## 4 Analysis of Sound Radiation Characteristics for Reinforced Laminated Cylindrical Shell Structures
### Effect of Reinforcement Method
#### 4.2.2 Effects of Ring Stiffening  
The radiated sound power levels of the cylindrical shell are calculated for 4 and 12 longitudinal reinforcements and rib configurations, and the results are shown in Figure 13.  
Figure 13: Structural sound power level curve with ring stiffening. (**a**) 4 circumferential ribs; (**b**) 12 circumferential ribs.  
The total radiated sound power levels of the cylindrical shell with 4 and 12 circumferential ribs and the unreinforced cylindrical shell are 90.81 dB, 80.02 dB, and 83.63 dB, respectively. From the perspective of the overall sound power level, the sound radiation performance of the cylindrical shell with 12 circumferential ribs is the best. At low frequencies, bending deformation is more likely to occur in the axial direction than in the circumferential direction, and it can be observed from the graph that the addition of circumferential ribs reduces the generation of structural sound radiation peaks. At high frequencies, it can be observed that the radiated sound power level of the cylindrical shell decreases with the increase in the number of circumferential ribs. This is because, in this case, the circumferential ribs effectively strengthen the axial strength of the cylindrical shell, thus suppressing the vibration phenomenon. Therefore, this is beneficial for improving the structural sound radiation performance.  
2.3 Effects of Different Reinforcement Forms on the Noise Radiation of Laminated Cylindrical Shell Structures  
Compare the radiated noise calculation results of the cylindrical shell with circumferential ribs and the cylindrical shell with longitudinal reinforcements with the same number of reinforcements, as shown in Figure 14.  
Figure 14: Effect of reinforcement on structural sound power level curves at different numbers of reinforcements. (**a**) Comparison of 4 reinforcements; (**b**) Comparison of 12 reinforcements.  
By comparing the radiated sound power level results of cylindrical shells with 4 and 12 reinforcements, it can be observed from the graph that, compared to the case of only circumferential rib reinforcement, the case of only longitudinal reinforcement will result in more radiated sound power peaks. The reason for the generation of more peaks can be analyzed as follows: At low frequencies, without reinforcements, the cylindrical shell is more prone to deform circumferentially, leading to more intense shell vibrations and resulting in more peaks in the radiated sound power. However, circumferential rib reinforcement enhances the axial strength of the cylindrical shell, preventing bending deformation and effectively suppressing shell vibrations, and resulting in fewer sound radiation peaks and a smoother sound radiation power level curve at this frequency range. On the other hand, at high frequencies, the cylindrical shell tends to undergo axial deformation, and longitudinal reinforcement exerts greater constraint on the circumferential direction. Therefore, compared to circumferential rib reinforcement, longitudinal reinforcement intensifies the cylindrical shell's vibration, leading to increased radiated noise. From the perspective of the overall sound power level, the cylindrical shell with 12 longitudinal reinforcements exhibits a sound power level of 96.21 dB, while the one with circumferential rib reinforcements shows a level of 80.02 dB. The difference between the two is 16.19 dB. Thus, circumferential rib reinforcement proves to be more effective in reducing the structural noise radiation capability. Therefore, subsequent reinforcement configurations will adopt circumferential rib reinforcements for further research and exploration.