## 3 Ship Towing Resistance Test
### Drag Measurement Test Plan  
A ship towing navigation test was conducted in a 1:40 scale model of a navigation tunnel with a width of 30 m, a length of 960 m, and a designed lowest navigation level of 5.0 m. The model tunnel has a length of 24 m and a width of 0.75 m, The bottom of the navigation tunnel is smoothed with ordinary mortar concrete, and the roughness value of the concrete is 0.013-0.017, which is converted into a prototype roughness value of 0.024-0.0314, basically meeting the actual engineering requirements. The side walls of the tunnel are made of organic tempered glass. The use of glass is to facilitate the adjustment of the cross-sectional width of different tunnels, and to clearly observe the posture and photography of the ship's towing and navigation during the testing process. The outer side of the glass is fixed with triangular braces to prevent displacement caused by water flow erosion and compression, as shown in Figure 3.  
The main equipment for the ship resistance measurement test includes: a 10,000-t experimental ship made at a scale ratio of 1:40, an electric-powered trolley, a current meter, and a tensile sensor. The parameters of the experimental ship are shown in Table 1, and the ship model is shown in Figure 4. An experimental track is arranged in the center above the navigation tunnel. The bow cable and stern cable are connected to the active traction trolley and passive traction trolley, respectively, through fixed pulleys and then connected to the tensile sensor, as shown in Figures 5 and 6. Figure 3: (**a**) Physical model of navigation tunnel; (**b**) Planar overall schematic diagram of the experimental model. Among them, the traction car adopts a wireless control module, which, in conjunction with the traction car control software, controls the speed and acceleration of the traction car. The software can realize the control of the main motor of the traction car and the servo motor of the traction rope. The calibration method of the tension sensor is to first suspend the tension sensor and measure an initial value, then hang a 1 kg standard hook code under the tension sensor, gradually add the 1 kg hook code, record data, and finally add 5 kg. Then, the measured data is fitted with the weight of the actual hook code to obtain a linear function of the actual hook code and the starting value, and input into the linear function into the tension sensor measurement software for zero-point calibration (Figure 7). The flow velocity system mainly consists of three parts: a wireless signal receiver, infrared wireless propeller flow velocity sensor, and flow velocity data processing software. These components work together to achieve the measurement and analysis of flow velocity. The ship model production is first scaled down proportionally according to the 1:40 scale of the prototype line diagram, and then 3D modeling is carried out using modeling software. The completed 3D model is processed and printed using 3D printing technology, and \begin{table}
\begin{tabular}{c c c} \hline \hline
**Ship Parameters** & **Actual Ship** & **Model Ship** \\ \hline length (m) & 115.7 & 2.8925 \\ breadth (m) & 21.6 & 0.54 \\ waterline length (m) & 113 & 2.825 \\ design draft (m) & 3.7 & 0.0925 \\ design displacement (t) & 7739.5 & 0.1209 \\ midship section coefficient & 0.985 \\ block coefficient & 0.837 \\ Scale ratio & 40 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Test ship parameters. Figure 4: Ship physical model. Figure 5: Schematic diagram of measuring equipment layout. Figure 6: Method for measuring ship resistance. the printing accuracy of the bulk cargo ship model is controlled within \(\pm 1\) mm, fully complying with relevant regulations and standards. The ship model is designed with full load balancing, and standard weights are placed at the bow, stern, and in the ship to ensure that the draft depth meets the standards. Our experimental environment is an ideal environment, which basically eliminates the influence of additional factors on the experimental results.