By means of the regular wave experiments in the wave-current flume, the phase differences between the total horizontal and vertical forces of regular waves acting on partially perforated caissons located on a rubble mound foundation are investigated. The effects of several significant dimensionless parameters including the relative foundation height, the relative chamber width, the relative water depth, the wave steepness and the porosity of perforated wall are examined, using single-dimensional correlation analysis. Also, the empirical formulas for calculating the phase differences of perforated caisson on the rubble mound foundation are presented by means of the least square method, which are useful for practical engineering.
Perforated caissons have been often used in practical engineering due to their merits of smaller reflection coefficients and wave forces. Since the initial study of Jarlan (1961), the hydrodynamic performance of perforated caissons has been examined many times by different researchers. The related studies have been mainly focused on the calculation of the reflection coefficient (e.g., Fugazza and Natale, 1992; Takahashi et al., 2002; Suh et al., 2006; Yueh and Chuang, 2010) and of the horizontal wave force (Takahashi, 1996; Tabet-Aoul and Lambert, 2003). However, in practice, the perforated caissons are generally constructed on rubble foundation. So, the vertical force acting on the perforated caissons should be considered for the engineering design. Recently, both the horizontal and vertical forces acting on perforated caissons located on a rubble fill foundation have been carefully examined by Li (2007) and Liu et al. (2008). It was found by experimental and numerical results that there was an obvious phase difference between the total horizontal and vertical forces acting on the perforated caissons. When the total horizontal wave force reached a peak, the in-phase total vertical wave forces were rather small or even downwards.