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OCR for page 287
Wave Devouring Propulsion Sea Trial
Y. Terao (Tokai University, lapan)
H. Isshiki (Hitachi Zosen Corporation, Japan)
ABSTRACT
The development of Wave Devouring
Propulsion System and results of it's
sea trial are presented in this paper.
WDP system is an idea not only for
the ship propulsion system which con-
verts wave energy directly into
thrust but also the ship motion reduc-
tion system. This system consist of a
ship hull and a hydrofoil installed at
the bow. Improvement of the propulsive
efficiency in waves and high seawor-
thiness is measured during the sea
trial.
NOMENCLATURE
.
a
B
g
Hw
K
L
Ra
Ra
~R
T
T
Tw
1/3
1.INTRODUCTION
It is well known that aquatic
mammals, dolphins or whales, which
propel themselves with their lunatic
tails have high propulsive efficiency.
Theoretical or experimental studies
have already- succeeded in explaining
this oscillating hydrofoil propulsion
system. The thrust generating mechanism
of these propulsion system is quite
simple. With forward speed and the com-
bined motion of heaving and pitching of
the fin Produces relative fluid veloci-
in
the fin. Due to the
ift theorem, lift
perpendicularly to
the flow. The mechanism of thrust
generation is shown schematically in
Fig.1 .
t.y whic h brings about an apparent
clined flow against
Kut t a- Joukowsky l
force is generated
wave ampl itude .
ship breadth.
2 2
C-Qg Hw B /L Ship speed
gravitational acceleration. \`
wave double amp] itude. \ I
Hw=2a \ I
signi f icant wave height . \ I
1
wave numbe r .
sh ~ p l ength .
added resistance in waves.
nond imens i anal added
res i stance .
Ra =Ra/C
res i stance _ _
AR =Ra-T
nondimens tonal coef f ic lent
of resistance increase.
R =dR/C
thrust of foil.
nondimens tonal
coefficient.
T =T/C
signif leant wave period.
mass dens it: of water .
pitch amplitude.
nondimensional pitch
amplitude.
6~=9p/(K.a)
wave length.
ncr`?~!:;~ 1 n WaV`~ .
thrust
Thrusts ~
Damping ~ oP ~ ng Point
force Lift A_
Fig. 1 Thrust generation of a fin
in waves.
I f we put a horizontal hydrofoil
in the oscillating flow field, such as
in waves, the relative flow acting on
the hydrofoil causes thrust.
The wave devouring propulsion
system (WDPS) consists of a ship hull
and hydrofoil, which acts as a direct
Y. Terao: Dept . Naval Archi lecture, 1'okai Un i v.; 3-2()-l, Orido Shi mi Mu, Shi z~toka 424, JAPAN
H. Isshiki :Hi tachi Rosen Corp.; 1 Sakura; ima, Konoharla-ku,Osaka 554,JAPAN
287
OCR for page 288
wave energy to the thrust converter
using these mechanisms. The hull is a
collector of wave energy, and the
motion of hydrofoil generates the
thrust. The hydrofoil is installed in
front of the ship's bow and the pitch
motion of the hydrofoil is controlled
under the sea.
The flow against the hydrofoil in
waves is (U + u , v). U is the ship's
forward speed. u, v is the wave's
vertical and horizontal velocity compo-
nent plus relative hydrofoil motion due
to ship motion and hydrofoil pitch
motion in the waves. Thrust is gener-
ated as a horizontal component of
lift(L), the magnitude of which is
periodically increased or decreased but
the thrust has a negative direction of
U . 'moreover, we must note the verti-
cal direction of the lift which has an
opposite direction to inflow velocity
v. This means that the lift force
creates pitch canceling moment, and
thus, decreases the ship's pitch mo-
tion.
Now, the object of this study will
be discuss. Our concern is the perform-
ance of the WDPS ship in waves. There-
fore, two important subjects were ex-
pected.
First, the improvement of the
propulsive efficiency of the ship using
an oscillating hydrofoil, because the
hydrofoil converts wave energy directly
into thrust.
- Second, the reduction of the ship
motion in waves is expected.
Moreover, it is needed for WDPS
ship production that the force acting
on the hull and hydrofoil quantitative-
ly through the sea trial.
Resistance increase of the ship in
waves is well known phenomena for naval
architects. This problem was studied
theoretically or experimentally by many
researchers. From the momentum theory,
the resistance increase in waves has a
physical explanation that the work done
by the relative hull motion against the
wave. Linear damping component is
concerned with the wave making resist-
ance which takes away the energy in the
form of progressive waves. If the
reduction of motion in waves was possi-
ble, we could expect the reduction of
"resistance increase in waves". But if
we consider it from such a view point
that the reduction in motion reduces
the increment of added resistance in
waves, there are few studies. It seems
that there is a field left not yet
studied . It may be true that there is
a limitation of the improvement in the
total ship resistance in waves by
normal hull design.
Furthermore, we can expect some
thrust increase in waves due to the
hydrofoil effect. For example, the
ship proceeding in the North Pacific
sea in the winter season was studied.
It was observed that the wave length
of about 100m has excessive wave power
in this area, therefore, a ship with a
length of less than 80m is desired for
WDPS system. From the feasibility
study of the thrust generation and the
reduction of resistance increase in
waves, we can expect the WDPS ship
running in waves at 8 kt without any
energy supply. Our approach, using a
hydrofoil in the wave, might be the
answer to improve the propulsive effi-
ciency and advance seaworthiness of
the ship.
Surprisingly enough, in 1985, H.
Linden(1) already field a British pat-
ent. He really built a 13-ft boat,
named "Autonaut", equipped with two
elastic fins both at bow and stern.
According to the contemporary report,
she could travel herself against the
wind and waves at a speed from 3 to 4
Kt.
Regarding recent experimental
studied of WDPS, which are concerned
with direct wave energy to the thrust
conversion, only Jakobsen(2) and the
author(3),(~) have carried out experi-
ments.
Abkowitz(5) reported on an anti-
pitching fin using a model test. He
used a pair of hydrofoils, total pro-
jected area of the hydrofoils is less
than 7% of the ship waterline area,
and the effectiveness of antipitching
fin was confirmed. He also mentioned a
significant improvement in speed in
waves. He was concerned with the
advancement of the lateral motion of
the ship, therefore, did not discussed
the trust generation of the fin.
T.Y. Wu(6) first showed theoreti-
cally that wave energy can be convert-
ed into thrust and propulsive efficien-
cy becomes more than one or even minus.
He studied the two dimensional oscil-
lating hydrofoil in waves.
Bessho(7) studied the restriction
of the lateral ship motion using two
fins one at the bow and stern. His
group showed the possibility of ship
with less heaving and pitching in
waves.
Naitou and the author(8) succeeded
in calculating the motion of a WDPS
ship and the propulsive efficiency,
especially the reduction in resistance
increase in waves using OSM and the
steady wing theory. The results will be
discussed later.
288
OCR for page 289
9.wnP~ ~F.A TnTAI. PRo.TF.cT
WDPS sea trial project was planned
using a 20-ton fishing vessel. Princi-
pal dimensions of the test ship, the
foil dimensions and foil section are
listed below. To know the thrust in-
crease in waves, a larger hydrofoil
area was selected compared with Abko-
witz's experiment. The projected area
of hydrofoil is 7~4°/O of the ship's
waterline area.
2.1 TEST SHIP PRINCIPAL DIMENSIONS
Lpp
B
d
Displacement:
Speed
Max : 10 kt ( 2000 rpm)
Service: 7. 4kt ( 1500 rpm)
: 15.7 m
: 3.8 m
1.1 m
19.9 ton
Hydrofoil Dimensions
Cord Length : 1.05 m
3.8 m
1.65 m
Span
Depth
Section : NACA0015
Center of the wing pitch motion is
length aft
w . _
located at a quarter cord
from the wing leading edge.
General arrangement of WDPS ship,
side view and top view are shown in
Figs. 2 and ~
2 2 THEORETICAL AND MODEL
TIONS
-
Model testing and
calculat ions are performed
actual sea trial.
A 3.5 m model was tested in a
tank in 1987, i ~ e . the hydrofoil cord
length was Lpp/15, span is same as the
ship breadth. The pivoting point of the
hydrofoil is located at the quarter
cord length of the hydrofoil span which
is identical to the center of the
steady 1 i f t f orce .
The thrust generation and resist-
ance increase is calculated theoreti-
cally. The coefficients of ship motion
was calculated by OSM, the hydrodynam-
ics force acting on the hydrofoil is
calculated using the quasi-steady
theory including the three-dimensional
effect. The resistance increase in
wares is calculated using a simplified
version of the Gerritsuma(9) formula.
INVESTIGA
theoretical
before the
Fig. 2 Side view of WDPS ship.
~ '
Fig. 3 Top view of WDPS ship.
289
OCR for page 290
Theoretical prediction and the
results of model testing of the pitch
motion, with and without hydrofoils
shown in Fig.4.
2. HI theory exp.
Without foil O O
~ with foil -a-
1 . 0 L
0
An,- t
/.e
al..
, a, . . . .
1.0 2.0
And L
Fig. 4 Theoretical and model
testing results of nondimensional
pitch ampl. itude at a head sea
condi t ion ( Fn=0 . 2 5 ) .
Up to 30% of the pitch reduction
compared to the original ship is seen
at the wave length to ship length ratio
is greater than 1.6, so we can expect
a pretty good pitch reduction effect,
but compared to the reduction of model
experiments, we had a much higher pitch
reduction efficiency.
Figure 5 shows the theoretical
results of the resistance increase in
the head sea condition at Fn=0.25.
Ra~
l
1. 01
I
0 ~ '
Or without foi 1 O ~1.
smith foi 1
R~
166F
- - - 10. th -
0. 4 - ·Q-~0
Ia _ ~.
I,, ~ ~=_1
1.0 2.0 3.0
A/J L
Fig. 5 Theoretical calculation of
the resistance increase in
head sea condition(Fn=0.25).
rt
This Figure shows the comparison
of the coefficients of resistance in-
crease with and without a hydrofoil at
sea.
Figure 6 shows the thrust increase
in waves. We can see that the reduction
in the resistance increase in waves is
due to the additive effects obtained by
the direct effect and indirect ef feet .
The direct ef feet is thrust generation
due to the hydrofoil and the indirect
effect is dependent on the reduction in
ship motion which is also effectively
affected by the existence of the hydro-
foil.
TO
2 OF
3~0 I_
1^0E
I At'
I,~
1.0 2.0 3.0
A L
Fig. 6 Calculation of the thrust
generation of a fin in head
sea condition (Fn=0.25).
.3 A, theory exp.
Without foi 1 - O O
~ smith foil ,^i -at- ~
,, ~
~i
~:
_
.~-. 1
, , ·- ·- i i, I
0 1.0 2.0
A / L
~ _
-0.4 _
290
3.0
Fig. 7 The theoretical calculation
of WDPS strip is resistance
increase in head sea
condition.(Fn=0,25)
OCR for page 291
Figure 7 shows the theoretical
calculation of resistance increase in
head seas. We can see a minus resist-
ance increase at the results of WDPS
ship in the wave length to ship length
ratio greater than 1.1. This is total
thrust gain from wave energy. If the
bull resistance during a calm sea is
less than the thrust gain from the
waves, the WDPS ship can sails against
waves without the need to use fuel for
power.
The results of 3.5m model towing
test during a head sea condition is
also plotted. Towing speed was
Fn=0.249. The difference between with
hydrofoil (WDPS) and without hydrofoil
is shown drastically. Frictional cor-
rec t ion i s not taken account. Theoreti-
cal prediction and tested results are
in fairly good agreement with this
f igure .
WDPS ships at sea i s shown in
Fig.8 and 9. It is observed in Fig.8
that the rather t iger splash in f rant
of the strut . This f igure shows speed
trial test using engine power and a
foil. In FIg.9, we can see a foil and
strut configurations which WDPS ship
was equipped with.
3 . WDPS SYSTEM DESIGN
Before the actual sea trial, a
WDPS structural analysis and design are
needed. Selected design wave height
to length ratio is 1/30 and design
wave length is 1.6 Lpp of the ship.
Taking into the consideration of
the actual sea trial using a rather
small Vessel, structural design was
decided carefully to have enough
strength. At the same time, reinforce-
ment of hull structure are investigat-
ed.
During the tank test in 1987, we
used the two bow hydrofoil system, left
and right, which was moved independent-
ly using two servo motor. But in this
actual sea trial, we selected one
hydrofoil and the passive control
system to simplify the experiment and
keep safety of the mechanism at sea.
WDPS hydrofoil supporting system
consists of two struts, a hydrofoil
pitch spring system, and the struts
up-down mechanism. The necessity to
change the spring constant easily on
board, variable spring constant system
consists of a hydraulic pressure cylin-
der and an accumulator was selected.
Changing the nitrogen gas pressure of
the accumulator, we were able to use
aide pitch spring constant.
Loading and equipment of the
system, hull reinforcement of the
testing ship were accomplished at
Kanasashi Ship Yard. The ship used in
the test was made of FRP and aged. The
structure of the ship is of a monocoque
type so that the fore deck shell
scarcely supports the external force or
weight of the testing apparatus. There-
fore extra reinforcement of the support
structures are needed in the bow sec-
tion.
Fig. 8 WDPS ship speed trial
(1500 rpm. at a heading sea
condition).
Fig. 9 WDPS ship raising a foil.
291
OCR for page 292
Support structures and equipment
weighting up to about 6 tons, were
installed at the bow, and more weight
(3 ton) is needed at the stern to keep
the even trim and to have enough GM
height. During the experiments, we had
a hard situation that the blue sea hit
the hydrofoil when hydrofoil was
hauled from sea but we had no damage to
the hull, struts, hydrofoil or any of
the instruments. So, we consider that
the reinforcement and structural design
were a success.
. RESULTS OF SEA TRIAL
The period of experiment was from
December 12th,1988 to January 13th,
1989.
The measurement and testing plan
is given below.
(1) Efficiency of WDPS using as a sub-
propulsi on s ys tem.
(2) Motion reduction effect of WDPS at
sea.
(3) Self propulsion test of WDP5 in
waves.
(4) Force measurements acting on the
hydrofoil and struts.
(1) and (2) measured the differ-
ence of the ship speed and motion, with
and without a hydrofoil in the same
sea condition at the same rotation of
the propeller. Tidal or ship wake
effects are canceled using a relative
flow speed-meter.
- (3) measured the forward speed of
the ship using a WDPS without engine
power.
(4) measured the force acting on
the straits using strain gauges.
4.1 APPARATUS OF SEA TRIAL
Suruga Bay ,offshore of Miho
Kunou was used as the test area.
items and apparatus used in the
are given below.
4 . 1 . 1 TEST I NG APPARATUS
Relative Ship Speed
: Relative Flow Meter
Propeller Rotation
: Optical Rotating Meter
Ship Motion(6 degree of Freedom)
: Rate Gyro
Wave Height
: Wave Prove (Drop type)
Wind Direction and Speed
: Wind Meter
Stress of the WDPS arm
: Strain Meter
Pitch Angle of Foil
: Linear Potentio Meter
and
The
test
An on board microcomputer was used
for data sampling, and at the same
time, data were recorded on a data re-
corder. Sampling program and analysis
program were made for this fast sam-
pling and analysis.
4.2 SPEED TRIAL IN WAVES
A calibration test of the relative
flow meter was carried out using the
mile post of the Miho beach. The output
of this flow speed data was adopted as
the standard of the ship log speed. To
know the basic propulsive performance
of the ship, original condition without
a fin, a speed trial was carried out on
a day in which the sea was calm.
Results of speed trials are shown
in Fig.10. This figure shows the speed
reductions in a rather slow speed
range, less than 1 Cod rpm' due to the
frictional resistance increase by the
existence of the hydrofoil and struts.
However the high speed range (2000 rpm)
there was no discrepancy between with
and without hydrofoil results because
the wave making resistance dominated at
the higher speed range for the total
resistance.
_
7.5 _
5.0 _
2.5 _
0
:,,--
.
/
~'
O Fo i 1 out of water
--I-- Foi 1 in water
506 1 000 1 500 2000
Prop. rev. (rpm)
Fig.10 Ship speed trial in calm
water.
It was normally observed that the
operators of such small ships drive
them at high cruising speeds. It may be
considered that the weakness of the
WDPS at rather the low speed range in a
calm sea is not so serious.
Figure 11 and Table 1 show the
results of the wave data. A significant
wave height and mean wave period can be
seen in Figs 12 and 13.
292
OCR for page 293
Table 1. Wave Statics Data (01/12/1989)
E lapsed
time
(min.)
30
75
EMS
(m)
0.192
0.192
.
120 0.196 _
T Max
(sec. )
11.00
11.00
10.20
T 1/3
(sec. )
5.77
6.18
_ 6.83
_
Along the coast of Hiho and Kunou,
it is known that the wave condition is
not so sever even in the winter season'
Also it is a one reason why we selected
the WDPS test f ield, but during abnor-
mall: hot weather in the winter sea-
son, we scarcely had a proper wind and
wale condition. You can see in Figs 12
and l3 that the wave is a wind wave,
because the wave period is shorter and
the length of waves are less than the
ship length.
3. RB _
2. R
~ n
E-BS ~ see_ - Pover Density
T mean
(s ec. )
3.41
3.37
~ en
Hw sax
(m)
1.20
1.22
~.vv 1.23
Hw 1/3
(m)
D.71
0.73
_ .0.70
.
.
Hw mean
(m)
0.43
0.40
_ 0.38
January 12th, 1989 we had a good
wave condition. The direction of the
incident waves and the swell were
different all day but in the after-
noon, wave height decreased and the
swell subsided. Table l and Fig. 11
shows changes in the wave height.
Hw 1/3 (m)
2.0
_
1.0 _
.~ - _~
25 .5 t 11z. ] .75 1.8 1.25
BITT i m e
( H our )
Fig.ll Example of wave power
spectrum (01/12/1989).
293
To mean(sec. )
4.0
3.0
2.8
1.0
~ -~.
N_ 1
, 1
12121 12/22 12/26 1/10 1111 1112 1/13
Day
Fig. 12 Significant wave height.
\
. _..___ ~
I N-
12/21 12122 12/26 1110 1111 1112 1/13
Day
Fig.13 Mean wave period.
OCR for page 294
On this day, we had a speed
kt in the head sea condition
using engine power. By the
Froude, this speed corresponds
kt with a ship length of 80
of 2.5
without
law of
to 5.6
m. In
season, the
than this
It might be possible that the
ship of a length of 80 m could
e art a speed 8 kt
North Pacific in the winter
wave condition was better
case.
WDPS
cruis
The steering speed of this WDPS
ship is 2.5 kt. Also it was observed in
the unidirectional incident wave, the
COPS ship turns her bow to the incident
wave s .
With
a hydrofoil in waves, the
speed increase in the head sea is
observed during the certain wave condi-
tions. Each speed, with or without a
hydrofoil in waves, are shown in Figs
13 and 14. The speed increase in waves,
especially in the head sea, is thought
as a propulsive efficiency increase in
waves. We can see the wave length
affecting the ship's advance speed in
Fig. 7 and model testing results are
also shown in Fig. 8. The wave condi-
tion strongly influenced the ship's
speed and significant wave height (Hw
l/3) and mean wave period (Tw mean) are
shown in wave tables in Table 2 and 3.
Table 2. Wave Data (01/12/1989 Heading Sea)
Prop.
(rpm)
to
1000
20 00
Hwl/3
(m)
0.965
0.965
0.955
_ 0.965
_ _
Tw mean
(sec.)
3. 12
3.12
3.06
3.12
Table 3. Wave Data (01/12/1989 Following Sea)
Prop.
(rpm)
to
1000
1500
2000
Hwl/3
(m)
0.965
0.965
0.955
_ 0.955
Tw mean
(sec.)
3. 12
3. 12
3.06
3.06
Sh i p speed (kt)
10.0
.
5.0
.
t.0. 0
5.0
0.0 (S~
294
Fol lowing
without .
.
. _ _ .
~Fnl lowin
.. . ~
0 ff
ea
il
,;'
W~
,f,^' "
, ~
\
Ca l m sea w
sea with oi l
.
th foil
1 000 1 500 2000
Prop. rev. (rpm)
Fig.14 Results of speed trial in
head sea condition.
Sh i p speed (kt)
~Ca l m~ sea ~w
_ -_ _ 7 _ _ _
_ _;
~ Head sea
.
ith foi l
i,,,.:
Head sea
with foi l
me,
.,
,::
. shout to i l
1 000 1 500 2000
Prop. rev. (rpm)
Fig.15 Results of speed trial
in a following sea
condition.
OCR for page 295
Sailing with a propeller rotation
speed 1500 rpm, against the swell, a
7.7 kt forward speed could be obtained.
This speed is equal to a calm sea
condition without a hydrofoil. This
data shows the possibility that the
WDPS is useful as a sub-propulsor for
the ship.
4.3 SEAWORTHINESS OF WDPS SHIP
The motion reduction effect, espe-
cially pitch motion, is discussed here.
From the theoretical analysis, it is
expected that the pitch reduction
effect is superior. Figure 15 shows the
rate of the significant pitch ampli-
tude, with hydrofoil data are divided
by the without hydrofoil data. If the
pitch motion of WDPS is less than the
ordinary ship, then the plotted values
become less than one. In this case, we
have a 20 to 35% pitch reduction at the
mean wave period is 1.75 to 2.7.
Ratio of pitch decrease
.0
_
0.5
.0 _
at'
0 1.0 2.0 3.0 4.0
Wave period To mean(sec.)
Fig.16 Results of pitch motion
in a head sea condition.
Not only can we see the pitch
reduction effect from this figure, but
also the crews of the ship mentioned
that she has less pitching motion in
the rough sea than they had experi
enced.
At first, the crew would not sail
WDPS ship during the rough sea condi-
t ion even the bay area because they
have no significance. However after the
e f f ec t ivene s s o f the hydrofoil was c on-
f irmed, they willingly tested the WDPS
ship in heavy sea conditions where
they had never sailed ordinary hydro-
foil-less ship at the test speed range.
We had a chance to compar e the sat 1 ing
test of her sister ship in the same
rough sea at the same time. The sister
ship could hardly sail together with
the WDPS ship dale to hard bow slamming
of the waves.
1
ILog data
. ~
l
1
0 ~Course trajectory 150~
,
~./' "W.,
~I, I
\\ \\ i/ ~
Hi j
1
~ \~
-ad,.
_ ~
Sampling Data 1200
1~0m without foil L 15 |
2
Fig.17 Turning trajectory of ship
(without foil 1600rpm).
Log data
~ - _ - - - - -~ ~ - - - 1
(min.)
Course trajectory 1504
a r
0
1
1
1
295
r W`
. ~N.
i'
/.'
~,,.
170m with foil L 15°
~.
a,
SAmpling data 1200 /
,- I
Fig.17 Turning trajectory of
ship (with foil 1500 rpm).
OCR for page 296
It was not observed during the
experiment which Abkowitz stated the
horizontal hull vibration of the anti-
pitching fin due to the hydrofoil
impact.
The author consider that it is
associated with the depth and projected
area of the foil, which we adopted was
deeper and larger area than the anti-
pitching fin. The larger hydrofoil
restricted the lateral motion of the
ship fairly well and the phenomena of
the foil penetration of the surface did
not occur because of the deeper hydro-
foil position.
4.4 TURNING ABILITY OF WDPS SHIP
Figure 17 and 18 show the turning
trajectory of the ship with a hydrofoil
and without a hydrofoil in waves. It is
apparent that the turning radius in-
creased about 15% compared with the
ordinary ship, but a lesser heeling
angle was observed* This tendency was
the same as a the calm sea turning
Lest.
Considering the demerit of the in-
creased turning radius, the merit of
the increase of safety due to a lesser
heeling angle especially in waves is
more attractive in this ship.
_. CONCLUS I ONS
From our experiment of the wave
devouring propulsion system at sea,
following results were obtained
a) Improvement of the ship propul-
sive performance in waves were ob-
ser`-ed.
b) Reduction in motion, especial-
ly the pitch motion was observed.
c) Vertical hull vibration due to
the foil was not observed.
6. ACKNOWLEDGEMENT
1
This work has been supported by
the Japan Shipbuilding Industry Founda-
t~on.
The authors would like to thank
the crew of Hokuto for their support
during the experiment at sea.
REFERENCES
(l)The Naval Architect(1973,Nov.)pp 239
(2)Jakobsen,E.,2nd Int. Symp. on Waves
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296
Representative terms from entire chapter:
resistance increase
