General Parallel System Research Articles

A neutral cross-efficiency measurement for general parallel production system

There are some problems in the efficiency evaluation for parallel systems. From the applicability of existing models, the parallel models based on self-evaluation may produce the low distinguishing power and unreasonable input–output weights. From the accuracy of efficiency, the weights of partial production-units may be assigned zero values, and thereby the fail of the production-units will lead to the incomprehensibility of system efficiency. The neutral cross-efficiency model maximizes the evaluated decision-making unit (DMU) and simultaneously makes each output of the DMU being as efficient as possible, which effectively avoids the difficulty in choosing between aggressive and benevolent models, and reduces the number of zero output weights. Based on this, this paper proposes the neutral cross-efficiency evaluation method fo r general parallel systems. First, the self-evaluation models for parallel system and its production-units are developed, and the model can enable each production-unit to participate in the evaluation effectively. Then, the neutral cross-efficiency model is proposed to overcome the defects of self-evaluation model. Particularly, the proposed model is also suitable to special general parallel systems with shared resources. More importantly, the proposed models assign different input–output weights for the production-units to avoid the production-units being forced to run under identical production mechanism. Finally, two real-world examples prove the availability and effectiveness of the proposed method.

On likelihood ratio ordering of parallel systems with exponential components

Let T(λ1,...,λ n ) be the lifetime of a parallel system consisting of exponential components with hazard rates λ1,...,λ n , respectively. For systems with only two components, Dykstra et. al. (1997) showed that if (λ1, λ2) majorizes (γ1, γ2), then, T(λ1, λ2) is larger than T(γ1, γ2) in likelihood ratio order. In this paper, we extend this theorem to general parallel systems. We introduce a new partial order, the so-called d-larger order, and show that if (λ1,...,λ n ) is d-larger than (γ1,...,γ n ), then T(λ1,...,λ n ) is larger than T(γ1,...,γ n ) in likelihood ratio order.

Synthesis and Analysis of Soft Parallel Robots Comprised of Active Constraints

In this paper, we introduce a new type of spatial parallel robot that is comprised of soft inflatable constraints called trichamber actuators (TCAs). We extend the principles of the freedom and constraint topologies (FACT) synthesis approach to enable the synthesis and analysis of this new type of soft robot. The concepts of passive and active freedom spaces are introduced and applied to the design of general parallel systems that consist of active constraints (i.e., constraint that can be actuated to impart various loads onto the system's stage) that both drive desired motions and guide the system's desired degrees of freedom (DOFs). We provide the fabrication details of the TCA constraints introduced in this paper and experimentally determine their appropriate FACT-based constraint model. We fabricate a soft parallel robot that consists of three TCA constraints and verify and validate its FACT-predicted performance using finite element analysis (FEA) and experimental data. Other such soft robots are synthesized using FACT as case studies.

Impact of copulas for modeling bivariate distributions on system reliability

A copula-based method is presented to investigate the impact of copulas for modeling bivariate distributions on system reliability under incomplete probability information. First, the copula theory for modeling bivariate distributions as well as the tail dependence of copulas are briefly introduced. Then, a general parallel system reliability problem is formulated. Thereafter, the system reliability bounds of the parallel systems are generalized in the copula framework. Finally, an illustrative example is presented to demonstrate the proposed method. The results indicate that the system probability of failure of a parallel system under incomplete probability information cannot be determined uniquely. The system probabilities of failure produced by different copulas differ considerably. Such a relative difference in the system probabilities of failure associated with different copulas increases greatly with decreasing component probability of failure. The maximum ratio of the system probabilities of failure for the other copulas to those for the Gaussian copula can happen at an intermediate correlation. The tail dependence of copulas has a significant influence on parallel system reliability. The copula approach provides new insight into the system reliability bounds in a general way. The Gaussian copula, commonly used to describe the dependence structure among variables in practice, produces only one of the many possible solutions of the system reliability and the calculated probability of failure may be severely biased.

Addendum to "Reliability Equivalence Factors of a General Parallel System with Mixture of Lifetimes", Applied Mathematical Sciences, Vol. 6, 2012, no. 76, 3769-3784

Addendum to "Reliability Equivalence Factors of a General Parallel System with Mixture of Lifetimes", Applied Mathematical Sciences, Vol. 6, 2012, no. 76, 3769-3784

Reliability analysis of a two-unit general parallel system with warm standbys

Abstract A parallel ( 2 , n - 2 ) -system is investigated here where two units start their operation simultaneously and any one of them is replaced instantaneously upon its failure by one of the ( n - 2 ) warm standbys. We assume availability of n non-identical, non-repairable units. The unit-lifetimes in full operational mode and in partial operational mode have general distribution functions G i and H i ( i = 1 , … , n ) respectively. The system reliability is evaluated by recursive relations.

A two-unit general parallel system with ( n − 2) cold standbys—Analytic and simulation approach

A parallel (2, n − 2)-system is investigated here where two units start their operation simultaneously and any one of them is replaced instantaneously upon its failure by one of the ( n − 2) cold standbys. We assume availability of n non-identical, non-repairable units for replacement or support. The system reliability is evaluated by recursive relations with unit-lifetimes T i ( i = 1, … , n) that have a general joint distribution function F( t). On the basis of the derived expression, simulation techniques have been developed for the evaluation of the system reliability and the mean time to failure, useful when dealing with large systems or correlated unit-lifetimes and less mathematically manageable distributions. Simulation results are presented for various lifetime distributions and comparisons are made with derived analytic results for some special distributions and moderate values of n.

Optimal replacement policy for general parallel reliability system

Recently Nakagawa (1979) has developed an optimal replacement policy for a parallel system operating in a random environment based on the model given by Rade (1976). The optimization policy (Nakagawa 1979) uses the idea of MTBF (mean time before failure) performance and is limited to systems comprised of ‘identical units’. We observe that relaxing the assumption of identical units and working with ‘general systems’ (i.e. systems comprised of not necessarily identical components) has several operational and practical advantages (Venugopal and Ahamed 1986 a, b, Venugopal 1987). Accordingly, an optimal replacement policy for a typical general parallel system is developed in this paper. Earlier results are recovered as special cases. Illustrative numerical work highlighting the applicational scope is also presented.

Extending CSP to Allow Dynamic Resource Management

In his paper "Communicating Sequential Processes," Hoare suggested the use of the input/output construct and Dijkstra's guarded commands for handling the task of communication and synchronization in distributed systems. Hoare's proposal was intended for programming general parallel systems; as a result, little consideration was given by Hoare to the question of how his mechanisms could be utilized in the construction of reliable dynamic resource management schemes. In this paper, we examine this problem and propose several simple extensions to Hoare's constructs that will make the extended Communicating Sequential Processes concept more suitable for the handling of such management schemes.