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ASME Conference Presenter Attendance Policy and Archival Proceedings

2018;():V011T00A001. doi:10.1115/IMECE2018-NS11.
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This online compilation of papers from the ASME 2018 International Mechanical Engineering Congress and Exposition (IMECE2018) 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presenter attendance policy, if a paper is not presented at the Conference by an author of the paper, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.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 Phononics: Computational Acoustics

2018;():V011T01A001. doi:10.1115/IMECE2018-86795.

The paper presents a new solution for the wind turbine profile shape modeling based on the concept of the maximum lift force, capable to be produced at different values of the wind velocities. The profile is designed and realized in accordance with the new concept emerged in the last decade, on the operation of the wind turbines with maximum lifting force. The purpose is to provide a low-noise during operation because a negative effect on the medium and long-term operation of the wind turbines (wind farms) is the noise that affects the flight of birds, terrestrial animal life, and especially human communities. Various sources generate independent acoustic emissions on wind profiles, such as the turbulent flow, the interaction of the turbulent boundary layer area of the trailing edge, the flow separation, and the boundary layer separation of vortices formed in the zone of the trailing edge. There is also considered the influence of the apparent wind on the incidence variation of the profile. In order to maintain an optimum angle of attack relative to the wind velocity, a fixed blade inclination must increase its speed to be proportional to the wind. Thus, to maximize the aerodynamic performance, the rotor must spin faster when the wind intensity increases. Measurement of the acoustic signal requires electronic devices that operate on electric signals obtained from the conversion of the pressure variations in voltage or variations in electrical current. The noise caused by the turbulent flow is generated primarily by the sharply pointed leading edge and cannot be diminished. There are presented some numerical results correlated with the measurements made in the field.

Commentary by Dr. Valentin Fuster
2018;():V011T01A002. doi:10.1115/IMECE2018-86873.

The pressure fluctuation over the fan blades can generate unpleasant noises that affect the fan performance. Therefore, the noise control is considered as a significant factor in the design process. The purpose of this study is to estimate the total acoustic power of the surface on a cooling fan as a key function to improve design parameters.

The design process of a cooling fan to achieve low acoustic power can be lengthy and expensive through prototyping and experiments. The Mesh Morpher Optimizer (MMO) in ANSYS Fluent in coupling with the Powell’s model was applied to estimate the acoustic power over a cooling fan surface at a low speed. The Powell’s model in ANSYS was proved successfully in reducing the total acoustic power on the surface of the cooling fan which is shown by the numerical results. Comparison of the base model and Powell’s model, the Acoustic Power Level was reduced from 23.68 to 21.69 dB. The Surface Acoustic Power Level dropped from 62.24 to 61.26 dB. Likewise, the Surface Acoustic Power decreased from 9.67e−5 to 5.24e−5 W/m2. Also, the contour visualization results verified the success of the Powell’s model in combination of the Mesh Morpher Optimizer (MMO) to evaluate the total acoustic power and propose a new model that will assist in the design process in minimizing the manufacturing process of a new design model.

Topics: Cooling , Acoustics
Commentary by Dr. Valentin Fuster

Acoustics, Vibration, and Phononics: Congress-Wide Symposium on NDE and SHM: Acoustic and Vibration Methods in Structural Health Monitoring and Nondestructive Testing

2018;():V011T01A003. doi:10.1115/IMECE2018-87476.

Rotors have wide applications in several aerospace and industrial heavy-duty systems. In most of these applications, the rotating system reaches its steady state operational speed after the passage through at least one of its critical rotational speeds. In real-life applications, the probable appearance of a residual slight unbalance in the system could cause an elevation in vibration amplitudes at the critical rotational speeds. Accordingly, propagation of cracks in rotating shafts usually influences the level of these vibration amplitudes during start-up and cost-down operations. For such rotating systems, the critical whirl speeds are usually associated with forward and backward whirl responses where it has been always assumed that the backward whirl zone should precede the forward whirl zone. Here, two configurations of cracked rotor-disk systems are considered to study the effect of the angular acceleration and the unbalance force vector orientation with respect to the crack opening direction on the whirl response at the backward whirl zone of rotational speeds. The obtained numerical simulation results are verified through a robust experimental testing for system startup operations. The backward whirl zone is found here to appear immediately after the passage through the critical forward whirl rotational speed. The onset of the backward whirl is also found to be associated with a sharp drop in vibration whirl amplitudes. This backward whirl zone is found to be significantly affected by the unbalance force angle vector orientation and the shaft angular acceleration. More importantly, this zone of backward whirl orbits is not found to be preceding the critical forward whirl zone for the considered cracked shaft-disk configurations.

Topics: Rotors , Whirls
Commentary by Dr. Valentin Fuster

Acoustics, Vibration, and Phononics: Congress-Wide Symposium on NDE and SHM: Ultrasonic Waves for Material Characterization and Damage Assessment

2018;():V011T01A004. doi:10.1115/IMECE2018-87910.

The structural health monitoring by piezoelectric wafer active sensor (PWAS) using electromechanical impedance method used for monitoring of structure. In present work impedance method of elasto-plastic beam structure is studied. In order to model the effect of a plastic in beam, the moment-curvature relationship for elasto-plastic region for loading and unloading is used. The finite difference method is used to discretize beam with piezoelectric. The piezoelectric actuator is modeled by equivalent moment. Then output current of piezoelectric sensor is calculated. Firstly, elastic modeling of beam is considered that this is leads to linear system equation. In linear system, time domain system equations are calculated and Fourier transform of current output obtained, and then impedance of PWAS in frequency domain is calculated. Secondly, the elasto-plastic of beam is modeled. This phenomenon leads to the nonlinear system equations. These nonlinear equations are solved using finite difference method for any harmonic voltage applied to actuator. Then impedance of PWAS is calculated. Two methods are used to detect elasto-plastic modeling on PWAS impedance. At the first, frequency response of elastic beam as intact model is compared with elasto-plastic results in a desired frequency range. Second, only frequency response of one harmonic is computed with its super-harmonics. Finally, the detection method of linear is compared with nonlinear model.

Commentary by Dr. Valentin Fuster

Acoustics, Vibration, and Phononics: Flow-Induced Acoustics and Human Perception of Noise

2018;():V011T01A005. doi:10.1115/IMECE2018-86303.

In recent years it has been discovered that besides non-uniform flow excitation such as from stator wakes; acoustic pressure pulsation can be a concern, especially for high pressure centrifugal compressor impellers. This has been termed “triple coincidence” and explains rare failures and likely a reason, at least partially, for some previous undocumented failures. Bladed disk interaction resonance discovered by the author in the mid 1970’s can be avoided such as for centrifugal impellers as needed, depending on vibratory mode involved, available damping, and potential excitation level. Especially for stages having vanes in the diffuser near impeller tips, concern for high cycle fatigue is very high as certain numbers of vanes combined with number of rotating blades can give correct phase to excite a highly responding mode. Intentional mistuning of disk-dominated modes has potential for reducing response. A similar but more complex interaction is with transverse acoustic modes having a specific number of nodal diameters. In this case acoustic gas modes in cavities at sides of impellers can match rotating acoustic pulsations at BPF (blade passing frequency) and/or harmonics, termed Tyler-Sofrin modes with increased noise. Also acoustic mode matching impeller structural mode can give the triple coincidence causing resonant response of the impeller. The concern for this coincidence is often difficult to evaluate. For some cases, calculations give enough evidence to modify number of vanes or blades to correct a possible cause of a fatigue failure. This coincidence can add to the direct response, e.g. from either upstream wakes or downstream diffuser vane interacting “potential flow” excitation, herein termed “quadruple coincidence resonance”. Dimensions of impeller side cavities are axisymmetric and are set by aerodynamics, so that outer and inner radii define transverse modes with small radial dimensional changes available. Often a minor aerodynamic performance compromise can be used to change designs to avoid serious resonances, e.g. revise numbers of vanes and/or blades, avoid the response of a matching diameter mode or have a different less responsive mode to alleviate concern. Besides turbomachinery e.g. compressors and pumps, some other methods as described could be utilized for any cavity that has diametrical mode shapes, or possibly other patterns for pressure pulsation frequencies. These modification(s), including patent-pending method, PCT/US2018/020880 described herein can alleviate if not eliminate concern for any mechanism having structural vibration excitation and/or environmental noise issues.

Commentary by Dr. Valentin Fuster
2018;():V011T01A006. doi:10.1115/IMECE2018-87716.

Deep surge is a violent fluid instability that occurs within turbomachinery compression systems and limits the low-flow operating range. It is characterized by large amplitude pressure and flow rate fluctuations, where the cross-sectional averaged flow direction alternates between forward and reverse. When a compressor transitions into deep surge, the time-averaged compressor outlet pressure and temperature decrease and increase, respectively, along with a drastic rise in narrowband, low-frequency noise.

The present study includes both measurements and predictions from a turbocharger centrifugal compressor installed on a gas stand. The compressor breathes air from ambient through an inlet duct with a bellmouth opening. The downstream compression system consists of a compressor outlet duct attached to a plenum with increased cross-sectional area, and an additional duct that connects the plenum outlet to a control valve. A detailed three-dimensional (3D) computational fluid dynamics (CFD) model of this compression system was constructed to carry out unsteady surge predictions. The results included here capture the transition from mild to deep surge, as the flow rate at the outlet boundary (valve) is reduced. During this transition, the amplitude of pressure and flow rate fluctuations greatly increase until they reach a repeating cyclic structure characteristic of deep surge. During the deep surge portion of the prediction, pressure fluctuations are compared with measurements at the corresponding compressor inlet and outlet transducer locations, where the amplitudes and frequency exhibit excellent agreement.

The predicted flow-field throughout the compression system is studied in detail during operation in deep surge, in order to characterize the unsteady and highly 3D structures present within the impeller, diffuser, and compressor inlet duct. Key observations include a core flow region near the center of the inlet duct, where the flow remains in the forward direction throughout the deep surge cycle. The dominant noise generation occurs at the fundamental surge frequency, which is near the Helmholtz resonance of the compression system, along with harmonics at integer multiples of this fundamental frequency.

Commentary by Dr. Valentin Fuster
2018;():V011T01A007. doi:10.1115/IMECE2018-88717.

This paper experimentally investigates the performance of a long smooth seal (length-diameter ratio L/D = 0.65 and radial clearance Cr = 0.140 mm) under laminar flow conditions. Tests are carried out at shaft speeds ω up to 10 krpm, pressure drops PD up to 48.3 bars, exit pressure Pe = 6.9 bars, and inlet temperature Ti = 39.4 °C. The seal is centered. Since there is no validated friction formula published for a liquid seal in the transitional regime, this paper uses San Andrés’s bulk-flow model with laminar-flow friction formula to produce predictions. Test results show that under laminar flow conditions, increasing ω decreases measured direct stiffness K, increases measured cross-coupled stiffness k, barely changes measured direct damping C, and generally increases measured cross-coupled damping c. The model correctly predicts these trends, and the predictions of K, k, C, and c are reasonably close to test results. Measured direct virtual-mass M values are normally larger than predictions.

This paper also judges two cases with high PD or high ω to be in the transitional regime. For these cases, the predictions of K, k, C, and c based on the laminar-flow friction formula are significantly different from test results. This discrepancy further strengthens the judgment that the flow in these cases is transitional.

For all test cases, measured leakage mass flow rate and measured effective damping Ceff are not sensitive to changes in ω, but increase as PD increases. The model with the laminar-flow friction formula adequately predicts and Ceff even when the flow within the seal annulus is at the start of the transitional flow regime. Also, Ceff predictions are lower than test results, allowing a safe margin for the pump design.

Topics: Laminar flow , Leakage
Commentary by Dr. Valentin Fuster

Acoustics, Vibration, and Phononics: General Noise and Vibration Control

2018;():V011T01A008. doi:10.1115/IMECE2018-86955.

The involute spur gear system has been widely utilized in the mechanical transmission domain, and the control of the acceleration noise of the involute spur gear system has become the key technology to solve the NVH performance of the power transmission system, especially in the automobile industry. In the process of the gear meshing, the unavoidable acceleration noise of the involute spur gear system is mainly caused by the meshing stiffness and error excitation due to the structural parameters. Therefore, the investigation on the effects of structure parameters on acceleration noise of the involute spur gear system is necessary.

In this paper, the numerical model for predicting the acceleration noise of the involute spur gear system has been established. The simulation results of the acceleration noise were compared with the experimental results, and the errors between these two results were only 2.9%, within permission.

The effects of structure parameters including base pitch error and pressure angle on the acceleration noise of the involute spur gear system have been discussed. Results showed that increasing the base pitch error, the acceleration noise level of the involute spur gear increased, and the gap of the noise level between different base pitch errors narrowed according to the increase of gear load and rotation speed. Increasing the pressure angle also increased the acceleration noise level, however, the gap between different pressure angles remained the same regardless the variations of gear load and rotation speed, which was different than the variations of base pitch error.

Commentary by Dr. Valentin Fuster
2018;():V011T01A009. doi:10.1115/IMECE2018-86983.

This paper proposes an improved optimal adaptive control algorithm to accelerate convergence for sine control of general multichannel coupled system, as well as enhance the stability. First of all, the convergence of traditional multi-input multi-output (MIMO) sine control method is analytically investigated in the presence of frequency response function (FRF) error. Then, the controller with the improved optimal adaptive control algorithm is developed, where a high-precision algorithm for amplitude and phase estimation is proposed to guarantee the accuracy of the response vector calculation. Numerical simulation results show that the proposed method possess excellent performance with fast convergence rate and strong robustness.

Commentary by Dr. Valentin Fuster
2018;():V011T01A010. doi:10.1115/IMECE2018-87011.

While driving a FCV during acceleration, many sorts of sounds could be heard, which influence the interior sound quality. A typical FCV is taken as a sample, four interior noises generated under the acceleration operation are collected in the whole vehicle semi-anechoic chamber, and the noise sample database of diesel engine radiation noise is established after preprocessing. Based on sound quality theory (physical and psychoacoustic features), the Kernel Principal Component Analysis (KPCA) is used to extract the key objective features mainly influencing the sound quality, which realize the dimension reduction target; the variations of objective features are analyzed to qualitatively analyze the law of the sound quality varying during acceleration. According to the objective evaluation of FCV interior sound quality, combining with FCV operating parameters, the influencing law of the FCV sound quality could be obtained.

Topics: Sound quality
Commentary by Dr. Valentin Fuster
2018;():V011T01A011. doi:10.1115/IMECE2018-87189.

Due to the stricter roles of the government and the higher requirement of a comfortable automobile, the NVH (Noise Vibration and Harshness) performance of vehicles has become one of the most important traits at the automobile market. Considering the cost, it is more economical and practical to improve the NVH performance by using the vibration-isolating or noise-reducing materials. Vibration damping alloy as one of the new material has a promising prospect due to its great damping characteristics.

In this paper, the vibration-isolating and noise-reducing performances of the vibration damping alloy have been experimentally investigated in a semi-anechoic room. Frequency response function test has been carried with the test rod made of vibration damping alloy and 45 steel to calculate the damping ratio of the two materials based on the half-power bandwidth method. The radiation noise characteristics of the two test rods under different excitation forces have also been evaluated.

Conclusions drawn from the experiment suggested that the damping ratio of 45 steel rod were 0.0125 in vertical axial direction and 0.0165 in axial direction. While, the damping ratio of vibration damping alloy rod were 0.0236 in vertical axial direction and 0.0234 in axial direction, 89% and 42% higher than the 45 steel sample, respectively. With the increase of the exciting force, the radiation noise increased for both two materials, and the radiation noise level of the vibration damping alloy rod was much lower than 45 steel rod. And the difference between these two materials remained unchanged with the increase of exciting force. In addition, the duration of noise attenuation for vibration damping alloy rod was much shorter than the 45 steel.

Commentary by Dr. Valentin Fuster
2018;():V011T01A012. doi:10.1115/IMECE2018-87240.

This paper explores several definitions of entropy that stem from the fields of statistical mechanics and thermodynamics for vibrating structures. This paper shows that these definitions are equivalent in the context of mechanically vibrating systems. However, one is more suitable for statistical energy analysis. This work is motivated by the usefulness of the entropy concept towards developing a framework for the statistical treatment of vibroacoustic systems. Specifically, entropy provides a thermodynamic framework to justify the methodology of statistical energy analysis.

Topics: Entropy
Commentary by Dr. Valentin Fuster

Acoustics, Vibration, and Phononics: Phononic Crystals and Metamaterials

2018;():V011T01A013. doi:10.1115/IMECE2018-87398.

Sonic Crystals are noise barriers wherein the incident sound waves are scattered multiple times by the periodically arranged scatterers placed inside a host fluid. Used as sound attenuators, sonic crystals attenuate sound over frequency bands known as bandgaps. Broadening and lowering the bandgaps is the primary objective of this work. Effect of changing the shape, size and orientations of the scatterers on the band characteristics have been reported here. Different shapes of the scatterers are found to affect the band characteristics of the sonic crystals. Adding local resonance to the scatterers introduce a new attenuation mechanism due to local acoustic resonances. A new type of double circle split-ring resonator is also proposed which use acoustic resonance to produce additional bandgaps. Size and orientation of the scatterers are also found to affect the bandwidth and center frequency of the bandgaps. The band diagram, transmission loss, eigenmodes are computed using finite element method. COMSOL Multiphysics, a commercially available finite element software has been used to implement FEM and model the two-dimensional unit cells and the sonic crystal arrays. Due to the large difference in impedance of the steel scatterer embedded in air, the scatterers are assumed to be sound hard (sound rigid) which imposes a condition where normal component of acceleration is zero.

Topics: Crystals , Energy gap , Shapes
Commentary by Dr. Valentin Fuster
2018;():V011T01A014. doi:10.1115/IMECE2018-87749.

Various types of acoustic metamaterials have been developed to control the flow of acoustical energy through these materials. Most of these metamaterials are passive in nature with pre-tuned and fixed material properties. In this paper, the emphasis is placed on the development of a class of one-dimensional acoustic metamaterials with programmable densities in order to enable the control the acoustic wave propagation in these media. With such unique capabilities, the proposed active acoustic metamaterials (AAMM) can be utilized to physically realize, for example, acoustic cloaks, wave shifters and focusers, tunable acoustic absorbers and reflectors, as well as non-reciprocal acoustic media.

The theoretical analysis of this class of AAMM with programmable effective dynamical densities is presented for an array of cavities separated by piezoelectric boundaries. These boundaries provide means for controlling the stiffness of the individual cavity and, in turn, its dynamical densities. In this regard, a disturbance rejection strategy is considered which is based on an H-∞ robust controller. The time and frequency response characteristics of a unit cell of the AAMM are investigated for various parameters of the controller in an attempt to optimize the performance characteristics.

Extension of this study to include active control capabilities of the bulk modulus of the metamaterials would enable the development of wide classes of AAMM that are only limited by our imagination.

Commentary by Dr. Valentin Fuster
2018;():V011T01A015. doi:10.1115/IMECE2018-88254.

We derive formulas for the gradients of the total scattering cross section (TSCS) with respect to positions of a set of cylindrical scatterers. Providing the analytic form of gradients enhances modeling capability when combined with optimization algorithms and parallel computing. This results in reducing number of function calls and time needed to converge, and improving solution accuracy for large scale optimization problems especially at high frequencies and with a large number of scatterers. As application of the method we design acoustic metamaterial structure based on a gradient-based minimization of TSCS for a set of cylindrical obstacles by incrementally re-positioning them so that they eventually act as an effective cloaking device. The method is illustrated through examples for clusters of hard cylinders in water. Computations are performed on Matlab using parallel optimization algorithms and a multistart optimization solver, and supplying the gradient of TSCS.

Commentary by Dr. Valentin Fuster

Acoustics, Vibration, and Phononics: Structural-Acoustic System Identification

2018;():V011T01A016. doi:10.1115/IMECE2018-86506.

This study will focus on the detection of misfire using Acoustic emission sensor in a multi-cylinder diesel engine. Detection of misfire is important since this malfunction can cause the engine to stall in a short time. In order to investigate the misfire, an experimental engine was run with and without injection of the fuel in the first cylinder. The acoustic emission signal was acquired synchronously with the crank angle signal, in order to have a reference for the transformation from time to angular domain. The AE signal was then processed using the squared envelope spectrum to highlight angle-periodic modulations in the signal’s power (cyclic bursts). This study will present the effectiveness of this combination of sensor technology and signal processing to detect misfire in a six-cylinder diesel engine connected to a hydraulic dynamometer.

Commentary by Dr. Valentin Fuster
2018;():V011T01A017. doi:10.1115/IMECE2018-87061.

Nonlinear vibration of a simply-supported Euler-Bernoulli microbeam with fractional Kelvin-Voigt viscoelastic model subjected to harmonic excitation is investigated in this paper. For small scale effects the modified strain gradient theory is used. For take into account geometric nonlinearities the Von karman theory is applied. Beam equations are derived from Hamilton principle and the Galerkin method is used to convert fractional partial differential equations into fractional ordinary differential equations. Problem is solved by using the method of multiple scales and amplitude-frequency equations are obtained for primary, super-harmonic and sub-harmonic resonance. Effects of force amplitude, fractional parameters and nonlinearity on the frequency responses for primary, super-harmonic and sub-harmonic resonance are investigated. Finally results are compared with ordinary Kelvin-Voigt viscoelastic model.

Commentary by Dr. Valentin Fuster
2018;():V011T01A018. doi:10.1115/IMECE2018-88058.

A continuously scanning laser Doppler vibrometer (CSLDV) system is capable of efficient and spatially dense vibration measurements by sweeping its laser spot along a scan path assigned on a structure. This paper proposes a new operational modal analysis (OMA) method based on a data processing method for CSLDV measurements of a structure, called the lifting method, under white-noise excitation and applies a baseline-free method to identify structural damage using estimated mode shapes from the OMA method. The lifting method enables transformation of raw CSLDV measurements into measurements at individual virtual measurement points, as if the latter were made by use of an ordinary scanning laser Doppler vibrometer in a step-wise manner. It is shown that a correlation function with non-negative time delays between lifted CSLDV measurements of two virtual measurement points on a structure under white-noise excitation and its power spectrum contain modal parameters of the structure, i.e., natural frequencies, modal damping ratios and mode shapes. The modal parameters can be estimated by using a standard OMA algorithm. A major advantage of the proposed OMA method is that curvature mode shapes associated with mode shapes estimated by the method can reflect local anomaly caused by small-sized structural damage, while those estimated by other existing OMA methods that use CSLDV measurements cannot. Numerical and experimental investigations are conducted to study the OMA method and baseline-free structural damage identification method. In the experimental investigation, effects of the scan frequency of a CSLDV system on the two methods were studied. It is shown in both the numerical and experimental investigations that modal parameters can be accurately estimated by the OMA method and structural damage can be successfully identified in neighborhoods with consistently high values of curvature damage indices.

Commentary by Dr. Valentin Fuster

Acoustics, Vibration, and Phononics: Vibration and Acoustic Measurements, Signal Processing, and Test Facilities

2018;():V011T01A019. doi:10.1115/IMECE2018-86892.

In this paper, chaotic system is applied to identify and extract the weak signals of bearing early fault which are often submerged in strong background noise. Chaotic system is an effective method in weak signal detection because of its properties of noise immunity and sensitivity to the weak periodic signal. However, chaotic system is not completely immune to noise in critical chaotic state. Aiming at this problem, four indicators are used to evaluate the detection performance of Duffing oscillators. Then, the influence of Duffing oscillator parameters on the four indicators is studied in detail and a new method is proposed to improve the detection performance of Duffing oscillator. The simulation and experimental results show that the proposed method can accurately obtain the characteristic signals of early bearing fault in a lower signal-to-noise ratio (SNR) situation.

Topics: Bearings , Signals
Commentary by Dr. Valentin Fuster
2018;():V011T01A020. doi:10.1115/IMECE2018-87131.

For gas temperature measurements in stratospheric balloons, traditional methods of measuring gas temperature do not work well due to radiant heating and insufficient heat transfer. To measure the gas temperature several methods of acoustic temperature measurement are being developed. One of these methods is the pitch catch method. A perceived distance pitch catch method using an ultrasonic distance sensor was proposed and tested. However, at low pressures the density of air is too low to allow sound to propagate well. This means that at a certain pressure, the ultrasonic distance sensor will not receive a reflected sound with sufficient amplitude to calculate the apparent distance accurately. Tests were conducted in a high altitude chamber to determine the accuracy of temperature measurements and the fail pressure. It was determined that the optimum configuration for this device would not allow it to function at a sufficient altitude nor give the temperature accuracy required. An alternative timing method using a piezo speaker, electret microphone, and time of flight measurements was explored. The timing method achieved a detectable signal down to 1.0kPa. Further work is being done on the timing method to increase the accuracy of the device.

Topics: Temperature , Signals
Commentary by Dr. Valentin Fuster
2018;():V011T01A021. doi:10.1115/IMECE2018-87247.

Aero engine is essentially the heart of an airplane. However, the high temperature and high pressure working environment of the aero engine can easily lead to fatigue cracks in turbine disks, and result in serious accidents. Therefore, early disk crack diagnosis is very important to guarantee safe flight of the airplane and reduce its maintenance cost, which, however, is challenging due to the difficulty in building a complex physical model under variable operating speeds. To tackle this problem, a novel deep convolutional neural network (CNN)-based method is proposed for early disk crack diagnosis. CNN, as one of the deep learning structures, can learn deep-seated features directly and automatically from the raw data without the need of physical model or prior knowledge. It shows the potential to deal with the challenge of early disk crack diagnosis. Since the proposed diagnosis method is signal-level, the collected vibration signals can be input into the CNN architecture directly without the need of feature extractor. In this paper, the vibration signals at both the beginning and the end of the test are used for training the CNN model, then the rest signals are input into the trained model as test data to diagnose when the incipient disk crack is generated. Experimental study conducted on the fatigue test of a real turbine disk has proved the effectiveness and robustness of the proposed method for early disk crack diagnosis. Meanwhile, comparison study with some state-of-the-art methods is also performed, and further highlights the superiority of the proposed method.

Commentary by Dr. Valentin Fuster
2018;():V011T01A022. doi:10.1115/IMECE2018-87420.

Detection and location of leaks in buried plastic fluid-filled pipes are topics of increasing concern for water distribution companies. Acoustic correlation techniques have been widely used to provide an accurate estimate of the position of a leak in order to reduce the wastage of water. However, this technique depends on an accurate estimate of the wave propagation speed along the pipe, which is heavily dependent on the type of soil in which the pipe is buried. The soil also affects the distance that leak noise will propagate along the pipe. This paper describes theoretical and experimental investigations into the way the coupling conditions between the pipe and the soil affects the propagation characteristics of the wave that propagates leak noise in the pipe. Two water pipe systems which have different soil properties are considered: one is in Brazil and the other one is in UK. For the Brazilian pipe system, it is found that the shear modulus rather than the bulk modulus of the soil, has a profound effect on the wave motion in the pipe since it is buried in a clay-like soil. In this case, only the shear wave in the soil propagates away from the pipe. For the UK pipe system, which has sandy soil, both compressional and shear waves propagate away from the pipe. An analysis of the physical effects of fluid-pipe-soil interface and their corresponding parameters on the pipe wave speed and attenuation is also carried out. The results show that the axial coupling between the pipe and the soil has an important effect in the UK pipe system, but has a negligible effect in the Brazilian pipe system.

Commentary by Dr. Valentin Fuster
2018;():V011T01A023. doi:10.1115/IMECE2018-87480.

Aircraft engines, aerospace rotating equipment, gas turbines, compressors, and rotors in several industrial and aerospace applications approach their nominal operational speeds after the passage through at least one of their critical rotational speeds. During the passage through the critical speeds, elevation in vibration amplitudes is usually observed due to the effect of residual unbalance in these real-life applications rotors. In all of the reported literature, the theoretical and numerical simulation results and the related Campbell diagrams suggest that the backward whirl (BW) zone should precede the passage through the critical forward whirl (FW) speed/speeds of such systems. Here, the existence of zones of rotational speeds at which BW orbits are expected to appear will be investigated immediately before and after the passage through the critical FW speed. Accordingly, startup operations of two different configurations of crack-free rotor-disk systems are considered in this numerical and experimental study. It is found out that there exist zone/zones of the shaft rotational speeds at which BW orbits are experimentally captured where these zones are localized immediately after the passage through the critical FW rotational speed during the startup operations. These BW zones are strongly affected by the acceleration of the shaft during the transient startup operations. These findings suggests that the BW should not necessarily precede the critical FW speed as suggested by the related Campbell diagrams.

Topics: Rotors
Commentary by Dr. Valentin Fuster
2018;():V011T01A024. doi:10.1115/IMECE2018-87535.

This paper presents the free vibration analysis of a sandwich beam with a tip mass using higher order sandwich panel theory (HSAPT). The governing equations of motion and boundary conditions are obtained using Hamilton’s principle. General Differential Quadrature (GDQ) is employed to solve the system governing equations of motion. The natural frequencies and mode shapes of the system are presented and Ansys simulation is performed to validate the results. Various boundary conditions are also employed to examine the natural frequencies of the sandwich beam without tip mass and the results are compared with those found in the literature. Parametric studies are conducted to examine the effect of key design parameters on the natural frequencies of the sandwich beam with and without tip mass.

Topics: Free vibrations
Commentary by Dr. Valentin Fuster
2018;():V011T01A025. doi:10.1115/IMECE2018-87757.

Microwave-induced Thermoacoustics (TA) sensing has the potential to be a breakthrough in subsurface imaging applications. This is because it combines the advantages of high contrast of microwave imaging and high resolution of ultrasound imaging. However, state-of-the-art TA hardware requires that the receiving transducer is scanned in a linear or rotational fashion in order to be able to collect enough orthogonal data needed to produce a TA image possessing high-spatial resolution both in range and cross-range. This process is slow, increases the detection time, and adds an extra complexity to the system. In order to address these problems, a Compressive Sensing (CS) methodology is presented in this paper as a mechanism to reduce the minimum number of data samples required to reconstruct a sparse signal. Furthermore, in order to reduce the mutual information shared by different measurements, a holey cavity structure is proposed to be used to perform 4D coding. In this work, the TA imaging theory is introduced; and the impact that the holey cavity parameters have in the imaging performance is studied. The imaging results in this work are carried out using a distributed Alternating Direction Method of Multipliers (ADMM) algorithm, capable of using norm-1 and norm-2 regularizers; and they reveal the effectiveness of the proposed holey-cavity and CS TA imaging approach.

Commentary by Dr. Valentin Fuster
2018;():V011T01A026. doi:10.1115/IMECE2018-88011.

Acoustic metamaterials have been proposed for numerous applications including subwavelength imaging, impedance matching, and lensing. Yet, their application in compressive sensing and imaging has not been fully investigated. When metamaterials are used as resonators at certain frequencies, they can generate random radiation patterns in the transmitted and received waves to and from a target. Compressive sensing favors such randomness inasmuch as it can increase incoherence by decreasing the amount of mutual information between any two different measurements. This study aims at assessing whether the use of resonating metamaterial unit cells in a single-layered array between a number of ultrasound transceivers and targets can improve the sensing capacity, point-spread function of the sensing array (their beam focusing ability), and imaging performance in pointlike target detection. The theoretical results are promising and can open the way for more efficient metamaterial designs with the aim of enhancing ultrasound imaging with lower number of transceivers compared to the regular systems.

Commentary by Dr. Valentin Fuster
2018;():V011T01A027. doi:10.1115/IMECE2018-88028.

Compressive sensing (CS) theory states that, if certain conditions are met, a signal can be retrieved at a sampling rate that is lower than what Nyquist theorem requires. Among these conditions are the sparsity of the signal and the incoherence of the sensing matrix, which is constructed based on how the sensing system is designed. One effective method to render the sensing matrix incoherent is to use random processes in its construction. Diverse approaches have been proposed to randomize the sensing matrix including transmission at random transmitter positions and spectral coding with the use of a physical structure that responds very differently at disparate frequencies. In this work, a holey cavity with various frequency modes is used to spectrally code the ultrasound wave fields. Then, with the use of CS theory and simulations, it is shown that the sensing system that is equipped with such a cavity performs meaningfully better than a regular system in terms of sensing capacity, beam focusing, and imaging. What is more, the validity of Born approximation is investigated in this work to show its extent of applicability in imaging relatively small targets. Due to computational limitations, the simulation domain has been selected to be comparatively small; yet, the achieved results evidently show the concept and warrant further studies on holey cavities in ultrasound imaging, including their fabrication and experimental corroboration. The decrease in the number of measurements necessary for correct image reconstruction can make ultrasound sensing systems more efficient in size and scan time in a variety of applications including medical diagnosis, non-destructive testing, and monitoring.

Commentary by Dr. Valentin Fuster

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