Current Issue : January - March Volume : 2017 Issue Number : 1 Articles : 5 Articles
In this paper, we have developed a new thermoacoustic model for predicting the resonance\nfrequency and quality factors of one-dimensional (1D) nanoresonators. Considering a nanoresonator\nas a fix-free Bernoulli-Euler cantilever, an analytical model has been developed to show the influence\nof material and geometrical properties of 1D nanoresonators on their mechanical response without\nany damping. Diameter and elastic modulus have a direct relationship and length has an inverse\nrelationship on the strain energy and stress at the clamp end of the nanoresonator. A thermoacoustic\nmultiphysics COMSOL model has been elaborated to simulate the frequency response of vibrating 1D\nnanoresonators in air. The results are an excellent match with experimental data from independently\npublished literature reports, and the results of this model are consistent with the analytical model.\nConsidering the air and thermal damping in the thermoacoustic model, the quality factor of a\nnanowire has been estimated and the results show that zinc oxide (ZnO) and silver-gallium (Ag2Ga)\nnanoresonators are potential candidates as nanoresonators, nanoactuators, and for scanning probe\nmicroscopy applications....
Acoustic Emission (AE) monitoring can be used to detect the presence of damage as well\nas determine its location in Structural Health Monitoring (SHM) applications. Information\non the time difference of the signal generated by the damage event arriving at different\nsensors in an array is essential in performing localisation. Currently, this is determined\nusing a fixed threshold which is particularly prone to errors when not set to optimal\nvalues. This paper presents three new methods for determining the onset of AE signals\nwithout the need for a predetermined threshold. The performance of the techniques is\nevaluated using AE signals generated during fatigue crack growth and compared to the\nestablished Akaike Information Criterion (AIC) and fixed threshold methods. It was found\nthat the 1D location accuracy of the new methods was within the range of< ââ?¬â?? 1 7.1% of the\nmonitored region compared to 2.7% for the AIC method and a range of 1.8ââ?¬â??9.4% for the\nconventional Fixed Threshold method at different threshold levels....
The procedures used to estimate structural modal parameters as natural frequency, damping ratios, and mode shapes are generally\nbased on frequency methods. However, methods of time-frequency analysis are highly sensible to the parameters used to calculate\nthe discrete Fourier transform: windowing, resolution, and preprocessing. Thus, the uncertainty of the modal parameters is\nincreased if a proper parameter selection is not considered. In this work, the influence of three different time domain windows\nfunctions (Hanning, flat-top, and rectangular) used to estimate modal parameters are discussed in the framework of ISO 18431\nstandard. Experimental results are conducted over an AISI 1020 steel plate, which is excited by means of a hammer element.\nVibration response is acquired by using acceleration records according to the ISO 7626-5 reference guides.Theresults are compared\nwith a theoretical method and it is obtained that the flat-top window is the best function for experimental modal analysis....
In X-ray tomography, the Fourier slice theorem provides a relationship between the\nFourier components of the object being imaged and the measured projection data.\nThe Fourier slice theorem is the basis for X-ray Fourier-based tomographic inversion\ntechniques. A similar relationship, referred to as the ââ?¬Ë?Fourier shell identityââ?¬â?¢ has been\npreviously derived for photoacoustic applications. However, this identity relates the\npressure wavefield data function and its normal derivative measured on an arbitrary\nenclosing aperture to the three-dimensional Fourier transform of the enclosed object\nevaluated on a sphere. Since the normal derivative of pressure is not normally measured,\nthe applicability of the formulation is limited in this form. In this paper, alternative\nderivations of the Fourier shell identity in 1D, 2D polar and 3D spherical polar coordinates\nare presented. The presented formulations do not require the normal derivative\nof pressure, thereby lending the formulas directly adaptable for Fourier based absorber\nreconstructions....
This paper shows the results of a study conducted on five different categories of vehicles in a specific test site. The aim was to\ninvestigate how the effect of the test site discontinuity determines variations of comfort related to the increase in speed and to the\nfive selected road vehicles of different classes. Measurements were obtained by combining data relating to vibrations in the three\nreference axes, detected through a vibration dosimeter (VIB-008), and geolocation data (latitude, longitude, and speed) identified\nby the GPS inside a smartphone. This procedure, through the synchronization between dosimeter and GPS location, has been\nhelpful in postprocessing to eliminate any measurement anomalies generated by the operator. After the survey campaign it was\ndetermined that a formulation allows defining a Comfort Index (CI) depending on velocity and five vehicles of different classes.\nThis study showed that the presence of speed bumps, in the test site investigated, appears to be uncomfortable even at speeds well\nbelow those required by the Highway Code....
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