Multiple model adaptive estimation with filter spawning

The purpose of the paper is two-fold. First, we introduce a general framework for extending restoration strategies developed for total link failures in a way enabling handling partial link failures as well. In particular, our framework combines a known rerouting method for total link failures (the so called Restricted Restoration — RR) and a recently developed restoration method for partial failures (called Flow Thinning — FT). In this way we achieve two goals: we define a unified approach to deal with both kinds of failures, and improve efficiency of FT. We study in detail such an extended version of RR (that can also be regarded as an extension of the MPLS Fast Reroute method) capable of managing links with variable capacities, (variable link capacities can be regarded as partial link failures). A general mathematical model for the framework, and a specific model for RR are presented together with numerical results. The second purpose is related to completeness of partial failures scenarios. In practice, partial failure scenarios correspond to partial losses in transmission capacity, occurring for example in wireless networks using microwave radio or free space optical transmission technology. As such failures are mainly caused by weather conditions, there arises a problem of how to translate weather conditions to link failures (this is necessary to ensure network robustness to weather conditions). We present a study on the way that different weather factors impact the transmission link capacity and how these effects can be measured.

A characteristic feature of dynamic networks is the notion of failure. A failure can be a partial failure [as in distributed systems] or total failure. A partial failure may happen when one component in a system fails. This failure may affect the proper operation of other components, while at the same time leaving yet other components totally unaffected. In contrast, a failure in any system is often total in the sense that it affects all components, and may easily bring down the entire system. Hence, it becomes important to design a system which can work even if (partial) failures occur. This paper proposes various approaches which help in making the designed system fault tolerant. Mainly the routing mechanism is focused upon with the help of the concept of acknowledgment and negative acknowledgment.KeywordsRoutingCrash failureOmission failureFault detectionFault recovery

IPv6 measurement studies have focussed on measuring IPv6 adoption, while studies on measuring IPv6 performance have either become dated or only provide a snapshot view. We provide a longitudinal view of the performance of dual-stacked websites. We show that (since 2013) latency towards ALEXA 10K websites with AAAA entries over the six years have reduced by 29% over IPv4 and by 57% over IPv6. As of Dec 2018, 56% of these websites are faster over IPv6 with 95% of the rest being at most 1 ms slower. We also identify glitches in web content delivery that once fixed can help improve the user experience over IPv6. Using a publicly available dataset, we show that 40% of ALEXA 1M websites with AAAA entries were not accessible over IPv6 in 2009. These complete failures have reduced to 1.9% as of Jan 2019. However, our data collection on partial failures helps identify further that 27% of these popular websites with AAAA entries still suffer from partial failure over IPv6. These partial failures are affected by DNS resolution errors on images, javascript and CSS content. For 12% of these websites, more than half of the content belonging to same-origin sources fails over IPv6, while analytics and third-party advertisements contribute to failures from cross-origin sources. Our results also contribute to the IETF standardisation process. We witness that using an happy eyeballs timer value of 250 ms, clients prefer IPv6 connections to 99% of ALEXA 10 K websites (with AAAA entries) more than 96% of the time. Although, this makes clients prefer slower IPv6 connections in 81% of the cases. Our results show that a Happy Eyeballs (MBA) timer value of 150 ms does not severly affect IPv6 preference towards websites. The entire dataset presenting results on partial failures, latency and HE used in this paper is publicly released.

Active Fault Tolerant Control for a Class of Networked Systems with Partial Actuator Failures

ABSTRACTThis study is concerned with the bumpless transfer problem for switched systems with partial actuator failures, in order to obtain smooth system performance output transition. Taking into account that the system requires a controller switching from current sub-controller to a fault-tolerant sub-controller after actuator fault. And bumpless transfer for control input cannot be traditionally designed when the actuator fault occurs, while performance smoothing can be considered and it is actually the ultimate goal of bumpless transfer. Specifically, the actuator fault model is firstly established and partial actuator fault is considered. Then, the system performance output signal is deemed as the main design variable of bumpless transfer, and closed-loop control systems both previous and after controller switching are constructed. Moreover, by using model matching thought and the adaptive sliding mode control technique, a bumpless transfer compensator design strategy is given to drive the performance output variable (after controller switching) to track the one of reference model. At last, simulation results of numeric and application examples demonstrate the effectiveness of the proposed bumpless transfer strategy.

In response to the limitations of modern industrial processes in terms of control accuracy and safety, this paper proposes a robust predictive fault-tolerant control method based on signal compensation. This method is generally applicable to nonlinear industrial processes with uncertainty and partial actuator failures. Firstly, a novel model is established for nonlinear industrial processes which includes fault factors and unknown lumped dynamic nonlinear terms. On this basis, sub-compensators are designed to eliminate the influence of unmodeled dynamics on the control effect. This method effectively reduces the conservatism of traditional fault-tolerant control and improves the tracking performance of the control system. In addition, this article provides a detailed demonstration of the stability and convergence of the closed-loop system, and verifies the effectiveness of the proposed method through comparative experiments. The experimental results demonstrate that the proposed method exhibits a excellent control performance in comparison to several mainstream methods.

Unmanned Underwater Vehicles (UUVs) are being deployed in advanced applications that require precise manoeuvring close to complex underwater structures such as oilrigs and subsea installations or moving objects such as ships and submarines. The effect of vehicle's hydrodynamic parameter variations is significant in such scenarios and in extreme conditions the UUV may experience loss of control. In addition, external disturbances and actuator failures degrade the performance of the UUV. Adaptive control has been identified as a promising solution that can improve the performance in such situations. However, adaptive control is not widely used in UUVs mainly due to the trade-off between fast learning and smooth control signals. The latter can be guaranteed at low learning rates but require additional input to improve learning. The Predictor Model Reference Adaptive Control (PMRAC) is one such method that uses a prediction error to improve learning. In this paper, the performance of PMRAC in UUV applications is investigated and compared to standard Model Reference Adaptive Control (MRAC) at low learning rates under normal operational conditions, partial actuator failure, and under the influence of external disturbances. Simulation results show that PMRAC significantly reduces the tracking error compared to MRAC. In addition, PMRAC is less affected and recovers quickly from actuator failure and external disturbances, while generating smooth control signals with less oscillation compared to MRAC.

Multiple model adaptive estimation (MMAE) is a method of estimating unknown system parameters by modeling different discrete parameter values in several filters that are run in parallel and compared. The parameters for this research are failure status conditions associated with flight control actuators and sensors on the LAMBDA unmanned research vehicle, an experimental aircraft. Six actuator failures and eight sensor failures are modeled, along with the fully functional aircraft, in fifteen elemental Kalman filters. These filters propagate and update their own aircraft state estimates in real time. A probability computation representing the likelihood of each elemental filter's match to the true condition of the aircraft is used to generate relative probabilities for each filter's hypothesis. The MMAE algorithm is extended for the identification of dual failures through the use of a hierarchical structure of filter banks. Aircraft state excitation is required for effective MMAE performance. Sinusoidal dither signals are applied to the command inputs of a flight control system which controls pitch rate, roll rate, and sideslip angle. >

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INTRODUCTION A piloted experimental study of potential enhanced task performance resulting from improved high-angle-of-attack aerodynamic and flight control capability was conducted in the Wright Laboratory's engineering flight simulator facility. The simulation database used was representative of the aerodynamics and inertias of the Variable-stability In-flight Simulator Test Aircraft (VISTA) / F-16. The VISTA variable-stability system was not used. This distinction should be noted whenever the VISTA is referred to in this paper. Flight test pilots evaluated both baseline and three modified versions of the simulated aircraft using a variety of high-angle-of-attack tasks. Aerodynamic modifications were based on wind tunnel data from a previous effort which examined various means of extending the aircraft aogk-of-attack limits. These focused primarily on the lateral-directional characteristics in the twenty-nine to thirtyseven degree range. Flight control modifications came from a new approach to control of lateral-directional dynamics which used variable structure control and describing functions. This controlled the forebody vortices to achieve improved roll coordination. The various configurations were compared relative to their departure resistance and maneuverability. This paper presents some quantitative and qualitative results of the study which show improved departure resistance and mixed results with respect to maneuverability. * Senior Member. AIAA Hying Qualities Engineer This paper is declared a work of the U.S. Government and is not subject to copyright protection in the United States. The Control Dynamics Branch of the USAF Wright Laboratory has been involved in highangle-of-attack (AOA) flight research for the last several years from the perspectives of aircraft dynamics, aerodynamics and flight control. The effort reported on here was a piloted simulation study of a configuration that represents the culmination of two previous efforts involving aerodynamic and related flight control law modifications to high-performance fighter designs. Aerodynamic modifications In [2], Simon et al performed a wind-tunnel test program to define the aerodynamics of an F-16 with (i) cut-back wing leading-edge extension (LEX), (ii) forebody chines and (iii) pneumatic forebody vortex control as shown in Figure 1. Figure 1 Active and Passive Modifications The high-AOA effects sought were, i) improved directional stability from the use of chines, ii) improved longitudinal stability and elimination of the high-AOA pitch trim point by a cut-back LEX, and iii) increased directional control power by means of forebody 303 American Institute of Aeronautics and Astronautics vortex control. Figures 2 through 6 show the specific beneficial changes to the total pitching, rolling and yawing moments due to the passive (i.e., no active vortex control) modifications as well as the rolling and yawing moments resulting from the active vortex control. angle of attack, depress

This article deals with the design of a parametric eigenstructure assignment (PEA)-based multi-objective reconfigurable output feedback controller for a multiple-input multiple-output (MIMO) system against partial actuator failure. The significance of the PEA technique is that it provides more design degrees of freedom to obtain multi-objective functions, namely robust stability and improved transient response. Robust stability and transient response are ensured by a minimum condition number of the eigenvector and a minimum norm of controller gain. These two objectives are conflicting in nature, and, hence, the main aim is to minimize both objectives simultaneously by means of a multi-objective evolutionary algorithm (MOEA). In this study, a multi-objective optimization problem is formulated and is solved by non-dominated sorting genetic algorithm-II (NSGA-II) and strength Pareto evolutionary algorithm-II (SPEA-II). Four indicators are used to evaluate each algorithm performance: spacing, error ratio, generational distance, and hypervolume. Then a reconfigurable controller is designed using PEA against actuator failure, which guarantees closed-loop stability. The effectiveness of the proposed controllers is demonstrated by implementing them in an interacting three-tank benchmark system.

Vibration suppression of flexible hose for autonomous aerial refueling based on adaptive boundary compound controller

The mean and covariance of a Kalman filter residual are computed for specific cases in which the Kalman filter model differs from a linear model that accurately represents the true system (the truth model). Multiple model adaptive estimation (MMAE) uses a bank of Kalman filters, each with a different internal model, and a hypothesis testing algorithm that uses the residuals from this bank of Kalman filters to estimate the true system model. At most, only one Kalman filter's model will exactly match the truth model and will produce a residual whose mean and standard deviation have already been analyzed. All of the other filters use internal models that mismodel the true system. We compute the effects of a mismodeled input matrix, output matrix, and state transition matrix on these residuals. The computed mean and covariance are compared to simulation results of flight control failures that correspond to mismodeled input matrices and output matrices.

Aim. To promote a better understanding, a wider and more correct application of the effectiveness retention ratio. That is the measure that is best suited for assessing the dependability of complex technical systems, in which partial failures are possible that put a system into intermediate states between complete up and down ones. Methods. The paper uses the methods of the probability theory and comparative analysis of texts of interstate (Euro-Asian), Russian and international dependability-related standards. Results. The principal contribution of Russian researchers to the creation and development of methods for applying effectiveness indicators to estimating the dependability of complex systems is pointed out. Shortcomings were identified in the basic dependability-related standards as regards the effectiveness retention ratio and related concepts. Namely, in terminology standard GOST 27.002–2015, the phrases that require improvement are indicated. They relate to the concepts of partial failure, partial up state and partial down state. A broader and more ac[1]curate definition of partial failure is suggested. It is noted that the relationship between partially up and partially down states are to be discussed and clarified. GOST 27.003–2016 that establishes the content and general rules for specifying dependability requirements contains wording errors in the classification of items according to the number of possible (taken into consideration) states and in the examples of possible variants of the effectiveness retention ratio in various branches of technology that are probabilities of task completion, etc. The paper suggests corrections to the appropriate wordings. It has been established that although the effectiveness retention ratio is not referred to in the international dependability-related terminology standard (IEC 60050-192:2015), it implicitly appears in two IEC standards (IEC 61703:2016 and IEC 62673:2013), in which it is assigned to availability measures. Conclusion. The paper’s findings will be useful to experts involved in the assessment and standardization of complex technical system dependability. Their implementation will help improve interstate, Russian and international dependability-related standards.

The article is devoted to the issue of partial failure in complex technical systems. The authors analyze the diagnostic procedure in agricultural machinery for various purposes, the results of which provide a diagram of a multi-level organization for assessing the condition of equipment. It is also proposed to expand the range of estimated diagnostic parameters for making a more reliable managerial decision. The introduction of expert systems and other similar intelligent systems (for example, expert decision support systems) for diagnosing complex malfunctions is justified.