Tutorial on Acoustic Fluid Loading of Structures

Any vibrating structure is loaded by the fluid surrounding it. Whether air, water, or something else, the fluid loading adds a spatially distributed resistance (in phase with the vibration) and reactance (out of phase with the vibration) over the structural surfaces. The resistance absorbs energy, and damps structural vibrations. The reactance is either mass-like, effectively adding to the structural density, reducing resonance frequencies and vibration amplitudes; or stiffness-like, increasing resonance frequencies. Usually, mass-like reactance is caused by fluids external to a structure, and stiffness-like reactance is caused by enclosed volumes of fluids. This tutorial uses analytic methods to compare and contrast external and internal fluid loading on a flat rectangular plate and demonstrates the effects of fluid loading on plate vibration and radiated sound. The well-known stiffening effect of the internal Helmholtz resonance is demonstrated for a thin panel and a shallow entrained cavity. The differences between heavy (water) and light (air) external fluid loading are also demonstrated, with significant reductions in resonance frequencies and peak vibration amplitudes for water loading.

Experimental Characterization of a High-Damping Viscoelastic Material Enclosed in Carbon Fiber Reinforced Polymer Components

This work aims to identify the damping properties of a commercial viscoelastic material that can be embedded and cured between the layers of composite laminates. The material may be adopted for reducing the vibration response of composite panels, typically used in automotive and aerospace applications, e.g., as vehicle body shell components. In order to objectively estimate the actual potential to enhance the noise vibration and harshness aspects, the effects of the viscoelastic material on the modal parameters of carbon/epoxy thin panels are quantitatively assessed through experimental modal analysis. Two different experiments are conducted, namely impact hammer tests and shaker excitation measurements. Based on the results of the experimental campaign, the investigated material is confirmed as a promising solution for possibly reducing the severity of vibrations in composite panels, thanks to its high damping properties. Indeed, the presence of just one layer proves to triple the damping properties of a thin panel. An approximate damping model is derived from the measured data in order to effectively simulate the dynamic response of new design solutions, including thin composite panels featuring the viscoelastic material.

Analytical study and structural treatment for a thin panel painting

Purpose This paper aims to provide a deeper understanding of the painting techniques, materials used and deterioration phenomena in a thin panel painting. As well as, straightening buckling in a thin panel painting and reinforcement have been used by an auxiliary support system. Design/methodology/approach This requires using several scientific and analytical techniques to provide a deeper understanding of the painting techniques, materials used, deterioration phenomena and a greater awareness of how well treatment the panel painting is. Visual observation and multispectral imaging (Visible Ultraviolet-induced luminescence, as well as Ultraviolet reflected and Infrared [IR]), optical Microscopy (OM), handheld X-ray fluorescence spectroscopy (XRF), X-ray diffraction, Fourier transform IR spectroscopy (FTIR) and gas chromatography were used in this case study. Findings The analytical study of a thin panel with different methods allowed defining that the thin panel painting consists of plywood panel, ground layer (white lead and animal glue) and painted layer (lead red, cobaltic black, chrome yellow, Venetian red, iron black and white lead and poppy oil). Also, these determined that a convex buckling was the main form of deterioration. The structure treatment was executed by using a wet compress to straighten the thin panel painting and followed by fixing a new special design of the second auxiliary support system on the back of the thin panel painting. Originality/value The importance of analytical study to determine the painting techniques, materials used, deterioration phenomena and how well treatment the panel painting is. As well as, using a wet compress to straightening of warping or buckling wooden panel painting. Also, the Plexiglas second auxiliary support system could use to reinforcement the wooden panel and control the wooden panel movements.