Availability Analysis of a Markovian System with Preventive Maintenance

This paper deals with a Markovian queueing system, in which the system can fail either partially or completely. The partially failed system can fail completely, or still be operative during maximum operting time. After maximum operintig time, the partially failed system is shutdown for preventive maintenance. When completely failed, the system is repaired. The system works as new after preventive maintenance or repair. The steady-state availability and the expected profit is analized analytically

Formal Availability Analysis using Theorem Proving

Availability analysis is used to assess the possible failures and their restoration process for a given system. This analysis involves the calculation of instantaneous and steady-state availabilities of the individual system components and the usage of this information along with the commonly used availability modeling techniques, such as Availability Block Diagrams (ABD) and Fault Trees (FTs) to determine the system-level availability. Traditionally, availability analyses are conducted using paper-and-pencil methods and simulation tools but they cannot ascertain absolute correctness due to their inaccuracy limitations. As a complementary approach, we propose to use the higher-order-logic theorem prover HOL4 to conduct the availability analysis of safety-critical systems. For this purpose, we present a higher-order-logic formalization of instantaneous and steady-state availability, ABD configurations and generic unavailability FT gates. For illustration purposes, these formalizations are utilized to conduct formal availability analysis of a satellite solar array, which is used as the main source of power for the Dong Fang Hong-3 (DFH-3) satellite.Comment: 16 pages. arXiv admin note: text overlap with arXiv:1505.0264

A2THOS: Availability Analysis and Optimisation in SLAs

IT service availability is at the core of customer satisfaction and business success for today’s organisations. Many medium-large size organisations outsource part of their IT services to external providers, with Service Level Agreements describing the agreed availability of outsourced service components. Availability management of partially outsourced IT services is a non trivial task since classic approaches for calculating availability are not applicable, and IT managers can only rely on their expertise to fulfil it. This often leads to the adoption of non optimal solutions. In this paper we present A2THOS, a framework to calculate the availability of partially outsourced IT services in the presence of SLAs and to achieve a cost-optimal choice of availability levels for outsourced IT components while guaranteeing a target availability level for the service

Availability analysis of flexible manufacturing system

This study presents a methodology for calculating the time-dependent availability of flexible manufacturing systems subject to independent exponential components failure. The advantages of failure mode analysis, as presented in this study, are that all potential failure modes are exposed, their associated probability of occurrence are determined and their effect on system performance is evaluated;Three Markovian models are developed considering failure modes. The first model considers a system with one or more flexible machining cells. The second model considers a system with one group of parallel machining cells. The third model considers a typical flexible manufacturing system linked with a material handling system to form a combined network. Application of this model to an existing flexible manufacturing system is analyzed in detail. The performance measures of the three models are determined;A computer program is developed to evaluate the system availability, production rate, component utilization and system effectiveness. The effect of failure modes on system availability is investigated and sensitivity analysis on different performance measures is conducted. Illustrative examples and typical recommendations are also presented and methods of enhancing the performance modeling capability of flexible manufacturing systems are discussed

Availability analysis of terrestrial free space optical (FSO) link using visibility data measured in tropical region

Haze and rain are the most impairments factors to free space optical (FSO) links. These weather conditions limit the visibility, and thereby causes high attenuation of the optical signal. This high attenuation reduces the availability performance of the FSO link. This study evaluates the performance of a terrestrial FSO link under tropical climate conditions. The performance analysis is evaluate over 5 km link distance. The cumulative distribution function (CDF) of the received signal to noise ratio (SNR) is used to study the outage performance of the FSO link under haze conditions. The performance analysis is based on three years measured visibility data in Malaysia. Based on the statistical analysis, link availability of 99.99% can be achieved for 37.44 dB SNR over 1 km link distance. Carrier class availability “five nine” can be achieved for 20 dBm transmission power using 1550 nm wavelength

Radial Basis Neural Network for Availability Analysis

The appliance of radial basis neural network is demostrated in this paper. The method applies failure and repair rate signals to learn the hidden relationship presented into the input pattern. Statistics of availability of several years is considered and collected from the management of concern plant. This data is considered to train and calidate the radial basis neural network (RBNN). Subsequently validated RBNN is used to estimate the availability of concern plant. The main objective of using neural network approach is that it’s not require assumption, nor explicit coding of the problem and also not require the complete knowledge of interdependencies, only requirement is raw data of system functioning

Availability analysis of waste-water recovery systems

The objective is to evaluate the energetic and entropic characteristics of the components of waste-water recovery systems that can be used in varying applications such as enclosed life support systems or industrial waste-water treatment processes. Techniques and methods that are used to evaluate these characteristics have been developed to model and analyze these systems;Availability analysis and pinch analysis are used to study the behavior of these systems in order to increase the efficiency of useful energy utilization, and therefore reduce the energy consumption and utilities loads. The availability analysis method, which is a combined first law and second law analysis method, can locate the irreversibility of the system components. The irreversibility of the components may be reduced and entropically optimal systems may be designed using availability analysis. Pinch analysis is an easy and effective method to analyze and optimize heat exchanger networks. The pinch analysis results for the heat exchanger network are used by the availability analysis to evaluate the entire system behavior. The integrated method will be more effective than either of these two methods;A generic model is established for treating waste-water containing solids, organic and inorganic contaminants using vapor compression distillation and gas-phase oxidation reactions. Solids and non-volatile species are removed by vapor compression distillation. Volatile organic and inorganic contaminants are destroyed by chemical oxidation reactions in the vapor phase. Because of the diversity of waste-water, it is unrealistic to list all possible contaminants in the waste-water stream. A simplified waste-water stream containing water, methanol, ammonia and sodium chloride is used in this study. Methanol represents the volatile organic species in waste-water, ammonia represents inorganic contaminants, while sodium chloride represents dissolved solids;Material and energy balances as well as the values of lost work and the second law efficiency of the components of this model under various operating conditions are computed and evaluated. The irreversibility of the components may be reduced and entropically optimal systems may be designed. The limiting relationships between contaminant level and energy consumption are obtained based on the results of the analysis

Connection availability analysis of span-restorable mesh networks

Dual-span failures are the key factor of the system unavailability in a mesh-restorable network with full restorability of single-span failures. Availability analysis based on reliability block diagrams is not suitable to describe failures of mesh-restorable networks with widely distributed and interdependent spare capacities. Therefore, a new concept of restoration-aware connection availability is proposed to facilitate the analysis. Specific models of span-oriented schemes are built and analyzed. By using the proposed computation method and presuming dual-span failures to be the only failure mode, we can exactly calculate the average connection unavailability with an arbitrary allocation rule for spare capacity and no knowledge of any restoration details, or the unavailability of a specific connection with known restoration details. Network performance with respect to connection unavailability, traffic loss, spare capacity consumption, and dual failure restorability is investigated in a case study for an optical span-restorable long-haul networ