Acosta, A. J.

Kiceniuk, Taras

Perry, Byrne

Caltech Authors - Main

A LAB ORA TORY EXPERIMENT 
ON 
SIMULATED WAVE- RIDING DOLPHINS 
by 
Byrne Perry, A.J. Acosta a nd T.Kice niuk 
~ 
tfYDROOYNAMICS lABORATORY 
&AliFORt!!: , · • · · :: E OF TECHNOLOGY 
1201 ~ - CALiFORNIA STREET 
PASADENA 4. CAliFORNIA 
A LABORATORY EXPERIMENT 
ON SIMULATED WAVE-RIDING DOLPHINS 
by 
Byrne Perry( l), A. J. Acosta ( 2 ) and Taras Kiceniuk( 2 ) 
(1) Department of Civil Engineering. Stanford University 
Stanford, California 
(2) Hydrodynamics Laboratory, California Institute of 
Technology, Pasadena, California 
August 1961 
ACKNOWLEDGMENT 
This work was supported, in part, by 
the Department of the Navy, under 
Contract N 123 (60530) 24917A. 
TABLE OF CONTENTS 
Bac kground .. 
Apparatus and Experimental Procedure 
Observations a nd Analysis of Data 
Conclusion 
Table I •• 
Figure 1 
Figures 2 and 3 
References 
1 
2 
3 
4 
6 
7 
8 
9 
J. J. 
Background 
The explanation of the mechanism by which dolphins are able to 
ride bow waves of ships, or natural surf and wind-generated w aves, 
has stimulated much discussion and controversy. Since an excellent 
summary of previous research on the wave-riding problem has been 
g iven by Fejer and Backus ( l) ,* only a few remarks by way of review 
will be given here. 
Although dolphins had been observed riding on bow waves of 
ships many times over the years, Woodcock (2, 3) published the first 
account which included considerations of the forc e s estimated to be 
required. Shortly thereafter, Woodcock and McBride ( 4) undertook 
to explain in more detail the nature of these forces. They found that 
a two hundred pound dolphin submerged in sea water would have, at 
most, a net wei ght of 9. 2 lbs. The component of this weight in the 
direction of the loc al flow was thus show n to be too small to overcome 
the expected viscous drag -- unless the dolphin w as in some manner 
able to maintain a laminar flow over his body surface. The Reynolds 
number for these obs e rvations was 8 . 4 x 106 based on body length. 
For rig id bodies tested under many conditions it is known that at such 
a Reynolds number the boundary layer is almost certainly turbulent; 
hence, the conclu sion would follow that the dolphin had achieved t he 
surprising feat of maintaining a laminar boundary layer (and hence, 
very low drag) at a very high Reynolds number. 
It was Hayes ( 5) who pointed out that it was the component of 
the total weight rather than the net weight in the direction of the 
local flow that provided the thrust. With this force available, there 
is no need to suppose the dolphin has a viscous drag appreciably 
lower than any other streamlined body mov ing at the same Reynolds 
number. 
In spite of the lucid arguments set forth by Hayes, some work-
ers remain unconvinced. Scholander 's experiments in the open sea (6), 
*Numbers in parentheses designate r e ferences at end of text. 
convinced him that the Hayes explanation was not satisfactory. Scholan-
der and Hayes (7, 8) thereupon arrived at an impasse, with Scholander 
sugges ting that further experiments be conducted under better-controlled 
conditions. 
In discussing thes e considerations with Prof. Scholander, it occurred 
to the pre sent writers that the Free-Surface Water Tunnel in the Hydrody-
namics Laboratory at this Institute, could be used to h e lp resolve this 
controversy. 
App ara tus and Experimental Procedure 
At tunnel operating speeds approximating 7 feet per second, it is 
p ossible to establish a stable, standing wave in the working section of 
the Free-Surface Water Tunnel (9). Such a w ave was formed and the 
simulated dolphin model (consisting of a streamlined body of r evolu-
tion two inches in d iameter and approximately one foot long) was 
immersed in the wave and the hydrodynamic reactions w ere measured. 
The test body, strut support, and force balance assembly are shown 
in Fig. 1. Extensive force m e asurements had already been made on 
this body in previous investig ations ( 10) using w ind tunnel, water tunne l 
and drop tank facilities, and were therefore available for comparison. 
The configuration of this body, howeve r, had been slig htly modified 
for the present experiments by replacing the original tail and boom 
assembly with a shorter one . Also, an adjustable streamlined strut 
had been attached to this boom, thereby p e rmitting the attitude o f the 
test body to b e determined within an ang l e of one-half degree . 
Prior to starting the tunnel, tare forces were m e asured with 
the test body in air, at each of the angl e s of the test body employed 
in the e xperiment. By means of an elevating mechanism, the bal-
ance and body assembly were lowe r e d until the centerline of the body 
was a t a depth of about 0. 2 ft. The buoyant force acting on the body 
in still wate r was then measured. The tunnel w as started and the 
standing w ave established. Force readings at the two tunne l loca-
tions we r e made for angles of 0° and ± 8° at various submergences. 
Position 1 (fig. 2), was located on the upstream slope of the wave, 
considerably ahead of the crest. It had been hoped that the body could 
be located somewhat farther downstream, but this could not be done 
easily because of interfe rence with a tunnel structural member. Posi-
tion 2 (Fig. 3), was in t he trough of the wave. The water velocity in 
thes e tests was of necessity near the critical channel velocity, but 
varied locally with position along the wave. A miniature HRS current 
meter about one-half inch in diameter was used to m easure these 
velocities at the same longitudinal position and depth in the tunnel as 
the midpoint of the test body. These data are summarized in Table I 
as well as are some other conditions not described. 
Observations and Analysis of Data 
When the test body was aligned with the slope of the water surface 
and submerged b eneath the upstream slope of the wave in position 1, it 
was immediately apparent that a small, forward thrust betwe e n 0 . 007 
and 0 . 11 lbs was measured (see runs 14-17). However, when the body 
was located in the trough of the wave at a similar submergence (runs 8, 
9, 10) the body experienced a drag force ranging fr om 0. 07 lb to 0. 106 lb. 
These figures can be compared to the still-water buoyant force of 0. 7 8 lb to 
establish scale. Although no attempt was made to find the optimum loca-
tion of the body with respect to the wave insofar as thrust is concerned, 
it is clear that a net thrust can be achieved with a rig id streamline body un-
der even the gentle slope of the wave produced i n the tunnel. 
The observed thrust varies with depth and changes to a drag both 
when the body broaches and when the submergence exceeds about three 
diameters of the body. It should be remembered that the drag of the 
strut is included in these results so that the present data do not r e -
flect the body drag alone. The submergence for least drag observe d 
herein -- about one body diameter -- is roug hly the same as that 
reported for dolphins in bow waves . 
Further insight into the mechanic s of the force system acting on 
the body is obtained by resolving the forces along axes paralle l to and 
perpendicular to the local flow angle ( 5) . For example, for run 14 of 
Table I (corresponding to Fig. 2), the resistance parallel to the local 
flow is 0. 054 lb and the force normal to the flow (or free surface) is 
0 . 745 lb, with the estimated local flow angle of 5°. This latter force, 
perpendicular to the wave surface, can be reg arded as an inclined 
buoyant force as mentioned by Hayes. Thes e forces, it must be re-
called, are hydrodynamic in origin and do not include the body weight . 
Let it be supposed now that the self-propelling capability of a body, 
whose weight is equal to that of the displaced fluid, is to be determined. 
This weight of 0 . 777 lb resolved along the direction of flow must ex-
ceed the flow resistance of 0. 054 lb. For the present example, this 
force is not only exceeded but there is, in fact, a net propelling force 
of 0. 013 lb available. The forces are not precisely in equilibrium for 
this example; the body, if free, would tend to sink to a slig htly g reater 
depth, w here the vertical force is seen to be larger. 
The flow resistanc e of 0. 055 lb resolved along the local flow 
angle i s r oughly comparable to the drag measured in the trough of the 
wave (run 8) and both are typical of viscous drag measurements i n a 
tur bul en t flow ( 9, ll) . Laminar skin friction is therefore s een not to 
be a necessary condition for b ow wave riding as was originally con-
tained in the suggestion by Woodcock. 
It is also interesting to observe that the vertical forces both 
1n the slope of the wave and in the trough differ noticeably from the 
buoyant force in still water . This is thought to be due to a combina-
tion of two effects: the well -known repulsion experienced by a sub-
merg ed body moving unde r an otherwise flat, free surface, and more 
important, the curvature of the local streamlines. Summary calcula-
tions have shown the contributions of the latter term to the lift force 
to be of the correct magnitude. 
Conclusion 
The mere existence of the measured forward-acting thrust on 
the test body in a wave demonstrates that a rig id body with turbulen t 
flow can perform the wave riding trick. Analysis of the m e asure -
ments shows further that the force system is equivalent to a dynamic buoyant 
force perpendicular to the inclined wave surface and a resistance parallel 
to this surface. The dynamic buoyancy is approximately equal to the 
weight of the displaced liquid, while the viscous resistance is substan-
tially equal to that measured on the body when not in the wave. 
In spite of these incomplete experimental results, it appears in-
escapable that Hayes 1 arguments are substantially correct. 
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Figure 1. The "dolphin-like body" mounted on the 
3 -component force balance used in these experiments 
Figure 2 . 11 Dolphin-Body" located at tunnel position 
No. 1 on the forward slope of a standing wave. 
Net forward thrust= 0. 007 lb at a velocity of 7. 02 fps. 
Figure 3. "Dolphin-Body" located at tunnel position 
No. 2 in the trough of the standing wave. Net drag 
= • 071 lb at 7. 24 fps. Note the dye streak ahead of 
the model near the model center line. 
8 


A laboratory experiment on simulated wave-riding dolphins

https://authors.library.caltech.edu/46199/1/A%20Laboratory%20Experiment%20on%20Simulated%20Wave-Riding%20Dolphins.pdf

A laboratory experiment on simulated wave-riding dolphins

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