Ships and offshore structures operating in harsh marine environments are easily exposed to wave impact loads such as green water and slamming due to high waves, and wave-in-deck loads of offshore structures. This can cause great damage to ships and offshore structures, or even cause capsizing (Faulkner, 2001; Ersdal and Kvitrud, 2000; Faltinsen, 2005; Kaiser et al., 2009). For the structural safety design of ships and offshore structures that can overcome the impact load caused by waves, the structural design criteria must first be established with an accurate estimation on the external force along with a quantitative understanding of the flow characteristics of the wave impact load. To this end, various experimental or numerical studies are being conducted to measure the pressure applied on the occurrence of wave impact loads and to quantitatively analyze the flow characteristics that cause them. The following representative studies have been conducted, and many other studies are currently being conducted: a study on the flow characteristics of the green water phenomenon that occurs in a simplified shape, and the measurement of the impact load by measuring the pressure applied on the deck and upper structure when a green water phenomenon occurs (Buchner and