## 3 Configurations of OC3 CM Model
### OC3 CM Models  
The innovation of this paper is attaching clump masses on the mooring lines to reduce the response of the platform. After numerous experiments and analysis of the OC3 CM models with clump masses of different weights and different locations, the influences of these differences on the platform response were found. The weight of the clump mass was set to be 7061.74 kg (one-tenth as heavy as the mooring line), 10,087.14 kg (one-seventh as heavy as the mooring line), 14,123.48 kg (one-fifth as heavy as the mooring line). It was found that the response of the platform is highly sensitive to the location of the clump masses, and the increase in the weight of clump masses can only reduce the motion of the platform in a very limited range. Based on the above trials, the weight of the clump masses is set to 7061.74 kg. Except for the additional clump masses, the other part of the structure remains the same as in the original OC3 model. In the present research, five different locations are examined. The properties of the mooring system are shown in Table 3, where P0 is the original model; \(L_{M}\) is the distance from connecting locations to the anchor, that is also called fixed node. In addition, \(L\) is the length of mooring line, equaling 902.2 m; \(m_{CM}\) is the weight of the clump masses, which is one-tenth the mass of the mooring line, equaling 70,109.96 kg.  
\begin{table}
\begin{tabular}{l l} \hline \hline
**Item** & **Value** \\ \hline Rating & 5 MW \\ Rotor type & Upwind, 3 blades \\ Total draft below sea water level (SWL) & 120 m \\ Tower base above SWL & 10 m \\ Hub height above SWL & 90 m \\ Nacelle dimension (length, width, height) & 14.2 m, 2.3 m, 3.5 m \\ Platform diameter above taper & 6.5 m \\ Platform diameter below taper & 9.4 m \\ Rotor nacelle assembly (RNA) mass & 350,000 kg \\ Tower mass & 249,718 kg \\ Platform mass & 7,466,330 kg \\ Hub mass & 56,780 kg \\ Number of mooring lines & 3 \\ Depth to fairleads below SWL & 70 \\ Global coordinates of the anchor point \(1\) & (853.87 m, 0, \(-\)320 m) \\ Global coordinates of the fairlead point \(1\) & (5.2 m, 0, \(-\)70 m) \\ Mooring line diameter & 0.09 m \\ Mooring line mass density & 77.71 kg m\({}^{-1}\) \\ \hline \hline \end{tabular}
\end{table}
Table 2: Main properties of the OC3-Hywind model.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Model** & \(L_{M}\) & \(m_{CM}\) \\ \hline P0 & 0 & 0 \\ P1 & 0.7L & 7061.74 kg \\ P2 & 0.6L & 7061.74 kg \\ P3 & 0.5L & 7061.74 kg \\ P4 & 0.4L & 7061.74 kg \\ P5 & 0.3L & 7061.74 kg \\ \hline \hline \end{tabular}
\end{table}
Table 3: Mooring system model properties.  
The angle between the neighboring mooring lines is 120\({}^{\circ}\). The shapes of the mooring lines of the original OC3 model and five OC3 CM models are shown in Figure 3. From Figure 3, the changes of the shape of the mooring lines can be clearly identified. Compared with Figure 3a, the segment of the mooring line from the connection node to the vessel node is obviously straightened by the clump masses, which will increase the tension of the mooring line and should limit the motion of the platform in return. This inference will be examined in detail in later sections.