Reliability prediction for repairable redundant systems

It is assumed that the mean time to failure and mean repair time are known for each of the subsystems of a system. The subsystems conform to the usual exponential failure (and repair) laws and their behaviors are mutually independent. The system includes redundant subsystems in active standby status. Whenever, after a system failure, repair of a failed subsystem re-establishes an adequate configuration, the system as a whole is returned to active status while repair of other failed subsystems (if any) continues. Under this set of assumptions, equations are developed which permit prediction of mean time to failure and mean down time for the system. The development differs somewhat from the use of birth-and-death equations which has been customary for similar problems in the past.     

Reliability consideration on a compound redundant system with repair

This paper considers a standby-redundant system consisting of 2 systems, in which one is main and the other is its standby-redundant system. These systems also consist of 2 subsystems connected in series.A feature of this system is that the system has 2 switching devices connecting subsystems, in addition to one connecting main and standby systems, in order to utilize surviving subsystem. In this consideration it is assumed that all the units are repairable.We shall obtain the system reliability, the mean time to system failure, the steady state availability, and examine numerically the effects of this model to the usual one without particular switching devices.     

Estimation of intrinsic and reflex contributions to muscle dynamics: a modeling study

This work evaluated system identification-based approaches for estimating stretch reflex contributions to muscle dynamics. Skeletal muscle resists externally imposed stretches via both intrinsic stiffness properties of the muscle and reflexively mediated changes in muscle activation. To separately estimate these intrinsic and reflex components, system identification approaches must make several assumptions. We examined the impact of making specific structural assumptions about the intrinsic and reflex systems on the system identification accuracy. In particular, we compared an approach that made specific parametric assumptions about the reflex and intrinsic subsystems to another that assumed more general nonparametric subsystems. A simulation-based approach was used so that the "true" characters of the intrinsic and reflex systems were known; the identification methods were judged on their abilities to retrieve these known system properties. Identification algorithms were tested on three experimentally based models describing the stretch reflex system. Results indicated that the assumed form of the intrinsic and reflex systems had a significant impact on the stiffness separation accuracy. In general, the algorithm incorporating nonparametric subsystems was more robust than the fully parametric algorithm because it had a more general structure and because it provided a better indication of the appropriateness of the assumed structure.     

On a compound redundant system with the particular switching devices

This paper considers a standby-redundant system consisting of 2 systems, in which one is main and the other is its standby-redundant system. These systems also consist of 2 subsystems connected in series, in which each one is composed of several identical units connected in parallel.A feature of this system is that the system has 2 switching devices connecting subsystems, in addition to one connecting main and standby systems, in order to utilize surviving units as many as possible. In this consideration it is assumed that all the units are not repairable.We shall obtain the system reliability and the mean time to system failure, and examine numerically the effects of this model to the usual one without particular switching devices.     

Optimal design of k-out-of-n:G subsystems subjected to imperfect fault-coverage

Systems subjected to imperfect fault-coverage may fail even prior to the exhaustion of spares due to uncovered component failures. This paper presents optimal cost-effective design policies for k-out-of-n:G subsystems subjected to imperfect fault-coverage. It is assumed that there exists a k-out-of-n:G subsystem in a nonseries-parallel system and, except for this subsystem, the redundancy configurations of all other subsystems are fixed. This paper also presents optimal design polices which maximize overall system reliability. As a special case, results are presented for k-out-of-n:G systems subjected to imperfect fault-coverage. Examples then demonstrate how to apply the main results of this paper to find the optimal configurations of all subsystems simultaneously. In this paper, we show that the optimal n which maximizes system reliability is always less than or equal to the n which maximizes the reliability of the subsystem itself. Similarly, if the failure cost is the same, then the optimal n which minimizes the average system cost is always less than or equal to the n which minimizes the average cost of the subsystem. It is also shown that if the subsystem being analyzed is in series with the rest of the system, then the optimal n which maximizes subsystem reliability can also maximize the system reliability. The computational procedure of the proposed algorithms is illustrated through the examples.     

Development of a Methodology for Improving Photovoltaic Inverter Reliability

In evaluating the energy-generation potential of a photovoltaic (PV) energy system, the system is usually assumed to work without interruptions over its entire life. PV energy systems are fairly reliable, but as any complex system, they may fail. In PV systems, the inverter is responsible for the majority of failures, and most inverter failures are blamed on the aluminum electrolytic capacitors typically used in the dc bus. This paper investigates the effects of common failure modes on the reliability of PV inverters and suggests a model framework for decomposing the inverter into subsystems for more detailed study. The challenges of statistical analysis based on small data sets are discussed, and simulations are performed to illustrate the proposed model using a simple decomposition into subsystems of the inverter used in the 342-kW PV system at the Georgia Tech Aquatic Center.     

Availability of the system with general repair time distributions and shut-off rules

A model which has main and secondary subsystems subject to shut-off rules is considered. In this model, the system has a single repair facility. The repair discipline that the main subsystem has the pre-emptive repeat priority is considered. Constant failure rate and general repair time distributions are assumed. The system availability is obtained by using the linear ordinary differential equation method and supplementary variable technique.     

On decentralized hierarchic stabilization of a large-scale system with constraints

A new stabilization method of a large-scale dynamic system, consisting of a set of interconnected subsystems, is presented in this paper. The topology of the interconnected subsystems is given as a network containing nodes with only one ingoing link, and none, one, or more outgoing links. Here, when the notion node is used a subsystem is assumed, and the links stand for the subsystem interconnections. The stabilization method is made only by the use of local linear state feedback around each subsystem, in order to satisfy constraints given in the problem. The interconnections among the subsystems are assumed to be nonlinear, time-varying. According to the topology of the large-scale system, the method of stabilization is hierarchic, one proceeds from node to node, and is applicable from a computer standpoint. A design algorithm follows directly, and can be made using the Generate and Test method for each subsystem independently, thus enabling designers to use a computer which has a video terminal as a peripheral unit and providing a possibility for interactive applications.     

A discrete-time queueing model of the shared buffer ATM switch with bursty arrivals

We model the shared buffer ATM switch as a discrete-time queueing system. The arrival process to each port of the ATM switch is assumed to be bursty and it is modelled by an interrupted Bernoulli process. The discrete-time queueing system is analyzed approximately. It is first decomposed into subsystems, and then each subsystem is analyzed separately. The results from the subsystems are combined together through an iterative scheme. The analysis of each subsystem involves the construction of the superposition of all the arrival processes to the switch. Comparisons with simulation data showed that the approximate results have a good accuracy.Supported in part by DARPA under Grant No. DAEA18-90-C-0039.Work done while on a sabbatical leave of absence at the Computer Science Department of North Carolina State University.     

Availability for 2/n: F and secondary subsystems with general repair-time distributions and shut-off rules

The model which main 2/n: F and secondary subsystems subject to shut-off rules is considered. In this model, the system has single repair facility. The repair discipline that the main subsystem has the preemptive repeat priority is considered. Constant failure rate and general repair-time distribution are assumed. The system availability is obtained by using linear ordinary differential equation method and supplymentary variable technique.     

Nonlinear system identification for cascaded block model: anapplication to electrode polarization impedance

A new algorithm has been developed to identify a system divided into cascaded blocks of dynamic linear (L), static nonlinear (N), and dynamic linear (L) subsystems based strictly on the input-output relationship. The nonlinear element is assumed to be equicontinuous, or must be satisfied by the Weierstrass criterion. Therefore, it could either be continuous type as represented by polynomial approximation or abrupt type as represented by piecewise-linear segments. The process uses a series of multilevel input to decouple the two linear subsystems from the nonlinear subsystem and then applies the predictor-corrector algorithm to minimize a cost function to obtain the parameter of the subsystem. The method does not restrict the type of input signal and no prior knowledge of the subsystems is necessary. Numerical example for a prescribed system is given and the results show almost identical values by any one of the three types of input, namely: step, sinusoidal, or white noise. Three computer programs have been developed for the identification of the system with odd, even, and piecewise abrupt types of nonlinearity. The method is applied to model the interfacial phenomenon of noble metal electrode (Pt) at the nonlinear range and the algorithm is verified by comparison with the result developed previously.     

雷达侦收自适应信号处理架构研究

针对复杂电磁环境中雷达侦察信号自适应处理的需求,对雷达信号侦察问题进行了建模与分析,讨论了若干可能的自适应侦察信号处理架构。在雷达侦察信号处理模块算法方面,研究了特征自适应检测与分析、信号自适应分选等处理架构,以提升低可识别信号的自适应处理能力;在侦察系统处理流程方面,研究了具有跟踪与预测能力的自适应处理架构,以增强对电磁环境态势的动态感知能力;在侦察系统与其他分系统协作层面,研究了基于雷达系统抗干扰需求和干扰机智能化干扰需求的自适应侦察协作架构,以提升电子战系统效能。该研究可为自适应雷达对抗处理研究提供有益思路。     

Suspended Slot Line Using Double Layer Dielectric

This paper presents a rigorous analysis of a) slot line on a double layer dielectric substrate, and b) slot line sandwiched between two dielectric substrates. The structure is assumed to be suspended inside a conducting enclosure of arbitrary dimensions. The dielectric substrates are assumed to be isotropic and homogeneous and are of arbitrary thickness and relative permittivity. The conducting enclosure and the zero thickness metallization on the substrate, are assumed to have infinite conductivity. The effect of shielding on the dispersion, characteristic impedance, and the effective dielectric constant are illustrated. These results should find application in the design and fabrication of MIC components and subsystems.     

Failure Time for a Redundant Repairable System of Two Dissimilar Elements

The distribution of time to failure for a system consisting of two dissimilar elements or subsystems operating redundantly and susceptible to repair is discussed. It is assumed that the times to failure for the two system elements are independent random variables from possibly different exponential distributions, and that the repair times peculiar to each element are independently distributed in an arbitrary fashion. For this basic model a derivation is given of the Laplace-Stieltjes transform of the distribution function of time to system failure, i.e, the time until both elements are simultaneously down for repair, measured from an instant at which both are operating. An explicit formula is given for the mean or expected time to system failure, a natural approximation to the latter is exhibited, and numerical comparisons indicate the quality of this approximation for various repair time distributions. In a second model the possibility of system failures due to overloading the remaining element after a single element failure is explicitly recognized. The assumptions made for the basic model are augmented by a stochastic process describing the random occurrence of overloads. Numerical examples are given. Finally, it is shown how the above models may be easily modified to account for delays in initiating repairs resulting from only occasional system surveillance, and to account for random catastrophic failures.     

Lie algebraic stability analysis for switched systems with continuous-time and discrete-time subsystems

We analyze stability for switched systems which are composed of both continuous-time and discrete-time subsystems. By considering a Lie algebra generated by all subsystem matrices, we show that if all continuous-time subsystems are Hurwitz stable, all discrete-time subsystems are Schur stable, and furthermore the obtained Lie algebra is solvable, then there is a common quadratic Lyapunov function for all subsystems and thus the switched system is exponentially stable under arbitrary switching. A numerical example is provided to demonstrate the result.     

Steady-State Reliability of Systems of Mutually Independent Subsystems

Predicting the reliability of a redundant system with repair is considerably simplified when the system can be subdivided into mutually independent subsystems. Results can be obtained without knowing the failure of repair time distributions of the subsystems. In this paper formulae are developed for the ``steady-state' availability and MTBF of a complex system in terms of the availabilities and MTBF's of its constituent subsystems. The basic concepts required are introduced and discussed in a review of a simplex system. These concepts are then applied to a complex system to obtain the main results of the paper. Finally, two examples are given to illustrate the application of these results.     

Tuning hydrostatic two-output drive-train controllers using reinforcement learning

When controlling a complex system consisting of several subsystems, a simple divide and conquer approach is to design a controller for each system separately. However, this does not necessarily result in a good overall control behavior. Especially when there are strong interactions between the subsystems, the selfish behavior of one controller might deteriorate the performance of the other subsystems. An alternative approach is to design a global controller for the entire mechatronic system. Such a design procedure might result in more optimal behavior, however it requires a lot more effort, especially when the interactions between the different subsystems cannot be modeled exactly or if the number of parameters is large.In this paper we present a hybrid approach to this problem that overcomes the problems encountered when using several independent subsystems. Starting from such a system with individual subsystem controllers, we add a global layer which uses reinforcement learning to simultaneously tune the lower level controllers. While each subsystem still has its own individual controller, the reinforcement learning layer is used to tune these controllers in order to optimize global system behavior. This mitigates both the problem of subsystems behaving selfishly without the added complexity of designing a global controller for the entire system. Our approach is validated on a hydrostatic drive train.     

Early integration of safety to the mechatronic system design process by the functional failure identification and propagation framework

The research goal of this paper is to introduce a risk analysis methodology that can be applied at the early concept design phase, whose purpose is to identify fault propagation paths that cross disciplinary boundaries, and determine the combined impact of several faults in software-based automation subsystems, electric subsystems and mechanical subsystems. Specifically, the Functional Failure Identification and Propagation (FFIP) analysis framework is proposed to perform a simulation-based analysis of functional failure propagation. The focus is on risk assessment, the earliest activities of the safety process, in which hazards are identified and safety requirements are derived. It is argued that current risk assessment methods are not sufficient for concurrent integration of the safety process to the design process of a complex mechatronic system. In order to facilitate the integration of risk assessment to such systems at the earliest design stages, the design is expressed with syntax and semantics that is able to describe the propagation of failures throughout the system and especially across the boundaries of the mechatronic domains. A boiling water nuclear reactor (limited to the reactor core and steam outlets) is used as a case study. The results demonstrate the capability to handle several fault propagation paths in one scenario for hazard identification at the early, functional, design stage. Specifically, it is shown that FFIP is able to identify fault propagation paths that cross disciplinary boundaries, and which in turn is able to determine the combined impact of several faults in software-based automation subsystems, electric subsystems and mechanical subsystems. The impact is expressed in degradation or loss of safety related functions.     

通过费用最小化分配可靠性

假定并行系统的每阶段的成分有相同的可靠性。提出ECAY算法,设计并行系统。已知目标可靠性,分配可靠性和冗余度到每个子系统,使系统费用最小化。结果显示ECAY可以在很短时间内最优化可靠性分配。和基于LM的算法相比,在分别含有4到9个子系统的系统中,ECAY生成最低的可靠性费用和最优的冗余度级别。因此,和基于LM的算法相比,大系统中ECAY在合理的计算时间里,生成一个更低费用的可靠性分配,且在最优化冗余度分配的过程中,最优化系统设计中的负担和空间阻塞。