Reliability and Condition-Based Maintenance Analysis of Deteriorating Systems Subject to Generalized Mixed Shock Model

For successful commercialization of evolving devices (e.g., micro-electro-mechanical systems, and biomedical devices), there must be new research focusing on reliability models and analysis tools that can assist manufacturing and maintenance of these devices. These advanced systems may experience multiple failure processes that compete against each other. Two major failure processes are identified to be deteriorating or degradation processes (e.g., wear, fatigue, erosion, corrosion) and random shocks. When these failure processes are dependent, it is a challenging problem to predict reliability of complex systems. This research aims to develop reliability models by exploring new aspects of dependency between competing risks of degradation-based and shock-based failure considering a generalized mixed shock model, and to develop new and effective condition-based maintenance policies based on the developed reliability models. In this research, different aspects of dependency are explored to accurately estimate the reliability of complex systems. When the degradation rate is accelerated as a result of withstanding a particular shock pattern, we develop reliability models with a changing degradation rate for four different shock patterns. When the hard failure threshold reduces due to changes in degradation, we investigate reliability models considering the dependence of the hard failure threshold on the degradation level for two different scenarios. More generally, when the degradation rate and the hard failure threshold can simultaneously transition multiple times, we propose a rich reliability model for a new generalized mixed shock model that is a combination of extreme shock model, δ-shock model and run shock model. This general assumption reflects complex behaviors associated with modern systems and structures that experience multiple sources of external shocks. Based on the developed reliability models, we introduce new condition-based maintenance strategies by including various maintenance actions (e.g., corrective replacement, preventive replacement, and imperfect repair) to minimize the expected long-run average maintenance cost rate. The decisions for maintenance actions are made based on the health condition of systems that can be observed through periodic inspection. The reliability and maintenance models developed in this research can provide timely and effective tools for decision-makers in manufacturing to economically optimize operational decisions for improving reliability, quality and productivity.Industrial Engineering, Department o

Labour Market Institutions and Structural Reforms: A Source for Business Cycle Synchronisation?

We focus on the influence of institutional variables on business cycle synchronisation for 20 OECD countries from 1979 to 2003. More precisely, this paper derives measures for similarity of institutions and structural reforms, and investigates direct and delayed reform effects on synchronisation by applying robustness tests to a panel data framework with bilateral data. Our findings indicate a strong instantaneous relationship between both similarity of institutions as well as common structural reforms and business cycle correlation. --Business cycle synchronisation,Institutions,Structural reforms,Robustness test

Notes on Optimal Growth, Climate Change Calamities, Adaptation and Mitigation

A strategy of inclusion of adaptation and mitigation expenses in a model of optimal growth under threat of climate change calamities is discussed in these exploratory notes. Calamity is the result of a shock that reduces the utility level (even to extinction forever) and/or triggers a fundamental change of the economic structure. Mitigation expenses reduce the long-run probability of a calamity or the speed of convergence to it; adaptation expenses help to improve the standard of living after the calamity. The willingness to contribute to those expenses and the effects on the long-run capital stock of the economy depend on perceptions on how they will modify the law of evolution of probabilities of the shock and the standard of living after the shock. The choice between a clean technology and one that increases GHG emissions is also discussed.Climate Change, Growth, Adaptation, Mitigation

Energy policies and risks on energy markets; a cost-benefit analysis

The key question dealt with in this report is whether and how governments should be involved in taking measures regarding security of energy supply. In order to answer this question, we developed a framework for cost-benefit analysis and applied this framework to a number of policy options. Read also the press release and accompanying�document ' Increasing the reliability of electricity production: a cost-benefit analysis '. The options chosen vary from government investments in strategic oil stocks to financial incentives for consumers to reduce their consumption of electricity. The set of options comprises several types of governmental action, including subsidies, regulation and government investments. Moreover, the selection includes measures meant to address risks on all three major energy markets: oil, natural gas, and electricity. The general picture following from the cases studied is that security of supply measures are hardly ever beneficial to welfare: benefits of policy measures do generally not outweigh costs. From an economic point of view, therefore, it would be often wiser to accept consequences of supply disruptions than to pursue security of supply at any cost. This implies that governments should exercise caution in imposing measures regarding security of supply. If serious market failure is detected, careful attention should be paid to the design of the corrective measure. Establishing and maintaining well-functioning markets appears to be an efficient approach in realising a secure supply of energy. That approach would include removal of entry barriers, securing equal access to essential facilities and increasing transparency of markets.

Predictive maintenance policy for a gradually deteriorating system subject to stress

International audienceThis paper deals with a predictive maintenance policy for a continuously deteriorating system subject to stress. We consider a system with two failure mechanisms which are, respectively, due to an excessive deterioration level and a shock. To optimize the maintenance policy of the system, an approach combining statistical process control (SPC) and condition-based maintenance (CBM) is proposed. CBM policy is used to inspect and replace the system according to the observed deterioration level. SPC is used to monitor the stress covariate. In order to assess the performance of the proposed maintenance policy and to minimize the long-run expected maintenance cost per unit of time, a mathematical model for the maintained system cost is derived. Analysis based on numerical results are conducted to highlight the properties of the proposed maintenance policy in respect to the different maintenance parameters

The Canadian Debt-Strategy Model: An Overview of the Principal Elements

As part of managing a debt portfolio, debt managers face the challenging task of choosing a strategy that minimizes the cost of debt, subject to limitations on risk. The Bank of Canada provides debt-management analysis and advice to the Government of Canada to assist in this task, with the Canadian debt-strategy model being developed to help in this regard. The authors outline the main elements of the model, which include: cost and risk measures, inflation-linked debt, optimization techniques, the framework used to model the government’s funding requirement, the sensitivity of results to the choice of joint stochastic macroeconomic term-structure model, the effects of shocks to macroeconomic and term-structure variables and changes to their long-term values, and the relationship between issuance yield and issuance amount. Emphasis is placed on the degree to which changes to the formulation of model elements impact key results. The model is an important part of the decision-making process for the determination of the government’s debt strategy. However, it remains one of many tools that are available to debt managers and is to be used in conjunction with the judgment of an experienced debt manager.Debt management; Econometric and statistical methods; Financial markets; Fiscal policy

Modeling of pipeline corrosion degradation mechanism with a Lévy Process based on ILI (In-Line) inspections

International audienceIn pipelines, one of the primary testing procedures used to identify the e↵ects and evolution of corrosion over time is through In-Line Inspections (ILI). ILI inspections provide detailed information regarding the inner and outer pipeline condition based on the remaining wall thickness. Based on this information, di↵erent approaches have been proposed to predict the degradation extent of the defects detected. However, these predictions are subject of uncertainties due to the inspection tool and the degradation process that poses some challenges for assessing an entire pipeline within the timespan between two inspections. To address this problem, ILI data was used to formulate a degradation model for steel-pipe degradation based on a Mixed Lévy Process. The model combines a Gamma and Compound Poisson Processes aimed for a better description of the degradation reported by the ILI data. The model seeks to estimate corrosion lifetime distribution and the mean time to failure (MTTF) more accurately. The model was tested on an actual segment of an oil pipeline, and the results have been used to support a preventive maintenance program

Imperfect Maintenance Models, from Theory to Practice

The role of maintenance in the industrial environment changed a lot in recent years, and today, it is a key function for long-term profitability in an organization. Many contributions were recently written by researchers on this topic. A lot of models were proposed to optimize maintenance activities while ensuring availability and high-quality requirements. In addition to the well-known classification of maintenance activities—preventive and corrective—in the last decades, a new classification emerged in the literature regarding the degree of system restoration after maintenance actions. Among them, the imperfect maintenance is one of the most studied maintenance types: it is defined as an action after which the system lies in a state somewhere between an “as good as new” state and its pre-maintenance condition “as bad as old.” Most of the industrial companies usually operate with imperfect maintenance actions, even if the awareness in actual industrial context is limited. On the practical definition side, in particular, there are some real situations of imperfect maintenance: three main specific cases were identified, both from literature analysis and from experience. Considering these three implementations of imperfect maintenance actions and the main models proposed in the literature, we illustrate how to identify the most suitable model for each real case