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.
On July 31st, 2016, an earthquake of MS5.4 occurred in Cangwu County, Guangxi Zhuang Autonomous Region, which is the first MS ≥ 5.0 earthquake in coastal areas of southern China in the past 17a. The moderate earthquake activities have come into a comparatively quiet period in coastal areas of southern China for decades, so the study about the Cangwu MS5.4 earthquake is very important. However, differernt research institutions and scholars have got different results for the focal depth of the Cangwu MS5.4 earthquake. For this reason, we further measured the focal depth by using CAP method and sPL phase method.
sPL phase was first put forward by Chong in 2010. It is often observed between P and S wave of continental earthquakes with epicentral distance of about 30km to 50km. The energy of sPL phase is mainly concentrated on the radial component. Arrival time difference between sPL phase and direct P wave is insensitive to epicentral distancs, but increases almost linearly with the increase of focal depth. Based on these characteristics and advantages, sPL phase method is chosen to measure the focal depth of Cangwu MS5.4 earthquake in the paper.
First of all, we selected the broadband waveform data through seismic stations distributed mainly in Guangxi and adjacent provinces from Data Management Centre of China National Seismic Network and Guangxi Earthquake Networks Center. And an appropriate velocity model of Cangwu area was constructed by the teleseismic receiver function method. Then, the focal mechanism and focal depth of Cangwu MS5.4 earthquake were determined by using the CAP(Cut and Paste)method. Next, we compared the synthetic waveforms simulated by F-K forward method of different focal depth models with the actual observed waveforms. According to the difference of arrival times between sPL and Pg phases, we finally obtained the focal depth of Cangwu earthquake. The results show that the focal depth is 11km measured by CAP method and 9km by sPL phase method. Based on the focal mechanism solution, isoseismal shapes, aftershocks distributions and investigation on spot, we conclude that the Cangwu MS5.4 earthquake is a left-lateral strike-slip earthquake which occurred in the upper crust. Our preliminary analysis considers that the seismogenic structure of Cangwu earthquake is a north-northwest branch fault, and the control fault of this earthquake is the Hejie-Xiaying Fault. 相似文献
The Western Yunnan Earthquake Predication Test Site set up jointly by the China Earthquake Administration, the National Science Foundation Commission of America, and United States Geological Survey has played an important role in development of early earthquake research work in China. Due to various objective reasons, most of the predicted targets in the earthquake prediction test site have not been achieved, and the development has been hindered. In recent years, the experiment site has been reconsidered, and renamed the “Earthquake Science Experimental Site”. Combined with the current development of seismology and the practical needs of disaster prevention and mitigation, we propose adding the “Underground Cloud Map” as the new direction of the experimental site. Using highly repeatable, environmentally friendly and safe airgun sources, we could send constant seismic signals, which realizes continuous monitoring of subsurface velocity changes. Utilizing the high-resolution 3-D crustal structure from ambient noise tomography, we could obtain 4-D (3-D space + 1-D time) images of subsurface structures, which we termed the “Underground Cloud Map”. The “Underground Cloud Map” can reflect underground velocity and stress changes, providing new means for the earthquake monitoring forecast nationwide, which promotes the conversion of experience-based earthquake prediction to physics-based prediction. 相似文献
In order to further deepen the understanding of seismic wave propagation characteristics induced by the large volume airgun source, experimental data from multiple fixed excitation points in Fujian Province were used to obtain the equivalent single excitation high signal-to-noise ratio velocity and displacement records through linear stacking and simulation techniques. Then the peak displacements of different epicentral distances were used to calculate the equivalent magnitude of the airgun source excitation at different fixed excitation points so as to establish the attenuation relationship between equivalent magnitude,epicenter distance and velocity peak. Our results show that:① Within 270 km of epicentral distance,for the large-volume airgun's single shot,the peak velocity range is about 700-4 nm/s,and the peak displacement range is about 200. 0-0. 2 nm;② The equivalent magnitude of the P-wave from the airgun source with a total capacity of 8,000 in 3 is 0. 181-0. 760,and the equivalent magnitude of the S-wave is 0. 294-0. 832. By contrast,the equivalent magnitude of the P-wave from the airgun source with a total capacity of 12,000 in 3 is 0. 533-0. 896,and the equivalent magnitude of the S-wave is 0. 611-0. 946. The S-wave energy is greater than the P-wave energy, and the excitation efficiency varies greatly with different excitation environment;③ The peak velocity increases with the equivalent magnitude,and decreases with the epicentral distance. The vertical component of the P-wave peak velocity is the largest among those three components,while the S-wave has the smallest vertical component and similar horizontal components. Hence,our research can provide an important basis for the quantitative judgment of the seismic wave propagation distance using the airgun and the design of the observation system in deep exploration or monitoring with airgun. 相似文献
The Global Boundary Stratotype Sections and Points(GSSPs) for the bases of all seven international Devonian stages have been formally defined and ratified by IUGS till 1996, and nowadays, the main tasks for Devonian stratigraphers include further subdivision of these standard stages, strictly constrained absolute ages for the boundaries, and precise neritic-pelagic and marine-terrestrial correlations using multidisciplinary stratigraphy methods. Establishment of high-resolution Devonian integrative stratigraphy framework and timescale of China would play an important role in improving regional and international correlation, facilitating the recognition of important stratigraphic levels in different paleogeographic settings, and understanding the evolution pattern of biota, paleoclimate and paleoenvironment during this critical interval. Based on well-studied bio-and chronostratigraphy of Devonian in South China and adjacent areas, in combination with recent achievements in carbon isotope stratigraphy, event stratigraphy and radioactive isotope ages, this paper briefly summarize the research history and current status of Devonian chronostratigraphy of China, and for the first time introduce Devonian integrative stratigraphy framework of China.Up to date, few studies have been conducted on the astronomical cyclostratigraphy and high-resolution radioactive isotope dating in Devonian of China, which should be our main focuses in the near future. 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