# Pressure Fluctuation and Flow-Induced Noise of the Fin and Rudder in a Water Tunnel
## 2 Experimental and Numerical Models of the Fin and Rudder
### Hydrodynamic Experiment  
An experiment was carried out in a water tunnel. Figure 2 shows the installation of the fin and rudder in a water tunnel during the experiment. Taking into account the intricacies of fluid-structure interaction and flow-induced noise, measurements were taken during the initial stages of experimental design to mitigate the impacts of the structure. This involved developing a structurally robust design to ensure high strength and stability. In this experiment, the model was constructed with a skin thickness of over 10 mm, and the internal structures were reinforced with ribs to enhance strength.  
The measurement of hydrodynamic performance and pressure fluctuation can be carried out in a water tunnel for various types of ships and underwater vehicles. The water tunnel used had a total length of 55.00 m and a height of 16.40 m. Figure 3 shows a schematic diagram of the water tunnel. The main parameters of the test section for the current experiment are presented in Table 2.  
The instruments used in this experiment and their parameters are listed in Table 3. The instruments used in this experiment were calibrated, ensuring their accuracy and reliability.  
A PCB HTM pressure sensor (FLSmidh A/S, Mariager, Denmark) was utilized in this experiment to measure the pressure fluctuation on the surface. The measurement locations on the surface were drilled for sensor installation. The sensor was fixed in place using adhesive, ensuring that the sensor head was flush with the outer surface of the model. The pressure fluctuation signal measured by the pressure sensor in the test was amplified by the filter amplifier. The data were collected synchronously using a real-time signal analysis system. A diagram of the data acquisition system used in the pressure fluctuation test is shown in Figure 4.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Number** & **Parameter** & **Dimension (m)** \\ \hline
1 & The maximum width of the fin and rudder & 0.2070 \\
2 & The height of the fin and rudder & 1.2250 \\
3 & The maximum length of the fin and rudder & 1.2256 \\
4 & The height of the rudder & 0.8000 \\
5 & The maximum length of the rudder. & 0.5502 \\ \hline \hline \end{tabular}
\end{table}
Table 1: The fundamental geometric measurements of the fin and rudder.  
Figure 1: The side view of the fin and rudder.  
Figure 3: The schematic diagram of the water tunnel.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Number** & **Parameter** & **Dimension (m)** \\ \hline
1 & Length & 10.50 m \\
2 & Width & 2.20 m \\
3 & Height & 2.00 m \\
4 & Velocity of flow & 1.0–15.0 m/s \\
5 & Turbulence intensity & \textless{}1.0\% \\ \hline \hline \end{tabular}
\end{table}
Table 2: The main dimensions of the test section in the water tunnel.  
Figure 2: The fin and rudder installed in the water tunnel: (**a**) side view of the fin; (**b**) side view of the rudder.  
The positions where the pressure sensors were installed on the fin and rudder are shown in Figure 5, with a total of 15 sensors deployed. Some points are not shown in Figure 5, but their locations can be derived from Table 4.