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OCR for page 98
Study on the CFD Application for VLCC Hull-Form Design
K.-S. Min. J.E. Choi, D.~. Yum, S.H. Shon, S.H. Chung, D.W. Park
(Hyundai Mantime Research Institute)
ABSTRACT
Flow characteristics around very large oil
carriers with 3 different aft-body hull forms have been
investigated by 4 different CFD codes and compared.
Hull forms were prepared by modifying the existing
form of 309,000 TOW VLCC recently designed by
Hyundai Heavy Industries, and classified as the basic
form, extreme U-form and extreme V-form. Model
tests were conducted to verify the results of numerical
analysis. Test results have shown that the extreme V-
shape aft-body hull form has the most superior
propulsion characteristics to the other two hull forms.
Presently, even the qualitative prediction of ship's
propulsive performance as well as the quantitative
prediction is not possible by the numerical method, and
hence, model test should be conducted to evaluate
superiority of hull forms. Therefore, much further
study should be performed for CFD to be utilized in the
hull form design.
INTRODUCTION
The processes of hull-form design at initial
stage are performed by the creation of totally new hull
or by the modification of existing hull form. The latter
is generally used in shipyards. Therefore, it is
necessary to predict the changes of flow characteristics
due to hull-form variations. The prediction of the flow
characteristics is traditionally carried out by
experimental method, that is, model test. The
experimental method has a merit of accuracy, but
demerits of longer time and higher cost. Recently, it is
possible to predict flow characteristics using
computational method so called computational fluid
dynamics(CFD) through highly developed computer
and CFD codes, and so, CFD has been applied from the
initial design stage at some shipyards. This method is
not only economical in time and cost, but also able to
estimate some characteristics which are not possible to
be measured by model tests. In general, however, the
computational method does not have sufficient
accuracy and reliability yet for the practical
applications. This is a disadvantage of the
computational method.
In order to utilize CFD for useful tool of hull-
form design, the CFD results should be accurate and
credible, and show the differences of the flow
characteristics according to the variations of hull form.
The studies to improve the CFD technology for the
prediction of flow characteristics around ship hull have
been actively carried out in the world through the
International CFD Workshops which have been held
four times in last two decades(Larsson, 1980, Larsson
et al., 1991, Kodama, 1994, Larsson et al., 2000~.
Following the worldwide trend and necessity, Hyundai
Maritime Research Institute(HMRI) has established the
long term R&D Program on this subject and carried out
the study. The flow characteristics of five different
ships in four different ship types were investigated
through the computational method using four CFD
codes(HMRI-SNU home code, STAR-CD, FLUENT,
SHIPFLOW) and the experimental method(Min et al.,
2000~. The objected ships were VLCC, bulk carrier,
LPG carrier, container carrier, and destroyer, which
were recently manufactured or studied at Hyundai
Heavy Industries Ltd.(HHI).
The purpose of this paper is to predict the
differences of the flow characteristics due to the hull-
form variations through the experimental and the
computational method. The basic hull form is a
309,000 TDW VLCC recently designed at HHI. After
selecting basic hull form, the frame lines of stern are
changed to extremely U- and V-shaped hull. For the
computations, four CFD codes(WAVIS, COMET,
STAR-CD, FLUENT), which gave relatively good
results at the previous work of Min et al.~2000), were
utilized. Model tests were carried out at the deep-water
towing tank of HMRI. The contents of model tests
were resistance and self-propulsion test, wake
measurements on a propeller plane, and paint test for
visualizing limiting streamlines on a hull.
This paper includes the following contents:
- Systematic hull-form variation of the stern of slow
speed full-ship
- Selection of CFD codes
- Model tests to predict flow characteristics including
resistance and propulsion performance
- Calculation of flow characteristics
- Evaluation of different stern hull form
OCR for page 99
NUMERICAL METHOD
The dual coordinate systems have been
adopted as shown in Figure 1. The global coordinate
system~x,y,z) is defined to represent the flow patterns Turbulence model
around hull as positive in the flow direction, positive y
starboard, and positive z upward where the origin is at
the bow and undisturbed free surface; while the local
coordinate system~x',y',z') to enhance the usefulness of
the calculated wake patterns in the propeller design
where the origin is at the center of propeller.
~ v
~
y
._
Figure 1 Coordinate System
Governing equation
The governing equations for turbulent flow in
the present study are the continuity equation for mass
conservation and Reynolds-averaged Navier-Stokes
equations for momentum transport. All the physical
quantities are non-dimensionalized by the ship
length(Lpp), ship speed(Vs), and fluid density" p ).
Continuity equation
auf = o
axi
Momentum transport equation
aUi+u~aUi = ap + a ~ 1 aUi UP) (2)
al ax, axi ax, Rn ax,
where Ui(=U,V,W) are velocity component in xi=(x,y,z)
directions, while p, Rn, and u ju ~ are static pressure,
Reynolds number, and Reynolds stress, respectively.
Turbulent kinetic energy transport equation
Dk a c k2 Ok Ok —auto
Do ax, ( k £ ax,+ Rn ax/)-Ui2l~ ax -£ (3)
Dissipation of turbulent energy equation
Dt ax, ~ £ axe Rn aX' ) Cal k uju/ a
£2
-Ce2 k
where k and ~ represent turbulent kinetic energy and
dissipation rate of turbulent kinetic energy,
respectively; and Ck, C e, Cal, and Cc2 are model
constants.
For turbulence closure, Reynolds-stress
(FLUENT, 2000) and eddy-viscosity model are applied.
For the eddy-viscosity model, Chen's(COMET, 2001),
cubic(STAR-CD, 2000), and realizable(WAVIS, 1999)
k-£ turbulence model are utilized.
ReYnolds-stress model
Reynolds stresses are expressed as the form of partial
differential equation deduced from Navier-Stokes
equation;
Du,z`~ 2
D = Dig + Gig 3 ~ij£ + PS (5)
where Dij, Gij, and PS are diffusion, generation, and
pressure strain term, respectively; and dij is Kronecker
delta.
a k2auiuj 1 aujuj
D = (Ck— + )
'I axe £ axe Rn OX
I ~ i ~ ax, i ~ at ) (6)
PS=-C~ k (uiuj - 3 dijk)-C2(Gij - 3 dijGk)
where Cat and C2 are model constants.
EddY-viscositY model
Reynolds stresses can be written using Boussinesq's
isotropic eddy viscosity hypothesis;
-uiu/ =-3k~y+2v,si; (7)
where v,(=C,u—) is turbulent eddy viscosity and
Sij[= 2(aa i + a j)] is rate of strain. In the Chen's
k- ~ model, Cu has constant value of 0.09 while in
realizable k- ~ model, C,u is expressed using
Sij and Qij[=2(a i_ a j) ], where Qii is
(4) vorticity.
OCR for page 100
An +Asu( )—
where the terms are defined as
U( ) =4SijSij + Q`yQij ~ An =4.,0
As = JO cos A, ~ =—arccos(~W),
~ f
S = ~SijSij
In the cubic k- ~ model, Reynolds stresses
are expressed with considering anisotropic and non-
linear relationships between Reynolds stresses and rate
of strain.
- u juj = - 3 k~ij + V,sij
—Cat v'—(Sik Skj—3 id Ski Sk! )
—C2v,—(Qik Sky + Q jk Ski ~
—C3 V,—(Q ik Q jk—3 id Qk! Q k! )
—C4 Vt 2 (Ski Q I + Sky Q y ) Sk!
—CsV, 2 (SkiSk~ + QkIQ~)Sij
where Cat, C2, C3, C4, and C5 are model constants.
Computational method
(9)
To solve the governing equations, the flow
domain is subdivided into a finite number of cells and
these equations are changed into algebraic form via the
discretization process. Finite volume method is used
for the discretization. Temporal derivative in the
governing equations is ignored by putting very big time
value. The convective terms are discretized using
QUICK(Quadratic Upwind Interpolation for
Convective Kinematics), LUD(Linearized Upwind), or
MARS(Monotone Advection and Reconstruction
Scheme). Central difference scheme is utilized for
diffusion terms. Then the algebraic form becomes
Ap~p=~Am~m+
m
where Maui (i = 1,2,3), k,£]
(8) represents convective
and diffusion terms, s ~ is
source term, and Ap =~Am . For the velocity-
m
pressure coupling, SIMPLE(Semi-Implicit Methods for
Pressure-Linked Equation) or SIMPLEC (SIMPLE
Consistent) is utilized. The characteristics of the
utilized four CFD codes are summarized at Table 1.
Table 1 Characteristics of CFD codes
WAVIS COMET STCADR- FLUENT
Turbulence Realizable Chen's Cubic Reynolds
model k-e k-e k-e stress
Convection QUICK WD MARS QUICK
Velocity-
pressure SIMPLEC SIMPLE SIMPLE SIMPLE
coupling
Boundary conditions and grid generation
Wall function is utilized for hull-surface
boundary condition. Symmetry condition is applied for
free-surface boundary condition by assuming double
body model. Uniform flow condition for the inlet and
the outer plane, symmetry condition for the centerplane,
and Neumann condition for the exit plane are applied.
The same girds are applied for the calculations
using four CFD codes. The grids are composed of
single block with O-H type. The number of grids is
253,831 with 3,900 on the hull surface. The space of
the 1st grid from the hull is y+~45. The calculations are
carried out at model scale with Rn=6.918xlO4.
SELECTION OF OBJECT SHIPS AND MODEL
TESTS
(10)
is variables, Am
Three kinds of hull form are investigated to
predict the change of hydrodynamic characteristics due
to hull-form variation. After selecting basic hull form,
frame lines of stern are changed to extremely U- and V-
shaped hull form with constraints of the same principal
particulars and the same bow shape. Hereinafter, the
extremely U- and V-shaped stern hull form is called
"extreme U-hull" and "extreme V-hull", respectively.
The basic hull form is a 309,000 TOW VLCC which
was recently designed at HHI. The model tests are
carried out to predict the resistance and propulsive
performances of ship, and to validate the computational
results. The contents of model tests are resistance and
self-propulsion tests, wake measurements at a propeller
plane, and paint tests to investigate the limiting
streamlines on the hull.
OCR for page 101
Selection of object ships
For the basic form, the shape of bow bulb is
middle bulb of plank type and frame line of stern is
moderate U-form. The plank typed bow bulb is
recently applied for slow speed full-ship because the
variation of ship performance due to the change of
draft is small and it is possible to generate hull-form
with moderate curvature. The constraint of extreme U-
form is to maintain the shape of sectional area curve if
possible, to satisfy the width for engine room, and to
maintain the width of the upperpart of propeller of
basic form. The constraint of extreme V-form is to
maintain the minimum of width for engine room. The
depth of transom is the same for three ships. The body
plans, side profiles, and sectional area curves for three
ships are shown in Figure 2. As shown in Figure 2, the
breadth of extreme U-form is relatively wide at the
-
Figure 2 Body plan, side profile and sectional area curve of 309,000 TDW VLCC
(red: basic form, green: extreme U-form, blue: extreme V-form)
Table 2 Hull form characteristics
Basic | Extreme l Extreme
form U-form V-form
LWL. (m) 326.50
LPP (m) 320.00
B (mj 58.00
T (m) 20.95
1` (tonnage) 322 314 322 651 1 322 168
. _ . , , , ,
S (m') 27 621 27 603 1 27 271
. , , . ,
LCB (m, fwd +) 9.952
CB 0.8089 1 0.8095 1 0.8083
CM 0.9978
lower part of propeller and nearly same at the upper
part of propeller. The breadth of extreme V-form is
narrow at the lower part of propeller and wide at the
upper part of propeller compared with those of basic
form. The principal particulars of ships and propeller
are shown in Table 2 and 3, respectively.
Model tests
The model tests were conducted at the deep
water Towing Tank of HMRI. The size of the tank is
210x14x6 m in length, width, and depth, respectively,
with maximum carriage speed of 1 lm/sec.
During the resistance test, the model ship was
provided with no appendages and free in vertical
motion. The resistances acting on the towing point of
model ship at various speeds were measured. The
towing point was located at (LCB, O. KB)-
,,/' /!
\
Fug.
Table 3 Characteristics of model propeller
Diameter (mm) 210.26
No. of Blades
Section Type ~~ ~ ~ ~ NACA
Chord Length at 0 7R(mm) 56.03
P/D at 0.7R 0.7451
OCR for page 102
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Representative terms from entire chapter:
hull form
During the self-propulsion test, the model ship
was provided with a rudder and a stock propeller. The
model ship was propelled with its own electrometer
and free in vertical motion. In order to compensate for
the model's excessive frictional resistance it was
additionally towed by the resistance dynamometer. The
tests were conducted at 6 carriage speeds. For each
speed, the propeller relative speed was varied to cover
at 3~4 loadings around a self-propulsion point. The
resistance, propeller relative speed, thrust and torque
acting on propeller were measured.
The fluid velocities were measured at
propeller plane using a rake consisting of five two-hole
Pitot tubes. The model ship was free in vertical motion
at design model speed of 1.171m/s. The rake was
attached to model ship. The center and side holes of
Pitot tubes were connected to pressure gauges through
vinyl tubes. The angular interval to be measured was 5°
to 15° at five radii.
The flow-line test was conducted by using
paint. The model ship was free in vertical motion at
design model speed of 1.171m/s. The paint was an
appropriate mixture of dye, oil paint, wax, and thinner.
The mixture rate was dependent on the local velocity
close to the hull.
The results of resistance and self-propulsion
test were analyzed to full scale by the method
recommended by ITTC Performance Committee(1978~.
RESULTS AND COMPARISONS
The computational and experimental results of
three varied hull forms of 309,000 TDW VLCC are
compared. The computations have been conducted
using four selected CFD codes, i.e., WAVIS, COMET,
STAR-CD, and FLUENT. The changes of
hydrodynamic characteristics to be investigated are as
follows;
- Resistance and propulsion performance
- Limiting streamline on the hull
- Hull pressure
- Wake on propeller plane
Resistance and propulsion performance
The viscous resistance coefficients(CvM) at
Rn=6.916X 106 of three hull forms from the
computations and experiments are summarized in Table
4. The magnitude order of CVM obtained from the
experiments is CVM (B) < CVM (V) < CVM (U), where B.
V, and U represents basic form, extremely U- and V-
form, respectively. The computational results show the
same tendencies, but their values are lower than those
of experiments.
Table 4 Comparison of viscous resistance
characteristics in model scale
Exp.
WAVIS
COMET
STAR-CD
FLUENT
Basic form
CVM
X103
3.914
3.583
3.856
3.854
3.65 1
Comp.
(%)
100.0
91.54
98.52
98.47
93;28
CVM
X103
.
4.189
3.722
4.073
3.953
3.856
Extreme
U-form
.
Comp.
(%)
100.0
88.85
97.23
94.37
_ 92.05
Extreme
V-form
CVM Comp.
X103 (%)
4.004 100.0
3.665 91.53
3.865 96.53
3.919 97.88
3.749 93.63
The wave resistance coefficients(Cw) and
effective horse powers(EHP) obtained from the
experiments at various speeds are shown in Table 5.
The magnitude order of Cw is Cw~v)
Table 6 Comparison of propulsive performance coefficients
Test
condition
VM=0.970m/S
Fn=0.119
Rn=l.8Ol X 10
VM= 1 .044m/S
Fn=O. 129
Rn=1.939X 106
VM=1. 11 9m/S
Fn=0.138
Rn=2.078X 106
V~1.193m/S
Fn=O. 147
Rn=2.216X 106
V~1.268m/S
Fn=0.156
Rn=2.355 X 106
V~1.343m/S
Fn=0.165
Rn=2.493 X 106
Hull form
Basic form
Extreme U
Extreme V
Basic form
Extreme U
Extreme V
Basic form
Extreme U
Extreme V
Basic forth
Extreme U
Extreme V
Basic form
Extreme U
Extreme V
Basic form
Extreme U
Extreme V
RPM
57.11
_ s7.23
58.22
.-
. 61.52
61.57
.-
62.55
66.03
65.98
66.95
70.55
70.48
.-
71.44
75.22
75.13
76.04
79.97
79.97
80.78
0.441
0.427
0.478
0.442
0.422
0.477
0.445
0.419
0.475
0.446
0.418
0.475
0.447
0.419
0.475
0.448
0.422
0.475
T 0.224
0.190
0.237
.
0.238
0.197
0.233
0.247
0.201
0.228
0.249
0.203
0.221
0.244
0.202
0.214
0.230
0.197
propulsive efficiency in open-water( n, o), and
propulsive efficiency rl p) at various speeds are shown
in Table 6. Here hull surface roughness is assumed to
be 150 ~m. Note that r,p includes the effect of
transmission efficiency~rc'=O.99), i.e., rip = llH X
II R X 11 o X ~ ~ and the brake horse power(BHP) is
obtained on the condition of Cp=1.00, CN=1.00. The
magnitude order of ws is ws~v)
-0.02
-0.06
-0.08
7.
-0.06
-0.08 .
o
-0.02
z
-0.08
. .
C. (~b,01~/ ~
-0.02
nn4
is.
0 0.02 0.04 0.06 0.08
y
A!
~o.9~/
,,·,1,,,,1,,,,1,,,,1,
0 0.02 0.04 0.06 0.08
y
/~ ~~ l
,,,,1,,,,1,,,,1,,,,1.
0 0.02 0.04 0.06 0.08
y
(a) Basic form
z
(b) Extreme U-form
non
non
(c) Extreme V-form
0.5
Rt, I 1~'I 1~ , 1` ~ ~ ~
0 0.02 0.04 0.06 0.08
y
-0.04
-n no
1 ', , ', , 1'
0 0.02 0.04 0.06 0.08
y
'`\
.,',\,,1,,,,1,,
0 0.02 0.04 0.06 0.08
y
Figure 3 Axial velocity contours and velocity vectors at the propeller plane (WAVIS)
Limiting streamline
Figure 4 shows the results of experiment and
calculation using COMET for limiting streamline in the
forward and afterward part. Same shapes of streamlines
in the forward part are shown for three hull forms since
the bow shapes are the same. For the upper part of
bow, the streamlines are parallel to the direction of ship.
However, the limiting streamlines are directed a little
upward for the upper region of bulb, and downward for
the lower region because of rapid change of hull form.
Other computational results using WAVIS, STAR-CD,
Experiment
-
-
._
-
_
and FLUENT codes also show same tendencies. In the
afterward part, the limiting streamlines of three hull
forms are quite different from each other. From the
experiments, the limiting streamlines incoming to
lower propeller plane are not clear, so the fluid velocity
near this region can be expected to be very slow. For
the case of extreme V-form, this region is the largest.
All the computational results are similar in tendency,
except for the WAVIS results showing reverse flow in
this region of extreme V-form.
Calculation (COMET)
(a) Bow
-
_!
-
(b) Stern of basic form
_
_.
my.
_ 1 _ .
—1 ~ ;
(c) Stern of extreme U-form
(d) Stern of extreme V-form
Figure 4 Limiting streamline
.
(a) Bow
(c) Stern of U-form
Figure 5 Pressure contours on the hull (STAR-CD)
Pressure distribution
Figure 5 shows the computed pressure
contours in the forward and afterward part of the hulls
using STAR-CD. The shapes of the pressure contours
on the forward part of the basic form are the same as
those of U- and V-form. Other computational results
using WAVIS, COMET, and FLUENT codes are the
same shapes. The bow region dashed against flow
shows very high pressure. At the lower part of bulbous
bow a rapid pressure gradient region exists. Passing
through this region, the fluid flow acceleration occurs
due to the change of hull curvature, so very low
pressure region exists. There is a little change of
pressure at the middle of hull. Pressure is increased at
the region of stern due to the hull curvature, but there is
no great pressure gradient region such as that of bow.
This may be due to the less hull curvature comparing to
the region of bow and thicker boundary layer. However,
the differences of pressure distribution are clear. Very
low pressure region exists at the lower part of extreme
U-form due to hull curvature. In the case of V-form,
such a low pressure region is relatively small and
locates at the stern region.
Wake(at the propeller plane)
The axial velocity contour on the propeller
plane is shown in Figure 6. The computational results
are from those using FLUENT code. The
characteristics of wake at the propeller plane show
clear differences. For the extreme U-form, wide region
of hook shape exists, the value of minimum velocity in
this region is relatively high, the radial gradient of the
(d) Stern of V-form
circumferentially averaged axial velocity is gentle, and
the value of nominal wake is larger. For the extreme V-
form, narrow region of hook shape exists, the value of
minimum velocity in this region is relatively low, the
radial gradient of the circumferentially averaged axial
velocity is steep, and the value of nominal wake is
smaller. The characteristics of wake at propeller plane
are very much dependent on the turbulence model. The
results applying Reynolds stress turbulence model
show good agreement with those of experiment. The
results applying realizable k- ~ turbulence model are
also good agreement, but the minimum axial velocity is
expected by 0.1 less at the hook-shape region. The
results applying Chen's and cubic k- ~ show similar
tendency, but decrease in accuracy. Note that the
unclear region of limiting streamline from the paint test
is coincident with the region of very low velocity
. .
Incoming.
Experiment Calculation (FLUENT)
(at Basic form
(b) Extreme U-form
(c) Extreme V-form
Figure 6 Axial velocity contour on the propeller
plane
The control plane for nominal waketwN) is a
circle located at propeller plane with the same center of
propeller, and with minimum and maximum radius of
r~=0.380 and r2=1.141, respectively, where r is radial
distance non-dimensionalized by propeller radius. So,
the nominal wake at control plane is
N A MA
where A is area of control plane. The nominal wake at
the control plane is shown Table 7. The values of WN
can be assumed to be proportion to those of ws because
the same propeller is used. Therefore, we can estimate
the propulsion performance of ship using the values of
WN as described in the previous section of Resistance
and propulsion performance.
Table 7 Comparison of nominal wake
fraction
\\
WAVIS
COMET
STAR-CD
FLUENT
I Basic form
WN
0.457
0.435
.
0.425
0.419
. 0.434
. Extreme .
U-form
WN Miff.* .
- ~ ~,~.~ ~~
1` A 0 ~ I: ~.~.~: Jo: -- A:.::: ~-
V.~tOV i.:'::. ~—''::
~~:~:~i~ ~~.~i .
0.510 6.30
0.5 16 7.40
0.475 -0.98
0.484 0.94
Diff .(%) = N ( 1-) WN (exp.) x 100
WN (exp ·)
DISCUSSIONS AND CONCLUSIONS
Extreme
V-form
WN I Diff.*
: ~~ ~~ ~ ~.~: i. . ~ . - ~:
tot A ~ ~ .:: ~:~:~ I: -I : ~:~:~ ~ ~ ~~ ~ ~ ~ ~ ~ ~
V.~4V i:. I'd i :~i:~.:—':i'- f:~:
:: ~~:~ ~,~ ~~ :. : -I ~:~:~ ~:~
0.410 -3.70
0.363 -14.87
0.374 -12.19
0.410 -3.63
The differences in flow characteristics
according to the variations of hull form, i.e., basic form,
extreme U- and V-form, are predicted by the
computational method and verified through the
experiments. The basic form is a 309,000 TOW VLCC,
which is recently developed as a standard full slow-
speed ship at HHI. For the computations, four CFD
codes, i.e., WAVIS, COMET, STAR-CD, and FLUENT
are used.
The values of viscous resistance from the
computations are generally lower than those from the
experiment. The predictions of wake at the propeller
plane are dependent on turbulence models. The results
applying Reynolds stress and realizable k- ~
turbulence model are similar to those of experiments.
The results applying Chen's and cubic k- ~ show
similar tendency, but decrease in accuracy. All the
results qualitatively show the differences due to the
changes of hull form, but are still quantitatively
different from those of experiment.
From the experimental studies, the V-form hull
is superior to both the basic and the U-form hull form
with the respect to the resistance and propulsion
performance. The propulsion performance according to
the hull-form variations cannot be evaluated from the
computational results only.
To apply CFD technology on the development
of fuel-economic hull-form at the initial design stage,
not only viscous resistance performance but also wave
resistance and propulsion performances should be
promptly predicted with accuracy. To predict the
propulsion performance, the flow around a hull
attached with propeller and rudder should be analyzed
in full scale. However, there may be many problems to
carry out computation in full scale, such as grid
generation and the lack of verification data, etc. Further
study will be necessary for the prediction of flow
characteristics in full scale using the results in model
scale.
REFERENCES
Larsson, L.(editor), "SSPA-ITTC Workshop on Ship
Boundary Layers" SSPA Publication No 90 1980
, . . .
Larsson, L., Patel, V.C., and Dyne, G(editor), "Ship
Viscous Flow: Proceedings of 1990 SSPA-CTH-IIHR
Workshop", Flowtech International AB, Gothenburg,
Sweden, 1991.
Kodama, Y.(editor), "Proceedings of CFD Workshop
Tokyo 1994", Japan, 1994.
Larsson, L., Stern, F., and Bertram, V.(editor),
"Proceedings of CFD Workshop Gothenburg 2000",
Sweden, 2000.
Min. K.S., Choi, J.E., Yum, D.J., Chung, K.N., Chang,
B.J., Chung, S.H., Han, B.W., "Study on the Prediction
of Flow Characteristics around a Ship Hull", Proc. of
the 23rd ONR Symposium on Naval Hydrodynamics
2000.
"WAVIS User's Guide", KRISO, 1999.
"COMET User Manual", ICCM, 2001.
"STAR-CD User Manual", Computational DYnamics
Limited, 2000.
"FLUENT User Manual", Fluent, 2000.
"Report of the Performance Committee", Proc. of the
1 5th ITTC, Hague, 1978
Prohaska, C., "A Simple method for the Elevation of
the Form factor and Low Speed wave Resistance",
Proc. of the 11th ITTC, Tokyo, 1966
DISCUSSION
Chi Yang
George Mason University, USA
Authors should be congratulated for their
detailed study on the CFD application for VLCC
hull-form design. The authors have used
systematic hull-form variation to study the
change of hydrodynamic characteristics due to
hull-form variation. However, the CFD tools
have only been used to predict the
hydrodynamics characteristics for given hull
forms. The next step would be the compiling of
CFD tools with optimization techniques, such as
gradient-based method, to optimized hull form
automatically. I would like to have authors'
comments on the hull form optimization using
CFD tools together with optimization techniques.
AUTHORS' REPLY
Thank you very much for your comment. I agree
with your comment to utilize the coupling of
CFD tools with optimization technique.
However, the object function is the speed-power
performance. This means not only resistance but
also propulsion performance is important. To get
this object function, I think, the flow
characteristics around a hull attached with
propeller and rudder should be predicted and
analyzed to full scale with sufficient accuracy
and reliability. It is possible at present stage to
make local hull-form variation based on CFD by
utilizing restricted object functions, i.e., wave
resistance or local vorticity, etc. Unfortunately,
however, it is impossible to apply CFD
technology on the hull-form optimization
considering the speed-power performance. We
hope you could send us your proposal or idea on
the hull form optimization utilizing CFD
technology in the view point of powering
performance. We will strongly think over the
cooperative research project. Thank you.
