Abstract:Wind turbines vibrate under the excitation of environmental loads and rotor movement in normal operating conditions, and vibrations of the tower affect the service life of such system. In order to analyze the vibration and dynamic characteristics of the wind turbine during startup and shutdown process, vibration of a 1.5 MW turbine tower was monitored for a long term. First-order natural frequencies and damping ratios of the wind turbine were identified utilizing a data-driven stochastic subspace identification method. Monitoring data revealed that the wind turbine usually operated near the rotation speed of grid connection. In addition, obvious resonance at the turbine startup was noted as it surpassed the rotation speed of grid connection, but was not apparent at the turbine shutdown. Modal identification results revealed that the first-order natural frequencies varied slightly under different operating conditions, while the damping ratios were found to be smaller when the wind turbine started up, and its rotation speed surpassed that of grid connection, which were found to be greater at turbine shutdown. In addition, the characteristics of different vibration phenomena in the turbine during startup and shutdown processes were explained with the Sommerfeld effect. Our findings contribute to the field of vibration analysis and allow for more efficient optimization of dynamic parameters in wind turbines of similar design.

Abstract:MHB rubblization technology is widely used in the reconstruction of the old cement concrete pavement (PCC) crushing, however, the impact of vibration on the adjacent buildings and residents during the impact crushing process needs to be urgently resolved. The attenuation law of physical parameters of the pavement panel under impact load were deduced and analyzed based on elastic theory and wave theory. Relying on the field vibration monitoring test on the old PCC pavement reconstruction project of Shandong provincial highway S245, and combing with ANSYS/LS-DYNA dynamic finite element numerical simulation, the three-dimensional dynamic response under different influence factors was studied. Then, the level safety distance of rubblization adjacent buildings and the comfortability critical distance of the residents were explored. The results show that MHB rubblization belongs to impact type vibration source, whose vibration is a negative exponential curve in the form of a sharp attenuation, and the results of calculation, measurement and numerical simulation are in agreement with the attenuation trend of the curve. With increasing stroke the peak time load continuously advances. The peak vibration velocity of 1cm/s can be used as a control index for judging the safety of adjacent building. When the hammer drop height is 0.8 m, 1.0 m, 1.2 m respectively, the level safety distance of adjacent building is 14 m, 18 m, 20 m respectively, and the comfortability critical distance of inhabitants is 24 m, 29 m, 31 m respectively.