Journal articles on the topic 'Disturbance'
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1
Phukapak, Sorawin, Daisuke Koyama, Kotaro Hashikura, Md Kama, Iwanori Murakami, and Kou Yamada. "Parameterization of All Disturbance Observers for Periodic Input Disturbances." ECTI Transactions on Electrical Engineering, Electronics, and Communications 21, no. 2 (June 27, 2023): 249809. http://dx.doi.org/10.37936/ecti-eec.2023212.249809.
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In this paper, we examine the parameterizations of all disturbance observers and all linear functional disturbance observers for periodic input disturbances. The plant disturbance observers have been used to estimate the disturbance in the plant. Several papers on design methods for disturbance observers have been published. Recently, the parameterization of all dis- turbance observers and all linear functional disturbance observers for plants with any input disturbance was clarified. However, no paper examines the parameteriza- tion of all disturbance observers or all linear functional disturbances for periodic input disturbances. In this paper, we propose parameterizations of all disturbance observers and all linear functional disturbance observers for periodic input disturbances.
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Dornelas, Maria. "Disturbance and change in biodiversity." Philosophical Transactions of the Royal Society B: Biological Sciences 365, no. 1558 (November 27, 2010): 3719–27. http://dx.doi.org/10.1098/rstb.2010.0295.
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Understanding how disturbance affects biodiversity is important for both fundamental and applied reasons. Here, I investigate how disturbances with different ecological effects change biodiversity metrics. I define three main types of disturbance effects: D disturbance (shifts in mortality rate), B disturbance (shifts in reproductive rates) and K disturbance (shifts in carrying capacity). Numerous composite disturbances can be defined including any combination of these three types of ecological effects. The consequences of D , B and K disturbances, as well as of composite DBK disturbances are examined by comparing metrics before and after a disturbance, in disturbed and undisturbed communities. I use simulations of neutral communities and examine species richness, total abundance and species abundance distributions. The patterns of change in biodiversity metrics are consistent among different types of disturbance. K disturbance has the most severe effects, followed by D disturbance, and B disturbance has nearly negligible effects. Consequences of composite DBK disturbances are more complex than any of the three types of disturbance, with unimodal relationships along a disturbance gradient arising when D, B and K are negatively correlated. Importantly, regardless of disturbance type, community isolation enhances the negative consequences and hinders the positive effects of disturbances.
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Yamada, Kou, Tatsuya Sakanushi, Iwanori Murakami, Yoshinori Ando, Yuki Nakui, and Da Zhi Gong. "A Design Method for Control System to Attenuate Unknown Input Andoutput Disturbances Using Disturbance Observers." Key Engineering Materials 497 (December 2011): 182–96. http://dx.doi.org/10.4028/www.scientific.net/kem.497.182.
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In this paper, we examine a design method for control system to attenuate unknown inputand output disturbances using disturbance observers. The disturbance observers have been usedto estimate the disturbance in the plant. Several papers on design methods of disturbance observershave been published. Recently, parameterizations of all disturbance observers and all linear functionaldisturbance observers for plants with any input and output disturbances were clarified. If parameterizationsof all disturbance observers and all linear functional disturbance observers for any input andoutput disturbances are used, there is a possibility that we can design control systems to attenuate unknowninput and output disturbances effectively. However, no paper has examined a design methodfor control system using parameterizations of all disturbance observers and all linear functional disturbanceobservers for plants with any input and output disturbances. In this paper, in order to attenuateunknown input and output disturbances effectively, we propose a design method for control systemusing parameterizations of all disturbance observers and all linear functional disturbance observersfor plants with any input and output disturbances. In addition, control characteristics of the proposedcontrol system are clarified.
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Murakami, Iwanori, Kou Yamada, Takaaki Hagiwara, Da Zhi Gong, Yoshinori Ando, Yoichi Imai, and Masahiko Kobayashi. "An Application of the Parameterization of all Disturbance Observers for Motor Control Experiment." Applied Mechanics and Materials 36 (October 2010): 210–19. http://dx.doi.org/10.4028/www.scientific.net/amm.36.210.
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Disturbance observers have been used to estimate the disturbance in the plant. Recently, parameterizations of all disturbance observers and all linear functional disturbance observers for plants with any output disturbance were clarified. If parameterizations of all disturbance observers and all linear functional disturbance observers for plants with any output disturbance are used, there is a possibility that we can design control systems to attenuate unknown output disturbances effectively. From this viewpoint, a design method for control system to attenuate unknown output disturbances using parameterizations of all disturbance observers and all linear functional disturbance observers was proposed. However, an application of control system to attenuate unknown output disturbances using parameterizations of all disturbance observers and all linear functional disturbance observers for real plants in motion-control field is not examined. In this paper, we show the effectiveness of the control system to attenuate unknown output disturbances using parameterizations of all disturbance observers and all linear functional disturbance observers for the angular velocity and the angle control for motor control experiment.
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Shimizu, Katsuto, Tetsuji Ota, and Nobuya Mizoue. "Accuracy Assessments of Local and Global Forest Change Data to Estimate Annual Disturbances in Temperate Forests." Remote Sensing 12, no. 15 (July 29, 2020): 2438. http://dx.doi.org/10.3390/rs12152438.
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Forest disturbances are generally estimated using globally available forest change maps or locally calibrated disturbance maps. The choice of disturbance map depends on the trade-offs among the detection accuracy, processing time, and expert knowledge. However, the accuracy differences between global and local maps have still not been fully investigated; therefore, their optimal use for estimating forest disturbances has not been clarified. This study assesses the annual forest disturbance detection of an available Global Forest Change map and a local disturbance map based on a Landsat temporal segmentation algorithm in areas dominated by harvest disturbances. We assess the forest disturbance detection accuracies based on two reference datasets in each year. We also use a polygon-based assessment to investigate the thematic accuracy based on each disturbance patch. As a result, we found that the producer’s and user’s accuracies of disturbances in the Global Forest Change map were 30.1–76.8% and 50.5–90.2%, respectively, for 2001–2017, which corresponded to 78.3–92.5% and 88.8–97.1%, respectively in the local disturbance map. These values indicate that the local disturbance map achieved more stable and higher accuracies. The polygon-based assessment showed that larger disturbances were likely to be accurately detected in both maps; however, more small-scale disturbances were at least partially detected by the Global Forest Change map with a higher commission error. Overall, the local disturbance map had higher forest disturbance detection accuracies. However, for forest disturbances larger than 3 ha, the Global Forest Change map achieved comparable accuracies. In conclusion, the Global Forest Change map can be used to detect larger forest disturbances, but it should be used cautiously because of the substantial commission error for small-scale disturbances and yearly variations in estimated areas and accuracies.
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Wang, Zhen, Zhong Wu, Lijun Li, and Jun Yuan. "A composite anti-disturbance control scheme for attitude stabilization and vibration suppression of flexible spacecrafts." Journal of Vibration and Control 23, no. 15 (December 9, 2015): 2470–77. http://dx.doi.org/10.1177/1077546315617632.
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Abstract: There exist multiple disturbances resulting from the structural vibrations of flexible appendages, unknown external and internal disturbances, and parameter uncertainties, which affect the attitude control performance seriously. To enhance the disturbance attenuation performance and vibration suppression ability, a composite anti-disturbance control scheme (CADCS) based on disturbance observer is proposed for attitude stabilization and vibration reduction of flexible spacecraft. The CADCS combines a composite disturbance observer (CDO) and a PD controller with feedforward. The multiple disturbances are equivalent to slowly varying disturbance and harmonic disturbance. The CDO can estimate two types of disturbance and compensate for them through feedforward. The PD controller realizes the asymptotic convergence by compensating the disturbance from CDO. The CADCS based on CDO and PD controller is not only simple and easy to realize, but also yields better vibration suppression and anti-disturbance performance. Simulation results of a certain spacecraft demonstrate the effectiveness of the proposed CADCS.
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Zhang, Huifeng, Xinjiang Wei, Lingyan Zhang, and Meiqin Tang. "Disturbance rejection for nonlinear systems with mismatched disturbances based on disturbance observer." Journal of the Franklin Institute 354, no. 11 (July 2017): 4404–24. http://dx.doi.org/10.1016/j.jfranklin.2017.03.009.
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Hart, Justin, and Jonathan Kleinman. "What Are Intermediate-Severity Forest Disturbances and Why Are They Important?" Forests 9, no. 9 (September 19, 2018): 579. http://dx.doi.org/10.3390/f9090579.
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The classification of discrete forest disturbance events is usually based on the spatial extent, magnitude, and frequency of the disturbance. Based on these characteristics, disturbances are placed into one of three broad categories, gap-scale, intermediate-severity, or catastrophic disturbance, along the disturbance classification gradient. We contend that our understanding of disturbance processes near the endpoints of the disturbance classification gradient far exceeds that of intermediate-severity events. We hypothesize that intermediate-severity disturbances are more common, and that they are more important drivers of forest ecosystem change than is commonly recognized. Here, we provide a review of intermediate-severity disturbances that includes proposed criteria for categorizing disturbances on the classification gradient. We propose that the canopy opening diameter to height ratio (D:H) be used to delineate gap-scale from intermediate-severity events and that the threshold between intermediate and catastrophic events be based on the influence of residual trees on the composition of the regeneration layer. We also provide examples of intermediate-severity disturbance agents, return intervals for these events, and recommendations for incorporating natural intermediate-severity disturbance patterns in silvicultural systems.
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Yi, Yang, Lubing Xu, Hong Shen, and Xiangxiang Fan. "Disturbance observer-based L1 robust tracking control for hypersonic vehicles with T-S disturbance modeling." International Journal of Advanced Robotic Systems 13, no. 6 (November 16, 2016): 172988141667111. http://dx.doi.org/10.1177/1729881416671117.
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This article concerns a disturbance observer-based L1 robust anti-disturbance tracking algorithm for the longitudinal models of hypersonic flight vehicles with different kinds of unknown disturbances. On one hand, by applying T-S fuzzy models to represent those modeled disturbances, a disturbance observer relying on T-S disturbance models can be constructed to track the dynamics of exogenous disturbances. On the other hand, L1 index is introduced to analyze the attenuation performance of disturbance for those unmodeled disturbances. By utilizing the existing convex optimization algorithm, a disturbance observer-based proportional-integral-controlled input is proposed such that the stability of hypersonic flight vehicles can be ensured and the tracking error for velocity and altitude in hypersonic flight vehicle models can converge to equilibrium point. Furthermore, the satisfactory disturbance rejection and attenuation with L1 index can be obtained simultaneously. Simulation results on hypersonic flight vehicle models can reflect the feasibility and effectiveness of the proposed control algorithm.
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Liu, Y., W. C. Guo, R. Cao, Z. Chen, and L. Wang. "Dynamic performance and sensitivity of grid-connected hydropower station under uncertain disturbance." IOP Conference Series: Earth and Environmental Science 1079, no. 1 (September 1, 2022): 012113. http://dx.doi.org/10.1088/1755-1315/1079/1/012113.
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Abstract The grid-connected operating condition of hydropower station is a common operation mode to provide electric energy for the load side. This paper investigates the dynamic performance and sensitivity of grid-connected hydropower station (GCHS) under uncertain disturbance. Firstly, the nonlinear uncertain model of GCHS under uncertain disturbance is established. Then, the dynamic performance of GCHS is studied when the governor parameters change under certain step disturbance, periodic disturbance and uncertain random disturbance, respectively. Finally, based on the sensitivity index of the uncertain output obtained from the extended Fourier amplitude sensitivity test method, the sensitivity of the uncertain random disturbance at different input positions is studied. The results indicate that the GCHS under periodic disturbances or random disturbances have more complex dynamic performance than that under certain step disturbance. Under periodic disturbance, the forced oscillations and high frequency resonances are generated in dynamic response of GCHS. Under the uncertain random disturbance, the system of GCHS always presents random oscillation. The state variables q H , z, qP, y, x s , x t , and δ of GCHS are the most sensitive to uncertain disturbances, which are introduced at the generator or surge tank. The uncertain disturbances have significant interaction on the dynamic response of GCHS.
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Haywood, A., J. Verbesselt, and P. J. Baker. "MAPPING DISTURBANCE DYNAMICS IN WET SCLEROPHYLL FORESTS USING TIME SERIES LANDSAT." ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLI-B8 (June 23, 2016): 633–41. http://dx.doi.org/10.5194/isprs-archives-xli-b8-633-2016.
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In this study, we characterised the temporal-spectral patterns associated with identifying acute-severity disturbances and low-severity disturbances between 1985 and 2011 with the objective to test whether different disturbance agents within these categories can be identified with annual Landsat time series data. We analysed a representative State forest within the Central Highlands which has been exposed to a range of disturbances over the last 30 years, including timber harvesting (clearfell, selective and thinning) and fire (wildfire and prescribed burning). We fitted spectral time series models to annual normal burn ratio (NBR) and Tasseled Cap Indices (TCI), from which we extracted a range of disturbance and recovery metrics. With these metrics, three hierarchical random forest models were trained to 1) distinguish acute-severity disturbances from low-severity disturbances; 2a) attribute the disturbance agents most likely within the acute-severity class; 2b) and attribute the disturbance agents most likely within the low-severity class. Disturbance types (acute severity and low-severity) were successfully mapped with an overall accuracy of 72.9 %, and the individual disturbance types were successfully attributed with overall accuracies ranging from 53.2 % to 64.3 %. Low-severity disturbance agents were successfully mapped with an overall accuracy of 80.2 %, and individual agents were successfully attributed with overall accuracies ranging from 25.5 % to 95.1. Acute-severity disturbance agents were successfully mapped with an overall accuracy of 95.4 %, and individual agents were successfully attributed with overall accuracies ranging from 94.2 % to 95.2 %. Spectral metrics describing the disturbance magnitude were more important for distinguishing the disturbance agents than the post-disturbance response slope. Spectral changes associated with planned burning disturbances had generally lower magnitudes than selective harvesting. This study demonstrates the potential of landsat time series mapping for fire and timber harvesting disturbances at the agent level and highlights the need for distinguishing between agents to fully capture their impacts on ecosystem processes.
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Haywood, A., J. Verbesselt, and P. J. Baker. "MAPPING DISTURBANCE DYNAMICS IN WET SCLEROPHYLL FORESTS USING TIME SERIES LANDSAT." ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLI-B8 (June 23, 2016): 633–41. http://dx.doi.org/10.5194/isprsarchives-xli-b8-633-2016.
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In this study, we characterised the temporal-spectral patterns associated with identifying acute-severity disturbances and low-severity disturbances between 1985 and 2011 with the objective to test whether different disturbance agents within these categories can be identified with annual Landsat time series data. We analysed a representative State forest within the Central Highlands which has been exposed to a range of disturbances over the last 30 years, including timber harvesting (clearfell, selective and thinning) and fire (wildfire and prescribed burning). We fitted spectral time series models to annual normal burn ratio (NBR) and Tasseled Cap Indices (TCI), from which we extracted a range of disturbance and recovery metrics. With these metrics, three hierarchical random forest models were trained to 1) distinguish acute-severity disturbances from low-severity disturbances; 2a) attribute the disturbance agents most likely within the acute-severity class; 2b) and attribute the disturbance agents most likely within the low-severity class. Disturbance types (acute severity and low-severity) were successfully mapped with an overall accuracy of 72.9 %, and the individual disturbance types were successfully attributed with overall accuracies ranging from 53.2 % to 64.3 %. Low-severity disturbance agents were successfully mapped with an overall accuracy of 80.2 %, and individual agents were successfully attributed with overall accuracies ranging from 25.5 % to 95.1. Acute-severity disturbance agents were successfully mapped with an overall accuracy of 95.4 %, and individual agents were successfully attributed with overall accuracies ranging from 94.2 % to 95.2 %. Spectral metrics describing the disturbance magnitude were more important for distinguishing the disturbance agents than the post-disturbance response slope. Spectral changes associated with planned burning disturbances had generally lower magnitudes than selective harvesting. This study demonstrates the potential of landsat time series mapping for fire and timber harvesting disturbances at the agent level and highlights the need for distinguishing between agents to fully capture their impacts on ecosystem processes.
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Hu, Jie, Kou Yamada, Tatsuya Sakanushi, Yuki Nakui, and Yusuke Atsuta. "A Design Method for Control System to Attenuate Periodic Input Disturbances Using Disturbance Observers for Time-Delay Plants." ECTI Transactions on Electrical Engineering, Electronics, and Communications 11, no. 1 (July 12, 2012): 37–46. http://dx.doi.org/10.37936/ecti-eec.2013111.170607.
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In this paper, we examine a design method for control system to attenuate periodic input disturbances using disturbance observers for time-delay plants. The disturbance observers have been used to estimate the disturbance in the plant. Several papers on design methods of disturbance observers have been published. Recently, parameterizations of all disturbance observers and all linear functional disturbance observers for time-delay plants with any input disturbance were clarified. If parameterizations of all such observers for time-delay plants with any input disturbance are used, there is a possibility that we can design control systems to attenuate input dis- turbances effectively. However, no paper examines a design method for control system using parameterizations of all disturbance observers and all linear functional disturbance observers for time-delay plants with any input disturbance. In this paper, to attenuate periodic input disturbances effectively, we propose a design method for control system using these parameterizations.
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Liu, Xia, Dandan Liu, and Hao Sheng. "Position Tracking Control of Robotic System Subject to Matched and Mismatched Disturbances." Mathematical Problems in Engineering 2020 (September 23, 2020): 1–11. http://dx.doi.org/10.1155/2020/9531354.
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For nonlinear coupled robotic system subject to matched and mismatched disturbances, this paper designs an adaptive disturbance observer-based exponential sliding mode controller to achieve position tracking. Firstly, matched disturbance, mismatched disturbance, and the derivative of mismatched disturbance are defined as the lumped disturbance in robotic system. Secondly, a nonlinear disturbance observer is constructed to estimate the lumped disturbance, and an adaptive law is proposed to estimate the bound of the lumped disturbance. Finally, an exponential sliding mode controller is derived by combining the nonlinear disturbance observer and exponential convergence law. Stability and tracking performance of the robotic system is analyzed via Lyapunov function approach. Simulation results show that, with the proposed approach, both matched and mismatched disturbances in robotic system can be effectively depressed while achieving position tracking.
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Pan, Shihao, Ting Wang, Haoran Zhang, and Tao Li. "Trajectory Tracking Control Based on a Composite Disturbance Observer for Unmanned Autonomous Helicopters under Multiple Disturbances." Machines 12, no. 3 (March 19, 2024): 201. http://dx.doi.org/10.3390/machines12030201.
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This paper studies the trajectory tracking anti-disturbance control of unmanned autonomous helicopters (UAHs) under matched disturbances and mismatched ones. Firstly, the six-degrees-of-freedom UAH nonlinear system is simplified via feedback linearization to handle strong coupling, in which the multiple disturbances are composed of modeled disturbances and time-varying bounded ones. Secondly, in order to estimate these disturbances, a new design method of a composite disturbance observer is proposed. On the one hand, for the mismatched disturbances, a normal disturbance observer (DO) combined with a backstepping control are utilized to handle their negative effect. On the other hand, two refined disturbance observers (RDOs) are constructed to estimate the matched disturbances, in which the coupling estimations are involved. Then, by designing two anti-disturbance composite controllers, the boundedness of the tracking errors is guaranteed by using the Lyapunov stability theory. Finally, some numerical simulations are provided to demonstrate the effectiveness and advantage of the proposed control scheme.
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Shimizu, Katsuto, Tetsuji Ota, and Nobuya Mizoue. "Detecting Forest Changes Using Dense Landsat 8 and Sentinel-1 Time Series Data in Tropical Seasonal Forests." Remote Sensing 11, no. 16 (August 14, 2019): 1899. http://dx.doi.org/10.3390/rs11161899.
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The accurate and timely detection of forest disturbances can provide valuable information for effective forest management. Combining dense time series observations from optical and synthetic aperture radar satellites has the potential to improve large-area forest monitoring. For various disturbances, machine learning algorithms might accurately characterize forest changes. However, there is limited knowledge especially on the use of machine learning algorithms to detect forest disturbances through hybrid approaches that combine different data sources. This study investigated the use of dense Landsat 8 and Sentinel-1 time series data for detecting disturbances in tropical seasonal forests based on a machine learning algorithm. The random forest algorithm was used to predict the disturbance probability of each Landsat 8 and Sentinel-1 observation using variables derived from a harmonic regression model, which characterized seasonality and disturbance-related changes. The time series disturbance probabilities of both sensors were then combined to detect forest disturbances in each pixel. The results showed that the combination of Landsat 8 and Sentinel-1 achieved an overall accuracy of 83.6% for disturbance detection, which was higher than the disturbance detection using only Landsat 8 (78.3%) or Sentinel-1 (75.5%). Additionally, more timely disturbance detection was achieved by combining Landsat 8 and Sentinel-1. Small-scale disturbances caused by logging led to large omissions of disturbances; however, other disturbances were detected with relatively high accuracy. Although disturbance detection using only Sentinel-1 data had low accuracy in this study, the combination with Landsat 8 data improved the accuracy of detection, indicating the value of dense Landsat 8 and Sentinel-1 time series data for timely and accurate disturbance detection.
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Huang, Liya, and Zhong Wu. "Extended harmonic disturbance observer-based attitude control for flexible spacecraft with control moment gyroscopes." Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering 233, no. 14 (April 22, 2019): 5331–46. http://dx.doi.org/10.1177/0954410019842503.
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In the flexible spacecraft with control moment gyroscopes, there are multiple disturbances including not only internal disturbances from actuators and flexible appendages, but also external disturbances from space environment. These disturbances are characterized by a wide frequency range and may degrade attitude control performance to a great extent. In this paper, the lumped disturbance is modeled as a harmonic plus a polynomial model, and an extended harmonic disturbance observer (EHDO) is proposed to estimate the total disturbance. Since the rotor dynamic imbalance disturbance from control moment gyroscopes is described by an internal harmonic model, the lumped disturbance can be estimated precisely via EHDO even with a lower bandwidth. Afterwards, a backstepping-based composite controller is designed to compensate the disturbances by combining the output of EHDO and realize high-precision attitude control for flexible spacecraft with control moment gyroscopes. Simulation results are presented to demonstrate the effectiveness of the proposed method.
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Zhang, Xiaohua, Junli Gao, Wenfeng Zhang, Tao Zeng, and Liping Ye. "Distributed Formation Control for Multiple Quadrotor Based on Multi-Agent Theory and Disturbance Observer." Mathematical Problems in Engineering 2019 (February 12, 2019): 1–11. http://dx.doi.org/10.1155/2019/7234969.
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This paper presents the disturbance observers-based distributed formation control for multiple quadrotor aircrafts with external disturbances and uncertain parameters using multi-agent theory and finite-time control method. Firstly, the finite-time disturbance observers are proposed to handle the external disturbances on the position-loop. Similarly, when there are both the uncertain parameters and external disturbances on the attitude-loop, the finite-time disturbance observers are designed to estimate the total lump disturbances. By skillfully using homogeneous system theory, Lyapunov theory, and multi-agent theory, the distributed formation control algorithms are developed. Finally, through simulations, the efficiency of the proposed method (including the convergence rate and disturbance rejection) is verified.
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Jacquet, Claire, and Florian Altermatt. "The ghost of disturbance past: long-term effects of pulse disturbances on community biomass and composition." Proceedings of the Royal Society B: Biological Sciences 287, no. 1930 (July 8, 2020): 20200678. http://dx.doi.org/10.1098/rspb.2020.0678.
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Current global change is associated with an increase in disturbance frequency and intensity, with the potential to trigger population collapses and to cause permanent transitions to new ecosystem states. However, our understanding of ecosystem responses to disturbances is still incomplete. Specifically, there is a mismatch between the diversity of disturbance regimes experienced by ecosystems and the one-dimensional description of disturbances used in most studies on ecological stability. To fill this gap, we conducted a full factorial experiment on microbial communities, where we varied the frequency and intensity of disturbances affecting species mortality, resulting in 20 different disturbance regimes. We explored the direct and long-term effects of these disturbance regimes on community biomass. While most communities were able to recover biomass and composition states similar to undisturbed controls after a halt of the disturbances, we identified some disturbance thresholds that had long-lasting legacies on communities. Using a model based on logistic growth, we identified qualitatively the sets of disturbance frequency and intensity that had equivalent long-term negative impacts on experimental communities. Our results show that an increase in disturbance intensity is a bigger threat for biodiversity and biomass recovery than the occurrence of more frequent but less intense disturbances.
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Li, Hai, Zhan Li, Tong Wu, Chen Dong, Quman Xu, Yipeng Yang, and Xinghu Yu. "A Novel Active Anti-Disturbance Control Strategy for Unmanned Aerial Manipulator Based on Variable Coupling Disturbance Compensation." Electronics 13, no. 8 (April 13, 2024): 1477. http://dx.doi.org/10.3390/electronics13081477.
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Inspired by the kangaroo’s active tail wagging to stabilize its body posture while jumping, this paper proposes an active anti-disturbance control strategy for unmanned aerial manipulators based on variable coupling disturbance compensation (AADCVCD), which can achieve the active and energy-saving anti-disturbance performance of “using the enemy’s strength against the enemy” to keep the UAM stable under disturbances. First, the goal of using the coupling disturbance generated by the active swing of the manipulator as a control input signal for active anti-disturbance is clarified. Then, based on the proposed variable coupling disturbance model, this goal is formulated as a nonlinear programming optimization problem under specific physical constraints and solved. Finally, the coupling disturbance torque generated when the manipulator executes an active swing to the solved desired joint angles can be used to compensate and suppress other disturbances of the UAM, thereby achieving active anti-disturbance. The effectiveness and superiority of the proposed AADCVCD were validated through two simulations in Simscape. The simulation results demonstrated that our approach achieved a good active anti-disturbance and energy-saving performance, significantly reducing the position offset of the UAM caused by disturbances and improving the UAM’s ability to maintain stability.
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Wu, Gaohua, Yiling Yang, Cunyao Li, Yuguo Cui, and Yanding Wei. "Anti-disturbance control of a piezo-driven micromanipulator with a non-minimum phase." AIP Advances 13, no. 3 (March 1, 2023): 035025. http://dx.doi.org/10.1063/5.0132217.
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In precision micromanipulation tasks, operation accuracy and anti-disturbance performance of micromanipulators are critical. This paper presents anti-disturbance control for a piezo-driven micromanipulator with a non-minimum phase. The micromanipulator is constructed by mounting a flexible manipulator on a parallel positioning stage. The micromotion and dynamic behavior of the micromanipulator are analyzed. Then, an anti-disturbance control strategy combining H-infinity feedback control and disturbance observer-based control for a non-minimum phase is designed to reduce disturbances and ensure control accuracy. Finally, the experimental measurement and control system is built. The observed phenomena show that sinusoidal disturbances are almost eliminated and the overshoot of step disturbances is significantly reduced. In addition, the time for suppressing the step disturbance is shortened from 0.9 to 0.3 s. Experiments verify the viability of the anti-disturbance control strategy.
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Sun, Shixiang, Xinjiang Wei, and Huifeng Zhang. "Composite hierarchical anti-disturbance control for stochastic systems with multiple disturbances." Transactions of the Institute of Measurement and Control 40, no. 6 (May 30, 2017): 1950–55. http://dx.doi.org/10.1177/0142331217695385.
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A class of stochastic systems with multiple disturbances, which includes white noises and disturbances whose time derivative is bounded, is considered in this paper. To estimate the unknown bounded disturbance, a stochastic disturbance observer is proposed. Based on the observer, a disturbance observer-based disturbance control scheme is constructed such that the composite closed-loop system is asymptotically bounded. Finally, a simulation example is given to demonstrate the feasibility and effectiveness of the proposed scheme.
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Zhang, Linqing, Xinjiang Wei, and Huifeng Zhang. "Disturbance Observer-Based Elegant Anti-Disturbance Control for Stochastic Systems with Multiple Disturbances." Asian Journal of Control 19, no. 6 (April 21, 2017): 1966–76. http://dx.doi.org/10.1002/asjc.1514.
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Zhang, Huifeng, Xinjiang Wei, Hamid Reza Karimi, and Jian Han. "Anti-disturbance control based on disturbance observer for nonlinear systems with bounded disturbances." Journal of the Franklin Institute 355, no. 12 (August 2018): 4916–30. http://dx.doi.org/10.1016/j.jfranklin.2018.05.018.
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Chung, M. H., and A. M. Wo. "Navier–Stokes and Potential Calculations of Axial Spacing Effect on Vortical and Potential Disturbances and Gust Response in an Axial Compressor." Journal of Turbomachinery 119, no. 3 (July 1, 1997): 472–81. http://dx.doi.org/10.1115/1.2841146.
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The effect of blade row axial spacing on vortical and potential disturbances and gust response is studied for a compressor stator/rotor configuration near design and at high loadings using two-dimensional incompressible Navier–Stokes and potential codes, both written for multistage calculations. First, vortical and potential disturbances downstream of the isolated stator in the moving frame are defined; these disturbances exclude blade row interaction effects. Then, vortical and potential disturbances for the stator/rotor configuration are calculated for axial gaps of 10, 20, and 30 percent chord. Results show that the potential disturbance is uncoupled locally; the potential disturbance calculated from the isolated stator configuration is a good approximation for that from the stator/rotor configuration upstream of the rotor leading edge at the locations studied. The vortical disturbance depends strongly on blade row interactions. Low-order modes of vortical disturbance are of substantial magnitude and decay much more slowly downstream than do those of potential disturbance. Vortical disturbance decays linearly with increasing mode except very close to the stator trailing edge. For a small axial gap, e.g., 10 percent chord, both vortical and potential disturbances must be included to determine the rotor gust response.
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Lugo, Ariel E. "Effects of Extreme Disturbance Events: From Ecesis to Social–Ecological–Technological Systems." Ecosystems 23, no. 8 (February 18, 2020): 1726–47. http://dx.doi.org/10.1007/s10021-020-00491-x.
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AbstractEcologists addressed the effects of disturbances from the onset of the field by focusing on ecesis, which is the process by which organisms migrate and establish under the environmental conditions created by disturbances. Ecesis is the onset of succession, a self-organizing process whose nature, speed, and outcome depend in part on the outcomes of ecesis and the residual legacies remaining after disturbances. A by-product of succession after a disturbance is the reorganization of species dominance, or novelty. The degree of novelty in the outcome increases with the severity of the disturbance event. Initially, ecologists focused mostly on non-anthropogenic disturbances, but as human activity intensified and became a global force, more attention was given to the effects of anthropogenic disturbances on ecosystems. Today, anthropogenic and non-anthropogenic disturbances and their interactions are increasingly affecting ecosystems, particularly those exposed to extreme disturbance events. Extreme disturbance events are complex and low probability events composed of several disturbance forces that individually and in synergy affect different sectors of ecosystems, including the conditions that drive ecesis. I review the literature on disturbance research including the effects of extreme disturbance events on social–ecological–technological systems (SETSs). A SETS is an ecosystem defined by the flow and accumulation of energy through the medium of organisms, constructed infrastructure, institutions, and their environment. Human intentions, values, and capacities are part of the functioning of SETS, and they can drive ecological processes as do non-anthropogenic forces. Moreover, human-directed activities after an extreme disturbance event affect whole landscapes. The passage of hurricane María over the Puerto Rico SETS established that extreme disturbance events are of such power and complexity that they can influence the level and kind of relationship between humans and the environment, including the structure and species composition of the ecological systems within SETS. However, extreme disturbance events such as hurricanes have not changed the successional trajectory originally impulsed by anthropogenic disturbances. Thus, the species composition and functioning of novel forests in Puerto Rico are tied to economic activity in the social and technological sectors of SETS. It is no longer possible to interpret ecosystem functioning without considering the synergy between anthropogenic and non-anthropogenic extreme disturbances.
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Zhang, Huifeng, Xinjiang Wei, Lingyan Zhang, and Jian Han. "Disturbance observer-based control for a class of strict-feedback nonlinear systems with derivative-bounded disturbances." Transactions of the Institute of Measurement and Control 42, no. 14 (June 1, 2020): 2601–10. http://dx.doi.org/10.1177/0142331220922464.
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An anti-disturbance control problem is investigated in this paper. The disturbance observer plus back-stepping (DOPBS) control scheme is proposed for a class of strict-feedback nonlinear systems with derivative-bounded disturbances. A nonlinear disturbance observer is designed to estimate the derivative-bounded disturbances. By combining the disturbance observer with back-stepping method, the DOPBS controller is designed to reject and attenuate the disturbances. Stability analysis proves that all the signals in the the closed-loop system are uniformly ultimately bounded (UUB). Finally, simulation examples demonstrate the feasibility and effectiveness of the proposed approach compared with existing methods.
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He, Wangyong, Haogui Li, Yuanjiang Wang, and Sanqiu Liu. "Suppression the Disturbance of Robotic Manipulators Based on Nonlinear Disturbance Observer and Fuzzy Logic System." Journal of Advanced Computational Intelligence and Intelligent Informatics 24, no. 7 (December 20, 2020): 846–54. http://dx.doi.org/10.20965/jaciii.2020.p0846.
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Robotic Manipulators (RM) are nonlinear and coupling system with time-variant and model uncertainties. In addition, RM are subject to different types of disturbances in practice, such as joint frictions, unknown payloads, and interferences from external systems. In this paper, these adverse factors are regarded as disturbance, and classifies them into internal disturbances and external disturbances. In order to achieve high-precision control, a Nonlinear Disturbance Observer (NDO) is designed to suppress external disturbances, and a Fuzzy Logic System (FLS) is designed to compensate internal disturbances. The scheme can effectively suppress the disturbance and improve the control accuracy. The validity of the scheme is shown by computer simulations of a two-link robot manipulator.
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Pan, Yanpeng. "Stochastic disturbance observer-based adaptive anti-disturbance control for non-linear systems with stochastic non-harmonic multiple disturbances." Transactions of the Institute of Measurement and Control 40, no. 10 (August 1, 2017): 3222–31. http://dx.doi.org/10.1177/0142331217718051.
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In this paper, the problem of anti-disturbance control is studied for non-linear systems with stochastic multiple disturbances. The multiple disturbances include two types: one is the stochastic harmonic disturbance and the other non-harmonic noise generated by a linear stochastic exogenous system. An adaptive stochastic disturbance observer (ASDO) is constructed to estimate both the two aforementioned disturbances. Combining the disturbance estimation with a conventional state feedback control law, a composite anti-disturbance control scheme is constructed such that the closed-loop system is stochastically stable, and different types of disturbances may be attenuated and rejected. By using the Lyapunov function method and linear matrix inequalities technique, sufficient conditions for the stochastic stability of the closed-loop system are established. Moreover, an adaptive stochastic extended state observer (ASESO) is proposed for the output feedback case. Finally, an application example is provided to demonstrate the effectiveness of the proposed method.
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Benmansour, Jalal eddine, and Boulanouare Khouane. "Attitude stabilization of slosh-coupled satellite with flexible appendage." Algerian Journal of Signals and Systems 6, no. 3 (September 30, 2021): 175–80. http://dx.doi.org/10.51485/ajss.v6i3.131.
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In this paper, a robust control scheme is proposed for flexible satellite attitude stabilization in the presence of multiple disturbances including the disturbances caused by flexible appendages with the sloshing dynamics of the liquid propellant and external disturbances from space environment. A composite control scheme is designed by combining a composite disturbance observer (CDO) with feed-forward controller. First, a CDO is constructed to estimate the lumped disturbances, where the lumped disturbances in the system are equivalent into two parts: a slow varying disturbance and periodic disturbance. Then a PD controller is adopted to stabilize the system and restrain the residue disturbance. Finally, the simulation results for flexible satellite verify that the proposed method can make the satellite asymptotically stable and demonstrate the effectiveness of the proposed scheme.
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Wang, Guohui, Yanan Yang, and Shuxin Wang. "Adaptive Digital Disturbance Rejection Controller Design for Underwater Thermal Vehicles." Journal of Marine Science and Engineering 9, no. 4 (April 11, 2021): 406. http://dx.doi.org/10.3390/jmse9040406.
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Underwater thermal vehicles, as ocean observation tools, are frequently affected by environment disturbances such as waves and currents, which may cause degradation of the observation accuracy of the vehicles. Consequently, it is important to design a controller for a vehicle that can resist ocean disturbance. In this study, an underwater thermal vehicle principle is introduced, and the mathematical model is established in the vertical plane motion. On this basis, an adaptive digital disturbance suppression control method is proposed. For known disturbance parameters, this controller could compensate for external disturbances by pre-setting control parameters using the internal model principle and parameterizations method. For the case where the disturbance parameters are unknown, disturbance parameter estimation method based on forgetting factor least-squares method is proposed to transform the unknown parameter disturbance into a disturbance with known parameters, which is then suppressed by the adaptive digital disturbance rejection control approach. This solution could effectively solve the challenges caused by parameter uncertainty and unknown time-varying ocean external disturbances. Finally, simulations are carried out for the Petrel underwater thermal glider as an example. The simulation results show the proposed control method’s superiority and inherent robustness.
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Wen, Xinyu. "Enhanced Disturbance-Observer-Based Control for a Class of Time-Delay System with Uncertain Sinusoidal Disturbances." Mathematical Problems in Engineering 2013 (2013): 1–8. http://dx.doi.org/10.1155/2013/805687.
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This paper is concerned with disturbance-observer-based control (DOBC) for a class of time-delay systems with uncertain sinusoidal disturbances. The disturbances are decomposed as precise and uncertain parts using nonlinear disturbance observer (DO) after appropriate coordinate transformation. And then the two parts can be compensated by corresponding controller, respectively, such that the classic DOBC method is extended to uncertain disturbance rejection. One novel feature of the proposed method is that even if the precise disturbance parameters are inaccessible, the merits of DOBC can be inherited. By integrating the disturbance observers with feedback control laws with time delay, the disturbances can be rejected and the desired dynamic performances can be guaranteed. Finally, simulations for a flight control system are given to demonstrate the effectiveness of the results.
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Stojković, Jelena, and Predrag Stefanov. "A Novel Approach for the Implementation of Fast Frequency Control in Low-Inertia Power Systems Based on Local Measurements and Provision Costs." Electronics 11, no. 11 (June 2, 2022): 1776. http://dx.doi.org/10.3390/electronics11111776.
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Transitioning towards carbon-free energy has brought severe difficulties related to reduced inertia in electric power systems. Regarding frequency stability, low-inertia systems are more sensitive to disturbance, and traditional frequency control is becoming insufficient to maintain frequency within acceptable limits. Consequently, there is a necessity for faster frequency support that can be activated before the primary frequency control and that can decelerate further frequency decay. This paper proposes a local control strategy for a multi-stage fast frequency response (FFR) provided as an ancillary service that considers the location of the disturbance and the distribution of system inertia. The novelty of the presented control strategy is the ranking of FFR resources by price, which takes the economic component into consideration. The proposed control is simple, based only on RoCoF measurements that trigger the activation of FFR resources. Its advantage over other methods is the ability to adapt the FFR resource response to the disturbance without complex calculations and the ability to ensure a bigger response closer to the disturbance, as well as in low-inertia parts of the system. In that way, there is a bigger activation of resources in the parts of the system that are more endangered by disturbances, which, as a result, minimizes the propagation of the disturbance’s impact on system stability. The applicability of the presented method is demonstrated in a simple 3-area power system and IEEE 68-bus system implemented in MATLAB/Simulink. The results show that the proposed control enables the largest response closer to the disturbance, thus mitigating the propagation of the disturbance. Furthermore, the results confirm that the proposed control enables lower provision costs and more support in low-inertia areas that are more vulnerable to disturbances.
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Zhang, Xiao-Yu, Run-Xiao Wang, Shun-Qi Zhang, Zhan-Xi Wang, Xian-Sheng Qin, and Rüdiger Schmidt. "Generalized-Disturbance Rejection Control for Vibration Suppression of Piezoelectric Laminated Flexible Structures." Shock and Vibration 2018 (2018): 1–17. http://dx.doi.org/10.1155/2018/1538936.
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In the framework of disturbance rejection (DR) control, the paper proposes a generalized-disturbance rejection (GDR) control with proportional-integral (PI) observer for vibration suppression of smart structures under any unknown continuous disturbances. In the proposed GDR-PI control, a refined state space model is first constructed, and a generalized disturbance including the disturbance influence matrices, unknown physical disturbances, and state variables is defined. In the closed loop of GDR-PI control, physical disturbances can be counteracted indirectly by feeding back estimated generalized disturbances. By this means, the GDR-PI control remedies most of the defects in conventional DR control and has excellent performances especially in the following situations: (i) the disturbances are completely unknown; (ii) the number of sensor signals is less than the number of disturbances; (iii) the unknown disturbances vary fast. Finally, the GDR-PI control is validated and compared with H∞ state feedback control and conventional DR control available in the literature for vibration suppression of smart beams.
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Burton, Philip J., Anke Jentsch, and Lawrence R. Walker. "The Ecology of Disturbance Interactions." BioScience 70, no. 10 (September 16, 2020): 854–70. http://dx.doi.org/10.1093/biosci/biaa088.
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Abstract Global change has been accompanied by recent increases in the frequency and intensity of various ecological disturbances (e.g., fires, floods, cyclones), both natural and anthropogenic in origin. Because these disturbances often interact, their cumulative and synergistic effects can result in unforeseen consequences, such as insect outbreaks, crop failure, and progressive ecosystem degradation. We consider the roles of biological legacies, thresholds, and lag effects responsible for the distinctive impacts of interacting disturbances. We propose a hierarchical classification that distinguishes the patterns and implications associated with random co-occurrences, individual links, and multiple links among disturbances that cascade in chains or networks. Disturbance-promoting interactions apparently prevail over disturbance-inhibiting ones. Complex and exogenous disturbance cascades are less predictable than simple and endogenous links because of their dependency on adjacent or synchronous events. These distinctions help define regional disturbance regimes and can have implications for natural selection, risk assessment, and options for management intervention.
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Liu, Chun Fang, Xiu Meng Ren, and Li Mei Wang. "The Linear Auto Disturbances Rejection Controller Application in Beam Magnetic Suspension System of Gantry Moving Type Numerical Control Machine Tool." Advanced Materials Research 499 (April 2012): 423–27. http://dx.doi.org/10.4028/www.scientific.net/amr.499.423.
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When gantry-moving type numerical control machine works, support beams of the maglev system will exist outside disturbance, internal system parameter variations and unmodeled dynamics and so on, these factors will reduce system processing accuracy. We presented that suspension air-gap of beam suspension system was controlled by using the auto disturbance rejection control technology. The auto disturbances rejection controller can regard system model parameter variations and external disturbance influence of system as comprehensive disturbance, automatic on-line estimation and compensation. Meanwhile, for solving the traditional auto disturbances rejection controller’s problems which are much more parameters and complex parameters adjustment, the linear auto disturbances rejection controller was used. Under the precondition of ensuring control effect, parameters adjustment process of the auto disturbances rejection controller was greatly simplified. The simulation results show that beam magnetic suspension system using the linear auto disturbance rejection control scheme can achieve control requirements and achieve beams friction-free stable suspension.
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Qiao, Jianzhong, and Lei Guo. "Antidisturbance Fault Tolerant Control of Attitude Control Systems for Microsatellite with Unknown Input Delay." Mathematical Problems in Engineering 2013 (2013): 1–9. http://dx.doi.org/10.1155/2013/804754.
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The antidisturbance fault tolerant control problem of attitude control systems for microsatellite is investigated in the presence of unknown input delay, stuck faults from the reaction wheel and the multiple disturbances. The multiple disturbances are supposed to include the vibration disturbance torque from the reaction wheel and modeling uncertainties. The fault diagnosis observer and disturbance observer are constructed to estimate stuck faults and vibration disturbance torque from the reaction wheel, respectively. A composite fault tolerant controller is designed by combining a PID controller, the fault accommodation estimation based on the fault diagnosis observer, and the disturbance compensator based on the disturbance observer. The controller and observer gains can be easily obtained via a set of linear matrix inequalities. Simulation results are given to show that the faults can be accommodated readily, and the disturbances can be rejected and attenuated simultaneously.
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Crausbay, Shelley D., and Patrick H. Martin. "Natural disturbance, vegetation patterns and ecological dynamics in tropical montane forests." Journal of Tropical Ecology 32, no. 5 (July 14, 2016): 384–403. http://dx.doi.org/10.1017/s0266467416000328.
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Abstract:Disturbance is a central process in forest dynamics, yet the role of natural disturbance in tropical montane forests (TMFs) has not been systematically addressed. We posit that disturbance in TMFs has a wider role than commonly acknowledged and its effects are distinctive because: (1) TMFs often have very low rates of productivity due to low resources, and so recovery from disturbance may be slow, (2) montane forests have marked environmental heterogeneity which interacts with disturbance, (3) a large percentage of TMFs are regularly exposed to high energy windstorms and landslides, and (4) TMFs contain a biogeographically rich mixture of tree species with divergent evolutionary histories that interact differently with different disturbance types. We reviewed the literature on natural disturbance in TMFs and found 119 peer-reviewed papers which met our search criteria. Our review shows that disturbance is widespread in TMFs with pronounced effects on structure, function, composition and dynamics. Disturbance is also evident in the ecology of TMF biota with clear examples of plant life-history traits adapted to disturbance, including disturbance-triggered germination, treefall gap strategies and resprouting ability. Important aspects of TMF disturbances are stochastic and site-specific, but there are broad patterns in disturbance type, frequency and severity along latitudinal, altitudinal and environmental gradients. Compared with the lowland tropics, TMF disturbances are more spatially structured, TMFs experience more disturbance types in a given area due to environmental complexity, and TMFs are much more prone to small-scale yet severe landslides as well the large and potentially catastrophic disturbances of cyclones, forest die-back and fire. On the whole, natural disturbance should assume a larger role in models of ecosystem processes and vegetation patterns in TMFs. An improved understanding of what creates variation in disturbance severity and post-disturbance recovery rates, how composition and diversity feedback on disturbance type and likelihood, and how global change will alter these dynamics are important priorities in future TMF ecology research.
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Peng, Fei Jin, Xiao Yun Huang, Hong Yuan Huang, and Zhi Wen Xie. "A Novel Power Quality Disturbances Detection and Classification Method." Applied Mechanics and Materials 737 (March 2015): 193–98. http://dx.doi.org/10.4028/www.scientific.net/amm.737.193.
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Power quality disturbance detection and identification is the prerequisite and basis for the power quality management and control. This paper presents a new power quality disturbance detection and classification method. Firstly, the time-time transform is applied to power quality disturbance signal analysis. According to spectrum analysis results of the diagonal elements of time-time transform matrix, a preliminary judge about whether the disturbance signal contains harmonics and inter harmonic was given. For disturbances with non-harmonics, based on time-time transform modulus matrix diagonal sequence, the beginning and ending time of the disturbance is located, and the disturbance amplitude is calculated. For the disturbances which contain harmonics, time-time transform is perform twice to get the row mean value curve and the column mean value curve, which are required by disturbance time location and amplitude measurement. Finally, disturbance classification had realized by using rule tree. Simulation results reveal that this method is very robust and adaptable, which can identify transient power quality disturbance with minor magnitude under noisy environment, and the recognition rate is satisfactory.
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Dong, Lewei, Xinjiang Wei, and Huifeng Zhang. "Anti-disturbance control based on nonlinear disturbance observer for a class of stochastic systems." Transactions of the Institute of Measurement and Control 41, no. 6 (August 8, 2018): 1665–75. http://dx.doi.org/10.1177/0142331218787608.
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In engineering, there exist lots of nonlinear disturbance dynamics, which can be described by nonlinear exogenous systems. The current stochastic linear disturbance observer is conservative and is not applicable for nonlinear disturbance dynamics. This paper studies a class of stochastic systems with multiple disturbances, including white noise and disturbances modelled by a nonlinear exogenous system. To estimate the disturbance with nonlinear dynamics, a stochastic nonlinear disturbance observer is proposed. Based on the observer, a nonlinear disturbance observer-based disturbance attenuation control (NDOBDAC) scheme is constructed such that the composite closed-loop system is asymptotically mean-square bounded. According to the simulation example, the state responses of the system diverge in the absence of control, but it tends to be [Formula: see text] under NDOBDAC, which demonstrates the effectiveness of the proposed scheme. In addition, the anti-disturbance control accuracy of NDOBDAC approximately improves [Formula: see text] times compared with [Formula: see text] control and active disturbance rejection control (ADRC). The simulation results demonstrate the feasibility and effectiveness of the proposed scheme.
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Oldfield, Callie, and Chris Peterson. "Aboveground Biomass and Carbon Accumulation 19 Years Post-Windthrow and Salvage Logging." Forests 12, no. 2 (February 2, 2021): 173. http://dx.doi.org/10.3390/f12020173.
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Natural disturbances shape forest ecosystem characteristics, including carbon storage and structure. Often, natural disturbances are compounded with anthropogenic disturbances, which may alter the trajectory of forest carbon stock recovery. Heterogeneous levels of disturbance severity in compound disturbance events add an additional layer of complexity. This paper examines the effect of a moderate-severity wind disturbance and subsequent salvage logging on forest biomass and carbon stock recovery over 19 years. We investigate the recovery of aboveground tree biomass following a wind disturbance and salvage logging and examine the role of wind disturbance severity on biomass accumulation rates. We use pre-disturbance, 3 years post-wind disturbance and 19 years post-wind disturbance measurements of tree biomass across two adjacent sites at Natchez Trace State Forest for Site A and Site B in east central Tennessee. We found no significant difference in the carbon storage at Site A (pre = 92 MgC/ha; 19 years post-disturbance = 83 MgC/ha) or Site B (pre = 66 MgC/ha; 19 years post-disturbance = 67) when comparing the pre-disturbance level of aboveground tree carbon storage with the 19-years post-disturbance levels. Furthermore, we found no evidence that salvage logging reduced the rate of live tree carbon accumulation. The corresponding rates of mean annual carbon accumulation (MgC/ha) are as follows: Site A Unsalvaged (1.07), Site A Salvaged (1.25) and Site B Salvaged (2.02). Contrary to our prediction, greater wind damage severity was weakly associated with higher rates of biomass accumulation (R2 = 0.17). While we found no negative effect of salvage logging on the aboveground tree carbon accumulation rate, salvage logging alters other carbon pools, including coarse woody debris. Salvage logging did not reduce the rate of carbon stock recovery, and a higher wind disturbance severity was associated with a greater rate of carbon stock recovery.
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Deng, Jiuqiang, Wenchao Xue, Xi Zhou, and Yao Mao. "On disturbance rejection control for inertial stabilization of long-distance laser positioning with movable platform." Measurement and Control 53, no. 7-8 (July 8, 2020): 1203–17. http://dx.doi.org/10.1177/0020294020935492.
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This paper focuses on the disturbance rejection control problem for inertial stabilization of long-distance laser positioning with the movable platform. Due to various disturbances of the movable platform, the positioning system has significant disturbances that affect the positioning accuracy. Moreover, the nonminimum-phase property of the inertial stabilization system leads to great challenges for designing traditional disturbance-observer-based as well as rejection control methods. In this paper, a dual-compensator disturbance-observer-based control algorithm is proposed to ensure a much stronger rejection of disturbances than those of conventional methods. In particular, it is proven that the two compensators in the proposed method effectively estimate disturbances in different frequency regions. Furthermore, the analytical tuning laws for the proposed dual-compensator disturbance-observer-based control method are presented. The experimental setup including the laser positioning platform demonstrated the validity of the proposed method, which effectively rejected various disturbances.
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Mahajan, Rahul B., and Gregory J. Hakim. "Spatial Growth of Perturbations in a Turbulent Baroclinic Jet." Journal of the Atmospheric Sciences 68, no. 11 (November 1, 2011): 2731–41. http://dx.doi.org/10.1175/jas-d-11-038.1.
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Abstract The spatial spreading of infinitesimal disturbances superposed on a turbulent baroclinic jet is explored. This configuration is representative of analysis errors in an idealized midlatitude storm track and the insight gained may be helpful to understand the spreading of forecast errors in numerical weather prediction models. This problem is explored through numerical experiments of a turbulent baroclinic jet that is perturbed with spatially localized disturbances. Solutions from a quasigeostrophic model for the disturbance fields are compared with those for a passive tracer to determine whether disturbances propagate faster than the basic-state flow. Results show that the disturbance spreading rate is sensitive to the structure of the initial disturbance. Disturbances that are localized in potential vorticity (PV) have far-field winds that allow the disturbance to travel downstream faster than disturbances that are initially localized in geopotential, which have no far-field wind. Near the jet, the spread of the disturbance field is observed to exceed the tracer field for PV-localized disturbances, but not for the geopotential-localized disturbances. Spreading rates faster than the flow for geopotential-localized disturbances are found to occur only for disturbances located off the jet axis. These results are compared with those for zonal and time-independent jets to qualitatively assess the effects of transience and nonlinearity. This comparison suggests that the average properties of localized perturbations to the turbulent jet can be decomposed into a superposition of dynamics associated with a time-independent parallel flow plus a “diffusion” process.
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Roberts, Mark R. "Response of the herbaceous layer to natural disturbance in North American forests." Canadian Journal of Botany 82, no. 9 (September 1, 2004): 1273–83. http://dx.doi.org/10.1139/b04-091.
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Most work on the disturbance ecology of North American forests has focused on the tree canopy and woody understory, with little consideration of the herbaceous layer. Understanding how this species-rich and ecologically important layer responds to natural disturbances is needed as a guide for conservation. As a framework for this review, selected natural disturbances common to North American forests are evaluated in terms of a three-axis model of disturbance severity: percentage of tree canopy removed, percentage of understory vegetation removed, and percentage of forest floor and soil removed or disrupted. Eight factors, which control herbaceous-layer response, are linked to the three axes; these factors vary in dominance, depending on disturbance type and severity. The relative importances of different species' regeneration mechanisms also vary along severity gradients. The disturbance-severity model, along with the linked response factors and regeneration mechanisms, provide a framework for evaluating impacts of both natural and anthropogenic disturbances. Long-term studies of herbaceous-layer response to disturbance are needed, particularly mechanistic studies that focus on the relative importance of the eight factors controlling response. The conceptual model proposed herein needs to be tested across the full spectrum of severity levels. Finally, comparisons between natural and anthropogenic disturbances are needed.Key words: disturbance, forests, herbaceous layer, life-history characteristics, succession, understory.
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Tyson, William, Trevor C. Lantz, and Natalie C. Ban. "Cumulative Effects of Environmental Change on Culturally Significant Ecosystems in the Inuvialuit Settlement Region + Supplementary Appendices 1 to 3 (See Article Tools)." ARCTIC 69, no. 4 (November 30, 2016): 391. http://dx.doi.org/10.14430/arctic4607.
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The Inuvialuit Settlement Region (ISR) in the western Canadian Arctic is experiencing environmental changes that affect subsistence harvesting practices and are of concern to local communities. In order to assess the impacts of multiple disturbances on culturally important ecosystems in the ISR, we created a cumulative disturbance map that represents relative intensity of terrestrial disturbances across the study region. We then assessed the relative level of environmental disturbance in important harvesting areas and management zones. Subsequently, we modeled nine future disturbance scenarios that included combinations of increased human impacts and more frequent and widespread wildfires. Using the conservation planning software Marxan, we assessed the potential to conserve large, contiguous areas of unaffected harvesting lands across all scenarios. Our results show that important management zones, wildlife harvesting areas, and community planning zones are all affected by environmental disturbances. Marxan optimizations show that existing disturbance levels create thresholds for current conservation potential and indicate that future disturbances will further limit conservation potential. These results suggest that conservation planners in the region must take steps to anticipate more widespread natural and human-caused disturbance in the ISR and work to maintain large contiguous landscapes that can support wildlife harvesting in the face of ongoing environmental disturbance.
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Sukkarnkha, Pisit, and Chanin Panjapornpon. "Two-degree-of-freedom Controller Design for Uncertain Processes Using Input/output Linearization Control Technique." ASEAN Journal of Chemical Engineering 11, no. 1 (August 5, 2011): 16. http://dx.doi.org/10.22146/ajche.50039.
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In this work, a new control method for uncertain processes is developed based on two-degree-of-freedom control structure. The setpoint tracking controller designed by input/output linearization technique is used to regulate the disturbance-free output and the disturbance rejection controller designed is designed by high-gain technique. The advantage of two-degree-of-freedom control structure is that setpoint tracking and load disturbance rejection controllers can be designed separately. Open-loop observer is applied to provide disturbance-free response for setpoint tracking controller. The process/disturbance-free model mismatches are fed to the disturbance rejection controller for reducing effect of disturbance. To evaluate the control performance, the proposed control method is applied through the example of a continuous stirred tank reactor with unmeasured input disturbances and random noise kinetic parametric uncertainties. The simulation results show that both types of disturbances can be effectively compensated by the proposed control method.
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Hillerstro¨m, G., and J. Sternby. "Adaptive Rejection of Periodic Disturbances With Unknown Period." Journal of Dynamic Systems, Measurement, and Control 118, no. 3 (September 1, 1996): 606–10. http://dx.doi.org/10.1115/1.2801187.
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A disturbance cancellation extension by means of Youla parametrization to a stabilizing nominal controller is investigated. In the case of a known disturbance model, disturbance frequencies or period time, it may be implemented directly as an add-on device to the existing control system. The nominal control system may be designed without consideration of the deterministic disturbances. This way it may suffice with a PID controller. It may also be a more complex one e.g., designed to obtain certain robustness properties. For known relation between the disturbance frequencies (one or more periodic signals) but unknown fundamental frequency, a frequency shaped disturbance model estimation scheme is utilized. This makes it possible to e.g., adapt the disturbance model to minimize the error directly with respect to the output. For periodic disturbances the scheme implements a self-tuning discrete time repetitive controller. To illustrate the feasibility of the approach taken it is used for rejecting a periodic disturbance acting on a nonminimum-phase plant.
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Lei, Xusheng, Kexin Guo, and Shuzhi Sam Ge. "Disturbance Observer Based Control of Small Unmanned Aerial Rotorcraft." Mathematical Problems in Engineering 2013 (2013): 1–9. http://dx.doi.org/10.1155/2013/464938.
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As a complex system, the control performance of small unmanned aerial rotorcraft is easily affected by the dynamic model errors, measurement errors, and environment disturbances. This paper proposes a disturbance observer based control method to improve performance. The disturbance observer based control is constructed by the feedback control and a series of integral filters. The system stability can be guaranteed by the feedback control method. Furthermore, the disturbances can be estimated and eliminated quickly by the integral filters. Therefore, the control performance can be improved effectively. The control performance of the disturbance observer based control has been validated by a series of flight tests. Compared with feedback control, the disturbance observer based control yields a better tracking performance in the presence of disturbances.
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Chung, Soon-Cheol, Byung-Chan Min, Chul-Jung Kim, and Zang-Hee Cho. "Effect of Various Disturbances on fMRI: A Study on Visual and Motor Cortices." Proceedings of the Human Factors and Ergonomics Society Annual Meeting 44, no. 21 (July 2000): 3–497. http://dx.doi.org/10.1177/154193120004402135.
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We have studied the effects of various disturbances of two different levels of difficulty, that is, with weak and with strong difficulty levels for primary visual and motor tasks. In the case of visual task with motor and mental disturbances, we found it decreased as motor and mental disturbance difficulty-level increased, ***compared with the cases without motor and mental disturbances. To the contrary, in the case of motor activity, the total activation of motor cortex with weak and with strong mental disturbance was increased as mental disturbance difficulty-levels increased.
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You, Lihong, Xinjiang Wei, Jian Han, Huifeng Zhang, Xiuhua Liu, and Xin Hu. "Elegant anti-disturbance control for stochastic systems with multiple heterogeneous disturbances based on fuzzy logic systems." Transactions of the Institute of Measurement and Control 42, no. 14 (June 4, 2020): 2611–21. http://dx.doi.org/10.1177/0142331220922732.
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There are a large number of non-harmonic disturbances generated by nonlinear exogenous systems in realistic engineering. The current disturbance observer is not applicable for estimating the non-harmonic disturbance with unknown nonlinear dynamics, thus greatly reducing the accuracy of the controller. This paper addresses a class of stochastic systems with multiple heterogeneous disturbances including white noise and non-harmonic disturbance with unknown smooth nonlinear function, which can be approximated by fuzzy logic systems. Based on the approximation of the unknown nonlinear function, an adaptive disturbance observer (ADO) is constructed to estimate non-harmonic disturbance. Combining disturbance observer-based control with fuzzy control, an elegant anti-disturbance control (EADC) scheme is proposed such that the composite system achieves asymptotically bounded in mean square. Simulation examples show that the state responses of the system gradually approache [Formula: see text] from divergence, indicating that the effectiveness of the controller is satisfactory. In addition, the anti-disturbance control accuracy of EADC approximately improves [Formula: see text] times compared with [Formula: see text] control. The simulation results demonstrate the feasibility and effectiveness of the proposed scheme.