Translated article

　

Locomotion by mechanical pectoral fins^*

　

NAOMI KATO

　

Department of Marine Design and Engineering, School of Marine Science and Technology, Tokai University, 3-20-1 Orido, Shimizu, Shizuoka 424-8610, Japan

　

Abstract： The objectives of this study were the development of a new device for maneuvering an underwater vehicle using the mechanism of a fish swimming, an experimental and theoretical analysis of the hydrodynamic characteristics of the

device, and its application to maneuvering a fish robot. Observations and experimental analysis of the pectoral fins of a black bass (Micropterus salmoides) revealed that the locomotion of the fish, such as swimming forward at low speed, swimming backward, and turning in a horizontal plane is generated by using a combination of a feathering motion and a lead-lag motion of the pectoral fins. A mechanical pectoral fin making a feathering motion and a lead-lag motion generates a thrust force in a range of phase differences between both motions. The unsteady vortex lattice method, including the effect of viscosity, can express fairly well the unsteady forces acting on the mechanical pectoral fin in the range of phase differences where it exerts the thrust force. The fish robot, consisting of a model fish body and a pair of mechanical pectoral fins, can not only swim forward and turn in almost the same position, but can also swim in a lateral direction without changing the yaw angle.

　

Key words： pectoral fin motion, feathering motion, lead-lag motion, unsteady vortex lattice met, hod, fish robot

　

Address correspondence to; N. Kato

Received for publication on Sept. 29, 1998; accepted on Oct. 12, 1998

* Translation of an article that appeared in the Journal of The Society of Naval Architects of Japan, vol. 182 (1997)： The original article won the SNAJ prize, which is awarded annually to the best papers selected from the SNAJ Journal. JMST, or other quality journals in the field of naval architecture and ocean engineering.

　

List of symbols

　

C chord length of pectoral fin

C_x' C_y' C_z' C_my' C _mz hydrodynamic force coefficients

F_x' F_y' F_z' M_y' M_z hydrodynamic forces

F_xo' M_yo' M_zo hydrodynamic forces acting on support setups alone without fin

K nondimensional frequency

L length of fish

n_p normal unit vector to surface of pectoral fin

O_e field out of pectoral fin

p pressure on pectoral fin

r_Qp position vector of point P where the velocity field is calculated from point Q on the singularity

r_p position vector of point P from

point O

Re Reynolds number

S surface area of pectoral fin

S_fin surface of pectoral fin

T period of motion

t time

t_o time when a free vortex filament is shed

T_s strength of the bound vortex sheet on the pectoral fin

U advancing velocity

U inflow velocity vector

V_w vortical field

Ve external velocity field outside pectoral fin

V_p velocity vector

w induced velocity vector from a vortex filament

W _oy W_oz mean value of tangential velocity in the Y" direction and in the Z" direction, respectively, on a pectoral fin normal to the X", axis

(X, Y, Z), (X', Y', Z'), (X", Y", Z") coordinate systems of the mechanical pectoral fin

x' measured span on the monitor

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