Advances in Acoustics and Vibration http://www.hindawi.com The latest articles from Hindawi Publishing Corporation © 2014 , Hindawi Publishing Corporation . All rights reserved. Fault Diagnosis of Beam-Like Structure Using Modified Fuzzy Technique Wed, 17 Dec 2014 06:31:02 +0000 http://www.hindawi.com/journals/aav/2014/491510/ This paper presents a novel hybrid fuzzy logic based artificial intelligence (AI) technique applicable to diagnosis of the crack parameters in a fixed-fixed beam by using the vibration signatures as input. The presence of damage in engineering structures leads to changes in vibration signatures like natural frequency and mode shapes. In the first part of this work, a structure with a failure crack has been analyzed using finite element method (FEM) and retrospective changes in the vibration signatures have been recorded. In the second part of the research work, these deviations in the vibration signatures for the first three mode shapes have been taken as input parameters for a fuzzy logic based controller for calculation of crack location and its severity as output parameters. In the proposed fuzzy controller, hybrid membership functions have been taken. Several fuzzy rules have been identified for prediction of crack depth and location and the results have been compared with finite element analysis. A database of experimental results has also been considered to check the robustness of the fuzzy controller. The results show that predictions for the nondimensional crack location, , deviate ~2.4% from experimental values and for the nondimensional crack depth, , are less than ~−2%. Dhirendranath Thatoi, Sasanka Choudhury, and Prabir Kumar Jena Jena Copyright © 2014 Dhirendranath Thatoi et al. All rights reserved. Analytical and Numerical Investigation of Lacing Wire Damage Induced Mistuning in Turbine Blade Packet Tue, 09 Dec 2014 06:01:11 +0000 http://www.hindawi.com/journals/aav/2014/164638/ Investigations of modal parameters for a mistuned packet of turbine blades due to lacing wire damage are reported using analytical and numerical studies with a simplified model. The turbine blade is assumed to be an Euler-Bernoulli beam connected with a lacing wire which is modeled as a mass less linear elastic spring. Thus, the blade is considered as a continuous system and lacing wire as a discrete system. The analytical results using Eigen value analysis are compared with numerical results obtained using commercial finite element package. In real life situation, though not reported in the literature, it is the failure of lacing wire that occurs quite often compared to the turbine blade and acts as precursor to the subsequent blade damage if it goes undetected. Therefore, studying the modal parameters of the grouped turbine blades in the context of lacing wire failure becomes important. The effect of variation of lacing wire location and stiffness indicative of damage resulting in the loss of stiffness on modal parameters is investigated. The study reveals a lot of fundamental understandings pertaining to dynamic behavior of grouped blades compared to the stand-alone blade under the influence of damaged lacing wire. Mangesh S. Kotambkar and Animesh Chatterjee Copyright © 2014 Mangesh S. Kotambkar and Animesh Chatterjee. All rights reserved. What Really Caused the ROKS Cheonan Warship Sinking? Thu, 20 Nov 2014 08:17:14 +0000 http://www.hindawi.com/journals/aav/2014/514346/ This paper is concerned with the sinking of the Korean naval warship (ROKS Cheonan) and the reported spectra of the seismic signals recorded at the time of the incident. The spectra of seismic signals show prominently amplitude peaks at around 8.5 Hz and its harmonics. These frequencies were explained with the vibrations of a water column due to an underwater explosion. This explanation is highly doubtful and concerns about its validity have already been raised in the scientific community. In this work an alternative explanation is presented: it is shown that the recorded seismic spectra are consistent with the natural frequencies of vibrations of a large submarine with a length of around 113 m. This finding raises the possibility that the ROKS Cheonan sunk because of the collision with a large submarine rather than the explosion of a torpedo or an underwater mine. Hwang Su Kim and Mauro Caresta Copyright © 2014 Hwang Su Kim and Mauro Caresta. All rights reserved. Doppler Velocity Estimation of Overlapping Linear-Period-Modulated Ultrasonic Waves Based on an Expectation-Maximization Algorithm Wed, 12 Nov 2014 12:41:01 +0000 http://www.hindawi.com/journals/aav/2014/921876/ The occurrence of an overlapping signal is a significant problem in performing multiple objects localization. Doppler velocity is sensitive to the echo shape and is also able to be connected to the physical properties of moving objects, especially for a pulse compression ultrasonic signal. The expectation-maximization (EM) algorithm has the ability to achieve signal separation. Thus, applying the EM algorithm to the overlapping pulse compression signals is of interest. This paper describes a proposed method, based on the EM algorithm, of Doppler velocity estimation for overlapping linear-period-modulated (LPM) ultrasonic signals. Simulations are used to validate the proposed method. Natee Thong-un and Minoru K. Kurosawa Copyright © 2014 Natee Thong-un and Minoru K. Kurosawa. All rights reserved. S1-ZGV Modes of a Linear and Nonlinear Profile for Functionally Graded Material Using Power Series Technique Sun, 21 Sep 2014 06:37:31 +0000 http://www.hindawi.com/journals/aav/2014/401042/ The present work deals with functionally graded materials (FGM) isotropic plates in the neighborhood of the first-order symmetric zero group velocity (S1-ZGV) point. The mechanical properties of functionally graded material (FGM) are assumed to vary continuously through the thickness of the plate and obey a power law of the volume fraction of the constituents. Governing equations for the problem are derived, and the power series technique (PST) is employed to solve the recursive equations. The impact of the FGM basic materials properties on S1-ZGV frequency of FGM plate is investigated. Numerical results show that S1-ZGV frequency is comparatively more sensitive to the shear modulus. The gradient coefficient does not affect the linear dependence of ZGV frequency as function of cut-off frequency ; only the slope is slightly varied. M. Zagrouba, M. S. Bouhdima, and M. H. Ben Ghozlen Copyright © 2014 M. Zagrouba et al. All rights reserved. Sound Scattering and Its Reduction by a Janus Sphere Type Thu, 18 Sep 2014 05:31:39 +0000 http://www.hindawi.com/journals/aav/2014/392138/ Sound scattering by a Janus sphere type is considered. The sphere has two surface zones: a soft surface of zero acoustic impedance and a hard surface of infinite acoustic impedance. The zones are arranged such that axisymmetry of the sound field is preserved. The equivalent source method is used to compute the sound field. It is shown that, by varying the sizes of the soft and hard zones on the sphere, a significant reduction can be achieved in the scattered acoustic power and upstream directivity when the sphere is near a free surface and its soft zone faces the incoming wave and vice versa for a hard ground. In both cases the size of the sphere’s hard zone is much larger than that of its soft zone. The boundary location between the two zones coincides with the location of a zero pressure line of the incoming standing sound wave, thus masking the sphere within the sound field reflected by the free surface or the hard ground. The reduction in the scattered acoustic power diminishes when the sphere is placed in free space. Variations of the scattered acoustic power and directivity with the sound frequency are also given and discussed. Deliya Kim, Eldad Jitzhak Avital, and Touvia Miloh Copyright © 2014 Deliya Kim et al. All rights reserved. The Effect of Perforation on the Dynamics of a Flexible Panel Wed, 17 Sep 2014 09:10:59 +0000 http://www.hindawi.com/journals/aav/2014/526045/ Introduction of holes into plate-like structures is commonly found as one of the practical noise control measures to reduce sound radiation. However, perforation also reduces the panel stiffness and hence increases its vibration. The discussion on this effect is lacking and hence this paper discusses the dynamics of a perforated panel from the results obtained from Finite Element (FE) model. Different hole geometries and arrangement are simulated to investigate their effect on the plate mobility. In general, it is found that increasing the perforation ratio increases the plate mobility. For a fixed perforation ratio, the mobility increases at high frequency (above 1 kHz) for a smaller hole density in the plate. The plate with holes concentrated at the middle shows the largest increase of vibration around the plate centre compared to those uniformly distributed or away from the middle and concentrated at the plate edges. This is because as the hole separation becomes smaller, the reduction of the global stiffness around the mid area of the plate becomes greater. This also corresponds to the finding here that the mobility is greater at the vicinity of the hole. Different conditions of the plate edges are found to give consistent trend of the effect of perforation. A. Putra, Y. M. Cheah, N. Muhammad, A. Rivai, and C. M. Wai Copyright © 2014 A. Putra et al. All rights reserved. Phase Portraits of the Autonomous Duffing Single-Degree-of-Freedom Oscillator with Coulomb Dry Friction Sun, 14 Sep 2014 12:38:07 +0000 http://www.hindawi.com/journals/aav/2014/465489/ The paper presents phase portraits of the autonomous Duffing single-degree-of-freedom system with Coulomb dry friction in its parameter space. The considered nonlinearities of the cubic stiffness and Coulomb dry friction are widely used throughout the literature. It has been shown that there can be more than one sticking region in the phase plane. It has also been shown that an equilibrium point occurs at the critical combinations of values of the parameters and which gives rise to zero eigenvalue of the linearised system. The unstable limit cycle may appear in the case of negative viscous damping ; . Nikola Jakšić Copyright © 2014 Nikola Jakšić. All rights reserved. A Combined Softening and Hardening Mechanism for Low Frequency Human Motion Energy Harvesting Application Sun, 07 Sep 2014 11:59:00 +0000 http://www.hindawi.com/journals/aav/2014/217032/ This paper concerns the mechanism for harvesting energy from human body motion. The vibration signal from human body motion during walking and jogging was first measured using 3-axes vibration recorder placed at various places on the human body. The measured signal was then processed using Fourier series to investigate its frequency content. A mechanism was proposed to harvest the energy from the low frequency-low amplitude human motion. This mechanism consists of the combined nonlinear hardening and softening mechanism which was aimed at widening the bandwidth as well as amplifying the low human motion frequency. This was realized by using a translation-to-rotary mechanism which converts the translation motion of the human motion into the rotational motion. The nonlinearity in the system was realized by introducing a winding spring stiffness and the magnetic stiffness. Quasi-static and dynamic measurement were conducted to investigate the performance of the mechanism. The results show that, with the right degree of nonlinearity, the two modes can be combined together to produce a wide flat response. For the frequency amplification, the mechanism manages to increase the frequency by around 8 times in terms of rotational speed. Khalis Suhaimi, Roszaidi Ramlan, and Azma Putra Copyright © 2014 Khalis Suhaimi et al. All rights reserved. Surface Wave Propagation in a Microstretch Thermoelastic Diffusion Material under an Inviscid Liquid Layer Mon, 04 Aug 2014 09:58:10 +0000 http://www.hindawi.com/journals/aav/2014/518384/ The present investigation deals with the propagation of Rayleigh type surface waves in an isotropic microstretch thermoelastic diffusion solid half space under a layer of inviscid liquid. The secular equation for surface waves in compact form is derived after developing the mathematical model. The dispersion curves giving the phase velocity and attenuation coefficients with wave number are plotted graphically to depict the effect of an imperfect boundary alongwith the relaxation times in a microstretch thermoelastic diffusion solid half space under a homogeneous inviscid liquid layer for thermally insulated, impermeable boundaries and isothermal, isoconcentrated boundaries, respectively. In addition, normal velocity component is also plotted in the liquid layer. Several cases of interest under different conditions are also deduced and discussed. Rajneesh Kumar, Sanjeev Ahuja, and S. K. Garg Copyright © 2014 Rajneesh Kumar et al. All rights reserved. In Situ Measurement of Discomfort Curves for Seated Subjects in a Car on the Four-Post Rig Mon, 04 Aug 2014 06:45:04 +0000 http://www.hindawi.com/journals/aav/2014/239178/ The aim of this study is to measure and quantify perceived intensity of discomfort due to vibration in a vehicle in situ considering complete vehicle dynamic behaviour. The shaker table based discomfort curves or the road test results may not accurately and universally indicate the true level of human discomfort in a vehicle. A new experimental method, using a seated human in a car on the four-post rig simulator, is proposed to quantify discomfort. The intensity of perception to vibration decreased with decreasing input and increasing frequency; the rate of change is different from the published literature; the difference is large for angular modes of inputs. Vehicle dynamic response is used to inform and analyse the results. The repeatability of the method and the fact that they are in situ measurements may eventually help reduce reliance on the road tests. Furthermore, discomfort curves obtained, subsequently, can be used in predictive models. T. Ibicek and A. N. Thite Copyright © 2014 T. Ibicek and A. N. Thite. All rights reserved. Prediction of Vibrational Behavior of Grid-Stiffened Cylindrical Shells Thu, 10 Jul 2014 14:16:02 +0000 http://www.hindawi.com/journals/aav/2014/242573/ A unified analytical approach is applied to investigate the vibrational behavior of grid-stiffened cylindrical shells with different boundary conditions. A smeared method is employed to superimpose the stiffness contribution of the stiffeners with those of shell in order to obtain the equivalent stiffness parameters of the whole panel. Theoretical formulation is established based on Sanders’ thin shell theory. The modal forms are assumed to have the axial dependency in the form of Fourier series whose derivatives are legitimized using Stoke's transformation. A 3D finite element model is also built using ABAQUS software which takes into consideration the exact geometric configuration of the stiffeners and the shell. The achievements from the two types of analyses are compared with each other and good agreement has been obtained. The Influences of variations in shell geometrical parameters, boundary condition, and changes in the cross stiffeners angle on the natural frequencies are studied. The results obtained are novel and can be used as a benchmark for further studies. The simplicity and the capability of the present method are also discussed. G. H. Rahimi, M. Hemmatnezhad, and R. Ansari Copyright © 2014 G. H. Rahimi et al. All rights reserved. A Mathematical Images Group Model to Estimate the Sound Level in a Close-Fitting Enclosure Thu, 12 Jun 2014 09:33:29 +0000 http://www.hindawi.com/journals/aav/2014/284362/ This paper describes a special mathematical images model to determine the sound level inside a close-fitting sound enclosure. Such an enclosure is defined as the internal air volume defined by a machine vibration noise source at one wall and a parallel reflecting wall located very close to it and acts as the outside radiating wall of the enclosure. Four smaller surfaces define a parallelepiped for the volume. The main reverberation group is between the two large parallel planes. Viewed as a discrete line-type source, the main group is extended as additional discrete line-type source image groups due to reflections from the four smaller surfaces. The images group approach provides a convergent solution for the case where hard reflective surfaces are modeled with absorption coefficients equal to zero. Numerical examples are used to calculate the sound pressure level incident on the outside wall and the effect of adding high absorption to the front wall. This is compared to the result from the general large room diffuse reverberant field enclosure formula for several hard wall absorption coefficients and distances between machine and front wall. The images group method is shown to have low sensitivity to hard wall absorption coefficient value and presents a method where zero sound absorption for hard surfaces can be used rather than an initial hard surface sound absorption estimate or measurement to predict the internal sound levels the effect of adding absorption. Michael J. Panza Copyright © 2014 Michael J. Panza. All rights reserved. Effect of Velocity and Time-Step on the Continuity of a Discrete Moving Sound Image Thu, 05 Jun 2014 07:46:47 +0000 http://www.hindawi.com/journals/aav/2014/950463/ As a basic study into 3-D audio display systems, this paper reports the conditions of moving sound image velocity and time-step where a discrete moving sound image is perceived as continuous motion. In this study, the discrete moving sound image was presented through headphones and ran along the ear-axis. The experiments tested the continuity of a discrete moving sound image using various conditions of velocity (0.25, 0.5, 0.75, 1, 2, 3, and 4 m/s) and time-step (0, 0.02, 0.04, 0.06, 0.08, 0.10, 0.12, and 0.14 s). As a result, the following were required in order to present the discrete moving sound image as continuous movement. (1) The 3-D audio display system was required to complete the sound image presentation process, including head tracking and HRTF simulation, in a time shorter than 0.02 s, in order to present sound image movement at all velocities. (2) A processing time longer than 0.1 s was not acceptable. (3) If the 3-D audio display system only presented very slow movement (less than about 0.5 m/s), processing times ranging from 0.04 s to 0.06 s were still acceptable. Yoshikazu Seki Copyright © 2014 Yoshikazu Seki. All rights reserved. Subband DCT and EMD Based Hybrid Soft Thresholding for Speech Enhancement Tue, 20 May 2014 05:19:01 +0000 http://www.hindawi.com/journals/aav/2014/765454/ This paper presents a two-stage soft thresholding algorithm based on discrete cosine transform (DCT) and empirical mode decomposition (EMD). In the first stage, noisy speech is decomposed into eight frequency bands and a specific noise variance is calculated for each one. Based on this variance, each band is denoised using soft thresholding in DCT domain. The remaining noise is eliminated in the second stage through a time domain soft thresholding strategy adapted to the intrinsic mode functions (IMFs) derived by applying EMD on the signal obtained from the first stage processing. Significantly better SNR improvement and perceptual speech quality results for different noise types prove the superiority of the proposed algorithm over recently reported techniques. Erhan Deger, Md. Khademul Islam Molla, Keikichi Hirose, Nobuaki Minematsu, and Md. Kamrul Hasan Copyright © 2014 Erhan Deger et al. All rights reserved. Experimental Study for Vibration Behaviors of Locally Defective Deep Groove Ball Bearings under Dynamic Radial Load Sun, 18 May 2014 12:40:23 +0000 http://www.hindawi.com/journals/aav/2014/271346/ Rolling element bearings are used in many mechanical systems at the revolute joints for sustaining the dynamic loads. Thus, the reliable and efficient functioning of such systems critically depends on the good health of the employed rolling bearings. Hence, health monitoring of rolling bearings through their vibration responses is a vital issue. In this paper, an experimental investigation has been reported related to the vibration behaviours of healthy and locally defective deep groove ball bearings operating under dynamic radial load. The dynamic load on the test bearings has been applied using an electromechanical shaker. The vibration spectra of the healthy and defective deep groove ball bearings in time and frequency domains have been compared and discussed. Overall vibration increases in presence of local defects and dynamic radial load. V. N. Patel, N. Tandon, and R. K. Pandey Copyright © 2014 V. N. Patel et al. All rights reserved. Vibration Analysis of Hollow Tapered Shaft Rotor Mon, 28 Apr 2014 07:17:40 +0000 http://www.hindawi.com/journals/aav/2014/410851/ Shafts or circular cross-section beams are important parts of rotating systems and their geometries play important role in rotor dynamics. Hollow tapered shaft rotors with uniform thickness and uniform bore are considered. Critical speeds or whirling frequency conditions are computed using transfer matrix method and then the results were compared using finite element method. For particular shaft lengths and rotating speeds, response of the hollow tapered shaft-rotor system is determined for the establishment of dynamic characteristics. Nonrotating conditions are also considered and results obtained are plotted. P. M. G. Bashir Asdaque and R. K. Behera Copyright © 2014 P. M. G. Bashir Asdaque and R. K. Behera. All rights reserved. Normal Incidence of Sound Transmission Loss from Perforated Plates with Micro and Macro Size Holes Thu, 17 Apr 2014 11:38:19 +0000 http://www.hindawi.com/journals/aav/2014/534569/ This paper studies the sound transmission loss of perforated panels and investigates the effect of the hole diameter on the sound insulation performance under normal incidence of acoustic loading. The hole diameters are distinguished into micro (submillimeter) and macro (millimeter) sizes. In general, the transmission loss reduces as the perforation ratio is increased. However, by retaining the perforation ratio, it is found that the transmission loss increases as the hole diameter is reduced for a perforate with micro holes due to the effect of resistive part in the hole impedance, which is contrary to the results for those with the macro holes. Both show similar trend at high frequency where the fluid behavior inside the hole is inertial. Simple analytical formulae for engineering purpose are provided. Validation of the models with measurement data also gives good agreement. A. Putra and A. Y. Ismail Copyright © 2014 A. Putra and A. Y. Ismail. All rights reserved. Monitoring Machines by Using a Hybrid Method Combining MED, EMD, and TKEO Thu, 20 Mar 2014 10:06:03 +0000 http://www.hindawi.com/journals/aav/2014/592080/ Amplitude demodulation is a key for diagnosing bearing faults. The quality of the demodulation determines the efficiency of the spectrum analysis in detecting the defect. A signal analysis technique based on minimum entropy deconvolution (MED), empirical mode decomposition (EMD), and Teager Kaiser energy operator (TKEO) is presented. The proposed method consists in enhancing the signal by using MED, decomposing the signal in intrinsic mode functions (IMFs) and selects only the IMF which presents the highest correlation coefficient with the original signal. In this study the first IMF1 was automatically selected, since it represents the contribution of high frequencies which are first excited at the early stages of degradation. After that, TKEO is used to track the modulation energy. The spectrum is applied to the instantaneous amplitude. Therefore, the character of the bearing faults can be recognized according to the envelope spectrum. The simulation and experimental results show that an envelope spectrum analysis based on MED-EMD and TKEO provides a reliable signal analysis tool. The experimental application has been developed on acoustic emission and vibration signals recorded for bearing fault detection. Mourad Kedadouche, Marc Thomas, and Antoine Tahan Copyright © 2014 Mourad Kedadouche et al. All rights reserved. Vibrational Suspension of Light Sphere in a Tilted Rotating Cylinder with Liquid Sun, 16 Mar 2014 09:10:38 +0000 http://www.hindawi.com/journals/aav/2014/608058/ The dynamics of a light sphere in a quickly rotating inclined cylinder filled with liquid under transversal vibrations is experimentally investigated. Due to inertial oscillations of the sphere relative to the cavity, its rotation velocity differs from the cavity one. The intensification of the lagging motion of a sphere and the excitation of the outstripping differential rotation are possible under vibrations. It occurs in the resonant areas where the frequency of vibrations coincides with the fundamental frequency of the system. The position of the sphere in the center of the cylinder could be unstable. Different velocities of the sphere are matched with its various quasistationary positions on the axis of rotating cavity. In tilted rotating cylinder, the axial component of the gravity force appears; however, the light sphere does not float to the upper end wall but gets the stable position at a definite distance from it. It makes possible to provide a vibrational suspension of the light sphere in filled with liquid cavity rotating around the vertical axis. It is found that in the wide range of the cavity inclination angles the sphere position is determined by the dimensionless velocity of body differential rotation. Victor G. Kozlov and Stanislav V. Subbotin Copyright © 2014 Victor G. Kozlov and Stanislav V. Subbotin. All rights reserved. Numerical Study on Energy Dissipation of Steel Moment Resisting Frames under Effect of Earthquake Vibrations Thu, 13 Mar 2014 12:22:25 +0000 http://www.hindawi.com/journals/aav/2014/510593/ In the regions near to active faults, if the fault rupture propagation is towards the site and the shear wave propagation velocity is near the velocity of fault rupture propagation, the forward directivity effect causes pulse-like long-period large-amplitude vibrations perpendicular to the fault plane which causes a large amount of energy to be imposed to structures in a short time. According to previous investigations, the amounts of input and dissipated energies in the structure represent the general performance of the structure and show the level of damage and flexibility of the structure against earthquake. Therefore, in this study, the distribution of damage in the structure height and its amount at the height of steel moment frames under the pulse-like vibrations in the near fault region has been investigated. The results of this study show that the increase rate of earthquake input energy with respect to increase in the number of stories of the structure in the near field of fault is triple that in the far field of fault which then leads to a 2–2.5 times increase in the earthquake input energy in the high rise moment frames in the near field of fault with respect to that in the far field of fault. Mohsen Gerami and Davood Abdollahzadeh Copyright © 2014 Mohsen Gerami and Davood Abdollahzadeh. All rights reserved. Optimization of Natural Frequencies and Sound Power of Beams Using Functionally Graded Material Thu, 20 Feb 2014 06:49:02 +0000 http://www.hindawi.com/journals/aav/2014/752361/ This paper presents a design method to optimize the material distribution of functionally graded beams with respect to some vibration and acoustic properties. The change of the material distribution through the beam length alters the stiffness and the mass of the beam. This can be used to alter a specific beam natural frequency. It can also be used to reduce the sound power radiated from the vibrating beam. Two novel volume fraction laws are used to describe the material volume distributions through the length of the FGM beam. The proposed method couples the finite element method (for the modal and harmonic analysis), Lumped Parameter Model (for calculating the power of sound radiation), and an optimization technique based on Genetic Algorithm. As a demonstration of this technique, the optimization procedure is applied to maximize the fundamental frequency of FGM cantilever and clamped beams and to minimize the sound radiation from vibrating clamped FGM beam at a specific frequency. Nabeel T. Alshabatat and Koorosh Naghshineh Copyright © 2014 Nabeel T. Alshabatat and Koorosh Naghshineh. All rights reserved. Effect of Two Temperatures on Reflection Coefficient in Micropolar Thermoelastic with and without Energy Dissipation Media Sun, 16 Feb 2014 14:34:13 +0000 http://www.hindawi.com/journals/aav/2014/846721/ The reflection of plane waves at the free surface of thermally conducting micropolar elastic medium with two temperatures is studied. The theory of thermoelasticity with and without energy dissipation is used to investigate the problem. The expressions for amplitudes ratios of reflected waves at different angles of incident wave are obtained. Dissipation of energy and two-temperature effects on these amplitude ratios with angle of incidence are depicted graphically. Some special and particular cases are also deduced. Rajneesh Kumar, K. D. Sharma, and S. K. Garg Copyright © 2014 Rajneesh Kumar et al. All rights reserved. Analysis of Excitation and Dead Vibration Modes of Quartz Resonators Mon, 10 Feb 2014 13:15:40 +0000 http://www.hindawi.com/journals/aav/2014/746847/ This study uses the finite element method (FEM) to analyze the excitation and dead vibration modes of two-dimensional quartz plates. We first simplify three-dimensional quartz plates with plane strain simplification and then compare the modes of the simplified three-dimensional plates to those of two-dimensional plates. We then analyze quartz vibrating elements of AT-cut plates and SC-cut plates. To understand the regularity of the resonance frequency of plates that are excitable by voltage loading, we compare the natural vibrations of quartz plates with the excitation frequency generated after the plates are excited by voltage loading. Zi-Gui Huang and Zheng-Yu Chen Copyright © 2014 Zi-Gui Huang and Zheng-Yu Chen. All rights reserved. Erratum to “Anomalous Dispersion of the Lamb Mode” Tue, 04 Feb 2014 12:02:07 +0000 http://www.hindawi.com/journals/aav/2014/714298/ Faiz Ahmad and Takasar Hussain Copyright © 2014 Faiz Ahmad and Takasar Hussain. All rights reserved. Energy Harvesting with Piezoelectric Element Using Vibroacoustic Coupling Phenomenon Mon, 23 Dec 2013 08:57:42 +0000 http://www.hindawi.com/journals/aav/2013/126035/ This paper describes the vibroacoustic coupling between the structural vibrations and internal sound fields of thin structures. In this study, a cylindrical structure with thin end plates is subjected to the harmonic point force at one end plate or both end plates, and a natural frequency of the end plates is selected as the forcing frequency. The resulting vibroacoustic coupling is then analyzed theoretically and experimentally by considering the dynamic behavior of the plates and the acoustic characteristics of the internal sound field as a function of the cylinder length. The length and phase difference between the plate vibrations, which maximize the sound pressure level inside the cavity, are clarified theoretically. The theoretical results are validated experimentally through an excitation experiment using an experimental apparatus that emulates the analytical model. Moreover, the electricity generation experiment verifies that sufficient vibroacoustic coupling can be created for the adopted electricity generating system to be effective as an electric energy-harvesting device. Hiroyuki Moriyama, Hirotarou Tsuchiya, and Yasuo Oshinoya Copyright © 2013 Hiroyuki Moriyama et al. All rights reserved. Optimal Placement of Piezoelectric Plates to Control Multimode Vibrations of a Beam Tue, 17 Dec 2013 15:56:41 +0000 http://www.hindawi.com/journals/aav/2013/905160/ Damping of vibrations is often required to improve both the performance and the integrity of engineering structures, for example, gas turbine blades. In this paper, we explore the possibility of using piezoelectric plates to control the multimode vibrations of a cantilever beam. To develop an effective control strategy and optimize the placement of the active piezoelectric elements in terms of vibrations amplitude reduction, a procedure has been developed and a new analytical solution has been proposed. The results obtained have been corroborated by comparison with the results from a multiphysics finite elements package (COMSOL), results available in the literature, and experimental investigations carried out by the authors. Fabio Botta, Daniele Dini, Christoph Schwingshackl, Luca di Mare, and Giovanni Cerri Copyright © 2013 Fabio Botta et al. All rights reserved. Static and Dynamic Characteristics of Composite Conoidal Shell Roofs Tue, 03 Dec 2013 15:15:01 +0000 http://www.hindawi.com/journals/aav/2013/539817/ A thorough review of the existing literature reflects that forced vibration studies of laminated composite conoidal shells with complicated boundary conditions are missing. Hence, the present paper aims to fill the lacuna. A finite element code utilizing eight-noded doubly curved elements together with modified Sanders’ first approximation theory for thin shells is used to study the forced vibration behavior of moderately thin laminated composite conoidal shells subjected to three different uniformly distributed time-dependent forces. Newmark’s direct time integration method is used to solve the dynamic problem. Results obtained using the present code are compared with the values available in the literature, and a good agreement of the results confirms the accuracy of the proposed code. The transient responses of the laminated shell are studied meticulously for parametric variations like boundary conditions and stacking orders of cross and angle-ply laminates and are compared with bending responses of the shell to conclude on the necessity of the dynamic study. Kaustav Bakshi and Dipankar Chakravorty Copyright © 2013 Kaustav Bakshi and Dipankar Chakravorty. All rights reserved. Differential Evolution: An Inverse Approach for Crack Detection Wed, 13 Nov 2013 15:51:50 +0000 http://www.hindawi.com/journals/aav/2013/321931/ This paper presents a damage detection technique combining analytical and experimental investigations on a cantilever aluminium alloy beam with a transverse surface crack. Firstly, the first three natural frequencies were determined using analytical methods based on strain energy release rate. Secondly, an experimental method was adopted to validate the theoretical findings. The damage location and severity assessment is the third stage and is formulated as a constrained optimisation problem and solved using the proposed differential evolution (DE) algorithm based on the measured and calculated first three natural frequencies as inputs. Numerical simulation studies indicate that the proposed method is robust and can be used effectively in structural health monitoring (SHM) applications. Prabir Kumar Jena, Dhirendra Nath Thatoi, and Dayal R. Parhi Copyright © 2013 Prabir Kumar Jena et al. All rights reserved. Biomass from Paddy Waste Fibers as Sustainable Acoustic Material Thu, 07 Nov 2013 13:19:11 +0000 http://www.hindawi.com/journals/aav/2013/605932/ Utilization of biomass for green products is still progressing in the effort to provide alternative clean technology. This paper presents the utilization of natural waste fibers from paddy as acoustic material. Samples of sound absorbing material from paddy waste fibers were fabricated. The effect of the fiber density, that is, the fiber weight and the sample thickness, and also the air gap on the sound absorption coefficient is investigated through experiment. The paddy fibers are found to have good acoustic performance with normal incidence absorption coefficient greater than 0.5 from 1 kHz and can reach the average value of 0.8 above 2.5 kHz. This result is comparable against that of the commercial synthetic glass wool. Attachment of a single layer of polyester fabric is shown to further increase the absorption coefficient. A. Putra, Y. Abdullah, H. Efendy, W. M. F. W. Mohamad, and N. L. Salleh Copyright © 2013 A. Putra et al. All rights reserved.