Transmission loss of orthogonally rib-stiffened double-panel structures with cavity absorption

Active Control of Sound Transmission through Orthogonally Rib Stiffened Double-Panel Structure: Mechanism Analysis

Physical mechanisms of active control of sound transmission through orthogonally two ribs stiffened double-panel structure are investigated. This is the continued work of the single rib stiffened case. For the orthogonally two ribs stiffened case, four different cluster mode groups can be coupled with each other, due to the interlaced coupling effects of the horizontal and vertical ribs. One cavity mode can couple with and transmit sound energy to any type of base plate mode of the radiating ribbed plate. Consequently, the main differences of the control mechanism, when compared with the single ribbed case, lie in two aspects. One is that a novel mechanism appears. That is, suppressing and rearranging the cavity modes simultaneously achieves the suppression of the base plate modes. The other is that rearrangement of the cavity modes to rearrange the base plate modes for achieving sound radiation cancellation almost does not appear. The reason is that all types of cavity mode can couple with any one of the base plate modes due to the coupling effects of the two ribs. There is only a need to rearrange several important cavity modes to achieve suppressing the base plate mode of the radiating ribbed plate.

A modal approach to piano soundboard vibroacoustic behavior

This paper presents an analytical method for modeling the vibro-acoustic behavior of ribbed non-rectangular orthotropic clamped plates. To do this, the non-rectangular plate is embedded in an extended rectangular simply supported plate on which a spring distribution is added, blocking the extended part of the surface, and allowing the description of any inner surface shapes. The acoustical radiation of the embedded plate is ensured using the radiation impedances of the extended rectangular simply supported plate. This method is applied to an upright piano soundboard: a non-rectangular orthotropic plate ribbed in both directions by several straight stiffeners. A modal decomposition is adopted on the basis of the rectangular extended simply supported plate modes, making it possible to calculate the modes of a piano soundboard in the frequency range [0;3000] Hz, showing the different associated mode families. Likewise, the acoustical radiation is calculated using the radiation impedances of a simply supported baffled plate, demonstrating the influence of the string coupling point positions on the acoustic radiated power. The paper ends with the introduction of indicators taking into account spatial and spectral variations of the excitation depending on the notes, which add to the accuracy of the study from the musical standpoint. A parametrical study, which includes several variations of soundboard design, highlights the complexity of rendering high-pitched notes homogeneous.

Vibroacoustics of orthotropic plates ribbed in both directions: Application to stiffened rectangular wood panels

This paper is focused on the vibroacoustic behavior of a rectangular ribbed wood panel. This is done by developing an analytical model based on a variational approach, taking into account the kinetic and strain energies of a special orthotropic plate, 11 ribs oriented in a first direction and 1 other strong stiffener oriented in the perpendicular direction, which are considered as beams tied to the plate. A modal decomposition is adopted on the basis of the simply supported orthotropic plate. This allows calculating the modes of the wood panel (ribbed modes) in the frequency range 0-5000 Hz. The acoustical radiation of the baffled panel is also calculated. The radiation coefficients of the ribbed modes are presented and compared, when possible, to similar unribbed plate modes. Finally, the vibroacoustic analysis of the structure shows that an excitation placed on the hard point makes the panel particularly radiative and decreases the apparent critical frequency.

Effects of mean flow on transmission loss of orthogonally rib-stiffened aeroelastic plates

This paper investigates the sound transmission loss (STL) of aeroelastic plates reinforced by two sets of orthogonal rib-stiffeners in the presence of external mean flow. Built upon the periodicity of the structure, a comprehensive theoretical model is developed by considering the convection effect of mean flow. The rib-stiffeners are modeled by employing the Bernoulli-Euler beam theory and the torsional wave equation. While the solution for the transmission loss of the structure based on plate displacement and acoustic pressures is given in the form of space-harmonic series, the corresponding coefficients are obtained from the solution of a system of linear equations derived from the plate-beam coupling vibration governing equation and Helmholtz equation. The model predictions are validated by comparing with existing theoretical and experimental results in the absence of mean flow. A parametric study is subsequently performed to quantify the effects of mean flow as well as structure geometrical parameters upon the transmission loss. It is demonstrated that the transmission loss of periodically rib-stiffened structure is increased significantly with increasing Mach number of mean flow over a wide frequency range. The STL value for the case of sound wave incident downstream is pronouncedly larger than that associated with sound wave incident upstream.