rough bed. Kalkanis (1964) showed that the velocity distribution in an 
oscillating flow with the same assumptions as described above can be 
approximated by: 
u/uy = [1 + £2(Y) - 2£, (1) cos f,(Y)]# sin(wt + 6) (5) 
where 
£,(Y) = exp(Y-103/agD), (6) 
a OO) = OaS(hQl 982 (7) 
and sin(wt + 6) describes the variance of the velocity with time and 
phase angle. In equations (6) and (7), Y is the elevation above the 
bed measured positively upwards; a is the amplitude of bed oscillation; 
B = (w/2v)?; v is the kinematic viscosity; and D is the representa- 
tive roughness diameter. For the flume roughness conditions used in this 
investigation (D = 0.05 foot), and the flow velocities studied (0.67 foot 
<a < 2.0 feet and 2.0 seconds < T < 15.0 seconds), equation (5) indicates 
the boundary layer thickness is no more than a few millimeters thick. 
To approximate the shear stresses and therefore the turbulence condi- 
tions near the ocean bed for a given water depth, wave period, and ampli- 
tude, a flume having a moving bed under a still body of water was used. 
The frame of reference, which describes the prototype fluid motion under 
the above assumed conditions, is then moving with the bed. It is only 
necessary to oscillate the bed in the harmonic motion described by the 
linear wave theory for y = -d. The swing flume used in this investiga- 
tion duplicates, on a one-to-one scale, these conditions. 
The swing flume is shown in Figure 1(a). The flume bed is shaped to 
an arc segment of a circle with an 8.92-foot radius, a 13.33-foot chord 
length, and a 12-inch width. The flume, suspended from the ceiling of 
the laboratory, is free to rotate about its center of curvature. The 
flume is oscillated about its center position by a 1.5-horsepower 
variable-speed motor connected to a drive wheel with an eccentric arm. 
The eccentric arm is connected by a 10-foot connecting rod to a linkage 
fixed to the flume bottom. The linkage at the flume is adjustable to 
allow correction of the asymmetry of motion which would result from a 
change in eccentricity. Variations in eccentricity and motor speed allow 
the amplitude and frequency of oscillation to be varied over a wide range 
of prototype wave conditions. 
Within the flume is a stationary horizontal board, slightly less than 
12 inches wide, 8 feet long, and at an elevation of 12 inches above the 
lowest point of the curved bottom. The board, which is separately sup- 
ported from the ceiling of the building and is not connected to the flume, 
Suppresses any standing surface waves in the flume caused by the flume 
motion. The fluid at this elevation must remain stationary to conform 
to the flow conditions described above. 
