Advances in Acoustics and Vibration https://www.hindawi.com The latest articles from Hindawi © 2017 , Hindawi Limited . All rights reserved. Effects of the Cone and Edge on the Acoustic Characteristics of a Cone Loudspeaker Sun, 21 May 2017 00:00:00 +0000 http://www.hindawi.com/journals/aav/2017/2792376/ Loudspeakers are designed for reproducing the original sound field as faithfully as possible. In order to faithfully reproduce sound, it is important to understand the relationships among the physical characteristics of the loudspeaker. This paper focuses on the cone, the edge, and the behavior of air around the voice coil, which are important elements in the design of cone loudspeakers and evaluates their effects on the acoustic characteristics of the loudspeaker. Yue Hu, Xilu Zhao, Takao Yamaguchi, Manabu Sasajima, Tatsushi Sasanuma, and Akira Hara Copyright © 2017 Yue Hu et al. All rights reserved. Dynamic Modal Correlation of an Automotive Rear Subframe, with Particular Reference to the Modelling of Welded Joints Mon, 03 Apr 2017 08:00:41 +0000 http://www.hindawi.com/journals/aav/2017/8572674/ This paper presents a comparison between the experimental investigation and the Finite Element (FE) modal analysis of an automotive rear subframe. A modal correlation between the experimental data and the forecasts is performed. The present numerical model constitutes a predictive methodology able to forecast the experimental dynamic behaviour of the structure. The actual structure is excited with impact hammers and the modal response of the subframe is collected and evaluated by the PolyMAX algorithm. Both the FE model and the structural performance of the subframe are defined according to the Ferrari S.p.A. internal regulations. In addition, a novel modelling technique for welded joints is proposed that represents an extension of ACM2 approach, formulated for spot weld joints in dynamic analysis. Therefore, the Modal Assurance Criterion (MAC) is considered the optimal comparison index for the numerical-experimental correlation. In conclusion, a good numerical-experimental agreement from 50 Hz up to 500 Hz has been achieved by monitoring various dynamic parameters such as the natural frequencies, the mode shapes, and frequency response functions (FRFs) of the structure that represent a validation of this FE model for structural dynamic applications. Vincenzo Rotondella, Andrea Merulla, Andrea Baldini, and Sara Mantovani Copyright © 2017 Vincenzo Rotondella et al. All rights reserved. A Discrete Model for Nonlinear Vibration of Beams Resting on Various Types of Elastic Foundations Wed, 15 Mar 2017 00:00:00 +0000 http://www.hindawi.com/journals/aav/2017/4740851/ This paper presents a discrete physical model to approach the problem of nonlinear vibrations of beams resting on elastic foundations. The model consists of a beam made of several small bars, evenly spaced. The bending stiffness is modeled by spiral springs, and the Winkler soil stiffness is modeled using linear vertical springs. Concentrated masses, presenting the inertia of the beam, are located at the bar ends. Finally, the nonlinear effect is presented by the axial forces in the bars, assumed to behave as longitudinal springs, due to the change in their length induced by the Pythagorean Theorem. This model has the advantage of simplifying parametric studies, because of its discrete nature, allowing any modification in the mass matrix, the stiffness matrix, and the nonlinearity tensor to be made separately. Therefore, once the model is established, various practical applications may be performed without the need of going through all the formulation again. The study of the nonlinear behavior makes the solution of the movement equation rise in complexity. By considering this discrete model and using the linearization method, one can achieve an idealized approach to this nonlinear problem and obtain quite easily approximate solutions. A. Khnaijar and R. Benamar Copyright © 2017 A. Khnaijar and R. Benamar. All rights reserved. Experimental Investigation on Flutter Similitude of Thin-Flat Plates Sun, 12 Mar 2017 00:00:00 +0000 http://www.hindawi.com/journals/aav/2017/7091425/ This paper shows the experimental results of the flutter speed of thin-flat plates with free leading edge in axial flow as a function of plates’ geometry, fluid densities, and viscosities, as well as natural frequencies of the plates. The experiment was developed based on similitude theory using dimensional analysis and Buckingham Pi Theorem. Dimensional analysis generates four dimensionless numbers. Experiment was conducted by placing the thin-flat plates in a laminar flow wind tunnel in order to obtain the relationship among those dimensionless numbers. The flutter speed was measured by varying the flow velocity until the instability occurred. The dimensional analysis gives a map of the flutter Reynolds number as a function of a new type of dimensionless number that is hereby called flutter fluid structure interaction number, thickness-to-length, and aspect ratios as the correcting factors. This map is a very useful tool for predicting the flutter speed of thin-flat plates in general. This investigation found that the flutter Reynolds number is very high at the region of high flutter fluid structure and thickness-to-length ratios numbers; however, it is very sensitive to the change of those two dimensionless numbers. The sensitivity is higher at lower aspect ratio. I. P. G. Sopan Rahtika, I. N. G. Wardana, A. A. Sonief, and E. Siswanto Copyright © 2017 I. P. G. Sopan Rahtika et al. All rights reserved. A Note on an Analytic Solution for an Incompressible Fluid-Conveying Pipeline System Mon, 06 Mar 2017 08:28:25 +0000 http://www.hindawi.com/journals/aav/2017/8141523/ This paper presents an integral transform analytic solution to the equations governing a fluid-conveying pipeline segment where a gyroscopic or Coriolis force effect is taken into consideration. The mathematical model idealizes a segment of the pipeline as an elastic beam conveying an incompressible fluid. It is clearly shown that when such a system is supported at both ends and in a free motion, the Coriolis force dissipates no energy (or simply does not work) as it generates conjugate complex vibratory components for all flow velocities. It is demonstrated that the modal natural frequencies can be computed from the algebraic products of the complex frequency pairs. Clearly, the patterns of the characteristics of the system’s natural frequencies are seen partly when the real and imaginary components are plotted, as widely seen in the literature. Nonetheless, results from this study revealed that a continuity profile exists to connect the subcritical, critical, and postcritical vibratory behaviours when the absolute values are plotted for any velocity. In the meantime, the efficacy and versatility of this method against the usual assumed spatial or temporal modal solutions are demonstrated by confirming the predictions and validity of results of earlier workers such as Paidoussis, Ziegler, and others where pre- and postdivergence behaviours are exhibited. Vincent O. S. Olunloyo, Charles A. Osheku, and Patrick S. Olayiwola Copyright © 2017 Vincent O. S. Olunloyo et al. All rights reserved. Corn Husk Fiber-Polyester Composites as Sound Absorber: Nonacoustical and Acoustical Properties Sun, 19 Feb 2017 00:00:00 +0000 http://www.hindawi.com/journals/aav/2017/4319389/ This study investigates the acoustical and nonacoustical properties of composites using corn husk fiber (CHF) and unsaturated polyester as the sound-absorbing materials. The influence of the volume fraction of CHF on acoustic performance was experimentally investigated. In addition, the nonacoustical properties, such as air-flow resistivity, porosity, and mechanical properties of composites have been analyzed. The results show that the sound absorptions at low frequencies are determined by the number of lumens in fiber, particularly the absorption coefficient, which increases the amount of fiber. For high-frequency sound, the absorption coefficient is determined by the arrangement of fibers in the composite. An absorption coefficient is close to zero when the fibers are arranged in a conventional pattern; however, when they are arranged in a random pattern, a high absorption coefficient can be obtained. The bond interface between the fiber and resin enhances its mechanical properties, which increases the longevity of the composite panel. Nasmi Herlina Sari, I. N. G Wardana, Yudy Surya Irawan, and Eko Siswanto Copyright © 2017 Nasmi Herlina Sari et al. All rights reserved. Vibroacoustic Analysis of a Refrigerator Freezer Cabinet Coupled with an Air Duct Thu, 09 Feb 2017 12:28:25 +0000 http://www.hindawi.com/journals/aav/2017/1960898/ In this study, the vibration and acoustic interactions between the structure and the cavity inside the freezer cabinet were investigated. Thus, a set of numerical and experimental analyses were performed. In the numerical analysis, the acoustic characteristics of the freezer cavity were solved, and the mixed finite element method was then implemented to analyse the coupled behaviour of the cavity with the air duct using the Acoustic Fluid-Structure Interaction (AFSI) technique. In the experimental analyses, an acoustic modal analysis of the freezer cavity and a structural modal analysis of the air duct were performed for the validation process. A good agreement was obtained among the results. Thus, the accuracy of the numerical model was confirmed. The validated models were used for optimizing the design. To solve the noise generation mechanism inside the freezer cabinet, the noise primarily generated by the freezer fan unit was measured under normal working conditions of the refrigerator, and the resonance frequencies were obtained. This information was compared with the normal modes of the air duct, and the overlapping frequencies were identified. To reduce the interaction between the source and the structure, a few design modifications were applied to the air duct. Thus, the structural-borne noise radiating from the air duct into the freezer cavity was reduced. Onur Çelikkan and Haluk Erol Copyright © 2017 Onur Çelikkan and Haluk Erol. All rights reserved. On the Development of Focused Ultrasound Liquid Atomizers Mon, 06 Feb 2017 00:00:00 +0000 http://www.hindawi.com/journals/aav/2017/7861726/ This paper reviews the evolution of focused ultrasonic transducers of various kinds for fluid atomization and vaporization. Ultrasonic transducers used for atomization purposes in biomedical, pharmaceutical, or industrial applications, such as surface acoustic wave (SAW) transducers, array of micromachined nozzles, and Fourier horn micromachined nozzles with or without a central channel, are all presented and compared. For simplicity of manufacturing and low cost, we focus on plates and curved and corrugated structures for biomedical humidification. Ahmed M. Al-Jumaily and Ata Meshkinzar Copyright © 2017 Ahmed M. Al-Jumaily and Ata Meshkinzar. All rights reserved. Optimization of Fixed Microphone Array in High Speed Train Noises Identification Based on Far-Field Acoustic Holography Wed, 01 Feb 2017 09:20:22 +0000 http://www.hindawi.com/journals/aav/2017/1894918/ Acoustical holography has been widely applied for noise sources location and sound field measurement. Performance of the microphones array directly determines the sound source recognition method. Therefore, research is very important to the performance of the microphone array, its array of applications, selection, and how to design instructive. In this paper, based on acoustic holography moving sound source identification theory, the optimization method is applied in design of the microphone array, we select the main side lobe ratio and the main lobe area as the optimization objective function and then put the optimization method use in the sound source identification based on holography, and finally we designed this paper to optimize microphone array and compare the original array of equally spaced array with optimization results; by analyzing the optimization results and objectives, we get that the array can be achieved which is optimized not only to reduce the microphone but also to change objective function results, while improving the far-field acoustic holography resolving effect. Validation experiments have showed that the optimization method is suitable for high speed trains sound source identification microphone array optimization. Rujia Wang and Shaoyi Bei Copyright © 2017 Rujia Wang and Shaoyi Bei. All rights reserved. Mathematical Modelling and Acoustical Analysis of Classical Guitars and Their Soundboards Tue, 27 Dec 2016 09:16:19 +0000 http://www.hindawi.com/journals/aav/2016/6084230/ Research has shown that the soundboard plays an increasingly important role compared to the sound hole, back plate, and the bridge at high frequencies. The frequency spectrum of investigation can be extended to 5 kHz. Design of bracings and their placements on the soundboard increase its structural stiffness as well as redistributing its deflection to nonbraced regions and affecting its loudness as well as its response at low and high frequencies. This paper attempts to present a review of the current state of the art in guitar research and to propose viable alternatives that will ultimately result in a louder and better sounding instrument. Current research is an attempt to increase the sound level with bracing designs and their placements, control of natural frequencies using scalloped braces, as well as improve the acoustic radiation of this instrument at higher frequencies by deliberately inducing asymmetric modes in the soundboard using the concept of “splitting board.” Various mathematical methods are available for analysing the soundboard based on the theory of thin plates. Discrete models of the instrument up to 4 degrees of freedom are also presented. Results from finite element analysis can be utilized for the evaluation of acoustic radiation. Meng Koon Lee, Mohammad Hosseini Fouladi, and Satesh Narayana Namasivayam Copyright © 2016 Meng Koon Lee et al. All rights reserved. Kaybob Revisited: What We Have Learned about Compressor Stability from Self-Excited Whirling Tue, 20 Dec 2016 09:25:09 +0000 http://www.hindawi.com/journals/aav/2016/7368787/ The Kaybob compressor failure of 1971 was an excellent historic example of rotordynamic instability and the design factors that affect this phenomenon. In the case of Kaybob, the use of poorly designed bearings produced unstable whirling in both the low and high pressure compressors. This required over five months of vibration troubleshooting and redesign along with over 100 million modern U.S. dollars in total costs and lost revenue. In this paper, the history of the Kaybob compressor failure is discussed in detail including a discussion of the ineffective bearing designs that were considered. Modern bearing and rotordynamic analysis tools are then employed to study both designs that were considered along with new designs for the bearings that could have ultimately restored stability to the machine. These designs include four-pad, load-between-pad bearings and squeeze film dampers with a central groove. Simple relationships based on the physics of the system are also used to show how the bearings could be tuned to produce optimum bearing stiffness and damping of the rotor vibration, producing insights which can inform the designers as they perform more comprehensive analyses of these systems. Edgar J. Gunter and Brian K. Weaver Copyright © 2016 Edgar J. Gunter and Brian K. Weaver. All rights reserved. Physical and Acoustical Properties of Corn Husk Fiber Panels Thu, 15 Dec 2016 07:35:41 +0000 http://www.hindawi.com/journals/aav/2016/5971814/ This research focuses on the development of a sustainable acoustic material comprising natural fibers of corn husk that were alkali modified by 1%, 2%, 5%, and 8% NaOH. The morphology and the acoustical, physical, and mechanical properties of the resulting fibers were experimentally investigated. Five different types of sample were produced in panel form, the acoustical properties of which were studied using a two-microphone impedance tube test. The porosity, tortuosity, and airflow resistivity of each panel were investigated, tensile tests were conducted, and the morphological aspects were evaluated via scanning electron microscopy. The sound absorption and tensile properties of the treated panels were better than those of raw fiber panels; the treated panels were of high airflow resistivity and had low porosity. Scanning electron micrographs of the surfaces of the corn husk fibers revealed that the different sound absorption properties of these panels were due to roughness and the lumen structures. Nasmi Herlina Sari, I. N. G. Wardana, Yudy Surya Irawan, and Eko Siswanto Copyright © 2016 Nasmi Herlina Sari et al. All rights reserved. Simulating the Effects of Surface Roughness on Reinforced Concrete T Beam Bridge under Single and Multiple Vehicles Wed, 30 Nov 2016 13:06:31 +0000 http://www.hindawi.com/journals/aav/2016/3594148/ This research focuses on the application of the spatial system of finite element modeling for the vehicle-bridge interaction on reinforced concrete US Girder Bridge in order to obtain the effect of surface roughness. Single vehicle and multiple vehicles on reinforced concrete T beam bridge were studied with variable surface roughness profiles. The effects of six different surface roughness profiles (very good, good, measured, average, poor, and very poor) were investigated for vehicle-bridge interaction. The values of the Dynamic Amplification Factor (DAF) were obtained for single and multiple vehicles on T Beam Bridge for different surface roughness profiles, along with the distances between the axles of heavy vehicle. It was observed that when the bridge has very good, good, measured, and average surface roughness, the DAF values for the single vehicle over the bridge were observed to be within acceptable limits specified by AASHTO. However, for the bridge with multiple vehicles only very good and measured surface roughness profiles showed a DAF and vehicle axle distances within the acceptable limits. From the current studies, it was observed that the spatial system showed reliable responses for predicting the behavior of the bridge under variable road surface roughness conditions and was reliable in vehicle axle detection, and therefore, it has a potential to be use for realistic simulations. Rahul Kalyankar and Nasim Uddin Copyright © 2016 Rahul Kalyankar and Nasim Uddin. All rights reserved. Sound Transmission in a Duct with Sudden Area Expansion, Extended Inlet, and Lined Walls in Overlapping Region Mon, 28 Nov 2016 14:31:22 +0000 http://www.hindawi.com/journals/aav/2016/9485163/ The transmission of sound in a duct with sudden area expansion and extended inlet is investigated in the case where the walls of the duct lie in the finite overlapping region lined with acoustically absorbent materials. By using the series expansion in the overlap region and using the Fourier transform technique elsewhere we obtain a Wiener-Hopf equation whose solution involves a set of infinitely many unknown expansion coefficients satisfying a system of linear algebraic equations. Numerical solution of this system is obtained for various values of the problem parameters, whereby the effects of these parameters on the sound transmission are studied. Ahmet Demir Copyright © 2016 Ahmet Demir. All rights reserved. Electricity Generation Characteristics of Energy-Harvesting System with Piezoelectric Element Using Mechanical-Acoustic Coupling Thu, 24 Nov 2016 17:37:02 +0000 http://www.hindawi.com/journals/aav/2016/4217517/ This paper describes the electricity generation characteristics of a new energy-harvesting system with piezoelectric elements. The proposed system is composed of a rigid cylinder and thin plates at both ends. The piezoelectric elements are installed at the centers of both plates, and one side of each plate is subjected to a harmonic point force. In this system, vibration energy is converted into electrical energy via electromechanical coupling between the plate vibration and piezoelectric effect. In addition, the plate vibration excited by the point force induces a self-sustained vibration at the other plate via mechanical-acoustic coupling between the plate vibrations and an internal sound field into the cylindrical enclosure. Therefore, the electricity generation characteristics should be considered as an electromechanical-acoustic coupling problem. The characteristics are estimated theoretically and experimentally from the electric power in the electricity generation, the mechanical power supplied to the plate, and the electricity generation efficiency that is derived from the ratio of both power. In particular, the electricity generation efficiency is one of the most appropriate factors to evaluate a performance of electricity generation systems. Thus, the effect of mechanical-acoustic coupling is principally evaluated by examining the electricity generation efficiency. Hirotarou Tsuchiya, Hiroyuki Moriyama, and Satoru Iwamori Copyright © 2016 Hirotarou Tsuchiya et al. All rights reserved. Sound Radiation Characteristics of a Rectangular Duct with Flexible Walls Thu, 24 Nov 2016 07:48:15 +0000 http://www.hindawi.com/journals/aav/2016/6053704/ Acoustic breakout noise is predominant in flexible rectangular ducts. The study of the sound radiated from the thin flexible rectangular duct walls helps in understanding breakout noise. The current paper describes an analytical model, to predict the sound radiation characteristics like total radiated sound power level, modal radiation efficiency, and directivity of the radiated sound from the duct walls. The analytical model is developed based on an equivalent plate model of the rectangular duct. This model has considered the coupled and uncoupled behaviour of both acoustic and structural subsystems. The proposed analytical model results are validated using finite element method (FEM) and boundary element method (BEM). Duct acoustic and structural modes are analysed to understand the sound radiation behaviour of a duct and its equivalence with monopole and dipole sources. The most efficient radiating modes are identified by vibration displacement of the duct walls and for these the radiation efficiencies have been calculated. The calculated modal radiation efficiencies of a duct compared to a simple rectangular plate indicate similar radiation characteristics. Praveena Raviprolu, Nagaraja Jade, and Venkatesham Balide Copyright © 2016 Praveena Raviprolu et al. All rights reserved. Vibration Sideband Modulations and Harmonics Separation of a Planetary Helicopter Gearbox with Two Different Configurations Thu, 10 Nov 2016 12:15:45 +0000 http://www.hindawi.com/journals/aav/2016/9820768/ This paper examines the spectrum and cepstrum content of vibration signals taken from a helicopter gearbox with two different configurations (3 and 4 planets). It presents a signal processing algorithm to separate synchronous and nonsynchronous components for complete shafts’ harmonic extraction and removal. The spectrum and cepstrum of the vibration signal for two configurations are firstly analyzed and discussed. The effect of changing the number of planets on the fundamental gear mesh frequency (epicyclic mesh frequency) and its sidebands is discussed. The paper explains the differences between the two configurations and discusses, in particular, the asymmetry of the modulation sidebands about the epicyclic mesh frequency in the 4 planets arrangement. Finally a separation algorithm, which is based on resampling the order-tracked signal to have an integer number of samples per revolution for a specific shaft, is proposed for a complete removal of the shafts harmonics. The results obtained from the presented separation algorithms are compared to other separation schemes such as discrete random separation (DRS) and time synchronous averaging (TSA) with clear improvements and better results. Nader Sawalhi Copyright © 2016 Nader Sawalhi. All rights reserved. Mixed Skyhook and FxLMS Control of a Half-Car Model with Magnetorheological Dampers Tue, 25 Oct 2016 12:02:58 +0000 http://www.hindawi.com/journals/aav/2016/7428616/ The problem of vibration attenuation in a semiactive vehicle suspension is considered. The proposed solution is based on usage of the information about the road roughness coming from the sensor installed on the front axle of the vehicle. It does not need any preview sensor to measure the road roughness as other preview control strategies do. Here, the well-known Skyhook algorithm is used for control of the front magnetorheological (MR) damper. This algorithm is tuned to a quarter-car model of the front part of the vehicle. The rear MR damper is controlled by the FxLMS (Filtered-x LMS) taking advantage of the information about the motion of the front vehicle axle. The goal of this algorithm is to minimize pitch of the vehicle body. The strategy is applied for a four-degree-of-freedom (4-DOF) vehicle model equipped with magnetorheological dampers which were described using the Bouc-Wen model. The suspension model was subjected to the road-induced excitation in the form of a series of bumps within the frequency range 1.0–10 Hz. Different solutions are compared based on the transmissibility function and simulation results show the usefulness of the proposed solution. Piotr Krauze and Jerzy Kasprzyk Copyright © 2016 Piotr Krauze and Jerzy Kasprzyk. All rights reserved. CAA of an Air-Cooling System for Electronic Devices Thu, 20 Oct 2016 14:48:48 +0000 http://www.hindawi.com/journals/aav/2016/4785389/ This paper presents the workflow and the results of fluid dynamics and aeroacoustic simulations for an air-cooling system as used in electronic devices. The setup represents a generic electronic device with several electronic assemblies with forced convection cooling by two axial fans. The aeroacoustic performance is computed using a hybrid method. In a first step, two unsteady CFD simulations using the Unsteady Reynolds-Averaged Navier-Stokes simulation with Shear Stress Transport (URANS-SST) turbulence model and the Scale Adaptive Simulation with Shear Stress Transport (SAS-SST) models were performed. Based on the unsteady flow results, the acoustic source terms were calculated using Lighthill’s acoustic analogy. Propagation of the flow-induced sound was computed using the Finite Element Method. Finally, the results of the acoustic simulation are compared with measurements and show good agreement. Sven Münsterjohann, Jens Grabinger, Stefan Becker, and Manfred Kaltenbacher Copyright © 2016 Sven Münsterjohann et al. All rights reserved. Vibrational Interaction of Two Rotors with Friction Coupling Tue, 18 Oct 2016 11:04:49 +0000 http://www.hindawi.com/journals/aav/2016/9275147/ A lumped parameter model is presented for studying the dynamic interaction between two disks in relative rotational motion and in friction contact. The contact elastic and dissipative characteristics are represented by equivalent stiffness and damping coefficient in the axial as well as torsional direction. The formulation accounts for the coupling between the axial and angular motions by viewing the contact normal force a result of axial behavior of the system. The model is used to investigate stick-slip behavior of a two-disk friction system. In this effort the friction coefficient is represented as an exponentially decaying function of relative angular velocity, varying from its static value at zero relative velocity to its kinetic value at very high velocities. This investigation results in the establishment of critical curve defining two-parameter regions: one in which stick-slip occurs and that in which stick-slip does not occur. Moreover, the onset and termination of stick-slip, when it occurs, are related to the highest component frequency in the system. It is found that stick-slip starts at a period nearly equal to that of the highest component frequency and terminates at a period almost three times that of the highest component frequency. H. Larsson and K. Farhang Copyright © 2016 H. Larsson and K. Farhang. All rights reserved. Vibrational Comfort on Board the Vehicle: Influence of Speed Bumps and Comparison between Different Categories of Vehicle Thu, 08 Sep 2016 17:36:14 +0000 http://www.hindawi.com/journals/aav/2016/2676021/ This paper shows the results of a study conducted on five different categories of vehicles in a specific test site. The aim was to investigate how the effect of the test site discontinuity determines variations of comfort related to the increase in speed and to the five selected road vehicles of different classes. Measurements were obtained by combining data relating to vibrations in the three reference axes, detected through a vibration dosimeter (VIB-008), and geolocation data (latitude, longitude, and speed) identified by the GPS inside a smartphone. This procedure, through the synchronization between dosimeter and GPS location, has been helpful in postprocessing to eliminate any measurement anomalies generated by the operator. After the survey campaign it was determined that a formulation allows defining a Comfort Index (CI) depending on velocity and five vehicles of different classes. This study showed that the presence of speed bumps, in the test site investigated, appears to be uncomfortable even at speeds well below those required by the Highway Code. Vincenzo Barone, Domenico Walter Edvige Mongelli, and Antonio Tassitani Copyright © 2016 Vincenzo Barone et al. All rights reserved. Comparison of the Time Domain Windows Specified in the ISO 18431 Standards Used to Estimate Modal Parameters in Steel Plates Mon, 29 Aug 2016 06:54:17 +0000 http://www.hindawi.com/journals/aav/2016/3837971/ The procedures used to estimate structural modal parameters as natural frequency, damping ratios, and mode shapes are generally based on frequency methods. However, methods of time-frequency analysis are highly sensible to the parameters used to calculate the discrete Fourier transform: windowing, resolution, and preprocessing. Thus, the uncertainty of the modal parameters is increased if a proper parameter selection is not considered. In this work, the influence of three different time domain windows functions (Hanning, flat-top, and rectangular) used to estimate modal parameters are discussed in the framework of ISO 18431 standard. Experimental results are conducted over an AISI 1020 steel plate, which is excited by means of a hammer element. Vibration response is acquired by using acceleration records according to the ISO 7626-5 reference guides. The results are compared with a theoretical method and it is obtained that the flat-top window is the best function for experimental modal analysis. Jhonatan Camacho-Navarro, R. Guzmán-López, Sergio Gómez, and Marco Flórez Copyright © 2016 Jhonatan Camacho-Navarro et al. All rights reserved. Development of an Experimental Model for a Magnetorheological Damper Using Artificial Neural Networks (Levenberg-Marquardt Algorithm) Thu, 18 Aug 2016 07:50:50 +0000 http://www.hindawi.com/journals/aav/2016/7027259/ This paper is based on the experimental study for design and control of vibrations in automotive vehicles. The objective of this paper is to develop a model for the highly nonlinear magnetorheological (MR) damper to maximize passenger comfort in an automotive vehicle. The behavior of the MR damper is studied under different loading conditions and current values in the system. The input and output parameters of the system are used as a training data to develop a suitable model using Artificial Neural Networks. To generate the training data, a test rig similar to a quarter car model was fabricated to load the MR damper with a mechanical shaker to excite it externally. With the help of the test rig the input and output parameter data points are acquired by measuring the acceleration and force of the system at different points with the help of an impedance head and accelerometers. The model is validated by measuring the error for the testing and validation data points. The output of the model is the optimum current that is supplied to the MR damper, using a controller, to increase the passenger comfort by minimizing the amplitude of vibrations transmitted to the passenger. Besides using this model for cars, bikes, and other automotive vehicles it can also be modified by retraining the algorithm and used for civil structures to make them earthquake resistant. Ayush Raizada, Pravin Singru, Vishnuvardhan Krishnakumar, and Varun Raj Copyright © 2016 Ayush Raizada et al. All rights reserved. Working and Limitations of Cable Stiffening in Flexible Link Manipulators Tue, 16 Aug 2016 06:18:36 +0000 http://www.hindawi.com/journals/aav/2016/4503696/ Rigid link manipulators (RLMs) are used in industry to move and manipulate objects in their workspaces. Flexible link manipulators (FLMs), which are much lighter and hence highly flexible compared to RLMs, have been proposed in the past as means to reduce energy consumption and increase the speed of operation. Unlike RLM, an FLM has infinite degrees of freedom actuated by finite number of actuators. Due to high flexibility affecting the precision of operation, special control algorithms are required to make them usable. Recently, a method to stiffen FLMs using cables, without adding significant inertia or adversely affecting the advantages of FLMs, has been proposed as a possible solution in a preliminary work by the authors. An FLM stiffened using cables can use existing control algorithms designed for RLMs. In this paper we discuss in detail the working principle and limitations of cable stiffening for flexible link manipulators through simulations and experiments. A systematic way of deciding the location of cable attachments to the FLM is also presented. The main result of this paper is to show the advantage of adding a second pair of cables in reducing overall link deflections. Rahul Dixit and R. Prasanth Kumar Copyright © 2016 Rahul Dixit and R. Prasanth Kumar. All rights reserved. Forced Response of Polar Orthotropic Tapered Circular Plates Resting on Elastic Foundation Wed, 03 Aug 2016 07:26:36 +0000 http://www.hindawi.com/journals/aav/2016/1492051/ Forced axisymmetric response of polar orthotropic circular plates of linearly varying thickness resting on Winkler type of elastic foundation has been studied on the basis of classical plate theory. An approximate solution of problem has been obtained by Rayleigh Ritz method, which employs functions based upon the static deflection of polar orthotropic circular plates. The effect of transverse loadings has been studied for orthotropic circular plate resting on elastic foundation. The transverse deflections and bending moments are presented for various values of taper parameter, rigidity ratio, foundation parameter, and flexibility parameter under different types of loadings. A comparison of results with those available in literature shows an excellent agreement. A. H. Ansari Copyright © 2016 A. H. Ansari. All rights reserved. Stability Analysis of a Flutter Panel with Axial Excitations Sun, 31 Jul 2016 08:26:44 +0000 http://www.hindawi.com/journals/aav/2016/7194764/ This paper investigates the parametric instability of a panel (beam) under high speed air flows and axial excitations. The idea is to affect out-of-plane vibrations and aerodynamic loads by in-plane excitations. The periodic axial excitation introduces time-varying items into the panel system. The numerical method based on Floquet theory and the perturbation method are utilized to solve the Mathieu-Hill equations. The system stability with respect to air/panel density ratio, dynamic pressure ratio, and excitation frequency are explored. The results indicate that panel flutter can be suppressed by the axial excitations with proper parameter combinations. Meng Peng and Hans A. DeSmidt Copyright © 2016 Meng Peng and Hans A. DeSmidt. All rights reserved. Generation of Hydroacoustic Waves by an Oscillating Ice Block in Arctic Zones Thu, 28 Jul 2016 14:11:53 +0000 http://www.hindawi.com/journals/aav/2016/8076108/ The time harmonic problem of propagating hydroacoustic waves generated in the ocean by a vertically oscillating ice block in arctic zones is discussed. The generated acoustic modes can result in orbital displacements of fluid parcels sufficiently high that may contribute to deep ocean currents and circulation. This mechanism adds to current efforts for explaining ocean circulation from a snowball earth Neoproterozoic Era to greenhouse earth arctic conditions and raises a challenge as the extent of ice blocks shrinks towards an ice-free sea. Surprisingly, unlike the free-surface setting, here it is found that the higher acoustic modes exhibit a larger contribution. Usama Kadri Copyright © 2016 Usama Kadri. All rights reserved. Optimization of Automotive Suspension System by Design of Experiments: A Nonderivative Method Wed, 27 Jul 2016 11:27:23 +0000 http://www.hindawi.com/journals/aav/2016/3259026/ A lot of health issues like low back pain, digestive disorders, and musculoskeletal disorders are caused as a result of the whole body vibrations induced by automobiles. This paper is concerned with the enhancement and optimization of suspension performance by using factorial methods of Design of Experiments, a nonderivative method. It focuses on the optimization of ride comfort and determining the parameters which affect the suspension behavior significantly as per the guidelines stated in ISO 2631-1:1997 standards. A quarter car test rig integrated with a LabVIEW based data acquisition system was developed to understand the real time behavior of a vehicle. In the pilot experiment, only three primary suspension parameters, that is, spring-stiffness, damping, and sprung mass, were considered and the full factorial method was implemented for the purpose of optimization. But the regression analysis of the data obtained rendered a very low goodness of fit which indicated that other parameters are likely to influence the response. Subsequently, steering geometry angles, camber and toe and tire pressure, were included in the design. Fractional factorial method with six factors was implemented to optimize ride comfort. The resultant optimum combination was then verified on the test rig with high correlation. Anirban C. Mitra, Tanushri Soni, and G. R. Kiranchand Copyright © 2016 Anirban C. Mitra et al. 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.