This paper is dedicated to an experimental implementation of active anechoicity control illustrating previous theoretical work. The aim of this experimental is to cancel the pressure scattered by the single rigid wall of a semi-anechoic room, turning the latter into a fully anechoic one over a given frequency range. The proposed method is presented in two steps: estimation of the scattered pressure

Quasi-periodic structures, as found in multi-span bridges, multi-bay and multi-storey buildings, are often characterized by a high modal density, even at low frequencies. This clustering of modes poses challenges in operational modal analysis, as well as in finite element model updating, where a pairing of experimental and numerically predicted modes is required. To overcome these difficulties, an

Conventional displacement sensing techniques (e.g., laser, linear variable differential transformer) have been widely used in structural health monitoring in the past two decades. Though these techniques are capable of measuring displacement time histories with high accuracy, distinct shortcoming remains such as point-to-point contact sensing which limits its applicability in real-world problems. Video

Few studies have successfully achieved high-efficiency energy harvesting in ultralow-frequency rotational motion where the rotational frequency is less than 2 Hz (120 rpm). In order to solve this challenge, this paper proposes a novel energy harvester with the centrifugal softening effect (CSE) and the magnet-induced nonlinearity. In a rotational coordinate system, the corresponding theoretical model

This article focuses on characterizing the nonlinear nature of the piezoelectric actuators’ ‘33’-electromechanical coupling and ‘3’-directional elasticity. Vibrations of a cantilever aluminum beam, attached with a pair of d33-mode surface bondable multilayer actuators, were studied to construct the required nonlinear constitutive equation. As both elasticity and electromechanical coupling were of equal

An approximate method is proposed for the strong nonlinear and non-homogenous boundary value problem of a pipe conveying fluid for the first time. Usually, the boundary value is satisfied transcendentally in the truncation processing acting on the partial differential governing equation. However, the nonlinear and non-homogenous boundary disables it. To overcome this problem, the method of modal correction

Acoustic mode detection is attached great significance for providing guidance to noise reduction design of commercial aero-engine with high-bypass ratio. Compressive sampling method has been creatively employed in this field due to its notable performance on reducing the number of microphones in acoustic mode measurements. However, the classical ℓ1-norm regularized compressive sampling model tends

This paper investigates the use of an augmented pendulum absorber for damping of tower vibrations in monopile-supported wind turbines. A shunted electromagnetic transducer is proposed to replace the classic viscous dashpot for pendulum absorbers, in order to improve performance and durability of the absorber. A series RCL (resistive-capacitative-inductive) network is designed as the supplemental shunt

This paper proposes a novel nonlinear dynamical system identification method based on the sparse regression algorithm and the separable least squares method. To effectively avoid solving the second derivative of the displacement signal and reduce the effect of noise, the Duhamel's integral is adopted to represent the dynamic relationship between the system input and output. In the expression form of

This paper presents new spectra of responses and control force for an active base-isolated building that uses the equivalent-input-disturbance (EID) approach for active structural control. The EID approach estimates the effect of disturbances and uses it to suppress building vibrations. This system plugs an EID estimator into a conventional state-feedback control system. Note that these kinds of d

Brake squeal is a major issue for car manufacturers as it is the reason for the return of many vehicles to customer services, representing high costs for the companies. To meet customer’s expectations, squeal must be accurately predicted during the design process. In the context of the automotive industry, squeal usually refers to friction-induced vibrations that generate noise. The main methodology

This study develops the dynamic condensation approach to improve the computational efficiency of response-based finite element model updating of large-scale structures. Using the dynamic condensation approach, a small number of degrees of freedom (DOFs) are selected as master DOFs. A transformation matrix is then derived to relate the master DOFs to the total DOFs. The global vibration equation is

Equivalent circuit analysis is a powerful tool for analysing acoustic systems where a lumped element model is valid. These equivalent circuits allow an overall impedance of the structure to be estimated which facilitates predictions of the reflectivity, transmissibility and/or absorptivity of the system. Complex acoustic systems are represented by non-planar equivalent circuits which are challenging

The effects of high-frequency parametric excitation on the principal parametric resonance of a nonlinear beam are studied both theoretically and experimentally. Only the first mode of vibration under simultaneous slow-fast parametric excitation is considered for investigation. The method of direct partition of motion yields slow dynamics of the system which is further analyzed by multiple time scale

Three compressible-flow direct numerical simulations (DNS) of aerofoils were conducted at a chord based Reynolds number of Rec=150,000: a Controlled-Diffusion (CD) aerofoil at two incidences and an untripped NACA 6512-63 aerofoil at 0∘ angle of attack (AoA). The aim of the simulations was to help improve the understanding of the generation mechanisms of aerofoil self-noise. To this end, the time-averaged

In this paper, the problem of non-linear vibrations of an articulated column subjected to two loads was considered. The first load is axial compression associated with the action of the mass element. The second is the heat load in the form of a local heat source. In such a system, the problem analysis was divided into two parts. The first illustrates the influence of temperature on the physical and

Under certain conditions, the dynamics of a nonlinear mechanical system can be represented by a single nonlinear modal oscillator. This holds, in particular, under external excitation near primary resonance or under self-excitation by negative damping of the respective mode. The properties of the modal oscillator can be determined by computational or experimental nonlinear modal analysis. The simplification

This paper presents a novel spectral element method to predict the electromechanical dynamics of panels having arbitrary geometries and multiple surface-bonded piezo-patches. The boundary value problem is derived following kinematic equations based on first order shear deformation and the generalized Hamilton’s principle. To solve the derived boundary value problem, a spectral element method based

A general methodology to simulate acoustic propagation in ducts with extended-reacting liners in the time domain is presented, including a generic perforated sheet on the air-material interface. The Linearized Euler Equations (LEE) with a mean flow profile are solved in the duct and the linearized equations on an equivalent fluid are solved in the liner material. The auxiliary differential equation

The inherent weakness of conventional panel speakers is the inevitable multi-modal vibration behavior, resulting in severe fluctuation in the radiated sound spectrum, which is detrimental to the sound quality. A panel speaker that is actively controlled by array actuators at the panel edges has been proposed as a solution to the problem, but the increased cost and complexity due to a large number of

Gas Foil Bearings (GFBs) possess significant potential for oil-free and environmentally friendly support of high-speed rotating machinery in a wide range of applications. Advances in GFB design and solid lubricants have significantly improved the capabilities of GFBs, but application in heavier machinery still leaves many technical limitations to be overcome. A possible path is through hybridization

The numerical prediction of vibration in buildings due to underground railways involves modelling many physical phenomena. Not least of these is the dynamic soil-structure interaction that exists between the various elements of the system. The majority of existing models assume that the interaction between the railway tunnel and the building’s foundation is negligible, with the two sub-systems behaving

A linear model is developed for a hanging pipe aspirating fluid with internal flow velocity Ui, flowing up the pipe from its lower end, and also subjected to an external flow of velocity Uo flowing down from the upper end of the annulus formed between the pipe and a relatively shorter rigid outer tube; both the tube and pipe are cantilevered from their top ends. In this model, the pipe is modelled

One way to enhance the performance of vibration control with piezoelectric shunt is to use a negative capacitance in the shunt circuit. This component is very effective and provides good results in terms of attenuation improvement without significantly increasing the complexity of the shunt network. However, negative capacitances are built using operational amplifiers and, in some applications, the

Low-order acoustic network models, treating the complex combustor geometry as a network of simple geometry elements, are typically used to analyse circumferential combustion instabilities in annular combustion chambers. These elements are typically assumed to have uniform cross-sectional surface area and average radius so that the analytical solutions of the acoustic field within them can be directly

Long-time prediction of future states has been challenging in data-driven modeling of nonlinear dynamical systems as the prediction error accumulates over the prediction horizon. One of the potential reasons is the lack of robustness for the data-driven model. In this study we present a recurrent neural network (RNN) framework with an adaptive training strategy to model nonlinear dynamical systems

The most popular strategy to reduce the complexity of flexible multibody systems modeled using the Floating Frame of Reference Formulation (FFRF) is based on reduced-order models (ROM) derived through component modes. In this paper, we propose the use of global modes to build a feasible modal basis of reduction. The global modes are derived from the assembled system and satisfy the reference conditions

In this study, a novel self-tuning adaptive-passive lever-type vibration isolation system for base excitations is described. Due to inertial coupling within the vibration isolation system, an antiresonance frequency is generated, which depends on the amplification ratio of the lever. At this frequency, the instantaneous center of zero velocity of the lever coincides with the hinge that is under the

During operation, a launcher is subjected to severe impact load that can be reduced and controlled by buffers inside the launcher. The present paper proposes a double-layer permanent-magnet axial buffer where the eddy current damper consumes recoil energy from impact load and regulates the displacement, velocity and recoil resistance of the recoiling part. Then the recuperator makes the recoiling part

This paper presents a new data-driven approach for the establishment of empirical models describing turbulent boundary layer wall-pressure spectra. Unlike other models presented in literature, the new models are not derived by extending previously existing ones, but are directly built from a given dataset through symbolic regression using a machine learning algorithm known as Gene Expression Programming

The complexity behind dissipative phenomenon is still a major source of uncertainty in structural dynamics. This phenomenon is usually simplified to a deterministic proportional damping, disregarding the effects of modal coupling in the analysis. In this work, a probabilistic model is developed for non-proportional damping by adding uncertainties globally in the damping operator. The two main hypotheses

This paper is concerned with emergence of novel effects in wave propagation in one-dimensional waveguides, when integrated with periodic nonlocalities. The nonlocalities are introduced by a connectivity superimposed to a conventional waveguide and depicted as a graph with trees and leaves, each with its own periodicity. Merging nonlocality and periodicity notions induces a distinction between homogenous

For a rotating thin-walled cylinder subject to flexural vibration, active control can be applied using surface-mounted actuators and sensors. To achieve acceptable vibration control performance, the dependency of the dynamic behaviour on rotational speed must be accounted for in the control system design, including the selection and positioning of actuators and sensors. A key issue is that the natural

The aim of this work is the development of a model-based methodology for the estimation of lateral track irregularities from measurements from different sensors mounted on an in-service vehicle: a gyroscope to measure wheelset yaw angular velocity, two accelerometers to measure lateral acceleration of the wheelset and bogie frame, and an encoder to obtain forward velocity of the vehicle. The proposed

Virtual prototyping in engineering design rely on modern numerical models of contacting structures with accurate resolution of interface mechanics, which strongly affect the system-level stiffness and energy dissipation due to frictional losses. High-fidelity modeling within the localized interfaces is required to resolve local quantities of interest that may drive design decisions. The high-resolution

Chatter suppression is investigated when time-periodic axial load is applied during the turning process of slender workpieces. The Euler–Bernoulli beam theory is used to construct the mathematical model of the workpiece that is clamped at the chuck and pinned at the tailstock. To improve the stability of the turning process, the workpiece is excited by a periodic compressive force with various waveforms

The study of vibrations of air-backed structures in water is necessary across a range of engineering applications, from naval to civil engineering. Common to these applications is the presence of geometric curvatures in the structure, which are responsible for rich, three-dimensional fluid-structure interactions. Toward a first theoretical understanding of these phenomena, we focus on the vibrations

Solid panels with additional poro-elastic materials are widely used in engineering, mainly for sound insulation. In many cases, the panels are constructed in such a way that they can be idealised to be infinitely long and uniform in one direction, forming a so-called two-and-a-half dimensional (2.5D) structure. Although the 2.5D finite element and boundary element methods (FEM-BEM) are particularly

We discuss high-order adjoint based degenerate perturbation theory of semisimple eigenvalues resulting from nonlinear eigenvalue problems, which are typical of acoustic problems and vibrational analysis. The theory is discussed for a general matrix operator L with no further properties assumed. The unperturbed operator is thus in general non-normal, which requires the use of adjoint methods. The main

We investigate the in-plane vibrations and electromechanical resonance characteristics of non-uniformly polarized rectangular piezoelectric wafers. Non-uniform polarization is represented as a non-uniform electromechanical coupling coefficient using a polarization function. Governing equations are derived for the forced in-plane vibrations of a thin wafer under the assumption of generalized plane stress

It is essential to optimize the position and coverage of damping material to mitigate the vibration and noise in vehicles. Modal strain energy and genetic algorithms are traditionally used for damping material optimization, but these methods do not consider a specific loading position and loading case. Therefore, the optimization results do not include an actual working load case. This paper introduced

This study investigates the mode transition phenomenon in a standing-wave thermoacoustic engine (TAE) by means of computational fluid dynamics (CFD). Firstly, the steady-state responses of the TAE at selected temperature ratios are examined via continuous wavelet transform. The bifurcation diagram and spectral map indicate that, as the temperature ratio increases, the TAE experiences a series of bifurcations

The characteristics of wind- and rain-wind-induced vibrations of bridge stay cables are studied by using ambient vibrations records acquired on a cable-stayed bridge. Mean wind speed and wind-cable angle, as well as the occurrence of rainfalls, were investigated to diagnose a possible excitation mechanism promoting the onset of large heave amplitude oscillations, which were occasionally reported. Light

The plane wave scattering problem for a rigid spherical shell with two coaxial circular holes has been solved rigorously by the Method of Analytical Regularization. An original approach to solving the triple series equations with Legendre polynomials as kernels that arise in the formulation of the problem led to its solution, which is uniformly valid with respect to aperture size. The solution presents

The dynamic mode decomposition (DMD) is one of the post-processing methods used in analyzing dynamic or transient flow field data from experiments or CFD analyses. This method extracts resonant frequencies, damping coefficients, and spatial structures of mode shapes without a priori physical knowledge of the specific form of structure or power spectrum density analysis. The optimized DMD method is

This work presents an efficient procedure to predict the sound reduction index (SRI) of a flat panel of arbitrary internal complexity starting from numerical finite element (FE) simulations. This hybrid analytical-FE procedure allows to perform narrow band calculations considering fluid coupling up to high frequencies. The exciting sound field is synthesised considering a series of uncorrelated plane

This study addresses a fundamental problem of linear friction-induced vibration (FiV), the intriguing role of damping on the instability of FiV in the form of mode-coupling. Two well-known classic 2-degree-of-freedom (DoF) slider-belt models are revisited, and a 4-DoF slider-belt model considering different damping configurations in the slider and the belt is investigated. Since proportional damping

In this paper one first shows that the slow flow of a mechanical system with one unstable mode coupled to a Nonlinear Energy Sink (NES) can be reduced, in the neighborhood of a fold point of its critical manifold, to a normal form of the dynamic saddle-node bifurcation. This allows us to then obtain a scaling law for the slow flow dynamics and to improve the accuracy of the theoretical prediction of

In this paper, three high-order shear deformation theories are presented to investigate in-plane dominated vibrations for circular transversely isotropic plates. The equations of motion for the in-plane dominated vibrations of circular plates based on high-order theories are first derived using Hamilton's principle. Natural frequencies and corresponding mode shapes are determined by solving the equations

In contrary to elastic media, it is easy to attain one-way coupling feature among electrical elements, which enables unidirectional transmission of electrical wave. In this paper, we explore and exploit the interaction of a piezoelectric beam with a one-way electrical transmission line to facilitate nonreciprocal transmission of elastic wave in the linear fashion. Theoretical dispersion analysis and

A new dynamic model of shrouded blades with elastic support and variable cross-section is derived based on the Timoshenko beam theory, in which factors to be considered include centrifugal stiffening, spin softening, Coriolis force, blade stagger angle, and twist angle. The proposed model (PM) is verified by comparing the dynamic frequency results of the finite element model (FEM) and the PM. An impact-friction

In this paper a piecewise linear nonlinear energy sink (PLNES) is developed for the purpose of simultaneous vibration suppression and energy harvesting. The apparatus consists of a cantilever beam attached by a mass at its free end. The beam is situated between a pair of double-stop blocks to constrain its lateral deflection. The stiffness characterization is conducted experimentally. The two combined

Recently, the increasing vibration isolation demands drove the interest of viscous damper development towards employing non-Newtonian fluids that allow tailoring of highly customized damper characteristics. Several attempts have been made for using shear-thickening fluids; however, most of these studies measured only the final, resulting damping characteristic for a particular fluid rheology. This

Research on phononic crystal architectures has produced many interesting designs in the past years, with useful wave manipulation properties. However, not all of the proposed designs can lead to convenient realizations for practical applications, and only a limited number of them have actually been tested experimentally to verify numerical estimations and demonstrate their feasibility. In this work

This article deals with the stochastic modeling of industrial mistuned bladed disks. More specifically, a cost-efficient implementation of polynomial chaos expansion is proposed, it is dedicated to mathematical systems exhibiting permutation invariance or cyclic permutation invariance of their random variables. Significant gains are obtained in comparison to the classical implementation of polynomial

This work presents group-theory-based vibration analysis to determine the highly structured, symmetry-related modal properties of symmetric systems and classify them into specific types. No eigenvalue problem solutions are required. In fact, the properties are obtained without a mathematical model. They derive only from symmetry and the degrees of freedom chosen to describe the deformation. Dynamic