Advances in Acoustics and Vibration
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The latest articles from Hindawi Publishing Corporation
© 2016 , Hindawi Publishing Corporation . All rights reserved.

Design of Corrugated Plates for Optimal Fundamental Frequency
Mon, 18 Jul 2016 09:43:31 +0000
http://www.hindawi.com/journals/aav/2016/4290247/
This paper investigates shifting the fundamental frequency of plate structures by corrugation. Creating corrugations significantly improves the flexural rigidities of plate and hence increases its natural frequencies. Two types of corrugations are investigated: sinusoidal and trapezoidal corrugations. The finite element method (FEM) is used to model the corrugated plates and extract the natural frequencies and mode shapes. The effects of corrugation geometrical parameters on simply supported plate fundamental frequency are studied. To reduce the computation time, the corrugated plates are modeled as orthotropic flat plates with equivalent rigidities. To demonstrate the validity of modeling the corrugated plates as orthotropic flat plates in studying the free vibration characteristics, a comparison between the results of finite element model and equivalent orthotropic models is made. A correspondence between the results of orthotropic models and the FE models is observed. The optimal designs of sinusoidal and trapezoidal corrugated plates are obtained based on a genetic algorithm. The optimization results show that plate corrugations can efficiently maximize plate fundamental frequency. It is found that the trapezoidal corrugation can more efficiently enhance the fundamental frequency of simply supported plate than the sinusoidal corrugation.
Nabeel Alshabatat
Copyright © 2016 Nabeel Alshabatat. All rights reserved.

Acoustical Measurement and Biot Model for Coral Reef Detection and Quantification
Wed, 06 Apr 2016 12:06:19 +0000
http://www.hindawi.com/journals/aav/2016/2350615/
Coral reefs are coastal resources and very useful for marine ecosystems. Nowadays, the existence of coral reefs is seriously threatened due to the activities of blast fishing, coral mining, marine sedimentation, pollution, and global climate change. To determine the existence of coral reefs, it is necessary to study them comprehensively. One method to study a coral reef by using a propagation of sound waves is proposed. In this research, the measurement of reflection coefficient, transmission coefficient, acoustic backscattering, hardness, and roughness of coral reefs has been conducted using acoustic instruments and numerical modeling using Biot theory. The results showed that the quantification of the acoustic backscatter can classify the type of coral reef.
Henry M. Manik
Copyright © 2016 Henry M. Manik. All rights reserved.

On Peculiarities of Propagation of a Plane Elastic Wave through a Gradient Anisotropic Layer
Mon, 28 Dec 2015 13:58:50 +0000
http://www.hindawi.com/journals/aav/2015/515263/
The problem of diffraction of a plane elastic wave by an anisotropic layer is studied. The diffraction problem is reduced to a boundary value problem for the layer. The grid method is used for solving the resulting boundary value problem. The diffraction of a plane longitudinal wave by the layer is considered. Some peculiarities of the gainfrequency and the gainangle characteristics of a normal component of an energy flow of a passed longitudinal wave are numerically studied.
Anastasiia Anufrieva, Dmitry Chickrin, and Dmitrii Tumakov
Copyright © 2015 Anastasiia Anufrieva et al. All rights reserved.

Modeling of Laterally Sliding Motion of a Magnetic Clamp
Tue, 15 Dec 2015 12:11:30 +0000
http://www.hindawi.com/journals/aav/2015/707043/
A sliding magnetic clamp is used to hold a thin aluminum panel during a milling operation. The design includes a permanent magnet group follower (slave module) which slides laterally over the panel attracted by another permanent magnet group (master module) attached to the industrial robot end effector from the machined side of the panel. The lateral sliding motion of the slave module in response to the master module motion is studied using a transfer function based motion model established considering the lateral magnetic stiffness. The model is validated experimentally.
A. Mahmud, J. R. R. Mayer, and L. Baron
Copyright © 2015 A. Mahmud et al. All rights reserved.

Eigennoise Speech Recovery in Adverse Environments with Joint Compensation of Additive and Convolutive Noise
Tue, 03 Nov 2015 08:23:11 +0000
http://www.hindawi.com/journals/aav/2015/170183/
The learningbased speech recovery approach using statistical spectral conversion has been used for some kind of distorted speech as alaryngeal speech and bodyconducted speech (or boneconducted speech). This approach attempts to recover clean speech (undistorted speech) from noisy speech (distorted speech) by converting the statistical models of noisy speech into that of clean speech without the prior knowledge on characteristics and distributions of noise source. Presently, this approach has still not attracted many researchers to apply in general noisy speech enhancement because of some major problems: those are the difficulties of noise adaptation and the lack of noise robust synthesizable features in different noisy environments. In this paper, we adopted the methods of stateoftheart voice conversions and speaker adaptation in speech recognition to the proposed speech recovery approach applied in different kinds of noisy environment, especially in adverse environments with joint compensation of additive and convolutive noises. We proposed to use the decorrelated wavelet packet coefficients as a lowdimensional robust synthesizable feature under noisy environments. We also proposed a noise adaptation for speech recovery with the eigennoise similar to the eigenvoice in voice conversion. The experimental results showed that the proposed approach highly outperformed traditional nonlearningbased approaches.
TrungNghia Phung, HuyKhoi Do, VanTao Nguyen, and QuangVinh Thai
Copyright © 2015 TrungNghia Phung et al. All rights reserved.

An Image Based Mathematical Model for the Propagation of Fan Noise in a Plenum with Large Side Openings
Sun, 04 Oct 2015 14:03:18 +0000
http://www.hindawi.com/journals/aav/2015/361678/
This paper presents another application of an images group model for a special enclosure geometry and source orientation. A previous work outlined the concept via application to a special tightfitting enclosure. Application of the concept to a fan plenum requires different mathematical descriptions for the image groups. This paper describes the sound reverberation inside a sound enclosure with mostly open sides where the primary noise sources are the air inlets and exhausts of axial type fans located at the top of the enclosure, the sound transmission through the air inlet openings, and the radiation to wayside positions. The main reverberation between the floor and ceiling is determined with an image based mathematical model. The model considers how the main reverberant part image group is amplified by its images from two parallel bulkheads and any side wall frame members. The method of images approach allows the hard surfaces of an untreated plenum to be represented by perfectly reflecting surfaces with zero sound absorption coefficients, thus not requiring any estimate or measurement for these surfaces. Numerical results show excellent comparison to experimental results for an actual plenum. The image model is also shown to be significantly more accurate than the standard large room diffuse field reverberant model.
Michael J. Panza
Copyright © 2015 Michael J. Panza. All rights reserved.

Evaluation of Seven TimeFrequency Representation Algorithms Applied to Broadband Echolocation Signals
Thu, 16 Jul 2015 11:20:38 +0000
http://www.hindawi.com/journals/aav/2015/342503/
Timefrequency representation algorithms such as spectrograms have proven to be useful tools in marine biosonar signal analysis. Although there are several different timefrequency representation algorithms designed for different types of signals with various characteristics, it is unclear which algorithms that are best suited for transient signals, like the echolocation signals of echolocating whales. This paper describes a comparison of seven different timefrequency representation algorithms with respect to their usefulness when it comes to marine biosonar signals. It also provides the answer to how close in time and frequency two transients can be while remaining distinguishable as two separate signals in timefrequency representations. This is, for instance, relevant in studies where echolocation signal component azimuths are compared in the search for the exact location of their acoustic sources. The smallest time difference was found to be 20 µs and the smallest frequency difference 49 kHz of signals with a −3 dB bandwidth of 40 kHz. Among the tested methods, the Reassigned Smoothed Pseudo WignerVille distribution technique was found to be the most capable of localizing closely spaced signal components.
Josefin Starkhammar and Maria HanssonSandsten
Copyright © 2015 Josefin Starkhammar and Maria HanssonSandsten. All rights reserved.

A Noncontact Method for the Detection and Diagnosis of Surface Damage in Immersed Structures
Tue, 19 May 2015 08:31:26 +0000
http://www.hindawi.com/journals/aav/2015/429749/
Detection and diagnosis method is proposed for surface damage in immersed structures. It is based on noncontact ultrasonic echography measurements, signal processing tools, and artificial intelligence methods. Significant features are extracted from the measured signals and a classification method is developed to detect the echoes resulting from surface damage in an immersed structure. The identification of the damage is also provided. Gaussian neural networks trained with a specific learning algorithm are developed for this purpose. The performance of the method is validated by laboratory experiments which indicate that this method could be suitable for the monitoring of inaccessible systems like marine turbines whose unavailability causes severe economic losses.
Y. Sidibe, F. Druaux, D. Lefebvre, F. Leon, and G. Maze
Copyright © 2015 Y. Sidibe et al. All rights reserved.

Free Vibrations of a Series of Beams Connected by Viscoelastic Layers
Thu, 12 Feb 2015 13:40:52 +0000
http://www.hindawi.com/journals/aav/2015/976841/
An exact solution for free vibrations of a series of uniform EulerBernoulli beams connected by KelvinVoigt is developed. The beams have the same length and end conditions but can have different material or geometric properties. An example of five concentric beams connected by viscoelastic layers is considered.
S. Graham Kelly and Clint Nicely
Copyright © 2015 S. Graham Kelly and Clint Nicely. All rights reserved.

Fault Diagnosis of BeamLike 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 fixedfixed 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 EulerBernoulli 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 standalone 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 LinearPeriodModulated Ultrasonic Waves Based on an ExpectationMaximization 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 expectationmaximization (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 linearperiodmodulated (LPM) ultrasonic signals. Simulations are used to validate the proposed method.
Natee Thongun and Minoru K. Kurosawa
Copyright © 2014 Natee Thongun and Minoru K. Kurosawa. All rights reserved.

S1ZGV 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 firstorder symmetric zero group velocity (S1ZGV) 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 S1ZGV frequency of FGM plate is investigated. Numerical results show that S1ZGV frequency is comparatively more sensitive to the shear modulus. The gradient coefficient does not affect the linear dependence of ZGV frequency as function of cutoff 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 platelike 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 SingleDegreeofFreedom 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 singledegreeoffreedom 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 3axes 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 frequencylow 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 translationtorotary 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. Quasistatic 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 FourPost 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 fourpost 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 GridStiffened 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 gridstiffened 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 CloseFitting 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 closefitting 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 linetype source, the main group is extended as additional discrete linetype 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 TimeStep 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 3D audio display systems, this paper reports the conditions of moving sound image velocity and timestep 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 earaxis. 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 timestep (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 3D 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 3D 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 twostage 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 crosssection 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 shaftrotor 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 MEDEMD 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 pulselike longperiod largeamplitude 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 pulselike 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.