## 2 Materials and Methods
### Experimental Description  
Laboratory experiments were conducted in a two-dimensional wave tank (length: 30 m, width: 0.7 m, depth: 0.9 m). A piston-type wave generator system was installed at one end of the water tank. As the hydraulic experiment using a wave generation system can generate the desired waves to simulate the ocean conditions, it can provide a lot of information about the designed WEC before the prototype experiments [41; 42]. Figure 1 illustrates a schematic diagram of the laboratory experiment. A reflection wall assuming a breakwater was set up 20 m away from the wave generator. Electric capacitive type water level gauges W1-W7 (KENEK, CHT 6-43-SQ) were installed at five positions between the wave generator and the flap and at two positions between the flap and the reflected wall to measure the water level variations. The experimental conditions are presented in Table 1. A total of 328 cases of experiments were performed with 7 different incident wave heights \(H_{in}\) (0.02 m interval), 5 wave periods \(T\) (0.4 s interval), 5 initial water depths \(h\) (= 0.0475 m, \(\pm\) 0.035 m, \(\pm\) 0.05 m), and 2 different distances \(D\) (= 1.09 m, 1.45 m) from the reflection wall. Some cases (22 cases) showing unstable wave generating were excluded in this study owing to the limitations of wave generators. The installed position of the flap \(D\) was changed to examine the effects of the distance from the reflected wall on the characteristics of the flap behavior and power generation performance. In particular, this study focused on the effects of the node and anti-node positions at which maximum and minimum wave energy capturing performances were expected. Therefore, unidirectional regular waves were generated to form idealized standing waves in front of a reflected wall. \(D\) was set for including the node (\(D/L\) = 0.25) and anti-node (\(D/L\) = 0.5) positions of standing waves. \(D/L\) indicates the distance from the reflection wall \(D\) and the wavelength \(L\) ratio. For \(D\) = 1.09 m, \(D/L\) ranged from 0.1667 to 0.4463, and for \(D\) = 1.45 m, \(D/L\) ranged from 0.2217 to 0.5937. It is noted that \(D/L\) was confined in this study by varying wave periods  
Figure 1: Schematic sketch of the experimental setup: (**a**) side view, (**b**) plan view. W1–W7 denote the water level gauges; \(h\) is the water depth; \(D\) indicates the distance between the flap and reflection wall; \(d\) is the submergence depth of the flap; and \(B\) and \(b\) are the width and length of the upper part of an inverted triangular prism, respectively. under the condition of the fixed flap position. Different water depths and wave heights were adopted to investigate the influences of still water depth and wave steepness on flap behaviors. As depicted in Figure 2, the flap was designed in the shape of an inverted triangular prism with a height of 0.40 m (height of the triangle), length of 0.68 m (distance between the triangular faces), and width of 0.15 m (length of one side of the triangle). The flap was composed of 1 cm thick acrylic plates in the body, 0.04 m thick triangular acrylic blocks at both ends, and two stainless steel bearings at the bottom that acted as hinges. Channels made of steel (length: 0.50 m, width: 0.125 m) were installed at the bottom to connect to the flap, and the position of the channel was fixed with a weight. The hinge of the flap and the channel were coupled using a hinge pin so that the pendulum could rotate around the hinge. As the flap was a floating body in the shape of an inverted triangular prism with an empty interior, it had the characteristic of restoring itself to its original position even when inclined by waves. A rack gear was attached to the upper part of the flap to operate a gear system connected to the rotary generators with the reciprocating motion of the flap.