•Modeling of a general component reassignment problem of degrading components.•Proposal of a time-dependent importance measure of degrading components (TID).•A TID-based greedy local search for the ...component reassignment problem.•A TID-based decomposition method with nonlinear optimization & genetic algorithm.•Exemplification of exponential degradation & consecutive degradation systems etc.
This paper studies a component reassignment problem of degrading components under two degradation termination modes: hot degradation and cold degradation. Consider a system in which components are functionally exchangeable but their degradation characteristics are different and the operational loads or environmental conditions or both that the components are exposed to are different. To improve overall performance of the system, it is critical to determine the time and plan of reassigning the components among the positions in the system by means of reliability and lifetime modeling. To address such the component reassignment problem, component degradation models incorporating the component reassignment and a system-lifetime maximization model are established, a new time-dependent importance measure for degrading components is proposed, and a decomposition method is developed for solving the component reassignment problem. The decomposition method uses the proposed importance measure and interactively uses a continuous nonlinear optimization algorithm and a heuristic combinatorial optimization method. Further, the system-lifetime model is exemplified for four systems with exponentially degrading components, including the k out of n systems, linear consecutive-k-out-of-n systems, and their derivative degrading systems. Finally, numerical experiments demonstrate efficiency of the method and benefits of component reassignment.
Aviation bearing bracket is an important part of aircraft and other aviation products. In this paper, based on additive and subtractive hybrid manufacturing technology with high manufacturing ...flexibility and high machining accuracy, a machining scheme of aviation bearing bracket is designed. First, milling simulation was carried out to obtain the influence law of different cutting parameters on machining deformation, so as to guide the selection of reasonable finish machining parameters in the subsequent process planning. Then, the temperature field distribution of workpiece in the additive manufacturing was simulated, and the influence of different additive manufacturing parameters on the results was analyzed to determine the parameter selection range. Finally, considering the material utilization rate, machining accuracy, machining efficiency and machinability in the machining process of aviation bearing bracket, and proceeding from additive, subtractive and alternating manufacturing methods, the manufacturing process arrangement and process planning for aviation bearing bracket were designed.
Industrial systems such as signal relay stations and oil pipeline systems can be modeled as linear multi-state consecutively connected systems, which comprise sequentially ordered elements and fail ...if the first and the final elements are not connected. The performance level of each element is controllable, which determines how many elements an element can connect and affects its degradation rate. Accumulated degradation can cause element failure, which may lead to costly system failure. This paper aims to minimize long-term maintenance-related costs, including system failure costs. We provide optimal maintenance planning and performance control for every system degradation state through Markov decision process modeling and a dynamic programming algorithm. Load-sharing, restricted maintenance capacity, maintenance setup costs, and the structural characteristics of the system are considered in the model, all of which influence the optimal maintenance and performance control policy. Regarding degradation management, reducing the difference in degradation levels between elements, e.g., replacing more-degraded elements first, can be cost-effective. However, increasing the difference in degradation by maintenance or performance control can also lower maintenance-related costs in specific situations, which is discussed in numerical experiments. We also illustrate structural insights regarding the proposed model, including sensitivity analyses of maintenance capacity, setup costs, and the difference between preventive and corrective replacement costs.
•Joint optimization of component reallocations and system overhauls for multi-component systems.•Multiple times of component reallocations and system overhauls in a life cycle are considered.•A ...decomposition method is proposed.•Virtual age is used to model the failure rate of the component.
Motived by cost savings, this paper studies a new periodic maintenance policy for multi-component systems, for which multiple component reallocations and system overhauls are jointly implemented aperiodically at fixed times and components are minimally repaired immediately after failures in a life cycle. Different workloads or conditions of different positions can lead to different degradation processes of components, thus component reallocation can be used to balance the degradation between components at different positions, which has been widely studied. System overhaul can improve the conditions of components by imperfect or perfect repair. Component reallocation and system overhaul are mutually dependent and jointly affect the degradation of components and the maintenance cost of a system. In this paper, the failure rate functions of components are modeled using virtual age, and then a binary mixed integer nonlinear programming model is established to determine the optimal time and assignment for component reallocations, and the optimal time and degree for system overhauls by minimizing the long-run average maintenance cost of the system. Further, the number of system overhauls is proved to be finite, and a decomposition method is proposed. Numerical examples are provided to show the effectiveness of the joint of component reallocations and system overhauls.
•Proposed an age-based joint system replacement and component reallocation policy.•Addressed that components are failure-undetectable and unevenly degraded.•Established an integrated optimization ...model for a system with an arbitrary structure.•Derived analytical results and compared results with an age-based replacement policy.•Showed effects of the policy on maintenance cost and resilience by numerical studies.
The component reallocation (CR) policy is an emerging and effective preventive maintenance policy for improving the system performance, which has attracted much attention in reliability engineering and is independent from the research of age-based system replacement (ASR). This paper is to explore advantages and characteristics of a joint ASR and CR (JASRCR) preventive maintenance policy for a system, for which it is hard or uneconomical to execute repair or replacement at the component level but easy to reallocate the functionally-interchangeable and unevenly degraded components. In the JASRCR policy, the CR is implemented before the system failure and preventive ASR, and the corrective maintenance is to replace the system whenever it fails. The CR is of capability of balancing the degradation processes of components and thus has potential on improving the system resilience in resisting the component failures. An integrated mixed binary nonlinear optimization model is proposed to determine the optimal assignment of CR and optimal times for ASR and CR with the objective of minimizing the expected total maintenance cost per unit time. Numerical experiments demonstrate efficiency of the JASRCR policy on improving system resilience and reducing system maintenance cost.
To explore the mechanism of calcium-sensing receptors (CaSRs) during the development of nephrolithiasis.
Wistar rats were treated with ethylene glycol to induce calcium oxalate crystallization, and ...gadolinium chloride (GdCl
3
, an agonist of CaSR) and NPS 2390 (an antagonist of CaSR) were added. Oxidative stress (OS) and calcium oxalate crystals in the kidney were observed. CaSR expression and the expression of extracellular signal-regulated protein kinase (ERK), OPN, and KIM-1 were determined by western blotting. In addition, renal tubular epithelial cells were isolated from the kidney to observe phosphatidylserine (PS) ectropion using flow cytometric analysis. Various biochemical parameters were assessed in serum and urine at the end of the experiment.
Calcium oxalate increased OS, crystal adhesion, PS ectropion, and the expression of CaSR and ERK, OPN, and KIM-1 in vivo. In addition, lower levels of urine citrate as well as increased serum creatinine and urea levels were observed after treatment with calcium oxalate (p < .05). Compared with calcium oxalate treatment alone, the above deleterious changes were further significantly confirmed by GdCl
3
but were reversed by NPS-2390. However, urine calcium excretion was decreased after ethylene glycol treatment but was significantly reduced by NPS 2390 and increased by GdCl
3
(p < .05).
The results suggest that CaSR might play significant roles in the induction of nephrolithiasis in rats by regulating reactive oxygen species (ROS) and PS ectropion and the composition of urine, OPN, KIM-1, and ERK expression.
This article proposes a new aperiodic preventive maintenance policy, which involves multiple reassignments of components in a system. Considering a multicomponent system, the components deteriorate ...according to heterogeneous stochastic processes because the components undertake different workloads and environmental stresses. Component reassignment (CR) is an action that reassigns the components to positions during system operation in order to improve overall system performance. The assignments of multiple CRs are mutually dependent decisions, and the execution times to conduct these CRs are also decision variables. All these decisions synthetically impact the system maintenance cost. The reliability functions and failure rates of components under the multiple CRs as well as the side effect of CR action on reducing the component reliability are formulated, using statistical virtual ages that establish links between decisions of consecutive CRs. To optimize the multi-CR based maintenance policy, a binary mixed integer nonlinear programming model is established with the objective of minimizing expected annual system maintenance cost that arises from the CRs, system replacement, and minimal repairs for emergency component failures. The optimal number of CRs is analytically shown to be finite and can be obtained by solving a series of optimization models. This article proposes two matheuristic approaches, an integrative construction approach and a sequential construction approach, to solve the models. Numerical experiments show the application of the proposed model and solution approaches in maintenance policy scheduling.
Component reallocation (CR) is receiving increasing attention in many engineering systems with functionally inter-changeable and unbalanced degradation components. This paper studies a CR and system ...replacement maintenance po-licy of series repairable systems, which undergoes minimal repairs for each emergency failure of components, and consi-ders constant downtime and cost of minimal repair, CR and sys-tem replacement. Two binary mixed integer nonlinear program-ming models are respectively established to determine the assignment of CR, and the uptime right before CR and system replacement with the objective of minimizing the system aver-age maintenance cost and maximizing the system availability. Further, we derive the optimal uptime right before system replacement with maximization of the system availability, and then give the relationship between the system availability and the component failure rate. Finally, numerical examples show that the CR and system replacement maintenance policy can effectively reduce the system average maintenance cost and improve the system availability, and further give the sensitivity analysis and insights of the CR and system replacement mainte-nance policy.
In a repairable system with multiple functionally interchangeable components, the components may work in different environmental or operational stresses associated with their positions, and thus, ...experience different failure rates and nonhomogeneous degradation processes. For such a system, the system lifetime can be improved by reassigning the components among the positions in the system after a period of operation. In this sense, the component reallocation (CR) is an option of preventive maintenances. This paper studies a new maintenance policy, which performs periodic preventive system replacements and periodic preventive CRs between system replacements as well as minimal repairs for emergency failures. An optimization model is established to determine the time and assignment for CRs and the time for system replacements with the objective of minimizing expected annual system maintenance cost. The model also justifies if the CR is economically beneficial and deserved to be implemented. The proposed CR-based maintenance policy is further specified for exponential component lifetime distributions and Rayleigh lifetime distributions, and analytical results are derived. Finally, numerical examples for general Weibull lifetime distributions are presented to demonstrate the efficiency and insights of CRs in maintenance.
PDF
