, and from 45⁰ to 60⁰ it
also decreased but not so much. Skew angle 0⁰ has the highest thrust value compared to the
other skew angles. While the skew angle which has the lowest thrust value is at the skew
angle 60⁰. From the variations that have been done, and from the graph above it can be
concluded that increasing the skew angle further reduces the thrust value.
3.1.2. Torque Analysis of Skew Angle Propeller B6-80
Graph 2 Torque Against the Skew Angle Propeller
From the graph that can be seen above, it can be seen that the effect of skew changes to
torque has a declining trendline. The torque value decreased significantly from the angle of
the skew 30⁰ to the skew angle of 45⁰, and again experienced a decrease in torque value but
not so large at the skew angle of 45⁰ and 60⁰. The skew angle that has the lowest torque value
is the skew angle 60⁰. While the skew angle that has the highest torque value is at the skew
angle 0⁰.
1300
1400
1500
1600
1700
1800
1900
2000
2100
2200
0 15 30 45 60
THRUST(KN)
SKEW ANGLE (⁰)
2000
2100
2200
2300
2400
2500
2600
2700
2800
0 15 30 45 60
TORQUE(NM)
SKEW ANGLE (⁰)
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3.1.3. Efficiency Analysis of Skew Angle Propeller B6-80
Graph 3 Efficiency Against the Skew Angle Propeller
From the graph that can be seen above it can be seen that the effect of skew changes on
efficiency. Increasing the skew angle can increase efficiency compared to the original skew
angle (14⁰) as can be seen in skew 14⁰ to skew 60⁰. Skew angle 0⁰ has the highest efficiency
value compared to the other skew angles. Whereas the lowest efficiency value is the skew
angle 14⁰.
3.2. Analysis of Cavitation Results Skew Angle Propeller B6-80
The simulation results on the numeca fine marine software can be obtained by adding
cavitation fraction to the output and additional models by entering cavitation number
parameters. Figure 8- 12 show the visual results of the simulations that have been carried out
on each skew propeller variation:
Figure 8 Skew 0⁰
Figure 9 Skew 14⁰ (Original)
0.65
0.7
0.75
0.8
0 15 30 45 60
EFFICIENCY(%)
SKEW ANGLE (⁰)
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Figure 10 Skew 30⁰
Figure 11 Skew 45⁰
Figure 12 Skew 60⁰
As shown in Figure 8-12, cavitation fraction can be seen the cavitation potential of each
skew angle variation based on color countour from the range 0-1. From the simulation results
show that the face has more cavitation potential compared to the back. At the original skew
angle of 14⁰ it shows that the cavitation potential produced is quite low according to the
calculation from the burril method that has been done before. From the picture above it can
also be seen that increasing the skew angle can reduce the cavitation potential at certain skew
angles.
At skew angle 0⁰ has a low cavitation potential in general but is so striking at the leading
edge because in this part the pressure that occurs is quite large. At a skew angle of 30⁰ it
shows a reduction in the cavitation potential compared to the previous skew angle in the
original B-Series propeller with reduced cavitation potential in the center of the leaf. The
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skew angle of 45⁰ experiences an increase in cavitation potential as can be seen in the image
with a countour of striking reddish orange colors. The potential for cavitation has decreased
again in the variation of skew angle 60⁰, with reduced cavitation potential in the middle part
of the leaf and switch to the edge of the leaf but not too large potential shown.
4. CONCLUSIONS
Based on the results of experiments and simulations that have been conducted, it can be
concluded the greater the skew angle, the value of the thrust and torque decreases, but this is
inversely proportional to the value of efficiency which experiences an upward trendline with
the magnitude of the skew angle. The skew angle which has the greatest thrust value, torque,
and efficiency is at the skew angle 0⁰. The resulting performance is thrust of 1930.979 kN
(increased 7.1%), torque of 2726,358 kNm (increased 4.13%), and efficiency of 0.71
(increased 2.8%) compared to the original skew angle .
The skew angle has the smallest thrust and torque value at the skew angle 60 sudut. The
resulting performance is thrust of 1501.4 kN (decreased 16.6%), torque of 2153.6 kNm
(decreased 17.7%), and efficiency of 0.669 (increased by 1.28%) compared to the angle of the
original skew. Increasing the skew angle can reduce the potential of cavitation at certain skew
angles. The skew angle which has a thrust value, torque, and efficiency that is quite high and
has a fairly low cavitation potential is at the skew angle 0⁰.
ACKNOWLEDGEMENTS
The authors thank to the members of the Laboratory of Marine Manufacturing and Design,
Department of Marine Engineering, Institut Teknologi Sepuluh Nopember (ITS) for support,
discussion and evaluation of simulation and other data.
REFERENCE
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