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Vibroacoustic behavior and application of single- and double-leaf partitions

The theoretical analyses of the vibroacoustic behavior of an infinite double-leaf partition consisting of vacuum-partition-gas-partition'-water are conducted. For comparison, those of an infinite single-leaf partition consisting of vacuum-partition-water are also accomplished. Both the vibration of partitions and the acoustic transmission in gas and water are taken into consideration. The two systems are both stimulated by a single-frequency force, of which the amplitude is of sinusoidal distribution along the partition. Thus the vibroacoustic behaviors of the two systems are studied in a single-frequency and single-wavelength method, which illustrated clearly the vibroacoustic behavior of the two systems. Also, the wavelength of the structural bending wave is determined. The wavelengths of structural bending waves and acoustic waves are compared, and the resulting evanescent and transmitting waves are discussed in detail. The formulas deduced are programmed using Matlab, and the frequency response curves obtained show that gases with larger sound velocities and proper thickness can reduce more of the noise of the double-leaf partition transmitted into the water. Conclusions are applied to the noise and vibration control of the underwater cylindrical shell. A gas-bag is coated onto the surface of the cylindrical shell, thus a gas-bag coated cylindrical shell is obtained. In the double-leaf partition system, the vacuum, partition, gas, partition', and water are equivalent to the interior; and the steel plate/inner coating, the gas, and the outer coating, are equivalent to the exterior water. The added mass and damping coefficients algorithm is adopted to calculate the underwater vibration and acoustic radiation of the bare and gas-bag coated cylindrical shells. Helium gas is selected to fill the gas-bag because of its largest sound velocity among all gases. Results show that the mean square velocity level and radiated power level of the helium-bag coated cylindrical shell are much lower than those of the bare shell.