0

Sound, Vibration and Design

2009;():1-8. doi:10.1115/IMECE2009-10397.

A tongue and groove joint test is being conducted to quantify the stability characteristics for this class of leakage joint. The test hardware was designed to facilitate comprehensive reconfiguration of the joint geometry so that all parameters affecting joint stability can be evalauated. Excursive (static) and oscillatory (dynamic) instabilities are expected dependent on joint configuration and operational parameters. Hydraulic-based stability analyses were conducted on a pre-test basis to examine joint response. It is concluded from these analyses that physically damaging oscillatory instabilities are most likely to occur when the joint is configured with a movable groove. Physical reasoning for this conclusion is provided in the paper.

Topics: Stability
Commentary by Dr. Valentin Fuster
2009;():9-18. doi:10.1115/IMECE2009-11445.

Turbulent boundary layer flows over rough surfaces are known to produce elevated far-field acoustic sound levels. The nature by which surface irregularities alter the near-field surface pressures and subsequently affect the sound generation to the scattering of high wavenumber convective pressures to low wavenumber acoustic pressures, which is typically interpreted as a dipole-like source. The focus of the current investigation is the experimental interrogation of both near- and far-field pressures due to the flow over roughened surfaces in order to identify the source mechanisms and to validate physical models of roughness sound. For rough surfaces composed of large geometrical elements (defined by large Reynolds numbers based on roughness height and friction velocity), such as hemispheres and cubes, the measured near-field surfaces pressures indicate that the local interstitial flows become important in determining the sound radiation characteristics. In order to describe the aeroacoustic source region, scaling laws are developed for surface pressures at locations around the roughness elements for various roughness configurations and flow speeds. Relationships between surface pressures amongst the rough surface elements and far-field pressures measured at several directional aspects were examined to identify roughness sound source mechanisms. Measurements of a dipole directivity pattern and dipole efficiency factors obtained when normalizing radiated sound by surface pressures offer support to the scattering theories for roughness sound. Using existing pressure scattering models as a basis, an empirical model for roughness sound is generated.

Commentary by Dr. Valentin Fuster
2009;():19-26. doi:10.1115/IMECE2009-11477.

This research intends to develop a method for predicting the sound absorption coefficient of various porous highway pavement materials. Since many of the existing prediction models for acoustic properties and traffic noise still have limitations and problems with accuracy, sound absorption coefficients are measured with the impedance tube method to verify numerical values obtained from the model. Results obtained from the experiment and numerical simulations are compared and presented to reveal the effect and influence of the control parameters.

Commentary by Dr. Valentin Fuster
2009;():27-35. doi:10.1115/IMECE2009-12214.

Side branch resonance can cause standing waves in the main line. The main line standing wave modifies the acoustic boundary condition between the side branch and the main line. This interaction leads to drift in the side branch resonant frequency, and to sensitivity in the side branch and main line resonant amplitude as a function of branch position along the main line standing wave. In many cases the mainline standing wave is not stationary, leading to temporal modulation of the side branch frequency and amplitude. These features are examined using novel signal interrogation techniques that expose frequency and amplitude variation in time. Data from a low pressure air test facility are used to reinforce the theory and demonstrate the system behavior. Finally, the connection between the dynamic pressure signal features and methods for main line and branch component endurance prediction is developed. Components such as steam dryers, safety relief valves, and heat exchangers would be candidates for endurance prediction using these methods.

Commentary by Dr. Valentin Fuster
2009;():37-41. doi:10.1115/IMECE2009-12462.

This work studies the fluid-structure interaction of a set-in, large aspect-ratio circular cylinder in cantilever subjected to a cross flow. Experiments were conducted in a water tunnel and observations were obtained using flow visualization techniques and direct observation of the deflection of the cylinder. The flow behavior was observed using dye injection. The experiments show that the dominant vibration of the cylinder is transversal to the flow direction, and that the first mode of vibration of the cylinder appears at a particular Reynolds number, which is a function of the mechanical properties of the cylinder. The deflection stops when the Reynolds number is increased. The peak deflection and frequency of oscillation, as a function of the Reynolds number, were also determined. The analysis shows a close relation between the frequency of oscillation and the frequency of appearance of a vortex shedding. For large deflections of the cylinder the flow structure is modified substantially, and the frequency at which vortex appears is different to the frequency that occurs for fixed cylinders.

Commentary by Dr. Valentin Fuster
2009;():43-50. doi:10.1115/IMECE2009-10468.

The Pennsylvania State University Applied Research Laboratory has a 1.22 meter (48 inches) diameter closed loop water tunnel. The flow is driven by an axial pump with three blade rows and powered by a 1.5 MW motor. The four blades of the impeller have the highest relative velocities of any lifting surface in the facility, and generate input acoustic power which acts as a background noise floor in tunnel measurements of turbomachinery and vehicle body performance. In this paper, we investigate the sound power radiated by the impeller and its propagation through the water tunnel. Trailing edge hydrodynamic forcing functions are computed for the impeller based on local relative velocities and turbulence properties. For lower frequencies, these forces are then applied to an experimentally validated structural finite element model (FEM) of the impeller. The input power to the water tunnel is determined using an acoustic boundary element model (BEM) of the impeller. A statistical energy (SEA) model of the water tunnel allows for an estimate of the rms pressure within the water tunnel test section to provide guidance on lowering background noise.

Commentary by Dr. Valentin Fuster
2009;():51-56. doi:10.1115/IMECE2009-10851.

In this study, a flexible rotor with variable support stiffness has been analyzed. Simple support models consisting of mass, spring systems are extracted from modal analysis of the isolated support and by applying static loads to the finite element model of the supports. The derived equivalent models of the supports are then implemented in the finite element based structural model which predicts the dynamic behavior of the rotor. Finally experimental modal analysis of the rotor is performed with different support stiffnesses. The experimental and theoretical results have been compared and different support modeling approaches have been examined.

Topics: Modeling , Rotors
Commentary by Dr. Valentin Fuster
2009;():57-63. doi:10.1115/IMECE2009-11414.

Measurements of the unsteady lift forces acting on airfoils in turbulent flow were made to determine the effect of thickness on the gust response and validate a previously developed analytical model. A family of NACA 65-series uncambered airfoils with a range of thickness-to-chord ratios were tested in a water tunnel with grid-generated turbulence. Piezoelectric force gages were used to measure the spectral density of the unsteady lift, and the system was calibrated using an impulse force hammer. An accelerometer-based multiple coherence noise removal technique was employed to eliminate background noise contamination from the facility. The experimental results are shown to agree well with an analytical model of the unsteady lift based on turbulence ingestion theory and an incompressible gust response which accounts for airfoil thickness.

Topics: Turbulence , Airfoils
Commentary by Dr. Valentin Fuster
2009;():65-79. doi:10.1115/IMECE2009-13344.

This work, the first of two parts, presents the development of a new analytic solution of acoustic scattering and/or radiation by arbitrary bodies of revolution under heavy fluid loading. The approach followed is the construction of a three-dimensional Wiener-Hopf technique with Fourier transforms that operate on the finite object’s arclength variable (the object’s practical finiteness comes about, in a Wiener-Hopf sense, by formally bringing to zero the radius of its semi-infinite generator curve for points beyond a prescribed station). Unlike in the classical case of a planar semi-infinite geometry, the kernel of the integral equation is non-translational and therefore with independent wavenumber spectra for its receiver and source arclengths. The solution procedure begins by applying a symmetrizing spatial operator that reconciles the regions of (+) and (−) analyticity of the kernel’s two-wavenumber transform with those of the virtual sources. The spatially symmetrized integral equation is of the Fredholm 2nd kind and thus with a strong unit “diagonal” — a feature that makes possible the Wiener-Hopf factorization of its transcendental doubly-transformed kernel via secondary spectral manipulations. The companion paper [1] will present a numerical demonstration of the new analysis for canonical problems of fluid-structure interaction for finite bodies of revolution.

Commentary by Dr. Valentin Fuster
2009;():81-92. doi:10.1115/IMECE2009-13366.

This study numerically demonstrates a new Wiener-Hopf technique for a generic family of straight finite cylinders capped by hemispheres [1]. The approach uses a three-dimensional Wiener-Hopf technique with Fourier transforms to calculate the radiated noise. A discussion of validity of the solution method through an energy conservation analysis is included. All of the cylinders investigated had the same extent of acoustically illuminated (hemispherical) area. Although the structure in the development is general the numerical results presented consider only locally reacting surfaces with uniform properties in a mass-controlled sense. The calculations are actually the result of a zeroth-order version of the theory that becomes increasingly valid with rising values of the basic cylinder’s aspect ratio. Lastly, using a function-splitting procedure we show that the Wiener-Hopf’s canonical essential singularity and square-root branch point generate the Fresnel integral as a fundamental function.

Commentary by Dr. Valentin Fuster
2009;():93-96. doi:10.1115/IMECE2009-10600.

A two-dimensional (2D) metamaterial possessing an effective anisotropic mass is investigated. This metamaterial is a composite material in the form of an internal mass connected in two directions to the host medium. A 2D mass-in-mass lattice model is used to characterize the dynamic behavior of the metamaterial. If modeled as an effective spring-mass lattice system, the metamaterial may possess a frequency-dependent effective mass. Moreover, if an equivalent homogenous elastic continuum is used to represent the metamaterial, an anisotropic mass density may result and may assume negative values for wave frequencies that are near the local resonance frequency of the internal mass. In fact, it was found that negative mass density occurs in the band-gap of the metamaterial. Unusual wave motion arises from the anisotropic band gap structure. In the present study, wave propagation in the representative continuum model for the metamaterial is studied in order to understand the unusual features of the dynamic behavior of the metamaterial.

Commentary by Dr. Valentin Fuster
2009;():97-102. doi:10.1115/IMECE2009-10727.

A method is proposed to design arbitrary shaped two dimensional (2D) isotropic-inertia acoustic cloaks without singularity. The method is based on the deformation view of the transformation method, where the transformation tensor A is identified as the deformation gradient tensor and the transformed material parameters can be expressed by the principal stretches in the principal system of the deformation. The infinite material parameters of a perfect 2D cloak is induced by an infinite principal stretch in one direction while the other two remains finite at the inner boundary during the transformation. To circumvent this difficulty, for a 2D cloak we can choose the principal stretch perpendicular to the cloak plane to be also infinite but in the same order as the infinite principal stretch in the cloak plane during the transformation, so the transformed material parameters may keep finite. To illustrate this idea, the analytical expressions of nonsingular material parameters for a cylindrical acoustic cloak are given. For the acoustic cloaks with irregular shapes, the numerical method is proposed to evaluate the principal stretches and in turn the nonsingular material parameters. The designed 2D cloaks are validated by numerical simulation.

Topics: Acoustics , Design
Commentary by Dr. Valentin Fuster
2009;():103-111. doi:10.1115/IMECE2009-11211.

We present here a technique to generate high frequency SAW in non-piezoelectric substrate with nanostructure grating of period less than 100 nm fabricated on it. A short pulse laser (with rise time less than 100fs) incident on this structure creates a periodic thermal stress due to the differential absorption in the substrate and the grating. We show that this stress sets up a surface acoustic wave on the substrate that can be detected optically. Modeling the generation process and analysis of SAW spectrum reveals the critical parameters to be controlled for obtaining SAW of high frequency. We show that the grating period less than 50 nm, a laser pulse of rise time less than 100fs and substrate properties like high optical absorption and high Rayleigh velocity are necessary for generating surface acoustic waves in near-THz range. This work provides quantitative guidelines on the design of near THz phononics.

Commentary by Dr. Valentin Fuster
2009;():113-114. doi:10.1115/IMECE2009-11254.

Significant research has recently been dedicated to reducing the interaction between acoustic waves and given objects. The coordinate transformation theory provides an elegant approach to the design of coatings capable of reaching this goal. First demonstrated for electromagnetic waves [1], this method has later been adapted to acoustic waves [2–5]. Its appeal stems from its generality: it can be applied to obtain coatings capable to conceal objects of arbitrary shapes and sizes. Moreover, its efficacy depends only on our ability to create materials having the right acoustic properties. However, these properties are quite restrictive. They include inhomogeneity, i.e. material parameters that vary continuously with position, and a high degree of anisotropy. In practice, one would relax these constraints but reduce the performance of the design. For example, in many instances an inhomogeneous material can be approximated by thin layers of homogeneous media. However, a large number of such layers are usually required to obtain acceptable results [6].

Commentary by Dr. Valentin Fuster
2009;():115-123. doi:10.1115/IMECE2009-11358.

This article introduces a numerical formulation for studying frequency band structure in multi-periodic acoustic composite structures. Herein, multi-periodic acoustic composite structures are defined as periodically-layered acoustic media wherein each layer is composed of periodically-repeated unit fluid cells, especially those arising from the study of rigid-frame porous materials. Hence, at least two periodic scales (microscopic and mesoscopic, respectively) comprise the macroscopic acoustic media. Under the Floquet-Bloch’s condition, exploitation of the multi-periodicity allows for efficient generation of dispersion curves via a multi-scale asymptotic method (for homogenizing the mesoscale) coupled to original acoustic transfer matrix methods (for the macroscale). The combined numerical formulation results in a general analysis procedure for evaluating complex dispersion relationships. The dispersion curves can be used to reveal frequency stop bands wherein the wave vector is highly imaginary—i.e., plane waves experience rapid attenuation. The formulation is applied to four infinite, multi-periodic acoustic composite structures in order to demonstrate the formulation’s utility and to reveal novel properties, particularly those which can be influenced by design of the mesoscopic unit cell.

Commentary by Dr. Valentin Fuster
2009;():125-127. doi:10.1115/IMECE2009-11811.

Micromechanically-fabricated phononic crystal (PnC) structures with phononic band gaps (PnBGs) are gaining a growing attention due to their high efficiency in controlling and confining mechanical energy in micro and nano-scale structures. Preliminary PnC devices such as waveguides and resonators based on the complete PnBG of the micro-machined PnC structures have shown a great potential to improve the characteristics of the conventional micro-mechanical (MM) devices [1–5]. Especially high-frequency, high-quality factor (Q) MM resonators are of great interest as they are main building blocks for realizing compact and complex devices such as filters, multiplexers and de-multiplexers for wireless communications and sensing applications. Therefore, development of high-Q, high-frequency PnC-based MM resonators is an important step towards realizing functional PnC-based devices with potentially better performance compared to their conventional counterparts. In this paper, we report, for the first time, a PnC slab piezoelectric-on-substrate MM resonator operating at VHF frequencies which supports high Q modes. The excitation of the resonant modes in these structures is done directly on the resonant structure (in contrast to the resonant tunneling excitation method reported earlier [5]) and therefore, no coupling from outside of the resonant structure is required. In such a structure, enough number of PnC periods can be placed around the resonant region to provide enough isolation from the surroundings; consequently the loss of the mechanical energy will be limited to material and friction losses only. We report a Fabry-Perot-type PnC slab resonator with an electrode and a piezoelectric medium directly fabricated on top of a resonant structure and show that high quality factors can be obtained in such a compact resonator. As a result, a flexural and a longitudinal mode are excited. Q’s of more than 3600 and 10,000 are obtained for the two modes with motional resistances of 1200 Ω and 5000 Ω. Such piezoelectrically excited high-Q resonators operating at such high frequencies evidence the possibility of suppressing support loss (an important source of loss) in MM resonators through the use of the especial structure of a PnC. Such PnC resonators can have a great impact on the current state-of-the-art MM devices used in wireless communication and sensing systems.

Topics: Energy gap
Commentary by Dr. Valentin Fuster
2009;():129-136. doi:10.1115/IMECE2009-12127.

Surface acoustic waves of piezoelectric half space with periodic surface electrodes are investigated. Since the boundary has periodic character, Bloch’s theorem and plane wave expansion method are employed in the analysis. Modeling the periodic electrode’s mechanical effects and electric boundary conditions of short grating and open grating are major tasks. Verification is performed on a 128°YX-LiNbO3 substrate covered by aluminum electrodes. Cases of different electrode aspect ratios are also investigated. Comparisons of dispersion curves corresponding to different boundary conditions are given. The effect of electrode aspect ratio on band gap width is obvious. The developed solution scheme finds the dispersion relations and propagation modes very efficiently and accurately.

Commentary by Dr. Valentin Fuster
2009;():137-147. doi:10.1115/IMECE2009-12508.

Scattering is the most fundamental problem in the research on phononic crystals and acoustic metamaterials; and scattering in a three-dimensional space poses challenging issues; and yet, the most challenging of all, is the scattering by elastic objects since an acoustic wave splits into different types of waves, propagating at different speeds, when it enters an elastic object. In this paper, a unified formalism is developed to analyze the scattering of an acoustic wave by a multilayer spherical object that is made of a mixture of an arbitrary number of concentric layers of elastic and acoustic media. Using this formalism, acoustical scattering by a multilayer spherical scatterer encasing an electrorheological (ER) fluid layer in an underwater environment is studied. Numerical examples show that ER fluids can alter the scattering characteristics above the first resonant frequency, which itself can be tuned by the applied electric field.

Commentary by Dr. Valentin Fuster
2009;():149-158. doi:10.1115/IMECE2009-12948.

Dynamic response of lattice structures in linear and nonlinear regime is investigated. In the linear regime, connections between vibration and buckling are revisited in the context of plane wave propagation. The power of wave technique in picking up the correct bifurcation mode and the associated critical load is illustrated. The stability of spatially localised structures arising from homoclinics is examined in the nonlinear regime. Simple analytical results will be presented and illustrated using numerical examples.

Topics: Waves
Commentary by Dr. Valentin Fuster
2009;():159-162. doi:10.1115/IMECE2009-13102.

The excellent applications and researches of so-called photonic crystals raise the exciting researches of phononic crystals. By the analogy between photon and phonon, repetitive composite structures that are made up of different elastic materials can also prevent elastic waves of some certain frequencies from passing by, i.e., the frequency band gap features also exist in acoustic waves. In this paper, we present the results of the tunable band gaps of acoustic waves in two-dimensional phononic crystals with reticular band structures using the finite element method. Band gaps variations of the bulk modes due to different thickness and angles of reticular band structures are calculated and discussed. The results show that the total elastic band gaps for mixed polarization modes can be enlarged or reduced by adjusting the orientation of the reticular band structures. The phenomena of band gaps of elastic or acoustic waves can potentially be utilized for vibration-free, high-precision mechanical systems, and sound insulation.

Commentary by Dr. Valentin Fuster
2009;():163-169. doi:10.1115/IMECE2009-13232.

In this work we study elastic wave propagation in homogeneous and periodic beams. Considering axial deformation, torsional deformation and Euler-Bernoulli bending deformation theory we develop finite element formulations to predict the dispersion characteristics. We compare the performance between applying the wave propagation solution directly to the governing equation versus applying it at the boundaries.

Commentary by Dr. Valentin Fuster
2009;():171-178. doi:10.1115/IMECE2009-10193.

Noise in large high voltage induction motors (500Hp and above) may be windage or magnetic in nature. Usually large high voltage induction motors induction motors are custom built and tailored to meet customers demand. In large high speed induction motors sometimes it is difficult to isolate windage noise from magnetic noise as the generated frequencies are similar in magnitude; hence reducing noise after motor is manufactured becomes extremely challenging. This paper will present the noise troubleshooting case study of 10,000Hp induction motor that shows overall noise of 100 dB during the factory testing. A variety of tests (e.g unloaded, variable speed, coupled loaded test and also test motor driven as load) were performed to isolate magnetic noise from air borne noise. Noise FFT data was collected to identify peak noise generating frequencies. Sound intensity and sound pressure data were also collected to calculate overall sound power level. After identifying the cause of noise, motor frame design was modified which results in overall noise level of 85 dB.

Commentary by Dr. Valentin Fuster
2009;():179-183. doi:10.1115/IMECE2009-10962.

In this paper, the dynamic model of the gearbox transmission for the wind turbine is proposed. The influence factor method is used to derive of the system’s dynamic equations, the natural characteristics of the transmission are obtained and the results are discussed. Finally, the influence of basic parts’ moment inertia on the natural characteristic is analyzed.

Commentary by Dr. Valentin Fuster
2009;():185-192. doi:10.1115/IMECE2009-11226.

Among underground coal miners, hearing loss remains one of the most common occupational illnesses. In response, the National Institute for Occupational Safety and Health (NIOSH) conducts research to reduce the noise emission of various underground coal mining equipment, an example of which is a roof bolting machine (RBM). After the removal of coal or rock, the remaining strata may be subject to fall, either from overhead (the roof) or from the side (the rib). One method used in underground coal-mines to prevent failures requires the installation of roof bolts. The roof bolting machine operator trams the machine to the required location, drills a hole into the strata, and then installs a roof bolt, supporting the roof or the rib, as the case may be. Field studies support the premise that, on average, drilling noise is the loudest noise that a roof bolting machine operator would be exposed to and contributes significantly to the operators’ noise exposure. NIOSH has determined that the drill steel radiates a significant amount of noise during drilling. NIOSH is developing bit and chuck isolators to reduce vibration, and thus noise radiation of the drill steel, with the longer-term goal of reducing roof bolting machine operator noise exposure. Laboratory testing has shown that operator ear sound pressure levels may be reduced by 3 to 7 dB(A), depending upon the test configuration and drilling media.

Commentary by Dr. Valentin Fuster
2009;():193-198. doi:10.1115/IMECE2009-11337.

Magnetic Resonance Imaging (MRI) is a powerful medical diagnostic tool. Unfortunately, the loud noise produced during scanning is unpleasant and potentially harmful to patients and may limit imaging protocol. A variety of approaches have been proposed to reduce noise exposure. Prior studies have been conducted in a sound quality chamber to aid in the development and implementation of hardware, algorithms, and procedures, which resulted in an active noise cancellation system tailored to conditions present during MRI. The active noise control system generates a secondary sound signal fed into a set of headphones worn by the patient. This system performs well during physical simulation of scanning conditions. In this study, the headphones are worn by a dummy during in-situ MRI scanning. Our specific effort is to take a selected successful experiment under simulated conditions and repeat it during live scanning to evaluate the real time performance of the system conducted in-situ. Evaluation of a common scanning sequence was conducted and the procedure adjusted to maximize the performance of the system. The sound pressure levels (SPLs) at the patient’s ear were measured with and without active control operational, and the results are compared to evaluate the active noise cancellation system’s performance during live scans.

Commentary by Dr. Valentin Fuster
2009;():199-203. doi:10.1115/IMECE2009-11879.

Reflection and refraction of magneto-elastic waves at the interface of two ferromagnetic half-spaces is considered. The space is in an external homogeneous magnetic field, the direction of which coincides with direction of the initial magnetization vector. A slipping contact on the interface of two ferromagnetic semi-spaces is considered. The existence of new type of waves is shown. These waves are localized on the interface of two ferromagnetic media and accompany the reflection and transmission waves and exist because of incident waves on the interface of two magneto-elastic media, and magneto-elastic properties of the media. These types of waves named as an accompanying surface magnetoelastic (ASM) waves. An analytical expression for the magnitudes of reflection, refraction, and ASM waves are derived. Coefficients of mentioned waves are strongly dependent on the applied magnetic field, material properties of each medium, as well as on frequency and the angle of an incident elastic wave. It has been shown that an applied magnetic field can totally eliminate or strengthen transmission and reflection waves and can be a control parameter for exchanging energies between these waves. Also, by eliminating transmission and reflection waves the magnetic field is able to control the ASM wave magnitudes. A new wave filtration mechanism can be drawn from these effects.

Commentary by Dr. Valentin Fuster
2009;():205-211. doi:10.1115/IMECE2009-12194.

In an effort to reduce Noise Induced Hearing Loss (NIHL) in the mining industry, the National Institute for Occupational Safety and Health (NIOSH) is conducting research to develop noise controls for mining equipment whose operators exceed the Permissible Exposure Level (PEL). The process involves three steps: 1) Noise source identification (NSI), 2) development of noise controls, and 3) evaluation of the developed noise controls. For the first and third steps, microphone phased array measurements are typically conducted and data are processed using the conventional beamforming (CB) algorithm. However, due to the size and complexity of the machines, this task is not straight forward. Furthermore, because of the low frequency range of interest, i.e., 200 Hz to 1000 Hz, results obtained using CB may show poor resolution issues which result in inaccuracy in the noise source location. To overcome this resolution issue, two alternative approaches are explored in this paper, namely the CLEAN-SC algorithm and a variarion of an adaptive beamforming algorithm known as Robust Capon Beamformer (RCB). These algorithms were used along with the CB algorithm to process data collected from a horizontal Vibrating Screen (VS) machine used in coal preparation plants. Results with the array in the overhead position showed that despite the use of a large array, i.e., 3.5-meter diameter, the acoustic maps obtained using CB showed “hot spots” that covered various components, i.e., the screen deck, the side walls, the I-beam, the eccentric mechanisms, and the electric motor. Thus, it was not possible to identify which component was the dominant contributor to the sound radiated by the machine. The acoustic maps obtained using the RCB algorithm showed smaller “hot” spots that in general covered only one or two components. Nevertheless, the most dramatic reduction in “hot” spot size was obtained using the CLEAN-SC algorithm. This algorithm yielded acoustic maps with small and well localized “hot” spots that pinpointed dominant noise sources. However, because the CLEAN-SC algorithm yields small and localized “hot” spots, extra care needs to be used when aligning the acoustic maps with the actual pictures of the machine. In conclusion, use of the RCB and the CLEAN-SC algorithms in the low frequency range of interest helped pinpoint dominant noise sources which otherwise would be very hard to identify.

Commentary by Dr. Valentin Fuster
2009;():213-222. doi:10.1115/IMECE2009-12272.

A-weighted sound levels around vibrating screens in coal preparation plants often exceed 90 dB(A). The National Institute for Occupational Safety and Health (NIOSH) is actively developing noise controls to reduce noise generated by horizontal vibrating screens. A 121-microphone, 3.5-meter-diameter array was used to perform beamforming to determine locations of significant noise radiation on the screen. Below about 1 kHz, the screen body was found to be the most significant noise source. The beamforming contour maps showed several key locations on the sides of the screen and the feedbox are the most significant contributors. Operating deflection shape (ODS) analysis was used to examine the screen behavior under actual operating conditions. This information is helpful in determining how to modify the screen body to reduce the noise radiated by the screen below 1 kHz. The analysis showed modal vibration patterns on the sides and feed box were the main contributors to noise. The results show several areas on the screen sides and feedbox that can be modified to reduce noise.

Commentary by Dr. Valentin Fuster
2009;():223-227. doi:10.1115/IMECE2009-12339.

Electrospun micro and nanofibers produced via electrospinning method were used for the sound absorption purposes. Polymers were initially dissolved in dimethyleformamide (DMF) or ethanol with a ratio of 80:20 and electrospun at 20 kV, 20 cm separation distance and 3 ml/hrs pump speed. The two-microphone transfer function method of the B&K impedance tube was used to determine the acoustical properties of the manufactured nanofibers at various frequencies. The test results showed that the absorption coefficients of nanofibers (∼500 nm) drastically increased. The reason behind this phenomenon may be attributed to the higher surface area of nanofibers and their interactions with more sound waves/air molecules. This result may open up new possibilities for the sound absorption problems in many fields, such as aircrafts, other transportation vehicles and infrastructures.

Commentary by Dr. Valentin Fuster
2009;():229-237. doi:10.1115/IMECE2009-12563.

Rolling bearings are widely used in domestic and industrial applications. Most of the industrial machinery often includes this kind of elements. Because of that, it is important to devise predictive maintenance tools in order to detect defects in the bearings and to avoid failure of the machinery. The number of rolling elements and their positions in the load zone change with bearing rotation, producing a periodical variation of the total stiffness of the bearing assembly. Hence, the bearing generates vibrations. When a bearing has a defect, these vibrations are increased. In this paper, a detection and classification system of fault bearings is presented. This system is based on the frequency domain response and the application of a Neuro-Fuzzy method. In the literature, different approaches in the frequency domain have been proposed. In this paper, a particular Neuro-Fuzzy approach has been chosen, given its learning properties and its capability of expressing the resultant detection and classification system by rules. A certain amount of trials have been carried out and it has been concluded that several Neuro-Fuzzy systems in a cascade configuration is a better option to solve the classification problem than other classification methods. In addition to, the results of these initial trials have determined the modifications of the learning phase suggested in this paper. The Neuro-Fuzzy systems with the proposed modifications and only two outputs improve the system performance and the rule association capability. Different results of the proposed approach are shown, where satisfactory results have been achieved.

Topics: Bearings
Commentary by Dr. Valentin Fuster
2009;():239-247. doi:10.1115/IMECE2009-12830.

The Mine Safety and Health Administration (MSHA) has been evaluating the job/task of air-arc gouging performed by mine shop welders. Air-arc gouging is the process of melting an old weld with a carbon based electrode (rod) and blowing the molten metal away with compressed air. Noise levels of 115 dBA or higher can be generated in this process. Three acoustical field evaluations were conducted at mine shops comparing both Constant Current (CC) and Constant Voltage (CV) techniques for air-arc gouging. The results indicate that by using the CV technique, the average overall A-Weighted Sound Pressure Level (SPLA ) was reduced by as much as 8 dBA from an average of 117.6 dBA to 109.3 dBA. As might be expected, dosimeter results indicated that the rate of noise accumulation was also reduced utilizing the CV technique. The average accumulation rate decreased from 4.5 percent Dose per minute for CC at varying air pressures to 2.0 percent Dose per minute for CV at 80 psig.

Commentary by Dr. Valentin Fuster
2009;():249-254. doi:10.1115/IMECE2009-12833.

Jackleg drills have proven to be a problem when it comes to overexposures to noise for coal miners as well as metal/nonmetal miners. These pneumatic drills are used to drill holes for roof bolting or blast holes in developmental and stoper mining. They are used when mining vertically or steeply inclined deposits. The “Leg” is a heavy metal support which allows the driller to keep the rig steady when collaring the hole as well as keeping it steady while drilling into the hard rock. Since drilling is done basically by hand, the operator remains in close proximity to the noise associated with the pneumatic hammer. Up until now, little has been done with the exception of Original Equipment Manufacturer (OEM) and retrofit mufflers to achieve compliance with the noise standards stated in Code of Federal Regulations (CFR) Title 30, part 62 for the drills of the type. Just recently an anthracite coal mining company, having noise problems associated with their jackleg drills, purchased a “Remote In-Stope Drill Rig” from a manufacturer in South Africa. A noise study was conducted by the Mine Safety & Health Administration (MSHA) and the cooperative mining company to determine the effectiveness of the remote control jackleg drill in reducing the operator’s overall noise exposure. The baseline test was conducted on the original jackleg drill. Once the new remote unit was received, it was tested as received from the manufacturer with their hammer and again with the company’s original hammer retrofitted to the drill rig. The company also made modifications to the 8 ft. hose extending it to 20 ft. to allow operation further from the noise source. The study was conducted to determine the effectiveness of the remote control unit in reducing not only the sound level, but also the overall noise dose. The unit was found to not only reduce the operator’s overall noise exposure when used with either hammer, but allowed drilling to be conducted from a location under permanently supported roof with no vibration on the operator’s hands.

Commentary by Dr. Valentin Fuster
2009;():255-262. doi:10.1115/IMECE2009-12835.

Currently, a number of manufacturers have developed and made commercially available badge-type (cordless) noise dosimeters. Previous studies conducted by the Mine Safety and Health Administration (MSHA) revealed that microphone size and placement/orientation significantly influence measurement error. The badge-type design houses the microphone within a significantly larger casing than does the traditional corded-type dosimeter. This presents concern that badge-type designs may significantly inhibit measurement accuracy. The purpose of this study is to evaluate the casing of various badge-type dosimeters in order to discern conditions and assess the extent to which the badge-type design contributes toward measurement error in comparison with the traditionally used corded dosimeter. For this, a series of laboratory measurements were conducted employing various commercially available badge-type casings and corded counterparts. Corresponding results are summarized and extended to conclusions regarding the effect of microphone casing design, badge-type versus corded, on measurement accuracy for personal noise dosimetry.

Commentary by Dr. Valentin Fuster
2009;():263-265. doi:10.1115/IMECE2009-10480.

After a background of operation through three years (2003–2005), the purpose of this paper is to summarize the status of our efforts to evaluate the potential of NOAA’s Infrasonic Detection Network (ISNet) for tornado detection and warning. The network implementation has involved parallel efforts at hardware design, detection algorithm development, designing displays, application of a fully compressible numerical model to understand infrasound generation processes, and modeling propagation using a 3-D acoustic ray tracing program. In combination, these efforts are placing us in a position to realistically assess the potential of infrasound to help with tornado detection and warning. One of our initial expectations, (that a 3-station network separated by about 200Km would robustly triangulate on acoustic tornadic sources) was shattered. Only at longer ranges (typically > 200Km because of an upper atmospheric wave guide) did the 3 stations (at Boulder, CO, Pueblo, CO, and Goodland, KS) monitor the same source with clear detections. On the other hand, individual stations showed regional tornado detection skill with different stations at times simultaneously detecting different regional tornadoes. Ray trace simulations have explained these regional detection differences, indicating that there is a need for closer network station spacing. Examples of both good and failed detections of tornadic storms are presented and recommendations are made for optimum network spacing. The needs for further evaluation are reviewed; including implementation of a denser network, improved verification (network stations can contribute guidance to field programs), improved display options, and timeliness. An intriguing aspect of our observations is that storms often produce infrasound about 30 minutes prior to a first tornado report. Numerical simulations completed and in progress should help illuminate the infrasonic source processes. Figure 1 below indicates the important elements involved with infrasonic tornado detection.

Topics: Networks
Commentary by Dr. Valentin Fuster
2009;():267-270. doi:10.1115/IMECE2009-10483.

Our simulations indicate that the presence of a vortex in or near acoustic propagation paths can have profound effects on the distributions of sound energy and cause sound waves to originate from virtual source positions. For example, recent studies have shown that infrasonic energy arrives from the regions of hurricanes. The azimuths measured for a limited number of cases published to date do not seem to originate from the vortex cores; but rather from the periphery of the system. This raises the questions: Is the sound being affected by strong wind and temperature gradients with the measured azimuths indicating virtual source positions? -or- Is the sound generation mechanism located outside of the vortex core?

Topics: Sound , Vortices
Commentary by Dr. Valentin Fuster
2009;():271-280. doi:10.1115/IMECE2009-10737.

This paper presents some aspects about sonic pollution and vibrations sources in urban area, respectively in Oradea town with its metropolitan zone, and suppressing solutions. The noise and vibration pollution in urban area represents an actual theme of environment protection in Europe and other world’s zone. In last time, Oradea Town has known a large urban and economical development, which due to including inside of urban zone two metallic railway bridges “Oradea East” and “Oradea West”, over “Crisul Repede” River. This ambient noise level and vibration loads produced by railway bridges on passing trains must be reduce, increasing of working bridge’s age and population’s comfort. The experiments about of automotive and tram traffic influence of historical monuments and public Oradea’s buildings have been extended, such as church and hospital. The tests have emphasized the necessity of suppressing noise and vibration pollution by mounting of sonic absorbent panels near buildings from railway bridges, phonic insulation of buildings walls, hour’s restriction program of traffic in these areas, and other solutions.

Topics: Vibration , Cities , Pollution
Commentary by Dr. Valentin Fuster
2009;():281-288. doi:10.1115/IMECE2009-10798.

Due to civilian noise complaints and damage claims, there is a need to establish an accurate record of impulse noise generated at military installations. Current noise monitoring systems are susceptible to false positive detection of impulse events due to wind noise. In order to analyze the characteristics of noise events, multiple channel data methods were investigated. A microphone array was used to collect four channel data of military impulse noise and wind noise. These data were then analyzed using cross-correlation functions to characterize the input waveforms. Four different analyses of microphone array data are presented. A new value, the min peak correlation coefficient, is defined as a measure of the likelihood that a given waveform originated from a correlated noise source. Using a sound source localization technique, the angle of incidence of the noise source can be calculated. A method was also developed to combine the four individual microphone channels into one. This method aimed to preserve the correlated part of the overall signal, while minimizing the effects of uncorrelated noise, such as wind. Lastly, a statistical method called the acoustic likelihood test is presented as a method of determining if a signal is correlated or not.

Commentary by Dr. Valentin Fuster
2009;():289-297. doi:10.1115/IMECE2009-11694.

Accuracy at the interface is an important aspect in simulating air/porous medium problems for sound propagation in the atmosphere. Currently, high-order schemes have been used in simulation for viscous flow around steady and moving solid bodies, but still have not been applied to simulating flow field in different media. The study in this paper is intended to apply a high-order scheme to improve the accuracy at the interface between air and porous medium. In the vicinity of the interface, spatial derivatives of flux are discretized using different high order schemes: second-order upwind scheme, third-order upwind scheme, and 5th -order WENO scheme. The calculations are performed on a staggered Cartesian grid. The model equations for flow in the air used in this paper are the Navier-Stokes equations for incompressible flow. Flow inside the windscreen (porous medium) is modeled with a modified Zwikker-Kosten equation (Sound Absorbing Materials, 1949). An immersed-boundary method using direct forcing is utilized. The problem of flow over a solid cylinder is used as a validation case for different schemes that are implemented and compared. The application of the study is to investigate the sound pressure level reduction between unscreened microphone and screened microphone under different frequencies of incoming wind turbulence. The wind turbulence in the present work is introduced by placing different sizes of solid cylinders in the upstream of the microphone. The simulation shows that for low-frequency turbulence, the windscreens with low flow resistivity are more effective in noise reduction, while for high-frequency turbulence, the windscreens with high flow resistivity are more effective.

Commentary by Dr. Valentin Fuster
2009;():299-303. doi:10.1115/IMECE2009-12478.

Acoustic travel-time tomography of the atmospheric surface layer (ASL) is based on measurements of travel time of sound impulse propagation between different pairs of sources (speakers) and receivers (microphones), which constitute the tomography array. Then, the temperature and wind velocity fields inside the tomography array are reconstructed with inverse algorithms. Improved knowledge about these fields is important in many applications: validation and input data for atmospheric models, studies of turbulence over complex topography and heterogeneous surfaces, input data for wave propagation models, etc.

Topics: Acoustics
Commentary by Dr. Valentin Fuster
2009;():305-314. doi:10.1115/IMECE2009-13181.

This paper presents a methodology for tracking and tracing multiple incoherent sound sources in 3D space in real time. A salient feature of this methodology is its capability of handling all types of sound signals, including broadband, narrowband, continuous, impulsive, and tonal (sinusoidal) sounds over the audible frequency range (20 to 20,000 Hz). Locations of sound sources are indicated in terms of the Cartesian coordinates in real time. The target sources are viewed through an automatic tracking camera covering 350 degree solid angle. The hardware includes four microphones, a thermometer, a webcam, a five-channel signal conditioner and a laptop. Thus, the system can be made light, portable, easy to setup and use and inexpensive. The underlying algorithm is a hybrid approach consisting of modeling of sound radiation from a point source in a free field, triangulation and signal processing techniques. To acquire better understanding of the performance of the device, numerical simulations are conducted to study the impacts of signal noise ratio, microphone spacing, source distance and frequency on the spatial resolution and accuracy of the results. Experiments are carried out to validate results over a wide variety of real-world sound signals such as helicopter noise, human conversations, truck pass-by noise, gun shots, impact sounds, clapping, coughing, etc. Satisfactory results are obtained in most cases, even when a source is behind the measurement microphones.

Topics: Sound
Commentary by Dr. Valentin Fuster
2009;():315-319. doi:10.1115/IMECE2009-10027.

One of the important challenges in the auto industry is to reduce the mass of the vehicle while meeting structural performance requirements for Crashworthiness, Noise, Vibration and Harshness (NVH) etc. In this paper, a multidisciplinary optimization (MDO) of a car back-bonnet is investigated by using the Response Surface Method (RSM). Firstly, a car body is fully surface modeled in CATIA and meshed in HYPERMESH software. Then, modal analysis of the finite element model is performed by NASTRAN software to find natural frequencies. Frequency map of that component is extracted and compared with a reference map to detect defects. Design of Experiments (DOE) methodologies is used for a screening of the design space and for the generation of approximation models using RSM techniques. Therefore, to optimize the model, improvement of the NVH behavior and minimization of the weight are imposed.

Commentary by Dr. Valentin Fuster
2009;():321-329. doi:10.1115/IMECE2009-10033.

In-plane free vibrations of an isotropic, elastic annular disk constrained at some points on the inner and outer boundaries are investigated. The presented study is relevant to various practical problems including disks clamped by bolts along the inner and outer edges or the railway wheel vibrations. The boundary characteristic orthogonal polynomials are employed in the Rayleigh-Ritz method to obtain the frequency parameters and the associated mode shapes. The boundary characteristic orthogonal polynomials are generated for the free boundary conditions of the disk while artificial springs are used to realize clamped conditions at discrete points. The frequency parameters for different point constraint conditions are evaluated and compared with those computed from a finite element model to demonstrate the validity of the proposed method. The computed mode shapes are presented for a disk with different point constraints at the inner and outer boundaries to demonstrate the free in-plane vibration behavior of the disk. Results show that addition of point supports causes some of the modes to split into two different frequencies with different mode shapes. The effects of different orientations of multiple point supports on the frequency parameters and mode shapes are also discussed.

Topics: Disks
Commentary by Dr. Valentin Fuster
2009;():331-336. doi:10.1115/IMECE2009-10044.

An analysis on nonlinear vibrations of a simply supported functionally graded materials (FGM) cylindrical shell at its two ends which subjected to the radial excitation in the uniform thermal environment is presented for the first time. Materials properties of the constituents are graded in the thickness direction according to a power-law distribution. In the framework of the First-order shear deformation shell theory, the nonlinear governing equations of motion for the functionally graded materials cylindrical shell is derived by using the Hamilton’s principle. The Galerkin’s method is utilized to discretize the governing equations of motion to a five-degree-of-freedom nonlinear system under combined thermal and external excitations. By using the numerical method, the five-degree-of-freedom nonlinear system is analyzed to find the nonlinear responses of the FGMs cylindrical shell.

Topics: Stress , Pipes
Commentary by Dr. Valentin Fuster
2009;():337-343. doi:10.1115/IMECE2009-10475.

Within the framework of the Three-Dimensional Linearized Theory of Elastic Waves in Initially Stressed Bodies, the influence is studied of the initial stretching of a composite thick plate containing a cylindrical hole on the stress concentration around a hole caused by the action of the additional uniformly distributed dynamic (time-harmonic) normal forces on the upper face of the plane. The corresponding problem formulation is presented and, in order to find the solution to this problem, the finite element method is employed. The numerical results on the concentration of the stress around the hole and the influence of the initial stretching on this concentration are presented. According to these results, in particular it is established that the stress distributions around the cylindrical hole changed significantly with the initial stretching force.

Commentary by Dr. Valentin Fuster
2009;():345-358. doi:10.1115/IMECE2009-11053.

This paper investigates the dynamic response to a time-harmonic oscillating moving strip load of a system comprising an initially stressed covering layer and initially stressed half-plane, within the scope of the piecewise homogeneous body model utilizing three-dimensional linearized wave propagation theory in the initially stressed body. It is assumed that the materials of the layer and half-plane are anisotropic (orthotropic), and that the velocity of the line-located time-harmonic oscillating moving load is constant as it acts on the free face of the covering layer. Our investigations were carried out for a two dimensional problem (plane-strain state) under subsonic velocity for a moving load in complete and incomplete contact conditions. The corresponding numerical results were obtained for the stiffer layer and soft half-plane system in which the modulus of elasticity of the covering layer material (for the moving direction of the load) is greater than that of the half-plane material. Numerical results are presented and discussed for the critical velocity and stress distribution for various values of the problem parameters. In particular, it was established that the critical velocity of the moving load is controlled mainly with a Rayleigh wave speed of a half-plane material and the initial stretching of the covering layer causes these values to increase. Moreover, it was established that with the oscillating frequency of the moving load, the values of the critical velocity decrease.

Commentary by Dr. Valentin Fuster
2009;():359-365. doi:10.1115/IMECE2009-11062.

Functionally graded materials (FGMs) are inhomogeneous composites which are usually made of a mixture of metals and ceramics. Properties of these kinds of materials vary continuously and smoothly from a ceramic surface to a metallic surface in a specified direction of the structure. The gradient compositional variation of the constituents from one surface to the other provides an elegant solution to the problem of high transverse shear stresses that are induced when two dissimilar materials with large differences in material properties are bonded. FGMs have attracted much attention as advanced structural materials in recent years. In this paper, free vibration of a rotating FGM cantilever arm is studied. The arm is modeled by an Euler-Bernoulli beam theory in which rotary inertia and shear deformation are neglected. The cross section area of the beam is rectangular with properties varying through the thickness following a simple power law exponent (n). This variation is a function of the volume fraction of the beam material constituents. The beam is composed of a mixture of aluminum and alumina. The deformation of the beam is considered to be in the plane of rotation. The equations of motion are derived using Hamilton’s principle and assumed mode method. Ten lowest polynomial functions are considered as mode shapes of the rotating beam. Natural frequencies of the arm are obtained and compared with the literature and verification is presented. Finally effects of various parameters on the natural frequencies and mode shapes are investigated.

Commentary by Dr. Valentin Fuster
2009;():367-375. doi:10.1115/IMECE2009-11067.

Free vibration analysis of a transversely stiffened circular thin hollow cylinder made of functionally graded materials (FGMs) is analytically evaluated. Functionally graded materials are inhomogeneous composites which are usually made from a mixture of metal and ceramic. The gradient compositional variation of the constituents from one surface to the other provides an elegant solution to the problem of high transverse shear stresses induced when two dissimilar materials with large differences in material properties are bonded. In this paper, application of an FGM made of two different materials is investigated by applying Ritz method. While cylinder is assumed to be thin, strain energy evaluation is performed by Sander’s theorem. Stiffeners which are not necessarily in the same uniform shape are treated as discrete elements and can be placed on both sides of the cylinder or concentrate in the middle wall. Bending, stretching and wrapping effects of stiffeners are considered in calculation of strain energy. Evaluation of kinetic energy of stiffeners is performed by taking into account rotary and translational inertia. To apply Ritz method, polynomial functions are used and natural frequencies and mode shapes of ring stiffened thin cylinder are investigated. Results are compared and verified with previous theoretical and experimental studies of stiffened thin cylinders. Comparison indicates a good agreement between results.

Commentary by Dr. Valentin Fuster
2009;():377-387. doi:10.1115/IMECE2009-11108.

In this study, the free vibration of partially fluid-filled functionally graded material (FGM) cylindrical shells with arbitrary boundary conditions has been investigated using the Rayleigh-Ritz method. The analysis has been carried out with strain-displacement relations from Love’s thin shell theory and the contained fluid is assumed irrotational, incompressible and inviscid. The Rayleigh-Ritz method is based on the energy parameters, so after determining the kinetic and potential energies of FGM shell filled with fluid, the eigenvalue problem has been obtained. To demonstrate the validity and accuracy of the obtained theoretical results, comparison has been made with the previous published results and also with the finite element results for the empty and partially fluid-filled shells. Finally, the effects of fluid level and power-law exponent on natural frequencies of partially fluid-filled FGM shells have been investigated.

Topics: Fluids , Pipes , Vibration
Commentary by Dr. Valentin Fuster
2009;():389-395. doi:10.1115/IMECE2009-11303.

Sensitive equipment utilized in aerospace applications experience vibrations from mechanical and thermal disturbances. Without proper vibration suppression systems, the delicate equipment can be severely damaged. A comparison between passive, active and hybrid control of light weight boom structure for space vehicles is carried out. Numerical and experimental analyses using NASTRAN finite element software are performed. Different control methods are applied, and a PID controller is implemented in the experiment. The main target of this research is to study the dynamic response of sensitive and light spacecraft structure like a boom antenna. In this experiment, the source of vibration disturbance is the force applied to one end of the structure and the response signal is captured by an accelerometer sensor at the free end of the beam. Piezoelectric Translator (PTS30 nanopositioning stage) (which is a linear actuator suitable for static and dynamic applications) is used for the reducing the vibration characteristics and thus damping out the vibrations. The maximum displacement provided by this actuator is +/− 15 mm and they provide pushing or pulling force of up to 30 N. The linear speed range of the PTS30 is 0 to 500 micrometer per second. The input to the actuator is provided by the accelerometer sensor through a power amplifier which is connected through a computer. The measured acceleration is integrated to obtain the corresponding velocities. Effectiveness of the control system highly depends on the position of the actuators. The average energy level taken over a frequency bandwidth of 4 Hz to 8 Hz will be considered as a parameter to be minimized. This research focuses on the reduction of vibration behavior of satellite boom structures over a wide frequency bandwidth using hybrid vibration control system. Here we present the results of damping effectiveness for different excitation amplitudes.

Commentary by Dr. Valentin Fuster
2009;():397-406. doi:10.1115/IMECE2009-11371.

The vibration properties of multi-layer beam structure comprising a partial magneto-rheological (MR) fluid layer are investigated to study the influences of size and location of the fluid treatment of the beam. The governing equations for the partially-treated multi-layered MR beam were formulated in the finite element form. The validity of the proposed finite element formulations is demonstrated by comparing the simulation results with those obtained from the Ritz formulation. Two different configurations of a partially treated MR-fluid beam are considered. Simulations are performed to investigate the influences of intensity of an external magnetic field, and the location and length of the MR-fluid layers on the dynamic characteristics of the beam with different boundary conditions. The properties and vibration responses of the partially-treated multi-layer beam are then compared with those of a fully-treated beam. The results suggest that the natural frequencies and transverse displacement response of the partially-treated MR beam are strongly influenced by the location and the length of the fluid pocket, and the boundary conditions, apart from the applied magnetic field.

Topics: Fluids
Commentary by Dr. Valentin Fuster
2009;():407-421. doi:10.1115/IMECE2009-12172.

The increasing application of composites in the aviation and automobile industry demands a better understanding of composite material behavior under high loading rate. This shall provide a better insight of actual loads on occupants while preserving livable crashworthy structure. In this study, a high stroke rate MTS servo-hydraulic testing machine is used to characterize the behavior of composite materials at high strain rates. At higher stroke rates, the output of the load detection system acquired by the load cell deviates from the true load-time wave form of the specimen. This is due to the convolution of the structural response of the detection system with the true characteristic of the specimen. To identify the true nature of the specimen load-time behavior, the de-convolution of the detection system response is necessary to restore the specimen characteristic wave form closer to its true behavior. The convolution of data set in the time domain is a time consuming process which explains the benefit of using the frequency domain; as the convolution in time domain corresponds to multiplication in the frequency domain. This process requires the transformation of the time domain data to frequency domain data via Fast Fourier Transform (FFT). In the frequency domain the complex division of the Fourier transfer of the detection system output with frequency response function of the detection system shall provide the true complex input characteristic. This paper elaborates the methodology utilized for obtaining the Frequency Response Function (FRF) of the load detection system using digital Fourier analysis with a single input/output data set. This also emphasizes precautions and guidelines for improving results with FFT to obtain true FRF measurements of the load detection system. The FRF obtained is successfully used to identify the actual specimen wave form characteristic. This is achieved by extracting the structural response of the load detection system from the load cell output.

Commentary by Dr. Valentin Fuster
2009;():423-428. doi:10.1115/IMECE2009-12382.

An analysis on nonlinear dynamic of a cantilevered functionally graded materials (FGM) plate which subjected to the transverse excitation in the uniform thermal environment is presented for the first time. Materials properties of the constituents are graded in the thickness direction according to a power-law distribution and assumed to be temperature dependent. In the framework of the Third-order shear deformation plate theory, the nonlinear governing equations of motion for the functionally graded materials plate are derived by using the Hamilton’s principle. For cantilever rectangular plate, the first two vibration mode shapes that satisfy the boundary conditions is given. The Galerkin’s method is utilized to discretize the governing equations of motion to a two-degree-of-freedom nonlinear system under combined thermal and external excitations. By using the numerical method, the two-degree-of-freedom nonlinear system is analyzed to find the nonlinear responses of the cantilever FGMs plate. The influences of the thermal environments on the nonlinear dynamic response of the cantilevered FGM plate are discussed in detail through a parametric study.

Commentary by Dr. Valentin Fuster
2009;():429-434. doi:10.1115/IMECE2009-12487.

Cracks and voids are common defects in rotating systems and are a precursor to fatigue-induced failure. The application of statistical analysis, as a tool for damage identification and health monitoring in rotating machinery, is investigated. Experimental vibration data were collected for a set of health and cracked shafts. Formal statistical models have been proposed to describe the relationship between the vibration signals and the existence of damage. Damage detection and diagnosis are implemented based on statistical estimation and hypothesis testing. Such a statistical model provides a screening technique to detect other damage types. As a result, the proposed methods can improve the power of damage detection.

Commentary by Dr. Valentin Fuster
2009;():435-443. doi:10.1115/IMECE2009-12660.

IBEX-Hi is an electrostatic analyzer spacecraft instrument designed to measure the energy and flux distribution of energetic neutral atoms (ENAs) emanating from the interaction zone between the Earth’s solar system and the Milky Way galaxy. A key element to this electro-optic instrument is an array of fourteen carbon foils that are used to ionize the ENAs. The foils are comprised of an ultrathin (50–100Å thick) layer of carbon suspended across the surface of an electroformed Nickel wire screen, which in turn is held taught by a metal frame holder. The electroformed orthogonal screen has square wire elements, 12.7 μm thick, with a pitch of 131.1 wires/cm. Each foil holder has an open aperture approximately 5 cm by 2.5 cm. Designing and implementing foil holders with such a large surface area has not been attempted for spaceflight in the past and has proven to be extremely challenging. The delicate carbon foils are subject to fatigue failure from the large acoustic and vibration loads that they will be exposed to during launch of the spacecraft. This paper describes the evolution of the foil holder design from previous space instrument applications to a flight-like IBEX-Hi prototype. Vibro-acoustic qualification tests of the IBEX-Hi prototype instrument and the resulting failure of several foils are summarized. This is followed by a discussion of iterative foil holder design modifications and laser vibrometer modal testing to support future fatigue failure analyses. The results of these activities indicate that there is no strong dependency of the natural frequencies or transmissibilities of the foils on the different foil holder and screen configurations. However, for all foil holder designs, the natural frequencies of the foils were observed to decrease noticeably from exposure to acoustic testing. These test results, when combined with foil holder assembly considerations, suggest that the welded frame and integrated screen designs should be incorporated into the architecture of the IBEX-Hi flight instrument.

Commentary by Dr. Valentin Fuster
2009;():445-451. doi:10.1115/IMECE2009-12672.

The damping and basic dynamic properties of a novel type of multifunctional hybrid material known as Metal Foam-Polymer Composite are investigated. This material is obtained by injection molding a thermoplastic polymer through an open cell Aluminum Foam, in essence creating two contiguous morphologies; an Aluminum Foam interconnected “skeleton” with the open pores filled with a similarly interconnected polymer substructure. This coexistence of both materials allows each to contribute its salient properties (e.g. the plastics contributing surface toughness and the metal foams contributing thermal stability). Basic damping testing results are presented for various Aluminum Foam porosities and pore sizes as well as for three types of polymers. A basic mathematical model of the damping is also presented. The integrity of the interface between the Aluminum Foam and the Polymer is discussed in terms of its effect on the overall material damping.

Commentary by Dr. Valentin Fuster
2009;():453-461. doi:10.1115/IMECE2009-12725.

The purpose of this research is to investigate the feasibility of utilizing the adaptive sandwich algorithm to find the optimal left and right eigenvectors for active structural noise reduction. As depicted in the previous studies, the structural acoustic radiation depends on the structural vibration behavior, which is strongly related to both the left eigenvectors (concept of disturbance rejection capability) and right eigenvectors (concept of mode shape distributions) of the system, respectively. In this research, a novel adaptive sandwich algorithm is developed for determining the optimal combination of left and right eigenvectors of the structural system. The sound suppression performance index (SSPI) is defined by combining the orthogonality index of left eigenvectors and the modal radiation index of right eigenvectors. Through the proposed adaptive sandwich algorithm, both the left and right eigenvectors are adjusted such that the SSPI decreases, and therefore one can find the optimal combination of left and right eigenvectors of the closed-loop system for structural noise reduction purpose. The optimal combination of left-right eigenvectors is then synthesized to determine the feedback gain matrix of the closed-loop system. The result of the active noise control shows that the proposed method can significantly suppress the sound pressure radiated from the vibrating structure.

Commentary by Dr. Valentin Fuster
2009;():463-469. doi:10.1115/IMECE2009-12738.

Line spectra in the radiated noise of marine vessels are the most visible signs, which can be detected, tracked and identified by enemy’s passive sonar, and hence it is of great significance to reduce the line spectra for improving the acoustic stealth of marine vessels. Insertion of resilient isolators between the machinery and the base is one of the most common methods for controlling unwanted vibration of the hull of submarine. Isolators in service are usually assumed to be linear and almost all the vibration isolation-n systems (VIS) are designed with linear theory, which satisfies engineering requirements in most situations. However, the nonlinear dynamical characteristics of VIS have attracted increasing attention in recent years due to the facts that onboard machinery trends towards more powerful and lighter, and that the demands in engineering for reducing vibration become more rigorous. Furthermore, some distinguishing features of nonlinear systems can be applied to achieve some special functions, among which the most important one is using chaos to reduce line spectra in the radiated noise of submarines based on the fact that response spectrum of a nonlinear system under harmonic excitation is a continuous one when chaos occurs. In this paper, a chaos synthesis method based on tracking control is prososed for a vibration isolation system (VIS) of on board machinery to make the chaotic motion in nonlinear VIS persistent. In this way, the line spectra in the radiated noise can be reduced effectively because the response spectrum of a chaotic system under harmonic excitations is a continuous and reduced one. Numerical simulations were carried out and the results showed that utilizing this method the nonlinear VIS not only possesses an excellent isolation performance of vibration and line spectra, but also reduces the amplitude of the isolated equipment notably.

Commentary by Dr. Valentin Fuster
2009;():471-478. doi:10.1115/IMECE2009-12828.

A new topology optimization technique is presented in this paper for optimal design of coupled structural-acoustic system with a current focus on interior noise reduction of automotive vehicles. The new topology optimization technique is based on an earlier published work on the analysis and sensitivity analysis of the coupled structural-acoustic system [1–2]. It is extended in this paper to consider the optimum material distribution in the structural domain as well as the optimum boundary shape between the structural and acoustic domains for the purpose of interior noise reduction. Firstly, a fixed boundary problem was considered with a focus on the material distribution in the structural domain to achieve the desired acoustic response inside the acoustic domain. The general formulation developed accounts for the full coupling effect of the structural vibration and acoustic pressure and can consider multiple (structural and acoustic) inputs and outputs over a predefined frequency domain. Secondly, optimization of the boundary shape between the structural domain and acoustic domain is considered with a focus on modifying acoustic resonant modes as well as the interaction between the structure and acoustic field. Finally, optimal material distribution and boundary determination are simultaneously considered to obtain a truly optimum structural-acoustic system for the desired performance requirements of the coupled system. Examples will be given to demonstrate the feasibility and effectiveness of the new topology optimization technique for various applications.

Commentary by Dr. Valentin Fuster
2009;():479-484. doi:10.1115/IMECE2009-12998.

Detailed investigations on the vibration suppression of beam-type structures using Multiple Tuned Mass Damper (MTMD) technology has been carried out in this study. A general curved beam has been utilized as a case study to illustrate the developed optimum design methodology. The governing differential equations of motion for the curved beam with the attached MTMD systems have been derived, and then solved using the finite element method. A hybrid optimization methodology, which combines the global optimization method based on Genetic Algorithm (GA) and the local optimization technique based on Sequential Quadratic Programming (SQP), has been developed. This has been utilized to find the optimum design parameters (damping coefficient, spring stiffness and position coordinate) of the attached Tuned Mass Damper (TMD) systems in order to suppress the vibration levels at a particular mode or several modes, simultaneously. Finally, a design principle for vibration suppression of beam-type structures using the MTMD technology has been proposed through extensive numerical investigations.

Commentary by Dr. Valentin Fuster
2009;():485-490. doi:10.1115/IMECE2009-13031.

Extraction of the frequency response of a musical instrument is the first step to analyze its vibration characteristic. This research introduces the results of several experiments implemented on Setar, a Persian long-necked lute. Setar has a wooden, reflective sound-box which is highly coupled with its surrounding air. High level of damping in addition to the composite properties in Setar, consequences dissimilar frequency domain vibration patterns. At lower frequencies, the response exhibits very distinct modal behavior, while in higher frequencies an overall effect of close modes is demonstrated. In this paper different approaches are utilized to handle both frequency regimes; and their advantages and limitations are compared to each other. The utilized methods are swept sine excitation, impact hammer, and the traditional Tap-Tone method. The characteristics of force excitation on body are first investigated, and then the frequency response function of Setar’s body is extracted between the excitation force as the input and resultant sound and acceleration as the outputs. This study not only leads us to modifications in design of Setar, but also serves as a platform for numerical modeling.

Commentary by Dr. Valentin Fuster
2009;():491-495. doi:10.1115/IMECE2009-13048.

This study aims to evaluate the amount of energy transfers through the bridge in Setar, a Persian long-necked lute. Stringed musical instruments are among the most complicated acoustical systems. When the string is plucked, its vibration distributes into the entire vibrating system (i.e. body, string, air enclosure) and produces sound. The resultant sound consists of three parts: the first is the string’s direct sound; the second is that part of sound-box vibration being excited by string’s direct sound, and the third is the part of sound-box vibration being excited by string force passing through bridge. The last part believed to have the major share and the others have minor effect. For this research, a specific fixture has been made and a precise plucking machine is installed to hold and pluck the instrument uniformly. Also, a novel approach is utilized to evaluate the share of each abovementioned part in the output near-field sound produced by Setar.

Topics: Sound
Commentary by Dr. Valentin Fuster
2009;():497-504. doi:10.1115/IMECE2009-13187.

The wireless sensor device which uses battery can cause problems when the wireless nodes are large in number and when the nodes are placed in the difficult area to access. Therefore, it is advantageous for the sensor node to be capable of extracting energy from the environment, making it self-powered, self-sustaining and lowering overall cost of the wireless network. Improvement in integrated circuit (IC) technology has made the overall power consumption of circuit very small which leads to a very promising application of the vibration-based energy harvester micro power generator (VEHM). This paper discusses on some practical design considerations in harvesting vibration from rotating machinery to power up a wireless sensor node. It also focuses on the effect of shape of the VEHM on its power output. These parameters are actually important as part of the key design parameters in harvesting the vibration from ambient. The energy harvester is made of piezoelectric bimorph bender materials poling in series to transform ambient vibrations into electrical energy. The power output for the VEHM made of single and multiple array of PZT bimorph bender are investigated and the effect of triangular and the rectangular PZT bimorph bender are compared. Two sets of VEHM device have been tested to work in the range of 50 Hz–110 Hz to power up a wireless sensor node for condition monitoring application. The experimental results are presented and compared to the previous similar work. It is found that the triangular shape bender generates more power compared to rectangular form whether it is single or multiple connected in series. Testing results proved that triangular VEHM of the same volume and fundamental frequency when compared to rectangular VEHM can improve the overall power generated by the generator.

Commentary by Dr. Valentin Fuster
2009;():505-511. doi:10.1115/IMECE2009-13201.

Vibro-acoustic responses of a vibrating rectangular plate were reconstructed using Helmholtz Equation Least Squares (HELS) method. The experiments were conducted on baffled rectangular plates of different aspect ratios with free as well as clamped boundary conditions under point force excitations via random and chirp sine signals. The radiated acoustic pressures were measured using a planar array of microphones at a very close distance to the plate surface, and taken as input to the HELS codes. The normal surface velocity distributions were reconstructed using HELS and compared against the benchmark data obtained using a laser vibrometer. Good agreements were obtained for both free and clamped boundary conditions. Finally, theoretical structural modes of the plate were compared against those obtained by HELS reconstruction and experimental modal analysis (EMA) for establishing their effectiveness in identifying closely coupled modes.

Topics: Acoustics , Equations
Commentary by Dr. Valentin Fuster
2009;():513-518. doi:10.1115/IMECE2009-10163.

Some recent development of the fast multipole boundary element method (BEM) for modeling acoustic wave problems in both 2-D and 3-D domains are presented in this paper. First, the fast multipole BEM formulation for 2-D acoustic wave problems based on a dual boundary integral equation (BIE) formulation is presented. Second, some improvements on the adaptive fast multipole BEM for 3-D acoustic wave problems based on the earlier work are introduced. The improvements include adaptive tree structures, error estimates for determining the numbers of expansion terms, refined interaction lists, and others in the fast multipole BEM. Examples involving 2-D and 3-D radiation and scattering problems solved by the developed 2-D and 3-D fast multipole BEM codes, respectively, will be presented. The accuracy and efficiency of the fast multipole BEM results clearly demonstrate the potentials of the fast multipole BEM for solving large-scale acoustic wave problems that are of practical significance.

Commentary by Dr. Valentin Fuster
2009;():519-525. doi:10.1115/IMECE2009-10843.

An acoustic finite-element model of an automobile passenger compartment that represents the more complicated vehicle interior acoustic characteristics is developed and experimentally assessed using loudspeaker excitation. The acoustic finite-element model represents the passenger compartment cavity, trunk compartment cavity, front and rear seats, parcel shelf, door volumes, and IP (Instrument Panel) volume. The model accounts for the coupling between the compartment cavity and trunk cavity through the rear seat and parcel shelf, and the coupling between the compartment cavity and the door and IP panel volumes. Modal analysis tests of a vehicle were conducted using loudspeaker excitation to identify the compartment cavity modes and sound pressure response at a large number of interior locations. Comparisons of the predicted versus measured mode frequencies, mode shapes, and sound pressure response at the occupant ear locations are made to assess the accuracy of the model to 400 Hz.

Commentary by Dr. Valentin Fuster
2009;():527-534. doi:10.1115/IMECE2009-11065.

A structural-acoustic finite element model of an automotive vehicle is developed and experimentally evaluated for predicting the structural-borne interior noise in the passenger compartment when the vehicle travels over a randomly rough road at a constant speed. The structural-acoustic model couples a structural finite element model of the vehicle with an acoustic finite element model of the passenger compartment. Measured random road profile data provides the prescribed power spectral density excitation applied at the tire-patch contact points to predict the structural-borne interior road noise. Comparisons of the predicted and measured interior noise for laboratory shaker excitation, tire patch excitation, and vehicle travel over a randomly rough road are used to assess the accuracy of the model.

Commentary by Dr. Valentin Fuster
2009;():535-547. doi:10.1115/IMECE2009-11222.

This study extends a recently-developed [1] cellular automata (CA) elastodynamic modeling approach to arbitrary two-dimensional geometries through development of a rule set appropriate for triangular cells. The approach is fully object-oriented (OO) and exploits OO conventions to produce compact, general, and easily-extended CA classes. Meshes composed of triangular cells allow the elastodynamic response of arbitrary two-dimensional geometries to be computed accurately and efficiently. As in the previous rectangular CA method, each cell represents a state machine which updates in a stepped-manner using a local “bottom-up” rule set and state input from neighboring cells. The approach avoids the need to develop partial differential equations and the complexity therein. Several advantages result from the method’s discrete, local and object-oriented nature, including the ability to compute on a massively-parallel basis and to easily add or subtract cells in a multi-resolution manner. The extended approach is used to generate the elastodynamic responses of a variety of general geometries and loading cases (Dirichlet and Neumann), which are compared to previous results and/or comparison results generated using the commercial finite element code, COMSOL. These include harmonic interior plate loading, uniform boundary traction, and ramped boundary displacement. Favorable results are reported in all cases, with the CA approach requiring fewer degrees of freedom to achieve similar accuracy, and considerably less code development.

Commentary by Dr. Valentin Fuster
2009;():549-557. doi:10.1115/IMECE2009-11316.

Sound propagation characteristics of various materials have been investigated. A methodology to evaluate and compare the acoustic responses of metallic and non-metallic materials was developed and validated. Various materials were acoustically examined under impact loading using a test set-up consisting of a solenoid-driven hammer, a microphone, and software to record, Fourier transform, and analyze the sound response. Materials studied for acoustic behavior included steel, cast and wrought aluminum, gray cast iron, titanium, and various composites. All materials were ranked based on their reduction of sound pressure compared to a reference material of hardened tool steel. Test data were normalized on an A-weighted scale to account for the enhanced sensitivity of the human ear at certain frequencies. The effects of specimen geometry and material composition on the resulting sounds were also incorporated in the investigation. A complete microstructural analysis was conducted on each material to relate its acoustic behavior to intrinsic material characteristics. The experimental and analytic tools and knowledge developed in this study were further applied in a manufacturing setting to redesign an impact stop for noise reduction. The proposed prototypes were tested in the industrial environment, and the results compared to the findings from the study. These developments will be systematically presented and discussed.

Topics: Acoustics
Commentary by Dr. Valentin Fuster
2009;():559-566. doi:10.1115/IMECE2009-11447.

This paper investigates a method called spectral decomposition and is presented as an alternate approach to determine the system frequency response functions of turbomachinery. Spectral decomposition is a method that is based on the principals established by the acoustic similarity laws to determine the spectral characteristics of a source function. The decomposition process was originally implemented to investigate the isolated acoustic source spectra of fans specifically excluding structureborne sources; however, this paper focuses on using the method for the purpose of characterizing the system response functions associated with rotating machinery. During this investigation, static impact test data was acquired on a large industrial motor to characterize the frequency response functions of the motor/compressor system. Spectral decomposition results are then calculated using the motor operational structureborne data and compared to the results of the static impact test. This paper shows that the spectral decomposition is a viable option to use in place of the static impact test results where qualitative frequency response functions are desired.

Commentary by Dr. Valentin Fuster
2009;():567-577. doi:10.1115/IMECE2009-11677.

When in-flight failures occur, rapid and precise decision-making under imprecise information is required in order to regain and maintain control of the aircraft. To achieve planned aircraft trajectory and complete landing safely, the uncertainties in vehicle parameters of the damaged aircraft need to be learned and incorporated at the level of motion planning. Uncertainty is a very important concern in recovery of damaged aircraft since it can cause false diagnosis and prognosis that may lead to further performance degradation and mission failure. The mathematical and statistical approaches to analyzing uncertainty are first presented. The damaged aircraft is simulated via a simplified kinematics model. The different sources and perspectives of uncertainties under a damage assessment process and post-failure trajectory planning are presented and classified. The decision-making process for an emergency motion planning to landing site is developed via the Dempster-Shafer evidence theory. The objective of the trajectory planning is to arrive at a target position while maximizing the safety of the aircraft under uncertain conditions. Simulations are presented for an emergency motion planning and landing that takes into account aircraft dynamics, path complexity, distance to landing site, runway characteristics, and subjective human decision.

Commentary by Dr. Valentin Fuster
2009;():579-589. doi:10.1115/IMECE2009-12157.

A finite element simulation of a through-wall ultrasonic communication system which permits data to be transferred from the inside of a sealed metal vessel to the outside without the need for physical penetrations is introduced. Two transducers are aligned axially on either side of a thick solid stainless steel wall. The outside transducer is forced with a continuous sinusoidal voltage at the crystal’s nominal 1 MHz longitudinal resonant frequency, launching a wave into the wall. The transmitted beam is partially reflected off of the inside of the wall where the inside transducer is located. The amplitude of the reflected wave is modulated by switching the electrical impedance placed across the leads of the inside transducer. The reflected wave is received at the outside transducer and the continuous wave amplitude is sensed to detect the transmitted data bits. The system is modeled and simulated using a commercial finite element modeling package. A coupled stress-strain and piezoelectric analysis is performed using an axisymmetric geometry. The model represents an existing system from which physical measurements were taken. Excellent correlation between the model and system were observed and the model has been used to further optimize the communication system.

Commentary by Dr. Valentin Fuster
2009;():591-597. doi:10.1115/IMECE2009-13015.

This paper introduces a finite element model of Setar, a Persian long-necked lute. Setar is modeled as a transfer function between the imposed force on the bridge and the near-field resulted sound. Numerical modeling of stringed musical instruments is a computationally challenging task which has always been done with extreme simplifications. Phenomena such as fluid-structure interaction, composite structure, preload effect and infinite boundary are considered in this model. The cycle of Software used in here is CATIA, HyperMesh, Nastran, and HyperGraph. The frequency response between the force of string and generated sound in near field are obtained, taking into account the fluid inside and outside of the soundbox. This model is useful to predict the effect of modification in specific parts to the sound generated by the instrument. The numerical results have excellent agreement with the experimental ones. The modeling procedure can be extended to other musical instruments as well as less complicated problems such as passenger compartment of vehicles.

Commentary by Dr. Valentin Fuster

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In