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Journal of Sound and Vibration
Journal Prestige (SJR): 1.36
Citation Impact (citeScore): 3
Number of Followers: 226  
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 0022-460X - ISSN (Online) 1095-8568
Published by Elsevier Homepage  [3206 journals]
  • Structured uncertainty for a pedestrian-structure interaction model
    • Abstract: Publication date: Available online 15 February 2020Source: Journal of Sound and VibrationAuthor(s): Daniel Gomez, Shirley J. Dyke, Shirley RietdykAbstractA yearning for visually appealing bridges that are longer and more slender is driving advances in construction materials and techniques, alongside the necessary improvements in design guidelines and standards. However, lighter and more slender structures are also more susceptible to vibration. Certain pedestrian structures do frequently exhibit excessive vibrations when they are dynamically excited by walking pedestrians. To improve pedestrian-structure design procedures, uncertainties in the human biodynamic subsystem should be systematically included, and should represent a suitable range of possible body characteristics. Variations in the representation of the human body are intended to capture differences in physical characteristics while that human is walking on a lively surface. Here these variations are described as parametric uncertainties, while the structure is assumed to be known and deterministic. A time-varying and coupled model of the pedestrian-structure system is adopted, and the corresponding perturbations are defined as a set of structured uncertainties describing imprecise biodynamic parameters that can adopt any value within their proposed intervals. This parametric model with structured uncertainty is then used to obtain the range of biodynamic parameters for a variety of pedestrians by comparing the predicted structural responses against the experimental data. Experimental results are used to determined a set of intervals of biodynamic parameters such as mass, damping, stiffness, and pace frequency for a walking pedestrian. The simulation results show that the developed human-structure model with associated parameter intervals is able to obtain realistic serviceability demands by predicting the range of structural responses for a wide range of pedestrians.
  • An alternative formulation for modeling self-excited oscillations of
           rotary drilling systems
    • Abstract: Publication date: Available online 12 February 2020Source: Journal of Sound and VibrationAuthor(s): He Zhang, Emmanuel DetournayAbstractThis paper describes an alternative formulation of the nonlinear equations governing the coupled axial and torsional dynamics of a discrete model of a rotary drilling system equipped with a drag bit. This model assumes a rate-independent bit/rock interface law that accounts for both cutting and frictional contact processes. The regenerative effect associated with the cutting introduces a term with delay, and thus a feedback, in the equations of motion, while the frictional contact results in set-valued contact forces and discontinuities in the boundary conditions, which are responsible for the occurrence of axial and torsional stick-slip oscillations. Inspired by P. Wahi and A. Chatterjee (Self-interrupted regenerative metal cutting in turning, International Journal of Non-Linear Mechanics 43:2, 111–123, 2008), the regenerative effect is captured by a bit trajectory function, whose evolution is governed by a first order partial differential equation. With this approach, the original state-dependent delay differential equations (SDDDEs) governing the dynamics of the discrete model are replaced by the partial differential equation of the bit trajectory function together with the axial and angular equations of motion of the two degrees-of-freedom model. The equation governing the evolution of the bit trajectory function is further approximated by a system of first order ordinary differential equations through application of the Galerkin method. The introduction of the bit trajectory function makes it possible to consider a bit with two state-dependent delays (and in principle multiple delays) without reducing the computational efficiency. The accuracy of this approximation is validated using published results, and the convergence and robustness properties of the proposed method are analyzed using three cases corresponding to different regimes of instability. Finally, we extend the discrete model to a more generic lumped-parameter model with multiple degrees-of-freedom, which captures the propagation of axial and torsional vibrations along the drillstring.
  • Mode shape transformation for model error localization with modal strain
    • Abstract: Publication date: Available online 12 February 2020Source: Journal of Sound and VibrationAuthor(s): Zi Huang, Chaoping Zang, Genbei Zhang, Michael I. FriswellAbstractA modeling error location method based on modal strain energy is presented in this paper. Errors in the design model with shell elements are located by an error indicator which is based on changes between the equivalent modal strain energy and the modal strain energy of the design model. The equivalent modal strain energy is defined as a quadratic form using the stiffness matrix of the design model and the mode shape of the reference coming from the sophisticated and high fidelity finite-element model, called the supermodel, or the full-field measurement. The major obstacle to obtain the equivalent modal strain energy is how to match the mode shapes of a solid element and those of a shell element since each node of the solid element contains only three translation degrees of freedom (dofs) while each node of the shell element has six dofs, including three translation and three rotation components. In order to solve this problem, a mode shape transformation method from the solid element to the shell element is proposed using the shape functions or linear approximation. Using this approach, the errors in the design model can be determined and the updating parameters can be selected so that the updated model has physical meaning and can represent the dynamic characteristics of the real structure. The simulation of a simple plate is used initially to illustrate the effectiveness of the proposed method. Then, a rotor test rig casing is taken as an example for further investigation. A comparison of the updating parameters selected by the proposed method and the traditional sensitivity analysis technique is then undertaken. It is verified that the updating parameters selected based on error location have physical sense and represent the true errors in the design model through the updating results. The advantage of this technique is that only detailed mode shapes from the reference is required. The approach shows potential for further industrial engineering applications.
  • A method for the observation of the anelastic behaviour of anisotropic
           porous materials using digital image correlation
    • Abstract: Publication date: Available online 11 February 2020Source: Journal of Sound and VibrationAuthor(s): Luca Manzari, Huina Mao, Peter Göransson, Jacques Cuenca, Inés López ArteagaAbstractThis paper proposes an experimental method for observing the anelastic anisotropic behaviour of poroelastic media. The setup relies on three-dimensional digital image correlation, enabling the acquisition of full-field displacement data from the visible faces of a vibrating cubic material sample. The latter is placed in a vacuum chamber, loaded with a seismic mass and excited uniaxially. The observability and relevance of the three-dimensional displacement field is assessed by means of a numerical simulation. A homogenised fully anisotropic model is used, implemented using the finite element method. Thus, a set of material properties obtained using single-point data is considered as the reference configuration for the numerical method. Selected experimental and numerical results are presented, highlighting the importance and the advantages that full-field observations yield over single-point measurements.
  • Vibration characteristics of matrix cracked pretwisted hybrid composite
           blades containing CNTRC layers
    • Abstract: Publication date: Available online 11 February 2020Source: Journal of Sound and VibrationAuthor(s): Lu-Wen Zhang, Zhou-Zhou Pan, Xiuhua ChenAbstractStiffness degradation due to matrix cracks is the main initial form of damage in composite laminates. Moreover, the vibration characteristics may change due to the degradation of blade stiffness caused by the introduction of matrix cracks. This paper presents a solution method for studying the static free vibration behaviors of pretwisted hybrid composite blade containing carbon nanotube reinforced composite (CNTRC) layers as well as matrix cracked fiber reinforced composite (FRC) layers. Two types of structure, namely Structure-I and Structure-II, are investigated. The CNTRC layers in Structure-I are considered with carbon nanotubes (CNTs) arranged in uniformly distributions, while Structure-II arranged in functionally graded distributions. The degraded stiffness of cracked layers is modeled via the self-consistent model (SCM) micromechanical framework. A shell model for pretwisted blade is proposed based on the theroy of differential geometry. To consider the effect of the transverse shear deformation and rotary inertia on the vibration behaviors, the first order shear deformation theory (FSDT) is adopted in describing the kinematics of blade. The improved moving least-squares Ritz (IMLS-Ritz) method is engaged to discretize the partial differential equations over the computational domain. Comparison studies indicate that the proposed predictive model can furnish very accurate results for pretwisted blades. Parametric studies on the effect of CNT distribution configuration, matrix crack density, aspect ratio, width-to-thickness ratio, twisted angle, as well as ply-angle on the vibration characteristics are revealed.
  • Nonlinear wave propagation and dynamic reconfiguration in two-dimensional
           lattices with bistable elements
    • Abstract: Publication date: Available online 11 February 2020Source: Journal of Sound and VibrationAuthor(s): Julien MeaudAbstractThis paper examines the propagation of elastic waves of large amplitudes in two-dimensional square lattices that include an alternating pattern of linear springs and nonlinear bistable springs. Because of the presence of bistable springs, these lattices have multiple stable configurations. In this paper, a theoretical model that takes into account the non-linearity of the bistable springs while neglecting geometric nonlinearities is used to study non-linear wave propagation in these lattices. Results from numerical simulations demonstrate that, for a lattice that is initially in a deformed stable equilibrium configuration, stimuli of large amplitudes are able to cause a reconfiguration of the lattice to a configuration of lower potential energy. Even for initial stable configurations that exhibit omnidirectional or directional bandgaps for infinitesimal wave propagation, waves of large amplitudes can propagate in the lattice due to its reconfiguration; however, due to the nonlinearity of bistable springs, the transmitted response tends to have multiple spectral peaks or be broadband for narrow-band stimuli of large amplitude. Simulations are used to study how the reconfiguration of the lattice depends on the amplitude and duration of the stimulus, on damping, and on the energy barrier between the two stable equilibria of the bistable springs. These numerical results suggest that these multistable lattices can serve as reconfigurable wave guides for which the amplitude of the stimulus offers opportunities for enhanced tunability.
  • Modelling approach for MEMS transducers with rectangular clamped plate
           loaded by a thin fluid layer
    • Abstract: Publication date: Available online 11 February 2020Source: Journal of Sound and VibrationAuthor(s): K. Šimonová, P. Honzík, M. Bruneau, P. GatignolAbstractThe paper is mainly concerned with the analytical approach of the behaviour of a two-dimensional miniaturized MEMS transducer, namely a rectangular or square clamped plate loaded by a fluid-gap (squeeze film), surrounded by a small cavity (reservoir), and excited by an incident acoustic field (assume to be uniform on the plate). Until now, the problem has not been analytically solved owing to the geometry of the device in conjunction with the nature of the diaphragm (elastic plate) and its boundary conditions (zero deflection and zero normal slope along all edges); namely analytical eigenfunctions do not exist for the clamped plate. On the other hand, the analytical approach classically used to express the acoustic field in the fluid-gap relies on a modal expansion which does not match correctly with both the displacement field of the diaphragm and the boundary conditions at the entrance of the reservoir. Then, two particular questions arise: how to derive analytically the modal behaviour of the loaded clamped plate, and what analytical approach for the acoustic field in the fluid gap is convenient to describe its coupling with the displacement field of the plate' The aim of the paper is both to provide basically an exact analytical approach and to handle a numerical implementation (FEM) against which the analytical results are tested.
  • Nonlinear instabilities and control of drill-string stick-slip vibrations
           with consideration of state-dependent delay
    • Abstract: Publication date: Available online 11 February 2020Source: Journal of Sound and VibrationAuthor(s): Xie Zheng, Vipin Agarwal, Xianbo Liu, Balakumar BalachandranAbstractIn this paper, a reduced-order drill-string model with coupled axial and torsion dynamics is studied. Nonlinear effects associated with dry friction, loss of contact, and the state-dependent delay, which all arise from cutting mechanics, are considered. The linearized system equations are derived, and the local stability analysis is carried out analytically by using the D-subdivision method. The obtained results are presented in terms of stability crossing curves, which are parameterized by using the rotation speed and the cutting depth. A numerical continuation method is developed and used to follow periodic orbits of systems with friction, loss of contact, and state-dependent delay. Bifurcation diagrams are constructed to capture the possible routes from either a nominal stable operational state or a stable limit-cycle motion without stick slip to a limit-cycle motion with stick slip. It is shown that the system can experience subcritical Hopf bifurcations of equilibrium solutions and cyclic fold bifurcations. Based on this work, an observer based control scheme is proposed by using a continuous pole placement method for time-delay systems. The effectiveness of the controller in suppressing stick-slip behavior is shown through simulations.
  • Design, construction and experimental performance of a nonlinear energy
           sink in mitigating multi-modal vibrations
    • Abstract: Publication date: Available online 10 February 2020Source: Journal of Sound and VibrationAuthor(s): Kevin Dekemele, Patrick Van Torre, Mia LoccufierAbstractTo passively reduce the vibration energy in mechanical systems under shock load, nonlinear energy sinks (NES) can be locally attached, serving as vibration absorbers. The NES is an alternative to the standard tuned-mass-damper (TMD). While the TMD has a linear connecting spring, the NES has a nonlinear one. As a consequence, the NES has an energy dependent natural frequency. Because of this property, the NES is able to mitigate multi-modal transient vibrations sequentially from high to low frequency through a resonance capture cascade (RCC). This is a major advantage over the TMD, which is tuned only to reduce vibrations in a narrow frequency band, typically a single mode. Recently, three performance measures for the NES were derived, 1) The energy dissipation, the amount of total vibration energy dissipated by the NES. 2) The pumping time that estimates the time required for the NES to absorb a single frequency and 3) the cascading time, estimating the time the NES engages in RCC, absorbing all the modal frequencies. The novelty of these measures is that they only require the knowledge of the system's parameters. In this research, a complete implementation of a NES is presented, from design and practical realization, to verifying the performance measures experimentally. The performance measures thus allow to predict experimental performance of the NES without simulations or experiments, opposite to what literature does. The NES is constructed with a novel design methodology. This methodology allows for tailor made purely nonlinear stiffness. The NES is placed on a frame representing a scale model single-story building, to validate the single-mode performance. To obtain resonance cascading, a second story is added to obtain a two-mode dominant vibrating structure. The cascading time is predicted and confirmed by the experiments. The experiments agree well with both simulations and predictions regarding performance. This work validates the ease of use of the performance measures and their ability to predict experimental performance of a NES mitigating multi-modal vibrations.
  • Inverse methods in aeroacoustic three-dimensional volumetric noise source
           localization and quantification
    • Abstract: Publication date: Available online 8 February 2020Source: Journal of Sound and VibrationAuthor(s): G. Battista, P. Chiariotti, M. Martarelli, P. CastelliniAbstractAcoustic source mapping usually involves planar microphone arrays and calculation points located on a surface at a certain distance with respect to the array. An implicit assumption that sources are located on this surface is therefore performed. However, in some application, such as aeroacoustic source identification, this assumption may be wrong and produce misleading results. For this reason, it is interesting to extend the common acoustic mapping techniques to three-dimensional volumetric mapping. Direct beamforming techniques are not suited for volumetric imaging due to poor spatial resolution in radial direction from the array centre. Therefore, more refined algorithms, like deconvolution techniques or inverse methods, are required to obtain intelligible and accurate results.This paper describes the use of inverse methods in the context of aeroacoustic three-dimensional volumetric noise imaging. An Equivalent Source Method is formulated, based on Iteratively Reweighted Least Squares and on Bayesian Regularization. Moreover, a novel approach based on CLEAN-SC as decomposition tool of Cross-Spectral-Matrix in coherent source components is presented.The method proposed is applied on an aircraft model in wind tunnel. Performance are preliminary assessed with simulated test cases. A comparative investigation in exploiting a single planar array or multiple planar arrays observing noise sources from different directions is performed.
  • Thorough understanding on the mechanism of vibration-induced loosening of
           threaded fasteners based on modified Iwan model
    • Abstract: Publication date: Available online 8 February 2020Source: Journal of Sound and VibrationAuthor(s): Hao Gong, Jianhua Liu, Xiaoyu DingAbstractUnder transversal vibration, the local slippage on the thread and bearing surfaces is typically nonlinear and its gradual accumulation with vibration cycles contributes to the loosening of threaded fasteners. The classical Iwan model is used widely to model the nonlinearity of contact interface, but not appropriate for analyzing the local slippage accumulation on the thread and bearing surfaces. In this paper, we proposed modified Iwan model to represent the nonlinear local slippage behavior. The acting forces on the internal thread were decomposed into three component forces along different directions. The effect of each component on the local slippage accumulation was analyzed theoretically based on the modified Iwan model. It was found that the cyclic component force along the radial direction dominates the local slippage accumulation of thread surface and other two cyclic component forces have no effects on it. Then, we also analyzed the local slippage accumulation on the bearing surface using the modified Iwan model and developed a thorough understanding on loosening mechanism. Based on the loosening mechanism, we proposed that the key to preventing local slippage accumulation and sustained loosening was to inhibit the slippage or relative motion occurring on the thread surface along the radial direction. Thus, several novel thread structures were designed for resisting loosening based on above findings. Finally, theirs superior anti-loosening abilities were validated by FEA method.
  • Active nonlinear inerter damper for vibration mitigation of Duffing
    • Abstract: Publication date: Available online 8 February 2020Source: Journal of Sound and VibrationAuthor(s): G. Zhao, G. Raze, A. Paknejad, A. Deraemaeker, G. Kerschen, C. ColletteAbstractIn this paper, a nonlinear active damping strategy based on force feedback is proposed. The proposed device is composed of a pair of collocated actuator and force sensor. The control law is formed by feeding back the output of the force sensor, through one single, one double integrator and another double integrator of its cube. An equivalent mechanical network which consists of a dashpot, an inerter and a cube root inerter is developed to enable a straightforward interpretation of the physics behind. Closed-form expressions for the optimal feedback gains are derived. Numerical validations are performed to demonstrate the proposed control strategy.
  • A novel binomial expansion method for evaluating a Neumann series for the
           response of a perturbed system
    • Abstract: Publication date: Available online 7 February 2020Source: Journal of Sound and VibrationAuthor(s): Alyssa T. Liem, J. Gregory McDanielAbstractThis paper presents a new method for evaluating the Neumann series approximation for the response of a dynamic system perturbed by two parameters. The proposed method will be valuable for iterative model updating methods, where major computational savings are gained when the approximation is evaluated multiple times. The method is based on the binomial expansion theory and requires the initial computational investment of formulating expansion vectors which will in turn accelerate the evaluation of the approximation. The proposed method is compared to the standard evaluation method which utilizes the recursive nature of the power series when computing the terms in the series. In comparison to the proposed method, the standard method requires no initial investment but suffers from a larger computational cost of evaluating the approximation. This paper investigates the efficiency of the two methods for evaluating the Neumann series approximation with respect to the number of evaluations, order of approximation, and size of the system. Central processing unit timing tests are performed in order to compare the two methods when used to evaluate the approximate displacement response of vibrating systems. In an analytical example, the standard and proposed evaluation method, as well as the traditional direct solve are applied to an iterative model updating method where the response of a perturbed finite element model is evaluated to compute the objective function. In the example, the proposed method performs up to 11 times faster than the standard evaluation method and 22 times faster than the traditional direct solve.
  • Simultaneous energy harvesting and vibration control in a nonlinear
           metastructure: A spectro-spatial analysis
    • Abstract: Publication date: Available online 7 February 2020Source: Journal of Sound and VibrationAuthor(s): Mohammad Bukhari, Oumar BarryAbstractConsiderable attention has recently been given to the study of simultaneous energy harvesting and vibration attenuation in metastructures. However, only linear metastructures were investigated although nonlinear metastructures and nonlinear electromechanical devices offer superior interesting wave propagation phenomena (e.g., birth of solitary waves, tunable bandgap, acoustic nonreciprocity) and broadband energy harvesting. In this paper, we investigate the wave propagation in a weakly nonlinear metastructure with electromechanical resonators. Explicit expressions are derived for the nonlinear dispersion relations using the method of multiple scales. These expressions are validated via direct numerical integration. We carried out parametric studies to investigate the role of different parameters of the electromechanical resonators on the linear and nonlinear band structure. To obtain further detailed information on the nonlinear wave propagation, we employ spectro-spatial analyses on the numerical simulations. This spectro-spatial analysis can reveal the output voltage distortion due to different types of nonlinearities. The results indicate that nonlinear chain can enhance energy harvesting through the birth of solitary wave and without degrading the boundary of the bandgap. The results also suggest that such a system is suitable for designing electromechanical diodes and rectifiers.
  • Numerical modeling of a flexural displacement-converter mechanism to
           excite a flat acoustic source driven by piezoelectric stack actuators
    • Abstract: Publication date: Available online 5 February 2020Source: Journal of Sound and VibrationAuthor(s): F. Tajdari, A.P. Berkhoff, A. de BoerAbstractThis paper studies an acoustic source with a relatively small thickness and a high bending stiffness. The acoustic source operates in the low frequency, quasi-static regime. The focus of the current study is on the actuation part in order to design an appropriate excitation mechanism. A flexural mechanism is modeled in combination with a piezoelectric actuator to convert an in-plane displacement of the actuator to the out-of-plane direction. First, an optimization simulation is used to determine the size of the required piezoelectric actuator. An equivalent electrical circuit of the lumped acoustic source is used for the optimization. A coupled 3D numerical finite element (FE) analysis is carried out using COMSOL Multiphysics software package. The fully-coupled analysis combines the suggested flexural mechanism, the piezoelectric stack actuator, and the thin acoustic source. Finally, the sound pressure field that is generated by the thin acoustic source is investigated and compared using both the finite element analysis and the lumped model.
  • Robust damage detection in the time domain using Bayesian virtual sensing
           with noise reduction and environmental effect elimination capabilities
    • Abstract: Publication date: Available online 5 February 2020Source: Journal of Sound and VibrationAuthor(s): J. KullaaAbstractVibration-based structural health monitoring aims at detecting changes in the dynamic characteristics of a structure. A direct time-domain damage detection method is proposed, in which no system identification is needed. In this data-based method, response signals are acquired using a sensor network. Utilizing hardware redundancy, each sensor signal can be estimated from the remaining signals in the network. The residuals, or the differences between the actual and estimated signals are used for damage detection. However, the measurement error affects the detection performance. Therefore, a novel two-step algorithm is proposed. The signal-to-noise ratio of the signals is first increased by developing Bayesian virtual sensors that are proved to be more accurate than the hardware. Virtual sensor data then replace the actual measurements in the subsequent data analysis. In the second step, environmental or operational influences can be eliminated by acquiring training data under different conditions and estimating the signal of each sensor using the remaining virtual sensors in the network. The excitation or the environmental or operational variables are not measured. In this two-step algorithm for damage detection, each sensor's signal is estimated twice. The novelty is how to apply Bayesian virtual sensors to residual generation resulting in enhanced damage detection. Principal component analysis is applied to the residuals and an extreme value statistics control chart is designed for damage detection. Vibrations of a healthy and damaged bridge structure were simulated under random excitation and temperature variability. Virtual sensors outperformed the actual measurements in damage detection making an early warning more plausible.
  • Influence of boundary conditions on the stop band effect in finite locally
           resonant metamaterial beams
    • Abstract: Publication date: Available online 4 February 2020Source: Journal of Sound and VibrationAuthor(s): Luca Sangiuliano, Claus Claeys, Elke Deckers, Wim DesmetAbstractThis paper investigates the influence of the boundary conditions on the stop band effect in finite locally resonant metamaterial beams. In a first step, a Timoshenko beam with tuned vibration absorbers is used to describe a metamaterial beam. The influence of different boundary conditions for beams with different lengths as well as of tuned vibration absorbers with different amounts of added mass or different tuned frequencies is assessed numerically. It is found that edge modes are present inside the stop band frequency region predicted by the unit cell analysis and these edge modes reduce the level of vibration attenuation achieved. Three solutions are analysed to reduce the effect of the edge modes: (i) varying the tuned frequency, (ii) the number or (iii) the positions of the individual tuned vibration absorbers added to the host structure. In a second step, the results of the numerical investigation are experimentally validated: the experimental results are in good agreement with the numerical results.
  • Development of large-scale bistable motion system for energy harvesting by
           application of stochastic resonance
    • Abstract: Publication date: Available online 4 February 2020Source: Journal of Sound and VibrationAuthor(s): Wei Zhao, Qiong Wu, Xilu Zhao, Kimihiko Nakano, Rencheng ZhengAbstractStochastic resonance has become an important topic in the collection of environmental vibrational energy; however, realization of sufficiently large-scale motion for effective energy harvesting remains a difficult problem. Therefore, unlike the conventional vibrational systems that use cantilever beams, this study proposes a novel bistable motion system based on application of an elastic spring that diagonally supports a lumped mass block that can move freely along a straight rail. Using a combination of theoretical analysis, numerical simulation, and experimental verification, it is shown that stochastic resonance phenomena can be activated reliably using the proposed bistable motion system, and correspondingly large-scale bistable responses can be generated to realize effective amplitude enlargement after input signals are received. Additionally, it is demonstrated that large amplitude motion can be achieved with a highly robust performance because the rail-guided motion can suppress the effects of accidental impact from the outside. Furthermore, as an important design factor, the influence of periodic excitation signals on the large-scale bistable motion activity is carefully discussed and a solid foundation is laid for further practical energy harvesting applications.
  • Dynamics of pipes conveying fluid of axially varying density
    • Abstract: Publication date: Available online 3 February 2020Source: Journal of Sound and VibrationAuthor(s): Dana B. Giacobbi, Christian Semler, Michael P. PaïdoussisAbstractThe dynamics of a flexible slender pipe conveying fluid the density of which varies along the pipe-length is investigated in this paper analytically and numerically. Apart from its academic interest, this problem has application to the pipes used in mining methane crystals from the bottom of the ocean, and to more mundane situations involving piping conveying a gas at high speed or piping in a temperature environment varying along its length. Some CFD results are presented first, and then a linear analytical model is developed using a Hamiltonian approach. Pipes with clamped ends and cantilevered pipes are considered. The former lose stability by static divergence (buckling) and the latter by flutter, as for a constant-density fluid. The most important findings are two: (i) the density at the discharging end of the pipe influences stability most crucially; (ii) for cantilevered pipes, the magnitude of density variation strongly influences the mode and critical flow velocity of flutter.
  • Evaluation of the gear noise reduction potential of geometrically uneven
           inequidistant gears
    • Abstract: Publication date: Available online 3 February 2020Source: Journal of Sound and VibrationAuthor(s): Philipp Neubauer, Joachim Bös, Tobias MelzRandomizing the periodic excitation is a well-known noise reduction measure, for example in fans and tire patterns. Due to a randomized excitation the tonal components of the generated noise are reduced while broadband noise is increased in amplitude. This less tonal noise with a more broadband character is perceived less annoying. In the presented research this approach is applied to gears – called inequidistant gears. They are characterized by uneven tooth positions and uneven tooth thicknesses. The deviations from regular, perfectly even gears may be up to several millimeters in both position and thickness. In the same way as in fans and tire patterns, the uneven design of inequidistant gears leads to a less tonal and less annoying noise. In this paper the design of inequidistant gears is introduced. Equations are derived to define the uneven geometry of an inequidistant gear wheel and to exactly match a pair of meshing inequidistant gears. The presented approach is valid for spur gears, helical gears, and double helical gears, but only spur gears are considered in this paper. Furthermore, a method to calculate the gear mesh stiffness, which is the main excitation mechanism in gear noise, and a method to calculate the gear mesh forces are presented. Experimental investigations are carried out on a back-to-back gear test bench. The calculated gear mesh force and the experimentally determined sound pressure of a regular, perfectly even spur gear set are compared to those of an equivalent inequidistant spur gear set. The results reveal that inequidistant gears not only reduce the tonality but are – in contrast to uneven designs of fans and tire patterns – capable of reducing the total sound pressure level.Graphical abstractImage 1
  • Enriched finite elements and local rescaling for vibrations of axially
           inhomogeneous Timoshenko beams
    • Abstract: Publication date: Available online 3 February 2020Source: Journal of Sound and VibrationAuthor(s): R. Cornaggia, E. Darrigrand, L. Le Marrec, F. MahéAbstractThis work presents a new enriched finite element method dedicated to the vibrations of axially inhomogeneous Timoshenko beams. This method relies on the “half-hat” partition of unity and on an enrichment by solutions of the Timoshenko system corresponding to simple beams with a homogeneous or an exponentially-varying geometry. Moreover, the efficiency of the enrichment is considerably increased by introducing a new formulation based on a local rescaling of the Timoshenko problem, that accounts for the inhomogeneity of the beam. Validations using analytical solutions and comparisons with the classical high-order polynomial FEM, conduced for several inhomogeneous beams, show the efficiency of this approach in the time-harmonic domain. In particular low error levels are obtained over ranges of frequencies varying from a factor of one to thirty using fixed coarse meshes. Possible extensions to the research of natural frequencies of beams and to simulations of transient wave propagation are highlighted.
  • Analytical and numerical studies on the slope inertia-based Timoshenko
    • Abstract: Publication date: Available online 3 February 2020Source: Journal of Sound and VibrationAuthor(s): Guiyun Xia, Wenya Shu, Ilinca StanciulescuAbstractIn this work, a comparative study is performed between the slope inertia-based Timoshenko (SIBT) beam and other classical beam theories. We prove that the SIBT beam comprehensively incorporates physical effects of shear deformation, rotary inertia, and shear inertia. The transcendental equations of frequency are derived from the initial parameter solutions, and then used to demonstrate that the frequency spectrum of the SIBT beam theory has only one branch. A finite element implementation of the SIBT beam is developed and verified using closed-form solutions. We find that the SIBT and Love theories predict the same mode shape but different frequencies. Comparisons of frequency spectra obtained from different beam theories also suggest that the shear deformation influences the frequency more than the rotary inertia and that the SIBT beam theory predicts lower frequency values due to its complete consideration of shear deformation, rotary inertia and shear inertia. Parametric studies demonstrate that boundary conditions influence lower order frequencies predicted by the SIBT beam theory significantly, but only marginally influence the high order frequencies; they also show that the frequency spectrum of the SIBT beam theory has an upper bound.
  • One-dimensional sonic black holes: Exact analytical solution and
    • Abstract: Publication date: Available online 3 February 2020Source: Journal of Sound and VibrationAuthor(s): Mikhail Mironov, Vladimir PislyakovAbstractWe discuss results of experiments made in the 2000s with two different models of acoustic (sonic) black holes. Both structures provide linear decrease of sound velocity. The first one is a series of rigid discs fixed on a rod and placed inside the tube, diameters of discs gradually increase according to a parabolic law. The second one is a tube where effective density of the medium increases due to mass layers placed inside, the concentration of these layers grows toward the end of the tube. If these structures were “perfect”, the sound velocity would decrease so that the wave would never reach the end of the tube. For imperfect (real) models, small addition of absorbers makes absorption very efficient. What is essential, both structures have exact analytical solutions for the wave propagation equation. We study these theoretical results and juxtapose them with the experiments.
  • A magnetic Bi-stable nonlinear energy sink for structural seismic control
    • Abstract: Publication date: Available online 1 February 2020Source: Journal of Sound and VibrationAuthor(s): Yang-Yang Chen, Zhi-Chao Qian, Wei Zhao, Chia-Ming ChangAbstractIn this paper, a magnetic bi-stable NES (MNES) is proposed for structural seismic control. Permanent magnets are configured to generate noncontact and smooth bi-stable restoring force for the present MNES device, by which the transient internal resonance between the primary structure and the attached MNES can be rapidly enhanced under seismic excitation. The governing equation of the present MNES is derived, and the numerical parameter optimization is carried out for its implementation in seismic control for a shear frame model. Seismic performance of this frame structure attached with the proposed MNES is evaluated, and compared to those of cubic NES and linear tuned mass damper (TMD) systems. As shown in the results, the proposed MNES is found to be robustly capable of protecting the shear frame under seismic excitations. Immediate cascade of broadband transient internal resonance captures under seismic excitations are found as the essential cause of the high efficiency of the present MNES system.
  • Time domain force localization and reconstruction based on hierarchical
           Bayesian method
    • Abstract: Publication date: Available online 1 February 2020Source: Journal of Sound and VibrationAuthor(s): Wei Feng, Qiaofeng Li, Qiuhai Lu, Bo Wang, Chen LiAbstractIn engineering practice, localization and reconstruction of external excitations is a tough problem in absence of prior knowledge. Traditional regularization approaches require assigning regularization parameters and shape parameters before implementing the reconstruction. However, a poor selection of these parameters generally leads to a poor reconstruction. In this paper a time domain hierarchical Bayesian method is proposed to locate and reconstruct the external excitations with automatic selection of parameters. The entire method is performed in two stages. First based on the property of posterior probability distribution function of shape parameters, a novel non-force criterion is proposed to determine the non-force locations quickly. Then based on the determined force locations, a reduced-dimension problem is constructed and the posterior distributions of parameters are sampled by a Metropolis-within-Gibbs sampler with nested blocking technique. Both numerical simulations and laboratory experiment of a cantilever beam under various load conditions are carried out to validate the proposed method.
  • Experiments on the geometrically nonlinear vibration of thin-walled
           cylindrical shells with points supported boundary condition
    • Abstract: Publication date: Available online 1 February 2020Source: Journal of Sound and VibrationAuthor(s): Chaofeng Li, Zixuan Zhang, Qingyu Yang, Peiyong LiAbstractA in-depth experimental investigation of the nonlinear vibration of thin-walled cylindrical shells with point supported condition is presented in this paper. Firstly the point-supported thin-walled cylindrical shell structure is designed, in which bolts are used to restrain the cylindrical shell, and the nonlinear response test system for cylindrical shells is built. Then, the error analysis of each degree of freedom during system alignment is given. The sensitivity indexes are used to guide the system alignment, and the Response Surface Method is used to identify the stiffness of the bolt. The comparisons of natural characteristics of points supported shell by experiment are conducted with the results by theory. Finally, the effects of supported stiffness and number of point on the nonlinear response of points-supported thin-walled cylindrical shells are investigated.
  • Reciprocity relationship for the diffuse reverberant loading on a general
    • Abstract: Publication date: Available online 31 January 2020Source: Journal of Sound and VibrationAuthor(s): Xianhui LiAbstractDiffuse field reciprocity relates the diffuse reverberant loading on a structure to its radiation impedance. Such a relationship has been previously derived for the ensemble average response of the structure in connection to structural or acoustical subsystems with uncertain boundaries. In the present work, a different reciprocity relationship is derived from the direct boundary integral formulation for the scattering problem, in which the diffuse reverberant loading on the structure depends on both the radiation impedance and the free field Green's function. It is revealed that the difference in the reciprocity relationships results from the different definitions of the diffuse fields. Diffuse reverberant loading is analytically investigated for two examples. Possible extension of the present reciprocity relationship to a structural system is also discussed. It is shown that the reciprocity relationships are equivalent when the definitions of the diffuse fields are identical or the curvature radius of the structure is much larger than the wavelength involved.
  • Operational transfer path analysis with crosstalk cancellation using
           independent component analysis
    • Abstract: Publication date: Available online 31 January 2020Source: Journal of Sound and VibrationAuthor(s): Wei Cheng, Yapeng Chu, Xuefeng Chen, Guanghui Zhou, Diane Blamaud, Jingbai LuAbstractTo eliminate crosstalk effects between reference signals of operational transfer path analysis (OTPA), a novel crosstalk cancellation method based on independent component analysis (ICA) for OTPA is proposed. Firstly, ICA is used to separate the measured signals at reference points and crosstalk between sources is significantly eliminated. Then, separated signals are identified based on the prior knowledge of the sources. In the next phase, amplitudes and phases of the separated signals are corrected and finally, the transmissibility function matrix is obtained based on the corrected separated signals and the measured signals at the target point. The performance of the proposed method is comparatively studied with the conventional methods, according to numerical case studies for an acoustical radiation system and experimental case studies on a test bed with thin shell structures. Generally, the proposed method can increase the accuracy of transfer path identification and contribution evaluation, which can benefit vibration monitoring, reduction and control of mechanical systems.
  • Physical mechanisms and performance of slitted leading-edge profiles for
           the reduction of broadband aerofoil interaction noise
    • Abstract: Publication date: Available online 30 January 2020Source: Journal of Sound and VibrationAuthor(s): Marine Cannard, Phillip Joseph, Jacob Turner, Jae Wook Kim, Paruchuri ChaitanyaAbstractAerofoil Turbulence Interaction (ATI) noise is an inviscid phenomenon generated by the impingement of turbulent flows onto the leading-edge of an aerofoil. This paper deals with a novel leading-edge serration geometry, composed of narrow slits, to reduce ATI noise. These profiles have been recently found to provide significantly better noise reductions than conventional leading edge geometries. A numerical and analytic investigation is performed into the mechanism and performance of its noise reduction. The far-field radiation is shown to be influenced by a system of induced vortices affecting the distribution of sources on the flat-plate and by destructive interference between the two sources generated at both ends of the slit. A simple two-source model is developed to predict the far-field noise reduction obtained and compared to straight leading-edge aerofoils.
  • Application of extremum response surface method-based improved
           substructure component modal synthesis in mistuned turbine bladed disk
    • Abstract: Publication date: Available online 29 January 2020Source: Journal of Sound and VibrationAuthor(s): Bin Bai, Han Li, Wei Zhang, Yanchao CuiAbstractTo improve the computational efficiency of vibration characteristics and reliability analysis for a detailed numerical model of the mistuned turbine bladed disk, a new methodology called extremum response surface method-based improved substructural component modal synthesis (ERSM-ISCMS) is proposed by combining the ISCMS and ERSM. First, the degrees of freedom of the detailed finite element model for the numerical mistuned turbine bladed disk are decreased by ISCMS, which is called as reduced-order model. Compared with high fidelity finite element model, the time saving ratio and the computational accuracy of the first 40 order frequencies are, respectively, 36.37% and 99.99%∼99.86% obtained by ISCMS under the same working environment, which can satisfy the engineering requirements. Then, the ERSM is applied to analyze the dynamic probability of the maximum vibration response for the numerical mistuned turbine bladed disk. The investigation indicates that the computational efficiency of ERSM is higher 38.92% than that of traditional RSM in the same computer and the same reduced-order model. Thus, the ERSM-ISCMS is a more effective method to investigate dynamic probabilistic analysis of the mistuned turbine bladed disk, it benefits for the complex structures and develops the theory method for the mechanical reliability design.
  • On the modeling of rotors with rolling element bearings using bond graphs
    • Abstract: Publication date: Available online 29 January 2020Source: Journal of Sound and VibrationAuthor(s): Jone Torsvik, Eilif PedersenAbstractThis paper describes the development of a generic rotordynamic model incorporating rolling element bearings. Aimed at examining model fidelity requirements for bearings, the work contributes to advancing knowledge on rotordynamic system models suitable for studying mechatronics- and controls-related applications, transient issues and fault conditions. The bond graph method is applied in a consistent manner, giving a clear model structure. Body-fixed equations of motion, derived from Lagrange's method, are contained in field elements. An alternative cage implementation and a flexible outer ring are introduced, providing a more complete basis for bearing modeling. The flexible outer ring is modeled using the modal approach with a solution for moving loads. The derivation of the equations of motion and the bond graph formulation are thoroughly presented. Following the display of versatility and connectivity in the modeling approach, a simulation example is presented to demonstrate the capability and usefulness of the model for transient analyses. A classic time-series analysis of a run-up of an unbalanced rotor, with and without a damaged bearing, directly yields interesting results; the complex interaction between model elements following the passing of the first critical speed leads to a stationary vibratory condition taking significantly long time to develop in the damaged bearing case and involves persistent slip.
  • Identification of blade operational mode shapes during wear of abradable
    • Abstract: Publication date: Available online 28 January 2020Source: Journal of Sound and VibrationAuthor(s): N. Tang, B. Zhang, C. Lord, M. MarshallAbstractAbradable liner materials are often used in turbine engines between the compressor blade tips and the casing. The abradable liner serves as a partially sacrificial material to improve the overall engine efficiency by creating a tight seal, minimising gas flow leakage. During operation, the rubbing interaction between the blade tips and abradable lined casing induces vibrations in the blades. These vibrations not only can have a significant influence on the wear mechanism and wear efficiency of the blade tips, but also the early fatigue failure of the blades, and therefore are of interest. In this paper, a newly developed approach is presented that can be used to identify the operational blade vibration modes. A non-contact single point laser sensor is used to measure the vibrational displacements during the wear process. A mathematical transform is introduced to correct for blade position due to its rotating frame of reference. After applying the transform, the vibrational energy is calculated at various positions throughout the blade. The continuous wavelet-based modal identification is then introduced to identify the blade mode shape. The Modal Assurance Criterion (MAC) is used to demonstrate the similarity of the mode shapes as a function of wear time illustrating that the blade mode shapes change slightly with the level of wear.
  • CAA simulations of the leading edge noise of a heaving airfoil
    • Abstract: Publication date: Available online 24 January 2020Source: Journal of Sound and VibrationAuthor(s): Yuhao Sun, Siyang Zhong, Teng Zhou, Xun Huang, Xin ZhangAbstractLeading edge noise of airfoil is a significant source of broadband noise for both aircraft and wind turbines. In this work, the noise generated by the interaction of incoming turbulence and a heaving airfoil was studied. Numerical experiments were performed using a hybrid computational aeroacoustics method, where the mean flow was computed by using computational fluid dynamics, and the acoustic field was obtained by solving the linearised Euler equations. Applying Fourier analysis, the periodic mean flows around the heaving airfoil can be accurately reproduced for the aeroacoustic simulations. The incoming isotropic and anisotropic turbulence was synthesised by a modified digital filter method. The effect of the heaving motion on the leading edge noise was evaluated through the comparisons of far-field directivities and noise spectra. The far-field noise results indicate that the effect of airfoil heaving motion on the leading edge noise is larger if the incoming turbulence is anisotropic. For turbulence with a larger integral length scale in the streamwise direction, more noise is produced, while less noise is generated when the larger integral length scale is in the transverse direction. It is expected that the proposed method and numerical results can be helpful in providing physical insights into the airfoil leading edge noise under realistic conditions.
  • Hyperchaos co-existing with periodic orbits in a frictional oscillator
    • Abstract: Publication date: Available online 23 January 2020Source: Journal of Sound and VibrationAuthor(s): Merten Stender, Martin Jahn, Norbert Hoffmann, Jörg WallaschekThis work reports observations of complex dynamical behavior and chimera-alike dynamics in a self-excited frictional oscillator with a weak stiffness nonlinearity. Multi-stability in the form of several co-existing stable limit cycle solutions are identified for a wide range of system parameters. For a particular system configuration, an unstable periodic orbit is found that gives rise to irregular long-term behavior. Trajectories starting from this orbit turn out to be hyper-chaotic with multiple positive Lyapunov exponents. Trajectories starting from different regions in phase space converge to stable limit cycles. Hence, this numerical study reveals co-existing regular and irregular dynamics at a fixed system configuration. This sensitive dependence of the qualitative system dynamics on initial conditions adds new aspects to a better understanding of the rich dynamic behavior of structures subjected to friction-induced vibrations.Graphical abstractImage 1
  • Description and application of a 2D-axisymmetric model for entropy noise
           in nozzle flows
    • Abstract: Publication date: Available online 22 January 2020Source: Journal of Sound and VibrationAuthor(s): Ariane Emmanuelli, Jun Zheng, Maxime Huet, Alexis Giauque, Thomas Le Garrec, Sébastien DucruixAbstractEntropy noise corresponds to acoustic fluctuations generated inside gas-turbine engines when temperature (entropy) spots are accelerated by the mean flow. This type of noise currently faces growing interest because of its contribution to global aero-engine noise as well as its impact on combustion instabilities. In the present article, a two-dimensional semi-analytical model is developed to predict entropy noise in nozzle flow. It complements the reference model of Marble and Candel (“Acoustic disturbance from gas non-uniformities convected through a nozzle”, J. Sound Vib., 55, pp. 225–243, 1977) and its more recent extensions which remain one-dimensional, by taking the radial variations of the flow into account in the noise generation computation. Validations are performed by comparison with computational aeroacoustics simulations with either entropy or acoustic excitations in a subsonic nozzle. Very good agreement is observed between the numerical simulations and the 2D model for all the frequencies considered. The role of entropy wave distortion in noise generation is demonstrated by comparison with a 1D model which fails to reproduce the simulated results for medium to large frequencies.
  • A two-step methodology for cable force identification
    • Abstract: Publication date: Available online 22 January 2020Source: Journal of Sound and VibrationAuthor(s): Songhan Zhang, Ruili Shen, Yuan Wang, Guido De Roeck, Geert Lombaert, Kaoshan DaiAbstractVibration-based force identification of cables has been studied for several decades. Most of this work relies on the natural frequencies of the cable for an estimation of the cable force. However, these natural frequencies are also affected by bending stiffness, sag effect and boundary conditions. In the present work, a two-step methodology is developed that allows taking into consideration these effects in the force identification. First, a segment of the cable is considered which is sufficiently short for the sag effect to be negligible. The axial force in this segment is estimated by fitting the measured response to the analytical solution for the transverse motion of the cable in the frequency domain. In this procedure, the bending stiffness is updated exploiting the fact that the estimated axial force should not depend on the frequency, while the boundary conditions do not need to be known. Next, an analytical solution of the static state of the entire cable is derived, taking into account the sag effect, bending stiffness and boundary conditions. The parameters of the entire cable model can then be updated, using the estimated value of the axis force at the location of the segment. Finally, the updated analytical model of the entire cable allows evaluating internal forces such as the cable force and bending moment, as required for estimating the stresses in the cable considering bending deformation. The feasibility of the proposed methodology is verified by means of numerical simulations considering measurement noise and an inaccurate initial guess of the bending stiffness, proving its potential for the health monitoring of cable structures.
  • Perturbation theory of nonlinear, non-self-adjoint eigenvalue problems:
           Simple eigenvalues
    • Abstract: Publication date: Available online 21 January 2020Source: Journal of Sound and VibrationAuthor(s): Georg A. Mensah, Alessandro Orchini, Jonas P. MoeckAbstractThe study of the vibrational modes and stability of a given physical system has strong bounds with the efficient numerical evaluation of its eigenvalues. The operators governing the eigenproblem are, in general, nonlinear in the eigenvalue and non-self-adjoint, which makes the repeated solution of the eigenvalue problem (necessary for example when the effect of several parameter values on the system needs to be assessed) expensive. This study reviews the adjoint-based incremental procedure for calculating the coefficients of power series expansion of simple (non-degenerate) eigenvalues and their eigenvectors. These expansions approximate the eigenvalues to any desired order in a finite region. An efficient numerical implementation of the theory is proposed, and it is shown how high-order power series approximations of the eigenvalues give very accurate results within the radius of convergence of the power series, which is finite and generally not small. Furthermore, the domain of convergence of the power series might be extended by considering Padé expansions of the eigenvalues. Examples involving the stability of the Orr–Sommerfeld equation, the biharmonic equation for the vibrational modes of a membrane, and the emission of sounds from a Rijke tube because of thermoacoustic feedback are used to assess and validate the theory.
  • Design of a Kelvin cell acoustic metamaterial
    • Abstract: Publication date: Available online 20 January 2020Source: Journal of Sound and VibrationAuthor(s): H.J. Rice, J. Kennedy, P. Göransson, L. Dowling, D. TrimbleAbstractAdvancements in 3D print technology now allow the printing of structured acoustic absorptive materials at appropriate microscopic scales and sample sizes. Optimisation of parameter sets associated with a Kelvin Cell structure have the potential to develop various metabehaviours in the associated acoustic responses. The repeatability of the fundamental cell unit also provide a route for the development of viable macro models to simulate built up structures based on detailed models of the individual cell units. This paper describes a process to model, print and test such a sample. Manufacturing restraints will initially guide the optimised design and introduce response uncertainties associated with surface finishes and critical geometric dimensions. A “micro to macro” model is developed using a full visco thermal acoustic model of a single cell to develop a frequency dependent cell transfer matrix. The transfer matrices for the repeated cells may then be combined until sufficient material depth is achieved and efficiently generate an absorptivity for the material layer. Two prints using different processes (digital light processing (DLP) and selective laser melting (SLM)) of nominally the same kelvin cell structure. For the metal print the model predicts the absorptivity well once an allowance is made for the surface roughness. The DLP has a smoother finish with a lower geometric fidelity however. The DLP sample is still well modelled by the process.
  • Multi-domain stability and modal analysis applied to Gas Foil Bearings:
           Three approaches
    • Abstract: Publication date: Available online 17 January 2020Source: Journal of Sound and VibrationAuthor(s): Sebastian von Osmanski, Jon S. Larsen, Ilmar F. SantosAbstractThe dynamic characteristics of rotors supported by Gas Foil Bearings (GFBs) are commonly assessed using linear force coefficients, which are usually derived from an analytical perturbation in combination with an implicit compliance model. This remains common practice even though discrepancies have been reported between the Onset Speed of Instability (OSI) predicted using such linear coefficients and observations from non-linear time integration. For the first time, the present paper pinpoints the root cause of this discrepancy by demonstrating an extended perturbation, akin to that used for tilting pad journal bearings, to predict exactly the same OSIs as obtained from an eigenvalue analysis based on the Jacobian of the full non-linear system of equations. To demonstrate this, the OSIs predicted using (i) the classical perturbation, (ii) the extended perturbation, and (iii) the Jacobian eigenvalues are compared over ea range of compliance levels covering essentially rigid bearings to modern heavily loaded industrial GFBs. Using carefully aligned implementations, the deficiency of the classical method is demonstrated to increase with the compliance level (up to 13% for the benchmark case), while the extended perturbation provides OSIs in agreement with the Jacobian eigenvalues for all compliance levels. Furthermore, the mode shapes attainable from the three approaches, encompassing only the rotor, the rotor and foil, and the rotor, foil and pressure respectively, are compared.
  • Experimental investigation of the noise radiated by a ducted air flow
           discharge though diaphragms and perforated plates
    • Abstract: Publication date: Available online 15 January 2020Source: Journal of Sound and VibrationAuthor(s): P. Laffay, S. Moreau, M.C. Jacob, J. RegnardAbstractAn experimental investigation of the noise radiated by a ducted high pressure flow discharge through diaphragms and perforated plates is carried out for a large range of subsonic and supersonic operating conditions (Nozzle Pressure Ratio (NPR) from 1.2 to 3.6). A parametric study of the geometrical parameters is also conducted to characterize their influence on the acoustic radiation. This covers configurations from single diaphragms to multi-perforated plates with variable hole diameters and arrangements that are placed inside a cylindrical duct. Compared with the free discharge analysed in a first part of the study (perforated plates placed directly at the output of the duct), the discharge into a duct, which is closer to the practical applications, generates strong acoustic modifications. As expected, the broadband noise is disturbed by strong modulations due to acoustic resonances in the output duct (longitudinal resonances and transversal duct modes). However, as in the free configuration, a strong effect of the plate geometries on the mixing noise is observed, allowing to adapt or reduce this source. In particular, the increase of the ratio between the perforation spacing and the perforation diameter allows reducing the maximum amplitude of the mixing noise. Compared to the free-field discharge, the Sound Pressure Level (SPL) in the ducted configuration is on average proportional to the 6-th power of the velocity instead of the 8-th power. Moreover, there are two dominant frequency humps in the sound spectra. The low frequency one is characterized by a constant Helmholtz number, suggesting that the sound is shaped by the duct geometry, whereas the high frequency one is characterized by a constant Strouhal number suggesting that the sound is directly generated by the flow. Finally, for supersonic operating points, the screech radiation appearing with diaphragms in the free configuration is suppressed when the output duct is added but new high amplitude and low frequency tones appear for the largest diaphragms and perforated plates. These lines are due to a coupling between normal shock oscillations and longitudinal resonances.
  • Controllability and actuator placement optimization for active damping of
           a thin rotating ring with piezo-patch transducers
    • Abstract: Publication date: Available online 10 January 2020Source: Journal of Sound and VibrationAuthor(s): Ziv Brand, Matthew O.T. ColeAbstractA study on optimal actuator placement for controlling flexural vibration of a thin rotating ring is reported. Piezoelectric patch actuators and sensors may be applied with feedback control to provide active damping of structural vibration involving circumferential travelling waves. To determine the optimum patch positions, a model-based cost function is defined involving a time-weighted controllability Gramian, with balanced model realization for combined treatment of sensors and actuators in collocated pairs. Analytical and numerical results indicate that, without rotation, at least two actuator/sensor pairs are required to achieve controllability of any given set of natural vibration modes. Also, the optimal angular separation varies with rotational speed due to the combined influence of initial damping and Coriolis forces on the vibratory dynamics. To obtain a practical solution, a finite range of speeds is considered within a mini-max optimization criterion for the placement problem. Experiments have been conducted on a thin steel ring where a synthetic proof-mass-damper control law was used to suppress vibration involving the six lowest frequency vibration modes (with natural frequencies of 161, 442 and 846 Hz without rotation). The results show that although a single actuator-sensor pair can achieve improved damping at high rotational speeds, the optimized configuration of two pairs provides effective damping over the full range of operating speeds.
  • Numerical investigation on the generation, mixing and convection of
           entropic and compositional waves in a flow duct
    • Abstract: Publication date: Available online 26 December 2019Source: Journal of Sound and VibrationAuthor(s): Jocelino Rodrigues, Andrea Busseti, Simone HochgrebAbstractRecent models and experiments have demonstrated that indirect noise can be generated via acceleration of either entropic or compositional perturbations through a nozzle. These studies found that the acoustic signature depends on the extent of the dispersion effects on the perturbation waves during the convection process. In this work, numerical simulations are undertaken using the URANS formulation to model the mixing of unsteady entropic and compositional waves in an open-ended flow duct in the transitional regime (2500 
  • Experimental study of plane wave propagation in a corrugated pipe: Linear
           regime of acoustic-flow interaction
    • Abstract: Publication date: Available online 19 December 2019Source: Journal of Sound and VibrationAuthor(s): Joachim Golliard, Yves Aurégan, Thomas HumbertAbstractAcoustic propagation in corrugated pipes offers interesting features in presence of a mean flow, which are investigated experimentally in this paper. The scattering matrix of the corrugated section is measured with and without a mean flow. The analysis of the results is based on the extraction of the wavenumbers of propagation within the corrugated pipe. Without flow, a small decrease of the speed of sound and a slight increase of the attenuation are observed. In presence of mean flow, oscillations against the frequency of both the real part and the imaginary part of the wavenumber occur. For sufficiently large flow velocities, the oscillation caused by the sound-flow interaction is such that the acoustic waves are amplified by the flow. The Strouhal number for maximum gain shows a small dependency on the Reynolds number, and converges to values of 0.4–0.5 depending on the presence of rounded or sharp upstream edges of the cavities. Non-linear effects begin to appear for an acoustic amplitude such that the acoustic velocity is about 1% of the flow velocity.
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