Sanjay Kumar Chaturvedi

Criticality Assessment Models for Failure Mode Effects and Criticality Analysis Using Fuzzy Logic

Traditional Failure Mode and Effects Analysis (FMEA) has shown its effectiveness in defining, identifying, and eliminating known and/or potential failures or problems in products, process, designs, and services to help ensure the safety and reliability of systems applied in a wide range of industries. However, its approach to prioritize failure modes through a crisp risk priority number (RPN) has been highly controversial. This paper proposes two models for prioritizing failures modes, specifically intended to overcome such limitations of traditional FMEA. The first proposed model treats the three risk factors as fuzzy linguistic variables, and employs alpha level sets to provide a fuzzy RPN. The second model employs an approach based on the degree of match and fuzzy rule-base. This second model considers the diversity and uncertainty in the opinions of FMEA team members, and converts the assessed information into a convex normalized fuzzy number. The degree of match (DM) is used thereafter to estimate the matching between the assessed information and the fuzzy number characterizing the linguistic terms. The proposed models are suitably supplemented by illustrative examples.

Fuzzy arithmetic based reliability allocation approach during early design and development

A fuzzy arithmetic based reliability allocation method at early system design stage.Linguistic variables are used to assess the ratings of allocation factors in an intuitive and easy manner.Use of trapezoidal fuzzy division linear programming method to reduce the fuzziness.More flexible to combine diversified opinions of multiple domain experts. During early design and development stages, every engineering system has to meet its specific reliability goals. The target reliability of the system is achieved through application of an effective reliability apportionment technique to its subsystems. There are various traditional methods exist to perform the reliability allocation based on engineering factors that are assessed in a subjective manner. The conventional reliability allocation approach requires the assessment of factors like complexity, cost, and maintenance. This may not be realistic in real applications if they are assessed in a crisp manner by the domain experts of their varied expertise and background.In this paper, we treat allocation factors as fuzzy numbers, which are evaluated in fuzzy linguistic terms. As a result, fuzzy proportionality factor scales are proposed for the subsystems. In order to accomplish fuzzy division to evaluate the fuzzy proportionality factor, an approximation method based on linear programming for trapezoidal fuzzy numbers is also proposed in this paper. For the evaluation of weighting factors from fuzzy proportionality factors, centroid method of defuzzification is being employed. The allocated reliability of each subsystem is computed with the help of weighting factor thereafter. An example is provided to illustrate the potential application of the proposed fuzzy based reliability allocation approach.

AN EFFICIENT MULTI-VARIABLE INVERSION ALGORITHM FOR RELIABILITY EVALUATION OF COMPLEX SYSTEMS USING PATH SETS

Reliability evaluation of a large and complex system is quite an involved and time-consuming process and its state-of-art is far from being called as satisfactory. This is mainly due to the fact that unionizing path sets results in large number of terms in the reliability expression. Thereafter, the process of computing numerical value of system reliability from its expression is a task not free from the build up of round-off errors. The entire process also restricts the use of a low-end PC for computing system reliability of such systems. In this paper, we propose an efficient methodology to evaluate reliability of large and complex systems based on minimal path sets; the path sets enumeration procedure used in this paper generates path sets in lexicographic and increasing order of cardinality — a condition, which is helpful in obtaining sum of disjoint products (SDP) of the system reliability expression in a compact form. Although we make use of the system connection matrix but no complicated matrix operations are performed to obtain the results. The paper further presents an improved multi-variable inversion (MVI) algorithm to evaluate system reliability in a compact form. Our approach offers an extensive reduction in the number of mutually disjoint terms and provides a minimized and compact system reliability expression. The procedure not only results in substantial saving of CPU time but also can be run on a low-end PC. To demonstrate this capability, we solve several problems of varied complexities on a low-end PC and also provide a comparison of our approach with earlier techniques available for the purpose.

Polyvinylidene fluoride/nickel composite materials for charge storing, electromagnetic interference absorption, and shielding applications

In this paper, the composites of polyvinylidene fluoride (PVDF)/nickel (Ni) prepared through simple blending and hot-molding process have been investigated for dielectric, electromagnetic shielding, and radar absorbing properties. In order to study complex permittivity of the composites in 40 Hz–20 MHz frequency range, impedance spectroscopy (IS) technique is used. Besides, the complex permittivity and permeability in addition to shielding effectiveness (SE), reflection coefficient (backed by air), and loss factor are calculated using scattering parameters measured in X-band (8.2–12.4 GHz) by waveguide method. Further, in X-band, a theoretical analysis of single layer absorbing structure backed by perfect electrical conductor is then performed. A flanged coaxial holder has also been designed, fabricated, calibrated, and tested for electromagnetic interference SE measurement in the broad frequency range (50 MHz–18 GHz). The IS results indicate large enhancement in dielectric constant as a function of Ni lo...

A Cutsets-Based Unified Framework to Evaluate Network Reliability Measures

This paper presents a minimal cutsets-based unified framework to evaluate some commonly used reliability measures: g-terminal, 2-terminal, and k-terminal reliability. In doing so, the paper proposes a single algorithm, which generates the network node sets. From these node sets, depending on the reliability measure(s), only those node sets are kept, which contains at least one node from the specified node set. These selected node sets form link-minimal cutsets. These minimal cutsets are used as an input to multi-variable inversion-based sum-of-disjoint product approach to obtain the unreliability expression thereafter. By solving several network examples of varied complexities, the comparison with the existing approach is provided.

A hybrid method to evaluate reliability of complex networks

In this paper, we propose a hybrid method to evaluate reliability of large and complex networks that incorporates the best features of earlier techniques such as KDH88 and CAREL. The present method combines CAREL’s COMpare and REDuce operators along with KDH88 and eliminates the use of the other two operators of CAREL, thus resulting in an extensive reduction in the number of exclusive and mutually disjoint terms. The procedure not only saves CPU time by an appreciable amount but also can be run even on a low‐end PC. To demonstrate the advantage of handling a large complex system on a relatively small computer, we provide a comparison of the present approach with CAREL and KDH88 and solve several problems of various complexities on a low‐end PC.

Design and Optimization of Multilayered Electromagnetic Shield Using a Real-Coded Genetic Algorithm

We report optimized design of multilayered electromag- netic shield using real coded genetic algorithm. It is observed that the shielding efiectiveness in multilayer design is higher than single layered counterpart of equal thickness. An efiort has been made to develop an alternative approach to achieve speciflc objective of identifying the design characteristics of each layer in the multilayered shielding con- flguration. The proposed approach incorporates interrelated factors, such as absorption and re∞ection in the design optimization as per speciflc shielding requirements. The design problem has been solved using shielding efiectiveness theory based on transmission line (TL) modeling and real-coded genetic algorithm (GA) with simulated bi- nary crossover (SBX) and parameter-based mutation. The advantage of real-coded GA lies in e-cient solution for electromagnetic interfer- ence (EMI) shielding design due to its strength in solving constraint optimization problems of continuous variables with many parameters without any gradient information. Additionally, the role of material parameters, such as permittivity and permeability on re∞ection char- acteristics and shielding efiectiveness, has also been investigated and optimized using the proposed models and real-coded GA. Theoretical optimization of electromagnetic parameters has been carried out for SE » 40dB for many industrial/commercial applications and SE » 80dB for military applications.

Prioritization of maintenance tasks on industrial equipment for reliability

Purpose – This paper aims to prioritize preventive maintenance actions on process equipment by evaluating the risk associated with failure modes using predictive maintenance data instead of maintenance history alone.Design/methodology/approach – In process plants, maintenance task identification is based on the failure mode and effect analysis (FMEA). To eliminate or mitigate risk caused by failure modes, maintenance tasks need to be prioritized. Risk priority number (RPN) can be used to rank the risk. RPN is estimated invariably using maintenance history. However, maintenance history has deficiencies, like limited data, inconsistency etc. To overcome these deficiencies, the proposed approach uses the predictive maintenance data clubbed with expert domain knowledge. Unlike the traditional single step approach, RPN is estimated in two steps, i.e. Step 1 estimates the “Possibility of failure mode detection” and Step 2 estimates RPN using output of step 1. Fuzzy sets and approximate reasoning are used to han...

Reliability analysis of generalized multi-state k-out-of-n systems

The recently proposed generalized multi-state k-out-of-n system model provides more flexibility in describing practical systems. In this model, there are n components in the system where each component and the system can be in one of M + 1 possible states: 0, 1, 2, …, M. The system is in below state j if there exists an integer value l, (1 ≤ i ≤ j) such that at least kl components are in states below l. Although the model has several practical applications, existing methods for computing either the exact or approximate reliability of these systems are computationally inefficient and limited to very small systems. This paper proposes an efficient method and a detailed algorithm to compute the exact reliability of multi-state k-out-of-n systems with independent and identically distributed components. The method is based on conditional probabilities and is applicable for all cases of multi-state k-out-of-n systems with respect to the recent definitions of this system.

SNEM: a new approach to evaluate terminal pair reliability of communication networks

Purpose – This paper proposes a new approach source node exclusion method (SNEM) to evaluate terminal pair reliability of complex communication networks.Design/methodology/approach – The proposed approach breaks a non‐series‐parallel network to obtain its sub‐networks by excluding the source node from rest of the network. The reliabilities of these sub‐networks are thereafter computed by first applying the series‐parallel‐reductions to it and if any sub‐network results into another non‐series‐parallel network then it is solved by the recursive application of SNEM.Findings – The proposed method has been applied on a variety of network and found to be quite simple, robust, and fast for terminal pair reliability evaluation of large and complex networks.Practical implications – The proposed approach is quite simple in application and applicable to any general networks, i.e. directed and undirected. The method does not require any prior information such as path (or cut) sets of the network and their pre‐proces...