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One of the major challenges in designing under pressure water transmission pipeline is the system protection against water-hammer pressures due to a pump trip. The best strategy is to use air-chamber; which imposes considerable costs. To mitigate the air-chamber volume, the use of air-inletvalvesis also suggested. Determination of air-chamber volume as well as the type and proper locations of air-inlet valves, aiming at the cost reduction, introduces an optimization problem. To solve this problem, this study exploitsthe central force optimization (CFO) method. Herein, a case study pipeline is optimized using the proposed model based on the CFO and is compared with results of a genetic algorithm (GA) based model. Both methods yielded almost the same results and led to about 30% saving in the system protection cost. However, a comparison between the methods showed that the CFO dramaticallyoutperforms GA in both terms of computational efficiency and reliability of the results.

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PurposePier scour is one of the main causes of damage to the columns of the river bridges. It is essential to select the best method among various repair methods based on different evaluation indices. However, there is no procedure for ranking these repair methods based on their attributes. The present study seeks to set an approach for this ranking.Design/methodology/approachIn this paper, a multi-attribute decision-making (MADM) model is presented for ranking the repair techniques, in which alternatives are examined using the most important evaluation criteria. In addition, a combination of entropy and eigenvector methods has been proposed for weighting these attributes. A case study is then used to demonstrate the applicability and the validity of the method.FindingsThe execution of the model using two multi-criteria methods yielded similar results, which confirms its accuracy and precision. Moreover, the research findings showed the consistency of the objective and subjective weighting methods and the conformity of the weights obtained for the attributes from the combination of these methods to the nature of the problem.Originality/valueThe selection of the proper method for repairing the bridge columns plays an essential role in success of the bridge restoration. The proposed model introduces an approach for ranking repair methods and selecting the best one that has not been presented so far. Also, the weighing method for attributes is an innovative method for ranking restoration methods that has been proven in a case study.

Transient protection is an important issue in pipeline design. As protective devices impose a huge cost on the project, it is better and more efficient to use optimization models for determination of their position and type with the aim of cost reduction. Except for the cost, the other important issue in obtaining the number and locating of protective devices is the consideration of important operational parameters during the utilization of the pipelines. This paper introduces a new objective function called 'serviceability factor' for achieving the best layout for protection devices by considering five main operational parameters. A double-objective model has been used to optimize the protective devices to obtain the minimum of cost and the most appropriate level of operational parameters. The presented model utilizes the non-dominated sorting genetic algorithm (NSGAII) simultaneously with transient analysis through the method of characteristics. A real pipeline has been optimized using this model and the results are presented in the form of Pareto optimal solutions.