Monitoring hydrodynamic bearings with acoustic emission and vibration analysis
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Acoustic Emission
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Acoustic Emission
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This paper describes new vibration analysis methods for the coupled vibration between the acoustic field and continuous structure located inside the acoustic field. Numerical analysis methods such as the finite element method and finite-difference time-domain method have been used to analyze the coupled vibration. These numerical analysis methods need spatial discretization; however, the proposed analysis methods do not need spatial discretization because the proposed methods use the superposition of the vibration modes of the original acoustic field as a continuous body. Mathematically, the superposition of the vibration modes is a kind of series. The coupled vibration is expressed by the series of the superposition of the vibration modes in the proposed methods. Based on this concept, two methods are proposed in this paper: one is referred to as a built-in method, and the other is referred to as a binding method. The characteristics of the continuous structure is built in the acoustic field in the built-in method. In contrast, the acoustic field and the continuous structure are bound by the sufficiently stiff elastic body in the binding method. The governing equations of the analytical models were derived, and the effectiveness of the proposed method was verified through simulations.
Acoustic wave equation
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A perturbation analysis of acoustic wave propagation properties for a stiff thin rod surrounded by a liquid is presented. A study is made of the velocity sensitivity of the lowest flexural acoustic mode, F(11), along a thin rod due to mass changes in the rod and variations in the surrounding liquid density. It is shown that the presence of the liquid decreases the velocity of the F(11 ) mode and also the mass sensitivity.
Gravimetric analysis
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The flyability of an air bearing in contact with a super smooth media causes substantial increase in frictional contact causing high vibrational resonances of both the slider and the head-gimbal1 assembly. Vibrations induced by the contact force prevent read/write operations
Contact Mechanics
Contact force
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In this paper, a novel imaging technique of acoustic emission from vibrating micro- and nano-structures is proposed and demonstrated for characterizing their mechanical energy losses via ambient air. A thermal probe is employed for the measurement of particle velocity involved in the acoustic emission. Imaging is obtained with scanning the vibrating sample under the thermal probe, which exhibits the geometry dependence on acoustic emission profile. Also it is found that strong acoustic emission is emitted from a mechanical detect formed on the vibrating beam.
Acoustic Emission
Physical acoustics
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Abstract In an attempt to analyze the feasibility of a rail monitoring scheme with a wheel-mounted acoustic emission measurement method, a two-dimensional analytical spring model was proposed to interpret the interactions between acoustic waves and stationary wheel–rail contact interfaces. The spring model represents the coupling strength of the interfaces with their stiffness. It accommodates the environmental information of contact stiffness and the acoustic source information, such as the feature frequency and the incident angle in the analysis of interface transmissibility. The fractal dimension of the interface is introduced into the spring model to interpret the effect of the axle load on the interface stiffness and the variation in transmissibility. Discrete Rayleigh integration is further combined to obtain the directivity of the interface and estimate the acoustic field intensity in the entire wheel. A wheel–rail contact rig was designed to simulate the actual contact conditions in a railway. Experimental data acquired from this test rig were utilized to validate the model, with regard to the interfacial stiffness in normal incidence and amplitudes of the transmitted waves in oblique incidence. After verifying the reliability of the model, the acoustic field intensity in the wheel was visualized under the assumed environmental conditions. Finally, a discussion is presented to determine a proper angular separation for the wheel-mounted sensor system, and substantiate the feasibility of the system.
Acoustic Emission
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Acoustic Emission
Separation (statistics)
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