This paper presents a numerical model of lamb wave propagation in a homogenous steel plate using elastodynamic finite
integration technique (EFIT) as well as its validation with analytical results. Lamb wave method is a long range inspection technique which is considered to have unique future in the field of structural health monitoring. One of the main problems facing the lamb wave method is how to choose the most appropriate frequency to generate the waves for adequate transmission capable of properly propagating in the material, interfering with defects/damages, and being received in good conditions. Modern simulation tools based on numerical methods such as finite integration technique (FIT), finite element method (FEM), and boundary element method (BEM) may be used for modeling. In this paper, two sets of simulation are performed. In the first set, group velocities of lamb wave in a steel plate are obtained numerically. Results are then compared with analytical results to validate the simulation. In the second set, EFIT is employed to study fundamental symmetric mode interaction with a surface braking defect.

Hussein Rappel

Aghil Yousefi-Koma

Jalil Jamali

Ako Bahari

Numerical Time-Domain Modeling of Lamb Wave Propagation Using Elastodynamic Finite Integration Technique

Hamid Mehdigholi

Hamid Ahmadian

Abdolreza Ohadi

International Conference on Acoustics and Vibration 2012

Experimental system identification of a flexible beam based on sweep square excitation is studied. For the purpose of nonparametric identification, an excitation signal is conducted to evaluate the frequency response of the system. The experiment is designed to excite the beam using a piezo actuator, in a way to raise the chance of exciting first three natural modes. In order to find the best linear representation of the real system, two different identification methods are applied. First, autoregressive moving average eXogenous method is employed to identify the transfer function of the beam. Then, the identification is carried out using the subspace identification method to obtain the state space model. A comparison is made between different orders of prediction and the best chosen models of the two identification methods are compared with each other to select the most accurate linear system. Furthermore, as the identified model has to fulfill the controllability and observability conditions, the amenable system is achieved after some order reductions. Two reduction methods called minimum truncation and maximum DC gains matching are utilized to find the most effective reduced order. The outcome of this study will bring in the best linear representation of the beam coupled with piezoelectric sensors/actuators.

Sajad Saraygord Afshari

Hadi Nobahari

Seyed Ali Hosseini Kordkheili

Experimental Parametric Identification of a Flexible Beam Using Piezoelectric Sensors and Actuators

Sound radiation from a beam resting on a viscoelastic foundation is analytically studied when it is subjected to a moving load. The topic could cover a range of applications such as submerged floating tunnels, buried pipelines, and railway tracks. Galerkin&#x2019;s method is employed to obtain the transverse vibration of the beam. Based on the Rayleigh integral approach, acoustic pressure distribution around the beam is obtained in the time domain. In the second part of this paper, corresponding displacement and acoustic pressure are obtained by the use of the Rayleigh-Ritz approach in conjunction with the Laplace transform method and by the use of the Fourier transform, respectively. Durbin&#x2019;s numerical Laplace transform inversion scheme is eventually employed to obtain dynamic responses. A parametric study is then carried out and influences of the design parameters as well as the loading conditions on the acoustic pressure field are investigated.

Rezgar Shakeri

Davood Younesian

Analytical Solution for the Sound Radiation Field of a Viscoelastically Supported Beam Traversed by a Moving Load

By new advancements in vehicle manufacturing, evaluation of vehicle quality assurance has got a more critical issue. Today noise and vibration generated inside and outside the vehicles are more important factors for customers than before. So far several researchers have focused on interior noise transfer path analysis and the results have been published in related papers but each method has its own limitations. In present work, the vibration transfer path analysis and vibration path ranking of a car interior have been performed. As interior vibration is a source of structural borne noise problem, thus, the results of this research can be used to present the structural borne noise state in a vehicle. The proposed  method in this paper does not need to disassemble the powertrain from the chassis. The procedure shows a good ability of vibration path ranking in a vehicle and is an effective tool to diagnose the vibration problem inside the vehicle. The simulated vibration spectrums in different speeds of the engine have a good compliance with the tested results; however, some incompatibilities exist and have been discussed in detail. The simulated results show the strength of the method in engine mount optimization.

B. Sakhaei

M. Durali

Vibration Transfer Path Analysis and Path Ranking for NVH Optimization of a Vehicle Interior

The major purpose of this paper is the development of wave dispersion curves calculation in multilayered composite-metal plates. At first, equations of motion and characteristic equations for the free waves on a single-layered orthotropic plate are presented. Since direction of wave propagation in composite materials is effective on equations of motion and dispersion curves, two different cases are considered: propagation of wave along an axis of material symmetry and along off-axes of material symmetry. Then, presented equations are extended for a multilayered orthotropic composite-metal plate using the transfer matrix method in which a global transfer matrix may be extracted which relates stresses and displacements on the top layer to those on the bottom one. By satisfying appropriate boundary conditions on the outer boundaries, wave characteristic equations and then dispersion curves are obtained. Moreover, presented equations may be applied to other materials such as monoclinic, transversely isotropic, cubic, and isotropic materials. To verify the solution procedure, a number of numerical illustrations for a single-layered orthotropic and double-layered orthotropic-metal are presented.

Ameneh Maghsoodi

Mojtaba Sadighi

Calculation of Wave Dispersion Curves in Multilayered Composite-Metal Plates

In many nonlinear structural systems, compared with the local regions with induced nonlinear effects, the main portions of the structures are linear. An exact condensation technique based on the harmonic balance method (HBM) in conjunction with the modal expansion technique is employed to convert the motion equations of such a system to a set of nonlinear algebraic equations that are considerably small and adequately accurate to determine periodic responses. To demonstrate the capability of the suggested method, few case studies consisting of discrete systems with weak and essential nonlinearities are studied, and the results are compared to other methodologies results.

M. Mohammadali

H. Ahmadian

Efficient Model Order Reduction of Structural Dynamic Systems with Local Nonlinearities under Periodic Motion

The homoclinic bifurcation and transition to chaos in gear systems are studied both analytically and numerically. Applying Melnikov analytical method, the threshold values for the occurrence of chaotic motion are obtained. The influence of system parameters on the character of vibration is studied. The numerical simulation of the system including bifurcation diagram, phase plane portraits, Fourier spectra, and time histories is considered to confirm the analytical predictions for the occurrence of homoclinic bifurcation and chaos in nonlinear gear systems.

Anooshirvan Farshidianfar

Amin Saghafi

Bifurcation and Chaos Prediction in Nonlinear Gear Systems

One of the interesting fields that attracted many researchers in recent years is the smart structures. The piezomaterials, because of their ability in converting both mechanical stress and electricity to each other, are very applicable in this field. However, most of the works available used various inexact two-dimensional theories with certain types of simplification, which are inaccurate in some applications such as thick shells while, in some applications due to request of large displacement/stress, thick piezoelectric panel is needed and two-dimensional theories have not enough accuracy. This study investigates the dynamic steady state response and natural frequency of a piezoelectric circular cylindrical panel using exact three-dimensional solutions based on this decomposition technique. In addition, the formulation is written for both simply supported and clamped boundary conditions. Then the natural frequencies, mode shapes, and dynamic steady state response of the piezoelectric circular cylindrical panel in frequency domain are validated with commercial finite element software (ABAQUS) to show the validity of the mathematical formulation and the results will be compared, finally.

Atta Oveisi

Mohammad Gudarzi

Seyyed Mohammad Hasheminejad

Dynamic Response of a Thick Piezoelectric Circular Cylindrical Panel: An Exact Solution

Echo and sound resonance in a conference room cause obscure speech and make listeners tired. 
                   Thus, the acoustical properties of a conference room are vitally important. 
                    The conference room 412 at Sharif University Physics Department failed to meet basic acoustical standards. 
                    The aim of this research is to improve reverberation time (RT) of the conference room using Helmholtz resonators with defined dimensions, 
                    diffusers, and sound absorbers. Helmholtz resonators are widely used to absorb sound noise especially at low frequencies. 
                    They are particularly useful when noise has a narrow-frequency band. One of the advantages of using Helmholtz resonators is their capacity to be tuned on different frequencies. 
                    We enhanced acoustical properties of Helmholtz resonators using proper absorbers and diffusers. 
                    In order to decrease the RT, a large number of Helmholtz resonators have been made and installed in proper positions in the conference room. 
                    The RT was measured before and after installation. The measurements indicate that the acoustical characteristics of the conference room have been significantly improved.

Hossein Namvar Arefi

Seyyed Mohammad Amin Ghiasi

Seyyede Mahshid Ghaffari

Farhad Ramezanghorbani

Shiva Sharifpour

Peyman Irajizad

Seyede Delaram Ghoreishi Langroudi

Ahmad Amjadi

Conference Room Reverberation Time Correction Using Helmholtz Resonators Lined with Absorbers

About this journal

Shock and Vibration publishes papers on all aspects of shock and vibration, especially in relation to civil, mechanical and aerospace engineering applications, as well as transport, materials and geoscience.&nbsp;

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Chief Editor&nbsp;Dr Tai Thai&nbsp;is based at the University of Melbourne and his current research focuses on high strength materials for sustainable construction of buildings, bridges and other infrastructure.

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Shock and Vibration publishes papers on all aspects of shock and vibration, especially in relation to civil, mechanical and aerospace engineering applications, as well as transport, materials and geoscience. 

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Shock and Vibration | Hindawi

Shock and Vibration

This Issue is now open for submissions.
Papers are published upon acceptance, regardless of the Special Issue publication date.

Shock and Vibration

International Conference on Acoustics and Vibration 2012

International Conference on Acoustics and Vibration 2012

Articles

Numerical Time-Domain Modeling of Lamb Wave Propagation Using Elastodynamic Finite Integration Technique

International Conference on Acoustics and Vibration 2012

Experimental Parametric Identification of a Flexible Beam Using Piezoelectric Sensors and Actuators

Analytical Solution for the Sound Radiation Field of a Viscoelastically Supported Beam Traversed by a Moving Load

Vibration Transfer Path Analysis and Path Ranking for NVH Optimization of a Vehicle Interior

Calculation of Wave Dispersion Curves in Multilayered Composite-Metal Plates

Efficient Model Order Reduction of Structural Dynamic Systems with Local Nonlinearities under Periodic Motion

Bifurcation and Chaos Prediction in Nonlinear Gear Systems

Dynamic Response of a Thick Piezoelectric Circular Cylindrical Panel: An Exact Solution

Conference Room Reverberation Time Correction Using Helmholtz Resonators Lined with Absorbers