Journal articles on the topic 'Disturbances'
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1
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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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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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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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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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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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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Taimoor, Muhammad, Li Aijun, and Rooh ul Amin. "Disturbances rejection based on sliding mode control." Aircraft Engineering and Aerospace Technology 91, no. 4 (April 1, 2019): 680–99. http://dx.doi.org/10.1108/aeat-04-2018-0121.
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Purpose The purpose of this paper aims to investigate an effective algorithm for different types of disturbances rejection. New dynamics are designed based on disturbance. Observer-based sliding mode control (SMC) technique is used for approximation the disturbances as well as to stabilize the system effectively in presence of uncertainties. Design/methodology/approach This research work investigates the disturbances rejection algorithm for fixed-wing unmanned aerial vehicle. An algorithm based on SMC is introduced for disturbances rejection. Two types of disturbances are considered, the constant disturbance and the sinusoidal disturbance. The comprehensive lateral and longitudinal models of the system are presented. Two types of dynamics, the dynamics without disturbance and the new dynamics with disturbance, are presented. An observer-based algorithm is presented for the estimation of the dynamics with disturbances. Intensive simulations and experiments have been performed; the results not only guarantee the robustness and stability of the system but the effectiveness of the proposed algorithm as well. Findings In previous research work, new dynamics based on disturbances rejection are not investigated in detail; in this research work both the lateral and longitudinal dynamics with different disturbances are investigated. Practical implications As the stability is always important for flight, so the algorithm proposed in this research guarantees the robustness and rejection of disturbances, which plays a vital role in practical life for avoiding any kind of damage. Originality/value In the previous research work, new dynamics based on disturbances rejection are not investigated in detail; in this research work both the lateral and longitudinal dynamics with different disturbances are investigated. An observer-based SMC not only approximates the different disturbances and also these disturbances are rejected in order to guarantee the effectiveness and robustness.
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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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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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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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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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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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Yang, Hong-yong, Hai-lin Zou, Hui-xia Liu, Fei Liu, Mei Zhao, and Fujun Han. "Consensus Tracking of Multiagent Systems with Time-Varying Reference State and Exogenous Disturbances." Mathematical Problems in Engineering 2014 (2014): 1–7. http://dx.doi.org/10.1155/2014/213862.
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The tracking control of multiagent dynamical systems with exogenous disturbances is studied. A path following algorithm with a time-varying reference state is proposed, and the path tracking of multiagent systems with exogenous disturbance is analyzed. Under the influence of the disturbances, a disturbance observer is developed to estimate the exogenous disturbances. Asymptotical consensus of the multiagent systems with time-varying reference state and exogenous disturbances under the disturbance observers-based control (DOBC) can be achieved for fixed and switching topologies. Finally, by applying an example of multiagent systems with switching topologies and exogenous disturbances, the consensus tracking of multiagent systems with time-varying reference state is reached under the DOBC with the designed parameters.
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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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Liu, Xiaolong, Zhengtao Shi, Guangcai Huang, Yanchen Bo, and Guangjie Chen. "Time Series Remote Sensing Data-Based Identification of the Dominant Factor for Inland Lake Surface Area Change: Anthropogenic Activities or Natural Events?" Remote Sensing 12, no. 4 (February 12, 2020): 612. http://dx.doi.org/10.3390/rs12040612.
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Inland lake variations are considered sensitive indicators of global climate change. However, human activity is playing as a more and more important role in inland lake area variations. Therefore, it is critical to identify whether anthropogenic activity or natural events is the dominant factor in inland lake surface area change. In this study, we proposed a method that combines the Douglas-Peucker simplification algorithm and the bend simplification algorithm to locate major lake surface area disturbances. These disturbances were used to extract the features that been used to classify disturbances into anthropogenic or natural. We took the nine lakes in Yunnan Province as test sites, a 31-year long (from 1987 to 2017) time series Landsat TM/OLI images and HJ-1A/1B used as data sources, the official records were used as references to aid the feature extraction and disturbance identification accuracy assessment. Results of our method for disturbance location and disturbance identification could be concluded as follows: (1) The method can accurately locate the main lake changing events based on the time series lake surface area curve. The accuracy of this model for segmenting the time series of lake surface area in our study area was 94.73%. (2) Our proposed method achieved an overall accuracy of 87.75%, with an F-score of 85.71 for anthropogenic disturbances and an F-score of 88.89 for natural disturbances. (3) According to our results, lakes in Yunnan Province of China have undergone intensive disturbances. Human-induced disturbances occurred almost twice as much as natural disturbances, indicating intensified disturbances caused by human activities. This inland lake area disturbance identification method is expected to uncover whether a disturbance to inland lake area is human activity-induced or a natural event, and to monitor whether disturbances of lake surface area are intensified for a region.
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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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Xu, T., Y. L. Hu, F. F. Wang, Z. Chen, and J. Wu. "Is there any difference in local time variation in ionospheric F2-layer disturbances between earthquake-induced and Q-disturbance events?" Annales Geophysicae 33, no. 6 (June 3, 2015): 687–95. http://dx.doi.org/10.5194/angeo-33-687-2015.
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Abstract. Ionospheric anomalies before earthquakes have become the subject of one of the most intensive studies in the area of ionospheric variation. The ionosphere has a large class of disturbances under quiet geomagnetic conditions, i.e., quiet time disturbances (Q disturbances). Hence, the characteristics of seismo-ionospheric anomalies obtained by statistical analysis should be compared with those of Q-disturbance events. Using the data of foF2 (F2-layer critical frequency) during the whole interval of 1978–2008 (~3 solar cycles), the local time (LT) variation in Q disturbances is investigated. The results showed that a well-pronounced nighttime peak took place for positive disturbances induced by Q-disturbance events, while positive disturbances related to earthquakes predominately occurred in the daytime, especially in the afternoon LT sector. This remarkable difference in local time variation in foF2 between the earthquake-triggered and Q-disturbance events is of great significance for the identification of ionospheric precursors.
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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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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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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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Wu, Bin-Yi, Xian-Sheng Qin, Shun-Qi Zhang, Jing Bai, Ting Xue, and Rüdiger Schmidt. "Unknown disturbance estimation for vibration systems using distributed piezoelectric sensors." Mechanics & Industry 19, no. 5 (2018): 506. http://dx.doi.org/10.1051/meca/2018042.
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Vibration is usually caused by external disturbances, which may lead to structural damage. Vibrations can be significantly suppressed by taking disturbances into account. However, in many cases disturbances are unknown or difficult to be measured directly. In order to estimate external unknown disturbances, this article develops a proportional-integral (PI) disturbance observer with measurement noises for smart structures using multiple distributed piezoelectric sensors. For simulation purpose, a dynamic finite element model of piezoelectric bonded smart structure is presented. This disturbance observation method is validated by estimating various kinds of unknown disturbances using piezoelectric measurements. Furthermore, the measurement numbers and the position of measurements are investigated.
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Wu, Zongkai, and Wei Wang. "Adaptive Anti-Disturbance Method for Magnetometer and INS Integration in a Road Vehicle." Journal of Navigation 72, no. 06 (May 23, 2019): 1513–32. http://dx.doi.org/10.1017/s0373463319000389.
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The integration of magnetometers and Inertial Navigation Systems (INS) is widely used in low-cost navigation systems. However, even if the system has been calibrated, random magnetic disturbances still appear in practical applications, which lead to large heading errors. To solve this problem, an adaptive anti-disturbance method to overcome random magnetic disturbance is proposed. First, disturbances are classified and analysed in detail based on actual road vehicle driving data. Then an Adaptive Robust Extend Kalman Filter (AREKF) is designed to resist sudden disturbances. However, an AREKF may accumulate errors slowly when a long-term disturbance exists. Considering this situation, this paper proposes that AREKF is used to maintain accuracy in the early stages, at the same time as the magnetometer is quickly calibrated with a Kalman filter. Then, the new magnetometer parameters are put into the AREKF to suppress long-term disturbances. Finally, cascading these two modules, not only the sudden disturbance can be overcome, but the situation of long-term disturbances can be suppressed. The results of simulation and an actual driving test show that the proposed method can effectively overcome random magnetic disturbances in both the short and long term.
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Qiao, Pengyu, Jun Yang, Chen Dai, and Xi Xiao. "Design of Composite Disturbance Observer and Continuous Terminal Sliding Mode Control for Piezoelectric Nanopositioning Stage." Electronics 10, no. 18 (September 13, 2021): 2242. http://dx.doi.org/10.3390/electronics10182242.
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The nonlinearities of piezoelectric actuators and external disturbances of the piezoelectric nanopositioning stage impose great, undesirable influences on the positioning accuracy of nanopositioning stage systems. This paper considers nonlinearities and external disturbances as a lumped disturbance and designs a composite control strategy for the piezoelectric nanopositioning stage to realize ultra-high precision motion control. The proposed strategy contains a composite disturbance observer and a continuous terminal sliding mode controller. The composite disturbance observer can estimate both periodic and aperiodic disturbances so that the composite control strategy can deal with the disturbances with high accuracy. Meanwhile, the continuous terminal sliding mode control is employed to eliminate the chattering phenomenon and speed up the convergence rate. The simulation and experiment results show that the composite control strategy achieves accurate estimation of different forms of disturbances and excellent tracking performance.
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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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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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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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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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Zhao, Guo Yong, and Yu Gang Zhao. "Simulation on Observe Compensation Control for Electric Disturbances in CNC Servo System." Applied Mechanics and Materials 44-47 (December 2010): 675–79. http://dx.doi.org/10.4028/www.scientific.net/amm.44-47.675.
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The various disturbances destroy CNC system tracking accuracy greatly. The ideal servo system should obtain high system precision and machining precision even if under disturbances action. The influence of electric disturbances to CNC servo system is researched in detail. Moreover, the electric disturbances on the electric interface of servo system driver elements are observed, and the observe compensation quantity is added to the position controller output. The simulations aimed at saw-tooth wave electric disturbance signal show that the developed approach can reduce tracking error and enhance the restrain disturbance characteristic.
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Suja, S., and Jovitha Jerome. "POWER SIGNAL DISTURBANCE CLASSIFICATION USING WAVELET BASED NEURAL NETWORK." ASEAN Journal on Science and Technology for Development 25, no. 2 (November 22, 2017): 205–17. http://dx.doi.org/10.29037/ajstd.243.
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In this paper, the power signal disturbances are detected using discrete wavelet transform (DWT) and categorized using neural networks. This paper presents a prototype of power quality disturbance recognition system. The prototype contains three main components. First a simulator is used to generate power signal disturbances. The second component is a detector which uses the technique of DWT to detect the power signal disturbances. DWT is used to extract disturbance features in the power signal. The third component is neural network architecture to classify the power signal disturbances.
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Gao, De Xin, and Rui Wei. "The Optimal Controller Design of Zero Steady-State Error for Nonlinear Systems with Composite Disturbances." Advanced Materials Research 383-390 (November 2011): 1343–49. http://dx.doi.org/10.4028/www.scientific.net/amr.383-390.1343.
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This paper considers the optimal rejection with Zero Steady-State Error for nonlinear systems with step and ramp composite disturbances. Firstly, the nonlinear system model with composite disturbances is transformed into linear system with disturbances, then we construct an augmented linear system without disturbances. With respect to the quadratic performance indexes of infinite horizon, consequently, the problem of disturbance rejection with zero steady-state error is transformed into the problem of designing an optimal controller for the augmented plant without disturbances, which can eliminate static error. Thus the disturbances can unfold of the signal through the Taylor series for the form of polynomial function of time, and obtain optimal controller design approach to eliminate the general disturbance. Finally, a practical example is given to illustrate the effectiveness of the theory.
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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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Hu, Yang, Boyang Li, Bailun Jiang, Jixuan Han, and Chih-Yung Wen. "Disturbance Observer-Based Model Predictive Control for an Unmanned Underwater Vehicle." Journal of Marine Science and Engineering 12, no. 1 (January 2, 2024): 94. http://dx.doi.org/10.3390/jmse12010094.
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This work addresses the motion control problem for a 4-degree-of-freedom unmanned underwater vehicle (UUV) in the presence of nonlinear dynamics, parametric uncertainties, system constraints, and time-varying external disturbances. A disturbance observer-based control scheme is proposed, which is structured around the model predictive control (MPC) method integrated with an extended active observer (EAOB). Compared to the conventional disturbance observer, the developed EAOB has the ability to handle both external disturbances and system/measurement noises simultaneously. The EAOB leverages a combination of sensor measurements and a system dynamic model to estimate disturbances in real-time, which allows continuous estimation and compensation of time-varying disturbances back to the controller. The proposed disturbance observer-based MPC is implemented by feeding the estimated disturbances back into the MPC’s prediction model, which forms an effective adaptive controller with a parameter-varying model. The proposed control strategy is validated through simulations in a Gazebo and robot operating system environment. The results show that the proposed method can effectively reject unpredictable disturbances and improve the UUV’s control performance.
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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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Ahmed, Nigar, and Mou Chen. "Robust model reference adaptive backstepping sliding-mode control for quadrotor attitude with disturbance observer." Aircraft Engineering and Aerospace Technology 93, no. 7 (June 17, 2021): 1156–70. http://dx.doi.org/10.1108/aeat-11-2020-0277.
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Purpose The purpose of this research paper is to design a disturbance observer-based control based on the robust model reference adaptive backstepping sliding-mode control for attitude quadrotor model subject to uncertainties and disturbances. Design/methodology/approach To estimate and reject the disturbance, a disturbance observer is designed for the exogenous disturbances with perturbation while a control criterion is developed for the tracking of desired output. To achieve the control performance, backstepping and sliding-mode control techniques are patched together to obtain robust chattering-free controller. Furthermore, a model reference adaptive control criterion is also combined with the design of robust control for the estimation and rejection of uncertainties and unmodeled dynamics of the attitude quadrotor. Findings The findings of this research work includes the design of a disturbance observer-based control for uncertain attitude quadrotor system with the ability of achieving tracking control objective in the presence of nonlinear exogenous disturbance with and without perturbation. Practical implications In practice, the quadrotor flight is opposed by different kinds of the disturbances. In addition, being an underactuated system, it is difficult to obtain an accurate mathematical model of quadrotor for the control design. Thus, a quadrotor model with uncertainties and disturbances is inevitable. Hence, it is necessary to design a control system with the ability to achieve the control objectives in the presence of uncertainties and disturbances. Originality/value Designing the control methods for quadrotor control without uncertainties and disturbances is a common practice. However, investigating the uncertain quadrotor plant in the presence of nonlinear disturbances is rarely taken into consideration for the control design. Hence, this paper presents a control algorithm to address the issues of the uncertainties and disturbances as well as investigate a control algorithm to achieve tracking performance.
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Hou, Linlin, and Haibin Sun. "Disturbance-observer-based l2–l∞ control for discrete-time Markovian jump system." Transactions of the Institute of Measurement and Control 40, no. 9 (January 24, 2018): 2807–12. http://dx.doi.org/10.1177/0142331217744486.
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This paper considers the problem of anti-disturbance control for discrete-time Markovian jump systems with multiple disturbances. The controller is constructed via disturbance-observer-based control and l2– l∞ control. The disturbances are divided into two parts. One, in the same channel as the control inputs, is described by an exogenous system. The other is assumed to be bounded with an [Formula: see text] norm. A disturbance observer is presented to estimate and reject the first-case disturbances for discrete-time Markovian jump systems, and an l2– l∞ control scheme is used to attenuate the second-case disturbances. By using linear matrix inequalities, a solvable sufficient condition is developed. Finally, the effectiveness of the proposed control scheme is demonstrated via a numerical example.
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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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Mikhailov, A. V., A. H. Depueva, and V. H. Depuev. "Daytime F2-layer negative storm effect: what is the difference between storm-induced and Q-disturbance events?" Annales Geophysicae 25, no. 7 (July 30, 2007): 1531–41. http://dx.doi.org/10.5194/angeo-25-1531-2007.
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Abstract. Negative F2-layer storms related to geomagnetic activity and quiet-time disturbances (Q-disturbances) belong to different classes of events and exhibit different morphology. Mid-latitude daytime Q-disturbances, unlike the usual negative F2-layer storms, demonstrate NmF2 and hmF2 in-phase variations. An analysis of Millstone Hill ISR observations for usual and Q-disturbances has shown the difference in the controlling aeronomic parameter variations for the two classes of events. The decrease in atomic oxygen concentration provides the main contribution to the hmF2 decrease below the monthly median level during Q-disturbance events. Unlike the usual negative storms, the negative effect takes place in the whole topside ionosphere under Q-disturbance conditions. The difference is due to different effective plasma scale heights in the two cases. Clustering of the usual negative F2-layer disturbances around equinoxes and Q-disturbances around winter solstice, as well as different latitudinal variations for the occurrence of the two types of disturbances is due to their different formation mechanisms.
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Sun, Xingyu, Jianming Miao, Kankan Deng, and Yanyun Wang. "The path-following control of the underactuated AUV with input saturation and multiple disturbances." Journal of Physics: Conference Series 2121, no. 1 (November 1, 2021): 012044. http://dx.doi.org/10.1088/1742-6596/2121/1/012044.
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Abstract Autonomous underwater vehicle (AUV) in marine resource surveys plays an important role. This paper proposes a new path-following control frame for the underactuated AUV with input saturation and multiple disturbances. The disturbances include external disturbances, model parameter uncertainties, unmodeled dynamics and other random disturbances. Compared to most of previously published literatures, which treat disturbances as lumped disturbances, a composite hierarchical anti-disturbance control (CHADC) strategy is adopted to achieve higher precision path following. A disturbance observer (DOB) is constructed to estimate and eliminate the disturbances with partial known information, while the H ∞ theory is used to optimize the path-following controller to attenuate the other disturbances satisfying the L 2-norm bound condition and improve the robustness of system. Besides, Lyapunov direct method and back-stepping method are used to design the path-following controller, where the input saturation is considered, the extended state observer (ESO) is used to estimate the uncertainty of kinematic controller and the nonlinear tracking differentiator (NTD) is used to simplify the controller. Finally, simulations are given to demonstrate the effectiveness of the proposed control law.
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Zhu, Dehuang, Suhong Peng, Jinyan Wang, and Dafeng Hui. "Responses of Nutrient Resorption to Human Disturbances in Phoebe bournei Forests." Forests 13, no. 6 (June 10, 2022): 905. http://dx.doi.org/10.3390/f13060905.
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Nutrient resorption plays an important role in the nutrient conservation of plants and ecosystem nutrient cycling. Although community succession and nutrient addition could regulate plant nutrient resorption, how resorptions of foliar nutrients vary with human disturbances remains unclear. With the economic development, Phoebe bournei forests (PF) have suffered varying degrees of human disturbances in China. In this study, the leaf nutrient resorption efficiency (RE) of the PF under two disturbances (i.e., severe and mild disturbances) were investigated. Results showed that the phosphorus (P) contents of green leaf, senesced leaf, and soil were low under both disturbances, reflecting that the PF had a potential P limitation. Phosphorus and potassium (K) REs were higher under the severe disturbance than those under the mild disturbance. The potassium resorption efficiency was the highest among the three REs under both disturbances. In addition, nutrient resorption efficiencies increased with green leaf nutrient contents under both disturbances. However, there were negative significant relationships of specific leaf area and leaf dry matter content with nutrient resorption under both disturbances. These findings provide a new perspective of nutrient resorption and revealed the potential impact of human disturbances on the nutrient cycle in forest ecosystems.
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Fu, Baozeng, Shihua Li, Lei Guo, Jun Yang, and Qixun Lan. "Finite-time stabilization of port-controlled Hamiltonian systems with nonvanishing disturbances." Transactions of the Institute of Measurement and Control 40, no. 10 (October 25, 2017): 2973–81. http://dx.doi.org/10.1177/0142331217712381.
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This paper concerns the problem of finite-time stabilization of nonlinear port-controlled Hamiltonian systems subject to nonvanishing disturbances via a composite control manner. The composite controller is developed by combining the damping injection, the finite-time feedback control and the finite-time disturbance observer techniques. The key idea is that a finite-time disturbance observer is designed to estimate disturbances and the estimation of disturbances is employed to feedforward compensate the disturbances. Finite-time stability analysis for the augmented system is presented. An example of a nonlinear circuit system with simulation results demonstrates the effectiveness of the proposed method.
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Shen, Hong, Xiaoli Zhang, and Yang Yi. "Integral Sliding Mode Anti-Disturbance Control for Markovian Jump Systems with Mismatched Disturbances." Electronics 10, no. 9 (May 2, 2021): 1075. http://dx.doi.org/10.3390/electronics10091075.
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This paper addresses an integral sliding mode-based anti-disturbance control algorithm for a type of Markovian jump systems (MJSs), which are influenced by different types of mismatched disturbances. On one hand, as for those disturbances that can be modeled, the disturbance observer (DO) method is introduced to realize the dynamical estimation of disturbances. Based on this, both the integral sliding surface (ISS) and the composite anti-disturbance controller are proposed in succession for rejecting unknown disturbances and guaranteeing the stability of the controlled MJS. Meanwhile, the states of the controlled system are ensured to reach ISS within a finite time. In addition, the L1 performance index is given to attenuate the effects of bounded disturbances. The controller and observer gains can be computed by using convex optimization techniques. The satisfactory stochastic stability and dynamical tracking performance are both also proved. Finally, the simulation results effectively verify all of the required performances.
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Hu, Weijun. "Nonlinear augmented state observer-based adaptive output feedback anti-disturbance control for nonlinear systems with non-harmonic multiple uncertainties." Transactions of the Institute of Measurement and Control 41, no. 7 (August 20, 2018): 1904–11. http://dx.doi.org/10.1177/0142331218790099.
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In this paper, a novel output feedback anti-disturbance control method is carried out for a class of nonlinear systems subject to non-harmonic multisource disturbances. By using a nonlinear exogenous system, a class of non-harmonic disturbances possessing complex and nonlinear characteristics are taken fully into consideration. Based on a nonlinear damping term, we establish an adaptive augmented state observer that can achieve robust asymptotic disturbance estimation for the system states, the harmonic disturbances and the non-harmonic disturbances. By fusing the augmented state observer and a state-feedback controller, a robust adaptive output feedback anti-disturbance control structure is constructed. The boundness of the combined controller–observer system is derived on the basis of Lyapunov analysis. Furthermore, aiming at the intense non-harmonic disturbances, the proposed method is extended and a new output feedback controller is obtained. The effectiveness of the proposed scheme is demonstrated through experimental studies on a practical example.
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Zhang, Yinhui, Huabo Yang, Zhenyu Jiang, Fan Hu, and Weihua Zhang. "Robust Predictive Functional Control for Flight Vehicles Based on Nonlinear Disturbance Observer." International Journal of Aerospace Engineering 2015 (2015): 1–16. http://dx.doi.org/10.1155/2015/878971.
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A novel robust predictive functional control based on nonlinear disturbance observer is investigated in order to address the control system design for flight vehicles with significant uncertainties, external disturbances, and measurement noise. Firstly, the nonlinear longitudinal dynamics of the flight vehicle are transformed into linear-like state-space equations with state-dependent coefficient matrices. And then the lumped disturbances are considered in the linear structure predictive model of the predictive functional control to increase the precision of the predictive output and resolve the intractable mismatched disturbance problem. As the lumped disturbances cannot be derived or measured directly, the nonlinear disturbance observer is applied to estimate the lumped disturbances, which are then introduced to the predictive functional control to replace the unknown actual lumped disturbances. Consequently, the robust predictive functional control for the flight vehicle is proposed. Compared with the existing designs, the effectiveness and robustness of the proposed flight control are illustrated and validated in various simulation conditions.
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Zang, Wanshun, Xiao Chen, and Jun Zhao. "Multi-Disturbance Observers-Based Nonlinear Control Scheme for Wire Rope Tension Control of Hoisting Systems with Backstepping." Actuators 11, no. 11 (November 6, 2022): 321. http://dx.doi.org/10.3390/act11110321.
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The objective of this paper is to pursue a wire rope control methodology for reducing the tension difference between two wire ropes of a hoisting system. As we know, complicated disturbances exist in the complex electro-hydraulic hoisting system, notably, some of these disturbances are coupled, such as high-speed airflow disturbances, structure vibrations and vibrations in flexible wire ropes. Furthermore, there are model errors in force modeling due to the Coulomb friction between two wire ropes and two moveable head sheaves in the real physical hoisting systems. To eliminate disturbances, two types of disturbance observers (DOs) are employed: a traditional disturbance observer (TDO) and a coupled disturbance observer (CDO), both of which are utilized to estimate and compensate for the Coulomb friction and coupled disturbances online. As a result, a nonlinear backstepping control scheme is presented with estimation values from the TDO and the CDO. The experiment’s results demonstrate the effectiveness of the proposed control methodology.
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Gulyaeva, T. L. "Disturbances in the Magnetosphere and Ionosphere during Spotless Sun." Геомагнетизм и аэрономия 63, no. 3 (May 1, 2023): 340–48. http://dx.doi.org/10.31857/s0016794022600582.
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Analysis of geomagnetic and ionospheric activity is performed for 541 disturbed days during spotlessSun (Kp 3.0) from 1995 to 2021. Variations of the global ionospheric indices WU (positive disturbancesof total electron content), WL (negative disturbances), their range WE and the planetary index Wp are analyzed.The source W-index characterizes a measure of deviation of the instant total electron content from thequiet median varying from −4 to +4 with a step 1, and the global indices WU, WL, WE, Wp are derived fromthe global maps GIM-TEC of Jet Propulsion Laboratory, JPL. Investigation of the seasonal dependence hasrevealed two levels of the ionosphere disturbances: the low disturbance of the ionosphere during 1996‒1998and 2018‒2021 and the high disturbance during 2004‒2010 and 2016‒2017. The seasonal ionosphere variationsare different for two sets of the data. The seasonal variations of the solar wind velocity Vsw near the Earthorbit are first identified for the 1st data set displaying the peaks at the equinoxes similar to variations of theKp-index. The 2nd set of the high disturbance of the ionosphere refers to the epoch of transition from the highsolar activity SA to low SA characterized by the total restructuring of the physical conditions on the Sun
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Niu, Dan, Xisong Chen, Xiaojun Wang, and Xingpeng Zhou. "Composite disturbance rejection control for hydraulic classification." Transactions of the Institute of Measurement and Control 40, no. 6 (March 15, 2017): 1863–72. http://dx.doi.org/10.1177/0142331217693917.
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In the hydraulic classification, precise control for the flow rate of overflow water is vital to guarantee the uniformity and stability of the powder product size. Usually the multiple overflow tanks are supplied by a shared overflow pipeline, which gives rise to large coupling effects in the controls for the flow rates of multiple overflow tanks simultaneously. To solve this issue, it is necessary to keep the water pressure in the shared overflow pipeline accurately constant, which is not easy due to strong disturbances. Several control strategies have been proposed to control the constant water pressure. However, most of them (such as proportional-integral-derivative and model predictive control) reject disturbances just through feedback regulation and do not reject disturbances directly. This may cause poor control performances in the presence of strong disturbances. For improving the disturbance rejection performance, a control scheme based on proportional-integral-derivatives and disturbance observer is put forward in this paper. The scheme employs disturbance observer as feedforward compensation and a proportional-integral-derivative controller as feedback regulation. The disturbance rejection properties under both model mismatches and external disturbances are discussed. The test results illustrate that the proposed method can remarkably improve the disturbance attenuation property compared with the conventional proportional-integral-derivative method in the hydraulic classification process.
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Zhou, Xiangyang, Yuan Jia, and Yong Li. "An integral sliding mode controller based disturbances rejection compound scheme for inertially stabilized platform in aerial remote sensing." Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering 232, no. 5 (April 19, 2017): 932–43. http://dx.doi.org/10.1177/0954410017703142.
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An integral sliding mode controller based disturbance rejection compound scheme is proposed to attenuate the influences of nonlinear disturbances and parameter uncertainties on stability accuracy of the three-axis inertially stabilized platform for the aerial remote sensing applications. The compound scheme is composed of an integral sliding mode controller and a disturbance measurement unit. The integral sliding mode controller is used to ensure robust stability against exterior nonlinear disturbances and parameter uncertainties, in which the saturation function is employed to reduce the chattering. The disturbance measurement unit is served as the disturbance measurement components of the rate loop and current loop of three closed-loop structure in the inertially stabilized platform control system, by which the interior high-frequency disturbances are compensated in real time. To verify the method, simulations and experiments are conducted. In simulations, the LuGre friction model is introduced to analyze the effects of disturbances. Further, a series of experiments are carried out. The results show that the compound scheme has excellent ability in both of disturbances rejection and robust stabilization, by which the stability accuracy of the inertially stabilized platform is improved significantly.
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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.