A selective maintenance model incorporating economic depende

A selective maintenance model incorporating economic dependence was recently presented by Dao et al. [27,28]. Time and cost savings are achieved when several components are simultaneously repaired in a selective maintenance strategy. The authors considered two types of time and cost savings in multi-state contexts as follows: (1) the fixed savings due to common set-up activities on all components and (2) the additional advantage due to specific maintenance activity on multiple identical components. However, these two interactions between components considered in Refs. [27,28] are not comprehensive enough and should entail more thorough discussion. Furthermore, GA was used to solve the proposed selective maintenance model for multi-state series–parallel system. In order to keep down the scope of solution space, they dealt with a series–parallel system with only nine components, which application is limited. On the basis of the previous works, the selective maintenance problem for the two-state series–parallel system under economic dependence was studied from the perspective of mathematic modeling and algorithm design in the present paper. First, the economic dependence was investigated seriously and distinguishedin three major categories (economic dependence in system, economic dependence in subsystem, and economic dependence between subsystems), and then the corresponding computation equations of total time and cost savings were given in a simple and consistent manner for the first time. Second, some existing improvements in Ref. [14] were analyzed and revised in order to fit the novel selective maintenance model, and then the contributions of each improvement on algorithm performance were also discussed. Note that these improvements are based on the classical exhaust algorithm and were proposed for the original selective maintenance model.
Selective maintenance model under economic dependence
Solution methodology
Experimental results and discussion
Conclusions
Acknowledgments This work was supported by the National Science Foundation of China (Grant No. 61305083).
Introduction The search for latest high energetic and high density material is an area of intense interest in military and industrial applications [1–4]. Defense services have been challenged to replace the high sensitive, high enkephalin propellants with materials that have similar energy but are less-sensitive, and can perform under a wide range of temperatures. HNIW is found to be more eco-friendly as well as reduces a missile\'s plume signature without encountering combustion stability problems [5,6]. HNIW is also found to be one of the most powerful non-nuclear explosive materials and shows great scientific advances in future weapon systems [7]. HNIW is superior in comparison to other high energetic explosive materials such as HMX, RDX, PETN, etc., with respect to density, velocity of detonation, detonation pressure and enthalpy of formation. A comparison of these is notified in Table 1. HNIW has high density (ρ > 2 g/cm3), a positive heat of formation (ΔHf=454 kJ/mol) [9], high detonation velocity (9.4 km/S) and an optimum oxygen balance (−11.0) as well as an optimum detonation pressure (420 kbar) [8]. HNIW also has a higher oxidizer-to-fuel ratio. With the aforementioned prominent parameters, HNIW attracts the attention of propellant and explosive manufacturers [14,15]. The reasons for higher detonation pressure of HNIW are due to the presence of NO2 groups in the FMR and SMR [16]. The greater energetic content of caged polycyclic nitramine [17] and its high molecular density over the remaining cyclic nitramine explosives like HMX and RDX make it a better candidate for propellant applications [10,11]. Based on the study of cylinder expansion and tantalum plate acceleration experiments, HNIW was found to be approximately 14% greater than HMX in its performance [18]. HNIW exists in four stable polymorphs with different crystal structures, viz., α-, β-, γ- and ε-forms. The ε-form among the remaining is the least sensitive and possesses the highest density (2.04 g/cm3) and detonation velocity. The physical parameters of the ε-form of HNIW are given in Table 1[19]. Murray et al. [20] discussed the importance of charge redistribution in the cage of HNIW based on the triggered linkage molecules (NNO2). Based on physical parameters, the ε-form of HNIW is considered to be the best suitable explosive material among all its polymorphs. The ε-form is prepared from the raw HNIW employing any of these techniques – solvent evaporation or precipitation method employing solvent and non-solvent (antisolvent). The recent report on the functionalization of ε-HNIW using reduced graphene oxide and Estane shows further improvement in the properties of pure ε-HNIW in terms of mechanical stability, sensitivity and density [21,22].