Class Of Disturbances Research Articles

Adaptive unified predictive control applied to first-order-plus-dead-time processes to eliminate unknown class of deterministic disturbance

A novel adaptive unified predictive control method (adaptive-UPC) is proposed and applied to the first-order-plus-dead-time (FOPDT) process models with model uncertainties (gain, time constant and dead-time) under unknown deterministic disturbances (step, ramp and the unknown frequency sinusoid). Based on indirect self-tuning regulator, this new control structure is constructed by combining UPC controller, recursive least-squares estimation with forgetting factor (RLS with forgetting factor) and variable regression estimation (VRE). By the simulation results, this scheme is proven to be applied to such process model with model uncertainties effectively.

Attitude control of a quadrotor aircraft subject to a class of time-varying disturbances

Here, the attitude control of a quadrotor aircraft subject to a class of disturbances is studied. Unlike disturbances mentioned in most of the existing literature, the disturbance considered here is time varying and non-vanished. An extended observer is designed to estimate the disturbance by treating it as a new unknown state. Based on the estimation, a feedback controller with a sliding mode term is designed to stabilise the attitude of the quadrotor. Furthermore, to avoid the discontinuity of the control law caused by the sliding mode term, a modified sliding mode term is designed. The resulting continuous feedback controller makes the attitude error uniformly ultimate bounded. Theoretical results are confirmed by numerical simulations.

On-line energy management for HEV based on particle swarm optimization

This study considers a Hybrid Electrical Vehicle supplied by a Fuel Cell stack and supercapacitances used as Storage Element. In such an application, real time energy management is of paramount importance in order to increase autonomy and be able to deal on-line with perturbed power demand. Many off-line power flow optimization principles are available but on-line algorithms are preferred and should be derived for optimal management of the instantaneous power splitting between the different available power sources. Based on particle swarm optimization algorithm, this study defines the parameters tuning of such algorithm in real time. The final power splitting allows not only recovering energy braking but also is robust to some disturbances occurring during the trip. The solution provides good-quality and high-robustness results in a certain class of mission profile and power disturbance.

The Effects of Copper Pollution on Fouling Assemblage Diversity: A Tropical-Temperate Comparison

BackgroundThe invasion of habitats by non-indigenous species (NIS) occurs at a global scale and can generate significant ecological, evolutionary, economic and social consequences. Estuarine and coastal ecosystems are particularly vulnerable to pollution from numerous sources due to years of human-induced degradation and shipping. Pollution is considered as a class of disturbance with anthropogenic roots and recent studies have concluded that high frequencies of disturbance may facilitate invasions by increasing the availability of resources.Methodology/Principal FindingsTo examine the effects of heavy metal pollution as disturbance in shaping patterns of exotic versus native diversity in marine fouling communities we exposed fouling communities to different concentrations of copper in one temperate (Virginia) and one tropical (Panama) region. Diversity was categorized as total, native and non-indigenous and we also incorporated taxonomic and functional richness. Our findings indicate that total fouling diversity decreased with increasing copper pollution, whether taxonomic or functional diversity is considered. Both native and non-indigenous richness decreased with increasing copper concentrations at the tropical site whereas at the temperate site, non-indigenous richness was too low to detect any effect.Conclusions/SignificanceNon-indigenous richness decreased with increasing metal concentrations, contradicting previous investigations that evaluate the influence of heavy metal pollution on diversity and invasibility of fouling assemblages. These results provide first insights on how the invasive species pool in a certain region may play a key role in the disturbance vs. non-indigenous diversity relationship.

Global Existence for a Translating Near-Circular Hele–Shaw Bubble with Surface Tension

This paper concerns global existence for arbitrary nonzero surface tension of bubbles in a Hele–Shaw cell that translate in the presence of a pressure gradient. When the cell width to bubble size is sufficiently large, we show that a unique steady translating near-circular bubble symmetric about the channel centerline exists, where the bubble translation speed in the laboratory frame is found as part of the solution. We prove global existence for symmetric sufficiently smooth initial conditions close to this shape and show that the steady translating bubble solution is an attractor within this class of disturbances. In the absence of side walls, we prove stability of the steady translating circular bubble without restriction on symmetry of initial conditions. These results hold for any nonzero surface tension despite the fact that a local planar approximation for the steady shape near the front of the bubble would suggest Saffman–Taylor instability. We exploit a boundary integral approach that is particularly suitable for the analysis of nonzero viscosity ratio between fluid inside and outside the bubble. An important element of the proof was the introduction of a weighted Sobolev norm that accounts for stabilization due to advection of disturbances from the front to the back of the bubble.

High gain adaptive control for a class of uncertain non-holonomic systems

It is well known that high gain feedback is one of the most powerful controller design technique for uncertain controlled systems. In this paper, a controller design method of high gain adaptive feedback for non-holonomic systems with unknown system parameters and a class of unbounded uncertainties and/or disturbances is proposed. The considered unbounded uncertainties and/or disturbances are decomposed by a known function and unknown constants. The designed adaptive controller is a rather simple structure, since it has only one adaptive adjusting term which is a feedback gain designed based on high gain technique. Further, the controller achieves not only the stability of the controlled system but also convergence to a small region around origin by increasing the design parameters. The application of the controller to a non-holonomic wheeled mobile robot is considered as an illustrative example.

Reaction of the critical frequency of the F2 layer to a sharp depletion in atmospheric pressure

Changes in the critical frequencies of the F2 layer at several midlatitude stations of ionospheric vertical sounding during a sharp depletion in atmospheric pressure under quiet solar and geomagnetic conditions are analyzed. It is shown that in such periods, the observed foF2 values differ from the mean values by approximately 10–15% and the deviations from the mean could be both negative (in the daytime hours) and positive (at night). Such variations in foF2 could be referred to the known class of ionospheric disturbances observed under a quiet geomagnetic situation, that is, to the so-called “Q-disturbances.” Analysis of wavelet spectra of foF2 variations shows the presence in the F region of oscillations of various periods (from 0.5 to 10 days). The decrease in the amplitude of daily variations during pressure depletion is found. Presumably, the observed effect is caused by the dynamic impact of waves formed in the lower atmosphere on the ionospheric F2 layer.

On a class of electromagnetic disturbances preceding strong earthquakes

The results of experimental observations over variations of the Earth’s magnetic field recorded by the instruments of the North Caucasus Geophysical Observatory are presented. We observed specific ultralow-frequency quasi-oscillatory waveforms preceding strong distant seismic events in the structure of electromagnetic signals.

A Disturbance Attenuation Approach for a Class of Continuous Piecewise Affine Systems: Control Design and Experiments

We consider the disturbance attenuation problem for a class of continuous piecewise affine systems. Hereto, observer-based output-feedback controllers are proposed that render the closed-loop system uniformly convergent. The convergence property ensures, first, stability and, second, the existence of a unique, bounded, globally asymptotically stable steady-state solution for each bounded disturbance. The latter property is key in uniquely specifying closed-loop performance in terms of disturbance attenuation. Because of its importance in engineering practice, the class of harmonic disturbances is studied in particular and performance measures for this class of disturbances are proposed based on so-called generalized frequency response functions for convergent systems. Additionally, the derived control strategy is extended by including conditions that guarantee the satisfaction of a bound on the control input. The effectiveness of the proposed control design strategy is illustrated by the application of the results to an experimental benchmark system being a piecewise affine beam system.

On Optimal Control under Program Disturbances

For the optimal control problem under dynamical uncertainties and terminal type quality index, the dependence of optimal guarantee on the restricting the set of admissible disturbances to program ones is considered for some classes of control strategies. The example of the control problem, for which the optimal guarantee is essentially changed when the set of disturbances is restricted to program ones is given. Some conditions making the optimal guarantee invariable to this restriction of class of disturbances is provided.

Intelligence, social class of origin, childhood behavior disturbance and education as predictors of status attainment in midlife in men: The Aberdeen Children of the 1950s study

In a birth cohort of 6281 men from Aberdeen, Scotland, social class of origin, childhood intelligence, childhood behavior disturbance and education were examined as predictors of status attainment in midlife (46 to 51 years). Social class of origin, intelligence and behavior disturbance were conceptualized as correlated predictors, whose effects were hypothesized to be partially mediated by educational qualifications. A structural equation model using Full Information Maximum Likelihood estimation confirmed that education had the strongest direct effect on status attainment at midlife. Furthermore, education partially mediated the effects of social class of origin and childhood intelligence, and fully mediated the effects of behavior disturbance on status attainment. Social class of origin, childhood intelligence and behavior disturbance were strongly inter-correlated. After controlling for these associations, educational and social status attainments were influenced to a considerably greater extent by childhood intelligence than by social class of origin.

Signal Decomposition With Reduced Complexity for Classification of Isolated and Multiple Disturbances in Electric Signals

In a previous work, the authors discussed and introduced a technique for the classification of isolated and multiple disturbances in electric signals. However, in that work, the decomposition of the electric signal into the fundamental, harmonic, and error component can be a very difficult task to be accomplished in real time. In this regards, this contribution proposes and analyzes the decomposition of electric signals into fundamental and error components. For each component, higher order statistics (HOS)-based features are selected and extracted and feed Bayesian classifiers that are designed for each class of disturbance. Comparison results with a standard HOS-based classification technique indicate that the proposed technique can offer improved performance not only for isolated disturbance, but also for multiples ones.

Resilience and collapse of artisanal fisheries: a system dynamics analysis of a shellfish fishery in the Gulf of California, Mexico

Analyzing different pathways by which social–ecological systems can loose resilience and enter trajectories of collapse constitutes an important aspect of our quest towards understanding resource sustainability. This paper’s goal was to better understand the effect of a particular class of disturbance—the accumulative effects of routine stressors—in the context of marine social–ecological systems. To that effect, we built a system dynamics model using empirically collected institutional and biological field data of an artisanal fishery in the Gulf of California, Mexico. Among our findings, we identified different scenarios under which even very small endogenous changes in the relationship between ecological and institutional variables can send a seemingly resilient system into a trajectory of collapse. We discuss why these types of disturbances are so difficult to prevent and be identified by the users of the resource, as well as potential strategies to address these challenges.

Three-dimensional stability of a thin film between two approaching drops

In most simulations of the coalescence process, the rupture of the thin film between two drops is assumed to be axisymmetric. In this paper, we examine the possibility of a nonaxisymmetric rupture by carrying out a three-dimensional linear stability analysis of an axisymmetric thin film region. First, the effect of tangential interfacial velocity on the stability of a flat film is analyzed and a scaling analysis is provided to predict the dependence of the critical film thickness on the dimensionless parameters of the problem: the capillary number Ca, the dimensionless Hamaker constant A∗, and the viscosity ratio λ. Multigrid integration and implicit eigensystem solution techniques are used to simultaneously solve the boundary integral and film evolution equations for the disturbance shape and growth rate. The calculations show that a fixed-end disturbance, which decays to zero at the edge of the film, exhibits maximum instability in the axisymmetric mode. On the other hand, the first nonaxisymmetric mode is the most unstable for the class of free-end disturbances that approach the edge of the film with zero slope. Next, the stability calculation is interfaced with the full axisymmetric simulation of two drops approaching in a biaxial extensional flow in order to obtain the correct base-state film shape at each time interval. In this case, the thin film first becomes unstable to a nonaxisymmetric disturbance for both kinds of boundary conditions. The critical thickness from the stability calculation is compared with the critical film thickness obtained earlier from numerical calculations of the collision and interaction of a pair of fully axisymmetric drops and the effect of base-state curvature on film stability is investigated.

Attitude Tracking and Disturbance Rejection of Rigid Spacecraft by Adaptive Control

In this technical note, we deal with the attitude tracking and disturbance rejection problem of spacecraft for a class of persistent disturbances with unbounded energy which include the sinusoidal disturbance as a special case. The approach involves the integration of techniques from robust control, adaptive control, and robust output regulation theory.

Design and experimental validation of a second-order sliding-mode motion controller for robot manipulators

This article presents an original motion control strategy for robot manipulators based on the coupling of the inverse dynamics method with the so-called second-order sliding mode control approach. Using this method, in principle, all the coupling non-linearities in the dynamical model of the manipulator are compensated, transforming the multi-input non-linear system into a linear and decoupled one. Actually, since the inverse dynamics relies on an identified model, some residual uncertain terms remain and perturb the linear and decoupled system. This motivates the use of a robust control design approach to complete the control scheme. In this article the sliding mode control methodology is adopted. Sliding mode control has many appreciable features, such as design simplicity and robustness versus a wide class of uncertainties and disturbances. Yet conventional sliding mode control seems inappropriate to be applied in robotics since it can generate the so-called chattering effect, which can be destructive for the controlled robot. In this article, this problem is suitably circumvented by designing a second-order sliding mode controller capable of generating a continuous control law making the proposed sliding mode controller actually applicable to industrial robots. To build the inverse dynamics part of the proposed controller, a suitable dynamical model of the system has been formulated, and its parameters have been accurately identified relying on a practical MIMO identification procedure recently devised. The proposed inverse dynamics-based second-order sliding mode controller has been experimentally tested on a COMAU SMART3-S2 industrial manipulator, demonstrating the tracking properties and the good performances of the controlled system.

A chemometric tool to monitor high-rate anaerobic granular sludge reactors during load and toxic disturbances

Knowing that wide fluctuations in flow rate and presence of toxic compounds can damage the high efficiency of high-rate anaerobic granular sludge reactors, the use of Principal Component Analysis (PCA) to detect organic and toxic disturbances was tested. As earlier these disturbances are detected, more accurate would be the corrective actions, and less damage will be caused to the microorganisms involved in the process. The PCA determined a latent variable, combining a weighted sum of operational, physiological, and morphological data, which showed high sensitivity to recognize the operational problems occurred when four organic loading disturbances (OLDs) and three toxic shock loads (TSLs) were applied to Expanded Granular Sludge Bed (EGSB) reactors. The high loadings/weights linked with the morphological parameters, specially the aggregates size distribution (>0.1, >1), obtained using quantitative image analysis techniques, demonstrate the usefulness of monitor the anaerobic granular sludge structural changes. The application of PCA chemometric tool to dataset gathering information from all disturbances allowed the differentiation between organic loading and toxic shock disturbances, as well as the main effects caused by each class of disturbance.

Actuator and controller scheduling in nonlinear transport-reaction processes

The objective of the present manuscript is to examine the performance improvement of a class of nonlinear transport processes subject to spatiotemporally varying disturbances through the employment of a comprehensive and systematic actuator activation and controller scheduling policy. To attain this objective, it is assumed that multiple groups of actuators are available with only one such actuator group being active over a time interval of fixed length while the remaining actuator groups are kept dormant. Using well-established enhanced controllability and performance improvement measures, the candidate actuator groups are first placed at locations that individually provide certain robustness with respect to an appropriately defined “worst” spatial distribution of disturbances. Once the multiple actuator groups are in place, a switching scheme that dictates the switching of a different actuator group at different time intervals, as well as the corresponding control signal supplied to it while being active, is developed. Embedded in the decision policy is the activation of actuators that lie spatially closer to the spatiotemporal disturbances, thereby improving the control authority of the actuators and enhancing the ability of the system to minimize the effects of this class of disturbances. Indeed, entering disturbances that excite different system modes at different time intervals are best handled by employing the actuators that have increased spatial controllability for the above disturbance modes while simultaneously satisfy certain performance measures. In this manner, the control system designed engages the actuators that are better suited to efficiently perform spatiotemporal disturbance compensation over the duration of certain time intervals. The proposed method is demonstrated through simulations using two typical quasi-linear highly dissipative partial differential equation examples.

Existence of Traveling Waves of Invasion for Ginzburg–Landau-type Problems in Infinite Cylinders

We study a class of systems of reaction–diffusion equations in infinite cylinders which arise within the context of Ginzburg–Landau theories and describe the kinetics of phase transformation in second-order or weakly first-order phase transitions with non-conserved order parameters. We use a variational characterization to study the existence of a special class of traveling wave solutions which are characterized by a fast exponential decay in the direction of propagation. Our main result is a simple verifiable criterion for existence of these traveling waves under the very general assumptions of non-linearities. We also prove boundedness, regularity, and some other properties of the obtained solutions, as well as several sufficient conditions for existence or non-existence of such traveling waves, and give rigorous upper and lower bounds for their speed. In addition, we prove that the speed of the obtained solutions gives a sharp upper bound for the propagation speed of a class of disturbances which are initially sufficiently localized. We give a sample application of our results using a computer-assisted approach.

Nature of sudden auroral activations at the beginning of magnetic storms

Certain large magnetic lays, registered by magnetometers in the auroral and subauroral zones simultaneously with SC instant and accompanying events, substantially differ from activations at the beginning of auroral substorm. Such basic substorm elements as energy accumulation during the growth phase and breakup—activation in the localized region near midnight—are absent. During such sudden auroral activations (SAs), a disturbance begins in a wide sector of longitudes and latitudes. It is proposed to combine SAs into an individual class of magnetospheric disturbances. The particle acceleration and injection mechanism, which causes SAs, is considered.