## 2 Physical Experiment
### Wave Conditions  
The physical experiment was conducted for irregular waves based on the JONSWAP spectrum [16] in the wave flume. The JONSWAP spectrum is defined as:  
\[S(f)=\beta_{I}H_{1/3}^{2}T_{p}^{-4}f^{-5}exp\Big{[}-1.25\Big{(}T_{p}f\Big{)}^{-4 }\Big{]}r^{exp\left[-(T_{p}f-1)^{2}/2\sigma^{2}\right]} \tag{1}\]  
where  
\[\beta_{I}=\frac{0.0624}{0.230+0.0336\gamma-0.185(1.9+\gamma)^{-1}}[1.094-0.0191 5\ln\gamma] \tag{2}\]  
\[T_{p}\cong T_{1/3}/\left[1-0.132(\gamma+0.2)^{-0.559}\right] \tag{3}\]  
\[\sigma=\left\{ \begin{array}{c}\sigma_{a}:f\leq f_{p}\\ \sigma_{b}:f>f_{p}\end{array} \right. \tag{4}\]  
\[\gamma=1\sim 7,\ \ \ \sigma_{a}\cong 0.07,\ \ \ \sigma_{b}\cong 0.09 \tag{5}\]  
where the peak enhancement factor \(\gamma\) controls the sharpness of the spectral peak, and 3.3 is the mean value. H\({}_{1/3}\) is the significant wave height, T\({}_{1/3}\) is the significant wave period, T\({}_{\rm p}\) is the wave period corresponding to the frequency f\({}_{\rm p}\) at the spectral peak, and \(\sigma\) is the narrowness of the peak parameter. A method for separating the incident and reflected waves was used to estimate the test waves using three wave gauges (Equations (9)-(11)), as shown in Figure 2[17]. The wave generation time is set to 30 min (assuming that the typhoon duration is 3 h for a full-scale time) for each test case. The number  
Figure 4: Photographs of the model structure; (**a**) non-standing barrier in a normal state; (**b**) standing barrier in an abnormal state. Figure 5: Location of the installed wave pressure gauges; (**a**) non-standing barrier in a normal state; (**b**) standing barrier in an abnormal state. of component waves is about 630 to 830, depending on the wave period. For example, when the wave period is 2.18 s in Table 2, the number of component waves is about 826, which is 30 min divided by 2.18 s. When test waves are estimated without the model structure, the sampling frequency is 50 Hz. In the test with the model structure, the sampling frequency is set to 600 Hz to measure the wave pressure acting on the movable barrier. If the impulsive wave pressure occurs in the test, 600 Hz is too low to measure the quantitative impulsive pressures. However, the sampling frequency is 600 Hz because the purpose of this experiment is to confirm the occurrence of impulsive pressures. As presented in Section 2.1, two different designed sea levels were selected based on the data of the Korea Hydrographic and Oceanographic Administration and some other reports [18; 19; 20]. On the target site, the significant wave heights and periods for the \"10- and 50-year return period\" were 4.35 m/13.10 s and 4.58 m/17.22 s, respectively [21]. The target site, which is geographically a cap, was opened to the seaside, and the sea bottom slope was too steep, at about 1/10. Therefore, the incident wave close to the breaking limit propagated to the target site with a large amount of energy. Hence, the target wave was difficult to generate in the laboratory experiment. To solve this problem, the sea bottom of the real site was reproduced up to 12.2 m (440 m for the full-scale distance) toward the wave paddle from the model structure in the wave flume. At the model scale, the significant wave height H\({}_{\text{s}}\) and significant wave period T\({}_{\text{s}}\) were expressed as the target wave in the Table 2.  
Test waves were generated several times to find values close to the target wave. Figure 6 shows two cases of the spectrum of test waves, since the other two cases had similar results. The solid line is the analytical solution, and the histogram shows the results of the experiment applying the method for separating the incident and reflected waves [17]. The peak enhancement factor \(\gamma\) is 3.3, and T\({}_{\text{p}}\) is the wave period corresponding to the frequency f\({}_{\text{p}}\) at the spectral peak. The results of the experiment have a similar tendency with those of the analytical solution.