## 4 Experimental Results and Analysis
### Orthogonal Test Analysis  
In order to discuss in more depth the primary and secondary relationships between the influence of the factors on the infrared characteristics of the underwater vehicle's wake, the interaction between the factors was analyzed using orthogonal tests based on their single-factor analysis, the discussion of the influence, and the correlation relationships between the factors, as shown in Table 3.  
The orthogonal table is denoted by L for the code of the orthogonal table, \(n\) is the number of trials, t is the number of levels, and c is the number of columns, i.e., the maximum number of factors that can possibly be arranged. For example, L8 (25) means that eight trials were required and up to five factors could be arranged, with each factor taking two levels, as shown in Table 4.  
In the experiment, the interaction between the factors should be fully considered. In order to reflect the relationship between the factors scientifically, the interaction analysis of the orthogonal test between the two factors shown above was carried out according to the requirements of the experiment. Six tests needed to be conducted. Three factors could be arranged at most, and three levels were taken for each factor. The table header design scheme of the experiment was obtained from the orthogonal table L6 (33) as Table 5.  
In accordance with the designed scheme to carry out experiments, we obtained the factors. Each factor in different combinations of levels of surge conditions, wake water surface thermal characteristics data, and orthogonal results are shown in the Table 6.  
The orthogonal test of the thermal characteristics of the water surface of the tail race was set up with two factors, depth (A) and surge height (B), with three levels taken for \begin{table}
\begin{tabular}{c c c c c} \hline \hline
3 & 1 & 2 & 2 & 1 & 2 \\ \hline
4 & 1 & 2 & 2 & 2 & 1 \\ \hline
5 & 2 & 1 & 2 & 1 & 2 \\ \hline
6 & 2 & 1 & 2 & 2 & 1 \\ \hline
7 & 2 & 2 & 1 & 1 & 1 \\ \hline
8 & 2 & 2 & 1 & 2 & 2 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Data on the thermal characteristics of the wake surface for each factor and each factor at different combinations of levels of surge conditions. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Level** & **Depth (A)** & **Surge Height (B)** \\ \hline
1 & 30 cm & 0 cm \\ \hline
2 & 40 cm & 0.3 cm \\ \hline
3 & 50 cm & 0.5 cm \\ \hline \hline \end{tabular}
\end{table} 
Table 4: The factor-level orthogonal testing design of thermal characteristics of surface under swell conditions. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Test Serial Number** & \multicolumn{4}{c}{**Column Number**} \\ \cline{2-5}  & **1** & **2** & **3** & **4** & **5** \\ \hline
1 & 1 & 1 & 1 & 1 & 1 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The form of orthogonal table. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Column Number** & 1 & 2 & 3 \\ \hline
**Factors** & A & B & AB \\ \hline \hline \end{tabular}
\end{table} 
Table 5: The orthogonal testing header design of thermal characteristics of surface under swell conditions. each factor. The three levels of factor A were A\({}_{1}\) = 30 cm, A\({}_{2}\) = 40 cm, and A\({}_{3}\) = 50 cm, respectively. The three levels of factor B were B\({}_{1}\) = 0 cm, B\({}_{2}\) = 0.3 cm, and B\({}_{3}\) = 0.5 cm, respectively. Thee orthogonal test design scheme is shown in the Table 7.  
According to the orthogonal table, the influence of this component on the wake temperature difference increased as the polar difference increased. By the magnitude of the polar difference R in Table 4, the following two variables and their interaction had an effect on the main and secondary relationships: A > B > AB; therefore, it was evident that the influence of the dive depth on the wake buoyancy diffusion to the water surface thermal characteristics was higher than the impact of the underwater surge on it.