Rubble structure design does not require differentiation between 

 all three types of wave action; problem types shown as IR, 2R, and 3R on 

 the figure need consider only nonbreaking and breaking wave design. 

 Horizontal forces on pile-supported structures resulting from broken 

 waves in the surf zone are usually negligible, and are not considered. 

 Determination of breaking and nonbreaking wave forces on piles is pre- 

 sented in Section 7.31, FORCES ON PILES. Nonbreaking, breaking and 

 broken wave forces on vertical (or nearly vertical) walls are considered 

 in Sections 7.32, NONBREAKING WAVE FORCES ON WALLS, 7.33, BREAKING WAVE 

 FORCES ON VERTICAL WALLS, and 7.34, BROKEN WAVES. Design of rubble struc- 

 tures is considered in Section 7.37, STABILITY OF RUBBLE STRUCTURES. 



7.31 FORCES ON PILES 



7.311 Introduction . Frequent use of pile-supported coastal and offshore 

 structures makes the interaction of waves and piles of significant practi- 

 cal importance. The basic problem is to predict forces on a pile due to 

 the wave-associated flow field. Because wave-induced flows are complex, 

 even in the absence of structures, solution of the complex problem of wave 

 forces on piles relies on empirical coefficients to augment theoretical 

 formulations of the problem. 



Variables important in determining forces on circular piles subjected 

 to wave action are shown in Figure 7-39. Variables describing nonbreaking, 

 monochromatic waves are the wave height H, water depth d, and either 

 wave period T, or wavelength L. Water particle velocities and acceler- 

 ations in wave-induced flows directly cause the forces. For vertical 

 piles, the horizontal fluid velocity u and acceleration du/dt and 

 their variation with distance below the free surface are important. The 

 pile diameter D and a dimension describing pile roughness elements e 

 are important variables describing the pile. In this discussion, the 

 effect of the pile on the wave-induced flow is assumed negligible. Intui- 

 tively, this assumption implies that the pile diameter D must be small 

 with respect to the wavelength L. Significant fluid properties include 

 the fluid density p and the kinematic viscosity v. In dimensionless 

 terms, the important variables can be expressed by: 



H ,. . , 

 = dimensionless wave steepness, 



_d_ 



p 

 L 



= dimensionless water depth, 



= ratio of pile diameter to wavelength (assumed small). 



e 

 — = relative pile roughness. 



and 



HP 



a form of the Reynolds' number. 



7-64 



