Frequency-independent radiation modes of interior sound radiation: An analytical study

Abstract

Global active control methods of sound radiation into acoustic cavities necessitate the formulation of the interior sound field in terms of the surrounding structural velocity. This paper proposes an efficient approach to do this by presenting an analytical method to describe the radiation modes of interior sound radiation. The method requires no knowledge of the structural modal properties, which are often difficult to obtain in control applications. The procedure is exemplified for two generic systems of fluid-structure interaction, namely a rectangular plate coupled to a cuboid cavity and a hollow cylinder with the fluid in its enclosed cavity. The radiation modes are described as a subset of the acoustic eigenvectors on the structural-acoustic interface. For the two studied systems, they are therefore independent of frequency.

Frequency-independent radiation modes of interior sound radiation: Experimental study and global active control

“…The interior radiation efficiencies and modes are calculated in [3], using an analytical formulation. For experimental application, the radiation modes of the rectangular plate are evaluated at the SLV measurement points.…”

“…In this study, the eigenforms are assumed to be invariant. It is shown in [3], that the acoustic potential energy E(ω) can be described in terms of the surrounding structural velocity v(x, y, ω) on the surface S. The acoustic potential energy E(ω) can be rewritten for the rectangular cavity as a function dependent on the interior radiation modes u l,m (x, y)…”

“…This requires a priori knowledge of the structural mode shapes which can necessitate a high identification effort. In Hesse et al [3], the structural vibration is decomposed into a set of interior radiation modes. The interior radiation modes are orthogonal functions that describe vibration modes of the structure, such that the contribution from each one of them to the acoustic potential energy in the enclosed fluid is uncoupled from any other.…”

“…The interior radiation modes are orthogonal functions that describe vibration modes of the structure, such that the contribution from each one of them to the acoustic potential energy in the enclosed fluid is uncoupled from any other. The interior radiation modes calculated in [3] do not presume the knowledge of structural mode shapes and are independent of frequency, as they are a subset of the cavity modes at the structural interface. Since the radiation modes are orthogonal with respect to the acoustic potential energy, their reduction by active means will lead to a global reduction of the enclosed sound field.…”

“…A reason for the absence of experimental work may be found in the frequency-dependence of the resulting radiation modes, when calculated numerically. These radiation modes have been proven frequency-independent for two considered systems of fluidstructure interaction in [3] using an analytical formulation and are used in this study for experimental investigations.…”