Structural–Acoustic Response Analysis of Variable Stiffness Laminates with Inherent Material Damping

A novel higher-order coupled finite-boundary element scheme is presented for the computation of the thermoacoustic responses of the layered panel structure under the harmonic excitation. The thermally pre-stressed vibrating composite panel model is derived mathematically using the higher-order shear deformation mid-plane kinematics. The eigen frequencies and the corresponding vibrational mode shapes are computed via the finite element method using Hamilton’s principle. Similarly, the surrounding medium is modeled via Helmholtz wave equations and solved numerically using the boundary element steps for the computation of the acoustic responses. The frequency and sound radiation output are computed numerically by means of an own computer code prepared in MATLAB environment. To avoid excess thermal loading during analysis, the critical buckling temperature of the composite panel structure is obtained and the range of thermal loading is selected accordingly. The model accuracy is demonstrated through the proper comparison studies of different structural responses (critical buckling temperature, natural frequency and radiated sound power level) of the curved composite panel with the available benchmark solutions. The reliability and the usefulness of the proposed novel scheme have been revealed by solving several numerical illustrations for different lamination schemes, panel geometries including the geometrical parameters.

In this article, natural frequencies of variable stiffness composite laminate (VSCL) plates with curvilinear fibers submerged in fluid with different depths of submersion are studied. In each layer of VSCL plate, the fiber-orientation angle changes linearly with respect to the horizontal coordinate. The problem is solved by using the hierarchical finite element method (HFEM) (p-version), with seven degrees of freedom per node and the higher-order shear deformation theory (HSDT) for C0 continuity. The plate theory ensures a zero shear–stress condition at the top and bottom surfaces of plate and does not require a shear correction factor. The fluid/structure interaction is examined in this study, in which the effect of fluid is assumed as pressure acting on the plate. The mathematical model of fluid is given by employing velocity potential and Bernoulli equation. The obtained frequency parameters shown an excellent agreement when compared with experimental and analytical results of available solutions in literature. Accurate results are obtained by increasing the degree of polynomial shape function of HFEM. In order to examine the effect of fluid on VSCL plate, different cases are studied to find out the effect of plate thickness, curvilinear fiber angle and depth of submerged plate.

In this paper, natural frequencies, large deflections and failure safety factors of variable stiffness composite laminate (VSCL) plates with curvilinear fibers are studied. In each ply of these rectangular VSCLs, the fiber-orientation angle changes linearly with respect to the horizontal coordinate. To carry out the static and dynamic analysis of the laminates, a new p-version finite element, which follows third-order shear deformation theory, is employed. Large deflections are considered, hence, the analysis is in the non-linear regime. To predict the failure onset, Tsai-Wu criterion is used. Taking into account manufacturing restrictions regarding the fiber curvatures, natural frequencies, deflections, and failure safety factors of some VSCL plates are determined. These results are compared with natural frequencies, deflections, and failure safety factors of constant stiffness composite laminate (CSCL) plates.

Vibration and damping analysis of thick sandwich cylindrical shells with a viscoelastic core under arbitrary boundary conditions

The effects of structural damping and wavenuwmber ratio on the acoustic power radiated by point-excited damped infinite beams and simply supported finite beams with same cross sections have been studied. The numerical calculations of the acoustic power were carried out using Keltie's equations based on the Heckl's power integral. The acoustic medium is assumed to be air, and the effect of the back reaction of the sound field is neglected in the beam response equation. Non-dimensional acoustic power, sound radiation efficiency, and acoustic power conversion efficiencies are presented as functions of wavenumber ratio and beam loss factors. It is shown that the power conversion efficiency of the infinite beam is inversely proportional to the wavenumber ratio and independent of the loss factor below coincidence, and is approximately proportional in inverse to the loss factor above coincidence. The power conversion efficiency of the finite beam has dull peaks with values roughly inverse-proportional to the loss factor at nonresonant frequencies. The similarity of acoustic power radiation between infinite beams and finite beams has been observed when the length and loss factor of beams is increased.

Numerical analysis of acoustic radiation responses of shear deformable laminated composite shell panel in hygrothermal environment

This work deals with lightweight and noise reduction of the gearbox by material change and rib arrangement. The gearbox is modeled into cylindrical shell and end plates. The non-ribbed gearbox and ribbed gearbox model with three different light material-aluminum, magnesium, and PMMA with aluminum end plates are used. Using the commercial FE software, modal and forced harmonic analysis on the non-ribbed gearbox and the ribbed gearbox with different materials are performed. Using the results of forced harmonic analysis, acoustic analysis was conducted by the commercial acoustic software. As the results, the ribbed gearbox has higher natural frequencies and lower displacement and generates lower sound pressure level and acoustic power level and higher radiation efficiency than the non-ribbed gearbox. The magnesium and the PMMA gearbox with aluminum end plates produce higher sound pressure and power level than the aluminum gearbox. The magnesium and the PMMA gearbox need the effective rib arrangement for identical noise level with the aluminum gearbox.

This paper aims to investigate the effects of circular cutout and hybridization to the failure behavior of Graphite Epoxy and Kevlar Epoxy composite laminates under uniaxial tension. The composite laminates made of Graphite Epoxy, Kevlar Epoxy and their hybridizations were modelled using commercially available finite element analysis software, ANSYS APDL. The laminates were modelled without and with circular cutout. Using the available built-in failure criteria function, the failure loads for all cases were determined for various angles of fiber orientation. The laminate was having the lamination scheme of [θ4/04/−θ4]s and failure at every increment of 10° angle, where θ, ranges from 0 to 90° were analyzed. Numerical validations were also carried out prior to the failure analysis. It is obvious that the cutout significantly weaken the laminates but it is interesting to observe that arranging fiber angles 45–90° could slightly improve the laminates, compared to smaller fiber angles. In contrary, the hybridization does not have significant effect on failure behavior of Graphite Epoxy and Kevlar Epoxy composite laminates, nevertheless it provides options to balance between strength and material costs. In all cases, the generated failure curves suggested that the failure behavior of composite laminates is very much dependent on the angles of fiber orientation. In terms of the effect of cutout, it is found that the cutout reduced the strength of the laminates significantly compared to the laminates without cutout. Nevertheless, there is slight improvement of strength when the fiber angle, θ, is arranged between 20 and 90°. The findings prove that the current study is useful and this knowledge could be expanded in designing composite laminates.

Passive tuned vibration absorbers (TVA) are widely used in reducing vibrations in machinery, buildings and many other vibrating structures. Recently, TVAs have been installed on structures for the purpose of reducing the sound radiation from the structure. As in the case of vibration control, the tuning and placement of TVAs for noise control is often based on the forced response of the structure, as opposed to the behavior of structural-acoustic interaction. This conventional approach for TVA placement on structures is not always effective for controlling sound radiation from the structure. This task requires proper control of the structural waves that couple well with the acoustic environment. This paper presents a preliminary study of acoustic radiation and radiation efficiency of panels instrumented with passive TVAs.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Squeal noise in simple numerical brake models

Aiming at the deficiencies of the traction helical gear transmission system when the EMU is running at high speed, this paper proposes and designs a kind of arc toothed cylindrical gear adapted to the traction of higher speed EMU. A parametric arc toothed cylindrical gear model was constructed using CREO, and its dynamic contact characteristics and acoustic response characteristics were analyzed under sustained operating conditions using the finite element boundary element method. The design of a tooth profile combined with the radius of the arc toothed line of the comprehensive trimming program put forward a virtual trimming prototype method through MATLAB and CREO reconstruction gear, and trimming before and after the gear transmission simulation experiments occurred for comparison and analysis. This study shows that the traction arc toothed cylindrical gear comprehensive modification method proposed in this study achieves better dynamic performance optimization, effectively reduces the contact stress and radiation noise of the gear transmission, and provides a theoretical basis for the development of a new generation of high-speed EMU stock traction drive systems.

The damage evolution of coal is accompanied by the generation of acoustic emission (AE) signal. Through the analysis and research of the AE response characteristics of coal deformation and failure, it is helpful to reveal the initiation, propagation, and fracture evolution of microcracks in coal. In this work, taking the anthracite coal as research object, the basic mechanical parameters of the coal samples were obtained by ultrasonic tests and uniaxial compression experiments. Meanwhile, the AE response characteristics of coal samples during uniaxial compression were obtained through AE experiments. The results show that when the density is low, the wave velocity of the coal sample decreases with the increase of density. When the density is higher than a certain value, the wave velocity of the coal sample increases with the increase of density. Through the measurement of ultrasonic wave velocity, it is found that there is some nonuniformity and anisotropy in raw coal samples. The ring counts, energy counts, and AE events with time in uniaxial compression process have approximately normal distribution. The AE events are concentrated in the elastic stage and yield stage, and the energy amplitude of AE events is higher in the plastic stage. Compared with the ring counts and energy counts, the AE events have a good positioning function, which can better reflect the evolution of internal cracks of coal samples during uniaxial compression.

Acoustic emission response characteristics and fracture behavior of dry-wet red sandstone under multistage fatigue loading

This paper examines the interaction of nonuniform flows with propeller blades in a submerged elastic duct. The acoustic radiation from the duct is calculated and correlated to the flow nonuniformities and the propeller and duct characteristics. The case of a stiffened duct with ribs is also considered and the dispersion relation of the duct modes is compared with that of a regular duct. The dispersion relation of the stiffened duct has a periodic structure similar to that of connected oscillators with large number of independent modes. Because of our interest in the acoustic radiation of such a system, we focus our attention on the flexure modes. The model is first tested with simple internal forces such as monopoles and dipoles. The results for unstiffened ducts show strong directivity as the dipole radial location moves closer to the duct wall. For stiffened ducts, the magnitude of the acoustic response as well as the directivity vary strongly and show large peaks near the stiffened duct free modes. For a propeller, an Euler code provides the pressure distribution along the blades. This represents the dipole strength distribution. Its radiated sound is calculated by summing up the contribution of the distributed dipoles. In this process, compact source effects are also taken into account.

A theoretical model is developed to describe the sound radiation by the surface vibration of in-service truck tires. The tire is modeled as an infinitely long incomplete circular cylindrical shell. The effects of inflation pressure and structural damping are included. The normal displacement, velocity, and acceleration resulting from a fluctuating load are determined using Flügge’s thin shell theory. Through numerical integration of the surface acoustic intensity, the radiated sound power is calculated as a function of damping, inflation pressure, and bending stiffness. Results indicate that the forced acoustic response is insensitive to small changes in the material loss factor and the bending stiffness. The inflation-induced membrane stresses determine the acoustic response character to a large extent and total neglect of the bending stiffness does not seriously affect the calculated sound power. The basic sound radiation mechanism is shown to be the damped progressive wave field on the structure in the vicinity of the applied force. The results indicate that the potential sound reduction might best be approached through study of the tire loading and vibration response mechanisms.