Applied Mechanics and Materials Vols. 239-240

Abstract: The use of ultrasonic nondestructive testing of material internal defect，ultrasonic signal acquired at actual working spot usually includes large amount of noise.Extraction of the defect characteristic information will be influeced greatly if the ultrasonic signal is not effectively denoised. A new method based on best wavelet packet base is present to denoise and detect the ultrasonic signal. The superiority of new method is verified by simulation examples. Experiment of processing ultrasonic signal which comes from the 45 Steel specimen with flaws has been implemented. The accurate information that characterizes of defect size,location can be extracted from the processing result, the results show that the new method based on best wavelet packet base is in favor of enhancing the degree of accuracy for quantitatively analyzing the defect inside the material.

Abstract: Abstract. To realize the sound pressure unit directly, the method of sound pressure measurement based on acoustic particle velocity was described. In order to get a simple acoustic field, a travelling wave tube was designed. The sound pressure distribution obtained by microphone along the tube was measured. The result showed the acoustic field inside the tube could be considered as travelling wave and the sound pressure is equal to the product of the air density, sound speed and the particle velocity. The laser Doppler Anemometry was used to measure the particle velocity in the acoustic field. The modulated Doppler signal was obtained by measurement system. With the spectral analysis of Doppler signal and the signal model, the particle velocity was obtained with the Bessel function analysis. The comparison of sound pressure measured by microphone and the value deduced from the velocity measured by laser Doppler system shows that deviations between two methods were 0.04 dB at 650 Hz and discrepancies were less than 0.34 dB at frequencies from 300 Hz to 1k Hz.

Abstract: In recent times, vocal fold problems have been increasing dramatically due to unhealthy social habits and voice abuse. Non-invasive methods like acoustic analysis of voice signals can be used to investigate such problems. Various feature extraction techniques are used to classify the voice signals into normal and pathological. Among them, long-time acoustical parameters are used by many researchers. The selection of best long-time acoustical parameters is very important to reduce the computational complexity, as well as to achieve better accuracy with minimum number of features. In order to select best long-time acoustical parameters, different feature reduction methods or feature selection methods are proposed by researchers. In this work, genetic algorithm (GA) based optimal selection of long-time acoustical parameters is proposed to achieve higher accuracy with minimum number of features. The classification is carried out using k-nearest neighbourhood (k-NN) classifier. In comparison with other works in the literature, the simulation results show that a minimum of 5 features are required to classify the voice signals by GA and a better accuracy of 94.29% is achieved.

Abstract: Ferrite cores are used in the manufacture of various electrical and electronic equipment. Thereby, ferrite degradation also occurs in various forms. In this paper, the characteristics of the degradation of ferrite cores are studied and the changes in amplitude are analyzed after subjecting specimens to artificial thermal shock. In this paper, two probes were used in direct contact penetrant method applying longitudinal waves and the change in amplitude was confirmed.

Abstract: The sound attenuation in ER fluid was experimentally studied. The results show that sound attenuation of ER fluid could be adjusted by the particle concentration of ER fluid and the intensity of electric field. Amplitude of sound wave in ER fluid increases with the increasing of particle concentration and field intensity; on the other hand, the attenuation of sound wave decreases with the increasing of propagation distance, as well as the particle concentration and field intensity. The experimental results indicate that the solidification effect of ER fluid is beneficial to the propagation of sound wave.

Abstract: The ultrasonic wave method was presented to pile test on the complex building engineering of China Mobile Group Gansu Co.,Ltd. The basic theory, tesing method of pile and judgment standard about the ultrasonic wave method are analyzed.

Abstract: The ultrasound sensor imitates the bats and the other animals’ abilities to use ultrasound frequencies for navigation in order to determine the distance between them and the obstacles. These sensors are recommended to be used for difficult applications, in gasiform environments and represent one of the mobile robot’s sensor options. Our purpose of this study lies in presenting a method of detecting the distance between the mobile robot and obstacles and recording it, and in the same time the possibility of implementing it in order for it to be used by individuals (subjects) in applied studies.

Abstract: Ultrasonic fatigue testing was conducted for 3000 MPa-class mould steel to investigate the fatigue behavior. The fatigue specimen is designed particularly due to the ultra-high strength. Ultrasonic fatigue tests are conduced using two types of specimen sizes and the test results are compared to investigate the size effect on the fatigue property.

Abstract: In the traditional vector data expressions, the outputs of a single 3D vector hydrophone are reorganized into a complex vector, which cannot retain the orthogonality of the velocity elements. In this paper, biquaternion formalism is used to model the vector hydrophone’s output and a novel MUSIC-like algorithm is proposed to estimate the DOA (Direction-Of-Arrival) of the sources. The three velocity channels outputs are placed in the imaginary parts of the biquaternion numbers, which retains the orthogonality of the particle velocities and is robust to correlated/coherent noises. What’s more, the biquaternion data model has a compact way of handing multi-component data, which results a much less memory requirements compared with the traditional approach.

Abstract: In this paper, the fatigue property of ultra-high strength mould steel is investigated. The fatigue specimen is designed particularly due to the ultra-high strength. Fatigue tests are conduced using ultrasonic and conventional fatigue testing machines respectively. The same geometry and size of the ultrasonic fatigue specimens and conventional fatigue specimens are adopted to overcome the size effects. The test results are compared to investigate the frequency effect.