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http://www.ijape.org/paperInfo.aspx?ID=7043 The purpose of this study is to predict the motion of a fish robot. The undulating caudal fin of the fish produces the lateral translational and rolling motions of the fish body in addition to the propulsive motion. In order to clarify how these motions influence propulsion, the interaction between the fish body and the fluid has been researchedby using the translational and rotational equations of motion of the body combined with two-dimensional numerical analysis based on the arbitrary Lagrangian and Eulerian finite difference method. In previous research, the fish model was fixed in space, or the lateral and rolling motions of the model were neglected in the analysis. The propulsive efficiency cannot be estimated exactly using such methods. The complex motion of the fish body has been computedby considering the surface forces acting on the body. As a result of the present study, it was determined that the propulsive efficiency of th
Citation preview
International Journal of Automation and Power Engineering (IJAPE) Volume 2 Issue 7, November 2013 www.ijape.org
355
Numerical Study on Swimming
Self‐propulsive Fish Model Itsuro Honda, Masashi Tada and Toshihiko Asami
Department of Mechanical Engineering, University of Hyogo, Japan
Email: [email protected]‐hyogo.ac.jp
Abstract
The purpose of this study is to predict the motion of a fish
robot. The undulating caudal fin of the fish produces the
lateral translational and rolling motions of the fish body in
addition to the propulsive motion. In order to clarify how
these motions influence propulsion, the interaction between
the fish body and the fluid has been researchedby using the
translational and rotational equations of motion of the body
combined with two‐dimensional numerical analysis based
on the arbitrary Lagrangian and Eulerian finite difference
method. In previous research, the fish model was fixed in
space, or the lateral and rolling motions of the model were
neglected in the analysis. The propulsive efficiency cannot be
estimated exactly using such methods. The complex motion
of the fish body has been computedby considering the
surface forces acting on the body. As a result of the present
study, it was determined that the propulsive efficiency of the
fish model is 50% higher than that of the model without
rotational movement. The reason is that the lateral force
acting on the body (which does not contribute to the
propulsive force) is decreased by the rolling motion of the
body.
Keywords
Fish Robot; Bio‐Fluid Mechanics; Propulsion; Propulsive
Efficiency; Vortex; Computational Fluid Dynamics; Moving
Boundary Problem; Finite Difference Method
Introduction
In recent years, the development of autonomous
underwater vehicles (AUVs) has been promoted (Ura,
T. and Nagahashi, K., 2008). Since an AUV does not
require a cable for electric power transmission, its
activity range is not limited to a narrow area. Taking
advantage of this feature, AUVs have been able to
perform various measurement surveys of the seabed.
On the other hand, existing AUVs still have not
reached the desired performance level. For example,
JAMSTEC has established the following performance
goal for AUVs: a dive depth of 6000 m and an activity
range of 5000 km (Japan Agency for Marine‐Earth
Science and Technology, 2009). However, the
performance of the currently operational AUVs is far
below the target values for both the depth and activity
range. In addition, the propulsion speed is around
several knots, which is not sufficient for chasing
aquatic animals (Ura, T., 2007). For this reason, it can
be said that insufficient power performance is the most
important issue for existing AUVs.
It is well known that aquatic creatures have a very
high athletic capability in the water. Therefore, a ``fish
robotʹʹ that adopts the movements of aquatic creatures
has the potential to surpass the performance of
existing AUVs. However, the propulsion motion of
aquatic creatures is delicate and very complex. For this
reason and since detailed experiments using living
aquatic creatures are very difficult, there are many
unexplained aspects of the generation mechanism that
affect their athletic capability. Therefore, with the
recent advancements in high‐performance computing,
computer simulation has become very effective to
investigate the propulsion mechanism of aquatic
creatures.
For numerical simulations, many research results have
been reported. Wolfgang et al. (Wolfgang, M. J.,
Anderson, F. M., Grosenbaugh, M.A., Yue, D.K.P. and
Triantafyllou, M.S., 1999) performed an experiment
using the particle image velocimetry (PIV) method and
a three‐ dimensional simulation of a swimming fish
(Danio malabaricus) and discussed the vortex
structure formed in the wake. Sato et al. (Sato, T.,
Takahira, H. and Kida, T.,2004) analyzed the flow
around a flexible wing using the vortex method and
reported that the flow pattern and the drag coefficient
are in good agreement with the experimental results.
Further, Sugiyama et al.(Sugiyama, H., Sato, M. and
Takato, K., 2002) took into account the heat transfer
and the flow around a flexible object to simulate a
rainbow trout. As a result, they pointed out that heat
transfer between the ambient fluid and the fish is
promoted by the motion of the caudal fin. Hoshino et
al.(Hoshino, H. and Yabe, T., 1999) computed the
three‐dimensional flow around the fish body using an
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hikawa, O.,
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ethod.
the studies
int that the
uid is not c
urpose of the
hind the a
velopment o
quired to co
rtex that is
opulsive for
om the vorte
arling et al. (
, 1998), Naka
d Takeuchi,
hen, Y. H., 20
uller, U.K. a
mphasis is pl
ructure rathe
dition, they
e moving di
ne of the auth
09) has o
opulsive pe
fected by the
opulsive dire
ony et al. (To
inted out th
stabilize the
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otion in the
urpose of dev
this paper, a
at combines
LE) finite d
otion of the
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nsidered in
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otion is given
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h is clarified
e propulsive
Intern
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2001) obtai
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1999) usin
mentioned
interaction
considered.
eir studies w
aquatic crea
of a fish robo
onsider not
s released
ce and the p
x. Such stud
(Carling, J., W
atsuka et al. (
S., 2004), To
007), and Kat
and Liu, H.,
laced on the
er than the
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hors (Tada, M
obtained th
erformance
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ection, even
ony, W., Sheu
hat the later
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Williams, T.
(Nakatsuka,
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tsumata et al
2007), but i
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propulsive
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M., Asami, T
he following
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fish robot.
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T. and Honda
g results:
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ting on the
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FIG. 2: DEFOR
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EMATIC DIAG
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Applied to th
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hown in Fig.
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mass mome
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GRAM OF THE F
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G. 3: DEFINITIO
XIS IS FIXED IN
THE R
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eral translatio
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ation metho
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ON OF THE RO
SPACE, AND T
RIGID PART OF
d Kawashim
ng grid can b
mation.
Discussion
ulation of th
merical metho
of the fish
d. Prior to
ow around
f the num
a result, it
ult of the pre
awamura et
hara, K., 1986
ed in our calc
the effect
er than the
formance wa
n addition to
onal motion
tion about th
where the
only the t
r 2013
he other half
was adopted
sinusoidal
lied to the la
he rectangul
center of th
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bol λ is the w
5.
al deformed
el at given t
odel, a new
h time step.
od that w
thors (Honda
OTATIONAL A
THE AXIS I
F THE FISH MO
ma, Y., 20
be formed, ev
n
he Fish Mode
od introduce
model was
its applicati
a circular
merical meth
t was confi
esent analysis
al.(Kawamu
6) in the Rey
culation.
of fish bo
traveling di
as investigat
o the analysi
in the horizo
he center of
e motion o
traveling di
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f is deformab
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atter part of
lar coordina
he fish mod
stants obtain
period of
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shapes of
times. Based
computatio
. By using
was previou
a, I., Sanno, T
NGLE (THE
IS ATTACHED
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004), a go
ven for the c
el
ed in Section
simulated in
ion to the f
cylinder as
hod has be
rmed that
s coincides w
ura, T., Taka
ynolds num
ody motion
irection on
ted. In order
is including
ontal plane a
f gravity of
of the fish
irection is a
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357
ble.
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and
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usly
T.,
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n a
fish
s a
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mber
in
the
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the
and
the
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(8)
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Nu
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IG. 5: TIME HIS
urthermore,
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gure 4 shows
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otal length of
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in the nu
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each other w
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E VELOCITY CO
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when the mo
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RID
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ure 5 show
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G. 6 : TIME HIS
FIG. 7 : TIME H
ich the fish
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ocity of the
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fish began
ocity and rea
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t the movem
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perimental v
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partial diffe
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velocity fo
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TORY OF THE
(CAS
HISTORY OF TH
(CAS
head does
forward dire
e experimen
fish after it
ndicates that
‐axis directio
n to accelera
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sh in the qu
65 for Case B
ment of the
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7 show the t
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lume 2 Issue 7
erentiation w
history of
. Thick solid
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VELOCITY CO
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ate the flow
si‐steady sta
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B. Therefore,
fish in any
on leads to
her, it can b
greater than
se A and 9%
time historie
the rolling a
ely, for Case
7, November 2
with respect
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and the brok
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OMPONENT OF
NAL ANGLE �
n any direct
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the swimm
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sion direction
A and Case
w from a z
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state is 0.47
, it can be s
direction ot
a reduction
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for Case B.
es of the late
angle about
e A. From th
2013
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ken
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The
n is
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the
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the
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ernational Jou
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ateral transla
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avity of the
ngth of the fi
e rolling ang
ndition.
FIG. 8: TI
hese values
atthey shoul
nsidered to
mall. That is,
e actual valu
the fish surfa
the fish
anslational an
e same time
is computati
gher Reynold
ree‐dimensio
eynolds numb
ow Reynolds
gure 8 show
odel to mov
own in this
lue of the t
proximately
opulsive effi
ase B, as show
an index ind
object for p
sed on the p
wer . He
tained by E
pression is
lculated by E
urnal of Autom
omes clear th
ational motio
zed with the
e of the late
fish is appr
ish in steady
gle is about 4
IME HISTORY
TABLE 1: PROPU
seem to b
d be for a re
be that ou
if the Reyno
ue, then a lar
ace. Based on
does not
nd rolling m
. By using o
onal grid, it
ds number, b
onal effect of
ber flow, the
s number.
ws the thrust
ve forward i
figure, it w
thrust force
75% compar
ciency of C
wn in Table
dicating how
propulsion an
propellant sp
re, the pow
Eq. (11), wh
the surface
Eq. (9).
mation and Po
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www.ijape.org International Journal of Automation and Power Engineering (IJAPE) Volume 2 Issue 7, November 2013
360
diagrams of the pressure coefficient shown in Figs. 10
and 11 that the fish in Case B sheds a stronger vortex
than the fish in Case A. It is evident from the fact that
the distance between two isobaric lines of the vortices
in Case B is narrower than that in Case A, and the
value of the pressure coefficient at the center of the
vortex in Case B is smaller than that in Case A. It is
thought that a difference in the vortex strength is the
cause of the difference in the thrust force between the
two cases.
FIG. 10: INSTANTANEOUS DISTRIBUTION OF CASE A
( . : THRUST FORCE IS MAXIMUM)
FIG. 11 : INSTANTANEOUS DISTRIBUTION OF CASE B
( . : THRUST FORCE IS MAXIMUM)
The maximum ratio of the fluid force acting on the fish
body in the lateral direction to the force in the traveled
direction (i.e., / ) is 9.8 in Case A and 14.3 in Case B.
This means that in Case B, the momentum is released
in a direction that does not contribute to the forward
travel of the fish. This can be explained by the fact that
the vortex street behind the fish model in Case B has
spread to the left‐ and right‐hand sides. That is, it can
be concluded that the high propulsive efficiency in
Case A is due to the fact that the ratio of the
momentum released laterally is low.
Conclusion
In order to investigate the effect of the lateral
translational and rolling motions of a fish on its
propulsive efficiency, an analytical method has been
proposed that combines finite difference analysis using
the ALE method and the equations of motion of a
deforming fish body. Using this analytical method, a
swimming simulation of a fish model was performed.
By comparing the results with those from the
conventional method based on the restricted motion
analysis (to limit the motion to translation in the
traveling direction), the followings were obtained:
(1) In the case where the motion is not
constrained, our fish model moves forward in a small
lateral translational motion with an amplitude of about
1/100 of the fish length and a rolling motion with an
angle of 4 degrees.
(2) If the motion of the fish body is free from
constraint, then the vortex strength shed from the fish
becomes weak. This causes the driving force of the fish
to be reduced by 75%, and the driving speed is
reduced by 25% compared with the constrained
motion.
(3) The propulsive efficiency of the fish model
was 62.5% in Case A, which does not restrict the
motion, and 43.9% in Case B, which restricts the
motion. This is because the increase in the ratio of the
momentum released in the lateral direction does not
contribute to the propulsion of the fish.
ACKNOWLEDGEMENT
Part of this research was performed with the aid of the
Takahashi Industrial and Economic Research
Foundation. We would like to acknowledge and
deeply thank them for their support.
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Itsuro Honda is a Professor in
Department of MechanicalEngineering,
Faculty of Engineering, University of
Hyogo, Himeji, Japan. He received his
B.E. degree in Mining Engineering from
the Kumamoto University, Kumamoto,
Japan and Ph.D. in the area of Industrial
Science from Kumamoto University. He has been studied the
area of CFD applications for Bioengineering and Heat
Exchanger. Email: [email protected]‐hyogo.ac.jp
Masashi Tada is a graduate student in
Department of Mechanical Engineering,
University of Hyogo, Japan. He
completed the course of graduate school
of the University of Hyogo in 2010 and
works now in Honda Motor Co., Ltd.
Toshihiko Asami is a Professor in
Department of Mechanical Engineering,
Faculty of Engineering, University of
Hyogo, Himeji, Japan. He received his
B.E. degree in Precision Engineering
from the Niigata University, Niigata,
Japan and Ph.D. in the area of
Mechanical Engineering from the
Himeji Institute of Technology. He has been studied the
area of vibration damping. Email: [email protected]‐hyogo.ac.jp