Vibroacoustic Behavior Research Articles

On a hybrid updating method for modeling vibroacoustic behaviors of composite panels

Composite panels, by virtue of their outstanding mechanical properties, have found various applications in different sectors like aerospace and transportation. Under certain assumptions like Kirchhoff–Love and Mead–Markus hypotheses, certain high-order differential equations can be used for vibroacoustic modeling of composite panels. However, for accurate modeling, updating parameters is an essential stage. Herein, we aim to theoretically and experimentally review this stage. For this purpose, a hybrid updating method is proposed, incorporating hierarchical functions, inhomogeneous wave correlation approach, and least squares optimizations. Then various laboratory measurements, including Laser Doppler Vibrometry measurements as well as sound pressure levels, are analyzed. The measurements were performed for a thick composite (sandwich) panel, and a thin composite (laminate) one, along with two isotropic (steel and aluminum) plates for additional validation. The experiments indicate the ability of the hybrid approach to adjust parameters and precisely model vibroacoustic behaviors of the panels. Furthermore, the proposed hybrid method can be used in studies whose goal is accurate vibroacoustic modeling for psychoacoustic issues and perceptual validations, which is also one of the future targets of this research.

Case study: Hybrid inverse method for aircraft noise abatement isolator: Experimental and vibroacoustic assessment

In the aeronautical industry, the vibrations generated by mechanical systems produce unwanted noise perceived by users, which affects their comfort. Engineers encounter several difficulties in carrying out experimental measurements when studying complex systems. To solve this problem, a solution was proposed for the manufacturers' benefit, allowing them to access the various identified measurement points, describe the systems' vibroacoustic behavior, whether coupled or decoupled, and share the work between several teams and reduce the time spent on measurements. This paper deals with the experimental study performed on an aircraft noise abatement isolator. The component-based transfer path analysis hybrid inverse method is developed to allow the work on the subsystems separately between several teams and characterize them on an external test bench outside real functioning conditions. The studied system consists of a mass coupled by a noise abatement isolator fixed in an aluminum plate backed by a concrete cavity. Several parameters are studied such as the number of transfer paths to be considered to see the effect of neglecting certain transfer paths, the effects of coupling versus decoupling of the connected substructures and the number of indicator points chosen and used in the inversion method. The results are compared to the direct method.

Programmable piezoelectric meta-rings with high-order digital circuits for suppressing structural and acoustic responses

In this paper, a programmable piezoelectric meta-ring equipped with high-order digital shunting circuits is designed for vibro-acoustic control. The structural and acoustic suppressing performance of the piezoelectric meta-ring in light fluid is tunable by re-programming transfer functions implemented in micro-controller units of the digital circuits. The radiated sound due to structural vibration of the meta-ring is attenuated in multiple local-resonance bandgaps, which is realized using high-order resonant circuits designed via the pole-zero placement method. An analytical model is developed for providing physical insights into vibro-acoustic behaviors of the piezoelectric meta-ring in light fluid. The analytical results agree well with numerical ones computed with the finite element method. The effects of electrical parameters such as gain parameter and electrical damping ratio on the sound radiation suppression of elastic rings are also discussed. To verify the programmability and high-order local-resonance bandgap performance of the piezoelectric meta-ring, the vibro-acoustic control experiment is carried out in the anechoic chamber. It is found that programmable bandgaps at different target frequencies of the piezoelectric meta-ring can be generated, which effectively suppress the structural–acoustic response peaks of the meta-ring.

Lightweight gearbox housing with enhanced vibro-acoustic behavior through the use of locally resonant metamaterials

Mass reduction of automotive components enhances vehicles’ performance and extends their driving range. However, lightweight construction typically leads to noise and vibration issues. Hence, the development of lightweight components must go in tandem with advancements in the field of noise and vibration. This work focuses on the lightweighting of the gearbox housings (GBHs) and on the introduction of vibroacoustic metamaterials to improve their Noise, Vibration, and Harshness (NVH) characteristics. Topology optimization methods were used to reduce the mass of a GBH. Its noise emission was evaluated numerically, before and after the mass reduction. Locally resonant metamaterial (LRM) solutions were applied in the GBH and then tested in numerical simulations. This analysis showed the LRM solutions reduce the emission of noise in the predicted band gaps (BGs), while also providing significant attenuation across the entire frequency spectrum under consideration. The experimental results confirmed the effectiveness of the LRM attenuation concept and the trends observed in the numerical results. Vibration was also attenuated in parts of the GBH where the LRM was not applied. Attenuation of in-plane housing vibration was also observed. The proposed LRM solutions are lightweight, passive and low-cost solutions that can implemented in housings to enhance their NVH characteristics.

Recent advances on research into high-speed railway noise

Abstract Around 42,000 km high-speed railways are in operation in China with a maximum speed of 350 km/h. Trains which can run at 400 km/h are also under development. To control both train pass-by and train interior noise, huge resources have been put into research on high-speed railway noise, and the authors of this paper and their teams have been involved in several key projects. This paper is to summarise some of the advances achieved in these projects by covering the following topics: measurement results and characteristics of high-speed railway pass-by noise; analyses on source contribution to pass-by noise based on microphone array measurement; modelling of high-speed rolling, aerodynamic, and viaduct bridge noise; prediction of the vibro-acoustic behaviour of car-body with poro-elastic media; analyses of vibration transmission in the suspension/bogie system; statistical energy analysis-based prediction of train interior noise. Open problems and potential technologies for controlling high-speed railway noise are also discussed.

Vibroacoustic analysis of multi-layered micro-perforated plates coupled to an acoustic enclosure

A vibroacoustic study of multi-layered micro-perforated plates (MPP) coupled to an enclosure cavity excited by internal and external acoustic excitations is presented. Most previous research centered on the multi-layered MPPs structure itself, the absorption and transmission performances were often calculated or tested in a simple acoustic environment. In a more realistic setting, the surrounding systems may affect the efficiency of MPPs. The proper modeling of the MPPs within acoustic enclosures requires careful study. The break-out sound from an enclosure via multi-layered MPP and the energy transmission of the structure into an acoustic enclosure undergoing exterior excitation are studied with an emphasis on the use of MPP in acoustic enclosures to suppress specific resonances of the enclosure. Therefore, an analytical formulation is proposed to model the behavior of the coupled system to address this issue. Using a modified Fourier series for the acoustic pressure, the continuity of the normal velocities at the interfaces of the plate or the MPP and the acoustic medium is assured accurately. A modified variational form for the acoustic and structure medium yields a completely coupled vibroacoustic system. Comparison with the finite element method (FEM) and available literature findings prove the efficacy and precision of the current approach. The effect of important parameters on the vibroacoustic behavior of multi-layered MPPs structure connected to an acoustic enclosure is examined. These parameters include micro-perforation of the plate, hole diameter, air gap thickness, acoustic enclosure dimensions, and the insertion of absorbent material in the gap.

An Integrated Method for the Vibroacoustic Evaluation of a Carbon Fiber Bouzouki

An integrated method, which combines Electronic Speckle Pattern Interferometry, impulse response measurements, finite element method simulations, and psychoacoustic tests, is proposed to evaluate the vibroacoustic behavior of a carbon fiber bouzouki. Three of the carbon fiber instruments are manufactured, and one is qualified via interferometric experimental measurements with reference to a traditional wooden bouzouki, which was evaluated for its sound and playability by the proposed method. Psychoacoustic tests were used to evaluate the sound and playability of the newly qualified carbon fiber bouzouki, which was further modeled by the finite element method and simulated. The simulation results agreed well with the experimental measurements. Furthermore, finite element simulation results of the qualified carbon fiber bouzouki were demonstrated with reference to the traditional wooden bouzouki experimental results, providing new findings crucial for the optimization of the manufacturing and the vibroacoustic behavior of the carbon fiber instrument. The proposed integrated method can be applied to a variety of carbon fiber stringed musical instruments.

An efficient SBFEM-based approach for transient exterior vibro-acoustic analysis of power-law functionally graded shells

An efficient approach for transient exterior vibro-acoustic analysis of power-law functionally graded (FG) shells is developed using the scaled boundary finite element method. In the structural formulation, a shell element is treated as a three-dimensional continuum and its middle surface is represented with a quadrilateral spectral element. Along the thickness, the middle surface is scaled and the displacements are approximated using a quadratic Lagrange interpolation. The assumed natural strain method is applied to treat numerical locking and the integral along the thickness is performed analytically. In the acoustic formulation, velocity potential acts as the basic unknown. An infinite fluid is truncated by a spherical surface. The exterior field is simulated through the improved doubly asymptotic open boundary while the interior region is split into subdomains with their impedance evaluated by the improved continued-fraction method. The structure and fluid are discretized independently. The collocation procedure is utilized to perform the data transfer across the nonconforming interface. A high-order implicit time integration scheme is applied to solve the coupled system of equations. Numerical examples demonstrate that the proposed approach is stable, accurate and highly efficient. The effects of the geometric and material parameters on the vibro-acoustic behaviors of FG shells are systematically studied.

Vibro-acoustics time domain FEM-BEM analysis of a Titian Stradivari violin: the role of the bridge

The acoustic behaviour of the violin is defined during manufacturing since the vibrational acoustic properties of the instrument are related to the top plate’s vibrational modes in a direct way. An important component of the violin assembly is the bridge. The bridge transfers the excitation forces from the strings to the soundboard via the bridge feet and acts as a sound filter. In this study the Titian Stradivari violin CAD geometry of the soundboard, including the f-holes and bass bar, and the bridge is modelled, and time domain coupled finite element method-boundary element method, vibro-acoustic, simulations are performed to analyse the interference of the instrument’s sound with its structural components. A comparison of the vibroacoustic behaviour for the soundboard with and without the bridge enlightens the crucial role of the bridge. This initial computational approach will be extended, with similar studies on the role of every structural component of the violin individually, aiming to decode the full violin soundbox vibroacoustic behaviour and provide key insights for violinmakers on how structural changes affect the quality of the emitted sound.

Underwater cylindrical sandwich meta-structures composed of graded semi re-entrant zero Poisson's ratio metamaterials with pre-strained wave propagation properties

Zero Poisson's ratio (ZPR) mechanical metamaterials can yield no transverse displacements when unidirectionally compressed, and cylindrical sandwich meta-structures composed of semi re-entrant (SRE) ZPR metamaterials are thus explored for applications on cylindrical shells of underwater equipment or submersible structures. A group of ZPR unit cells with specified pre-strained wave propagation characteristics and adequate load-bearing capabilities is optimally designed based on the periodic boundary condition (PBC) and Bloch's Theorem. The sound transmission and pressure-resistant performance of cylindrical sandwich meta-structures comprising the homogeneous and graded SRE ZPR unit cells are then investigated. The results show that the designed meta-structures can perfectly yield better vibroacoustic attenuation behavior within the specified frequency regions corresponding to the pre-strained band gaps and safely bear the hydrostatic pressure equivalent to 1000 m depth with low weight-bulk ratios. In addition, the functionally graded metamaterial core can boost vibroacoustic performance within broader frequency ranges.

Study on vibro-acoustic performance of composite laminates under transient impact excitation

With the widespread use of composite structures in ship superstructures, their vibro-acoustic response under transient impact loads is of increasing concern. This paper studies the vibro-acoustic behavior of a carbon fibre reinforced composite laminate under transient impact excitation based on the time-domain hybrid FEM/BEM method. Firstly, the numerical method is verified through the model test of a homogeneous plate. Subsequently, the vibration and sound radiation characteristics of composite laminates are studied. It was found that the impact noise energy mainly concentrated in the low-frequency range of 10~200Hz, and the peak noise spectrum was 9dB lower than that of the steel plate. The variation of lay-up orientations causes differences in the structural properties of the laminates, resulting in differences in their vibro-acoustic radiation performance. In this study, the laminate with the [0°/90°]5s orthogonal lay-up scheme has better acoustic radiation performance under the impact load.

Forced vibroacoustic response of a cylindrical shell in an underwater acoustic waveguide

An analytical approach is proposed to analyze vibroacoustics of an infinitely long thin cylindrical shell under line-distributed harmonic excitation immersed in an underwater waveguide formed by a free surface and a rigid floor. Equations of motion of the thin shell are modeled using Flügge’s shell theory, the fluid–structure coupling is implemented with the image source method to account for the infinite reflections of acoustic waves off the waveguide boundaries and Graf’s addition theorem is used to reconcile the coordinate systems of the image sources in the analytical expressions. The vibroacoustic response from the proposed analytical model is verified by numerical results obtained from a finite element model, showing excellent agreement. The analytical approach provides a computationally efficient tool for parametric investigation into the relative effects of the proximity of the free surface and/or rigid floor on the vibroacoustic behavior of the shell.

FEM-BEM Vibroacoustic Simulations of Motion Driven Cymbal-Drumstick Interactions

The transient acoustic dynamics of a splash cymbal are investigated via the Finite Element Method-Boundary Element Method. Real three-dimensional motion data recorded from the interaction of drummer–drumstick–cymbal provide the initial and the loading conditions to the simulated interaction of the drumstick–cymbal Finite Element Models. Progressively intensified free strokes are used as loading conditions for both experiment and simulation. The velocity values of the moving drumstick in various drumming conditions are monitored, recorded, and analysed to provide input data into the time domain simulations. The synergy of motion capturing and numerical methods allows computing the sound generated by the combined interaction of the vibroacoustic behaviour of the cymbal with the motor-interaction of the performer. The proposed methodology promotes a novel perspective in musical instrument design, optimization, and manufacturing considering performance discrepancies intentionally introduced by performers.

Combination of Acoustic Black Holes with point masses

Passive acoustic measures are suitable for the targeted improvement of the vibration behaviour of technical products. In this context, Acoustic Black Holes (ABH) as innovative measures have shown great effect for an efficient damping of vibrations and a simultaneous mass reduction. The vibration reducing effect, however, is primarily apparent in the higher frequency range. The thickness reduction results in a mass reduction of the system, which could worsen the vibroacoustic behaviour in the lower frequency range. The idea of the approach here is to use the saved material in form of point masses to counteract this disadvantage at low frequencies by a targeted placement or direct consideration in the manufacturing process. The result is a mass-neutral acoustic design measure. In order to investigate the effectiveness of the ABH point mass combination, finite element models of generic beam and plate structures with ABH are used in this paper. In addition, the influence of point masses in terms of their position and number on the vibroacoustic behaviour is simulated. One focus is the assessment of the advantage by combining ABH with point masses. To validate the results, experimental investigations are carried out and compared with the numerical results.

High-resolution vibro-acoustic measurement and analysis of the DLR ISTAR aircraft to assess engine-induced cabin noise

Aircraft engines, especially when mounted directly to the fuselage, inject a considerable amount of tonal vibrations into the airframe causing audible and comfort reducing cabin noise. Reducing this noise requires the development of specialised noise reduction systems. This is a time consuming and expensive endeavour. To speed up and ease this process a sufficiently detailed numerical model of the aircraft structure and the force injected by the engines is required. The DLR ISTAR, a Dassault Falcon 2000, was used for an extensive vibration measurement campaign. The goal of this campaign was twofold: Getting spatially dense information about the aircrafts vibro-acoustic behaviour to later update a finite element model for calculations in the mid-frequency range and to analyse the vibration injected by running engines into the fuselage structure. The measurements include the vibrational response to both shaker excitation and engine vibration of the DLR ISTAR at about 1400 positions acquired by a rowing grid of sensors. The results are presented in the form of operational deflection shapes and energy transfer paths calculated using structural intensity analysis.

Practical Tutorial on cylindrical structure vibro-acoustics Part 1 - Vibrations

The mathematics which describe the vibroacoustic behavior of cylindrical structures are imposing to say the least. Part 1 of this practical tutorial demystifies cylindrical shell vibration theory by using measured data from actual shells and pipes to explain key concepts. For any shell, you can estimate frequency ranges where shells behave like simple beams and flat plates, greatly simplifying calculations of modes of vibration and mobilities. The key is first calculating the ring frequency - the frequency where membrane waves can propagate fully around the shell circumference. Simple infinite structure theory may then be used to compute mean mobilities for beam, shell, and flat plate behavior. Modes of vibration for a cylinder depend on both longitudinal and circumferential harmonics, or a helical wavenumber. Cremer's simple approximate resonance frequency formula is used to show examples for a large diameter short shell and a small diameter long shell (a pipe). Finally, the measured modal densities of an elbowed pipe are compared to estimates from an empirical expression for modal density of a shell. In all cases in this tutorial, measurements and simple estimates agree well, showing that cylindrical shell vibrations may be estimated without difficult math or complex computer models.

Vibroacoustic metamaterials as add-on solution for noise reduction in existing housing structures

Vibroacoustic metamaterials (VAMM) have the potential to reduce unwanted noise components in a very targeted and narrow-band frequency range. Many VAMM concepts are based on mechanical resonators that act as vibration absorbers in their natural frequency and thus absorb energy that would otherwise be radiated in the form of airborne sound and perceived as noise. Often, during the design phase, it is not yet possible to adequately assess which surfaces will be acoustically problematic and in which frequency ranges disturbing noise components are going to be. In addition, many VAMM concepts can only be manufactured using additive manufacturing (AM) processes, due to their complex geometry. However, AM parts often have strongly anisotropic material behavior, depending on the manufacturing process, which makes a prediction of the vibroacoustic behavior even more difficult. Direct integration into casing structures during the design phase is therefore not practical and economically feasible in most cases. This paper therefore investigates the extent to which retrofitted resonators can be effectively used in existing casing structures. For this purpose, FDM-printed bending resonators made of ABS and PLA are used, which have already been measured with regard to their natural frequencies in a previous publication. Different variants are attached to a demonstrator housing and the surface vibration velocity is measured using a 3D laser scanning vibrometer, and compared with the basic variant without resonators. The radiated airborne sound is also measured. Furthermore, a comparison is made with a dynamic FEM simulation in order to be able to evaluate its prediction quality, in particular with regard to the additively manufactured resonators.

Vibroacoustic behavior of a rectangular composite plate in thermal environment

This paper is a study of the vibroacoustic behavior of orthotropic laminated composite rectangular plate under a sound wave excitation in thermal environments. An improved analytical procedure has been developed that allows for an efficient solution of the finite composite plate sound transmission problem. A symmetrically orthotropic laminated composite plate is considered. The plate is modeled with classic thin-plate theory and is assumed to be clamped on all four sides. The incident acoustic pressure is modeled as a harmonic plane wave impinging on the plate at an arbitrary angle. The sound transmission loss is calculated from the ratio of incident to transmitted acoustic powers.

Coupled Simulation of Fluid Flow and Vibro-Acoustic Processes in the Channel with a Circular Cylinder

Vibro-acoustic processes are an interacting set of pulsations of the working fluid and vibrations of mechanical structural elements. The simulation of vibro-acoustic processes in a long pipe with an elastic round cylinder is considered. The mathematical model is developed in a coupled formulation, when not only pressure pulsations cause pipe vibrations, but also vibrations of the mechanical subsystem affect sound wave propagation in the working fluid. The influence of vortex formation processes in the channel on the system dynamics is taken into account. The fluid flow is found using delayed detached eddy simulation. The flow regimes around a single round cylinder corresponding to various Reynolds numbers are investigated to validate the computational algorithm. The distributions of the flow quantities and vibro-acoustic behavior of the system are discussed.

Determination of optimal probing frequency for enhancing nonlinear vibro-acoustic modulation behaviors of delaminated CFRP based on local defect resonance

The magnifying effect of resonance vibration on vibro-acoustic modulation (VAM) is important for the study of nonlinear ultrasonic behaviors and yet to be completely investigated. In this paper, the determination of optimal probing frequency for enhancing nonlinear VAM behaviors of delaminated carbon fiber reinforced plastics (CFRP) based on local defect resonance (LDR) is studied through a twofold approach, i.e., a 3D finite element model and a non-contact experimental setup based on laser scanning Doppler vibrometer (LSDV). A searching procedure based on scaling subtraction method (SSM) is proposed to better determine the LDR of a delaminated CFRP and the magnifying effect of probing frequency in a considerable bandwidth including LDR on the VAM behavior is examined. Damage contour maps based on modulated sidebands are established to identify the delamination existence and the maximum response amplitude (MRA) is proposed to quantify the enhancement of nonlinear VAM response. Results are presented and show that the LDR can improve the delamination detection compared to arbitrary frequency and global resonance frequency. The highest sensitivity of delamination detection is achieved when the probing frequency is selected as the sum or difference of the LDR and pumping frequency.