## 2 Materials and Methods
### Physical Model Experiment  
Load results of numerical simulation model are verified by physical model experiment. Physical model experiments can analyze the hydrodynamic field and the mechanical characteristics under variable TCC arrangement patterns by measuring the water velocities and loads [28]. The physical model experiment was performed at the Hydraulic Engineering Laboratory at Tianjin University, and the experimental model is shown in Figure 5. The experimental model is designed according to gravity similarity theory and with a geometric scale of 1/25 (Table 1).  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Similarity Criterion** & **Physical Quantity** & **Scale Relation** & **Scale** \\ \hline \multirow{4}{*}{Gravity similarity theory} & Length & \(\lambda_{L}\) & 25 \\  & Velocity & \(\lambda_{t}\) = \(\lambda_{L}\)0.5 & 5 \\  & Force & \(\lambda_{F}\) = \(\lambda_{L}\)3 & 15,625 \\  & Time & \(\lambda_{t}\) = \(\lambda_{L}\)0.5 & 5 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Experimental hydraulic parameters and geometric scale.  
Figure 5: Schematic of physical model experiment and force measurement (**a**) test site; (**b**) TCC; (**c**) schematic of force measurement (measured parameters: flow velocity (v), pulling force (T), gravity of the rubber block (G), bottom friction coefficient (\(\mu\)), angle between pulling force and flow direction (\(\theta\) ), and water depth (H)).  
The experimental instruments mainly include acoustic-doppler velocimeter (ADV), force sensors, a dynamic strain gauge, a flowmeter, and a digital alias-free signal processing (DASP) digital acquisition instrument (Figure 6). The experimental materials mainly include impermeable nylon cloth, nylon ropes, sensor support frames, a protractor and rubber blocks. The physical quantities measured by the physical model experiments include the flow velocity, pulling force, angle between pulling force and flow direction, gravity of the rubber block, bottom friction coefficient and water depth.  
The TCC is connected to the force sensor through a nylon rope to measure the top tension. Three force measuring points are arranged above the curtain, connected to the left, middle and right parts of the curtain. Rubber blocks are located at the bottom of the structure to maintain stability of the TCC system. The bottom friction coefficient is 0.45, as determined through experimentation with rubber blocks and different weights. The load of the water flow on the TCC can be obtained by measuring the tension at the top, the angle between the nylon rope and the water flow direction, and the bottom friction force.  
The load of the TCC at different flow velocities was measured under two working conditions in the physical model experiments. In the first working condition, the height of the water level, the flow depth above the curtain and the water blocking rate are 1.44 m, 0.16 m, and 0.828, respectively. In the second working condition, the height of the water level, the flow depth above the curtain and the water blocking rate are 1.3 m, 0.25 m, and 0.716, respectively. The scenarios and results of the physical model experiments are shown in Table 2.  
Figure 6: Experimental measuring instruments: (**a**) force sensor; (**b**) dynamic strain gauge; (**c**) ADV; and (**d**) DASP.