The avian feather combines mechanical properties of robustness and flexibility while maintaining a low weight. Under periodic and random dynamic loading, the feathers sustain bending forces and vibrations during flight. Excessive vibrations can increase noise, energy consumption, and negatively impact flight stability. However, damping can alter the system response, and result in increased stability and reduced noise. Although the structure of feathers has already been studied, little is known about their damping properties. In particular, the link between the structure of shafts and their damping is unknown. This study aims at understanding the structure-damping relationship of the shafts. For this purpose, laser Doppler vibrometry (LDV) was used to measure the damping properties of the feather shaft in three segments selected from the base, middle, and tip. A combination of scanning electron microscopy (SEM) and micro-computed tomography (µCT) was used to investigate the gradient microstructure of the shaft. The results showed the presence of two fundamental vibration modes, when mechanically excited in the horizontal and vertical directions. It was also found that the base and middle parts of the shaft have higher damping ratios than the tip, which could be attributed to their larger foam cells, higher foam/cortex ratio, and higher percentage of foam. This study provides the first indication of graded damping properties in feathers.
During flight, vibrations potentially cause aerodynamic instability and noise. Besides muscle control, the intrinsic damping in bird feathers helps to reduce vibrations. The vanes of the feathers play a key role in flight, and they support feathers’ aerodynamic function through their interlocked barbules. However, the exact mechanisms that determine the damping properties of the vanes remain elusive. Our aim was to understand how the structure of the vanes on a microscopic level influences their damping properties. For this purpose, scanning electron microscopy (SEM) was used to explore the vane’s microstructure. High-speed videography (HSV) was used to record and analyze vibrations of feathers with zipped and unzipped vanes upon step deflections parallel or perpendicular to the vane plane. The results indicate that the zipped vanes have higher damping ratios. The planar surface of the barbs in zipped vanes is responsible for aerodynamic damping, contributing 20%–50% to the whole damping in a feather. To investigate other than aerodynamic damping mechanisms, the structural and material damping, experiments in vacuum were performed. High damping ratios were observed in the zipped vanes, even in vacuum, because of the structural damping. The following structural properties might be responsible for high damping in feathers: (i) the intact planar surface, (ii) the interlocking of barbules, and (iii) the foamy inner material of the barb’s medulla. Structural damping is another factor demonstrating 3.3 times (at vertical deflection) and 2.3 times (at horizontal deflection) difference in damping ratio between zipped and unzipped feathers in vacuum. The shaft and barbs filled with gradient foam are thought to increase the damping in the feather further.
Bird feathers sustain bending and vibrations during flight. Such unwanted vibrations could potentially cause noise and flight instabilities. Damping could alter the system response, resulting in improving quiet flight, stability, and controllability. Vanes of feathers are known to be indispensable for supporting the aerodynamic function of the wings. The relationship between the hierarchical structures of vanes and the mechanical properties of the feather has been previously studied. However, still little is known about their relationship with feathers’ damping properties. Here, the role of vanes in feathers’ damping properties was quantified. The vibrations of the feathers with vanes and the bare shaft without vanes after step deflections in the plane of the vanes and perpendicular to it were measured using high-speed video recording. The presence of several main natural vibration modes was observed in the feathers with vanes. After trimming vanes, more vibration modes were observed, the fundamental frequencies increased by 51–70%, and the damping ratio decreased by 38–60%. Therefore, we suggest that vanes largely increase feather damping properties. Damping mechanisms based on the morphology of feather vanes are discussed. The aerodynamic damping is connected with the planar vane surface, the structural damping is related to the interlocking between barbules and barbs, and the material damping is caused by the foamy medulla inside barbs.
The condenser vacuum influences the steam turbine’s safety and economy. The dirty level of the water side tube and the air accumulation of the steam side affect overall heat transfer coefficient .That make the condenser vacuum low and terminal temperature difference increase. It is a generally interested problem that making a distinction between fouling loss and air accumulation loss for the operating personnel and maintenance person. In this article, we judged the vacuum system work normal or not by comprehensive cleaning curve, and further calculation and curve analysis were done so as to distinguish the affection of the dirty level of the water side tube and the air accumulation of the steam side to overall heat transfer coefficient and terminal temperature difference.
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