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ASME Conference Presenter Attendance Policy and Archival Proceedings

2016;():V013T00A001. doi:10.1115/IMECE2016-NS13.
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This online compilation of papers from the ASME 2016 International Mechanical Engineering Congress and Exposition (IMECE2016) represents the archival version of the Conference Proceedings. According to ASME’s conference presenter attendance policy, if a paper is not presented at the Conference by an author of the paper, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.

Commentary by Dr. Valentin Fuster

Acoustics, Vibration, and Wave Propagation: Acoustics and Structural Interaction

2016;():V013T01A001. doi:10.1115/IMECE2016-65810.

Effect of signal kurtosis value on the response of the beam with different boundary conditions has been studied. The signals with various Kurtosis have been generated in a Signal generator code- combined with an algorithm for random data generation for various kurtosis values. Subsequently, a simple Finite Element model of a rectangular Euler-bernoulli beam is introduced and the PSD1s are applied to the model in the form of low frequency base excitation acceleration input. The results show that, generally, the signals with higher kurtosis tend to create more stress and deformation in the structure due to the more frequent existence of peaks with higher amplitudes. However, at lower kurtosis values near normal distribution, the response behavior is different. Also, the stress induced in the beam end is the most critical in clamped-clamped conditions, and where both ends are excited.

Commentary by Dr. Valentin Fuster
2016;():V013T01A002. doi:10.1115/IMECE2016-66193.

The purpose of this paper is to document the process required to design and prototype a two-axis acoustic levitator and to show that the two-axis levitator improves the stability of a particle in an acoustic levitation field. The levitator design consists of the following subsystems: the transducer assemblies, which are responsible for generating the acoustic pressure field needed for levitation; the electrical system, which is responsible for providing the transducer assemblies with adequate power to maintain levitation; and the frame structure, which is responsible for locating and rigidly supporting the transducer assemblies.

The two-axis levitator is designed to have four transducers that operate at 27.2 kHz, and simulated results show that the system satisfies nearly all the design criteria and objectives. A transducer test stand and prototype were constructed to verify the design. The test stand was used to characterize all four transducers, and once the assembly was constructed the prototype operating frequency was determined to be 27.5 kHz. The prototype was used to successfully levitate Styrofoam pellets, a plastic pellet, and water droplets of various sizes. The displacement of a water droplet of approximately 1 mm in diameter was measured when levitated with both one-axis (vertical) and two-axis (vertical and horizontal) levitation. Using one-axis levitation, the water droplet displaced a maximum of 1.1 mm in the horizontal direction and 0.17 mm in the vertical direction. Using two-axis levitation, the horizontal displacement was 0.07 mm and the vertical displacement was 0.05 mm. Therefore, the two-axis acoustic levitator provides significant improvements in levitated particle stability.

Commentary by Dr. Valentin Fuster
2016;():V013T01A003. doi:10.1115/IMECE2016-66367.

The study of nonlinear aeroelastic instability mechanism of nonconservative acousto-elastic system is the focus here. The acousto-elastic system consists of a spinning disc in a compressible fluid filled enclosure. The nonlinear rotating plate is coupled with the linear acoustic oscillations of the surrounding fluid. Based on the acousto-elastic theory, the coupled field equations are discretized and solved for various rotation speeds in order to obtain the coupled system dynamics. The study shows that the coupled system undergoes a flutter instability at a particular rotation speed and the instability takes the form of supercritical Hopf bifurcation. Subsequently, the effect of randomness associated with the structural and the acoustic damping parameters are quantified on the nonlinear instability behaviour by means of a spectral projection based polynomial chaos expansion technique.

Commentary by Dr. Valentin Fuster
2016;():V013T01A004. doi:10.1115/IMECE2016-67678.

This paper presents the acoustic finite element method and the modal solution method for coupling sound absorbing materials with an air cavity to predict the sound pressure frequency response. The sound absorbing materials are represented with complex, frequency-dependent, effective mass-density and bulk-modulus properties obtained from the acoustic impedance of material samples. To couple the sound absorber cavity and air cavity, the boundary conditions at the interface between the cavities requires equality of pressure and equality of acoustic volume flow. Two modal solution methods are developed to compute the frequency response of the coupled system with frequency dependent material properties: the component mode method and the coupled mode method. The finite element and modal solution methodology is developed in a form readily adaptable for implementation in commercially available codes. The accuracy of the modal solution methodology is assessed for modeling a one-dimensional air tube terminated with absorbent material and the seats in an automobile passenger compartment.

Commentary by Dr. Valentin Fuster

Acoustics, Vibration, and Wave Propagation: Aero-Acoustics and Sound Propagation

2016;():V013T01A005. doi:10.1115/IMECE2016-65966.

The simulation is developed for the purpose of simulating ultrasound propagation through biological tissues. The simulation is based on the time-domain conservation laws with the governing equations for acoustic pressure and velocity, with frequency dependent absorption and dispersion effects. We use forward differencing for velocity and backward differencing for pressure on the non-fractional derivative operator terms in spatial discretization. The fractional Laplacian operators are treated as Riesz derivatives. The shifted standard Grunwald approximation method is used to solve fractional derivative operator terms. To accommodate complicated biological tissue geometries, an immersed boundary method is developed that enables a Cartesian computational grid mesh to be used. The results are compared with those for a non-absorption homogeneous medium to discuss absorption and dispersion effects of biological material.

Commentary by Dr. Valentin Fuster
2016;():V013T01A006. doi:10.1115/IMECE2016-66099.

When sound generated in jet flow propagates to outside of flow field, direction of sound propagation changes because of wave convection and refraction of shear layer. In wind tunnel, sound source drift appears when sound source is located with out-flow microphone array based on beamforming algorithm. In some cases, angles between jet flow direction and microphone array or sound source plane are inevitable due to geometric position, which increases the number of parameters affecting sound source drift distance. Geometrical acoustics and basic beamforming algorithm were used in this paper to deduce the relation between sound source drift and the angles. Equations for drift prediction and method for error reduction were given. Experimental verification was completed in a full-scale aero-acoustic wind tunnel with 2 loudspeakers set on an auto-body surface and microphone array with 120 channels. The experimental results prove that the equations for sound drift prediction in complicated geometric position relationship have a high accuracy, could help quick locating sound sources in engineering application.

Commentary by Dr. Valentin Fuster
2016;():V013T01A007. doi:10.1115/IMECE2016-67449.

The blades of coaxial, contra-rotating rotor systems cross each other in close proximity and at high relative speeds. This crossing event is a potential source of noise and severe blade loads. Effects of compressibility can aggravate the interaction and significantly alter the pressure field signature and phase relationships. A 2-D analysis of this phenomenon is performed by simulating two airfoils passing each other at specified speeds and vertical separation distances. Several test cases spanning a relevant range of Reynolds numbers, angles of attack, and relative Mach number are considered. The Mach number is varied to simulate the radial variation of velocity from the root to tip of a rotor blade to capture the pressure signature, lift, and drag of the airfoils. The velocity and pressure distributions on the airfoils, and in the space between the airfoils are computed before, at, and after airfoil crossing. The variations of lift and drag coefficients through the interaction are captured. The upper airfoil experiences an increase in lift followed by a very sharp drop in lift during the interaction. When relative Mach numbers are transonic, the region of interaction is greatly extended, with shock interactions occurring. The results show the complex nature of the aerodynamic and fluid dynamic impulses generated by blade-blade interactions, with implications to aeroelastic loads and aeroacoustic sources.

Commentary by Dr. Valentin Fuster

Acoustics, Vibration, and Wave Propagation: Flow-Induced Noise and Vibration

2016;():V013T01A008. doi:10.1115/IMECE2016-65247.

Audible noise inside a vehicle compartment has substantial negative impact on the customer opinions on the vehicle quality. Since significant progress has been achieved on reducing the major noise sources, such as powertrain noise and wind noise, traditional minor noise sources, such as the refrigerant flow-induced whistle of the vehicle climate control system, become more audible and annoying due to their high frequency characteristics and the reduced masking level. In this paper, a high-pitched whistle around 6.6 KHz of the climate control system is investigated and studied experimentally and theoretically. A joint on the suction tube is identified as the noise source by a systematic approach. The mechanism of the noise generation, propagation and interaction are studied theoretically. Due to the excessively large gap (around 1 mm) at the joint, a wall cavity is formed at this location. When the R134a refrigerant flows over the joint, the induced tones inside the wall cavity are generated by the low-Reynolds number mean flow and transmitted through the tube walls. The magnitude of the whistle is increased more rapidly during the transmission as the result of the interaction with tube walls when the acoustic diametric mode is coupled with the structural circumferential mode. Good coincidence between the calculated and the tested results is found, which proves the accuracy of the proposed theoretical analysis. The modified design of the joint gap is implemented and the high-pitched whistle is eliminated. Finally, a guideline for suppressing the flow-induced whistle of the vehicle climate control system is provided.

Commentary by Dr. Valentin Fuster
2016;():V013T01A009. doi:10.1115/IMECE2016-66170.

Noise reduction is considered as a challenging task in the engineering field. The main objective of this study is focused on providing an optimal new design of a cooling fan with better performance by minimizing the acoustic signature using the surface dipole acoustic power as function. The process of designing a new cooling fan with optimal performance and reduced acoustic signature can be fairly lengthy and expensive. With the use of CFD and specific tools like mesh morphing, in conjunction with state-of-the-art optimization techniques such as Simple model, a given baseline design can be optimized for performance and acoustics. The present study focuses on minimizing the acoustic signature of a given cooling fan using the surface dipole acoustic power as the objective function. The Mesh Morpher Optimizer (MMO) in ANSYS Fluent is used in conjunction with a Simplex model of the broadband acoustic modeling. The broadband model estimated the acoustic power of the surface dipole sources on the surface of the blade without the need for expensive unsteady simulations. It has been shown in the previous work that such a model can provide reliable design guidance. The new promising approach has shown a reduced dipole surface intensity of around 46% of the original value. Other acoustics sources (quadropole noise) are ignored due to the relatively low fan speed considered in this study. Considering this as first attempt study, it is believed that advanced additional studies may improve the model in changing the mesh and objective function.

Topics: Cooling , Acoustics
Commentary by Dr. Valentin Fuster
2016;():V013T01A010. doi:10.1115/IMECE2016-67010.

This paper deals with turbomachinery, such as pumps or turbines, which are very sensitive to changes in fluid speed over the contours of the blades when the volumetric flow is varied. These changes modify the fluid incidence angle, causing a rapid decline in pump performance. Our research focuses on an analysis of the performance or efficiency of a centrifugal pump with a variable frequency drive, where losses in efficiency are caused by turbulence generating harmful vibrations in the installation. The methodology consists of measuring the magnitude of the vibrations. The data obtained are compared to the performance reached when the change in velocity has been produced with the regulation of the volumetric flow to a partial load of the pump. This suggests an analysis to attempt to resolve the issue of density variation that occurs when pumping liquefied petroleum gas (LPG) under regular operating conditions.

Commentary by Dr. Valentin Fuster

Acoustics, Vibration, and Wave Propagation: General Noise and Vibration Control

2016;():V013T01A011. doi:10.1115/IMECE2016-65301.

Recent experimental investigations demonstrate that the level of noise generated by double helical synchronous belt (DHSB) is lower than that by straight-toothed synchronous belt (STSB). The present study is to theoretically elucidate the mechanisms whereby DHSB produces lower noise. In the theoretical analysis, a model DHSB is divided into several parallel narrow DHSBs with equal width. Let each narrow DHSB’s helical angle be 0° so each narrow DHSB becomes a narrow STSB. The theory of the one-dimensional sound field is then applied to obtain the standing wave solution of impact sound pressure. The sum of impact sound pressures by the narrow STSBs derived from one pair (left- and right-handed) of helical teeth of the model DHSB represents transmission impact noise. Computational results reveal that the power of impact sound at the damping-frequency decreases as the helical tooth’s angle increases. In addition, the impact sound power decreases as the degree of tooth’s offset of a double helical offset-toothed synchronous belt (DHOTSB) increases. Impact sound power is in the following order from high to low: STSB » DHSB > DHOTSB. In experimental investigations, the noise was in the following order from high to low: STSB » DHSB > DHOTSB, consistent with theoretical prediction. Also, the sound power at high frequency was markedly attenuated in DHSB or DHOTSB, the impact noise is the major sources of noise. Thus, the reduced noise in DHSB and DHOTSB can be explained by the one-dimensional standing wave sound field theory.

Commentary by Dr. Valentin Fuster
2016;():V013T01A012. doi:10.1115/IMECE2016-66815.

In-situ calibration methods using a single spherical-shaped transmitting hydrophone (idealized as a monopole acoustic source) have traditionally been used for radiated sound measurements of turbomachinery performed in the Garfield Thomas 1.22-m diameter water tunnel located at The Pennsylvania State University’s Applied Research Laboratory (ARL Penn State). In this reverberant field, the monopole source containing known transmitting characteristics was used to calibrate acoustic sensors that were either near or far from the source. This method typically works well when the type of source is monopole in nature; however, many acoustics sources can be dipole or quadrupole in nature. In this study we investigated the applicability of using dipole sources in a space such as a well-characterized reverberant tank, and we found through a virtual dipole method that the radiation still appears monopole in the reverberant field. The method was extended for the vibration of a panel (a known dipole source) and once again the monopole assumption for the in-situ calibration for a near-field hydrophone and conventional reverberant hydrophones remained consistent.

Commentary by Dr. Valentin Fuster
2016;():V013T01A013. doi:10.1115/IMECE2016-66990.

Vortex induced vibration or widely known as VIV, is a very complex hydrodynamic phenomenon. There are relatively very few experimental and numerical references for oscillating pair of cylinders because of the early assumption that the interference between the two cylinders is weak and thus each of the cylinders may have the same behavior as found in the case of a single cylinder, but recent researches showed this assumption was not true. For tandem arrangement, several parameters govern the nature of VIV of downstream cylinders, such as spacing, upstream cylinders VIV amplitude etc. The nature of downstream cylinders response isn’t same as classical VIV or WIV (wake induced vibration). Oscillation frequency of a cylinder subjected to flow induced vibration is one of the important characteristics Oscillation frequency is highly dependent on natural frequency of the cylinder. By changing spring stiffness or mass ratio, natural frequency can be altered. The aim of this study is to investigate the effect of upstream cylinder’s oscillation frequency on the vibration of downstream cylinder. Numerical simulations have been conducted to understand the nature of vortex induced vibration (VIV) of a pair cylinder in tandem arrangement at high Reynolds numbers. Cylinders were subjected to uniform flows in sub-critical flow regime and have been allowed to oscillate in cross flow direction only. The spacing between the upstream and downstream cylinders was four times of the cylinder diameter. The oscillation frequency of the upstream cylinder has been altered by varying the mass ratio of the upstream cylinder. It was found that for same Reynolds number, downstream cylinder’s VIV amplitude is increased quite significantly if the upstream cylinder oscillates relatively slowly. The shear stress transport detached eddy turbulence model has been used for simulating the turbulent flow around the two cylinders. An advanced mesh movement known as “mesh morphing” model was employed to lessen the requirement for re-meshing which help to increase the accuracy of the prediction. Calculation of accurate results due to large domain deformations was achieved by re-positioning existing mesh points. The numerical results of a single cylinder subjected to one degree of freedom (1DOF) vibration have been compared with the available experimental results to validate the present study. The study is important in terms of designing VIVACE (Vortex Induced Vibration for Aquatic Clean Energy) converter for low speed current. In recent past, multiple cylinders have been used for VIVACE converter. So, the study of VIV of two equal-diameter cylinders in tandem arrangement at low current speed is very significant.

Commentary by Dr. Valentin Fuster
2016;():V013T01A014. doi:10.1115/IMECE2016-67710.

Measurements were obtained by sending high frequency acoustic waves through a reinforced concrete column. Past work involved through-wall digital communications and power delivery through metallic barriers; this paper extends that work to a reinforced concrete column. A pair of 35 mm diameter circular transducers with a thickness of 10 mm (corresponding to a resonance of 200 kHz) were epoxied to opposite sides of a 0.7 m thick reinforced concrete column. A vector network analyzer (VNA) obtained the characteristics of the acoustic channel formed between the two sensors. A voltage transfer function for this channel was found in the range of 30 kHz – 150 kHz. Although this transfer function shows a significant amount of frequency selectivity, i.e. variation with frequency, resulting from the multipath created by the acoustic energy interacting with the complex structure of column (rebar, aggregate, voids) and its surfaces, the channel is seen to be capable of supporting data transmission. The magnitude of the transfer function is seen to be highest in the region 40 kHz – 70 kHz with its theoretical capacity to be approximately 400 kbits/s for a received signal-to-noise ratio (SNR) of 60 dB. Lower SNR’s would still be able to provide data rates well in excess of 50 kbits/s, permitting the passing of low frequency data across the concrete column.

Commentary by Dr. Valentin Fuster

Acoustics, Vibration, and Wave Propagation: Numerical Methods in Vibration and Acoustics

2016;():V013T01A015. doi:10.1115/IMECE2016-65438.

The current paper investigates the use of perfectly-matched layers (PML) as absorbing elements for a finite element (FE) model simulating a semi-infinite medium. This formulation is convenient for application of Craig-Bampton reduction (CBR), which significantly reduce the number active degrees-of-freedom in the model in an attempt to improve the computational efficiency. The results from this investigation suggest the PML elements worked seamlessly with the FE elements to approximate the elastodynamic response of a 2D layered halfspace subjected to a surface load; the wave energy appears to be fully absorbed by the PMLs regardless of incident angle or wavelength. The size of the model is reduced by approximately 77% using the CBR, which transforms the system into a mixed set of coordinates, including both modal and spatial coordinates. The model reduction is accomplished by neglecting modal frequencies for the system above one and a half times the maximum forcing frequency of interest. By only transforming the frequency-independent FE section into modal coordinates, and leaving the frequency-dependent PML elements as spatial degrees-of-freedom, the mode-shapes must only be solved once and can then be reused for different forcing frequencies. The results from this investigation suggest this could provide computational benefits if a number of cases are being computed for different frequencies.

Commentary by Dr. Valentin Fuster
2016;():V013T01A016. doi:10.1115/IMECE2016-65487.

For the dynamic analysis of thin plate bending problems, the Finite Element Methods (FEMs) are the most commonly used numerical techniques in engineering. However, due to the deficiency of low computing efficiency and accuracy, the FEMs can’t be directly used to effectively evaluate dynamic analysis of thin plate with high modal density within low-high frequency domain. In order to solve this problem, the Wavelet Finite Element Methods (WFEMs) has been introduced to solve the problem by improving the computing efficiency and accuracy in this paper. Due to the properties of multi-resolution, the WFEMs own excellently high computing efficiency and accuracy for structure analysis. Furthermore, for the destination of predicting dynamic response of thin plate within high frequency domain, this paper introduces the Multi-wavelet element method based on c1 type wavelet thin plate element and a new assembly procedure to significantly promote the calculating efficiency and accuracy which aim at breaking up the limitation of frequency domain when using the existing WFEMs and traditional FEMs. Besides, the numerical studies are applied to certify the validity of the method by predicting state response of thin plate within 0∼1000Hz based on a special numerical example with high modal density. According to the literature, the frequency domain between 0 to 1000Hz contains the low-high frequency domain aiming at the numerical example. The numerical results show excellent agreement with the reference solutions captured by FEM and analytical expressions respectively. Among these, it is noteworthy that the relative errors between the analytical solutions and numerical solution are less than 0.4% when the dynamic response involved with 1000 modes.

Commentary by Dr. Valentin Fuster
2016;():V013T01A017. doi:10.1115/IMECE2016-65500.

The tire/road interaction process results in generation of noise, which is transmitted and audible in the inside and outside of the car. In the recent years, the structural-borne noise in a tire has been extensively studied. However, very few studies have been conducted on air-borne noise. Various studies and indoor experimental measurements suggest that among all air-borne tire noise mechanisms, air-pumping mechanisms, i.e. rapid displacement of air near the tire/road contact patch, is the dominant source of noise for certain tires and operating conditions. This research focuses on studying air-pumping mechanisms and uses a previously developed computational model to predict air-borne noise generated using a hybrid approach. The basis of the hybrid approach is a direct prediction of near-field solution using compressible Navier-Stokes equations with turbulence modeling, combined with an analytical prediction of far-field acoustics using an acoustic model. Only the near-field acoustic characteristics are discussed in this paper. The tire rotation and groove deformations at the tire/road contact is modeled through mesh motion and prescribed deformation functions, thereby circumventing the need for coupling with a structural solver for fluid-structure interactions. The capability of the developed computational model in estimating the tire noise is shown and the effects of varying different parameters such as tire speed and geometry on the evolution of the estimated responses at various near-field receiver locations are studied.

Commentary by Dr. Valentin Fuster
2016;():V013T01A018. doi:10.1115/IMECE2016-65567.

This paper examines an approach to determining the entropy of coupled oscillators that does not rely on the assumption of weak coupling. The results of this approach are compared to the results for a weakly coupled system. It is shown that the results from each methodology agree in the case of weak coupling, and that a correction term is required for moderate to strong coupling. The correction term is shown to be related to the mixed energy term from the coupling spring as well as the geometry and stiffness of the system. Numerical simulations are performed for a symmetric system of identical coupled oscillators and an asymmetric system of nonidentical oscillators to demonstrate these findings.

Topics: Entropy
Commentary by Dr. Valentin Fuster

Acoustics, Vibration, and Wave Propagation: Phononic Crystals and Metamaterials

2016;():V013T01A019. doi:10.1115/IMECE2016-66169.

In this work, we consider elastic wave prorogation in deformable microstructured materials. In particular, we focus on the influence of externally applied deformation on the acoustic characteristic of periodic layered phononic crystals. Based on an analytical solution for the finitely deformed layered media, an analysis of the superimposed on the finitely deformed state small amplitude motions is performed. The analysis provides the information about the important acoustic characteristics such as phase and group velocities, illustrated by the slowness and energy curves. The influence of deformation on these characteristics of phononic crystals is investigated, showing the strong tunability of the phononic crystals by applied deformations.

Commentary by Dr. Valentin Fuster
2016;():V013T01A020. doi:10.1115/IMECE2016-66359.

Metamaterials demonstrate unique frequency dependent responses due to the presence of internal resonators; hence, it can be used to filter, absorb, cloak, or otherwise manipulate waves in unique ways. However, its applicability is normally limited to a very narrow frequency range (bandwidth) due to a dependency on linear resonance. The applications of these linear metamaterials are limited when used under the broadband excitation spectra that are common in real life applications. This paper numerically investigates the effect of introducing the two main classes of Duffing type cubic nonlinearities, namely monostable and bistable, on the attenuation bandwidth of an elasto-dynamic metamaterial.

From the analysis, it is found that the attenuation bandwidth of a bistable nonlinear system is two to three times wider than that of an equivalent linear system; whereas, in case of a monostable system the bandwidth is remained same. In both cases, the attenuation bandwidth shifts towards the higher end of the frequency spectra and for higher nonlinearity and excitation amplitude, second transmission zone completely vanishes.

Commentary by Dr. Valentin Fuster
2016;():V013T01A021. doi:10.1115/IMECE2016-66928.

The numerical modeling of phononic crystals using the finite element method requires a mesh that accurately describes the geometric features. In an optimization setting, involving shape and/or topological changes, this implies that a new matching mesh needs to be generated in every design iteration. In this paper a mesh-independent description for both the interior and exterior boundaries of the periodic unit cell is proposed. A method is developed to apply Bloch-Floquet periodic boundary conditions to edges that are non-matching to the mesh. The proposed method is applied to a one-dimensional phononic crystal and is demonstrated to exhibit improved performance over the commonly used interface material averaging. We show that this method provides an accurate mesh-independent model.

Commentary by Dr. Valentin Fuster
2016;():V013T01A022. doi:10.1115/IMECE2016-67036.

The idea to use metamaterials to mitigate mechanical waves is recent and constitutes a technology under development. These materials have a special design, presenting characteristics not found in nature. The interesting feature is a negative effective mass density. This property is achieved by creating in the structure masses linked by springs which act as internal resonators and, as a result, it is observed that metamaterials act as mechanical filters, preventing or reducing the intensity of propagation of mechanical waves that travel in the structure, when the frequency of propagation is close to the resonance frequencies of the internal resonators.

An internal combustion generates a blast wave which acts on a structure as an impulsive effort. This is a basic phenomenon in the shooting of an armament leading to this research that target to investigate the possible application of metamaterials to improve recoil mechanism technology. A recoil mechanism moderates the firing loads on the supporting structure by prolonging the time of resistance to the propellant gas forces. Depending on application of the armament, recoil can be very undesirable. Firstly, carriage mount where the armament is fixed will suffer premature wear. Secondly and more critical, if the armament is mounted onto a vehicle, its dynamics during shooting is completely affected and an accident can be caused when shooting occurs during a critical situation, like a curvilinear path for example.

It is intended to use numerical simulations and experimental validation to verify the behavior of the designed metamaterial under a controlled impulse input. Finite Element Method (FEM) is used to simulate wave propagation through a common material and then through a special designed metamaterial to evaluate how this kind of pulse will be affected by internal resonators. After the simulations, a prototype adequate to validate numerical results will be investigated on a test bench. In a further development the impulse input will be adapted to real measured blast efforts.

Topics: Stress , Waves , Metamaterials
Commentary by Dr. Valentin Fuster
2016;():V013T01A023. doi:10.1115/IMECE2016-67140.

Acoustic metamaterials have received much attention recently. In the past decades, countless structures have been studied for their novel physical phenomenon or potential applications. The goals of many of the works were to explore ways to enlarge the band gap, lower the band gap frequency, and/or generate greater attenuation of vibration. However, most of the work was limited to simulation, with experimental studies rarer. In this work, we would like to experimentally present the transmission spectrum of an acoustic metamaterial with a proposed structure called the coated double hybrid lattice (CDHL) [1]. The CDHL has both crystalline structure and local resonators, which provide high-frequency and low-frequency band gaps, respectively. A structure was fabricated and tested to experimentally determine the transmission spectrum. Both, a higher frequency band gap and a lower frequency band gap, were obtained. Vibration is clearly attenuated in the frequency range of 70–90 kHz. This is due to the Bragg scattering effect. At the same time, around the frequency of 4.8kHz, another band gap is observed which is attributed to local resonance. It turns out that our experimental results coincide with our previous simulation quite well.

Commentary by Dr. Valentin Fuster

Acoustics, Vibration, and Wave Propagation: Structural-Acoustic System Identification

2016;():V013T01A024. doi:10.1115/IMECE2016-66807.

There is an increasing interest towards the use of non-conventional material such as Functionally Graded Materials (FGM) for aerospace and automotive mechanical applications. Classical material models, e.g. Kelvin or Zener, can show some limitations in describing the viscoelastic behavior of these materials. A numerical and experimental approach to identify the optimal model order and the parameters of the constitutive material relationship in the frequency domain is proposed. The constitutive equation is modeled by means of a generalized Kelvin model and expressed in the form of a rational function. To describe the complex material behavior, high order polynomials are needed for the rational function and the problem of finding the function coefficients can be ill-conditioned. Different approaches for the rational function parameters identification are compared. A least square error identification technique adopting Forsythe orthogonal polynomials is proposed. The selected procedure is first applied on numerically estimated measurements with noise, and then on real measurement data obtained by forced vibration testing of Polytetrafluoroethylene specimens.

Commentary by Dr. Valentin Fuster
2016;():V013T01A025. doi:10.1115/IMECE2016-67303.

A system identification method for estimating natural frequencies is proposed. This method developed based on the stochastic subspace identification method can identify modal parameters of structures in operating conditions with harmonic components in excitation. It benefits wind turbine tower structural health assessment because classical operational modal analysis methods can fail as periodic rotation excitation from a turbine introduces strong harmonic disturbance to tower structure response data. The effectiveness, accuracy and robustness of the proposed method were numerically investigated and verified through a lumped-mass system model.

Commentary by Dr. Valentin Fuster
2016;():V013T01A026. doi:10.1115/IMECE2016-67463.

Modal testing is being investigated as a non-destructive test (NDT) method for wood poles. Modal properties of the pole must be extracted from sensor data containing frequency content associated with the interaction of the pole with its conductors. A dynamic model of a utility pole with attached conductors has been developed and validated through experimentation. The model will allow controlled, repeatable simulations of modal hammer hits for preliminary verification of pole property identification methods. The cable is modeled as a series of point masses connected by translational springs. The pole is represented by a modal expansion based on separation of variables. To facilitate creating and connecting the pole and cable models, scaling the model to represent longer pole lines, and introducing modal hammer inputs; the bond graph formalism was employed. To validate the model, an instrumented reduced-scale pole and cable system was built and tested in the laboratory. Time series measurements of cable tension and transverse motion, along with frequency-domain accelerometer data, show that the simulation model has sufficient fidelity to predict the effect of conductors on a pole’s response spectrum over the frequency range of interest.

Commentary by Dr. Valentin Fuster

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