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Journal Cover Journal of Sound and Vibration
  [SJR: 1.494]   [H-I: 121]   [186 followers]  Follow
    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 0022-460X - ISSN (Online) 1095-8568
   Published by Elsevier Homepage  [3043 journals]
  • Fractional-order positive position feedback compensator for active
           vibration control of a smart composite plate
    • Authors: L. Marinangeli; F. Alijani; S. Hassan HosseinNia
      Pages: 1 - 16
      Abstract: Publication date: 6 January 2018
      Source:Journal of Sound and Vibration, Volume 412
      Author(s): L. Marinangeli, F. Alijani, S. Hassan HosseinNia
      In this paper, Active Vibration Control (AVC) of a rectangular carbon fibre composite plate with free edges is presented. The plate is subjected to out-of-plane excitation by a modal vibration exciter and controlled by Macro Fibre Composite (MFC) transducers. Vibration measurements are performed by using a Laser Doppler Vibrometer (LDV) system. A fractional-order Positive Position Feedback (PPF) compensator is proposed, implemented and compared to the standard integer-order PPF. MFC actuator and sensor are positioned on the plate based on maximal modal strain criterion, so as to control the second natural mode of the plate. Both integer and fractional-order PPF allowed for the effective control of the second mode of vibration. However, the newly proposed fractional-order controller is found to be more efficient in achieving the same performance with less actuation voltage. Moreover, it shows promising performance in reducing spillover effect due to uncontrolled modes.

      PubDate: 2017-10-02T02:15:46Z
      DOI: 10.1016/j.jsv.2017.09.009
      Issue No: Vol. 412 (2017)
       
  • Computational and experimental studies of microvascular void features for
           passive-adaptation of structural panel dynamic properties
    • Authors: Nicholas C. Sears; Ryan L. Harne
      Pages: 17 - 27
      Abstract: Publication date: 6 January 2018
      Source:Journal of Sound and Vibration, Volume 412
      Author(s): Nicholas C. Sears, Ryan L. Harne
      The performance, integrity, and safety of built-up structural systems are critical to their effective employment in diverse engineering applications. In conflict with these goals, harmonic or random excitations of structural panels may promote large amplitude oscillations that are particularly harmful when excitation energies are concentrated around natural frequencies. This contributes to fatigue concerns, performance degradation, and failure. While studies have considered active or passive damping treatments that adapt material characteristics and configurations for structural control, it remains to be understood how vibration properties of structural panels may be tailored via internal material transitions. Motivated to fill this knowledge gap, this research explores an idea of adapting the static and dynamic material distribution of panels through embedded microvascular channels and strategically placed voids that permit the internal movement of fluids within the panels for structural dynamic control. Finite element model and experimental investigations probe how redistributing material in the form of microscale voids influences the global vibration modes and natural frequencies of structural panels. Through parameter studies, the relationships among void shape, number, size, and location are quantified towards their contribution to the changing structural dynamics. For the panel composition and boundary conditions considered in this report, the findings reveal that transferring material between strategically placed voids may result in eigenfrequency changes as great as 10.0, 5.0, and 7.4% for the first, second, and third modes, respectively.

      PubDate: 2017-10-02T02:15:46Z
      DOI: 10.1016/j.jsv.2017.09.024
      Issue No: Vol. 412 (2017)
       
  • Vibration analysis of partially cracked plate submerged in fluid
    • Authors: Shashank Soni; N.K. Jain; P.V. Joshi
      Pages: 28 - 57
      Abstract: Publication date: 6 January 2018
      Source:Journal of Sound and Vibration, Volume 412
      Author(s): Shashank Soni, N.K. Jain, P.V. Joshi
      The present work proposes an analytical model for vibration analysis of partially cracked rectangular plates coupled with fluid medium. The governing equation of motion for the isotropic plate based on the classical plate theory is modified to accommodate a part through continuous line crack according to simplified line spring model. The influence of surrounding fluid medium is incorporated in the governing equation in the form of inertia effects based on velocity potential function and Bernoulli's equations. Both partially and totally submerged plate configurations are considered. The governing equation also considers the in-plane stretching due to lateral deflection in the form of in-plane forces which introduces geometric non-linearity into the system. The fundamental frequencies are evaluated by expressing the lateral deflection in terms of modal functions. The assessment of the present results is carried out for intact submerged plate as to the best of the author's knowledge the literature lacks in analytical results for submerged cracked plates. New results for fundamental frequencies are presented as affected by crack length, fluid level, fluid density and immersed depth of plate. By employing the method of multiple scales, the frequency response and peak amplitude of the cracked structure is analyzed. The non-linear frequency response curves show the phenomenon of bending hardening or softening and the effect of fluid dynamic pressure on the response of the cracked plate.

      PubDate: 2017-10-02T02:15:46Z
      DOI: 10.1016/j.jsv.2017.09.016
      Issue No: Vol. 412 (2017)
       
  • Energy dissipation/transfer and stable attitude of spatial on-orbit
           tethered system
    • Authors: Weipeng Hu; Mingzhe Song; Zichen Deng
      Pages: 58 - 73
      Abstract: Publication date: 6 January 2018
      Source:Journal of Sound and Vibration, Volume 412
      Author(s): Weipeng Hu, Mingzhe Song, Zichen Deng
      For the Tethered Satellite System, the coupling between the platform system and the solar panel is a challenge in the dynamic analysis. In this paper, the coupling dynamic behaviors of the Tethered Satellite System that is idealized as a planar flexible damping beam-spring-mass composite system are investigated via a structure-preserving method. Considering the coupling between the plane motion of the system, the oscillation of the spring and the transverse vibration of the beam, the dynamic model of the composite system is established based on the Hamiltonian variational principle. A symplectic dimensionality reduction method is proposed to decouple the dynamic system into two subsystems approximately. Employing the complex structure-preserving approach presented in our previous work, numerical iterations are performed between the two subsystems with weak damping to study the energy dissipation/transfer in the composite system, the effect of the spring stiffness on the energy distribution and the effect of the particle mass on the stability of the composite system. The numerical results show that: the energy transfer approach is uniquely determined by the initial attitude angle, while the energy dissipation speed is mainly depending on the initial attitude angle and the spring stiffness besides the weak damping. In addition, the mass ratio between the platform system and the solar panel determines the stable state as well as the time needed to reach the stable state of the composite system. The numerical approach presented in this paper provides a new way to deal with the coupling dynamic system and the conclusions obtained give some useful advices on the overall design of the Tethered Satellite System.

      PubDate: 2017-10-10T06:53:24Z
      DOI: 10.1016/j.jsv.2017.09.032
      Issue No: Vol. 412 (2017)
       
  • Dynamic interaction of monowheel inclined vehicle-vibration platform
           coupled system with quadratic and cubic nonlinearities
    • Authors: Shihua Zhou; Guiqiu Song; Maojun Sun; Zhaohui Ren; Bangchun Wen
      Pages: 74 - 94
      Abstract: Publication date: 6 January 2018
      Source:Journal of Sound and Vibration, Volume 412
      Author(s): Shihua Zhou, Guiqiu Song, Maojun Sun, Zhaohui Ren, Bangchun Wen
      In order to analyze the nonlinear dynamics and stability of a novel design for the monowheel inclined vehicle-vibration platform coupled system (MIV-VPCS) with intermediate nonlinearity support subjected to a harmonic excitation, a multi-degree of freedom lumped parameter dynamic model taking into account the dynamic interaction of the MIV-VPCS with quadratic and cubic nonlinearities is presented. The dynamical equations of the coupled system are derived by applying the displacement relationship, interaction force relationship at the contact position and Lagrange's equation, which are further discretized into a set of nonlinear ordinary differential equations with coupled terms by Galerkin's truncation. Based on the mathematical model, the coupled multi-body nonlinear dynamics of the vibration system is investigated by numerical method, and the parameters influences of excitation amplitude, mass ratio and inclined angle on the dynamic characteristics are precisely analyzed and discussed by bifurcation diagram, Largest Lyapunov exponent and 3-D frequency spectrum. Depending on different ranges of system parameters, the results show that the different motions and jump discontinuity appear, and the coupled system enters into chaotic behavior through different routes (period-doubling bifurcation, inverse period-doubling bifurcation, saddle-node bifurcation and Hopf bifurcation), which are strongly attributed to the dynamic interaction of the MIV-VPCS. The decreasing excitation amplitude and inclined angle could reduce the higher order bifurcations, and effectively control the complicated nonlinear dynamic behaviors under the perturbation of low rotational speed. The first bifurcation and chaotic motion occur at lower value of inclined angle, and the chaotic behavior lasts for larger intervals with higher rotational speed. The investigation results could provide a better understanding of the nonlinear dynamic behaviors for the dynamic interaction of the MIV-VPCS.

      PubDate: 2017-10-10T06:53:24Z
      DOI: 10.1016/j.jsv.2017.09.027
      Issue No: Vol. 412 (2017)
       
  • Uncertainty quantification in structural dynamic analysis using two-level
           Gaussian processes and Bayesian inference
    • Authors: K. Zhou; J. Tang
      Pages: 95 - 115
      Abstract: Publication date: 6 January 2018
      Source:Journal of Sound and Vibration, Volume 412
      Author(s): K. Zhou, J. Tang
      A probabilistic framework for efficient uncertainty quantification in structural dynamic analysis is presented. This framework is built upon the combination of two-level Gaussian processes emulator and Bayesian inference technique. The underlying idea is to employ the two-level Gaussian processes emulator to integrate together small amount of high-fidelity data from full-scale finite element analysis and large amount of low-fidelity data from order-reduced analysis to improve the response variation prediction. As component mode synthesis (CMS) is adopted in order-reduced modeling, we then utilize the improved response variation prediction on modal characteristics to update the CMS model to facilitate the efficient probabilistic analysis of any responses of concern. The effectiveness of this framework is demonstrated through systematic case studies.

      PubDate: 2017-10-10T06:53:24Z
      DOI: 10.1016/j.jsv.2017.09.034
      Issue No: Vol. 412 (2017)
       
  • Smooth adaptive sliding mode vibration control of a flexible parallel
           manipulator with multiple smart linkages in modal space
    • Authors: Quan Zhang; Chaodong Li; Jiantao Zhang; Jianhui Zhang
      Pages: 1 - 19
      Abstract: Publication date: 22 December 2017
      Source:Journal of Sound and Vibration, Volume 411
      Author(s): Quan Zhang, Chaodong Li, Jiantao Zhang, Jianhui Zhang
      This paper addresses the dynamic model and active vibration control of a rigid-flexible parallel manipulator with three smart links actuated by three linear ultrasonic motors. To suppress the vibration of three flexible intermediate links under high speed and acceleration, multiple Lead Zirconium Titanate (PZT) sensors and actuators are collocated mounted on each link, forming a smart structure which can achieve self-sensing and self-actuating. The dynamic characteristics and equations of the flexible link incorporated with the PZT sensors and actuator are analyzed and formulated. The smooth adaptive sliding mode based active vibration control is proposed to suppress the vibration of the smart links, and the first and second modes of the three links are targeted to be suppressed in modal space to avoid the spillover phenomenon. Simulations and experiments are implemented to validate the effectiveness of the smart structures and the proposed control laws. Experimental results show that the vibration of the first mode around 92 Hz and the second mode around 240 Hz of the three smart links are reduced respectively by 64.98%, 59.47%, 62.28%, and 45.80%, 36.79%, 33.33%, which further verify the multi-mode vibration control ability of the smooth adaptive sliding mode control law.

      PubDate: 2017-09-13T00:36:26Z
      DOI: 10.1016/j.jsv.2017.08.052
      Issue No: Vol. 411 (2017)
       
  • Damage detection using sideband peak count in spectral correlation domain
    • Authors: Peipei Liu; Hoon Sohn
      Pages: 20 - 33
      Abstract: Publication date: 22 December 2017
      Source:Journal of Sound and Vibration, Volume 411
      Author(s): Peipei Liu, Hoon Sohn
      Nonlinear ultrasonic techniques have been proven to be more sensitive to the presence of an early-stage damage than linear techniques. Among various nonlinear techniques, laser nonlinear wave modulation spectroscopy (LNWMS) utilizes a pulse laser to exert a broadband input and a damage on the target structure exhibits nonlinear wave modulation among various input frequency components. A sideband peak count (SPC) technique in the spectral frequency domain was proposed to estimate the damage-induced nonlinearity. In this study, the SPC operation is conducted in the spectral correlation domain so that noise has less influence on damage detection performance and a higher sensitivity to damage can be achieved. In addition, through spatial comparison of SPC over an inspection area, damage can be detected without relying on the baseline data obtained from a pristine condition. The performance of the proposed technique is validated using a numerical simulation performed on an aluminum plate with a simulated crack, and experiments performed on an aluminum plate with a fatigue crack and a carbon fiber reinforced polymer plate with delamination.

      PubDate: 2017-09-13T00:36:26Z
      DOI: 10.1016/j.jsv.2017.08.049
      Issue No: Vol. 411 (2017)
       
  • Stochastic resonance in an underdamped system with FitzHug-Nagumo
           potential for weak signal detection
    • Authors: Cristian López; Wei Zhong; Siliang Lu; Feiyun Cong; Ignacio Cortese
      Pages: 34 - 46
      Abstract: Publication date: 22 December 2017
      Source:Journal of Sound and Vibration, Volume 411
      Author(s): Cristian López, Wei Zhong, Siliang Lu, Feiyun Cong, Ignacio Cortese
      Vibration signals are widely used for bearing fault detection and diagnosis. When signals are acquired in the field, usually, the faulty periodic signal is weak and is concealed by noise. Various de-noising methods have been developed to extract the target signal from the raw signal. Stochastic resonance (SR) is a technique that changed the traditional denoising process, in which the weak periodic fault signal can be identified by adding an expression, the potential, to the raw signal and solving a differential equation problem. However, current SR methods have some deficiencies such us limited filtering performance, low frequency input signal and sequential search for optimum parameters. Consequently, in this study, we explore the application of SR based on the FitzHug-Nagumo (FHN) potential in rolling bearing vibration signals. Besides, we improve the search of the SR optimum parameters by the use of particle swarm optimization (PSO). The effectiveness of the proposed method is verified by using both simulated and real bearing data sets.

      PubDate: 2017-09-13T00:36:26Z
      DOI: 10.1016/j.jsv.2017.08.043
      Issue No: Vol. 411 (2017)
       
  • On optimization of energy harvesting from base-excited vibration
    • Authors: Wei-Che Tai; Lei Zuo
      Pages: 47 - 59
      Abstract: Publication date: 22 December 2017
      Source:Journal of Sound and Vibration, Volume 411
      Author(s): Wei-Che Tai, Lei Zuo
      This paper re-examines and clarifies the long-believed optimization conditions of electromagnetic and piezoelectric energy harvesting from base-excited vibration. In terms of electromagnetic energy harvesting, it is typically believed that the maximum power is achieved when the excitation frequency and electrical damping equal the natural frequency and mechanical damping of the mechanical system respectively. We will show that this optimization condition is only valid when the acceleration amplitude of base excitation is constant and an approximation for small mechanical damping when the excitation displacement amplitude is constant. To this end, a two-variable optimization analysis, involving the normalized excitation frequency and electrical damping ratio, is performed to derive the exact optimization condition of each case. When the excitation displacement amplitude is constant, we analytically show that, in contrast to the long-believed optimization condition, the optimal excitation frequency and electrical damping are always larger than the natural frequency and mechanical damping ratio respectively. In particular, when the mechanical damping ratio exceeds a critical value, the optimization condition is no longer valid. Instead, the average power generally increases as the excitation frequency and electrical damping ratio increase. Furthermore, the optimization analysis is extended to consider parasitic electrical losses, which also shows different results when compared with existing literature. When the excitation acceleration amplitude is constant, on the other hand, the exact optimization condition is identical to the long-believed one. In terms of piezoelectric energy harvesting, it is commonly believed that the optimal power efficiency is achieved when the excitation and the short or open circuit frequency of the harvester are equal. Via a similar two-variable optimization analysis, we analytically show that the optimal excitation frequency depends on the mechanical damping ratio and does not equal the short or open circuit frequency. Finally, the optimal excitation frequencies and resistive loads are derived in closed-form.

      PubDate: 2017-09-18T08:13:05Z
      DOI: 10.1016/j.jsv.2017.08.032
      Issue No: Vol. 411 (2017)
       
  • Aerofoil broadband and tonal noise modelling using stochastic sound
           sources and incorporated large scale fluctuations
    • Authors: S. Proskurov; O.R. Darbyshire; S.A. Karabasov
      Pages: 60 - 74
      Abstract: Publication date: 22 December 2017
      Source:Journal of Sound and Vibration, Volume 411
      Author(s): S. Proskurov, O.R. Darbyshire, S.A. Karabasov
      The present work discusses modifications to the stochastic Fast Random Particle Mesh (FRPM) method featuring both tonal and broadband noise sources. The technique relies on the combination of incorporated vortex-shedding resolved flow available from Unsteady Reynolds-Averaged Navier-Stokes (URANS) simulation with the fine-scale turbulence FRPM solution generated via the stochastic velocity fluctuations in the context of vortex sound theory. In contrast to the existing literature, our method encompasses a unified treatment for broadband and tonal acoustic noise sources at the source level, thus, accounting for linear source interference as well as possible non-linear source interaction effects. When sound sources are determined, for the sound propagation, Acoustic Perturbation Equations (APE-4) are solved in the time-domain. Results of the method's application for two aerofoil benchmark cases, with both sharp and blunt trailing edges are presented. In each case, the importance of individual linear and non-linear noise sources was investigated. Several new key features related to the unsteady implementation of the method were tested and brought into the equation. Encouraging results have been obtained for benchmark test cases using the new technique which is believed to be potentially applicable to other airframe noise problems where both tonal and broadband parts are important.

      PubDate: 2017-09-18T08:13:05Z
      DOI: 10.1016/j.jsv.2017.08.036
      Issue No: Vol. 411 (2017)
       
  • Study of cumulative fatigue damage detection for used parts with nonlinear
           output frequency response functions based on NARMAX modelling
    • Authors: Honglan Huang; Hanying Mao; Hanling Mao; Weixue Zheng; Zhenfeng Huang; Xinxin Li; Xianghong Wang
      Pages: 75 - 87
      Abstract: Publication date: 22 December 2017
      Source:Journal of Sound and Vibration, Volume 411
      Author(s): Honglan Huang, Hanying Mao, Hanling Mao, Weixue Zheng, Zhenfeng Huang, Xinxin Li, Xianghong Wang
      Cumulative fatigue damage detection for used parts plays a key role in the process of remanufacturing engineering and is related to the service safety of the remanufactured parts. In light of the nonlinear properties of used parts caused by cumulative fatigue damage, the based nonlinear output frequency response functions detection approach offers a breakthrough to solve this key problem. First, a modified PSO-adaptive lasso algorithm is introduced to improve the accuracy of the NARMAX model under impulse hammer excitation, and then, an effective new algorithm is derived to estimate the nonlinear output frequency response functions under rectangular pulse excitation, and a based nonlinear output frequency response functions index is introduced to detect the cumulative fatigue damage in used parts. Then, a novel damage detection approach that integrates the NARMAX model and the rectangular pulse is proposed for nonlinear output frequency response functions identification and cumulative fatigue damage detection of used parts. Finally, experimental studies of fatigued plate specimens and used connecting rod parts are conducted to verify the validity of the novel approach. The obtained results reveal that the new approach can detect cumulative fatigue damages of used parts effectively and efficiently and that the various values of the based nonlinear output frequency response functions index can be used to detect the different fatigue damages or working time. Since the proposed new approach can extract nonlinear properties of systems by only a single excitation of the inspected system, it shows great promise for use in remanufacturing engineering applications.

      PubDate: 2017-09-18T08:13:05Z
      DOI: 10.1016/j.jsv.2017.08.023
      Issue No: Vol. 411 (2017)
       
  • Dynamic output feedback control for seismic-excited buildings
    • Authors: Ali Kazemy; Xian-Ming Zhang; Qing-Long Han
      Pages: 88 - 107
      Abstract: Publication date: 22 December 2017
      Source:Journal of Sound and Vibration, Volume 411
      Author(s): Ali Kazemy, Xian-Ming Zhang, Qing-Long Han
      This paper deals with the H ∞ dynamic output feedback control problem of a seismic-excited building. The control aims to reduce the vibration of a building caused by an earthquake. Instead of system states, the system output measurements are used to design suitable H ∞ controllers. Depending on whether the system measurements are sampled or not, two kinds of dynamic output feedback control schemes are investigated. By the Lyapunov stability theory, some bounded real lemmas are formulated such that the closed-loop system is asymptotically stable and achieves a prescribed H ∞ disturbance attenuation level. The cone complementary algorithm is employed to design H ∞ controllers based on a solution to a nonlinear minimization problem subject to a set of linear matrix inequalities. Finally, a three-storey building model is given to show the effectiveness of the proposed method.

      PubDate: 2017-09-18T08:13:05Z
      DOI: 10.1016/j.jsv.2017.08.017
      Issue No: Vol. 411 (2017)
       
  • An adaptive proper orthogonal decomposition method for model order
           reduction of multi-disc rotor system
    • Authors: Yulin Jin; Kuan Lu; Lei Hou; Yushu Chen
      Pages: 210 - 231
      Abstract: Publication date: 22 December 2017
      Source:Journal of Sound and Vibration, Volume 411
      Author(s): Yulin Jin, Kuan Lu, Lei Hou, Yushu Chen
      The proper orthogonal decomposition (POD) method is a main and efficient tool for order reduction of high-dimensional complex systems in many research fields. However, the robustness problem of this method is always unsolved, although there are some modified POD methods which were proposed to solve this problem. In this paper, a new adaptive POD method called the interpolation Grassmann manifold (IGM) method is proposed to address the weakness of local property of the interpolation tangent-space of Grassmann manifold (ITGM) method in a wider parametric region. This method is demonstrated here by a nonlinear rotor system of 33-degrees of freedom (DOFs) with a pair of liquid-film bearings and a pedestal looseness fault. The motion region of the rotor system is divided into two parts: simple motion region and complex motion region. The adaptive POD method is compared with the ITGM method for the large and small spans of parameter in the two parametric regions to present the advantage of this method and disadvantage of the ITGM method. The comparisons of the responses are applied to verify the accuracy and robustness of the adaptive POD method, as well as the computational efficiency is also analyzed. As a result, the new adaptive POD method has a strong robustness and high computational efficiency and accuracy in a wide scope of parameter.

      PubDate: 2017-09-25T06:34:55Z
      DOI: 10.1016/j.jsv.2017.09.001
      Issue No: Vol. 411 (2017)
       
  • Nonlinearity measure based assessment method for pedestal looseness of
           bearing-rotor systems
    • Authors: Mian Jiang; Jigang Wu; Xinsheng Peng; Xuejun Li
      Pages: 232 - 246
      Abstract: Publication date: 22 December 2017
      Source:Journal of Sound and Vibration, Volume 411
      Author(s): Mian Jiang, Jigang Wu, Xinsheng Peng, Xuejun Li
      In this paper, nonlinearity measure based assessment method is proposed for the pedestal looseness of bearing-rotor systems under constant rotational speeds. A nonlinear mathematical model is developed for a bearing-rotor system which including the effect of pedestal looseness. Also, piecewise-linear stiffness, damping force, and nonlinear elastic force are considered in the model. These parameters depend on the position of pedestal looseness. Nonlinearity measure is used to quantify the degree for nonlinear behaviors of the bearing-rotor systems with different looseness clearances. A linear model is obtained by linearizing the nonlinear terms via the Taylor expansion from the static equilibrium position. Moreover, the dynamic behaviors predicted by the linear model are compared to the predictions of the nonlinear model. Then, nonlinearity can be quantified by evaluating the difference between linear and nonlinear models. The fourth order Runge-Kutta method was used to calculate the dynamic responses. The trend of nonlinearity degree is obtained by nonlinear fitting method under different looseness clearances. The performance of the proposed approach is validated numerically and experimentally. The relationship between for looseness clearances and nonlinearity degree can be used to assess the pedestal looseness in rotor systems.

      PubDate: 2017-09-25T06:34:55Z
      DOI: 10.1016/j.jsv.2017.09.002
      Issue No: Vol. 411 (2017)
       
  • Multimodal modeling and validation of simplified vocal tract acoustics for
           sibilant /s/
    • Authors: T. Yoshinaga; A. Van Hirtum; S. Wada
      Pages: 247 - 259
      Abstract: Publication date: 22 December 2017
      Source:Journal of Sound and Vibration, Volume 411
      Author(s): T. Yoshinaga, A. Van Hirtum, S. Wada
      To investigate the acoustic characteristics of sibilant /s/, multimodal theory is applied to a simplified vocal tract geometry derived from a CT scan of a single speaker for whom the sound spectrum was gathered. The vocal tract was represented by a concatenation of waveguides with rectangular cross-sections and constant width, and a sound source was placed either at the inlet of the vocal tract or downstream from the constriction representing the sibilant groove. The modeled pressure amplitude was validated experimentally using an acoustic driver or airflow supply at the vocal tract inlet. Results showed that the spectrum predicted with the source at the inlet and including higher-order modes matched the spectrum measured with the acoustic driver at the inlet. Spectra modeled with the source downstream from the constriction captured the first characteristic peak observed for the speaker at 4 kHz. By positioning the source near the upper teeth wall, the higher frequency peak observed for the speaker at 8 kHz was predicted with the inclusion of higher-order modes. At the frequencies of the characteristic peaks, nodes and antinodes of the pressure amplitude were observed in the simplified vocal tract when the source was placed downstream from the constriction. These results indicate that the multimodal approach enables to capture the amplitude and frequency of the peaks in the spectrum as well as the nodes and antinodes of the pressure distribution due to /s/ inside the vocal tract.

      PubDate: 2017-09-25T06:34:55Z
      DOI: 10.1016/j.jsv.2017.09.004
      Issue No: Vol. 411 (2017)
       
  • Vibration suppression of a piezo-equipped cylindrical shell in a
           broad-band frequency domain
    • Authors: Ali Loghmani; Mohammad Danesh; Moon K. Kwak; Mehdi Keshmiri
      Pages: 260 - 277
      Abstract: Publication date: 22 December 2017
      Source:Journal of Sound and Vibration, Volume 411
      Author(s): Ali Loghmani, Mohammad Danesh, Moon K. Kwak, Mehdi Keshmiri
      This paper focuses on the dynamic modeling of a cylindrical shell equipped with piezoceramic sensors and actuators, as well as the design of a broad band multi-input and multi-output linear quadratic Gaussian controller for the suppression of vibrations. The optimal locations of actuators are derived by Genetic Algorithm (GA) to effectively control the specific structural modes of the cylinder. The dynamic model is derived based on the Sanders shell theory and the energy approach for both the cylinder and the piezoelectric transducers, all of which reflect the piezoelectric effect. The natural vibration characteristics of the cylindrical shell are investigated both theoretically and experimentally. The theoretical predictions are in good agreement with the experimental results. Then, the broad band multi-input and multi-output linear quadratic Gaussian controller was designed and applied to the test article. An active vibration control experiment is carried out on the cylindrical shell and the digital control system is used to implement the proposed control algorithm. The experimental results show that vibrations of the cylindrical shell can be suppressed by the piezoceramic sensors and actuators along with the proposed controller. The optimal location of the actuators makes the proposed control system more efficient than other configurations.

      PubDate: 2017-09-25T06:34:55Z
      DOI: 10.1016/j.jsv.2017.08.051
      Issue No: Vol. 411 (2017)
       
  • Novel design of microgyroscopes employing electrostatic actuation and
           resistance-change based sensing
    • Authors: M. Ghommem; A. Abdelkefi
      Pages: 278 - 288
      Abstract: Publication date: 22 December 2017
      Source:Journal of Sound and Vibration, Volume 411
      Author(s): M. Ghommem, A. Abdelkefi
      The nonlinear dynamics of a microgyroscope consisting of a vibrating beam with attached proof mass and operating at high frequency is numerically investigated. The working principle of this inertial sensor is based on exploiting the transfer of the mechanical energy among two vibrations modes via the Coriolis effect to measure the rotation rate. The flexural motion (drive mode) is generated by applying a DC electrostatic load and an AC harmonic load. We propose a novel sensing technique based on resistance change to detect the induced vibrations of the microbeam (sense mode) and extract the rotation rate. The sensing technique is based on transmitting the Coriolis force acting on the proof mass to a probe that affects the resistance of an electrical circuit acting as a variable voltage divider. This is achieved by integrating the probe dipping μpool (PDP) technology deploying a probe electrode that is dipped into a μpool filled with a conductive nonvolatile fluid. Large magnitude of the AC harmonic load is observed to give rise to dynamic pull-in bandwidth in the frequency response characterized by large and uncontrollable vibrations of the microbeam. Operating near the primary frequency while selecting moderate AC voltage results in linear calibration curves while maintaining high sensitivity of the output voltage to the change in the rotation speed. The simulation results demonstrate the feasibility of the novel technique for sensing the induced vibrations to deliver measurements of the angular speed.

      PubDate: 2017-09-25T06:34:55Z
      DOI: 10.1016/j.jsv.2017.09.010
      Issue No: Vol. 411 (2017)
       
  • Nonlinear convergence active vibration absorber for single and multiple
           frequency vibration control
    • Authors: Xi Wang; Bintang Yang; Shufeng Guo; Wenqiang Zhao
      Pages: 289 - 303
      Abstract: Publication date: 22 December 2017
      Source:Journal of Sound and Vibration, Volume 411
      Author(s): Xi Wang, Bintang Yang, Shufeng Guo, Wenqiang Zhao
      This paper presents a nonlinear convergence algorithm for active dynamic undamped vibration absorber (ADUVA). The damping of absorber is ignored in this algorithm to strengthen the vibration suppressing effect and simplify the algorithm at the same time. The simulation and experimental results indicate that this nonlinear convergence ADUVA can help significantly suppress vibration caused by excitation of both single and multiple frequency. The proposed nonlinear algorithm is composed of equivalent dynamic modeling equations and frequency estimator. Both the single and multiple frequency ADUVA are mathematically imitated by the same mechanical structure with a mass body and a voice coil motor (VCM). The nonlinear convergence estimator is applied to simultaneously satisfy the requirements of fast convergence rate and small steady state frequency error, which are incompatible for linear convergence estimator. The convergence of the nonlinear algorithm is mathematically proofed, and its non-divergent characteristic is theoretically guaranteed. The vibration suppressing experiments demonstrate that the nonlinear ADUVA can accelerate the convergence rate of vibration suppressing and achieve more decrement of oscillation attenuation than the linear ADUVA.
      Graphical abstract image

      PubDate: 2017-09-25T06:34:55Z
      DOI: 10.1016/j.jsv.2017.09.013
      Issue No: Vol. 411 (2017)
       
  • Control strategies for DC motors driving rotor dynamic systems through
           resonance
    • Authors: Alfa Bisoi; A.K. Samantaray; Ranjan Bhattacharyya
      Pages: 304 - 327
      Abstract: Publication date: 22 December 2017
      Source:Journal of Sound and Vibration, Volume 411
      Author(s): Alfa Bisoi, A.K. Samantaray, Ranjan Bhattacharyya
      Rotor dynamic systems require considerably higher power/torque to accelerate through the structural resonance. However, most sources of mechanical power are non-ideal, i.e., they can only provide a limited amount of power. If there is insufficient power to overcome the resonance then the rotor speed may get caught at resonance and the persistent high vibrations can damage the machine. Various proposed solutions to this problem deal with modifications to the mechanical structure and active/semi-active control of structural parameters. This article proposes modification to the prime mover so that peak available power is delivered exactly at the structural resonance frequency. The limited power/non-ideal prime mover considered in this article is a direct current (DC) motor and the structural resonance happens due to forcing from an eccentric rotor disk and vibrations of a flexible weakly damped foundation. Various control strategies to modify the torque-speed characteristics of permanent magnet, shunt and series wound DC motors to promote escape through resonance are considered. Also, the characteristic curves for rotor/motor speed versus the DC supply voltage are obtained for the considered DC motor types from which the unattainable steady angular speeds and the speed jumps due to Sommerfeld effect are computed. Transient simulations are performed using bond graph models for this multi-energy domain (here, electro-mechanical) system. It is shown that a switched control permitting to switch between shunt and series DC motor configurations gives better regulation over the power delivery at the resonant frequency as well as super-critical operating speeds in the neighborhood of structural resonance.

      PubDate: 2017-09-25T06:34:55Z
      DOI: 10.1016/j.jsv.2017.09.014
      Issue No: Vol. 411 (2017)
       
  • Numerical eduction of active multi-port data for in-duct obstructions
    • Authors: Stefan Sack; Michael Shur; Mats Åbom; Michael Strelets; Andrey Travin
      Pages: 328 - 345
      Abstract: Publication date: 22 December 2017
      Source:Journal of Sound and Vibration, Volume 411
      Author(s): Stefan Sack, Michael Shur, Mats Åbom, Michael Strelets, Andrey Travin
      A numerical method for aeroacoustic source characterization of in-duct components at frequencies beyond the cut-on frequencies of several acoustic modes is presented. Assuming linearity and time invariance, any ducted component can be fully characterized using a network (multi-port) model including source strength and scattering. A two-step multi-source approach is applied to numerical data in order to educe the multi-port characteristics. First, a scale resolving compressible flow simulation, here the Improved Delayed Detached Eddy Simulation (IDDES), is run to compute the channel flow that also contains the acoustic sources. Second, a linear acoustic computation, here the Linearized Navier Stokes Equations (LNSE), around a mean flow is solved for different acoustic loads to determine the component's scattering. The work uncovers the high potential of two-step numerical multi-port eduction methods. Particularly, it is shown that the acoustic source power spectra can be accurately extracted from IDDES data and the total acoustic power prediction is very good. Furthermore, a good result in the scattering data obtained from a second computationally inexpensive LNSE computation is achieved. The approach is interesting when describing mid-size duct systems, for example ventilation systems in aircraft and buildings, with a moderate number of higher order modes propagating in the considered frequency range. Therefore, the increasing availability of compressible flow data opens a wide field of applications.

      PubDate: 2017-09-25T06:34:55Z
      DOI: 10.1016/j.jsv.2017.09.012
      Issue No: Vol. 411 (2017)
       
  • A numerical and experimental study on optimal design of multi-DOF
           
    • Authors: Eduardo Afonso Ribeiro; Eduardo Márcio de Oliveira Lopes; Carlos Alberto Bavastri
      Pages: 346 - 361
      Abstract: Publication date: 22 December 2017
      Source:Journal of Sound and Vibration, Volume 411
      Author(s): Eduardo Afonso Ribeiro, Eduardo Márcio de Oliveira Lopes, Carlos Alberto Bavastri
      Viscoelastic materials have played an important role in passive vibration control. Nevertheless, the use of such materials in supports of rotating machines, aiming at controlling vibration, is more recent, mainly when these supports present additional complexities like multiple degrees of freedom and require accurate models to predict the dynamic behavior of viscoelastic materials working in a broad band of frequencies and temperatures. Previously, the authors propose a methodology for an optimal design of viscoelastic supports (VES) for vibration suppression in rotordynamics, which improves the dynamic prediction accuracy, the speed calculation, and the modeling of VES as complex structures. However, a comprehensive numerical study of the dynamics of rotor-VES systems, regarding the types and combinations of translational and rotational degrees of freedom (DOFs), accompanied by the corresponding experimental validation, is still lacking. This paper presents such a study considering different types and combinations of DOFs in addition to the simulation of their number of additional masses/inertias, as well as the kind and association of the applied viscoelastic materials (VEMs). The results - regarding unbalance frequency response, transmissibility and displacement due to static loads - lead to: 1) considering VES as complex structures which allow improving the efficacy in passive vibration control; 2) acknowledging the best configuration concerning DOFs and VEM choice and association for a practical application concerning passive vibration control and load resistance. The specific outcomes of the conducted experimental validation attest the accuracy of the proposed methodology.

      PubDate: 2017-09-25T06:34:55Z
      DOI: 10.1016/j.jsv.2017.09.008
      Issue No: Vol. 411 (2017)
       
  • Seismic control performance for Pounding Tuned Massed Damper based on
           viscoelastic pounding force analytical method
    • Authors: Qichao Xue; Jingcai Zhang; Jian He; Chunwei Zhang; Guangping Zou
      Pages: 362 - 377
      Abstract: Publication date: 22 December 2017
      Source:Journal of Sound and Vibration, Volume 411
      Author(s): Qichao Xue, Jingcai Zhang, Jian He, Chunwei Zhang, Guangping Zou
      This paper focuses on vibration control performance of Pounding Tuned Massed Damper (PTMD) with viscoelastic pounding layers, which can dissipate energy during collision process. By using of viscoelastic pounding force analytical method, two types of pounding force models for different contact geometries are developed to illustrate interactions among pounding components in PTMD. A shake table test based on a simplified experimental structure is conducted to verify the effectiveness of single PTMD as well as the viscoelastic pounding force model. Furthermore, a parametric study for a 14-storeys steel structure is presented to investigate the performance of PTMD device in multiple degree of freedom (MDOF) system. Results from numerical simulations demonstrated that properties of viscoelastic material and gaps between mass block and the limiters in PTMD are key factors for vibration control performance. By inputting a series of seismic excitations into MDOF system, comparisons between PTMD and traditional TMD reveals that the optimized PTMD has better performance than the traditional TMD in vibration suppression in certain cases.

      PubDate: 2017-10-02T02:15:46Z
      DOI: 10.1016/j.jsv.2017.08.035
      Issue No: Vol. 411 (2017)
       
  • Church acoustics: A state-of-the-art review after several decades of
           research
    • Authors: Sara Girón; Lidia Álvarez-Morales; Teófilo Zamarreño
      Pages: 378 - 408
      Abstract: Publication date: 22 December 2017
      Source:Journal of Sound and Vibration, Volume 411
      Author(s): Sara Girón, Lidia Álvarez-Morales, Teófilo Zamarreño
      This work describes and analyses the principal contributions to the acoustics of occidental Christian churches from the second half of the last century to the present day, mainly in ancient historical churches. After more than six decades of research, it seems appropriate to summarise the major pieces of work in this field, and, to this end, this paper aims to provide an up-to-date document of all the most relevant studies which describe the exhaustive investigations of acoustic characterisation in time-consuming experimental campaigns carried out by several groups of researchers in various European countries. The article presents, for the research into church acoustics developed in each country, the experimental procedures, the results, discussions, the theoretical interpretations of the sound propagation in these spaces, the subjective aspects in the listening experience, and the method of implementation of computer simulation techniques and their applications in these complex enclosures. Other contributions from Asian and American continents are also included. Findings and advances in each of these areas as well as perspectives on their future challenges are summarized and discussed in this work.

      PubDate: 2017-10-02T02:15:46Z
      DOI: 10.1016/j.jsv.2017.09.015
      Issue No: Vol. 411 (2017)
       
  • Parameter identification of pedestrian's spring-mass-damper model by
           ground reaction force records through a particle filter approach
    • Authors: Haoqi Wang; Jun Chen; James M.W. Brownjohn
      Pages: 409 - 421
      Abstract: Publication date: 22 December 2017
      Source:Journal of Sound and Vibration, Volume 411
      Author(s): Haoqi Wang, Jun Chen, James M.W. Brownjohn
      The spring-mass-damper (SMD) model with a pair of internal biomechanical forces is the simplest model for a walking pedestrian to represent his/her mechanical properties, and thus can be used in human-structure-interaction analysis in the vertical direction. However, the values of SMD stiffness and damping, though very important, are typically taken as those measured from stationary people due to lack of a parameter identification methods for a walking pedestrian. This study adopts a step-by-step system identification approach known as particle filter to simultaneously identify the stiffness, damping coefficient, and coefficients of the SMD model's biomechanical forces by ground reaction force (GRF) records. After a brief introduction of the SMD model, the proposed identification approach is explained in detail, with a focus on the theory of particle filter and its integration with the SMD model. A numerical example is first provided to verify the feasibility of the proposed approach which is then applied to several experimental GRF records. Identification results demonstrate that natural frequency and the damping ratio of a walking pedestrian are not constant but have a dependence of mean value and distribution on pacing frequency. The mean value first-order coefficient of the biomechanical force, which is expressed by the Fourier series function, also has a linear relationship with pacing frequency. Higher order coefficients do not show a clear relationship with pacing frequency but follow a logarithmic normal distribution.

      PubDate: 2017-10-02T02:15:46Z
      DOI: 10.1016/j.jsv.2017.09.020
      Issue No: Vol. 411 (2017)
       
  • Reflection and transmission of SH waves at a very rough interface and its
           band gaps
    • Authors: Pham Chi Vinh; Tran Thanh Tuan; Do Xuan Tung; Nguyen Thi Kieu
      Pages: 422 - 434
      Abstract: Publication date: 22 December 2017
      Source:Journal of Sound and Vibration, Volume 411
      Author(s): Pham Chi Vinh, Tran Thanh Tuan, Do Xuan Tung, Nguyen Thi Kieu
      This paper deals with the reflection and transmission of SH waves at a very rough interface separating two dissimilar isotropic elastic solids. The interface oscillates between two straight lines. By means of homogenization, the domain containing the very rough interface is replaced by an effective material layer whose elastic constants depend on the thickness variable. The reflection and transmission of SH waves at the very rough interface is then reduced to the ones at a FGM layer. The exact analytical formulas for the reflection and transmission coefficients have been derived. Based on them, the dependence of the reflection and transmission coefficients on the incident angle, the wave frequency, the material constants and the geometry of the rough interface are examined. Remarkably, it has been shown that a very rough interface of comb-type with the comb-tooth width varying periodically can produce band-gaps to SH waves. With this fact, many potential applications can be expected coming from very rough interfaces of comb-type with periodic comb-tooth width. It is also shown that the width and the location of band-gaps depend strongly on the contrast of rigidities of two half-spaces, the amplitude of the variation of the comb-tooth width, the incident angle of SH waves and the number of periods of comb-tooth.

      PubDate: 2017-10-02T02:15:46Z
      DOI: 10.1016/j.jsv.2017.08.046
      Issue No: Vol. 411 (2017)
       
  • A general model for preload calculation and stiffness analysis for
           combined angular contact ball bearings
    • Authors: Jinhua Zhang; Bin Fang; Jun Hong; Shaoke Wan; Yongsheng Zhu
      Pages: 435 - 449
      Abstract: Publication date: 22 December 2017
      Source:Journal of Sound and Vibration, Volume 411
      Author(s): Jinhua Zhang, Bin Fang, Jun Hong, Shaoke Wan, Yongsheng Zhu
      The combined angular contact ball bearings are widely used in automatic, aerospace and machine tools, but few researches on the combined angular contact ball bearings have been reported. It is shown that the preload and stiffness of combined bearings are mutual influenced rather than simply the superposition of multiple single bearing, therefore the characteristic calculation of combined bearings achieved by coupling the load and deformation analysis of a single bearing. In this paper, based on the Jones quasi-static model and stiffness analytical model, a new iterative algorithm and model are proposed for the calculation of combined bearings preload and stiffness, and the dynamic effects include centrifugal force and gyroscopic moment have to be considered. It is demonstrated that the new method has general applicability, the preload factors of combined bearings are calculated according to the different design preloads, and the static and dynamic stiffness for various arrangements of combined bearings are comparatively studied and analyzed, and the influences of the design preload magnitude, axial load and rotating speed are discussed in detail. Besides, the change rule of dynamic contact angles of combined bearings with respect to the rotating speed is also discussed. The results show that bearing arrangement modes, rotating speed and design preload magnitude have a significant influence on the preload and stiffness of combined bearings. The proposed formulation provides a useful tool in dynamic analysis of the complex bearing-rotor system.

      PubDate: 2017-10-02T02:15:46Z
      DOI: 10.1016/j.jsv.2017.09.019
      Issue No: Vol. 411 (2017)
       
  • Distributed parameter and finite element models for wave propagation in
           railway contact lines
    • Authors: S. Sorrentino; D. Anastasio; A. Fasana; S. Marchesiello
      Pages: 1 - 18
      Abstract: Publication date: 8 December 2017
      Source:Journal of Sound and Vibration, Volume 410
      Author(s): S. Sorrentino, D. Anastasio, A. Fasana, S. Marchesiello
      A distributed parameter model of a railway two-level catenary system is presented for the analysis of the coupled wave dynamics. The wires are modelled as two straight axis parallel beams, with linear equilibrium equations, and the moving load applied by the pantograph is modelled as a constant concentrated travelling force. The general solution is sought by an application of the Ritz–Galerkin method, and then compared with direct time integrations of a finite element model (FEM), achieved by two different integration schemes. The proposed model provides a valid reference for appropriately selecting the FEM parameters, in order to reduce the errors due to spurious modes, affecting the numerical integrations especially at high speeds of the moving pantograph.

      PubDate: 2017-08-31T09:17:14Z
      DOI: 10.1016/j.jsv.2017.08.008
      Issue No: Vol. 410 (2017)
       
  • Chatter mitigation using moving damper
    • Authors: Jixiong Fei; Bin Lin; Shuai Yan; Mei Ding; Juliang Xiao; Jin Zhang; Xiaofeng Zhang; Chunhui Ji; Tianyi Sui
      Pages: 49 - 63
      Abstract: Publication date: 8 December 2017
      Source:Journal of Sound and Vibration, Volume 410
      Author(s): Jixiong Fei, Bin Lin, Shuai Yan, Mei Ding, Juliang Xiao, Jin Zhang, Xiaofeng Zhang, Chunhui Ji, Tianyi Sui
      Chatter vibration will lead to poor surface quality of the resulting component and shorten the life of the machine tool unless it is avoided. Damping method is widely used in the engineering practice to mitigate the chatter. Using a moving damper, present paper concerns with the chatter suppression during milling the flexible components. It is realized by supporting the damper at the back surface of the workpiece. During milling process, the damper will move with the cutter at the same velocity. Considering the varying dynamics of the component, coupled with the moving damper, the chatter equation is constructed. The so-called stability lobe diagram (SLD) of the novel method, which describes the relationship between the critical stable depth of cut and corresponding rotational speed of the milling cutter, is also presented and it is compared with the SLD of flexible milling without damper. It is founded that the novel method can significantly improve the system stability. At the end of the paper, the method is experimentally validated.

      PubDate: 2017-09-18T08:13:05Z
      DOI: 10.1016/j.jsv.2017.08.033
      Issue No: Vol. 410 (2017)
       
  • Relative sensitivity analysis of responses using transmissibility
    • Authors: Kyung-Hoon Joo; Yeon June Kang
      Pages: 87 - 102
      Abstract: Publication date: 8 December 2017
      Source:Journal of Sound and Vibration, Volume 410
      Author(s): Kyung-Hoon Joo, Yeon June Kang
      To identify the most effective position for solving vibrational problems, it is necessary to analyze the system sensitivities. In this study, new sensitivity indices based on the concept of transmissibility are proposed for analyzing the relative sensitivities of the responses with respect to the design variables that are used to indicate the sensitive positions where small design modifications can be applied, and analyze the effect of these modifications on the responses. The transmissibility concept is applied after differentiating the equation of motion to consider the crosstalk effects. More important information regarding the relative sensitivity characteristics of a system with easily measured response data to reduce unintended responses can be acquired by using the proposed indices. Further, the proposed indices are applicable to the variables of mass, stiffness, and damping. The indices are validated analytically and numerically, and the results demonstrate the effectiveness of the proposed indices.

      PubDate: 2017-09-06T09:18:41Z
      DOI: 10.1016/j.jsv.2017.08.031
      Issue No: Vol. 410 (2017)
       
  • Eigenvectors phase correction in inverse modal problem
    • Authors: Guandong Qiao; Salam Rahmatalla
      Pages: 151 - 168
      Abstract: Publication date: 8 December 2017
      Source:Journal of Sound and Vibration, Volume 410
      Author(s): Guandong Qiao, Salam Rahmatalla
      The solution of the inverse modal problem for the spatial parameters of mechanical and structural systems is heavily dependent on the quality of the modal parameters obtained from the experiments. While experimental and environmental noises will always exist during modal testing, the resulting modal parameters are expected to be corrupted with different levels of noise. A novel methodology is presented in this work to mitigate the errors in the eigenvectors when solving the inverse modal problem for the spatial parameters. The phases of the eigenvector component were utilized as design variables within an optimization problem that minimizes the difference between the calculated and experimental transfer functions. The equation of motion in terms of the modal and spatial parameters was used as a constraint in the optimization problem. Constraints that reserve the positive and semi-positive definiteness and the inter-connectivity of the spatial matrices were implemented using semi-definite programming. Numerical examples utilizing noisy eigenvectors with augmented Gaussian white noise of 1%, 5%, and 10% were used to demonstrate the efficacy of the proposed method. The results showed that the proposed method is superior when compared with a known method in the literature.

      PubDate: 2017-09-18T08:13:05Z
      DOI: 10.1016/j.jsv.2017.08.021
      Issue No: Vol. 410 (2017)
       
  • Doubly negative isotropic elastic metamaterial for sub-wavelength
           focusing: Design and realization
    • Authors: Joo Hwan Oh; Hong Min Seung; Yoon Young Kim
      Pages: 169 - 186
      Abstract: Publication date: 8 December 2017
      Source:Journal of Sound and Vibration, Volume 410
      Author(s): Joo Hwan Oh, Hong Min Seung, Yoon Young Kim
      In spite of much progress in elastic metamaterials, tuning the effective density and stiffness to desired values ranging from negatives to large positives is still difficult. In particular, simultaneous realization of double negativity and isotropy, critical in sub-wavelength focusing, is very challenging since anisotropy is usually unavoidable in resonance-based metamaterials. The main difficulty is that there is no established systematic design method for simultaneous achieving of double negativity and isotropy. Thus, we propose a unique elastic metamaterial unit cell with which simultaneous realization can be achieved by an explicit step-by-step approach. The unit cell of the proposed metamaterial can be accurately modeled as an equivalent mass-spring system so that the effective properties can be easily controlled with the design parameters. The actual realization was carried out by acquiring the desired properties in sequential steps which is in detail. The specific application for this study is on sub-wavelength focusing, which will be demonstrated by waves from a single point source focused on a region smaller than half the wavelength. Actual experiments were performed on an aluminum plate where the designed metamaterial flat lens was imbedded. The results acquired through simulations and experiments suggest potential applications of the proposed metamaterial and the systematic design approach in advanced acoustic surgery or non-destructive testing.

      PubDate: 2017-09-18T08:13:05Z
      DOI: 10.1016/j.jsv.2017.08.027
      Issue No: Vol. 410 (2017)
       
  • Strain sensors optimal placement for vibration-based structural health
           monitoring. The effect of damage on the initially optimal configuration
    • Authors: T.H. Loutas; A. Bourikas
      Pages: 217 - 230
      Abstract: Publication date: 8 December 2017
      Source:Journal of Sound and Vibration, Volume 410
      Author(s): T.H. Loutas, A. Bourikas
      We revisit the optimal sensor placement of engineering structures problem with an emphasis on in-plane dynamic strain measurements and to the direction of modal identification as well as vibration-based damage detection for structural health monitoring purposes. The approach utilized is based on the maximization of a norm of the Fisher Information Matrix built with numerically obtained mode shapes of the structure and at the same time prohibit the sensorization of neighbor degrees of freedom as well as those carrying similar information, in order to obtain a satisfactory coverage. A new convergence criterion of the Fisher Information Matrix (FIM) norm is proposed in order to deal with the issue of choosing an appropriate sensor redundancy threshold, a concept recently introduced but not further investigated concerning its choice. The sensor configurations obtained via a forward sequential placement algorithm are sub-optimal in terms of FIM norm values but the selected sensors are not allowed to be placed in neighbor degrees of freedom providing thus a better coverage of the structure and a subsequent better identification of the experimental mode shapes. The issue of how service induced damage affects the initially nominated as optimal sensor configuration is also investigated and reported. The numerical model of a composite sandwich panel serves as a representative aerospace structure upon which our investigations are based.

      PubDate: 2017-09-18T08:13:05Z
      DOI: 10.1016/j.jsv.2017.08.022
      Issue No: Vol. 410 (2017)
       
  • An enhanced flexible dynamic model and experimental verification for a
           valve train with clearance and multi-directional deformations
    • Authors: Changjiang Zhou; Bo Hu; Siyu Chen; Liping He
      Pages: 249 - 268
      Abstract: Publication date: 8 December 2017
      Source:Journal of Sound and Vibration, Volume 410
      Author(s): Changjiang Zhou, Bo Hu, Siyu Chen, Liping He
      An enhanced flexible dynamic model for a valve train with clearance and multi-directional deformations is proposed based on finite element method (FEM), and verified by experiment. According to the measured cam profile, the available internal excitations in numerical solution to the model are achieved by using piecewise cubic Hermite interpolating polynomial. The comparative analysis demonstrates that the bending deformation of the rocker arm is much larger than the radial deformation, signifying the necessities of multi-directional deformations in dynamic analysis for the valve train. The effects of valve clearance and cam rotation speed on contact force, acceleration and dynamic transmission error (DTE) are investigated. Both theoretical predictions and experimental measurements show that the amplitudes and fluctuations of contact force, acceleration and DTE become larger, when the valve clearance or cam speed increases. It is found that including the elasticity and the damping will weaken the impact between the rocker arm and the valve on the components (not adjacent to the valve) at either unseating or seating scenario. Additionally, as valve clearance or cam rotation speed becomes larger, the valve lift and the working phase decrease, which eventually leads to inlet air reduction. Furthermore, our study shows that the combustion rate improvement, input torque, and components durability can be improved by tuning valve clearance or adjustment the cam profile.
      Graphical abstract image

      PubDate: 2017-09-18T08:13:05Z
      DOI: 10.1016/j.jsv.2017.08.016
      Issue No: Vol. 410 (2017)
       
  • Nonlinear modeling and validation of air spring effects in a sealed tuned
           liquid column damper for structural control
    • Authors: Soumi Bhattacharyya; Aparna (Dey) Ghosh; Biswajit Basu
      Pages: 269 - 286
      Abstract: Publication date: 8 December 2017
      Source:Journal of Sound and Vibration, Volume 410
      Author(s): Soumi Bhattacharyya, Aparna (Dey) Ghosh, Biswajit Basu
      The present study focuses on an experimental investigation of nonlinear air spring effects in a passive sealed Tuned Liquid Column Damper (TLCD). The aim is to quantify the polytropic process representing the pressure-volume variation in a sealed air column and examine the extent of stiffness nonlinearity present in the system. This is accomplished by measuring pressure data using pressure transducers and liquid elevations using wave gauges. The mathematical model of the sealed TLCD considering the pressure-volume relation in the sealed air column as an isentropic process is presented and validated with the experimental results. The expressions for nonlinear and linearized air spring stiffness and linearized natural frequency of the damper are presented. The effect of linearization of the air spring stiffness on damper performance is examined and found to be acceptable under certain conditions. It is seen that though the passive sealed TLCD is intrinsically nonlinear, both in damping and in stiffness, the effect of the stiffness nonlinearity is small and the system possesses a natural frequency which may be effectively used for the purpose of tuning. Finally, the variation of the damper frequency due to change in different design parameters is presented to demonstrate the options to utilize this damper in the high frequency range where the conventional open TLCD is not applicable.

      PubDate: 2017-09-06T09:18:41Z
      DOI: 10.1016/j.jsv.2017.07.046
      Issue No: Vol. 410 (2017)
       
  • Super-resolution imaging of low-frequency sound sources using a corrected
           monopole time reversal method
    • Authors: Chuan-Xing Bi; Yong-Chang Li; Yong-Bin Zhang; Liang Xu
      Pages: 303 - 317
      Abstract: Publication date: 8 December 2017
      Source:Journal of Sound and Vibration, Volume 410
      Author(s): Chuan-Xing Bi, Yong-Chang Li, Yong-Bin Zhang, Liang Xu
      A limitation of the monopole time reversal (MTR) method, which records and retransmits the monopole field only, is that the spatial resolution of the focus cannot be better than half a wavelength, and therefore it is not suitable for locating low-frequency sound sources. In this paper, the time-reversed pressure field obtained by the MTR method is first transformed into the wavenumber domain, and is then decomposed into a filter term that controls the spatial resolution of the focus and a source term that is related to the sound source and focusing plane. Subsequently, a correction is made to the time-reversed pressure field of the MTR method by replacing its filter with the filter for the time-reversed pressure gradient field of the dipole TR (DTR) method, a constant filter and an empirical filter, which makes it possible to include many more evanescent waves and obtain subwavelength focusing. Numerical simulation and experimental results show that compared to the original MTR method, the corrected one is able to dramatically improve the spatial resolution of the focus at low frequencies. It is also found that the constant filter is applicable when the signal-to-noise ratio (SNR) is high (generally above 30 dB), the filter for the time-reversed pressure gradient field of the DTR method works stably even in the situation of low SNR, and the empirical filter performs best when the SNR is above 10 dB.

      PubDate: 2017-09-06T09:18:41Z
      DOI: 10.1016/j.jsv.2017.08.039
      Issue No: Vol. 410 (2017)
       
  • Simulation of vertical dynamic vehicle–track interaction in a railway
           crossing using Green's functions
    • Authors: X. Li; P.T. Torstensson; J.C.O. Nielsen
      Pages: 318 - 329
      Abstract: Publication date: 8 December 2017
      Source:Journal of Sound and Vibration, Volume 410
      Author(s): X. Li, P.T. Torstensson, J.C.O. Nielsen
      Vertical dynamic vehicle–track interaction in the through route of a railway crossing is simulated in the time domain based on a Green's function approach for the track in combination with an implementation of Kalker's variational method to solve the non-Hertzian, and potentially multiple, wheel–rail contact. The track is described by a linear, three-dimensional and non-periodic finite element model of a railway turnout accounting for the variations in rail cross-sections and sleeper lengths, and including baseplates and resilient elements. To reduce calculation time due to the complexity of the track model, involving a large number of elements and degrees-of-freedom, a complex-valued modal superposition with a truncated mode set is applied before the impulse response functions are calculated at various positions along the crossing panel. The variation in three-dimensional contact geometry of the crossing and wheel is described by linear surface elements. In each time step of the contact detection algorithm, the lateral position of the wheelset centre is prescribed but the contact positions on wheel and rail are not, allowing for an accurate prediction of the wheel transition between wing rail and crossing rail. The method is demonstrated by calculating the wheel–rail impact load and contact stress distribution for a nominal S1002 wheel profile passing over a nominal crossing geometry. A parameter study is performed to determine the influence of vehicle speed, rail pad stiffness, lateral wheelset position and wheel profile on the impact load generated at the crossing. It is shown that the magnitude of the impact load is more influenced the wheel–rail contact geometry than by the selection of rail pad stiffness.

      PubDate: 2017-09-06T09:18:41Z
      DOI: 10.1016/j.jsv.2017.08.037
      Issue No: Vol. 410 (2017)
       
  • An implementation of an aeroacoustic prediction model for broadband noise
           from a vertical axis wind turbine using a CFD informed methodology
    • Authors: J.D.M. Botha; A. Shahroki; H. Rice
      Pages: 389 - 415
      Abstract: Publication date: 8 December 2017
      Source:Journal of Sound and Vibration, Volume 410
      Author(s): J.D.M. Botha, A. Shahroki, H. Rice
      This paper presents an enhanced method for predicting aerodynamically generated broadband noise produced by a Vertical Axis Wind Turbine (VAWT). The method improves on existing work for VAWT noise prediction and incorporates recently developed airfoil noise prediction models. Inflow-turbulence and airfoil self-noise mechanisms are both considered. Airfoil noise predictions are dependent on aerodynamic input data and time dependent Computational Fluid Dynamics (CFD) calculations are carried out to solve for the aerodynamic solution. Analytical flow methods are also benchmarked against the CFD informed noise prediction results to quantify errors in the former approach. Comparisons to experimental noise measurements for an existing turbine are encouraging. A parameter study is performed and shows the sensitivity of overall noise levels to changes in inflow velocity and inflow turbulence. Noise sources are characterised and the location and mechanism of the primary sources is determined, inflow-turbulence noise is seen to be the dominant source. The use of CFD calculations is seen to improve the accuracy of noise predictions when compared to the analytic flow solution as well as showing that, for inflow-turbulence noise sources, blade generated turbulence dominates the atmospheric inflow turbulence.

      PubDate: 2017-09-18T08:13:05Z
      DOI: 10.1016/j.jsv.2017.08.038
      Issue No: Vol. 410 (2017)
       
  • Active structural control of a floating wind turbine with a stroke-limited
           hybrid mass damper
    • Authors: Yaqi Hu; Erming He
      Pages: 447 - 472
      Abstract: Publication date: 8 December 2017
      Source:Journal of Sound and Vibration, Volume 410
      Author(s): Yaqi Hu, Erming He
      Floating wind turbines are subjected to more severe structural loads than fixed-bottom wind turbines due to additional degrees of freedom (DOFs) of their floating foundations. It's a promising way of using active structural control method to improve the structural responses of floating wind turbines. This paper investigates an active vibration control strategy for a barge-type floating wind turbine by setting a stroke-limited hybrid mass damper (HMD) in the turbine's nacelle. Firstly, a contact nonlinear modeling method for the floating wind turbine with clearance between the HMD and the stroke limiters is presented based on Euler-Lagrange's equations and an active control model of the whole system is established. The structural parameters are validated for the active control model and an equivalent load coefficient method is presented for identifying the wind and wave disturbances. Then, a state-feedback linear quadratic regulator (LQR) controller is designed to reduce vibration and loads of the wind turbine, and two optimization methods are combined to optimize the weighting coefficients when considering the stroke of the HMD and the active control power consumption as constraints. Finally, the designed controllers are implemented in high fidelity simulations under five typical wind and wave conditions. The results show that active HMD control strategy is shown to be achievable and the designed controllers could further reduce more vibration and loads of the wind turbine under the constraints of stroke limitation and power consumption. “V”-shaped distribution of the TMD suppression effect is inconsistent with the Weibull distribution in practical offshore floating wind farms, and the active HMD control could overcome this shortcoming of the passive TMD.

      PubDate: 2017-09-13T00:36:26Z
      DOI: 10.1016/j.jsv.2017.08.050
      Issue No: Vol. 410 (2017)
       
  • Theoretical and experimental investigation of position-controlled
           semi-active friction damper for seismic structures
    • Authors: Lyan-Ywan Tzu-Kang; Lin Rong-Jie Jheng Hsin-Hsien
      Abstract: Publication date: 6 January 2018
      Source:Journal of Sound and Vibration, Volume 412
      Author(s): Lyan-Ywan Lu, Tzu-Kang Lin, Rong-Jie Jheng, Hsin-Hsien Wu
      A semi-active friction damper (SAFD) can be employed for the seismic protection of structural systems. The effectiveness of an SAFD in absorbing seismic energy is usually superior to that of its passive counterpart, since its slip force can be altered in real time according to structural response and excitation. Most existing SAFDs are controlled by adjusting the clamping force applied on the friction interface. Thus, the implementation of SAFDs in practice requires precision control of the clamping force, which is usually substantially larger than the slip force. This may increase the implementation complexity and cost of SAFDs. To avoid this problem, this study proposes a novel position-controlled SAFD, named the leverage-type controllable friction damper (LCFD). The LCFD system combines a traditional passive friction damper and a leverage mechanism with a movable central pivot. By simply controlling the pivot position, the damping force generated by the LCFD system can be adjusted in real time. In order to verify the feasibility of the proposed SAFD, a prototype LCFD was tested by using a shaking table. The test results demonstrate that the equivalent friction force and hysteresis loop of the LCFD can be regulated by controlling the pivot position. By considering 16 ground motions with two different intensities, the adaptive feature of the LCFD for seismic structural control is further demonstrated numerically.

      PubDate: 2017-10-10T06:53:24Z
       
  • Rotational degree-of-freedom synthesis: An optimised finite difference
           method for non-exact data
    • Authors: T.J. Gibbons; N.D. Sims
      Abstract: Publication date: 6 January 2018
      Source:Journal of Sound and Vibration, Volume 412
      Author(s): T.J. Gibbons, E. Öztürk, N.D. Sims
      Measuring the rotational dynamic behaviour of a structure is important for many areas of dynamics such as passive vibration control, acoustics, and model updating. Specialist and dedicated equipment is often needed, unless the rotational degree-of-freedom is synthesised based upon translational data. However, this involves numerically differentiating the translational mode shapes to approximate the rotational modes, for example using a finite difference algorithm. A key challenge with this approach is choosing the measurement spacing between the data points, an issue which has often been overlooked in the published literature. The present contribution will for the first time prove that the use of a finite difference approach can be unstable when using non-exact measured data and a small measurement spacing, for beam-like structures. Then, a generalised analytical error analysis is used to propose an optimised measurement spacing, which balances the numerical error of the finite difference equation with the propagation error from the perturbed data. The approach is demonstrated using both numerical and experimental investigations. It is shown that by obtaining a small number of test measurements it is possible to optimise the measurement accuracy, without any further assumptions on the boundary conditions of the structure.

      PubDate: 2017-10-10T06:53:24Z
       
  • On using the Hilbert transform for blind identification of complex modes:
           A practical approach
    • Authors: Jose Antunes; Vincent Debut Pilippe Piteau Xavier Delaune Laurent Borsoi
      Abstract: Publication date: 6 January 2018
      Source:Journal of Sound and Vibration, Volume 412
      Author(s): Jose Antunes, Vincent Debut, Pilippe Piteau, Xavier Delaune, Laurent Borsoi
      The modal identification of dynamical systems under operational conditions, when subjected to wide-band unmeasured excitations, is today a viable alternative to more traditional modal identification approaches based on processing sets of measured FRFs or impulse responses. Among current techniques for performing operational modal identification, the so-called blind identification methods are the subject of considerable investigation. In particular, the SOBI (Second-Order Blind Identification) method was found to be quite efficient. SOBI was originally developed for systems with normal modes. To address systems with complex modes, various extension approaches have been proposed, in particular: (a) Using a first-order state-space formulation for the system dynamics; (b) Building complex analytic signals from the measured responses using the Hilbert transform. In this paper we further explore the latter option, which is conceptually interesting while preserving the model order and size. Focus is on applicability of the SOBI technique for extracting the modal responses from analytic signals built from a set of vibratory responses. The novelty of this work is to propose a straightforward computational procedure for obtaining the complex cross-correlation response matrix to be used for the modal identification procedure. After clarifying subtle aspects of the general theoretical framework, we demonstrate that the correlation matrix of the analytic responses can be computed through a Hilbert transform of the real correlation matrix, so that the actual time-domain responses are no longer required for modal identification purposes. The numerical validation of the proposed technique is presented based on time-domain simulations of a conceptual physical multi-modal system, designed to display modes ranging from normal to highly complex, while keeping modal damping low and nearly independent of the modal complexity, and which can prove very interesting in test bench applications. Numerical results for complex modal identifications are presented, and the quality of the identified modal matrix and modal responses, extracted using the complex SOBI technique and implementing the proposed formulation, is assessed.

      PubDate: 2017-10-10T06:53:24Z
       
  • Experimental identification of closely spaced modes using NExT-ERA
    • Authors: S.A. Hosseini; Kordkheili S.H. Momeni Massouleh Hajirezayi Bahai
      Abstract: Publication date: 6 January 2018
      Source:Journal of Sound and Vibration, Volume 412
      Author(s): S.A. Hosseini Kordkheili, S.H. Momeni Massouleh, S. Hajirezayi, H. Bahai
      This article presents a study on the capability of the time domain OMA method, NExT-ERA, to identify closely spaced structural dynamic modes. A survey in the literature reveals that few experimental studies have been conducted on the effectiveness of the NExT-ERA methodology in case of closely spaced modes specifically. In this paper we present the formulation for NExT-ERA. This formulation is then implemented in an algorithm and a code, developed in house to identify the modal parameters of different systems using their generated time history data. Some numerical models are firstly investigated to validate the code. Two different case studies involving a plate with closely spaced modes and a pulley ring with greater extent of closeness in repeated modes are presented. Both structures are excited by random impulses under the laboratory condition. The resulting time response acceleration data are then used as input in the developed code to extract modal parameters of the structures. The accuracy of the results is checked against those obtained from experimental tests.

      PubDate: 2017-10-10T06:53:24Z
       
  • Non-conservative stability of spinning pretwisted cantilever beams
    • Authors: Karimi-Nobandegani S.A.; Fazelzadeh Ghavanloo
      Abstract: Publication date: 6 January 2018
      Source:Journal of Sound and Vibration, Volume 412
      Author(s): A. Karimi-Nobandegani, S.A. Fazelzadeh, E. Ghavanloo
      The stability of a pretwisted cantilever beam spinning about its longitudinal axis and subjected to non-conservative force is investigated. In this study, it is assumed that the cantilever is embedded in viscoelastic medium, which is modeled by the Kelvin-Voigt foundation. Two different types of the non-conservative force are considered. The governing equations of motion and boundary conditions are derived by using Hamilton's principle. The finite element method is utilized to transform the coupled equations of motion to a general eigenvalue problem. The proposed model is justified by an excellent agreement between the present results and those reported in the literature. The effects of several design parameters including the pretwist angle, the cross section ratio, the viscoelastic parameters and load span length on the stability of the spinning pretwisted cantilevers are also examined. Moreover, the critical load and spinning speed and stability regions of the spinning cantilevers are identified. The results show that the design parameters significantly change the stability of the spinning pretwisted cantilever beams.

      PubDate: 2017-10-10T06:53:24Z
       
  • Investigation into the bistatic evolution of the acoustic scattering from
           a cylindrical shell using time-frequency analysis
    • Authors: Agounad Houcein; Aassif Younes Khandouch Maze Dominique
      Abstract: Publication date: 6 January 2018
      Source:Journal of Sound and Vibration, Volume 412
      Author(s): Said Agounad, El Houcein Aassif, Younes Khandouch, Gérard Maze, Dominique Décultot
      The time and frequency analyses of the acoustic scattering by an elastic cylindrical shell in bistatic method show that the arrival times of the echoes and the resonance frequencies of the elastic waves propagating in and around the cylindrical shell are a function of the bistatic angle, β, between the emitter and receiver transducers. The aim of this work is to explain the observed results in time and frequency domains using time-frequency analysis and graphical interpretations. The performance of four widely used time-frequency representations, the Smoothed Pseudo Wigner-Ville (SPWV), the Spectrogram (SP), the reassignment SPWV, and the reassignment SP, are studied. The investigation into the evolution of the time-frequency plane as a function of the bistatic angle β shows that there are the waves propagating in counter-clockwise direction (labeled wave+) and the waves which propagate in clockwise direction (labeled waves−). In this paper the A, S 0, and A 1 circumferential waves are investigated. The graphical interpretations are used to explain the formation mechanism of these waves and the acoustic scattering in monostatic and bistatic configurations. The delay between the echoes of the waves+ and those of the waves− is expressed in the case of the circumnavigating wave (Scholte-Stoneley wave). This study shows that the observed waves at β = 0 ° and β = 18 0 ° are the result of the constructive interferences between the waves+ and the waves−. A comparative study of the physical properties (group velocity dispersion and cut-off frequency) of the waves+, the waves− and the waves observed in monostatic configuration is conducted. Furthermore, it is shown that the ability of the time-frequency representation to highlight the waves+ and the waves− is very useful, for example, for the detection and the localization of defaults, the classification purposes, etc.

      PubDate: 2017-10-10T06:53:24Z
       
  • Exact nonstationary responses of rectangular thin plate on Pasternak
           foundation excited by stochastic moving loads
    • Authors: Guohai Chen; Zeng Meng Dixiong Yang
      Abstract: Publication date: 6 January 2018
      Source:Journal of Sound and Vibration, Volume 412
      Author(s): Guohai Chen, Zeng Meng, Dixiong Yang
      This paper develops an efficient method termed as PE-PIM to address the exact nonstationary responses of pavement structure, which is modeled as a rectangular thin plate resting on bi-parametric Pasternak elastic foundation subjected to stochastic moving loads with constant acceleration. Firstly, analytical power spectral density (PSD) functions of random responses for thin plate are derived by integrating pseudo excitation method (PEM) with Duhamel's integral. Based on PEM, the new equivalent von Mises stress (NEVMS) is proposed, whose PSD function contains all cross-PSD functions between stress components. Then, the PE-PIM that combines the PEM with precise integration method (PIM) is presented to achieve efficiently stochastic responses of the plate by replacing Duhamel's integral with the PIM. Moreover, the semi-analytical Monte Carlo simulation is employed to verify the computational results of the developed PE-PIM. Finally, numerical examples demonstrate the high accuracy and efficiency of PE-PIM for nonstationary random vibration analysis. The effects of velocity and acceleration of moving load, boundary conditions of the plate and foundation stiffness on the deflection and NEVMS responses are scrutinized.

      PubDate: 2017-10-10T06:53:24Z
       
  • Piezoelectricity induced defect modes for shear waves in a periodically
           stratified supperlattice
    • Authors: Davit Piliposyan
      Abstract: Publication date: 6 January 2018
      Source:Journal of Sound and Vibration, Volume 412
      Author(s): Davit Piliposyan
      Properties of shear waves in a piezoelectric stratified periodic structure with a defect layer are studied for a superlattice with identical piezoelectric materials in a unit cell. Due to the electro-mechanical coupling in piezoelectric materials the structure exhibits defect modes in the superlattice with full transmission peaks both for full contact and electrically shorted interfaces. The results show an existence of one or two transmission peaks depending on the interfacial conditions. In the long wavelength region where coupling between electro-magnetic and elastic waves creates frequency band gaps the defect layer introduces one or two defect modes transmitting both electro-magnetic and elastic energies. Other parameters affecting the defect modes are the thickness of the defect layer, differences in refractive indexes and the magnitude of the angle of the incident wave. The results of the paper may be useful in the design of narrow band filters or multi-channel piezoelectric filters.

      PubDate: 2017-10-10T06:53:24Z
       
  • Analysis of the power flow in nonlinear oscillators driven by random
           excitation using the first Wiener kernel
    • Authors: D.H. Hawes; R.S. Langley
      Abstract: Publication date: 6 January 2018
      Source:Journal of Sound and Vibration, Volume 412
      Author(s): D.H. Hawes, R.S. Langley
      Random excitation of mechanical systems occurs in a wide variety of structures and, in some applications, calculation of the power dissipated by such a system will be of interest. In this paper, using the Wiener series, a general methodology is developed for calculating the power dissipated by a general nonlinear multi-degree-of freedom oscillatory system excited by random Gaussian base motion of any spectrum. The Wiener series method is most commonly applied to systems with white noise inputs, but can be extended to encompass a general non-white input. From the extended series a simple expression for the power dissipated can be derived in terms of the first term, or kernel, of the series and the spectrum of the input. Calculation of the first kernel can be performed either via numerical simulations or from experimental data and a useful property of the kernel, namely that the integral over its frequency domain representation is proportional to the oscillating mass, is derived. The resulting equations offer a simple conceptual analysis of the power flow in nonlinear randomly excited systems and hence assist the design of any system where power dissipation is a consideration. The results are validated both numerically and experimentally using a base-excited cantilever beam with a nonlinear restoring force produced by magnets.

      PubDate: 2017-10-10T06:53:24Z
       
  • Real-time nearfield acoustic holography in a uniformly moving medium
    • Authors: Bi-Chun Dong; Chuan-Xing Xiao-Zheng Zhang Yong-Bin Zhang
      Abstract: Publication date: 8 December 2017
      Source:Journal of Sound and Vibration, Volume 410
      Author(s): Bi-Chun Dong, Chuan-Xing Bi, Xiao-Zheng Zhang, Yong-Bin Zhang
      Real-time nearfield acoustic holography (RT-NAH) is an effective tool to identify nonstationary sound sources and predict the time-dependent sound field via a temporal convolution between the time-dependent wavenumber spectrum on the hologram plane and an impulse response. However, the conventional RT-NAH procedures are developed for sound sources situated in a static medium. As for sound sources located in a moving medium, the conventional RT-NAH procedures cannot be applied directly due to the fact that the impulse response will be changed by flow effects. In this paper, two analytical impulse responses in a uniformly moving medium, corresponding to two cases that the flow direction is parallel to and perpendicular to the hologram plane, are derived first with consideration of flow effects, and then RT-NAH is extended to realize forward and backward propagation of time-dependent signals in the moving medium. Numerical simulations are conducted to check the performances of the proposed method. The results show that the proposed method not only can be used to predict nonstationary sound fields but also can be utilized to identify nonstationary sources in a moving medium for both the parallel and perpendicular cases.

      PubDate: 2017-09-13T00:36:26Z
       
 
 
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