Each of the four situations has the same Froude number' F = U^/gJi, where 

 U is the maximum particle velocity at the wave crest, g is the accel- 

 eration due to gravity, and i is some characteristic flow length, 

 which can be taken to be either the d, X, or H (Table 3). (Several 

 subscripted Froude numbers based on different length scales are used 

 where appropriate in this report.) The Froude number measures the ratio 

 of inertial to gravitational forces and therefore describes stagnation 

 effects in flow with a free surface. 



Electrical gages were used for pen-and-ink records of water level in 

 time, according to well-defined Coastal Engineering Research Center (CERC) 

 laboratory procedures (Stafford, Ray, and Jones, 1973). Generally, one 

 gage recorded the transformed wave near the pile, e.g., within a channel, 

 and a second gage recorded the incident wave, between the wavemaker and 

 the pile, (see insets in Fig. 3). Several different water level probes 

 were used during the study for more accuracy and compactness. Also, 

 most test data for circular piles consist only of the measured peak 

 water, recorded by the wetting of a paper sleeve wrapped around the pile 

 or by the removal of a powder deposit on the pile. Appendix A discusses 

 the techniques used in measuring water level; these techniques give 

 accurate peak water measurements and are fairly interchangeable. How- 

 ever, the wave gages were calibrated only in still water, so their 

 response to rapid water level fluctuations was not well defined; the 

 measured waveforms have been treated as qualitative information. 



The test wave condition is specified by the T,d combination, along 

 with E and the distance, G, from the wave generator to the test pile. 

 G must be specified because of the nonlinearity of the finite-amplitude 

 test waves in fairly shallow water (d/L < 0.13) (see the waveforms in 

 App. B) . The test pile was near G = 25 feet (7.6 meters) and the other 

 wave gage near G = 23 feet (7.0 meters) in most 96-foot tank tests; the 

 test waves had smooth and sharp crests. The secondary waveform features 

 are relatively unimportant in this study, since the major data reported 

 are peak water levels caused by the main crest. 



In each tank, the wave field was slightly variable due to wave re- 

 flection and other effects (see App. B) . Most tests were conducted 

 during the approximately steady state attained after the wavemaker had 

 generated at least 20 waves. One-wave tests were conducted in each tank 

 in the brief interval after starting the wavemaker when reflection 

 effects had not yet accumulated and the water surface was glassy smooth. 



The 12 test piles had the horizontal cross sections shown to scale in 

 Figure 2. The piles were constructed of Plexiglas, and the flat plate 

 was made of varnished plywood, for stiffness. Noncircular piles are 

 designated HP shapes according to standard usage (American Institute of 

 Steel Construction, Inc., 1970). The H-section piles are named according 

 to the ratio of their flange to web size in inches; e.g., the 5x1 H-pile 

 has deep, narrow channels, and the 1x2 H-pile has shallow, wide channels. 

 The orientation of a noncircular pile is specified by the yaw angle B 

 between the direction of wave propagation and the inward normal to the 



