# Impact Force Mechanism of a Trimaran Model and Its Experimental Validation
## 5 Water-Slamming Experiment and Force Analysis
### Slamming Experiment When the Trimaran Entered the Water
#### 5.2.1 Experiment without Flexible Cladding  
For this group, the results of all the processed curves for a certain drop height are listed here as an example, and the subsequent data are only listed in Table 2. The processed data curves under the H16 working conditions are shown in Figure 10. Figure 11 gives the raw data. Figure 9: Flexible cladding. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Working** & & & & & & & & & \\
**Condition** & & & & & & & & & \\ \hline  & **Pressure/Pa** & **Speed** & **Slamming-** & & & & & & & \\
**Pressure/Pa** & **Speed** & **Pressure/Pa** & **Speed** & **m/s** & **Pressure** & **Pressure/Pa** & **Speed** & **Slamming-** \\  & **Pressure** & **Coefficient** & & & & & & & \\
**Coefficient** & & & & & & & & & \\ \hline P01 & 27,480.2 & 1.534 & 23.36 & 29,835.9 & 1.466 & 27.77 & 30,384.1 & 1.562 & 24.91 \\ \hline P02 & 36,281.8 & 1.534 & 30.84 & 45,019.8 & 1.541 & 37.92 & 41,038.5 & 1.596 & 32.22 \\ \hline P03 & 28,308.6 & 1.534 & 24.06 & 34,970.3 & 1.483 & 31.80 & 31,898.7 & 1.623 & 24.22 \\ \hline P04 & 18,139.5 & 1.534 & 15.42 & 19,830.9 & 1.546 & 16.59 & 19,869.8 & 1.596 & 15.60 \\ \hline P05 & 11,799.7 & 1.283 & 14.34 & 13,128.7 & 1.373 & 13.93 & 14,460.7 & 1.402 & 14.71 \\ \hline P06 & 10,164.7 & 1.283 & 12.35 & 14,691.0 & 1.373 & 15.59 & 13,099.9 & 1.402 & 13.33 \\ \hline P07 & 14,135.8 & 1.444 & 13.56 & 15,306.5 & 1.477 & 14.03 & 15,032.3 & 1.509 & 13.20 \\ \hline P08 & 29,783.5 & 1.466 & 27.72 & 31,638.4 & 1.515 & 27.57 & 34,132.7 & 1.592 & 26.93 \\ \hline P10 & 31,434.6 & 1.466 & 29.25 & 28,924.7 & 1.521 & 25.01 & 36,065.3 & 1.592 & 28.46 \\ \hline  & **H14** & & & & & & & **H16** & \\ \hline P01 & 30,384.1 & 1.562 & 24.91 & 31,540.7 & 1.761 & 20.34 & 57,849.5 & 1.772 & 36.85 \\ \hline P02 & 41,038.5 & 1.596 & 32.22 & 50,928.1 & 1.817 & 30.85 & 53,697.0 & 1.870 & 30.71 \\ \hline P03 & 31,898.7 & 1.623 & 24.22 & 51,839.3 & 1.786 & 32.50 & 48,982.7 & 1.828 & 29.32 \\ \hline P04 & 19,869.8 & 1.596 & 15.60 & 23,013.6 & 1.828 & 13.77 & 21,497.6 & 1.870 & 12.30 \\ \hline P05 & 14,460.7 & 1.402 & 14.71 & 18,892.2 & 1.539 & 15.95 & 15,017.5 & 1.522 & 12.97 \\ \hline P06 & 13,099.9 & 1.402 & 13.33 & 19,620.1 & 1.547 & 16.40 & 12,238.8 & 1.477 & 11.22 \\ \hline P07 & 15,032.3 & 1.509 & 13.20 & 16,545.6 & 1.670 & 11.87 & 19,016.0 & 1.659 & 13.82 \\ \hline P08 & 34,132.7 & 1.592 & 26.93 & 39,170.9 & 1.790 & 24.45 & 40,130.2 & 1.865 & 23.08 \\ \hline P10 & 36,065.3 & 1.592 & 28.46 & 39,475.1 & 1.787 & 24.72 & 42,549.5 & 1.844 & 25.03 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Experiment without flexible cladding. Figure 10: Speed and pressure versus time. (**a**) Speed versus time, (**b**) pressure versus time. The test data and the calculated slamming-pressure coefficients for each working condition are listed in Table 2.  
The slamming-pressure coefficient is calculated by  
\[k=\frac{p_{\text{peak}}}{0.5\rho V^{2}} \tag{8}\]  
where \(p_{\text{peak}}\) is the peak slamming pressure, \(\rho\) is the fluid density, and \(V\) is the velocity of the model when the peak slamming pressure is achieved. As observed in Figure 10, the trimaran model slowed down during this period, especially after the slamming pressure reached the peak. The slamming-pressure coefficient from the falling experiment without flexible cladding at six different heights (H11-H16)is shown in Figure 12.  
Figure 11: Raw data. Figure 12: Slamming-pressure coefficient in the case without flexible cladding. In Figure 7, P2, P9 and P3, P8 are two pairs of measuring points that are symmetrical, and the slamming pressures measured at these points are high. In contrast, while P4, P7 and P5, P6 are also symmetrical, the corresponding slamming pressures are low. For H11-H16, the obtained slamming-pressure coefficients have a similar varying trend. As the drop height increased, the water-entry speed increased, while the slamming pressure dropped slightly.