To enhance the floating raft vibration isolation system’s effect, a new two-stiffness floating raft vibration isolation experimental was constructed. First, the system’s mathematical model was established. The vibration transfer function was deduced via substructure derivative synthesis and four-end parameter matrix methods, and the structural parameter impacts on it were analyzed. Then, a modal test was conducted, and a finite element model was built. Comparing finite element analysis with test results verified the model’s validity, followed by a study of the support structure’s vibration characteristics. Finally, by measuring acceleration responses at the isolator’s upper and lower ends and using the difference as an evaluation index, the isolator’s vibration isolation effect on land and underwater was investigated, along with its impact on the device’s underwater acoustic radiation. The results demonstrate that the two-stiffness vibration isolator can reduce vibration transmission within a specific frequency range both on land and underwater, guiding practical engineering vibration isolation research.

The split-sleeve cold expansion technology is widely used in the aerospace industry, particularly for fastening holes, to enhance the fatigue life of components. However, to ensure proper assembly and improve surface integrity, reaming of the cold-expanded holes is necessary. This study investigates the effects of cold expansion and reaming processes on the fatigue performance of 7050-T7451 aluminum alloy. Fatigue tests, residual stress measurements, and microstructural analyses of the hole edges were conducted on specimens with four different hole diameters after cold expansion and reaming. It was found that the depth of reaming significantly affects fatigue life. During the cold expansion process, the compressive residual stress formed around the hole effectively improves fatigue performance. The experiments demonstrated that reaming by 0.2 mm to 0.4 mm helps eliminate minor defects, thereby improving fatigue life. However, reaming beyond 0.5 mm may lead to stress relief and the removal of dense grains at the hole edges, reducing fatigue life. Therefore, determining the optimal reaming size is crucial for enhancing the reliability of aerospace fasteners.

Optimizing isolator stiffness is essential for controlling vibration transmission in cylindrical shell structures operating in cross-environment conditions. This study investigates the influence of isolator stiffness on vibration transmission and fluid-coupled response through coordinated land-based experiments, water-immersed experiments, and ABAQUS simulations. Two damped spring isolators with stiffness values of 290 N/mm and 970 N/mm were tested under representative excitations of 25 Hz and 40 Hz. The results show that the lower-stiffness isolator provides consistently stronger vibration attenuation and produces higher vibration level differences than the higher-stiffness isolator. The measured vibration level differences between land-based and water-immersed conditions remain generally within 3 dB, indicating good cross-environment consistency. The numerical results agree well with the experimental trends, with deviations generally below 5 dB in the main low-frequency range. Mechanism analysis indicates that reducing isolator stiffness weakens the transmission of excitation energy from the raft frame to the base and shell, thereby reducing near-field fluid-coupled response around the excitation region. These findings support the use of lower-stiffness isolators and provide a practical framework for vibration assessment and parameter selection in cylindrical shell structures working under coupled air–water conditions.

Shipboard equipment vibration is the main source of underwater radiated noise for marine vessels, and floating raft isolation (FRI) systems are widely used for vibration and noise reduction. Current land-based air tests cannot directly reflect the actual isolation performance of FRI systems in underwater service conditions. To address this gap, this paper conducts a systematic experimental study on the vibro-acoustic characteristics of a typical ship cylindrical cabin with an FRI system, in both air and underwater environments. The vibration transfer laws and underwater radiated noise characteristics of the structure are obtained, and the isolation performance of the FRI system is quantitatively evaluated. The research results can provide a direct experimental basis and reference for the design, test, and optimization of marine vibration isolation systems. Compared with previous studies that mainly considered bare or simply stiffened shells, or evaluated floating raft isolation through numerical or air-based tests, this work tests an integrated vibration source to raft with isolator to stiffened-shell to water configuration and provides source-path-receiver benchmark data for assessing the environmental robustness of FRI systems.

In order to improve the vibration isolation effect of the floating raft vibration isolation system, a new experimental platform for floating raft vibration isolation with two stiffnesses was built. First, the mathematical model of the vibration isolation system was established. The vibration transfer function of the vibration isolation system was deduced by using the substructure derivative synthesis method and the four-end parameter matrix method. The transfer function under the structural parameters was calculated, and the influence of structural parameters on the vibration transfer function was analyzed. Then the floating raft modal test was carried out and the three-dimensional finite element model of the floating raft vibration isolation structure was established. The finite element analysis results were compared with the test results to verify the validity of the finite element model, and then the vibration characteristics of the support structure were studied. Finally, by measuring the acceleration responses at the upper and lower ends of the isolator, the difference is taken as the evaluation index of the vibration isolation effect to investigate the isolation effect of the isolator under the conditions of on-land and underwater usage, and to preliminarily explore its influence on the underwater acoustic radiation of the device. The results demonstrate that the vibration isolator with two stiffnesses can reduce the vibration transmission within a specific frequency range in both on-land and underwater application scenarios, which holds guiding significance for the research of vibration isolation technology in practical engineering.