In coal-fired power generation, it is necessary to pulverize coal, and a vertical roller mill with excellent crushing efficiency has become the mainstream. However, In the process of pulverization by compression and shear, abnormal vibrations, which are considered to be self-excited vibration, occurs rarely. As a method of reducing self-excited vibration, adding water has been empirically performed in the field. Since the powder state changes due to water addition, it is necessary to investigate how the vibration characteristics and slip characteristics change. In this paper, we examined the effects of adding water to Artificial coal, Sub-bituminous coal A, and Sub-bituminous coal B with different powder characteristics on the dynamic friction characteristics and dynamic response generated between the roller and the powder. Investigating the relation between the RMS value of the horizontal acceleration response and the slip ratio indicates the degree of slippage of the roller. Next, we investigated the relation between the dynamic frictional characteristics generated during rolling and the slip ratio and found that the Slip-Stick phenomenon remarkably appeared at the test machine speed at which the vibration acceleration was maximum even when water was added. Also, a frequency analysis showed that when the vibration acceleration increased, the resonance frequency decreased, and the phenomenon of uniting was confirmed for all types of coal, suggesting that the abnormal vibration that occurred was self-excited vibration.

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Simultaneous multi-band very long baseline interferometry (VLBI) observations at millimeter wavelengths have huge potential for various science cases. However, there exist difficulties in expanding the scientific targets, as the sensitivity of radio telescopes at millimeter wavelengths is typically lower compared to that at centimeter wavelengths. In order to realize high-sensitivity mm-VLBI observations in the East Asia region, we are promoting the HINOTORI (Hybrid Installation project in NObeyama, Triple-band ORIented) project, which aims to launch the wide-band and simultaneous triple-band (22/43/86 GHz) VLBI system with the Nobeyama 45 m Radio Telescope (NRO45). The simultaneous 22/43 GHz observation mode has already been operated for the open-use program. We have recently completed the performance evaluation of the receiver and observing system at 86 GHz. In addition, a new wide-band VLBI back-end system has been installed on the NRO45 and the performance of this receiving system has been found to be sufficient to meet scientific requirements. Currently, we are performing commissioning observations to establish regular VLBI operation with simultaneous triple-band mode together with the Korean VLBI Network. The participation of the NRO45 is expected to strengthen the mm-VLBI observation network in the East Asia region and to be a very powerful addition with respect to the science of of black hole jets.

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