Abstract
Twin rotor damper for the damping of stochastically forced vibrations using a power-efficient control algorithm
The twin rotor damper (TRD), an active mass damper, uses the centrifugal forces of two eccentrically rotating control masses. In the continuous rotation mode, the preferred mode of operation, the two eccentric control masses rotate with a constant angular velocity about two parallel axes, creating, under further operational constraints, a harmonic control force in a single direction. In previous theoretical work, it was shown that this mode of operation is effective for the damping of large, harmonic vibrations of a single-degree-of-freedom (SDOF) oscillator. In this article, the SDOF oscillator is assumed to be affected by a stochastic excitation force and consequently responds with several frequencies. Therefore, the TRD must deviate from the continuous rotation mode to ensure the anti-phasing between the harmonic control force of the TRD and the velocity of the SDOF oscillator. It is found that the required deviation from the continuous rotation mode increases with lower vibration amplitude. Therefore, an operation of the TRD in the continuous rotation mode is no longer efficient below a specific vibration-amplitude threshold. To additionally dampen vibrations below this threshold, the TRD can switch to another, more energy-consuming mode of operation, the swinging mode in which both control masses oscillate about certain angular positions. A power-efficient control algorithm is presented which uses the continuous rotation mode for large vibrations and the swinging mode for small vibrations. To validate the control algorithm, numerical and experimental investigations are performed for a SDOF oscillator under stochastic excitation. Using both modes of operation, it is shown that the control algorithm is effective for the cases of free and stochastically forced vibrations of arbitrary amplitude.
Method development of damage detection in asymmetric buildings
Aesthetics and functionality requirements have caused most buildings to be asymmetric in recent times. Such buildings exhibit complex vibration characteristics under dynamic loads as there is coupling between the lateral and torsional components of vibration and are referred to as torsionally coupled buildings. These buildings require three-dimensional modelling and analysis. In spite of much recent research and some successful applications of vibration-based damage detection methods to civil structures in recent years, the applications to asymmetric buildings have been a challenging task for structural engineers. There has been relatively little research on detecting and locating damage specific to torsionally coupled asymmetric buildings. This article aims to compare the difference in vibration behaviour between symmetric and asymmetric buildings and then use the vibration characteristics for predicting damage in them. The need for developing a special method to detect damage in asymmetric buildings thus becomes evident. Towards this end, this article modifies the traditional modal strain energy–based damage index by decomposing the mode shapes into their lateral and vertical components and to form component-specific damage indices. The improved approach is then developed by combining the modified strain energy–based damage indices with the modal flexibility method which was modified to suit three-dimensional structures to form a new damage indicator. The procedure is illustrated through numerical studies conducted on three-dimensional five-story symmetric and asymmetric frame structures with the same layout, after validating the modelling techniques through experimental testing of a laboratory-scale asymmetric building model. Vibration parameters obtained from finite element analysis of the intact and damaged building models are then applied into the proposed algorithms for detecting and locating the single and multiple damages in these buildings. The results obtained from a number of different damage scenarios confirm the feasibility of the proposed vibration–based damage detection method for three-dimensional asymmetric buildings.
Numerical and experimental investigation on structure-borne sound transmission in multilayered concrete structures
Environmental vibrations in cities are transmitted to buildings and propagate through the buildings via complex paths composed of the structural elements in the building, such as concrete slabs, beams and columns. In this study, the transmission characteristics of such structure-borne sound in building structures composed of concrete were experimentally and numerically investigated. The vibration and radiated sound characteristics of a five-storey concrete structure obtained experimentally through an excitation test using the hammering method and numerically through wave-based numerical calculations are presented and compared. In this study, the finite-difference time-domain (FDTD) method, which treats the target structure as a composition of two-dimensional plate and one-dimensional beam elements to enable a low-cost calculation, is applied as a wave-based scheme. The propagation characteristics of the vibration and sound within the same floor and across different floors were investigated by considering various combinations of receiver and source points, and the structure-borne sound transmission characteristics of a concrete structure with frame elements are discussed.
Dynamic properties and damping predictions for laminated plates: high-order theories – Timoshenko beam
The main aim of this study is to predict the elastic and damping properties of composite laminated plates. This problem has an exact elasticity solution for simple uniform bending and transverse loading conditions. This article presents a new stress analysis method for the accurate determination of the detailed stress distributions in laminated plates subjected to cylindrical bending. Some approximate methods for the stress state predictions for laminated plates are presented here. The present method is adaptive and does not rely on strong assumptions about the model of the plate. The theoretical model described here incorporates deformations of each sheet of the lamina, which account for the effects of transverse shear deformation, transverse normal strain–stress and nonlinear variation of displacements with respect to the thickness coordinate. Predictions of the dynamic and damping values of laminated plates for various geometrical, mechanical and fastening properties are presented. Comparison with the Timoshenko beam theory is systematically made for analytical and approximation variants.
Overall judgment of loudness of time-varying sounds
Listeners can judge the overall loudness of time-varying sounds quite easily, that is, assign a single value that represents the loudness of the entire sound. This holds even if the duration is long and the judgment includes memory effects. Different metrics for calculating overall loudness have been developed. They agree that overall loudness is higher than the mean of loudness over time. Percentiles like the N5, the loudness being exceeded 5% of the time, are adopted by ISO 532-1. In the present study, the concept of an energy mean known from level measurements (ISO 1996-1) was applied to the loudness domain. This equivalent continuous loudness level, LLP, was compared with the N5 using a set of real-world sounds that was orthogonal between the two metrics over a wide dynamic range of 30 phon. Cross-modality matching with line length was used in three experiments with a focus on either the overall judgment of loudness, continuous judgment while a sound was played, or both. The LLP showed considerably higher correlations with overall judgments than N5. Comparing continuous instantaneous judgment with calculated instantaneous loudness suggests that the participants might have focused on the sounds’ prominent portions.
Comparison of acoustoelastic Lamb wave propagation in stressed plates for different measurement orientations
High-order Lamb waves are investigated for the effects of stress on both symmetrical and anti-symmetrical modes in aluminium plate for wave propagation and load parallel. Data are compared with those for the case of load and measurement axis perpendicular. It is the S1 mode which exhibits significantly higher sensitivity to stress than other Lamb modes. For aluminium, the use of the S1 mode for stress measurement is found to be about six times more sensitive, than bulk waves, for the load–measurement axes parallel case and this compares with about 10 times for the case of load–measurement axes perpendicular.
Effect of noise dose bin-width on dose–response curves
Dose–response curves lie at the heart of most global community noise laws/policies. Yet, there is no standard on how to choose the noise dose bins that underlie the curves which describe the relationship between noise and annoyance. This article strives to understand whether the binning process affects the modelled relationship by examining common binning and curve-fitting procedures. It was found that the subjective choice of bin-width can considerably affect the resulting dose–response curves. The implications of these findings are discussed and recommendations are given to ameliorate the situation so that future studies and policies can avoid these potential pitfalls.
Comparison between acoustic measurements of brass instruments and one-dimensional models with curved wavefronts and transformed axial coordinates
A progressive spherical or spheroidal wavefront approximation has previously been found to be a necessary step for a more accurate application of Webster’s wave equation to rapidly flaring horns. This leads to a necessary transformation of the horn area function, from the usual flat cross-sectional area in terms of the axial coordinate, into a curved cap-like wavefront area as a function of either the axial coordinate, the arc-length coordinate along the horn profile, the leading curved wavefront coordinate, or still other possible longitudinal coordinates. In this article, horn functions and related frequency potential functions are calculated from the measured horn profiles of a trombone and a trumpet for several of the above parameterizations. From them, cut-off frequencies and effective lengths are determined. A comparison is drawn between theoretical results using different parameterizations, results calculated via transfer-matrix models, and experimental measurements of the acoustical input impedance and reflection function of both instruments. Results indicate that one-dimensional models accurately predict the effective lengths and consequently the fundamental resonance frequency of the instruments within ±25 cents, but fail noticeably in predicting cut-off frequencies, leading to what is probably an inaccurate representation of perceived timbre.
Higher order dispersion, stability and waveform invariance in nonlinear monoatomic and diatomic systems
Recent studies have presented first-order multiple time-scale approaches for exploring amplitude-dependent plane wave dispersion in weakly nonlinear chains and lattices characterised by cubic stiffness. These analyses have yet to assess solution stability, which requires an analysis incorporating damping. Furthermore, due to their first-order dependence, they make an implicit assumption that the cubic stiffness influences dispersion shifts to a greater degree than the quadratic stiffness, and they thus ignore quadratic shifts. This article addresses these limitations by carrying-out higher order, multiple scales perturbation analyses of linearly damped nonlinear monoatomic and diatomic chains. The study derives higher order dispersion corrections informed by both quadratic and cubic stiffness and quantifies plane wave stability using evolution equations resulting from the multiple scales analysis and numerical experiments. Additionally, by reconstructing plane waves using both homogeneous and particular solutions at multiple orders, the study introduces a new interpretation of multiple scales results in which predicted waveforms are seen to exist over all space and time, constituting an invariant, multiharmonic wave of infinite extent analogous to cnoidal waves in continuous systems. Using example chains characterised by dimensionless parameters, numerical studies confirm that the spectral content of the predicted waveforms exhibits less growth/decay over time as higher order approximations are used in defining the simulations’ initial conditions. Thus, the study results suggest that the higher order multiple scales perturbation analysis captures long-term, nonlocalized invariant plane waves, which have the potential for propagating coherent information over long distances.
Number of wavevectors for each frequency in a periodic structure
Periodic structures have interesting acoustic and vibration properties making them suitable for a wide variety of applications. In a periodic structure, the number of frequencies for each wavevector depends on the degrees of freedom of the unit cell. In this article, we study the number of wavevectors available at each frequency in a band diagram. This analysis defines the upper bound for the maximum number of wavevectors for each frequency in a general periodic structure which might include damping. Investigation presented in this article can also provide an insight for designing materials in which the interaction between unit cells is not limited to the closest neighbour. As an example application of this work, we investigate phonon dispersion curves in hexagonal form of boron nitride to show that first neighbour interaction is not sufficient to model dispersion curves with force–constant model.
Dynamics of transition regime in bi-stable vibration energy harvesters
Vibration energy harvesting can be an effective method for scavenging wasted mechanical energy for use by wireless sensors that have limited battery life. Two major goals in designing energy harvesters are enhancing the power scavenged at low frequency and improving efficiency by increasing the frequency bandwidth. To achieve these goals, we derived a magnetoelastic beam operated at the transition between mono- and bi-stable regions. By improving the mathematical model of the interaction of magnetic force and beam dynamics, we obtained a precise prediction of natural frequencies as the distance of magnets varies. Using the shooting technique for the improved model, we present a fundamental understanding of interesting combined softening and hardening responses that happen at the transition between the two regimes. The transition regime is proposed as the optimal region for energy conversion in terms of frequency bandwidth and output voltage. Using this technique, low-frequency vibration energy harvesting at around 17 Hz was possible. The theoretical results were in good agreement with the experimental results. The target application is to power wildlife bio-logging devices from bird flights that have consistent high power density around 16 Hz.
Passive control of piston secondary motion using nonlinear energy absorbers
The impulsive behaviour of the piston in the cylinder liner plays a key role in the noise, vibration and harshness (NVH) of internal combustion engines. There have been several studies on the identification and quantification of piston impact action under various operation conditions. In the current study, the dynamics of the piston secondary motion are initially explored in order to describe the aggressive oscillations, energy loss and noise generation. The control of piston secondary motion (and thus, impacts) is investigated using a new passive approach based on energy transfer of the highly transient oscillations to a nonlinear absorber. The effectiveness of this new method for improving the piston impact behaviour is discussed using a preliminary parametric study that leads to the conceptual design of a nonlinear energy absorber.
Identification of road pavement types using Bayesian analysis and neural networks
A new method to classify and identify different types of road pavements by analysing the near-field sound profile and texture using statistical learning methods is proposed. A set of characteristics were extracted from the noise profile and from the road surface texture. Sound measurements were carried out following the close-proximity method with the texture descriptors being provided by a high-speed profilometer system. As a first approach, it is assumed that the features extracted from the noise and texture characteristics follow normal distributions. However, this assumption is not completely verified for all types of road surfaces. The method presented herein exploits the use of Bayesian analysis complemented by a neural network in order to improve the classification results.
The Effect of coaxial ring masses with different contact areas, mass and distribution on membrane-type acoustical metamaterials’ transmission loss
The transmission loss (TL) of the membrane-type acoustical metamaterials with coaxial ring masses is investigated using the finite element method. The results show that the TL peak and resonance frequencies of the membrane-type acoustical metamaterials depend on mass, distribution of coaxial ring masses and the contacting area of coaxial ring masses with the membrane. It is also shown that the coaxial ring masses only affect the TL at low frequencies, while the membrane is effective at all frequencies. Additionally, the double-leaf membrane-type acoustical metamaterials structure has been constructed. The roles of the membrane and ring masses of double-leaf membrane-type acoustical metamaterials structure on TL are investigated. The influence of the depth of air-cavity on the TL is then discussed.
Tool condition monitoring in turning using statistical parameters of vibration signal
In this study, the relationship between vibration and tool wear is investigated during high-speed dry turning using statistical parameters. It is aimed to show how tool wear and the work piece surface roughness changes with tool vibration signals. For this purpose, a series of experiments were conducted in a CNC lathe. An indexable CBN tool and a 16MnCr5 tool steel that was hardened to 63 HRC were both used as material twins in the experiments. The vibration was measured only in the machining direction using an acceleration sensor assembled on a machinery analyser since this direction has more dominant signals than the other two directions. In addition, tool wear and work piece surface roughness are measured at different cutting time intervals where the cutting speed, radial depth of cut and feed rate are kept constant. The vibration signals are evaluated using statistical analysis. The statistical parameters in this study are the root mean square (RMS), crest factor and Kurtosis values. When the flank wear increases, the Kurtosis value and RMS also increase, but the crest factor exhibited irregular variations. It is concluded that these statistical parameters can be used in order to obtain information about tool wear and work piece surface roughness.
Nonlinear transverse vibrations of a slightly curved beam resting on multiple springs
In this study, nonlinear vibrations of a slightly curved beam of arbitrary rise functions are handled in case it rests on multiple springs. The beam is simply supported on both ends and is restricted in longitudinal directions using the supports. Thus, the equations of motion have nonlinearities due to elongations during vibrations. The method of multiple scales (MMS), a perturbation technique, is used to solve the integro-differential equation analytically. Primary and 3 to 1 internal resonance cases are taken into account during steady-state vibrations. Assuming the rise functions are sinusoidal in numerical analysis, the natural frequencies are calculated exactly for different spring numbers, spring coefficients and spring locations. Frequency–amplitude graphs and frequency–response graphs are plotted using amplitude–phase modulation equations.
Buckling instability of a violin bow
This article addresses the phenomenon of lateral buckling that could occur on an improperly adjusted violin bow during playing. A finite element model taking into account geometric nonlinearity is used to simulate the static response of a tightened bow to the applied bow force. It is shown that the addition of a small lateral perturbation load enables out-of-plane buckling of the stick once the bow force reaches a certain value. The link between this critical bow force and the critical tension of the bow is clarified. The way the perturbation load smoothes the transition between in-plane and out-of-plane deformation of the stick is illustrated. The influence of camber (curvature of the stick) on buckling is examined. A possible way to increase the lateral stability of a bow without altering its vertical stiffness is proposed.
Investigation of the relationships between perceived qualities and sound parameters of saxophone reeds
The perceived quality of cane reeds used on saxophones or clarinets may be very different from one reed to another, even though the reeds have the same shape and strength. The aim of this work is to better understand the differences in the perceived quality of reeds by making use of acoustical measurements. A perceptual study, involving a panel of 10 musicians, was first conducted on a set of 20 reeds of the same strength. Each musician assessed each of the 20 reeds according to three descriptors: Brightness, Softness and Global quality. Second, signal recordings during saxophone playing (saxophone playing by a musician in the laboratory, called in vivo measurements) were made of the pressures in a player’s mouth, in the mouthpiece and at the bell of the instrument. These measurements enable us to deduce specific acoustical variables, such as the threshold pressure and the spectral centroid of the notes. After an analysis of the perceptual and acoustical data (assessment of the agreement among the assessors and the main consensual differences between the reeds), correlations between the perceptual and acoustical data were performed. A modelling of the descriptors Brightness and Softness according to the acoustical variables is proposed using multiple linear regression. Results show that the pressure in the mouth at the beginning of the permanent regime is an important variable to predict the softness of the reed. The performance of the models in the prediction of the perceptual dimensions provides important clues for a more objective assessment of perceived reed qualities.
Developing and evaluating a hybrid wind instrument
A hybrid wind instrument generates self-sustained sounds via a real-time interaction between a computed excitation model (such as the physical model of human lips interacting with a mouthpiece) and a real acoustic resonator. Attempts to produce a hybrid instrument have so far fallen short, in terms of both the accuracy and the variation in the sound produced. The principal reason for the failings of previous hybrid instruments is the actuator which, controlled by the excitation model, introduces a fluctuating component into the air flow injected into the resonator. In the present paper, the possibility of using a loudspeaker to supply the calculated excitation signal is evaluated. A theoretical study has facilitated the modelling of the loudspeaker-resonator system and the design of a feedback and feedforward filter to successfully compensate for the presence of the loudspeaker. The resulting self-sustained sounds are evaluated by a mapping of their sound descriptors to the input parameters of the physical model of the embouchure, both for sustained and attack sounds. Results are compared with simulations. The largely coherent functioning confirms the usefulness of the device in both musical and research contexts.
Low-complexity, listener’s position-adaptive binaural reproduction over a loudspeaker array
This work presents a method for binaural reproduction over a loudspeaker array that adapts to the listener’s position using a cross-talk cancellation approach that is updated in real-time. This is obtained by combining the audio signal processing system together with a computer vision mechanism that estimates listener’s position. A novel approach to adapt the cross-talk cancellation filters is introduced here, which employs filters created for a central listening position using a free-field propagation model and far-field beamforming techniques, hence requiring little memory and processing. The paper introduces simulations to show the effectiveness and robustness of the formulation together with free-field measurements of performance using a 16 loudspeaker compact array.