Spare Components Research Articles

The ‘final orderrs problem

When the service department of a company selling machines stops producing and supplying spare parts for certain machines, customers are offered an opportunity to place a so-called final order for these spare parts. We focus on one customer with one machine. The customer plans to use this machine up to a fixed horizon. Based on this horizon, and on the failure rates of the components, the prices of spare components and the consequences of the machine failing before the critical lifetime is reached, the size of the final order is determined.

Availability based spare optimization using renewal process

In this article, we develop mathematical models for spare components with exponential, gamma, normal and Weibull time to failure distribution using a renewal process. The models can be used to predict the number of spares required for a component or system to achieve specified inherent availability. The paper also presents optimization models for systems with components in series where the time to failure distribution of the components follow any general distribution. The objective of the optimization problem is to maximize the availability of the system satisfying constraints on cost and weight. The optimization model developed in the paper can be solved using many general purpose software like LINDO, SOLVER of EXCEL etc. An efficient branch and bound procedure which can be used to solve the optimization problem is also presented in the article.

Note: Optimal allocation of resources to nodes of series systems with respect to failure-rate ordering

Allocation of spare components in a system in order to optimize the lifetime of the system with respect to a suitable criterion is of considerable interest in reliability, engineering, industry, and defense. We consider the problem of allocation of K active spares to a series system of independent and identical components in order to optimize the failure-rate function of the system.

Tolerating faults in a mesh with a row of spare nodes

We present an efficient method for tolerating faults in a two-dimensional mesh architecture. Our approach is based on adding spare components (nodes) and extra links (edges) such that the resulting architecture can be reconfigured as a mesh in the presence of faults. We optimize the cost of the fault-tolerant mesh architecture by adding about one row of redundant nodes in addition to a set of k spare nodes (while tolerating up to k node faults) and minimizing the number of links per node. Our results are surprisingly efficient and seem to practical for small values of k. The degree of the fault-tolerant architecture is k + 5 for odd k, and k+6 for even k. Our results can be generalized to d-dimensional meshes.

Fault-tolerant extensions of star networks

Advances in computer technology have made the construction of complex networks with many processors economically feasible. Because of the complexity of such networks, reliability has become a major concern. In some applications, it is critical that the system must be able to operate correctly despite the presence of certain faults. To achieve this fault-tolerance capability, some spare processors and interconnection links need to be added. In this case, when some of the basic components of the network fail, their tasks can be dynamically transferred to the spare components and the network can continue to operate. The three main criteria that it is desirable to minimize in a fault-tolerant design are the number of nodes (processors), the number of edges (links), and the maximum number of connections to a node. Minimizing these attributes is important in practice, as it is unlikely that unbounded increase in the number of nodes, edges, or connections per node would be acceptable in a real design. In this paper, we shall consider this optimization problem when the (nonredundant) network under consideration is organized as a star. We study all possible variations of the problem under the assumption that minimizing nodes has the highest priority.

Spares strategies for transformers and transmission plant

Earlier articles have described how the use of major strategic spare components can improve the availability of large turbogenerators and experience of this strategy in the United Kingdom electricity supply industry. This article outlines the complementary strategies which have been adopted for generator transformers and transmission plant. Applications in respect to transmission transformers, switchgear and circuit and other substation equipment are described. The mutual advantages arising from sharing arrangements and co-operation on the basis of these strategies by the United Kingdom mainland generating boards is noted

Designing optimal fault‐tolerant star networks

AbstractThe advance in VLSI technology and the continuing decline in the cost of computer hardware have made the construction of complex networks with many processors economically feasible. Due to the complexity of such systems, reliability has become a major issue. In some applications, it is critical that the system must be able to operate correctly despite the presence of certain faults. Multiprocessor networks with such capability are called fault‐tolerant networks. These networks increase reliability by replicating some of the basic components, i.e., by including spare processors and interconnection links. The problem that arises naturally is that of minimizing the spare components that are needed to tolerate failure. In this paper, we consider this problem when the network under consideration is organized in the form of a star. The paper describes how to design optimal m‐FT (m‐fault‐tolerant) graphs with respect to the star configuration, for all values of m ≥ 0.

Improving generator availability by use of strategic spares

In order to improve the availability of its large high-merit generating units, the UK electricity-supply industry has developed a strategy of holding major strategic spare components. These are deployed in the event of failures or when required to expedite overhauls or modifications. Displaced major components are then repaired, refurbished or modified while the unit remains in service. Analysis techniques which can be used to evaluate the likely capabilities of one, two or more spare components for a particular plant family were also developed and the basis of these is described. This article describes the application of the strategies to generator components, complementing an earlier paper to the Institution of Mechanical Engineers relating to turbine components

Schemes of dynamic redundancy for fault tolerance in random access memories

For large memory capacities, stand-by systems usually need a considerable amount of redundant hardware, not only because of the spare components, but for storing fault conditions and for carrying out the necessary reconfiguration. As alternatives, two methods of implementing fault tolerance by means of dynamic redundancy in random-access memories are proposed which allow the treatment of memory-chip faults at the interface of the memory. The memory reliability for both approaches is estimated by a simple model. These methods improve the reliability considerably compared to conventional memory fault tolerance methods, and the size of the units of reconfiguration can be tailored to the demands of the system user. >

Economic analysis of production system duplication policies using the RAMCOST model

Automated production systems consist of a number of interconnected stations which may be liable to failure or breakdown. In the absence of a backup or spare, when any component fails in a serially configurated system, the entire system is shut down. To counter such occurrences, standby components, or spares are installed at locations where failures are expected. The installed cost of the back ups is a negative factor, whereas the additional production time gained is a positive one. Whether installation of a spare component improves the net revenue of the production process is a question requiring some economic analysis for justification. The solution methodology and analysis employs a simulation algorithm known as RAMCOST.

Economic analysis of production system duplication policies using the RAMCOST model

Automated production systems consist of a number of interconnected stations which may be liable to failure or breakdown. In the absence of a backup or spare, when any component fails in a serially configurated system, the entire system is shut down. To counter such occurences, standby components, or spares are installed at locations where failures are expected. The installed cost of the back ups is a negative factor, whereas the additional production time gained is a positive one. Whether installation of a spare component improves the net revenue of the production process is a question requiring some economic analysis for justification. The solution methodology and analysis employs a simulation algorithm known as RAMCOST.

Unavailability evaluation in non-Markovian systems with spare components

Markovian models for repairable systems assume constant state transition rates. If the operating components are in their useful life phase then the assumption of a constant failure rate is valid. This assumption may not extend, however, to the repair and installation process. the inclusion of non-exponential residence times will make the process non-Markovian. This paper presents a range of studies for a repairable system containing an increasing number of spare components. The effect on system unavailability of various distributions is compared for a wide range of failure, repair and installation rates using Monte-Carlo simulation. The failure rate is assumed to be constant and the distributional variation is applied to the repair and installation processes. In order to facilitate comparison, the mean values associated with the repair and installation times are held constant. The change in unavailability is therefore due entirely to the change in the shape of the distribution.

Scheduling spares with exponential lifetimes in a two‐component parallel system

AbstractA set of n spare components whose life lengths are exponentially distributed with rates μ1, …,μn are available to keep a two‐component parallel system in operation. We derive the optimal order of replacement of failed components in order to maximize the system life length.

Reliability and Availability Studies for Industrial Power System Analysis

Reliability and availability (R&A) studies have been made a part of the IEEE Recommended Practice For Industrial and Commercial Power System Analysis (IEEE Standard 399-1980). R&A studies should improve the selection of system configurations and components by basing decisions on quantitative information rather than on intuitive and qualitative decisions. The R&A indices for any electric power system design can be computed from knowledge of the statistical performance of individual components within the system. One of the important indices is the system overall downtime, which has a direct cost impact due to plant process interruption. In addition to R&A computation of electrical components in simple series or parallel configurations, other commonly encountered electrical power systems situations are considered such as a) scheduled maintenance of system components, b) manual switching of system components, c) transformer overloading practices, d) parallel redundant connections within a system, e) spare components available on short notice, and f) local generator units. These situations will be discussed, and the methods of calculation required to include them in R&A studies will be presented.

Behaviour of a complex system having stand-by components in spares

The reliability characteristics of a stand-by redundant complex system with instantaneous switch over have been discussed in two sections of this paper. In Section (I), it has been assumed that spare components can not fail in the stand-by interval where as in Section (II), it has been considered that they can fail even in the stand-by interval. TheLaplace-Stieltjes transforms of the distribution of the first time to system failure have been derived by using the signal flow graph method [Chow-Cassignol, 1962]. In the end, the mean time to system failure (MTSF) has also been evaluated.

Inventory allocation among an assembly and its repairable subassemblies

AbstractIn this paper we consider a major assembly composed of two or more subassemblies. The failure of any subassembly causes the major assembly to not function. Every failed subassembly is repaired or replaced. A total investment in stocks of spare components is to be distributed among the various subassemblies and the major assembly so as to provide the best possible customer service. This is a complicated problem: relevant factors are the failure rates, unit costs, and repair times of the various components. For the case of Poisson failures, a heuristic solution is developed which is a compromise between theoretical optimality and practical usefulness.

Optimal spares for stochastically failing equipment

AbstractA mathematical model is formulated for determining the number of spare components to purchase when components stochastically fail according to a known life distribution function and there is a cost incurred when a component is replaced. Bounds are determined for the optimal inventory which indicate that the inclusion of the replacement cost lowers the optimal inventory.Since these bounds are no easier to calculate than the optimal spares level, the theory is specialized to components with exponentially distributed time to failure. Procedures are given for calculating the optimal spares level, and numerical examples are provided.

Jointly Optimal Inventory and Maintenance Policies for Stochastically Failing Equipment

A dynamic programming problem is formulated to find the inventory, x, of a spare component and a sequence of maintenance intervals r= (r1,…,rx + 1) that minimize the expected cost of operating an equipment for a finite planning horizon, T. It is assumed that the component fails according to a life distribution function, F(⋯), with an increasing hazard function and that it is cheaper to replace components prior to failure. An operating cost function is found to be strictly convex in the time remaining to the end of the period and that at any time there is a finite nonincreasing sequence of economical maintenance policies, each a continuous nondecreasing function of the time remaining. A procedure is given for calculating the optimal initial inventory and reorders when the procurement cost function is K + c ⋯ x.

Requirements planning of production components and spare parts at a farm equipment manufacturing company

This paper deals with the way in which AB Bolinder-Munktell is solving the requirements explosion problem of spare parts and production components using an IBM 1410 data processing machine.

Cost Functions for Systems with Spare Components

Cost functions for determining the optimum number of spare elements to be assigned to systems of identical components under a certain replacement scheme are investigated. The properties of one cost function are studied for component life as an exponentially distributed random variable, and tables are presented of the number of spare components that minimize the function for specified cost ratios. The problem of the optimum number of spares is also considered for systems in which unfailed components may be salvaged for use with later systems.