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Journal of Sound and Vibration    [44 followers]  Follow    
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
     ISSN (Print) 0022-460X - ISSN (Online) 1095-8568
     Published by Elsevier Homepage  [2556 journals]   [SJR: 1.359]   [H-I: 88]
  • The effect of external mean flow on sound transmission through
           double-walled cylindrical shells lined with poroelastic material
    • Abstract: Publication date: 31 March 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 7
      Author(s): Jie Zhou , Atul Bhaskar , Xin Zhang
      Sound transmission through a system of double shells, lined with poroelastic material in the presence of external mean flow, is studied. The porous material is modeled as an equivalent fluid because shear wave contributions are known to be insignificant. This is achieved by accounting for the energetically most dominant wave types in the calculations. The transmission characteristics of the sandwich construction are presented for different incidence angles and Mach numbers over a wide frequency range. It is noted that the transmission loss exhibits three dips on the frequency axis as opposed to flat panels where there are only two such frequencies—results are discussed in the light of these observations. Flow is shown to decrease the transmission loss below the ring frequency, but increase this above the ring frequency due to the negative stiffness and the damping effect added by the flow. In the absence of external mean flow, porous material provides superior insulation for most part of the frequency band of interest. However, in the presence of external flow, this is true only below the ring frequency—above this frequency, the presence of air gap in sandwich constructions is the dominant factor that determines the acoustic performance. In the absence of external flow, an air gap always improves sound insulation.


      PubDate: 2014-01-16T04:37:36Z
       
  • Numerical investigation of dispersion relations for helical waveguides
           using the Scaled Boundary Finite Element method
    • Abstract: Publication date: 31 March 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 7
      Author(s): Yijie Liu , Qiang Han , Chunlei Li , Huaiwei Huang
      In this paper, the dispersion properties of elastic waves in helical waveguides are investigated. The formulation is based on the Scaled Boundary Finite Element method (SBEFM). With a set of orthogonal unit basis introduced as the contravariant basis, the helical coordinate is firstly considered, where components of tensor retain the dimension of original quantity. Based on the strain–displacement relation, the eigenvalue matrix is obtained about wavenumbers and frequencies. The cross section of the waveguides is discretized by using high-order spectral elements. Moreover, the formulated linear matrix is utilized to design efficient and accurate algorithms to compute the eigenvalues of helical waveguides. Compared with the Pochhammer–Chree curves, the convergence and accuracy of the SBFEM are discussed. Finally, we give some dispersion curves for a wide range of lay angles and analyze in detail properties of cut-off frequency, mode separation and mode transition for elastic wave propagation in the helical waveguides.


      PubDate: 2014-01-16T04:37:36Z
       
  • Two-dimensional wave propagation in a rotating elastic solid with voids
    • Abstract: Publication date: 31 March 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 7
      Author(s): S.K. Tomar , R.W. Ogden
      Two-dimensional wave propagation is studied in an isothermal linear isotropic elastic material with voids rotating with constant angular velocity based on a theory of elastic material with voids developed by Ieşan (1986) in the thermoelastic context. It is found that there exist three coupled plane waves propagating with distinct phase speeds. The presence of voids and the rotation of the medium are responsible for this coupling. In the absence of voids, the classical longitudinal and transverse waves are found to be coupled through the rotation of the medium. At very large frequency or when the angular rotation is very small relative to the wave frequency the waves are decoupled and propagate with distinct phase speeds. These are (i) a longitudinal wave, (ii) a transverse wave and (iii) a longitudinal wave corresponding to the change in void volume fraction. The first two correspond to the waves of classical elasticity, while the third is new and arises from the presence of the voids. The results are illustrated graphically.


      PubDate: 2014-01-16T04:37:36Z
       
  • Use of nonlinear asymmetrical shock absorber to improve comfort on
           passenger vehicles
    • Abstract: Publication date: 31 March 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 7
      Author(s): M. Silveira , B.R. Pontes Jr. , J.M. Balthazar
      In this study the behaviour of two different types of shock absorbers, symmetrical (linear) and asymmetrical (nonlinear) is compared for use on passenger vehicles. The analyses use different standard road inputs and include variation of the severity parameter, the asymmetry ratio and the velocity of the vehicle. Performance indices and acceleration values are used to assess the efficacy of the asymmetrical systems. The comparisons show that the asymmetrical system, with nonlinear characteristics, tends to have a smoother and more progressive performance, both for vertical and angular movements. The half-car front asymmetrical system was introduced, and the simulation results show that the use of the asymmetrical system only at the front of the vehicle can further diminish the angular oscillations. As lower levels of acceleration are essential for improved ride comfort, the use of asymmetrical systems for vibrations and impact absorption can be a more advantageous choice for passenger vehicles.


      PubDate: 2014-01-16T04:37:36Z
       
  • Complex modal analysis of rods with viscous damping devices
    • Abstract: Publication date: 31 March 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 7
      Author(s): Natale Alati , Giuseppe Failla , Adolfo Santini
      The complex modal analysis of rods equipped with an arbitrary number of viscous damping devices is addressed. The following types of damping devices are considered: external (grounded) spring-damper, attached mass-spring-damper and internal spring-damper. Within a standard 1D formulation of the vibration problem, the theory of generalized functions is used to model axial stress and displacement discontinuities at the locations of the damping devices. By using the separate variable approach, a simple solution procedure of the motion equation leads to exact closed-form expressions of the characteristic equation and eigenfunctions, which inherently fulfill the required matching conditions at the locations of the damping devices. Based on the characteristic equation, a closed-form sensitivity analysis of the eigensolution is implemented. The displacement eigenfunctions exhibit orthogonality conditions. They can be used with the complex mode superposition principle to tackle forced vibration problems and, in conjunction with the stress eigenfunctions, to build the exact dynamic stiffness matrix of the rod for complex modal analysis of truss structures. Numerical results are discussed for a variety of parameters.


      PubDate: 2014-01-16T04:37:36Z
       
  • A time domain approach to diagnose gearbox fault based on measured
           vibration signals
    • Abstract: Publication date: 31 March 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 7
      Author(s): Liu Hong , Jaspreet Singh Dhupia
      Spectral analysis techniques to process vibration measurements have been widely studied to characterize the state of gearboxes. However, in practice, the modulated sidebands resulting from the local gear fault are often difficult to extract accurately from an ambiguous/blurred measured vibration spectrum due to the limited frequency resolution and small fluctuations in the operating speed of the machine that often occurs in an industrial environment. To address this issue, a new time-domain diagnostic algorithm is developed and presented herein for monitoring of gear faults, which shows an improved fault extraction capability from such measured vibration signals. This new time-domain fault detection method combines the fast dynamic time warping (Fast DTW) as well as the correlated kurtosis (CK) techniques to characterize the local gear fault, and identify the corresponding faulty gear and its position. Fast DTW is employed to extract the periodic impulse excitations caused from the faulty gear tooth using an estimated reference signal that has the same frequency as the nominal gear mesh harmonic and is built using vibration characteristics of the gearbox operation under presumed healthy conditions. This technique is beneficial in practical analysis to highlight sideband patterns in situations where data is often contaminated by process/measurement noises and small fluctuations in operating speeds that occur even at otherwise presumed steady-state conditions. The extracted signal is then resampled for subsequent diagnostic analysis using CK technique. CK takes advantages of the periodicity of the geared faults; it is used to identify the position of the local gear fault in the gearbox. Based on simulated gear vibration signals, the Fast DTW and CK based approach is shown to be useful for condition monitoring in both fixed axis as well as epicyclic gearboxes. Finally the effectiveness of the proposed method in fault detection of gears is validated using experimental signals from a planetary gearbox test rig. For fault detection in planetary gear-sets, a window function is introduced to account for the planet motion with respect to the fixed sensor, which is experimentally determined and is later employed for the estimation of reference signal used in Fast DTW algorithm.


      PubDate: 2014-01-16T04:37:36Z
       
  • Vibration quenching in a large scale rotor-bearing system using journal
           bearings with variable geometry
    • Abstract: Publication date: 31 March 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 7
      Author(s): Athanasios Chasalevris , Fadi Dohnal
      In large scale rotating machinery the resonance amplitude during the passage through resonance is a matter of consideration because of its influence in the surrounding environment of the rotational system and foundation. In this paper, a variable geometry journal bearing (VGJB), recently patented, is applied for the mounting of a large scale rotor bearing system operating at the range of medium speed. The simulation of the rotor-bearing system incorporates a recent method for simulation of a multi-segment continuous rotor in combination with nonlinear bearing forces. The use of the current bearing gives results that encourage the use of such a bearing in rotating machinery since the vibration amplitude during the passage through the critical speed can be reduced up to 60–70%. In the presented study, the developed amplitude and the rotor stresses are severely reduced compared to those of the system with normal cylindrical journal bearings during a virtual start up of the system.


      PubDate: 2014-01-16T04:37:36Z
       
  • A stabilization process applied to a hidden variables method for
           evaluating the uncertainties on foundation impedances and their effect on
           vibrations induced by railways in a building
    • Abstract: Publication date: 31 March 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 7
      Author(s): Pierre Ropars , Guy Bonnet , Philippe Jean
      The paper is devoted to stochastic foundation impedance modeling for buildings submitted to vibrations. The hidden-variables method used in seismic engineering is revisited, due to a larger frequency range used in vibration prediction. Indeed, in this new context, instability of the solution and non-physical nature of mass and stiffness random matrices have been observed. The hidden variable method has been therefore implemented by enforcing explicitly the stability of the solution and the positiveness of mass and stiffness matrices. The effects of numerical parameters used throughout the process are shown and the improved hidden-variables method has been used for predicting the level of vibrations inside a building induced by railway sources. We present here steps of stabilization process, and then discuss on an example of application.


      PubDate: 2014-01-16T04:37:36Z
       
  • Erratum to “Explicit form of an implicit method for inverse force
           identification” [J. Sound Vib. 333 (3) (2013) 730–744]
    • Abstract: Publication date: 31 March 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 7
      Author(s): K. Liu , S.S. Law , X.Q. Zhu , Y. Xia



      PubDate: 2014-01-16T04:37:36Z
       
  • Corrigendum to: “Singular spectrum analysis for enhancing the
           sensitivity in structural damage detection”
    • Abstract: Publication date: 31 March 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 7
      Author(s): K. Liu , S.S. Law , Y. Xia , X.Q. Zhu



      PubDate: 2014-01-16T04:37:36Z
       
  • Introducing a Green–Volterra series formalism to solve weakly
           nonlinear boundary problems: Application to Kirchhoff's string
    • Abstract: Publication date: 31 March 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 7
      Author(s): David Roze , Thomas Hélie
      This paper introduces a formalism which extends that of “Green's function” and that of “the Volterra series”. These formalisms are typically used to solve, respectively, linear inhomogeneous space–time differential equations in physics and weakly nonlinear time-differential input-to-output systems in automatic control. While Green's function is a space–time integral kernel which fully characterizes a linear problem, the Volterra series expansions involve a sequence of multi-variate time integral kernels (of convolution type for time-invariant systems). The extension proposed here consists in combining the two approaches, by introducing a series expansion based on multi-variate space–time integral kernels. This series allows the representation of the space–time solution of weakly nonlinear boundary problems excited by an “input” which depends on space and time. This formalism is introduced on and applied to a nonlinear model of a damped string that is excited by a transverse mass force f ( x , t ) . The Green–Volterra kernels that solve the transverse displacement dynamics are computed. The first-order kernel exactly corresponds to Green's function of the linearized problem. The higher order kernels satisfy a sequence of linear boundary problems that lead to (both) analytic closed-form solutions and modal decompositions. These results lead to an efficient simulation structure, which proves to be as simple as the one based on the Volterra series, that has been obtained in a previous work for excitation forces with separated variables f ( x , t ) = ϕ ( x ) f tot ( t ) . Numerical results are presented.


      PubDate: 2014-01-16T04:37:36Z
       
  • Strongly nonlinear beats in the dynamics of an elastic system with a
           strong local stiffness nonlinearity: Analysis and identification
    • Abstract: Publication date: 31 March 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 7
      Author(s): Mehmet Kurt , Melih Eriten , D. Michael McFarland , Lawrence A. Bergman , Alexander F. Vakakis
      We consider a linear cantilever beam attached to ground through a strongly nonlinear stiffness at its free boundary, and study its dynamics computationally by the assumed-modes method. The nonlinear stiffness of this system has no linear component, so it is essentially nonlinear and nonlinearizable. We find that the strong nonlinearity mostly affects the lower-frequency bending modes and gives rise to strongly nonlinear beat phenomena. Analysis of these beats proves that they are caused by internal resonance interactions of nonlinear normal modes (NNMs) of the system. These internal resonances are not of the classical type since they occur between bending modes whose linearized natural frequencies are not necessarily related by rational ratios; rather, they are due to the strong energy-dependence of the frequency of oscillation of the corresponding NNMs of the beam (arising from the strong local stiffness nonlinearity) and occur at energy ranges where the frequencies of these NNMs are rationally related. Nonlinear effects start at a different energy level for each mode. Lower modes are influenced at lower energies due to larger modal displacements than higher modes and thus, at certain energy levels, the NNMs become rationally related, which results in internal resonance. The internal resonances of NNMs are studied using a reduced order model of the beam system. Then, a nonlinear system identification method is developed, capable of identifying this type of strongly nonlinear modal interactions. It is based on an adaptive step-by-step application of empirical mode decomposition (EMD) to the measured time series, which makes it valid for multi-frequency beating signals. Our work extends an earlier nonlinear system identification approach developed for nearly mono-frequency (monochromatic) signals. The extended system identification method is applied to the identification of the strongly nonlinear dynamics of the considered cantilever beam with the local strong nonlinear stiffness at its free end.


      PubDate: 2014-01-16T04:37:36Z
       
  • Fokker–Planck equation analysis of randomly excited nonlinear energy
           harvester
    • Abstract: Publication date: 31 March 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 7
      Author(s): P. Kumar , S. Narayanan , S. Adhikari , M.I. Friswell
      The probability structure of the response and energy harvested from a nonlinear oscillator subjected to white noise excitation is investigated by solution of the corresponding Fokker–Planck (FP) equation. The nonlinear oscillator is the classical double well potential Duffing oscillator corresponding to the first mode vibration of a cantilever beam suspended between permanent magnets and with bonded piezoelectric patches for purposes of energy harvesting. The FP equation of the coupled electromechanical system of equations is derived. The finite element method is used to solve the FP equation giving the joint probability density functions of the response as well as the voltage generated from the piezoelectric patches. The FE method is also applied to the nonlinear inductive energy harvester of Daqaq and the results are compared. The mean square response and voltage are obtained for different white noise intensities. The effects of the system parameters on the mean square voltage are studied. It is observed that the energy harvested can be enhanced by suitable choice of the excitation intensity and the parameters. The results of the FP approach agree very well with Monte Carlo Simulation (MCS) results.
      Graphical abstract image Highlights A novel Fokker–Plank equation based approach is proposed for nonlinear energy harvesting under stochastic excitation.

      PubDate: 2014-01-16T04:37:36Z
       
  • Nonlinear model order reduction of jointed structures for dynamic analysis
    • Abstract: Publication date: 31 March 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 7
      Author(s): H. Festjens , G. Chevallier , J.L. Dion
      Assembled structures generally show weak nonlinearity, thus it is rather commonplace to assume that their modes are both linear and uncoupled. At small to modest amplitude, the linearity assumption remains correct in terms of stiffness but, on the contrary, the dissipation in joints is strongly amplitude-dependent. Besides, the modes of any large structure may be LOCALLY collinear in the localized region of a joint. As a result the projection of the structure on normal modes is not appropriate since the corresponding generalized coordinates may be strongly coupled. Instead of using this global basis, the present paper deals with the use of a local basis to reduce the size of the problem without losing the nonlinear physics. Under an appropriate set of assumptions, the method keeps the dynamic properties of joints, even for large amplitude, which include coupling effects, nonlinear damping and softening effects. The formulation enables us to take into account FE models of any realistic geometry. It also gives a straightforward process for experimental identification. The formulation is detailed and investigated on a jointed structure.


      PubDate: 2014-01-16T04:37:36Z
       
  • Instability regimes and self-excited vibrations in deep drilling systems
    • Abstract: Publication date: 31 March 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 7
      Author(s): Alexandre Depouhon , Emmanuel Detournay
      This paper analyzes the stability of the discrete model proposed by Richard et al. (2004 [1], 2007 [2]) to study the self-excited axial and torsional vibrations of deep drilling systems. This model, which relies on a rate-independent bit/rock interaction law, reduces to a coupled system of state-dependent delay differential equations governing the axial and angular perturbations to the stationary motion of the bit. A linear stability analysis indicates that, although the steady-state motion of the bit is always unstable, the nature of the instability depends on the nominal angular velocity Ω 0 of the drillstring imposed at the rig. On the one hand, if Ω 0 is larger than a critical velocity Ω c , the angular dynamics is responsible for the instability. However, on the timescale of the resonance period of the drillstring viewed as a torsional pendulum, the system behaves like a marginally stable one, provided that exogenous perturbations are of limited magnitude. The instability then only appears on a much larger timescale, in the form of slowly growing oscillations that ultimately lead to an undesired drilling regime such as bit-bouncing or stick-slip vibrations. On the other hand, if Ω 0 is smaller than Ω c , the instability manifests itself on the timescale of the bit motion due to a dominating unstable axial dynamics; perturbations to the steady-state motion then rapidly degenerate into stick-slip limit cycles or bit-bouncing. For typical deep drilling field conditions, the critical angular velocity Ω c is virtually independent of the axial force acting on the bit and of the bit bluntness. It can be approximated by a power law monomial, a function of known parameters of the drilling system and of the intrinsic specific energy (a quantity characterizing the energy required to drill a particular rock). This approximation holds on account that the dissipation in the drilling structure is negligible with respect to that taking place through the bit/rock interaction, as is typically the case. These findings are further illustrated on an example of deep drilling and shown to match the trends observed in the field.


      PubDate: 2014-01-16T04:37:36Z
       
  • Structural–acoustic model of a rectangular plate–cavity system
           with an attached distributed mass and internal sound sour Theory and
           experiment
    • Abstract: Publication date: 31 March 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 7
      Author(s): Miha Pirnat , Gregor Čepon , Miha Boltežar
      In this paper three approaches are combined to develop a structural–acoustic model of a rectangular plate–cavity system with an attached distributed mass and internal sound source. The first approach results from a recently presented analysis based on the Rayleigh–Ritz method and is used to circumvent the difficulties in obtaining the natural frequencies and mode shapes of a plate with an attached, distributed mass. Furthermore, different plate boundary conditions can be accommodated. The resulting mode shapes are defined as continuous functions; this is advantageous as they can be directly used in the second approach, i.e., the classic modal-interaction approach in order to obtain the coupled equations of the system. Finally, in the third approach a group of point sources emitting a pressure pulse in the time domain is used to model an internal sound source. For the validation of the developed model an experiment was conducted in two configurations using a simply supported aluminium plate and a clamped plate coupled with a plexiglas box containing a loudspeaker. Good agreement was found between the analytical and experimental data.


      PubDate: 2014-01-16T04:37:36Z
       
  • Rotating beamforming – motion-compensation in the frequency domain
           and application of high-resolution beamforming algorithms
    • Abstract: Publication date: 31 March 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 7
      Author(s): Wolfram Pannert , Christian Maier
      A method is presented for the location of rotating sound sources by a microphone array. In contrast to other methods which are formulated in the time domain, this method works completely in the frequency domain and allows the application of advanced, high resolution beamforming techniques. Following the work by Lowis and Joseph for ducted sources, it is shown that a generalized cross-spectral matrix in the rotating frame of reference can be calculated which can serve as a starting point for advanced beamforming techniques. The Green's function of a moving point source under free space conditions is expressed in spherical coordinates, which are, for numerical reasons, more convenient than cylindrical coordinates. The microphones on the array have to be arranged in a ring. As a practical example high resolution beamforming deconvolution methods are applied to simulated data and measured data from rotating sources.


      PubDate: 2014-01-16T04:37:36Z
       
  • The effect of a cavity on airfoil tones
    • Abstract: Publication date: 31 March 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 7
      Author(s): Karn L. Schumacher , Con J. Doolan , Richard M. Kelso
      The presence of a cavity in the pressure surface of an airfoil has been found via experiment to play a role in the production of airfoil tones, which was attributed to the presence of an acoustic feedback loop. The cavity length was sufficiently small that cavity oscillation modes did not occur for most of the investigated chord-based Reynolds number range of 70,000–320,000. The airfoil tonal noise frequencies varied as the position of the cavity was moved along a parallel section at the airfoil's maximum thickness: specifically, for a given velocity, the frequency spacing of the tones was inversely proportional to the geometric distance between the cavity and the trailing edge. The boundary layer instability waves considered responsible for the airfoil tones were only detected downstream of the cavity. This may be the first experimental verification of these aspects of the feedback loop model for airfoil tonal noise.


      PubDate: 2014-01-16T04:37:36Z
       
  • Solution to the problem of Nicolai
    • Abstract: Publication date: 31 March 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 7
      Author(s): A.P. Seyranian , A. Di Egidio , A. Contento , A. Luongo
      We consider the problem of Nicolai on dynamic stability of an elastic cantilever rod loaded by an axial compressive force P and a twisting tangential torque L in continuous formulation. The problem is to find the stability region for non-equal principal moments of inertia of the rod in the space of three parameters: P, L and the parameter α for the ratio of principal moments of inertia. New governing equations and boundary conditions, which form the basis for analytical and numerical studies, are derived. An important detail of this formulation is that the pre-twisting of the rod due to the torque L is taken into account. The singular point on the stability boundary at the critical Euler force P E is recognized and investigated in detail. For an elliptic cross-section of a uniform rod the stability region is found numerically with the use of the Galerkin method and the exact numerical approach. The obtained numerical results are compared with the analytical formulas of the asymptotic analysis.


      PubDate: 2014-01-16T04:37:36Z
       
  • Structural optimization of an asymmetric automotive brake disc with
           cooling channels to avoid squeal
    • Abstract: Publication date: 31 March 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 7
      Author(s): Andreas Wagner , Gottfried Spelsberg-Korspeter , Peter Hagedorn
      Brake squeal is still a major issue in the automotive industry due to comfort complaints of passengers and resulting high warranty costs. Many measures to avoid squeal have been discussed in the engineering community reaching from purely passive measures like the increase of damping, e.g. by the application of shims, to the active or semiactive suppression of squeal. While active measures can be effective but are elaborate and therefore more expensive, passive measure are less complex in most cases. This leads to the necessity to develop passive, economic and robust measures to avoid squeal. Asymmetry of the brake rotor has been proposed to achieve this goal and the resulting split of all double eigenfrequencies of the brake rotor has lately been shown to stabilize the system. Thus, a structural optimization of an automotive brake disc with cooling channels is presented in this paper with the objective to split all eigenfrequencies of the brake rotor in a certain frequency range by introducing asymmetry to the cooling channels. Constraints of the optimization are balance constraints, to guarantee a balanced operation for all rotor speeds, and minimal and maximal distance constraints of the cooling ribs, due to cooling and material strength requirements. First, a modeling approach of the brake disc with cooling channels is shortly presented which helps to avoid remeshing during the structural optimization. The introduced optimization problem is known to be highly nonlinear, nonconvex and with many local optima to be expected. Therefore, two approaches for the solution of the problem are chosen. The first, a deterministic one, is a Sequential Quadratic Programming (SQP) approach efficiently targeting local optima. In order to increase the possibility to find the global optimum, a set of randomly distributed starting configurations is chosen, leading to satisfying results. The other, a heuristic approach, uses a Genetic Algorithm (GA) directly aiming for the global optimum. The GA also delivers very satisfying results, nevertheless, the best solution has been found with the SQP approach. In order to validate the basic idea that a defined separation of eigenfrequencies helps to avoid squeal, modal analysis and squeal tests have been performed with a simplified disc with radial holes. The conducted experiments strongly support the theoretical findings and demonstrate the superior squeal behavior of the optimized disc.


      PubDate: 2014-01-16T04:37:36Z
       
  • Editorial Board
    • Abstract: Publication date: 31 March 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 7




      PubDate: 2014-01-16T04:37:36Z
       
  • Comparison of various decentralised structural and cavity feedback control
           strategies for transmitted noise reduction through a double panel
           structure
    • Abstract: Publication date: 31 March 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 7
      Author(s): Jen‐Hsuan Ho , Arthur Berkhoff
      This paper compares various decentralised control strategies, including structural and acoustic actuator–sensor configuration designs, to reduce noise transmission through a double panel structure. The comparison is based on identical control stability indexes. The double panel structure consists of two panels with air in between and offers the advantages of low sound transmission at high frequencies, low heat transmission, and low weight. The double panel structure is widely used, such as in the aerospace and automotive industries. Nevertheless, the resonance of the cavity and the poor sound transmission loss at low frequencies limit the double panel's noise control performance. Applying active structural acoustic control to the panels or active noise control to the cavity has been discussed in many papers. In this paper, the resonances of the panels and the cavity are considered simultaneously to further reduce the transmitted noise through an existing double panel structure. A structural–acoustic coupled model is developed to investigate and compare various structural control and cavity control methods. Numerical analysis and real-time control results show that structural control should be applied to both panels. Three types of cavity control sources are presented and compared. The results indicate that the largest noise reduction is obtained with cavity control by loudspeakers modified to operate as incident pressure sources.


      PubDate: 2014-01-16T04:37:36Z
       
  • Influence of inerter on natural frequencies of vibration systems
    • Abstract: Publication date: 31 March 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 7
      Author(s): Michael Z.Q. Chen , Yinlong Hu , Lixi Huang , Guanrong Chen
      This paper investigates the influence of inerter on the natural frequencies of vibration systems. First of all, the natural frequencies of a single-degree-of-freedom (SDOF) system and a two-degree-of-freedom (TDOF) system are derived algebraically and the fact that the inerter can reduce the natural frequencies of these systems is demonstrated. Then, to further investigate the influence of inerter in a general vibration system, a multi-degree-of-freedom system (MDOF) is considered. Sensitivity analysis is performed on the natural frequencies and mode shapes to demonstrate that the natural frequencies of the MDOF system can always be reduced by increasing the inertance of any inerter. The condition for a general MDOF system of which the natural frequencies can be reduced by an inerter is also derived. Finally, the influence of the inerter position on the natural frequencies is investigated and the efficiency of inerter in reducing the largest natural frequencies is verified by simulating a six-degree-of-freedom system, where a reduction of more than 47 percent is obtained by employing only five inerters.


      PubDate: 2014-01-16T04:37:36Z
       
  • Green's functions of the forced vibration of Timoshenko beams with damping
           effect
    • Abstract: Publication date: 17 March 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 6
      Author(s): X.Y. Li , X. Zhao , Y.H. Li
      This paper is concerned with the dynamic solutions for forced vibrations of Timoshenko beams in a systematical manner. Damping effects on the vibrations of the beam are taken into consideration by introducing two characteristic parameters. Laplace transform method is applied in the present study and corresponding Green's functions are presented explicitly for beams with various boundaries. The present solutions can be readily reduced to those for others classical beam models by setting corresponding parameters to zero or infinite. Numerical calculations are performed to validate the present solutions and the effects of various important physical parameters are investigated.


      PubDate: 2014-01-04T04:35:22Z
       
  • Revisiting a magneto-elastic strange attractor
    • Abstract: Publication date: 17 March 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 6
      Author(s): Jee Ian Tam , Philip Holmes
      We revisit an early example of a nonlinear oscillator that exhibits chaotic motions when subjected to periodic excitation: the magneto-elastically buckled beam. In the paper of Moons and Holmes (1980) [1] magnetic field calculations were outlined but not carried through; instead the nonlinear forces responsible for creation of a two-well potential and buckling were fitted to a polynomial function after reduction to a single mode model. In the present paper we compute the full magnetic field and use it to approximate the forces acting on the beam, also using a single mode reduction. This provides a complete model that accurately predicts equilibria, bifurcations, and free oscillation frequencies of an experimental device. We also compare some periodic, transient and chaotic motions with those obtained by numerical simulations of the single mode model, further illustrating the rich dynamical behavior of this simple electromechanical system.


      PubDate: 2014-01-04T04:35:22Z
       
  • Efficient model order reduction for dynamic systems with local
           nonlinearities
    • Abstract: Publication date: 17 March 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 6
      Author(s): Mohsen Mohammadali , Hamid Ahmadian
      In the nonlinear structural analysis, the nonlinear effects are commonly localized and the rest of the structure behaves in a linear manner. Considering this fact, this research work proposes a harmonic balance solution in order to determine the nonlinear response of the structures. The solution is simplified by using an exact dynamic reduction along with the modal expansion technique. This novel approach, which is applicable to both discrete and continuous systems, converts the system equations of motion in each harmonic to a small set of nonlinear algebraic equations. The full set of system equations is reduced to a discrete system with a few generalized degrees of freedom (DOFs) confined to the localized nonlinear regions. The resultant reduced order model is shown to be accurate enough for determining the periodic response. To demonstrate the capability of the proposed method, numerical case studies for continuous and discrete systems, including systems with internal resonance, have been studied and the outcomes are validated with benchmark studies. In addition, the method is applied in the identification process of an experimental test setup with unknown frictional support parameters, and the results are presented and discussed.


      PubDate: 2014-01-04T04:35:22Z
       
  • A driven system of impacting pendulums: Experiments and simulations
    • Abstract: Publication date: 17 March 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 6
      Author(s): T. Witelski , L.N. Virgin , C. George
      This paper studies a system composed of two pendulums attached to a common base that is oscillated horizontally. The pendulums share a common pivot line, but move independently and are only coupled together through collisions. Impact dynamics for the collisions of the pendulums with each other and with fixed barriers yield complex nonlinear behaviors. Careful numerical simulation of the equations of motion demonstrates a close correlation with experimental data collected from the system. There are many independent parameters in this system, and one of the motivations for the present study is to establish the extent to which we can capture observed behavior with a relatively simple hybrid differential equation model in the face of several independent energy dissipation mechanisms coming from friction and impact. Comparison between experiments and simulations is based on the standard nonlinear dynamical system analyses of time series, phase projections, time-lag embedding, Poincaré sections, and frequency content. Grazing bifurcations and co-existence of impacting/non-impacting periodic/chaotic states are observed.


      PubDate: 2014-01-04T04:35:22Z
       
  • Flutter and divergence instability of the multi-cracked cantilever
           beam-column
    • Abstract: Publication date: 17 March 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 6
      Author(s): S. Caddemi , I. Caliò , F. Cannizzaro
      For conservative systems instability can occur only by divergence and the presence of damage can produce both a reduction of the buckling loads and modification of the corresponding mode shapes, depending on the positions and intensities of the damage distribution. For nonconservative systems instability is found to occur by divergence, flutter, or both, characterised by multiple stable and unstable ranges of the loads whose boundary can be altered by the damage distribution. This paper focuses on the stability behaviour of multi-cracked cantilever Euler beam-column subjected to conservative or nonconservative axial loads. The exact flutter and divergence critical loads are obtained by means of the exact closed form solution of the multi-cracked beam-column, derived by the authors in a previous paper. The extensive numerical applications, reported in the paper, aimed at evaluating the influence of several damage scenarios for different values of the degree of nonconservativeness. It is shown how the presence of damage can strongly modify the ranges of divergence and flutter critical loads of the corresponding undamaged cantilever column, which has been the subject of several papers starting from the Pflüger paradoxical results.


      PubDate: 2014-01-04T04:35:22Z
       
  • Efficient parametric uncertainty analysis within the hybrid Finite
           Element/Statistical Energy Analysis method
    • Abstract: Publication date: 17 March 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 6
      Author(s): Alice Cicirello , Robin S. Langley
      This paper is concerned with the development of efficient algorithms for propagating parametric uncertainty within the context of the hybrid Finite Element/Statistical Energy Analysis (FE/SEA) approach to the analysis of complex vibro-acoustic systems. This approach models the system as a combination of SEA subsystems and FE components; it is assumed that the FE components have fully deterministic properties, while the SEA subsystems have a high degree of randomness. The method has been recently generalised by allowing the FE components to possess parametric uncertainty, leading to two ensembles of uncertainty: a non-parametric one (SEA subsystems) and a parametric one (FE components). The SEA subsystems ensemble is dealt with analytically, while the effect of the additional FE components ensemble can be dealt with by Monte Carlo Simulations. However, this approach can be computationally intensive when applied to complex engineering systems having many uncertain parameters. Two different strategies are proposed: (i) the combination of the hybrid FE/SEA method with the First Order Reliability Method which allows the probability of the non-parametric ensemble average of a response variable exceeding a barrier to be calculated and (ii) the combination of the hybrid FE/SEA method with Laplace's method which allows the evaluation of the probability of a response variable exceeding a limit value. The proposed approaches are illustrated using two built-up plate systems with uncertain properties and the results are validated against direct integration, Monte Carlo simulations of the FE and of the hybrid FE/SEA models.


      PubDate: 2014-01-04T04:35:22Z
       
  • Effects of internal mass distribution and its isolation on the acoustic
           characteristics of a submerged hull
    • Abstract: Publication date: 17 March 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 6
      Author(s): Herwig Peters , Roger Kinns , Nicole Kessissoglou
      The primary aim of machinery isolation in marine vessels is to isolate structural vibration of the onboard machinery from the hull and to reduce far-field radiation of underwater noise. A substantial proportion of the total submarine mass is on flexible mounts that isolate supported masses from the hull at frequencies above the mounting system resonant frequency. This reduces the dynamically effective mass of the hull and affects the signature of the marine vessel due to propeller excitation. A fully coupled finite element/boundary element (FE/BE) model has been developed to investigate the effect of mass distribution and isolation in a submerged hull. The finite element model of the structure includes internal structures to represent the machinery and other flexibly mounted components. Changes in the radiated sound power demonstrate the effect of machinery isolation on the acoustic signature of the submerged hull due to the external propeller forces. Results are also presented to show how the arrangement of flexible mounts for a large internal structure can influence the radiation due to machinery forces.


      PubDate: 2014-01-04T04:35:22Z
       
  • Vibrational analysis of structures with stochastic interfaces in the
           medium-frequency range: Experimental validation on a touch screen
    • Abstract: Publication date: 17 March 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 6
      Author(s): Philippe Rouch , Claude Blanzé
      This paper proposes a dedicated approach and its experimental validation when dealing with structures (including stochastic parameters, such as interface parameters) in medium-frequency vibrations. The first ingredient is the use of a dedicated approach – the Variational Theory of Complex Rays (VTCR) – to solve the medium-frequency problem. The VTCR, which uses two-scale shape functions verifying the dynamic equation and the constitutive relation, can be viewed as a means of expressing the power balance at the different interfaces between substructures. The second ingredient is the use of the Polynomial Chaos Expansion (PCE) to calculate the random response. Since the only uncertain parameters are those which appear in the interface equations (which, in this application, are the complex connection stiffness parameters), this approach leads to very low computation costs. This method is validated on a new kind of touch screen. The simulated mobilities are compared with experimental ones obtained with a laser vibrometer and a good agreement is founded on a large medium-frequency bandwidth.


      PubDate: 2014-01-04T04:35:22Z
       
  • External damping losses in measuring the vibration damping properties in
           lightly damped specimens using transient time-domain methods
    • Abstract: Publication date: 17 March 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 6
      Author(s): Joachim Vanwalleghem , Ives De Baere , Mia Loccufier , Wim Van Paepegem
      The contaminating effect of external damping sources to the overall measured damping of mechanical structures has always been an issue. Although these sources are qualitatively known, they are often not considered if damping properties are experimentally determined, yielding erroneous results. The aim of this paper is to quantify some of these undesired effects on the overall measured damping value. Free vibrations of steel plate specimens are used to list up several causes of external damping sources. As small modifications to the test setup may lead to totally different results, appropriate actions are offered to design a more accurate test setup. Known observations, such as the damping value’s dependence on the specimen size and the excitation level, are confirmed. Finally, it is shown that the damping capacity of one type of steel alloy can usually not be generalised to other steel alloys.


      PubDate: 2014-01-04T04:35:22Z
       
  • Tuned mass absorber on a flexible structure
    • Abstract: Publication date: 17 March 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 6
      Author(s): Steen Krenk , Jan Høgsberg
      The classic design of a tuned mass absorber is based on a simple two-mass analogy in which the tuned mass is connected to the structural mass with a spring and a viscous damper. In a flexible multi-degree-of-freedom structure the tuned mass absorber is typically introduced to provide damping of a specific mode. The motion of the point of attachment of the tuned mass absorber to the structure has not only a contribution from the targeted mode, but also a background contribution from other non-resonant modes. Similarly, the force provided by the tuned mass absorber is distributed between the targeted mode and the background modes. It is demonstrated how this effect can be included via a non-dimensional dynamic background flexibility coefficient, extracted from a classic modal analysis for the particular frequency of the selected mode. An explicit calibration procedure is developed starting with the desired maximum amplification, from which the device damper, mass and stiffness are determined, accounting for the background flexibility. Examples demonstrate the influence of the flexibility effect and the efficiency of the proposed procedure.


      PubDate: 2014-01-04T04:35:22Z
       
  • Galloping of iced quad-conductors bundles based on curved beam theory
    • Abstract: Publication date: 17 March 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 6
      Author(s): Zhitao Yan , Eric Savory , Zhengliang Li , William E. Lin
      Galloping refers to wind-induced, low-frequency, large-amplitude oscillations that have been more frequently observed for a bundle conductor than for a single conductor. In the present work two different models are built to investigate the galloping of a bundle conductor: (1) a finite curved beam element method and (2) a hybrid model based on curved beam element theory. The finite curved beam element model is effective in dealing with the spacers between the bundled conductors and the joint between the conductors and spacers that can be simulated as a rigid joint or a hinge. Furthermore, the finite curved beam element model can be used to deal with large deformation. The hybrid model invokes the small deformation hypothesis and has a high computational efficiency. A hybrid model based on conventional cable element theory is also programmed to be compared with the aforementioned models based on curved beam element theory. Numerical examples are presented to assess the accuracy of the different models in predicting the equilibrium conductor position, natural frequencies and galloping amplitude. The results show that the curved beam element models, involving more degrees of freedom and coupling of translational and torsional motion, are more accurate at simulating the static and dynamic characters of an iced quad-conductor bundle. The use of hinges, rather than rigid connections, reduces the structural response amplitudes of a galloping conductor bundle.


      PubDate: 2014-01-04T04:35:22Z
       
  • A frequency shift curve based damage detection method for cylindrical
           shell structures
    • Abstract: Publication date: 17 March 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 6
      Author(s): Yao Zhang , Seng Tjhen Lie , Zhihai Xiang , Qiuhai Lu
      A novel damage detection method based on frequency shift curve (FSC) is developed for cylindrical shell structures. The FSC is caused by auxiliary mass containing both the natural frequencies and mode shapes information. According to axis-symmetry, the FSC is flat when there is no damage. However, it shows obvious periodic peaks when localized imperfections or damages occur. Furthermore, for the +2nd FSC, the trough with minimum value indicates the circumferential location of the damage and the difference between the lowest trough value and the values of the other three troughs represents the severity of the local damage. Through changing the location of the accelerometer, which can be considered as an auxiliary mass itself, around the cylindrical shell circumference, the FSCs can be measured and then the damage can be detected and located. Moreover, the difference between the averages of ±2nd FSCs also reflects the severity of damages. Numerical simulation and experimental tests have confirmed the finding. Compared with other vibration based methods, the proposed method is fast, sensitive and feasible to implement in practice as the measured frequency is more accurate than the mode shapes, and only a single accelerometer is required in the tests.


      PubDate: 2014-01-04T04:35:22Z
       
  • Stochastic stability of a fractional viscoelastic column under bounded
           noise excitation
    • Abstract: Publication date: 17 March 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 6
      Author(s): J. Deng , W.-C. Xie , M.D. Pandey
      The stability of a viscoelastic column under the excitation of stochastic axial compressive load is investigated in this paper. The material of the column is modeled using a fractional Kelvin–Voigt constitutive relation, which leads to that the equation of motion is governed by a stochastic fractional equation with parametric excitation. The excitation is modeled as a bounded noise, which is a realistic model of stochastic fluctuation in engineering applications. The method of stochastic averaging is used to approximate the responses of the original dynamical system by a new set of averaged variables which are diffusive Markov vector. An eigenvalue problem is formulated from the averaged equations, from which the moment Lyapunov exponent is determined for the column system with small damping and weak excitation. The effects of various parameters on the stochastic stability and significant parametric resonance are discussed and confirmed by simulation results.


      PubDate: 2014-01-04T04:35:22Z
       
  • Determination of modal parameters from off-diagonal FRFs using the
           double-exponential windowing method
    • Abstract: Publication date: 17 March 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 6
      Author(s): X. Sheng , Q. Feng
      In a recently published paper (Sheng, 2012) [1], the double-exponential windowing method has been developed for the determination of modal parameters for lightly damped structures. This method, like many others, requires the driving-point frequency response function (FRF) to be measured. However, this requirement is sometimes practically hard to meet, especially when the structure is small, since it is difficult, if not impossible, to avoid interference between the force transducer and the laser beam as a response pick-up, thus limiting the usefulness of the method. To overcome this shortcoming, an alternative is therefore developed in this paper: a similar process but without requiring the measuring of any driving-point FRF.


      PubDate: 2014-01-04T04:35:22Z
       
  • Assessing impact force localization by using a particle swarm optimization
           algorithm
    • Abstract: Publication date: 17 March 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 6
      Author(s): Abdelali El-Bakari , Abdellatif Khamlichi , Eric Jacquelin , Rachid Dkiouak
      This paper focuses on the inverse problem regarding force localization in the case of impacts not concentrated at a point but which occur on elastic beams. Following the identification approach proposed to solve this problem and which is based on the reciprocity theorem, the impact location characteristics were determined by using particle swarm optimization algorithm. To eliminate numerical trouble due to the trivial solutions appearing in this formulation, the fitness function was customized by introducing a set of weighting coefficients. Four different formulations of the fitness function were considered and their performances with regards to the number of sensors used and their positions were analyzed. They enabled a selection of the best combination of weighting coefficients to be used in the context of an impact force localization process based on the particle swarm optimization technique. Three sensors were found to be required and comparison with a genetic algorithm has revealed the effectiveness of the proposed method in terms of accuracy and computational time.


      PubDate: 2014-01-04T04:35:22Z
       
  • Nonlinear analysis, design and vibration isolation for a bilinear system
           with time-delayed cubic velocity feedback
    • Abstract: Publication date: 17 March 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 6
      Author(s): X. Gao , Q. Chen
      This paper combines cubic nonlinearity and time delay to improve the performance of vibration isolation. Nonlinear dynamics properties, design methodology and isolation performance are studied for a piecewise bilinear vibration isolation system with the time-delayed cubic velocity feedback control. By the multi-scale perturbation method, the equivalent stiffness and damping are first defined to interpret the effect of feedback control loop on dynamics behaviours, such as frequency island phenomenon. Then, a design criterion is proposed to suppress the jump phenomenon induced by the saddle-node bifurcation. With the purpose of obtaining the desirable vibration isolation performance, stability conditions are obtained to find appropriate feedback parameters including gain and time delay. Last, the influence of the feedback parameters on vibration transmissibility is assessed. Results show that the strategy developed in this paper is practicable and feedback parameters are significant factors to alter dynamics behaviours, and more importantly, to improve the isolation effectiveness for the bilinear isolation system.


      PubDate: 2014-01-04T04:35:22Z
       
  • Editorial Board
    • Abstract: Publication date: 17 March 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 6




      PubDate: 2014-01-04T04:35:22Z
       
  • Damage identification for beams in noisy conditions based on Teager energy
           operator-wavelet transform modal curvature
    • Abstract: Publication date: 17 March 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 6
      Author(s): Maosen Cao , Wei Xu , Wieslaw Ostachowicz , Zhongqing Su
      Modal curvatures have been widely used in the detection of structural damage. Attractive features of modal curvature include great sensitivity to damage and instant determination of damage location. However, an intrinsic deficiency in a modal curvature is its susceptibility to the measurement noise present in the displacement mode shape that produces the modal curvature, likely obscuring the features of damage. To address this deficiency, the Teager energy operator together with wavelet transform is tactically utilized to treat modal curvature, producing a new modal curvature, termed the Teager energy operator-wavelet transform modal curvature. This new modal curvature features distinct capabilities of suppressing noise, canceling global trends, and intensifying the singular feature caused by damage for a measured mode shape involving noise. These features maximize the sensitivity to damage and accuracy of damage localization. The proposed modal curvature is demonstrated in several analytical cases of cracked pinned–pinned, clamped–free and clamped–clamped beams, with emphasis on characterizing damage in noisy conditions, and it is further validated by an experimental program using a scanning laser vibrometer to acquire mode shapes of a cracked aluminum beam. The Teager energy operator-wavelet transform modal curvature essentially overcomes the deficiency of conventional modal curvature, providing a new dynamic feature well suited for damage characterization in noisy environments. (The Matlab code for implementing Teager energy operator-wavelet transform modal curvature can be provided by the corresponding author on request.)


      PubDate: 2014-01-04T04:35:22Z
       
  • A refined use of the residue theorem for the evaluation of band-averaged
           input power into linear second-order dynamic systems
    • Abstract: Publication date: 17 March 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 6
      Author(s): R. D'Amico , D. Huybrechs , W. Desmet
      In a recent work, a strategy was proposed which exploits the residue theorem as an efficient tool for evaluating the frequency averaged input power into vibrating systems. In this paper, such a technique is generalised and further insight and improvements are presented. Evaluating band-averages requires the solution of a weighted integral over a real frequency variable. In this paper, the integration path is moved to the complex plane, where the input mobility shows a smoother behaviour. Consequently, a smaller number of quadrature points are needed to perform an accurate integration, which leads to a significant reduction of computational time. In addition, the connection between the use of quadrature rules in the complex plane and weighting functions on real frequencies is considered. Two application examples prove the accuracy of the present strategy for different quadrature rules. Adaptive integration schemes are also investigated.


      PubDate: 2014-01-04T04:35:22Z
       
  • Spatial, temporal, and thermal contributions to focusing contrast by time
           reversal in a cavity
    • Abstract: Publication date: 17 March 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 6
      Author(s): Charles Hudin , José Lozada , Vincent Hayward
      The accuracy of wave focusing by time reversal depends on a quantity termed ‘contrast ratio’ that measures the amplitude of a localized peak of velocity relatively to background noise. A comprehensive expression for the contrast ratio in a lossy cavity is derived by modal decomposition of the wave field. This expression accounts for the effects of the mechanical and the dimensional properties of the cavity, the bandwidth of the excitation signal, the number of sources, and the duration of time reversal window. The expression can predict the characteristics of a given process such as the long-time saturation and the single-channel time reversal limit. The expression also models the effect of temperature variations on focusing accuracy and shows that thermal drift exhibits two regimes. In the first regime, small temperature variations have little effect on contrast. The second regime is characterized by a rapid deterioration of contrast. Experimental measurements show close agreement with the theory.


      PubDate: 2014-01-04T04:35:22Z
       
  • On damage diagnosis for a wind turbine blade using pattern recognition
    • Abstract: Publication date: 17 March 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 6
      Author(s): N. Dervilis , M. Choi , S.G. Taylor , R.J. Barthorpe , G. Park , C.R. Farrar , K. Worden
      With the increased interest in implementation of wind turbine power plants in remote areas, structural health monitoring (SHM) will be one of the key cards in the efficient establishment of wind turbines in the energy arena. Detection of blade damage at an early stage is a critical problem, as blade failure can lead to a catastrophic outcome for the entire wind turbine system. Experimental measurements from vibration analysis were extracted from a 9m CX-100 blade by researchers at Los Alamos National Laboratory (LANL) throughout a full-scale fatigue test conducted at the National Renewable Energy Laboratory (NREL) and National Wind Technology Center (NWTC). The blade was harmonically excited at its first natural frequency using a Universal Resonant EXcitation (UREX) system. In the current study, machine learning algorithms based on Artificial Neural Networks (ANNs), including an Auto-Associative Neural Network (AANN) based on a standard ANN form and a novel approach to auto-association with Radial Basis Functions (RBFs) networks are used, which are optimised for fast and efficient runs. This paper introduces such pattern recognition methods into the wind energy field and attempts to address the effectiveness of such methods by combining vibration response data with novelty detection techniques.


      PubDate: 2014-01-04T04:35:22Z
       
  • Discussion on “Nonlinear vibration of functionally graded circular
           cylindrical shells based on improved Donnell equations” by D.H. Bich
           and N. Xuan Nguyen, Journal of Sound and Vibration 331(25) (2012)
           5488–5501
    • Abstract: Publication date: 17 March 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 6
      Author(s): M. Amabili



      PubDate: 2014-01-04T04:35:22Z
       
  • Reply to: Discussion on “Nonlinear vibration of functionally graded
           circular cylindrical shells based on improved Donnell equations” by
           D.H. Bich and N. Xuan Nguyen, Journal of Sound and Vibration 331 (25)
           (2012) 5488–5501
    • Abstract: Publication date: 17 March 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 6
      Author(s): Dao Huy Bich , Nguyen Xuan Nguyen



      PubDate: 2014-01-04T04:35:22Z
       
  • Corrigendum to “Wavenumber prediction and measurement of
           axisymmetric waves in buried fluid-filled pipes: Inclusion of shear
           coupling at a lubricated pipe/soil interface” [J. Sound Vib. 332 (5)
           (2013) 1216–1230]
    • Abstract: Publication date: 17 March 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 6
      Author(s): J.M. Muggleton , J. Yan



      PubDate: 2014-01-04T04:35:22Z
       
  • Editorial Board
    • Abstract: Publication date: 28 February 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 5




      PubDate: 2013-12-15T16:31:54Z
       
  • Disturbance rejection control for vibration suppression of piezoelectric
           laminated thin-walled structures
    • Abstract: Publication date: 28 February 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 5
      Author(s): S.Q. Zhang , H.N. Li , R. Schmidt , P.C. Müller
      Thin-walled piezoelectric integrated smart structures are easily excited to vibrate by unknown disturbances. In order to design and simulate a control strategy, firstly, an electro-mechanically coupled dynamic finite element (FE) model of smart structures is developed based on first-order shear deformation (FOSD) hypothesis. Linear piezoelectric constitutive equations and the assumption of constant electric field through the thickness are considered. Based on the dynamic FE model, a disturbance rejection (DR) control with proportional-integral (PI) observer using step functions as the fictitious model of disturbances is developed for vibration suppression of smart structures. In order to achieve a better dynamic behavior of the fictitious model of disturbances, the PI observer is extended to generalized proportional-integral (GPI) observer, in which sine or polynomial functions can be used to represent disturbances resulting in better dynamics. Therefore the disturbances can be estimated either by PI or GPI observer, and then the estimated signals are fed back to the controller. The DR control is validated by various kinds of unknown disturbances, and compared with linear-quadratic regulator (LQR) control. The results illustrate that the vibrations are better suppressed by the proposed DR control.


      PubDate: 2013-12-15T16:31:54Z
       
  • Optimal locations and orientations of piezoelectric transducers on
           cylindrical shell based on gramians of contributed and undesired
           Rayleigh–Ritz modes using genetic algorithm
    • Abstract: Publication date: 28 February 2014
      Source:Journal of Sound and Vibration, Volume 333, Issue 5
      Author(s): Mojtaba Biglar , Hamid Reza Mirdamadi , Mohammad Danesh
      In this study, the active vibration control and configurational optimization of a cylindrical shell are analyzed by using piezoelectric transducers. The piezoelectric patches are attached to the surface of the cylindrical shell. The Rayleigh–Ritz method is used for deriving dynamic modeling of cylindrical shell and piezoelectric sensors and actuators based on the Donnel–Mushtari shell theory. The major goal of this study is to find the optimal locations and orientations of piezoelectric sensors and actuators on the cylindrical shell. The optimization procedure is designed based on desired controllability and observability of each contributed and undesired mode. Further, in order to limit spillover effects, the residual modes are taken into consideration. The optimization variables are the positions and orientations of piezoelectric patches. Genetic algorithm is utilized to evaluate the optimal configurations. In this article, for improving the maximum power and capacity of actuators for amplitude depreciation of negative velocity feedback strategy, we have proposed a new control strategy, called “Saturated Negative Velocity Feedback Rule (SNVF)”. The numerical results show that the optimization procedure is effective for vibration reduction, and specifically, by locating actuators and sensors in their optimal locations and orientations, the vibrations of cylindrical shell are suppressed more quickly.


      PubDate: 2013-12-15T16:31:54Z
       
 
 
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