Active Control of the Accordion Modes of a Submerged Hull

Abstract

This work investigates active vibration control of tonal hull axial resonances to attenuate the structural and acoustic responses of a submarine. A submerged hull can be idealised as a ring-stiffened finite cylinder with external fluid loading. At low frequencies, rotation of the propeller results in discrete tones at the blade passing frequency and its harmonics. The fluctuating forces at the propeller are transmitted through the propulsion system, resulting in excitation of the low frequency hull vibrational modes, which in turn results in a high level of structure-borne radiated noise. Global hull modes are difficult to attenuate since passive control techniques such as damping materials and isolators are not practical due to size and weight constraints. This work numerically investigates the application of active vibration control based on a feedforward algorithm to suppress the axial and radial hull displacements. The effect of various cost functions and control arrangements on the structure-borne radiated noise is presented.

Low-frequency sound transmission through rough bubbly air–water interface at the sea surface

“…The average received acoustic pressure can be calculated for a statistically rough surface by taking the ensemble average and by assuming that the height distribution of the surface is Gaussian. Therefore, equation (17), which is called the coherent component of the transmitted pressure, can be obtained as follows 36…”

“…Therefore, the total relative intensity is obtained by adding the square of equations (17) to (21) and dividing by p 2 2m as in where the first and second terms in equation (22) are called coherent and incoherent terms of transmission, respectively. The TC for a localized point source in the air, which emits sound towards a smooth surface, can be obtained by utilizing the coherent term of the equation 22as 36 TC…”

“…Although these theories suggest a new approach towards sound transmission through the air-water interface, for practical applications in the ocean, it is imperative to consider a more realistic air-water interface for obtaining accurate solutions. There are other theoretical [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] and experimental 15,19,24,26,28,[29][30][31][32][33][34] approaches for sound transmission or/and scattering which consider the water-air interface which focus on the acoustic field in water due to the existence of powerful airborne noise sources such as helicopters, [31][32][33] propeller-driven aircraft [26][27][28]34 and supersonic transport. 24,25,27,28,35 Medwin and Hagy, 36 by solving Helmholtz integral and deriving the transmitted pressure to the second medium, studied sound transmission through air-water rough interface.…”

Theoretical and Experimental Study of Active Vibration Control of a Cylindrical Shell Using Piezoelectric Disks

“…Li et al [21] used piezoelectric materials for active vibration control of conical shells. Gangemi et al [22] controlled the accordion modes of a ring-stiffened cylinder with external fluid loading. They considered only the structural and acoustic responses of the submerged hull under tonal frequency excitation of the propeller.…”

Low Frequency Sound Scattering from Rough Bubbly Ocean Surface: Small Perturbation Theory Based on the Reformed Helmholtz-Kirchhoff-Fresnel Method

“…Effects of sea surface on the incident sound have been examined by different acousticians due to its important role on sound propagation and reverberation and wide variety of sound applications in underwater environment. Underwater acoustic communication channels [1][2][3][4][5], sound emission from the submerged and floating objects [6,7], sound scattering of underwater sources from the sea surface [8] are among the most important subjects in underwater acoustics related to sea surface effects. In most of these subjects, it is necessary to provide an appropriate acoustic model in order to entail sea surface effects on the entry sound.…”