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121.
122.
Jung-Ryul Lee He-Jin Shin Chen Ciang Chia Dipesh Dhital Dong-Jin Yoon Yong-Hak Huh 《Optics and Lasers in Engineering》2011,49(12):1361-1371
Wind turbine blade failure is the most prominent and common type of damage occurring in operating wind turbine systems. Conventional nondestructive testing systems are not available for in situ wind turbine blades. We propose a portable long distance ultrasonic propagation imaging (LUPI) system that uses a laser beam targeting and scanning system to excite, from a long distance, acoustic emission sensors installed in the blade. An examination of the beam collimation effect using geometric parameters of a commercial 2 MW wind turbine provided Lamb wave amplitude increases of 41.5 and 23.1 dB at a distance of 40 m for symmetrical and asymmetrical modes, respectively, in a 2 mm-thick stainless steel plate. With this improvement in signal-to-noise ratio, a feasibility study of damage detection was conducted with a 5 mm-thick composite leading edge specimen. To develop a reliable damage evaluation system, the excitation/sensing technology and the associated damage visualization algorithm are equally important. Hence, our results provide a new platform based on anomalous wave propagation imaging (AWPI) methods with adjacent wave subtraction, reference wave subtraction, reference image subtraction, and the variable time window amplitude mapping method. The advantages and disadvantages of AWPI algorithms are reported in terms of reference data requirements, signal-to-noise ratios, and damage evaluation accuracy. The compactness and portability of the proposed UPI system are also important for in-field applications at wind farms. 相似文献
123.
This paper presents a system that accurately measures the distance travelled by ultrasound waves through the air. The simple design of the system and its obtained accuracy provide a tool for non-contact distance measurements required in the laser’s optical system that investigates the surface of the eyeball. 相似文献
124.
Measurements of coating density using ultrasonic reflection coefficient phase spectrum 总被引:1,自引:0,他引:1
A nondestructive method to determine the density of coating has been proposed in this paper based on the ultrasonic reflection coefficient phase spectrum (URCPS). A model was set up first to represent the ultrasonic waves reflected from a coating system at normal incident, and the relation between the extremum of URCPS and the coating density was established to provide the principle of determining the density. The ultrasonic method was validated on a series of ZrO2-7 wt.%Y2O3 (YSZ) coatings with various density. The specimens were prepared by electric beam physical vapor deposit (EB-PVD). After deposition, the specimens were irradiated using high-intensity pulsed ion beam (HIPIB) at different ion current density of 100 and 200 A/cm2 to change coating density. The coating densities of as-deposited and post irradiation by HIPIB were derived to be 4940-5030, 5200-5320 and 5390-5470 kg/m3, respectively. The relative error between the coating density measured by the ultrasonic method and Archimedean principle ranging from 2.53% to 6.11%, indicates that the proposed ultrasonic quantification method provides a reliable nondestructive way to determine coating density. 相似文献
125.
Xi X Cegla FB Lowe M Thiemann A Nowak T Mettin R Holsteyns F Lippert A 《Ultrasonics》2011,51(8):1014-1025
The use of bubbles in applications such as surface chemistry, drug delivery, and ultrasonic cleaning etc. has been enormously popular in the past two decades. It has been recognized that acoustically-driven bubbles can be used to disturb the flow field near a boundary in order to accelerate physical or chemical reactions on the surface. The interactions between bubbles and a surface have been studied experimentally and analytically. However, most of the investigations focused on violently oscillating bubbles (also known as cavitation bubble), less attention has been given to understand the interactions between moderately oscillating bubbles and a boundary. Moreover, cavitation bubbles were normally generated in situ by a high intensity laser beam, little experimental work has been carried out to study the translational trajectory of a moderately oscillating bubble in an acoustic field and subsequent interactions with the surface. This paper describes the design of an ultrasonic test cell and explores the mechanism of bubble manipulation within the test cell. The test cell consists of a transducer, a liquid medium and a glass backing plate. The acoustic field within the multi-layered stack was designed in such a way that it was effectively one dimensional. This was then successfully simulated by a one dimensional network model. The model can accurately predict the impedance of the test cell as well as the mode shape (distribution of particle velocity and stress/pressure field) within the whole assembly. The mode shape of the stack was designed so that bubbles can be pushed from their injection point onto a backing glass plate. Bubble radial oscillation was simulated by a modified Keller–Miksis equation and bubble translational motion was derived from an equation obtained by applying Newton’s second law to a bubble in a liquid medium. Results indicated that the bubble trajectory depends on the acoustic pressure amplitude and initial bubble size: an increase of pressure amplitude or a decrease of bubble size forces bubbles larger than their resonant size to arrive at the target plate at lower heights, while the trajectories of smaller bubbles are less influenced by these factors. The test cell is also suitable for testing the effects of drag force on the bubble motion and for studying the bubble behavior near a surface. 相似文献
126.
Longitudinal and transverse wave attenuation coefficients are obtained in a simple integral form for ultrasonic waves in cubic polycrystalline materials with elongated grains. Dependences of attenuation on frequency and grain shape are described in detail. The explicit analytical solutions for ellipsoidal grains in the Rayleigh and stochastic frequency limits are given for a wave propagating in an arbitrary direction relative to ellipsoid axes. The attenuation exhibits classic frequency dependence in those frequency limits. However, the dependence on the grain shape in the stochastic limits is unexpected: it is independent of the cross-section of the ellipsoidal grains and depends only on the grain dimension in the propagation direction. In the Rayleigh region attenuation is proportional to effective volume of the ellipsoidal grain and is independent of its shape. A complex behavior of attenuation on the grain shape/size and frequency is exhibited in the transition region. The results obtained reduce to the classic dependences of attenuation on parameters for polycrystals with equiaxed grains. 相似文献
127.
This paper presents a new standing-wave-type linear ultrasonic motor using combination of the first longitudinal and the second bending modes. Two piezoelectric plates in combination with a metal thin plate are used to construct the stator. The superior point of the stator is its isosceles triangular structure part of the stator, which can amplify the displacement in horizontal direction of the stator in perpendicular direction when the stator is operated in the first longitudinal mode. The influence of the base angle θ of the triangular structure part on the amplitude of the driving foot has been analyzed by numerical analysis. Four prototype stators with different angles θ have been fabricated and the experimental investigation of these stators has validated the numerical simulation. The overall dimensions of the prototype stators are no more than 40 mm (length) × 20 mm (width) × 5 mm (thickness). Driven by an AC signal with the driving frequency of 53.3 kHz, the no-load speed and the maximal thrust of the prototype motor using the stator with base angle 20° were 98 mm/s and 3.2 N, respectively. The effective elliptical motion trajectory of the contact point of the stator can be achieved by the isosceles triangular structure part using only two PZTs, and thus it makes the motor low cost in fabrication, simple in structure and easy to realize miniaturization. 相似文献
128.
A one-step, economical nanoemulsion method has been introduced to synthesize low-melting-point metallic nanoparticles. This nanoemulsion technique exploits the extremely high shear rates generated by the ultrasonic agitation and the relatively large viscosity of the continuous phase - polyalphaolefin (PAO), to rupture the molten metal down to diameter below 100 nm. Field’s metal nanoparticles and Indium nanoparticles of respective average diameters of 15 nm and 30 nm have been obtained. The nanoparticles size and shape are determined by transmission electron microscopy (TEM). Their phase transition behavior is examined using a differential scanning calorimeter (DSC). It is found that these nanoparticles dispersed in PAO can undergo reversible, melting-freezing phase transition, and exhibit a relatively large hysteresis. The experimental results suggest that the nanoemulsion method is a viable route for mass production of low-melting nanoparticles. 相似文献
129.
Two kinds of spinel LiMn2O4 thin film for lithium ion micro-batteries were successfully prepared on polycrystal Pt substrates by spin coating methods, which were carried out under ultrasonic irradiation (USG) and magnetic stirring (MSG), respectively. The microstructures and electrochemical performance of LiMn2O4 thin films were characterized by thermogravimetry analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), and galvanostatic charge-discharge measurements. It was found that the crystalline structure of USG samples grew better than that of the MSG samples. At the same time, higher discharge capacity and better cycle stability were obtained for the LiMn2O4 thin films of USG at the current density of 50 μAh/cm2 between 3.0 and 4.3 V. The 1st discharge capacity was 57.8 μAh/cm2-μm for USG thin films and 51.7 μAh/cm2-μm for MSG thin films. After 50 cycles, 91.4% and 69% of discharge capacity could be retained respectively, indicating that ultrasonic irradiation condition during spin coating was more suitable for preparing spinel LiMn2O4 thin films with better electrode performance for lithium ion micro-batteries. 相似文献
130.
G. Cynthia Jemima SwarnavalliV. Joseph D. RoopsinghV. Kannappan 《Journal of Molecular Liquids》2011,164(3):243-249
Nanocrystallite silver and silver sol were prepared and characterized by UV-visible spectra, XRD, TEM and HRTEM. The crystallite silver is re-dispersed in two different media, namely, water and alcohol and sonicated before ultrasonic investigation. The silver sol was used as such. Three different models for the propagation of ultrasound through two phase media are compared in these three different types of nano suspensions. Effect of particle size and medium on ultrasonic velocity (U), compressibility (κ) impedance (Z) and viscous relaxation time (τ) is studied. The particle concentration range was 0.2-1 v/v. Density and viscosity of the dispersion and sol are measured at different particle volume fractions. Effective density and ultrasonic velocity are computed by Urick, Kuster and Toksöz and Urick and Ament models and compared with experimental velocities. Values of effective density obtained by using Urick and Urick and Ament equations closely agree with experimental results of density while Urick's equation prediction of velocity is in close agreement with the experimental velocities. This comes as a surprise in view of the large density difference between the medium and suspended particle and suggests the possibility of the balancing effect of the inertial and viscous forces operating in the suspension. 相似文献