Control of Radiated Noise from Fluid-Loaded Stiffened Structures
- Publication Type:
- Thesis
- Issue Date:
- 2024
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Periodically stiffened structures are widely used in many engineering applications, including aeronautics, marine, and rail systems. In these structures, so called Bloch-Floquet (BF) waves are generated due to the interaction between flexural waves in the host structure and flexural/torsional waves in the stiffeners. These waves are a primary source of undesirable noise and vibrations when a stiffened structure is excited by a force. Hence, this work aims to understand the propagation of BF waves and their contribution to the radiated sound power by utilising non-negative intensity (NNI) technique. Additionally, a passive control technique based on the acoustic black holes (ABHs) is developed to control vibroacoustic responses of fluid-loaded stiffened plates. This has been achieved by incorporating ABHs into stiffeners and by analysing their effects on the propagation of BF waves.
An analytical model is used to evaluate the vibroacoustic responses of a three-dimensional fluid-loaded infinite stiffened plate subjected to point force excitation. This model, is formulated in the wavenumber domain, allowing efficient simulations. The NNI, which is also expressed in the wavenumber domain, has been derived, and NNI maps show that when the excitation frequency is within a radiating BF passband, the intensity is concentrated at the stiffener's position. Further, the research explores the integration of ABHs as stiffeners in the fluid-loaded infinite plate while maintaining the host structure’s integrity, to mitigate the propagation of BF waves.~A semi-analytical model in the wavenumber domain is developed to predict the forced vibroacoustic response of a two-dimensional fluid-loaded infinite plate with ABH stiffeners. This model incorporates the translational and rotational dynamic stiffnesses of the stiffeners, estimated using the Finite element method, and couples these with the fluid-loaded plate’s analytical formulation. The results indicate substantial reductions in mean quadratic velocity and radiated sound power when using ABH stiffeners.
Finally, an experimental study compares the vibrational response of two finite stiffened beams with ABH and rectangular stiffeners, providing empirical data to confirm the effectiveness of the proposed passive control method and the theoretical and numerical findings in practice for the case in air. The damping effect caused by the addition of damping layers is compared for both stiffeners, considering the stiffeners without damping layers, with viscoelastic damping layers and constrained viscoelastic damping layers. The combined analytical, numerical, and experimental approaches underscore the potential of ABH stiffeners to mitigate the vibroacoustic response in stiffened structures.
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