WAVE TRANSFORMATION 

 AT ISOLATED VERTICAL PILES IN SHALLOW WATER 



hy 

 Robert J. Eallermeier and Robert E, Ray 



I . INTRODUCTION 



Context of Study. 



This report presents the results of a laboratory investigation of 

 wave height measurements at an isolated pile. The investigation was 

 motivated by the possibility that wave transformation near a pile can 

 be used to measure nearshore wave directions (Galvin and Hallermeier, 

 1972) . Usual test situations with a straight wave crest incident on a 

 vertical pile, either smooth or with channels, are shown in Figure 1. 

 Figure 2 shows the cross sections and the types of piles tested. These 

 tests investigated the dependencies of transformed crest height near a 

 pile on incident wave characteristics and on the cross-sectional shape 

 and orientation of the pile. This account completes several brief 

 reports on these data (Galvin and Hallermeier, 1972; Hallermeier, 1976; 

 James and Hallermeier, 1976) . 



The tests differed from previous laboratory studies of waves on 

 piles in that the pile's effect on the wave was measured, rather than 

 the wave's effect on the pile. Previous studies primarily investigated 

 wave force or pressure on circular vertical piles (Table 1). The report 

 extends the previous work, as indicated in Table 1, by recording water 

 levels at a wide variety of piles, and thoroughly examining the effects 

 of pile orientation with respect to wave direction. The tests were 

 conducted in relatively shallow water with relatively steep waves; the 

 test piles have small cross sections compared to wavelength. 



2. Test Situations and Water Level Records. 



The tests were conducted in two indoor wave tanks with length, width, 

 and height dimensions of 96 by 1.5 by 2 feet (29.3 by 0.5 by 0.6 meters) 

 and 85 by 14 by 4 feet (25,9 by 4.3 by 1.2 meters), hereafter called the 

 96-foot tank and the 85-foot tank, respectively. Figure 3 shows plan 

 views of these wave tanks. Each tank had a piston- type wavemaker, a 

 vertical flat plate across the width of the tank, driven horizontally in 

 nearly sinusoidal motion with a set period, T, and amplitude controlled 

 by the radius setting, E, of the rod connecting a rotating drive wheel 

 to the wavemaking plate. At the end oppos.ite the wavemaker, each tank 

 had an unchanging wave absorber, a steep beach of about 3 -inch -diameter 

 (0.1 meter) rubble in the 85-foot tank, and a gently inclined plane of 

 permeable rubberized hogshair in the 96-foot tank. A vertical surface- 

 piercing pile was rigidly mounted in the long section of the tanks with 

 constant water depth, d. 



The major test conditions are listed in Table 2. These laboratory 

 conditions represent the prototype s^ituations listed in Table 3. 



II 



