The goal of this paper is to present a comparative study on the principal features and scaling properties of time-harmonic vibration energy harvesting with electromagnetic and piezoelectric reactive transducers. The study is organised around two prototype reactive harvesters having one end connected to ground. The two harvesters are composed respectively by a coil-magnet and a composite piezoelectric

In this article, we offer a fast calculation method for the dispersive properties of three-dimensional micro-structured solids with one-dimensional and two-dimensional translation symmetry. We review mathematical methods to obtain the complex dispersion diagram for such structures (i.e. the Bloch vector as a function of frequency). This can be done by solving a Bloch-Floquet eigenvalue problem which

The energy dissipation in assembled metal structures is mainly related to various physical phenomena – usually modelled as dry friction – on the contact surfaces. However, the reliable numerical modelling of assemblies is a challenging task due to the complexity of the contact mechanisms. To fit the models to experimental results, it is beneficial if the material damping can be separated from the contact

The article analyses two potential metamaterial designs, the metafoundation and the metabarrier, capable to attenuate seismic waves impact on buildings or structural components in a frequency band between 3.5 and 8 Hz. The metafoundation serves the dual purpose of reducing the seismic response and supporting the superstructure. Conversely the metabarrier surrounds and shields the structure from incoming

A high-speed rotating rotor system mounted on an aircraft is inevitably induced by parametric excitations, inertial forces and gyroscopic moments caused by maneuvering flights. With the increase of maneuverability, this effect becomes more significant, which may lead to severe vibrations and even abnormal operation. Using Lagrange's principle, equations of motion for a squeeze film damped rotor system

Vibration analysis of rods that are subjected to rotation is presented. It is shown that flexural-flexural, longitudinal-flexural and torsional-flexural wave coupling occur due to the Coriolis Effect. First, we carried out our analysis for thin rods where the wavelength is much larger than the radius. It is shown that the wavenumbers change due to the Coriolis Effect. Then, we characterize the 3-D

Pipes have multiple applications in daily life and they are subjected to different types of defects. Nonlinear guided wave has attracted significant attention in detecting microstructural change at early stage of material deterioration. Extensive research using wave mixing with different wave modes has focused on plate-like structures. However, limited experimental studies have been conducted on the

In this study, a new optimal control law associated with sliding mode control is developed based on basis of the Bolza-Meyer criterion. The salient characteristic of the proposed controller is to have gains adjustability, where the gain values can be larger than one. This leads to enhancing control system performances with a given cost function. It should be pointed out that conventional optimal controllers

Flexible cylinder structures, such as top-tensioned risers (TTRs) and tethers of tension leg platforms (TLPs), display complicated dynamic characteristics under the combined excitation of vortex-induced vibration (VIV) and time-varying axial tension, which causes serious fatigue damage and is a major concern in ocean engineering fields. In this paper, model tests were conducted on a flexible cylinder

The perforated components are widely used in the intake and exhaust mufflers. The coupling between instable shear layer and acoustic fluctuation has a significant influence on the acoustic impedance of perforated components. To obtain practical and precise acoustic impedance of perforated plates in the presence of grazing flow, the three-dimensional (3D) time-domain computational fluid dynamics (CFD)

This paper defines a criterion called the overall efficiency (OE) for evaluating the efficiency of acoustic sources. In practice, the conventional efficiency (CE), is not capable of giving a comprehensive overview of the power consumption, especially in the connected amplifier drivers. The reason for this is that the CE is defined based on the nominal input electrical power. The nominal input electrical

Rolling bearing skidding can seriously affect the service life and aggravate the performance degradation process of rolling bearings. Once skidding occurs under variable speed and load, the movement of rolling elements relative to the inner and outer rings is no longer strictly pure rolling. As a result, the speed of rolling bearing cage becomes more complex. In this case, fault signature extraction

Parts energy of nonlinear system such as the closed detached response (CDR), primary response (PR), closed detached voltage (CDV), and primary voltage (PV) are resultant of the resonance response interaction and represent their corresponding dynamic characteristics. In this paper, we proposed a promising novel device by integrating a lever-type nonlinear energy sink (LNES) and a levitation magnetoelectric

As a typical inverse problem, impact force identification tends to be a challenge owing to its ill-posedness. Recently, the sparse characteristic of the impact force in time domain are taken into consideration to convert the ill-posed problem into a sparse recovery task. The classic way to obtain sparse approximate solutions of impact force is to use the L1-norm regularization. However, underestimating

Underplatform dampers (UPD) represent an effective way to limit blade vibration in turbomachinery via frictional energy dissipation, leading to a wide range of applications. The design of an effective and reliable UPD is highly challenging, due to the inherently nonlinear nature of the contact forces, the associated computational cost for high fidelity simulation, and the manufacturing uncertainties

This paper examines the possibility of controlling jet-wing interaction noise by plasma actuators. The low-frequency part of the jet installation noise is considered as produced by the diffraction of instability wave packets developing in the jet shear layer. Thus, the main idea of noise control comes to the attempt to reduce the amplitude of these wave packets near the wing trailing edge. A simplified

Particle dampers (PDs) are becoming a popular alternative to conventional damping devices due to their simple design and their ability to dissipate energy over a wide frequency range. The energy dissipation in PDs takes place due to relative motion between solid particles within the PD enclosure. The degree of relative motion depends on various parameters, especially it is highly sensitive to vibration

The modelling of sound propagation in the ocean by the solution of mode parabolic equations is discussed. Mode parabolic equations can be obtained as the one-way approximation to horizontal refraction equations for modal amplitudes. Their wide-angle capabilities depend on the order of the Padé approximation of the involved pseudo-differential operators. Various aspects of numerical solution methods

A general class of acoustic impedance conditions is considered where a linear dependence is assumed between the fluid velocity and the surface traction. In addition to the classical impedance relating pressure and normal velocity, this generalised definition of the impedance includes effects such as the friction along the surface as well as coupling between the normal velocity and the tangential force

The Council of European Aerospace Societies (CEAS) Aeroacoustics Specialists Committee (ASC) supports and promotes the interests of the scientific and industrial aeroacoustics community on a European scale and European aeronautics activities internationally. In this context, “aeroacoustics” encompasses all aerospace acoustics and related areas. Each year the committee highlights some of the research

In this paper we study the reconstruction of the acoustic field on an arbitrarily shaped vibrating surface using the Time domain Boundary Element Method (TBEM) based Near-field Acoustic Holography technique, or Inverse TBEM (ITBEM). The main focus of our study is the indirect formulation known as the single layer representation and the impact of the dicretization using higher order polynomial basis

This paper presents a theoretical examination of wave propagation in a cylindrical duct loaded with an array of closely spaced flush-mounted annular resonators forming a simple reactive silencer. A semi-analytical mathematical model is proposed considering higher evanescent modes in the duct and plane-wave- and first transverse mode in annular resonators. Viscothermal losses in annular resonators are

Analytical mode decomposition (AMD) is one of dynamic response decomposition methods. However, the discretization of the dynamic responses and the selection of the bisecting frequency may cause the failure of the decomposition. In this study, the discrete analytical mode decomposition (DAMD) is investigated. In addition, an automatic bisecting frequency selection algorithm based on the auto-regressive

This paper presents a new method to compute the sound radiation emanating from a thin plate structure due to complex inputs that include normal force and in-plane bending moments. A set of new formulas for the sound radiation of baffled and unbaffled plates are derived by substituting the moment components of the plates with the equivalent couples using finite difference analysis. This approach allows

Vibration analysis of nominally axisymmetric plate structures with either imperfections or geometric asymmetries due to practical motivations is of interest in designing and developing some mechanical structures. Semi-analytical methods to model such structures suffer from either choosing inappropriate admissible functions or both plausible convergence issues and additional computations owing to employing

Spatially dense vibration measurement can be obtained by use of a continuously scanning laser Doppler vibrometer (CSLDV) system that sweeps its laser spot along a scan path. For a linear, time-invariant, viscously damped structure undergoing free vibration, a type of vibration shapes called free response shapes was defined and obtained by the authors using a CSLDV system with the demodulation method

Modal expansion techniques are typically used to expand the experimental modal displacements at sensor positions to all unmeasured degrees of freedom. Since in most cases, sensors can be attached only at limited locations in a structure, an expansion is essential to determine mode shapes, strains, stresses, etc. throughout the structure which can be used for structural health monitoring. Conventional

This paper presents the results of investigations into the applicability of the Reynolds equation for analyzing near field levitation (NFL) phenomena. Two separate approaches were developed, experimentally verified, and applied to meet the research objective. One was based on the Reynolds equation and the other was based on general conservation equations for fluid flow solved using computational fluid

Determination of the model order is a challenging problem in system identification, especially in output-only or operational modal identification where some modes are weakly excited. Although existing methods such as the stabilization diagram method (spectral information) are effective, they do not scale to high-dimensional data, which is usually needed for high-fidelity characterization of structural

Topology optimization for the shape of noise barrier taking into account the aeroacoustic sound source is presented based on Lighthill's acoustic analogy approach. In the previous acoustic topology optimization based on the Helmholtz equation, only simple acoustic sound sources were taken into account. To overcome this limitation, the present aeroacoustic topology optimization is performed using Lighthill's

Dynamic response of beams on elastic foundations is of great theoretical significance in the field of engineering. Galerkin truncation method is the most commonly used powerful method to study the vibration of these structures. The number of truncation terms affects the convergence of the analysis and determines the accuracy of the dynamic responses. However, there is still no basis for how to choose

In order to identify quickly and accurately the load state of structures in some complex environments, a non-iterative inversion method based on finite element method and Newmark method is proposed. By exploring the relationship between measurement data and loads that need to be identified, the error function is established. Based on the least square method and the matrix decomposition scheme, the

Severe vibrations and sound production can occur in dry gas flow through corrugated pipes. The addition of very small amounts of liquid to the dry gas flow potentially mitigates these flow-induced vibrations (FIVs) and noise. The different mechanisms behind this whistling mitigation are studied in this work, where acoustic measurements are combined with flow visualization and droplet sizing. Different

Metamaterials represent a new trend in the field of seismic engineering. Their capacity to attenuate waves at the superstructure level is highly desirable and sought after in recent years. One of their main drawbacks to date, is the excessive size of the necessary resonators and, consequently, the uneconomic design they require. In order to tackle this problem, we apply the concept of negative stiffness

This paper presents a one-dimensional thermoacoustic model for a dump combustor in terms of two acoustic impedances just before and after a flame/area-expansion location. A key findings is that, as long as combustion instability is concerned, those two impedances fully crystallize the geometry of a combustor, steady operating conditions and inlet-outlet boundary conditions. From this impedance-based

Direct numerical simulations (DNS) based on advanced computational aeroacoustic (CAA) methods are conducted to study the acoustic impedance of a uniformly distributed multi-slit liner under grazing incident sound waves at different frequencies and sound pressure levels (SPL), in the absence of mean-flow. The liner consists of a series of fifteen identical slit Helmholtz resonators. Numerical results

This paper proposes a novel method to detect and localize disturbances in dynamical systems using non-collocated acoustic arrays by processing their data such that established artificial intelligence techniques can be used. Methods are proposed to compress time-domain based separate microphone data into frequency-domain based images. Furthermore, a data augmentation solution is given to significantly

This work presents benchmark examples related to the modelling of sound absorbing porous media with rigid frame based on the periodic geometry of their microstructures. To this end, rigorous mathematical derivations are recalled to provide all necessary equations, useful relations, and formulas for the so-called direct multi-scale computations, as well as for the hybrid multi-scale calculations based

Torsional vibrations due to stick-slip phenomena may yield large variations in the drilling angular velocity which in turn may cause failures in the drilling process such as damage in drill pipes, due to large torsional deformation, and in drill bits, due to large angular velocities. It has been shown that standard linear proportional-integral (PI) control laws, in which the control torque is proportional

Acoustic resonance induced by vortex shedding from a flat plate in a flow duct has been widely concerned in a variety of engineering applications. However, the unsteady vortex sound interaction is still an open issue. A nonlinear physical model is established based on three meshless sub-models, including the discrete vortex method (DVM) for vortex shedding, the vortex sound theory for sound radiation

This study used the wave based method (WBM) to investigate the optimum layout of an absorbing material on a vibrating surface. The structural dynamic behavior was examined using the finite element model, and the acoustic response was computed using the WBM. The thickness of the absorbing material on each structural element was considered as the design variable. The sensitivity of the acoustic response

Vibroacoustical problems are sometimes treated by modal analyis, which has been applied to air-filled shells. It is suggested to use the method for various types of liquid-structure interaction systems. Potential applications are water or oil hydraulic pipelines and heavy machinery actuated by fluid power. Modal testing of such systems should be accompanied by sensor placement strategies, test data

Low frequency sound attenuation is a challenging task, because of the severe mass, stiffness and volume constraints on the absorbing and/or reflecting barriers. Recently, significant improvements in low frequency sound attenuation has been achieved by introducing the acoustic metafoam concept, which combines the mechanism of conventional acoustic foams - high viscothermal dissipation - with the working

A driveline model with 6° of freedom is established, the detailed structure of a clutch with three stages nonlinear stiffness and damping is presented and modeled, and the model for a driveline with unloaded gears and the nonlinear clutch is proposed. Taking the angular acceleration amplitude of the input shaft for a transmission as an evaluation index, the influence of model parameters on the angular

The vibro-acoustic behavior of a semi-submerged finite cylindrical shell is studied theoretically and experimentally. An analytical form of the vibro-acoustic coupling equation is developed using the wavenumber transformation and separation of variables for the sound pressure and the mode expansion for the shell's motion. The far-field radiation sound pressure is derived by utilizing the stationary-phase

The role that acoustic reflections from duct boundaries play in aeroengine fan flutter is theoretically investigated. To make a systematic parametric study attainable, a three-dimensional semi-analytical approach is employed. Based on the transfer element method combined with a boundary integral equation method, this approach effectively captures the acoustic coupling effect of an annular rotor undergoing

Wave based method is a numerical technique to predict steady-state vibration and solve vibroacoustic problems. It is a deterministic approach that is acknowledged to be more efficient than the element based methods in the mid-frequency range. The wave based method for plates with prescribed boundary conditions has been proposed and verified for the ideal constraint cases such as clamped, free and simply

Train wheelset is an important part of the train. After long-time and high load working, fatigue damage will appear. Then the micro-cracks will form and expand into macro cracks, which may cause a serious accident. Therefore, it is necessary to study the fatigue damage detection methods for train wheelset. Fatigue damage will cause nonlinear effects. The Nonlinear Output Frequency Response Functions

Hybrid methods for trailing edge noise prediction are applied to a NACA 6512-63 airfoil at zero angle of attack embedded in the actual narrow stream of the Siegen open-jet anechoic wind-tunnel. Incompressible large-eddy simulations (LES) of the airfoil trailing-edge flow yield the noise sources, and different analytical acoustic analogies then predict the acoustic far-field pressure. The chord-based

This paper deals with the development of a three-dimensional (3D) array for imaging aeraocoustic sources in the open section of an anechoic wind-tunnel, together with the associated signal processing techniques, and presents an application to the case of a wall-mounted airfoil in a flow. The 3D antenna is made of 256 digital Micro ElectroMechanical Systems (MEMS) microphones, arranged into three nearly

It has been suggested that by mounting the jet engines of an aircraft over the wings, the wings would act as a noise shield. In 2015, Zaman et al. (J. Fluid Mech. vol. 779 (2015) 751–775) reported the results of their experiment intended to explore the feasibility of such an engine-wing configuration. Unexpectedly, they found that tones were emitted from their scaled laboratory experiment. They identified

With an explosion of the internet of things (IoT), vibration energy harvesting provides an environmentally friendly solution to replace consumable batteries in powering IoT wireless sensors. Yet, when implemented in practice, ambient vibration input energy is much less periodic than assumptions adopted in previous studies. This becomes especially important given that asymmetries are inevitable in nonlinear

The dynamic instability of a thin-walled carbon-fibre reinforced composite cylindrical shell is studied. The analysis is performed with the Finite Element code, ABAQUS, estimating the dynamic buckling load using the Budiansky–Roth criterion. The influence of the following factors on the dynamic behaviour of the shell is analysed: the shape of pulse loading, the initial geometric imperfection and the

With increasing demands for better image quality, the aperture and size of a space telescope are becoming larger, and stability requirements are becoming more stringent. To reduce the influence of micro-vibrations on image quality from telescope platform, isolating vibrations of the whole telescope optical payload must be taken into account. To this end, a method to design and optimize a vibration

The prediction of vibrations in an unbounded medium and their interaction with structures on the ground surface or within the soil requires adequate approaches. Therefore the numerical methods addressing the dynamic Soil Structure Interaction (SSI) have to account for both, the infinite extent of the soil by satisfying the radiation condition for the wave propagation towards infinity and the detailed