The passive control of low-frequency duct noise remains a technical challenge. Herschel-Quincke (HQ) tube is effective in low frequency noise reflection. Previous studies showed that, when the bypass of the HQ tube is filled with a lighter gas and covered by tensioned membranes, the HQ tube becomes a flute-like silencer [L.Huang, Attenuation of low frequency duct noise by a flute-like silencer, Journal

Built-up vibro-acoustic systems may contain components whose vibration field is sensitive to uncertainty from small spatial variations in geometry, material properties, or boundary conditions, which have a wave scattering effect. Such components can be modeled as diffuse. Statistical energy analysis (SEA) and related approaches are frequently employed for analyzing built-up systems with diffuse components

The aim of the paper is to formulate a complete set of design rules for a vibro-impact nonlinear energy sink (VI NES). Hereto, analytical and numerical methods to extract the backbone curve of vibro-impact systems are presented. The adopted approach exploits the multiple scales method and is applied to a linear oscillator coupled with a VI NES. The dynamics of the system are explored and the system’s

Theoretical, numerical and experimental results are presented on the reactive and dissipative properties of backed or unbacked multilayer partitions made up of macro- or micro-perforated rigid panels in linear regime. The objective is to provide an enhanced multi-modal (EMM) formulation that accounts for high-order modes within the panel holes as well as visco-thermal boundary layers (VTBLs) over the

Post-buckled structures are prone to snap-through instabilities when external loading causes the structure to lose local stability and jump to a remote equilibrium. However, using piezoelectric actuation, structures can undergo entirely stable transitions between remote equilibria, thereby avoiding snap-through. This paper investigates the linearized vibrational properties of post-buckled beams along

Blade tip timing (BTT) is one of the most important non-contact monitoring methods for blade vibration estimation. BTT predominantly consists of two steps: 1) acquiring the original pulse signal generated by the rotating blade through optical probes. 2) Obtaining the arrival time of the original pulses through a high-precision counter and then transforming it to deflection. Multiple noise is involved

In this paper, the steady-state and transient sound fields inside 3D enclosed spaces were examined theoretically using the modal expansion method. An analytic formula for the Green’s function was derived allowing to predict the interior sound field for both the harmonic and impulse boundary excitations. A theoretical model was tested numerically for a 3D car-like cavity with a sound absorbing material

The possibility of reconstructing the response of a system, starting from the response of a reference one, has always been a point of great interest in structural dynamics. This is proved by the increasing attention about the similitude and scaling methods, although the associated predictions are still not fully reliable. Therefore, the aim of this paper is to present a method aimed at defining a transformation

The determination of accurate global and local modal information is a crucial step for any structural model updating process. Existing modal extraction methods can extract global modal properties with a good degree of accuracy; however, they have difficulties extracting accurate local information under transient excitations. This work presents a novel method, called Extended Empirical Wavelet Transformation

This paper makes use of high-order finite beam elements to perform stability evaluations and transient analyses of asymmetric rotors on anisotropic supports. Periodically time-varying motion equations are derived in the co-rotating reference frame, and they include all effects due to the rotational speed and angular acceleration. The periodic system stability is evaluated through the analysis of the

To date, the phenomenon of zero group velocity (ZGV) Lamb wave in a stress-free elastic plate has been well studied and used in non-destructive material characterization, electroacoustic devices and some other applications. This phenomenon is associated with the backward mode appearing in the range limited by the ZGV and cutoff frequencies. The modal frequency response of the structure, primarily the

In this paper, a highly straightforward approach is presented to simulate acoustic wave propagation in the presence of barriers. This formulation is particularly suited to tackle practical problems requiring the maximisation of noise loss by the optimal location of barriers, since the standard finite element approach has a significant computational burden from remeshing. The discontinuity-enriched

Semi-active vibration reduction techniques are defined as techniques in which controlled actions do not operate directly on the system’s degrees of freedom (as in the case of active vibration control) but on the system’s parameters, i.e., mass, damping, or stiffness. Cyclic variations in the stiffness of a structural system have been addressed in several previous studies as an effective semi-active

This article presents a methodology dedicated to the vibration analysis of turbomachine blades accounting for both geometric nonlinearities and nonlinear blade-tip/casing contacts in a numerically efficient way through the use of reduced order models. Contact is numerically handled with Lagrange multipliers and the equation of motion is integrated forward in time using an explicit central difference

This article proposes a novel mean for tuning the natural frequency of an electromagnetic resonant shunt, using a pulse-width modulation (PWM) circuit. It is used to modulate the value of the capacitance of the shunt, and the electrical frequency is shown to be proportional to the command parameter of the PWM, the duty cycle. An easy and efficient strategy to tune the resonant shunt in real time is

The ultimate goal in this study is to investigate the effects of tooth profile modifications (TPMs) on PGTs by performing parametric studies. For this purpose, firstly a nonlinear planetary gear dynamics model with time-varying stiffness is introduced. A time-varying stiffness function is included into the analysis by using loaded static transmission error (LSTE) for sun-planet and ring-planet gear

As a passive damping technique for vibration and noise mitigation, acoustic black hole (ABH) structures have been drawing an increasing attention because of their easy-to-realize and broadband wave focusing and energy dissipation characteristics. Structures with embedded ABHs, however, inevitably compromise the overall structural stiffness and strength, which hampers their use as critical structural

Conventional harvester systems usually have linear behavior. One of the great matters in these systems is that energy is harvested in a low frequency bandwidth. In this study, double cantilever beams connected at the end through a linear spring are used for energy harvesting. The bimorph piezoelectric patches are attached to the top beam by using double-sided tapes for energy harvesting. A pair of

Acoustic source identification using compressive beamforming has been extensively investigated and applied in numerous fields. In this paper, a generalized minimax-concave (GMC) penalty based compressive beamforming method is proposed. The method solves acoustic inverse problems using the GMC penalty, by which the capacity of sound field reconstruction in low-frequency and low-signal-to-noise ratio

Accurate measurement of the contact stress on the mating surface of the core engine's multi-stage rotor is of great significance for improving the structural connection quality and comprehensive performance of aero-engines. The phase reversal Fresnel zone plate (PR-FZP) can realize the focusing of ultrasonic wave and its focusing ability has an important influence on the measurement accuracy of contact

Fan/Outlet-Guide-Vane (OGV) interaction is a major broadband noise source in high bypass ratio turbofan engines. This paper assesses the acoustic shielding created by the fan rotor on the broadband noise generated by the interaction between the fan and the OGV. With this objective in mind, an efficient methodology to account for broadband noise transmission through a fan rotor using two-dimensional

This paper proposes a local approach for the on-line tuning of a semi-active vibration control unit, which is set to reduce the resonant response of target low-order flexural modes of distributed structures subject to broadband stochastic disturbances. The idea is to have multiple self-contained units, which can be fixed on thin walled structures to reduce flexural vibration and sound radiation at

We propose a tapered phononic beam with a broad low-frequency band gap for flexural waves. A unit cell of the phononic beam consists of two identical uniform parts and a thickness- and width-varying part sandwiched between them. Thickness and width profiles and uniform beam length are controlled to change the shear and rotational stiffnesses of the phononic beam, changing the starting and ending frequencies

Acoustic vector hydrophones are well-known for their ability in estimating the direction of arrival (DOA) of incoming signals. Moreover, despite its directivity, a vector hydrophone is capable of providing information about the received signal strength (RSS), just as an isotropic hydrophone. In this paper, a heterogeneous positioning system consisting of an isotropic and a vector hydrophone is considered

Autoparametric pendulum absorbers can transmit vibrational energy from the hosting structure to the motion of the pendulum and are effective if properly tuned. The motion of the pendulum can be also used to produce electrical power which can be harvested as renewable energy. This paper focuses on a novel configuration of the pendulum absorber-harvester that allows to improve its vibration suppression

This paper presents the improved sound insulation performance obtained from a new type of acoustic metamaterial, built by attaching periodic inertial amplification (IA) mechanisms to a host beam. The IA mechanism is a triangular bar-and-hinge device, which connects a small mass to the host beam at two separate locations. The band structure of a unit-cell and the Sound Transmission Loss (STL) of a finite-length

Predicting the vibratory response of bladed-disks in turbomachinery is of the utmost importance to design a reliable and optimized engine. Yet, such simulations are challenging mainly due to the large size of the finite-element model used to describe the system, the existence of random mistuning created by manufacture tolerances, and the nonlinear effects arising from the different components and their

Due to their special characteristics, angular contact ball bearings (ACBBs) are broadly applied in various mechancial systems. The working performance of rotating machinery can be determined by the internal ACBBs. Vibration and acoustic characteristics of ACCBs in various rotating machinery are becoming increasingly significant for the high-performance mechanical systems. An in-depth recognition of

Broadband shock-associated noise (BBSAN) is one dominant component from off-design supersonic jets. A time-domain BBSAN model is proposed and evaluated, which is based on the vector Green’s function solution of the decomposed Navier–Stokes equations. The source term is the scalar product of the anisotropic velocities with the mean pressure gradient. The approach uses large-eddy simulation (LES) databases

Experimental vibration responses of beams with nonlinear boundary conditions were interpreted using a bilinear spring model. Two systems of beams were considered: one is a single rod and the second one is a cluster of parallel rods linked together. The boundary conditions at the beam ends, for both systems, were provided by spacer grids, which are specific supports used in nuclear industry. The experiments

Although the characteristic Reynolds number of small horizontal axis wind turbines is only in the order of 100,000, their noise emissions can be annoying. Three different modifications of the blades aiming at attenuating the aerodynamic noise mechanisms are investigated: (i) Optimization of the blade profile, (ii) application of boundary layer tripping and (iii) addition of serrations to the trailing

In this article the estimation of mechanical parameters using vibrational output-only measurements due to ambient excitations is elaborated. The estimated mechanical parameters are solely based on measurements. They are equivalent to analytically derived mechanical parameters of models, which are discretized corresponding to the measurement set-up. In comparison to the analytically derived models no

This paper proposes a new hybrid actuation system for near-elimination of the small oscillations of articulated flexible-robot systems (AFRS). The hybrid actuation control forces are obtained by solving a fully-constrained inverse-dynamics (FCID) problem of relatively stiff robots experiencing small deformations, which lead to deterioration of their performance and precision. The FCID procedure is

The use of active vibration control may induce a delay leading to detrimental degradation of the performance of active vibration control. This is particularly true in the case of mechanical systems subjected to friction-induced vibration and noise for which such time-delays can lead to the appearance of undesirable instability. Furthermore, conducting a stability analysis of time-delay systems and

Substructuring methods are a very common and efficient way to solve complex vibroacoustic problems. The Condensed Transfer Function (CTF) approach is a substructuring method based on the concept of subsystem condensed transfer functions (corresponding to admittances or impedances) that allows assembling acoustical or mechanical subsystems coupled along lines or surfaces. For certain practical applications

Piezoelectric energy harvesters (PEHs) have been taken considerable attention in decades. To evaluate the performance of the harvester in large deformation and high electric field conditions, nonlinear effects (geometric, material and damping nonlinearities) should be involved in analyzing the characteristic of the harvesters. In this article, the unimorph L-shaped harvester is investigated and influence

The optimum position and minimum restraint stiffness of a flexible point support to raise a natural frequency of a thin bending plate is investigated, with the inclusion of the corresponding additional support mass. First the derivatives of the natural frequencies of the plate structure are derived with respect to the support movement using a finite element model. Second, the minimum support stiffness

In this study, the effects of near-field waves on the sound absorption and insulation performance of elastic micro-perforated plates (MPPs) installed in impedance tubes are studied. The sound absorption coefficient and the sound transmission loss (STL) of MPPs are computed by solving structure-acoustic coupled equations, and the results are compared to those by the finite element method (FEM) to confirm

A rigid rotor system which is driven through a Universal joint (U-joint) and is mounted on weakly-damped flexible supports exhibits principal and combination type parametric instabilities at certain torque-speed combinations. In this article, the transient dynamics of such a non-linear system driven by a non-ideal source (a DC motor) is studied through numerical simulation of the bond graph model of

Equivalent or condensed plate models are being used in various industries to reduce the computation time in finite element modelling. Out of the available equivalent plate models, the model developed by J.L.Guyader in 1978 exhibits high agreement with Lamb wave theory but it requires some time for implementation. Therefore, in this paper, a simple model is proposed to quickly compute the dynamic equivalent

Modeling of vibro/acoustic systems with embedded acoustic components of complex geometries is a challenging task. In particular, the presence of irregular-shaped acoustic modules, which are usually treated by finite element (FE) method, increases system complexities and makes the use of existing sub-structuring modeling techniques cumbersome. To tackle the problem, an efficient three-dimensional sub-structuring

Local nonlinear attachments can affect the global dynamics of their linear host structures through modal interactions. This was shown previously in experimental and computational studies of a model airplane with local nonlinear attachments at its wings, under impulsive forcing. Here we study nonlinear modal interactions in the model airplane subject to harmonic excitation. We consider the case of both

A new approach for time-varying (TV) modal parameters identification is proposed in this research. In the identification process, the entire signal is divided into successive short time windows, where the structure response under white noise excitation is transformed into modal coordinates by the Independent Component Analysis (ICA) method. The decoupled time-varying Auto-Regressive Moving-Average

The gradient term suppression (GTS) method for removing the hydrodynamic instability appearing in the time-domain solutions of the linearized Euler equations (LEE) along a lined flow duct is assessed. For this, the characterization of a convective instability in the time domain, with the aid of a complementary modal analysis, is first presented. The effect of the mesh size and spatial filtering on

This study provides a quasi-three-dimensional (quasi-3D) dynamic model for rotating pre-twisted functionally graded (FG) blades based on the three-dimensional elasticity shell theory and Carrera unified formulation. The material properties of the pre-twisted FG blades alter continuously in the direction of the thickness. The boundary conditions (clamped-end and free-edge) are realized by utilizing

A one dimensional active vibration absorber with time delayed feedback known as delayed resonator proved to be well applicable for entire vibration absorption of mechanical structure at known excitation frequency. As the main and so far unique result, the delayed resonator concept is transferred from one dimensional to two dimensional vibration absorption. In the first step, an ideal two dimensional

A rich variety of resonance scenarios induced in thin elastic plates by periodic axial strains is investigated to describe the morphing capability of flexible, ultra-lightweight panels. The strain-induced excitation is provided by embedded piezoelectric strips actuated by time-varying voltages. The study deals with plates characterized by geometric and mechanical symmetry entailing cylindrical motions

This paper is concerned with the resonance manifestation of a stochastically driven system consisting of dual Duffing oscillators with coupled active-passive hybrid control (APHC), i.e., time-delayed feedback control and viscoelastic damping. Analytic solutions are successively determined in both deterministic and stochastic modes. Based on our simulations in the deterministic mode, changes to the

Wheel flat, as a common defect of railway vehicles, can cause large impact forces on both the vehicle and infrastructure components and thus seriously hinder the vehicle running stability and safety. Considering the complex track irregularities and variable-speed conditions, the vehicle vibration responses often contain strong interference signal components and exhibit time-varying frequency contents

Carbon nanotube sheets exhibiting extremely low heat capacity have enabled the development of thermoacoustic projectors (TAPs) for a wide range of frequencies (1- 106 Hz). The sound pressure level of carbon nanotube (CNT) based TAPs is proportional to the frequency, resulting in a reduced performance at low frequencies. Hence, there is a need to determine the governing parameters of TAPs that can be

The use of exhaust gas turbochargers in modern engine concepts is essential to achieve high efficiencies, low fuel consumption, and low emissions. However, the high rotational speed, a wide range of compression ratios, and dynamic acceleration and deceleration processes cause both tonal and broadband sound radiation. Due to packaging constraints, the intake cycle is often characterized by deflections

This paper investigates the application of flow-permeable materials as a solution for reducing jet-installation noise. Experiments are carried out with a flat plate placed in the near field of a single-stream subsonic jet. The flat plate is modular and the solid surface near the trailing edge can be replaced with different flow-permeable inserts, such as a metal foam and a perforated plate structure

The wheel-rail dynamic resonance (W-RDR) under multi wheelset-rail nonlinear interactions in the mid-high frequency range is still unclear regarding wheelset flexibility, wave transmissions and reflections (W-TF) among each wheel-rail interaction. To clearly elucidate W-RDR and its induced modes, a double vehicle-track coupled dynamic model of multiple flexible wheelset-rail interactions is established

This paper presents a study on nonlinear elastic wave modulation due to an applied periodic thermal field. The experimental study is performed with a thermal analogy of the vibro-acoustic wave modulation (VAM) technique. The aim is to identify sources of nonlinear effects appearing in the response signal of a damaged structure. Assigning specific nonlinear effects to their corresponding sources is

This work focuses on the study of composite metamaterials to be employed as possible lightweight insulation systems for noise and vibrations. In particular, the dispersion relations are derived by applying the Bloch-Floquet theory to the unit cell of the periodic microstructure. Advanced beam finite elements based on Carrera Unified Formulation are here extended, for the first time, to the dynamic

In-situ Transfer Path Analysis is a diagnostic method used to analyse the propagation of noise and vibration through complex built-up structures. Its defining feature is the invariant characterisation of an assembly’s active components (i.e. vibration sources) by their blocked forces. This invariant characterisation enables the downstream structural modification of an assembly without affecting the