In this study, a series of numerical simulations of wave forces on a perforated comb-type breakwater at water levels below the bottom of the superstructure were conducted based on a 3D numerical wave flume. The influences of configuration parameters, such as the location of the side plate, the height of perforation below the side plate, and wave parameters, including the wave period, the wave height and water depth, on the horizontal wave force were investigated and an empirical formula for wave force coefficient was proposed. The critical conditions for the occurrence of impulsive wave forces were also discussed.
The comb-type breakwater (CTB) is a new type of coastal protection structure that has been proposed and investigated in recent years (e.g., Dong et al., 2003; Fang et al., 2011; Zang et al., 2018; Wang et al., 2019) as shown in Fig. 1(a). The CTB has evolved from the conventional caisson breakwater, with part of the main caisson being replaced by a thin side plate, and the CTB looks like a comb in plan view (see Fig. 1b). In application, the CTB is composed of a series of units (in Fig. 1a, three units are shown), and each unit consists of three portions: a main caisson, two side plates and a superstructure, as shown in Fig. 1c. Compared with the traditional caisson breakwater, its material consumption is relatively small and thus has a smaller base area, reducing the requirement of the foundation bearing capacity (Niu et al., 2001). Moreover, perforation can be designed below the side plates (see Fig. 1a), which allows passing of the current and keeping water exchange. This perforation can significantly reduce the flow velocity near the breakwater entrance, guaranteeing navigation safety, as well as keeping water clear in the harbour (Wang et al., 2019). At present, a perforated CTB has been successfully applied in the port area of Dayao Bay, Dalian, China. There are wider application prospects of this type of structure in terms of wave absorption, deep-water adaptability, water exchange and material savings.