-A review of multi-criteria optimization concepts and methods is presented. The techniques provide solutions to the problems involving conflicting and multiple objectives. Several methods based on weighted averages, priority setting, outranking and their combinations are employed. The application and procedure in respect to material selection is presented. It is observed from the literature that no single approach is superior, rather, the selection of a specific method depends on the type of information that is provided in the problem, the designer"s preferences, the solution requirements and the availability of software adopted.

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Purpose -This paper aims to revisit the preventive maintenance scheduling literature. The problem to be solved is the simultaneous scheduling of resource-constrained preventive maintenance and operations. In particular, the expression that defines the period-dependent cost function for a preventive maintenance scheduling activity is redefined. A case study is presented from the shipping industry. Design/methodology/approach -In this paper a mathematical theory of differential calculus known as three-dimensional wave equation is applied. The methodology involves transforming the preventive maintenance cost function that is expressed in terms of several variables into a more precise framework. The motivation for the work is the need to measure the total preventive maintenance scheduling cost more precisely than with the use of the existing linear cost structure. Findings -In this paper the findings from the analysis carried out found evidence that validates the claim of the feasibility of analyzing preventive maintenance cost using the approach proposed.Research limitations/implications -The paper shows that, in practice, maintenance managers strive to reduce the cost of preventive maintenance activities in order to achieve low cost production of goods. This would encourage a high patronage of customers and prevent decisions being made on wrong data. The approach presented here aims at correcting this weakness by revealing a more precise and reliable method of preventive maintenance scheduling cost computation. This is a scientific tool that should be of immense benefit to maintenance planners, particularly those actively engaged in scheduling functions. Originality/value -The work in this paper is new, since a novel framework is presented in a way that has not been documented earlier.

PurposeManaging a safety programme and ensuring that change is in accordance with suitable performance measures requires continuing improvement in the support of analytical power and empirical information. This paper aims to consider different approaches and modeling efforts on safety performance evaluation.Design/methodology/approachReview and synthesis of literature.FindingsTen major safety performance evaluation approaches are identified including expectation function, risk assessment, statistical quality control, price deflation, engineering economic factor, system analysis, artificial intelligence, and systems theory. Based on the approaches, quantitative and qualitative models have been proposed. The quantitative models use measuring indicators such as frequency, severity, percentages, relative weight and economic gains/loss of safety programme. However, qualitative models employ hazard analysis and hazard operability.Research limitations/implicationsSeveral research questions remain to be answered in order to completely improve and optimize the impact of these provisional safety performance measures.Originality/valueThis study offers a set of interesting lessons for academics, industry and safety practitioners by providing guidelines that will assist in ensuring a correct focus to select an appropriate safety performance evaluation model.

The issue of scheduling a long string of multi-period activities which have to be completed without interruption has always been an industrial challenge. The existing production/maintenance scheduling algorithms can only handle situations where activities can be split into two or more sets of activities carried out in non-contiguous sets of work periods. This study proposes a contiguous-periods production/maintenance scheduling approach using the Transportation Model. Relevant variables and parameters of contiguous-cells scheduling problem were taken from the literature. A scheduling optimization problem was defined and solved using a contiguous-cells transportation algorithm (CCTA) which was applied in order to determine the optimal maintenance schedule of a fleet of ships at a dockyard in South-Western Nigeria. Fifteen different problems were solved. It is concluded that the contiguous-cells transportation approach to production/ maintenance scheduling is feasible. The model will be a useful decision support tool for scheduling maintenance operations.