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Application of the bispectrum for detection of small nonlinearities excited sinusoidally 总被引:1,自引:0,他引:1
C.R.P. Courtney S.A. Neild P.D. Wilcox B.W. Drinkwater 《Journal of sound and vibration》2010,329(20):4279-4293
The nonlinear behaviour of damaged systems excited by vibration or ultrasound offers potential as a technique for damage detection in machine condition monitoring and non-destructive testing applications. The bispectrum, a third-order spectrum, has properties that lend themselves to the measurement of nonlinearities in systems. The properties of interest are insensitivity to Gaussian noise and ability to detect quadratic phase coupling. However, thus far analysis of the statistics of bispectrum estimation has been mainly aimed at stochastic systems. Many applications to vibration and ultrasound involve primarily deterministic, periodic excitations in the presence of stochastic noise. This paper considers the properties of a bispectrum estimate when applied to a system with weak quadratic nonlinearity excited by the superposition of two sinusoids in the presence of additive Gaussian noise. This is compared, using signal-to-noise ratios, to the powerspectrum, with the results validated using numerical data. Also addressed is the effect of quadratic phase coupling on such a system (in the absence of noise). 相似文献
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Scattering of plane guided waves obliquely incident on a straight feature with uniform cross-section
Wilcox PD Velichko A Drinkwater BW Croxford AJ Todd MD 《The Journal of the Acoustical Society of America》2010,128(5):2715-2725
A frequency-domain finite element (FE) method is presented for modeling the scattering of plane guided waves incident on an infinitely-long, straight feature with uniform cross-section in a planar host waveguide. The method utilizes a mesh of 2-dimensional finite elements with harmonic shape functions in the perpendicular direction. The model domain comprises a cross-section through the feature and short lengths of the adjoining host waveguide. A spatial frequency equal to the wavenumber of the desired incident mode multiplied by the sine of the desired incidence angle is prescribed for the element shape functions. An integral representation of the incident mode is used to determine a suitable system of harmonic forces to uniquely excite that mode. These are applied at nodes through the thickness of the host waveguide on one side of the feature. The displacement field is measured at nodes through the thickness of the host waveguide on either side of the feature and decomposed into reflected and transmitted modes. The cases of guided wave transmission in a featureless waveguide and the reflection of guided waves from a free-edge are examined as validation cases. Finally, the results for transmission at an adhesively-bonded stiffener are presented and compared with experimental measurements. 相似文献
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van de Waal BW 《Physical review letters》1991,67(23):3263-3266
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Drinkwater BW Castaings M Hosten B 《The Journal of the Acoustical Society of America》2003,113(6):3161-3170
Guided waves in an elastic plate surrounded by air propagate with very low attenuation. This paper describes the effect on this propagation of compressively loading an elastomer with high internal damping against one surface of the elastic plate. The propagation of both A0 and S0 Lamb modes is considered. The principal effect is shown to be increased attenuation of the guided waves. This attenuation is caused by leakage of energy from the plate into the elastomer, where it is dissipated due to high viscoelastic damping. It is shown that the increase in attenuation is strongly dependent on the compressive load applied across the solid-solid interface. This interface is represented as a spring layer in a continuum model of the system. Both normal and shear stiffnesses of the interface are quantified from the attenuation of A0 and S0 Lamb waves measured at each step of the compressive loading. The normal stiffness is also measured independently by normal incidence, bulk longitudinal wave ultrasound. The resulting predictions of wave propagation behavior, such as attenuation, obtained by the model are in excellent agreement with those measured experimentally. 相似文献
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This paper concerns a study of the detectability of dry contact kissing bonds in adhesive joints using three ultrasonic inspection techniques. Conventional normal incidence longitudinal and shear wave inspection were conducted on dry contact kissing bonds using a standard damped ultrasonic transducer and an electro-magnetic acoustic transducer (EMAT) respectively. The detectability of the dry contact kissing bonds was assessed by calculating the reflection coefficient of the imperfect interface at varying loads for a number of surface roughnesses. A high power ultrasonic method was also employed to determine the non-linear behavior of the adhesive interface. The non-linearity of the interface was determined by the ratio of the amplitudes of the first harmonic and fundamental frequencies of the transmitted waveform. It was found that the high power technique showed the greatest sensitivity to these kissing bonds at low contact pressures, however at high loads conventional longitudinal wave testing was more sensitive. It was also noted that a combination of two or more techniques could provide enhanced information about the kissing bond compared to a single technique alone. 相似文献
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Donald E. Drinkwater Frantisek Turecek Fred W. McLafferty 《Journal of mass spectrometry : JMS》1991,26(6):559-562
An improved data-acquisition and management system interfaces an IBM-compatible personal computer to a tandem mass spectrometer. In addition to increased spectral resolution and storage, the control system measures the absolute abundance (peak areas) of product ions, and also that of the precursor; these are capabilities critical for collisional activation, metastable ion decomposition and neutralization-reionization mass spectra. Improved experimental control features include multiple mass range and repetitive scan selection, spurious transient rejection and comparative spectral display. 相似文献
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Donald E. Drinkwater Aberra Fura Mei-Yi Zhang Fred W. McLafferty 《Journal of mass spectrometry : JMS》1991,26(11):1032-1035
Increased differential pumping improves the simultaneous sequential operation of ion-beam neutralization, neutral dissociation, neutral product ionization, and ion product dissociation for neutralization-reionization (NR) mass spectrometry. Following Porter's developments for neutralized ion-beam spectroscopy, instrument modifications allow a wider variety of metals (vaporization up to 800 °C) to be used for neutralization and eliminate multiplier instabilities seen previously using neutralization metals such as sodium. Irreproducibility of recovered precursor ion signals using metal vapors of low ionization potential has been traced to mercury background. Double focusing of the ionized neutral beam yields NR mass spectra of the highest resolution yet reported. 相似文献
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Courtney CR Ong CK Drinkwater BW Wilcox PD Demore C Cochran S Glynne-Jones P Hill M 《The Journal of the Acoustical Society of America》2010,128(4):EL195-EL199
A method of manipulating microparticles in a liquid using ultrasound is proposed and demonstrated. An ultrasonic standing wave with nodal planes whose positions are controllable by varying the relative phase of two applied sinusoidal signals is generated using a pair of acoustically matched piezoelectric transducers. The resulting acoustic radiation force is used to trap micron scale particles at a series of arbitrary positions (determined by the relative phase) and then move them in a controlled manner. This method is demonstrated experimentally and 5 μm polystyrene particles are trapped and moved in one dimension through 140 μm. 相似文献
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