pile in the wake, which is skewed toward the right o£ the frame. The 

 crest is at the pile in Figure 10(b), taken one-eighth second later. 

 The top of the bow wave is above the frame. The points of flow separa- 

 tion are farther away from a = 180° than in Figure 10 Ca), and the wake 

 has become flatter, wider, and skewed toward the left of the frame. 

 Figure 11 shows the pattern of average peak water recorded in the same 

 test situation by wetting a paper sleeve on the pile. This pattern 

 resembles the water levels visible in Figure 10(b), with about the 

 same minimum locations and a low wake skewed to the same side. 



The photo sequence in Figure 12 views a circular pile from the side 

 through a wave cycle, starting during trough flow of a wave traveling 

 toward the right. Test conditions are: 2a = 0.25 foot (7.6 centimeters), 

 d = 1.00 foot, T = 2.32 seconds, H = 0.49 foot (14.9 centimeters), 

 W = 0.30 foot (9.2 centimeters), 32 frames per second film speed (Fig. 12 

 shows every fourth frame). Figure 13 shows the incident waveform and two 

 waveforms recorded on the pile's surface in the same test situation. 



These photos show an intricate water surface near the pile. Figure 

 12 (a and b) reveals flow toward the left associated with the wave trough; 

 the water level is higher on the right segment of the pile due to flow 

 stagnation near a = 180°. The flow is reversing in Figure 12(c) and has 

 increasing velocity toward the right in the next three frames. Crest 

 stagnation near a = 0° is maximum in Figure 12(f), as is the slope in 

 water level near a = 90°, The flow then subsides and is weak in Figure 

 12(i), which shows practically no relief in water level around the pile. 

 Another definite effect is visible in Figure 12 (o), where the higher 

 water level at the left of the pile corresponds to stagnation of the 

 waveform's secondary crest. 



The waveforms in Figure 13 complement the pictorial record in 

 Figure 12. The transformed crest recorded at the pile is broader than 

 the incident crest, as flow stagnation increases the duration of peak 

 water. At a = 0°, crest height is significantly increased by runup, 

 while peak water at a = 180° is slightly lower than the incident crest. 

 After the main crest passes, the a = 0° waveform shows a small peak, 

 perhaps caused by a splash of falling water; this effect is visible at 

 the left side of Figure 12(j). The lowest part of the incident wave, 

 midway between the main and secondary crests, results in a slight 

 secondary peak in the a = 180° waveform, due to flow stagnation; as this 

 trough passes, recorded water level, is nearly the same at a = 0° and 

 at a = 180° (Fig. 12, i). The secondary crest of the incident waveform 

 rises to about SWL, and stagnation results in a higher water level at 

 a = 0° than at a = 180°, as in Figure 12 (n and o) . 



2. Circular and Finned Circular Piles . 



Figure 14 shows a wave crest in the 85-foot tank simultaneously 

 striking the 6- inch-diameter pile, at the right of the frame, and the 

 pile with 25 radial fins (12 in total diameter) . Every eighth frame at 

 64 frames per second is shown. The wave condition is d = 2.33 feet (71.1 



25 



