Rolling bearing with a localized defect usually generates periodically impact vibration responses, which carry important information for bearing fault diagnosis. Due to the inevitable noise disturbances, extracting accurate impact features of faulty bearing is still a hard task. In view of the superiority of sparse decomposition on feature extraction, a novel sparse dictionary design method is proposed

The system considered consists of a hanging cantilevered pipe, surrounded at its upper part by a concentric rigid cylindrical tube, mounted in a tank full of water. Water enters the pipe at its upper and is discharged into the tank at its free end. This generates an upwards flow in the annulus between the pipe and the rigid tube, exiting the system at its upper end. The reverse flow configuration is

This work is a contribution to the ongoing debate about the role of quadrupoles in low Mach number flows, studied through the use of solid and permeable surface Ffowcs-Williams & Hawkings (FW-H) integrals for landing gear numerical noise predictions. It rests upon the key idea that the dominance of surface sources over volume sources can only be guaranteed when the compact-source condition is met.

Dynamic acoustic fields offer an interesting alternative for acoustic standing-wave fields in acoustic separation applications. This paper reports on an investigation of two methods for generating dynamic acoustic fields and their applicability for selective particle separation. The first method applies a dual-frequency excitation to generate a standing-wave field that in which the pressure nodes travel

Chatter vibrations strongly limit productivity in milling. Due to the presence of rotating parts with asymmetric stiffness and stability enhancement strategies which act through a periodic variation of stiffness, there is growing interest in estimating the stability maps of systems with Linear Time Periodic dynamics together with periodic cutting excitation. Applying Exponentially Periodic Modulated

In this paper, the effects of the turbulence integral scale on the buffeting response of a long-span suspension bridge are studied via the proposed three-dimensional (3D) two-wavenumber buffeting analysis method. The root mean squares (RMS) of the buffeting lift and displacement of the streamlined bridge girder are analyzed in cases with different ratios of the turbulence integral scale to the half-width

In time domain force reconstruction problems, regularization techniques are widely adopted to solve the intrinsic ill-posedness or ill-conditioning. Different techniques are selected for forces with different temporal profiles, such as Tikhonov regularization for smooth forces and ℓ1 regularization for sparse forces. However, in lack of prior information on force temporal distribution, choosing the

The aim of this paper is to propose a methodology for identifying the pressure field applied on a laminated composite plate from its measured vibration response. The general framework of this study is the Corrected Force Analysis Technique (CFAT), which was previously used on isotropic plates. This method estimates the spatial derivatives of the equation of motion with a finite difference scheme and

In this work, we study the influences of environmental temperature variation on the static and dynamic behaviours of cables, and we develop a very accurate method for identifying the tension of a cable while considering environmental temperature fluctuation. The dynamic equation of a cable that includes the sag effect, the inclination angle and thermal fluctuations is derived, and the numerical solution

The present article deals with the development and validation of a hybrid finite element-statistical energy analysis (FE-SEA) formulation employed to obtain the ensemble-average of the time-averaged vibrational energy response of dynamic systems with nonlinear joints. The proposed FE-SEA formulation is validated via a nonlinear stochastic benchmark model. The theoretical formulation related to the

In this study, a first attempt is made to develop an up-to-date symplectic superposition method for some new analytic free vibration solutions of side-cracked rectangular thin plates that were not obtained by conventional semi-inverse methods. In contrast with the classical Lagrangian system and Euclidean space, the present method is implemented within the Hamiltonian-system framework and symplectic

Identification of elastic and damping properties is a challenge for fabrication of composite materials, which can have complex shapes. A new approach based on the Force Analysis Technique was developed to identify structural parameters from local equation of motion. For structures with known analytical models, this method gave good results. This work presents a similar approach to extend the previous

This paper presents a sensitivity and parametric study of the sound generation at the non-tortuous and wall-normal permeable trailing edge of an aerofoil. Design parameters for the porous properties include the porosity, pore-size and porous-coverage. For a combination of large pore-size, small porosity and large porous-coverage, wake vortex shedding is likely to be triggered, and either sharp tone

Similitude laws in vibro-acoustics are potentially interesting to extrapolate measurements performed on small structures to the response of larger structures. This paper examines similitude laws for the vibroacoustic response of flat orthotropic flexural rectangular panels radiating sound in a semi-infinite light fluid medium. The scaling parameters considered are the panel size and thickness, its

An adaptive extended Kalman filter (EKF) with two computation modes is proposed for system estimation of civil engineering structures under seismic excitations. The KF, in general, requires the process noise covariance matrix, which defines the uncertainty of the system model used in the filter, to be set appropriately. However, process noise is usually not known in practice, and tuning process noise

This paper investigates a passive self-tuning piezoelectric energy harvester based on a beam-slider structure. The hardening nonlinearity is imparted to the system by two repulsive magnets to achieve broad bandwidth. The slider on the slightly tilted cantilever beam can automatically move along the beam to destabilize the low-energy orbit and track the high-energy orbit. The results of simulation and

Low-frequency vibration isolation is essential for safety, accuracy and stability in various engineering areas. Traditional methods are generally limited to the adjustment of vibration bandwidth and frequency, so broadband tunability is challenging in practical low-frequency isolation applications. This paper proposed a stiffness-mass-coding metamaterial (SMCM) to achieve broadband tunability for low-frequency

Dirac point, the cornerstone of topological insulators, has been attracting ever-increasing attention due to its extraordinary properties. In this paper, a bottom-up topology optimization approach is established to systematically design the acoustic Dirac cones with customized double, triple and quadruple degeneracies at different wavelength scales. Using the proposed methodology, novel square-symmetric

In this paper, a novel reduction method for planar flexible mechanisms based on global flexible modes is proposed. Using the framework provided by the finite-element floating frame of reference formulation (FE-FFRF), the global flexible modes of a planar mechanism are derived from the linearized modal equations of motion at a given linearization point. The global flexible modes are consistent with

Cavitation detection is important in ensuring the reliability of fluid machinery, such as pumps. Vibration signal analysis is widely accepted as an effective tool in condition monitoring and fault diagnosis due to its ability to obtain substantial information and convenience of sensor arrangement. However, cavitation characterization based on vibration measurement is challenging because of the complicated

Passive health monitoring in real time is an effective approach to ensure the integrity and safety of aircraft composite structures. A two-step method based on a parameterized laminate model is proposed as a way to locate acoustic sources for laminates with stiffeners: calibration and monitoring, which requires neither prior knowledge of material parameters nor a large number of training samples. In

Post-buckled beams have been the basic elements of many mechanical devices used for energy harvesting, low-frequency vibration isolation, etc. This paper focuses on the theoretical analysis of nonlinear bending and forced vibration of the post-buckled sandwich beams with graphene reinforced composites (GRC) face sheets. It is assumed that the graphene nanoplatelets are directional in the beam's length

Conventional model updating methods are based on frequency response function (FRF) and/or modal parameter estimates obtained from freely suspended, or sometimes rigidly constrained, sub-structures. These idealised boundary conditions are however often difficult to realise in a practical scenario. Furthermore, they are in conflict with the requirement that the sub-structure should also be measured whilst

This study proposes a new solution to control low-frequency noise in acoustic duct. The control device is in the shape of a Helmholtz resonator combined with a tensioned membrane in the air cavity, referred to as a membrane resonator. The membrane resonator is connected to the main waveguide through two necks. A theoretical model is developed to evaluate its acoustic performance when attached to a

Acoustic-entropy waves are considered as linear, compressive perturbations of a non-dissipative non-homentropic uniform flow. The acoustic-entropy wave equation for the pressure satisfies a modified convected wave equation with non-uniform sound speed. In the case of plane flow with a linear entropy shear profile the exact solution is obtained in terms of Bessel functions of an exponential variable

This paper presents algorithms to compute eigenvalues, eigenvectors and frequency response matrix of a linear structure with non-proportional damping. The method is based on derivatives of repeated or unrepeated complex eigenvalues and complex eigenvectors . Since eigenvectors are not unique for a repeated eigenvalue, a special algorithm is developed to select the correct eigenvector for a given non-proportional

It is important to conduct structural damage detection using only output time histories of structures under ambient excitations. Recently, an approach has been proposed for structural damage detection under ambient excitations using the synthesis of cross-correlation functions of partial structural responses and the extended Kalman filter (EKF). However, structural mass is assumed known in this approach

Impedance eduction experiments on acoustic liners with flow have systematically shown the educed impedance depending on the direction of the incident wave. Recent attempts to model this dependence include impedance boundary conditions with an additional degree of freedom. In this case, both upstream and downstream acoustic sources must be used to educe both the liner impedance and the extra degree

Aerodynamic noise generated by aerofoil-vortex interaction has widely been studied in the past where the primary noise source mechanism is the scattering of the vortex at the leading edge (LE) of the aerofoil. In this paper the secondary source mechanism – the subsequent vortical scattering at the trailing edge (TE) – is investigated in detail, which shows that this mechanism is essentially due to

Current wind turbine modelling packages mainly adopt a complex methodology in which aerodynamic forces are coupled with the motion of the wind turbine components at every time step. This can result in long simulation run times, detrimental for the large number of simulations required for fatigue or reliability analyses. This contribution presents an efficient wind turbine modelling methodology based

This discussion gives counsels on the paper “Eulerian models of the rotating flexible wheelset for high frequency railway dynamics", published in Journal of Sound and Vibration 449 (2019) 300-314. Specifically, it raises concerns about Eq. (55) and the predicted natural frequencies of the rotating wheelset. In the end of this discussion, the nonrotating natural frequency, rotating natural frequency

This paper describes the control design of an active horizontal seat suspension with an electromagnetic actuator. First, physical and mathematical models of an active vibration reduction system with a seated human body are established. Then, a novel control strategy for the permanent magnet synchronous motor is developed to improve the vibro-isolation properties of the horizontal seat suspension. A

Hysteretic damping model is consistent with experiment results within a wide frequency range, and is usually employed in structural dynamic analysis. However, hysteretic damping time-domain model has the two shortcomings, namely damped natural frequency increases with the increase of structural loss factor and the vibration response is non-causal. In order to overcome the two shortcomings, an improved

The vibration and sound properties of a type of metamaterial sandwich panels are investigated in this paper. The metamaterial sandwich panels consisting of a host sandwich panel and periodically attached resonant units are designed. Both the panels with and without damping are considered. Via the comparison of metamaterial and bare panels, the effects of the periodic design on wave propagation, vibration

The interaction of a wing/blade profile with turbulent inflow is one of the main sources of sound generation in turbomachines. There are already several noise prediction methodologies available which either appear not to account for the influence of geometrical and flow parameters on noise generation or have been able to account for a remarkably limited extent due to the requirement of high-performance

The video of vibrating structure provides dense quantitative continuous spatial information that is harnessed using various computer vision algorithms in the past decade. Computer vision algorithms that implement sparse optical flow, have been successful in acquiring the Lagrangian representation of motion. Such vision-based measurement already proved its potential in replacing the need for a contact

The nonlinear interaction of a dual-frequency Lamb wave with a breathing edge-crack leads to the generation of frequency sidebands in the response spectrum; a phenomenon referred to as the nonlinear frequency mixing. These sidebands appear at algebraic combinations of the two central interrogation frequencies and can serve as a reliable precursor to the existence of an incipient damage. In this paper

Accurate and efficient models of the dynamics of a laminated transformer core structure are essential for the design of quiet power transformers. However, owing to the complex structure of the transformer core, the dynamic response of the core has not yet been accurately modelled. In this paper, the strains in different laminas and the strain differences between them are included as key parameters

Non-Synchronous-Vibration (NSV) in high-speed turbomachinery compressors is an aeroelastic phenomenon which can have devastating consequences, including loss of rotor blades. Despite extensive research over the past two decades its underlying mechanisms are not yet understood. This paper aims to explain the physical mechanisms causing NSV in a modern transonic compressor rotor. Referring to previous

Identification of regions on a vibrating structure which radiate energy to the far field is critical in many areas of engineering. Non-negative intensity is a means to visualize contributions of local surface regions to sound power from vibrating structures. Whilst the non-negative intensity has been used for structures under deterministic excitation due to structural forces or harmonic incident acoustic

In urban communities, parallel barriers are commonly erected for controlling environmental noise such as traffic and construction noise. However, owing to the multiple reflections between the parallel barriers, their performance may be worse than that of a single barrier. To improve the performance of parallel barriers, a small piece of flush-mounted panel backed by a slender cavity in an otherwise

This study investigates psychoacoustic aspects of the noise of multi-rotor type unmanned aerial vehicles (UAV). Two psychoacoustic experiments were performed for a dual purpose: to examine the difference of annoyance induced by the noise from three types of UAVs and a civil aircraft and also to identify the acoustic factors influencing the annoyance from UAV noise. In the first experiment, the annoyance

Depending on its mounting orientation, the rotational piezoelectric harvester can be subjected to the centrifugal softening or stiffening effects, which may pose a positive or negative influence on the energy harvesting performance. This paper firstly presents the comprehensive comparison of the centrifugal softening and stiffening harvesters with a unified dimensionless analytical model. The analytical

To determine the radiated sound power of an underwater sound source below the first resonance frequency in a non-anechoic tank, a sound intensity measurement technique based on separating near-field acoustic energy flux is proposed. A theoretical analysis of vibration and acoustic radiation of underwater structures shows that the variation in the radiation impedance of the sound source in the given

Rotor systems play a vital role in processing machinery, aero engines, and wind turbines. Since moving parts can be worn during operation, the system performance is variable throughout the service period actually, especially for the rotor system with various defects. Unfortunately, the existing models about bearing defects are established neglecting the changes of dynamic behaviors, which may not reflect

Many issues of concern in the railway industry are fundamentally caused by dynamic wheel-rail interaction. To deal with these issues, the characteristics of the interaction must be accurately predicted and fully understood; this becomes even more challenging when the train speed is high. Although much research has dealt with wheel-rail interaction, some aspects related to high speed trains still need

This paper presents a novel time-domain method for non-stationary random vibration analysis of linear structures. Specifically, using the well-known spectral representation method, the stochastic excitation process is first decomposed into a set of trigonometric basis functions (TBFs) modulated by a series of orthogonal basis random variables (BRVs). Next, each TBF is used as a deterministic excitation

This paper is concerned with a theoretical and experimental investigation into the pressure spectrum in a pressurised fluid-filled pipe containing a leak. A general theoretical framework for predicting the leak noise spectrum is derived. A simple relationship is developed between the leak noise pressure spectrum in the pipe and the velocity spectrum at the leak orifice. Measurements of the leak noise

This study presents a strategy of vibration suppression of a beam when multiple resonant frequencies of the structure are excited. The methodology operates on the ability of local resonators attached to the beam to create frequency ranges corresponding to locally resonant bandgaps in which the vibration of the beam is attenuated. This study discusses the mechanism of multiple bandgap formation by first

A full-scale quantitative diagnostic method is proposed in this study for inner-race fault-size estimation of ball bearings. The fault size is generally estimated using time interval between double impacts if the fault size is smaller than ball angular spacing. This method may be inapplicable when fault sizes become larger than integral multiples of ball angular spacing, which means they have the same

Effective incipient fault detection requires a method that can separate fault signatures under constant and time-varying operating conditions. In this work, we focus on improving informative frequency band identification methods for applications under constant and time-varying operating conditions. Many automatic band selection techniques exist and have proven effective under constant speed and load

When a primary actuator excites the centre point of a rectangular panel speaker, the reflected bending waves at the edges of the plate are superposed with the incident wave and other reflected waves, and this results in a strong modal behaviour. Accordingly, the radiated sound spectrum possesses strong amplitude fluctuations, which results in a poor sound quality. This paper considers via simulations

In the present paper, the damper force characteristics of dampers using a particle assemblage instead of oil have been reported. A separated dual-chamber single-rod-type damper using an elastomer particle assemblage was produced. The effects of the packing ratio of the particles, the vibration frequency, and the materials of the particles on the damper force characteristics of the damper with elastomer

This paper presents a theoretical study on the modelling and active control of bending waves propagating in an orthotropic rectangular panel. The main objectives are to clarify the characteristics of the wave dynamics of an orthotropic rectangular panel and to propose the feedforward control of wave propagation based on a transfer matrix method. As a result of the numerical investigation of the wave

We show how spectral submanifold (SSM) theory can be used to extract forced-response curves without any numerical simulation in high-degree-of-freedom, periodically forced mechanical systems. We use multivariate recurrence relations to construct the SSMs, achieving a major speed-up relative to earlier autonomous SSM algorithms. The increase in computational efficiency promises to close the current

Minimum quantity lubrication (MQL) is an efficient and sustainable technology, which has been considered to be an option of conventional flood cutting process. Even though MQL provides green solution for the cooling and lubrication function during machining, it brings about unendurable aeroacoustic jet noise from the high velocity spray. The acoustic pollution has seriously affected the operator's

Entropy noise is produced when temperature fluctuations (entropy spots) are accelerated by the mean flow, through a nozzle or a turbine stage for instance. When it propagates outside the engine it contributes to community noise and may generate thermoacoustic instabilities when reflected back towards the combustor, hence the need for its modelling. Among all the inviscid models proposed in the literature

The low inherent damping for thin-walled structures often leads to prominent vibrational problem. This paper proposes a friction patch to enhance the damping for thin-walled structures. The damping patch is simple in structure and easy to adjust the normal preload. Based on a beam finite element model, parameters including geometry, stiffness and position of the proposed damper are optimized numerically