EXPERIMENTAL STUDY ON THE VALIDITY RANGE OF VARIOUS WAVE THEORIES

Abstract

In the design of coastal structures and the study of nearshore dynamics, rational predictions of the wave kinematics are very important but difficult procedures. Although a large number of nonlinear wave theories have been proposed and used for computing the wave kinematics, there are no theories applicable from the deep water to very shallow water. It is, therefore, very important for coastal researchers and engineers to know which of theories describe well a wave field specified by the wave characteristics and water depth, and to select a particular wave theory for a problem of interest. Many intensive efforts have been made to examine the validity as well as the applicability of various wave theories. However, there are still no well-accepted guidlines for the application range of the wave theories. The validity evaluation of a particular wave theory has been basically made by means of the following two versions: the analytical (mathematical) validity and the experimental (physical) validity. The analytical validity study has been conducted by various researchers (Dean, 1970; Komar, 1976; Horikawa et al., 1977; Swart, 1978) and revealed the degree of mathematical satisification to the governing equations and boundary conditions for each wave theory. The analytical validity study probably tends to show the relative applicability for various wave theories. It does not ensure that the theory describe well laboratory or field phenomena. Based on the analytical validity of various wave theories by Horikawa et al., Isobe (1985) proposed application ranges for the finite amplitude wave theories in terms of the relative water depth and relative wave height. The experimental validity refers to how well the prediction of various wave theories agrees with actual measurements (Dean & Dalrymple, 1984). As the wave shoals, wave form becomes more asymmetrical, especially under high wave conditions of interest to design. Such nonlinearity influences greatly the wave kinematics and it makes difficult to predict readily the wave kinematics by several theories. From a practical viewpoint, it is , therefore, requested to establish the application ranges of available wave theories for shoaling waves.