Wind turbine technology is well known around the globe as an eco-friendly and effective renewable power source. However, this technology often faces reliability problems due to structural vibration. This study proposes a smart semi-active vibration control system using Magnetorheological (MR) dampers where feedback controllers are optimized with nature-inspired algorithms. Proportional integral derivative (PID) and Proportional integral (PI) controllers are designed to achieve the optimal desired force and current input for MR the damper. PID control parameters are optimized using an Ant colony optimization (ACO) algorithm. The effectiveness of the ACO algorithm is validated by comparing its performance with Ziegler-Nichols (Z-N) and particle swarm optimization (PSO). The placement of the MR damper on the tower is also investigated to ensure structural balance and optimal desired force from the MR damper. The simulation results show that the proposed semi-active PID-ACO control strategy can significantly reduce vibration on the wind turbine tower under different frequencies (i.e., 67%, 73%, 79% and 34.4% at 2 Hz, 3 Hz, 4.6 Hz and 6 Hz, respectively) and amplitudes (i.e. 50%, 58% and 67% for 50 N, 80 N, and 100 N, respectively). In this study, the simulation model is validated with an experimental study in terms of natural frequency, mode shape and uncontrolled response at the 1st mode. The proposed PID-ACO control strategy and optimal MR damper position is also implemented on a lab-scaled wind turbine tower model. The results show that the vibration reduction rate is 66% and 73% in the experimental and simulation study, respectively, at the 1st mode.
This study examined the effect of different salinities(0, 5, 10, 15, 20, 25 and 30) on the growth performance and energy budget of juveniles of two different ecotypes of Oncorhynchus mykiss, landlocked rainbow trout and anadromous steelhead trout. In the 42 d experiment, fish were cultured in three replicate tanks per salinity treatment(eight fish per tank). At the end of the experiment, the growth of rainbow and steelhead trouts was significantly higher at salinities of 5 and 10, respectively, than at all other salinities. The protein, lipid and energy content of both ecotypes declined with the increase of salinity. Based on their energy budgets, the percentage of energy consumed for growth by rainbow and steelhead trouts were significantly higher at salinities of 5(34.00% ±1.69%) and 10(43.76% ± 1.29%), respectively, than at all other salinities. The percentage of energy consumed for respiration by rainbow and steelhead trouts was lower at salinities of 5(54.90% ± 1.77%) and 10(46.73% ± 0.62%), respectively, than at all other salinities. Our results indicated that the salinity adaptation ability of juvenile steelhead trout was slightly better than that of juvenile rainbow trout, and salinities of 10 and 5, respectively, were most suitable for growth of these two fishes. 相似文献
Glacial tills are highly compressible soils composed of loosely cemented sandy silt particles. Their role, for instance, as initial filler materials in geo-technical projects along temperate glacier regions warrant a systematic evaluation of their compressive characteristics. As such, we carry out a series of onedimensional compression tests on re-compacted glacial till samples obtained from Tianmo Gully, Tibet, with the aims of evaluating their compressive behavior under controlled initial stress conditions. The yield stress was determined from the void ratio versus consolidation pressure(e-log) planes. Its compression and swelling behaviors were observed during the primary and secondary compressions of the consolidation tests. From the compression curves, a correlation can be found between the consolidation stress and the void index. In addition, we find that the compression curves of glacial tills collapse into a single curve when normalized by the compression index. The experimental results in this study provide a basic understanding of the compression characteristics of the glacial tills in Tibet, China. 相似文献
Grain price volatility during historical periods is regarded as an important indicator of the impact of climate change on economic system, as well as a key link to adjust food security and social stability. The present study used the wheat prices in Baoding Prefecture, China, during 1736–1850 to explore connections between climatic transition and grain price anomalies in the North China Plain. The main findings were as follows:(1) The grain price change showed an apparent correspondence with climatic transition. The period 1781–1820 was a transition phase, with more extremes and decreased precipitations when the climate shifted from a warm phase to a cold one. Corresponding with the climatic transition, the grain price during 1781–1820 was characterized by that the mean of the original grain price series was significantly higher(lower) than the previous(later)phase, and the variance and anomaly amplitude of the detrended grain price series was the highest during 1736–1850.(2) The correspondence between grain price extremes and drought events occurred in phases. Five grain price extremes occurred following drought events during 1781–1810, while extreme droughts were the direct cause of the grain price spike during 1811–1820.(3) Social stability affected by climate change also played an important role in the grain price spike between 1811 and 1820. Paralleling the pathway of "precipitation-grain production-grain price", climate change could have an impact on grain price via the pathway of "precipitation-grain production-grain price-famine-uprising-grain price", as shown during the Tianli Uprising in 1813. These findings could contribute to an improved understanding of the interaction between climate change and human society during the historical period. 相似文献