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The Volume 21, No 4, December 2016



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https://doi.org/10.20855/ijav.2016.21.4E82

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The Effect of Coaxial Ring Masses with Different Contact Areas, Mass, and Distribution on Membrane-Type Acoustical Metamaterials' Transmission Loss

Xiao-Ling Gai, Xian-Hui Li, Bin Zhang, Yan-Qin Liu, Peng Xie, Zhi-Hui Ma


https://doi.org/10.20855/ijav.2016.21.4431


The transmission loss (TL) of the membrane-type acoustical metamaterials with coaxial ring masses are investigated using the finite element method. The results show that the TL peak and resonance frequencies of the membrane-type acoustical metamaterials depends on mass, distribution of coaxial ring masses, and the contacting area of coaxial ring masses with the membrane. It is also shown that the coaxial ring masses only affect the TL at low frequencies, while the membrane is effective at all frequencies. Additionally, the double-leaf membrane-type acoustical metamaterials structure has been constructed. The roles of the membrane and ring masses of double-leaf membrane-type acoustical metamaterials structure on TL are investigated. The influence of the depth of air-cavity on the TL is then discussed.


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Tool Condition Monitoring in Turning Using Statistical Parameters of Vibration Signal

Hakan Arslan, Ali Osman Er, Sadettin Orhan, Ersan Aslan


https://doi.org/10.20855/ijav.2016.21.4432


In this study, the relationship between vibration and tool wear is investigated during high-speed dry turning by using statistical parameters. It is aimed to show how tool wear and the work piece surface roughness changes with tool vibration signals. For this purpose, a series of experiments were conducted in a CNC lathe. An indexable CBN tool and a 16MnCr5 tool steel that was hardened to 63 HRC were both used as material twins in the experiments. The vibration was measured only in the machining direction using an acceleration sensor assembled on a machinery analyzer since this direction has more dominant signals than the other two directions. In addition, tool wear and work piece surface roughness are measured at different cutting time intervals where the cutting speed, radial depth of cut, and feed rate are kept constant. The vibration signals are evaluated using statistical analysis. The statistical parameters in this study are the Root Mean Square (RMS), Crest Factor, and Kurtosis values. When the flank wear increases, the Kurtosis value and RMS also increase, but the Crest factor exhibited irregular variations. It is concluded that these statistical parameters can be used in order to obtain information about tool wear and work piece surface roughness.


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Nonlinear Transverse Vibrations of a Slightly Curved Beam resting on Multiple Springs

Erdogan Ozkaya, Murat Sarigul, and Hakan Boyaci


https://doi.org/10.20855/ijav.2016.21.4433


In this study, nonlinear vibrations of a slightly curved beam of arbitrary rise functions is handled in case it rests on multiple springs. The beam is simply supported on both ends and is restricted in longitudinal directions using the supports. Thus, the equations of motion have nonlinearities due to elongations during vibrations. The method of multiple scales (MMS), a perturbation technique, is used to solve the integro-differential equation analytically. Primary and 3 to 1 internal resonance cases are taken into account during steady-state vibrations. Assuming the rise functions are sinusoidal in numerical analysis, the natural frequencies are calculated exactly for different spring numbers, spring coefficients, and spring locations. Frequency-amplitude graphs and frequency-response graphs are plotted by using amplitude-phase modulation equations.


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Topology Optimization of a Constrained Layer Damping Plate Coupled with an Acoustical Cavity

Zheng Ling, Zhang Dongdong, LiuChengfeng, Li Yinong, Xiang Shuhong, Li Ye and Fang Guiqian


https://doi.org/10.20855/ijav.2016.21.4434


An acoustical topology optimization of a constrained layer damping (CLD) plate coupled with a rigid acoustical cavity is presented to minimize the sound radiation power. A mathematical model is developed to simulate the sound radiation based on the theories of the finite element and boundary element methods together. The model is integrated with the acoustical topology optimization approach, which utilizes the genetic algorithm with an elitist strategy. The obtained results demonstrate the effectiveness of the proposed approach in attenuating the sound radiation power and the sound pressure inside the acoustical cavity simultaneously by proper layout of the CLD materials. Furthermore, experimental verification is carried out by manufacturing topology optimized CLD/plate and monitoring the sound pressure in the acoustical cavity. The experimental results are a good match with the predictions of the mathematical model. The study shows that the proposed acoustical topology optimization approach can be an effective tool in the design of a wide variety of critical structures, which is lightweight and operates quietly, such as the panels in the vehicle body and aircraft cabin.


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Direct Drive Valve Model for Use as an Acoustic Source in a Network Model

Roel A. J. Müller, J. Hermann and Wolfgang Polifke


https://dx.doi.org/10.20855/ijav.2016.21.4435


Direct Drive Valves (DDVs) can be used as acoustic actuators in duct systems when requirements on mechanical or thermal robustness are high, e.g., for the active control of aerodynamic or combustion instabilities. This paper presents a model of a DDV that is used as an active element in an acoustic network model. In acoustic network modelling tools, acoustic sources are often implemented as simple velocity or mass flow boundary conditions. In practice, however, DDVs are not necessarily situated at the boundary of the system and the throughflow depends on the fluctuating pressure drop over the valve. This paper presents an acoustically compact model, based on mass conservation and a time-varying hydraulic resistance. The resistance depends on the fluctuating valve opening. The results are compared to the experiment in terms of acoustic wave transfer function.


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Free Vibration Bahaviour of Fiber Metal Laminates, Hybrid Composites, and Functionally Graded Beams using Finite Element Analysis

Harshan Ravishankar, Revathi Rengarajan, Kaliyannan Devarajan and Bharath Kaimal


https://doi.org/10.20855/ijav.2016.21.4436


In this study, the free vibration analysis of rotating and non-rotating fiber metal laminate (FML) beams, hybrid composite beams (HCB), and functionally graded beams (FGB) are investigated. FML beams are high-performance hybrid structures based on alternating stacked arrangements of fiber-reinforced plastic (FRP) plies and metal alloy layers. Hybrid composite beams are materials that are made by adding two different fibers. Functionally graded beams are new materials that are designed to achieve a functional performance with gradually variable properties in one or more directions. The effects of different metal alloys, composite fibers, and different aspect ratios and angular velocities on the free vibration analysis of FML beams are studied. The effects of different angular velocities and different aspect ratios of rotating and non-rotating hybrid composite beams are also investigated. Finally, the effects of different angular velocities and different material distributions, namely the power law, exponential distribution, and Mori Tanaka's scheme on the free vibration analysis of FGB, are also invesigated.


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Vibration Interaction Analysis of Non-uniform Cross-Section Beam Structure under a Moving Vehicle

Masoud Asgari


https://doi.org/10.20855/ijav.2016.21.4437


One of an engineer's concern when designing bridges and structures under a moving load is the uniformity of stress distribution. The dynamic behavior of a vehicle on a flexible support is also of great importance. In this paper, an analysis of a variable cross-section beam subjected to a moving load (such as a concentrated mass), a simple quarter car (SQC) planar model, and a two-axle dynamic system with four degrees of freedom (4DOF) is carried out. The finite element method with cubic interpolation functions is used to model the structure based on the Euler-Bernoulli beam and a direct integration method is implemented to solve time dependent equations implicitly. The effects of variation of a cross-section and moving load parameters on the deflection, natural frequencies, and longitudinal stresses of the beam are investigated. The interaction between vehicle body vibration and the support structure is also considered. The obtained results indicate that using a beam of parabolically varying thickness with a constant weight can decrease the maximum deflection and stresses along the beam while increasing the natural frequencies of the beam. The effect of moving mass inertia at a high velocity of a moving vehicle is also investigated and the findings indicate that the effect of inertia is significant at high velocities.


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Stability Control of Linear and Nonlinear Dynamic Systems

Marcel Migdalovici, Daniela Baran and Gabriela Vladeanu


https://doi.org/10.20855/ijav.2016.21.4438


The behavior of linear or nonlinear dynamic systems depends on different parameters (identifiable or free) that are involved in their definition. The stability analysis of such dynamical systems is realized by using a domain of selected free parameters. In this paper, we discuss specific theorems that concern the stability of linear dynamical systems, the stability of nonlinear dynamical systems in terms of ''first linear approximations'', and other stability criteria. We study the stable/unstable separation property in the free parameters domain and present a rigorous mathematical justification of this property with specific examples from various branches of science. Furthermore, we investigate specific conditions when the separation property is passed on to the nonlinear dynamical system from its first order linear approximation. The stable/unstable separation property is also emphasized as an important property of the environment that can contribute to its mathematical modeling.


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Backtracking Search Optimization Algorithm and its Application to Roller Bearing Fault Diagnosis

HungLinh Ao, T. Nguyen Thoi, V. Ho Huu, Linh Anh-Le, TrangThao Nguyen and Minh Quang Chau


https://doi.org/10.20855/ijav.2016.21.4439


It is clearly known that support vector machine (SVM) parameters have significant effects on the accurate rate of classification result. Adjusting the SVM parameters improves its effectiveness and accuracy, which is always a challenge. On the other font, the Backtracking Search Optimization Algorithm (BSOA), an evolutionary algorithm for solving optimization problems, is proposed and proven to be effective through various benchmark problems. This paper proposes an optimization method for the SVM parameters based on BSOA. For convenience, the proposed method has been named BSOA-SVM. This method is tested with some real-world benchmark data sets to verify its robustness and effectiveness. Then, BSOA-SVM is applied for diagnosing roller bearing fault, which is a real world problem. In this diagnosing process, the original acceleration vibration signals are first decomposed into product function (PFs) by using the local mean decomposition (LMD) method. Next, initial feature matrices are extracted from PFs by singular value decomposition (SVD) techniques to give single values. Finally, these values serve as input vectors for the BSOA-SVM classifier. The results from the problem show that the combination of the BSOA-SVM classifiers obtains higher classification accuracy with a lower cost time compared to other methods.


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Vibroacoustic Models of Air-Core Reactors

Thiago A. Fiorentin, Leonardo Ferreira Lopes, Olavo Mecias da Silva Junior, and Arcanjo Lenzi


https://doi.org/10.20855/ijav.2016.21.4440


The purpose of this paper is to provide an overview of the sound power radiation mechanism of air-core reactors and to describe the method that is used to calculate sound power by using the electrical load. Sound power radiation of an air-core reactor is related to the alternating current harmonics, the mechanical tension stiffness and, most importantly, the breathing mode resonance. An analytical model that is based on electrical loads and mechanical properties of the air-core reactor is developed to calculate radial and axial forces caused by the radial and axial magnetic induction fields. This study employs the hemispherical spreading theory, which is a simple and common method that is used to predict sound propagation. Additionally, a numerical model is proposed. In this, the excitation of the acoustic field that surrounds the reactor is introduced by considering the radial and axial displacements of the reactor's windings, as the windings are subjected to the action of the radial and axial electromagnetic forces. Finally, a comparison is presented between analytical and numerical models and it is observed that the models are correlated.


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Detection and Contribution of Outliers for Subjective Evaluation of Sound

Samir N. Y. Gerges, Roberto A. Dias and Rafael N. C. Gerges


https://doi.org/10.20855/ijav.2016.21.4441


The subjective evaluation of noise perception is a very broad topic that has many applications in the field of acoustics. Large variability is usually associated with a subjective evaluation that appears in the standard deviation. This is due to a small amount of subjects (the outliers), who had different responses compared to most of the other subjects. By using the Bootstrap statistical method, this paper shows how to identify the outliers and quantify the contribution to the final results with and without considering the outliers in the calculation.


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Implementation of a Boundary Element Method for High Frequency Scattering by Convex Polygons with Impedance Boundary Conditions

Mosiamisi Mokgolele


https://doi.org/10.20855/ijav.2016.21.4442


Many acoustic and electromagnetic wave scattering problems can be formulated as the Helmholtz equation. Standard finite and boundary element method solution of these problems becomes expensive, as the frequency of incident wave increases. On going research has been devoted to finding methods that do not loose robustness when the wave number increases. Recently, Chandler-Wilde et al. have proposed a novel Galerkin boundary element method to solve the problem of acoustic scattering by a convex polygon with impedance boundary conditions. They applied approximation spaces consisting of piecewise polynomials supported on a graded mesh with smaller elements adjacent to the corners of the polygon and multiplied by plane wave basis functions. They demonstrated via rigorous error analysis that was supported by numerical experiments that the number of degrees of freedom required to achieve a prescribed level of accuracy need only grow logarithmically as frequency increases. In this paper, we discuss issues related to detail implementation of their numerical method.


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Changes to the Vibration Response of a Model Power Transformer with Faults

Yuxing Wang and Jie Pan


https://doi.org/10.20855/ijav.2016.21.4443


Current vibration-based techniques for transformer condition monitoring mostly rely on the vibration response caused by operating excitations, which consist of electrical excitations from the core and winding. Therefore, it is worthwhile to study the electrically-excited frequency response function ({FRF), as it carries information of transformer mechanical and electromagnetic properties. This paper includes a sensitivity analysis of the mechanically and electrically excited FRFs of a model transformer to the reasons behind its failures. A model power transformer is used as an example to demonstrate the variation of its vibration response to a couple of causes of transformer faults, such as looseness of clamping forces in winding and core. Experimental evidence is presented to show the quantitative description of the causes of artificial faults and to extract features of variations of FRFs that might be useful to the vibration-based detection of the causes of transformer faults in general.


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Sound Absorption in the Low Audible Frequency Range of Microfibrous Parylene-C Thin Films

Wasim A. Orfali


https://doi.org/10.20855/ijav.2016.21.4444


Microfibrous thin films (mftf s) of Parylene C are deposited to a thicknesses of about 100~textmu{m by physicochemical vapor deposition with the intention of determining the sound absorption of these films in the lower audible frequency range. The objective is to determine the sound absorption by the mftf{s by using dynamic loading experiments. The mftf{s were subjected to cyclic elastic loads in the frequency range of 5 to 200~Hz over a temperature range of 25 to 50~$^circ$C to determine their dynamic moduli and thus extract the Parylene-C mftf{s sound absorption properties. The absorption coefficient of microfibrous Parylene-C is found to be weakly dependent on temperature, however it increases with increasing frequency. Peaks in the spectra of the absorption coefficient were attributed to resonant coupling between incident sound waves and vibrating microfibers.


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