Abstract:The root mean square (RMS) value of a vibration signal is an important indicator used to represent the amplitude of vibrations in evaluating the quality of highspeed spindles. However, RMS is unable to detect a number of common fault characteristics that occur prior to bearing failure. Extending the operational life and quality of spindles requires reliable fault diagnosis techniques for the analysis of vibration signals from three axes. This study used empirical mode decomposition to decompose signals into intrinsic mode functions containing a zero-crossing rate and energy to represent the characteristics of rotating elements. The MSE curve was then used to identify a number of characteristic defects. The purpose of this research was to obtain vibration signals along three axes with the aim of extending the operational life of devices included in the product line of an actual spindle manufacturing company.

Molecular dynamics simulation is used to investigate the dynamic properties of water molecules inside an Au nanotube in different water densities. From the oxygen density profiles, some characteristic peaks appear at specific regions. In order to observe the dynamical behaviors of water molecules in different portions in the Au nanotube, these specific peaks are divided into three regionsI, II, and IIIwhich are 0−4, 4−7, and 7−10 Å, respectively, as measured from the center of the tube to the inside wall of the tube. Since the strength of hydrogen bonds between water molecules within regions I and II can overcome the interaction between the Au nanotube and the water molecules within those regions, the major peaks of the region I and II spectra are similar to those of bulk water. However, the strength of hydrogen bonds between water molecules within region III cannot overcome the interaction between the Au nanotube and the water molecules within that region, so the major peak of the region III spectrum shifts to a higher frequency. In addition, the shoulder structure, which can be observed in the spectra of those regions at different densities, exists at high frequency. In the vibration spectra for region I, the shoulders at each different density appears at around 100 cm−1, and those of regions II and III at different densities occur around 200 cm−1. This is because the shoulder corresponds to O−O stretching intermolecular vibrations of pairs of H-bonded molecules, so the shoulder will gradually appear as the average number of hydrogen bonds increases. Finally, the shoulder in the region I spectrum completely disappears at a bulk density of 0.8 cm−1.

A molecular dynamics simulation of water molecules through a Au nanotube with a diameter of 20 A at bulk densities 0.8, 1, and 1.2 gcm(3) has been carried out. The water molecules inside a nanoscale tube, unlike those inside a bulk tube, have a confined effect. The interaction energy of the Au nanotube wall has a direct influence on the distribution of water molecules inside the Au tube in that the adsorption of the water molecules creates shell-like formations of water. Moreover, the high number of adsorbed molecules has already achieved saturation at the wall of the Au nanotube at three bulk densities. This work compares the distribution percentage profiles of hydrogen bonds for different regions inside the tube. The structural characteristics of water molecules inside the tube have also been studied. The results reveal that the numbers of hydrogen bonds per water molecule influence the orientational order parameter q. In addition, the phenomenon of a group of molecules bonded inside the tube can be observed as the number of hydrogen bonds increase.

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