## 3 Numerical Results and Discussion
### Wave Energy Converter Integrated with Breakwater  
The dynamic response of the WEC in front of the wall-type breakwater was analyzed using the FR-NWT, to which the ADZ and SRC were applied together. Figure 14 shows an overview of the computational fluid domain, and Equations (8) and (12) were used for the radiation and diffraction boundary conditions of the breakwater, respectively. A single WEC integrated with a seawall-type breakwater of infinite length was considered. In addition, no artificial damping zone was installed on the free surface near the breakwater to examine the effect of wave reflection. To verify this numerical model, the heave-motion RAO of a cylindrical floating WEC in the presence of a breakwater was estimated and compared with the results reported elsewhere [33] (Figure 15). The WEC had a diameter of (\(D\)) = 2.0 m and draft of (\(d\)) = 1.0 m. The distance between the breakwater and WEC was set to five times the floater's diameter (\(D\)). The calculation results were agreed upon well in both cases with or without a breakwater. The interaction between the WEC and the breakwater amplified the heave RAOs at the frequency region lower than the natural frequency, although the amplitude of the RAOs was reduced at \(w\) =2.05-2.2 rad/s. Therefore, the distance between a floater and breakwater should be carefully selected to enhance the power take-off performance. The hydrodynamic performance of a hemispherical heaving-buoy-type WEC integrated with a breakwater was investigated. Table 3 lists the calculation conditions of the WEC system. The distance between the body and the wall (\(\alpha\)) was established by fixing the diffraction parameter (\(D\)/1) and comparing the heave RAOs according to \(a\)/1 (Figure 16). Figure 14: Overview of the computation domain with a WEC and breakwater (yellow: seawall-type breakwater, blue: ADZ). Figure 16: Heave RAOs under various distance conditions between the wall and floater. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Characteristics** & **Value** & **Unit** \\ \hline \multirow{3}{*}{Body (Hernisphere)} & Diameter (D) & 2.0 & m \\  & Draft (d) & 1.0 & m \\  & Mass (m) & 2084 & kg \\ \hline \multirow{3}{*}{Wave condition} & Incident wave & 1.2–4.0 & \multirow{3}{*}{rad/s} \\  & frequency (\(w\)) & (D\(w\) = 0.05 ) & \\  & Wave height (H) & 1.0 & m \\ \hline \multirow{3}{*}{Wall} & Nondimensional distance between wall and body (\(\alpha\)/1) & \multirow{3}{*}{0.2–0.5} & \multirow{3}{*}{-} \\ \cline{1-1} \cline{3-3} \cline{5-5}  & & & \\ \cline{1-1} \cline{3-3} \cline{5-5}  & & & \\ \cline{1-1} \cline{3-3} \cline{5-5}  & & & \\ \cline{1-1} \cline{3-3} \cline{5-5}  & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Analysis conditions of a WEC integrated with a breakwater. Figure 15: Comparison of the heave RAO of a cylindrical WEC with and without a breakwater. As _D/1_ was smaller than 0.2, that is, the body is slender, _a/1_ with the minimum heave RAO of the WEC was 0.25, and _a/1_ with the maximum heave RAO was 0.5. It seems that standing waves are caused by waves reflected from the breakwater. Therefore, the motion amplification is greater when the WEC lies at half the incident wavelength. On the other hand, as _D/1_ increases, _a/1_ with the maximum heave RAO of WEC decreases. Therefore, a must be determined according to the wavelength. If \(\alpha\) becomes too large or small, it is too difficult to integrate with the breakwater; hence, only two cases were analyzed (case 1-2). Thus, \(a\) was fixed to 2.41 m in case 1 and 3.85 m in case 2. Assuming that a hemispherical WEC has a radius of 1 m, the heave RAO of the WEC (see Figure 17) was obtained. Motion amplification occurred up to 1.87 times in the low-frequency region in case 1 (see Table 4). In addition, the maximum motion amplification occurred approximately 2.24 times near the resonance frequency region in the presence of a breakwater compared to the case of a WEC with no breakwater. This is caused by the interaction between the wall and the WEC.