Dynamic influences in multi-component maintenance

Most maintenance-optimisation models assume an infinite planning horizon and suppose that the failure process is stationary. Hence, information which is not known beforehand and which beocmes available in the short term only, must be ignored. We consider in this paper a multi-component system with economically dependent components, and we compare the costs of a stationary-planning method with the costs according to an approach which can adapt this long-term plan to dynamically changing information (such as a variable use of components and the occurrence of maintenance opportunities). With numerical experiments we show that incorporating short-term information can yield considerable cost savings

Joint replacement in an operational planning phase

We consider the problem of combining replacements of multiple components in an operational planning phase. Within an infinite or finite time horizon, decisions concerning replacement of components are made at discrete time epochs. The optimal solution of this problem is limited to only a small number of components. We present a heuristic rolling horizon approach that decomposes the problem; at each decision epoch an initial plan is made tha

A dynamic policy for grouping maintenance activities

A maintenance activity carried out on a technical system often involves a system-dependent set-up cost that is the same for all maintenance activities carried out on that system. Grouping activities thus saves costs since execution of a group of activities requires only one set-up. Many maintenance models consider the grouping of maintenance activities on a long-term basis with an infinite horizon. This makes it very difficult to incorporate short-term circumstances such as opportunities or a varying use of components because these are either not known beforehand or make the problem intractable. In this paper we propose a rolling-horizon approach that takes a long-term tentative plan as a basis for a subsequent adaptation according to information that becomes available on the short term. This yields a dynamic grouping policy that assists the maintenance manager in his planning job. We present a fast approach that allows interactive planning by showing how shifts from the tentative planning work out. We illustrate our approach with examples

A Dynamic Policy for Grouping Maintenance Activities

A maintenance activity carried out on a technical system often involves a system-dependent set-up cost that is the same for all maintenance activities carried out on that system. Grouping activities thus saves costs since execution of a group of activities requires only one set-up. Many maintenance models consider the grouping of maintenance activities on a long-term basis with an infinite horizon. This makes it very difficult to incorporate short-term circumstances such as opportunities or a varying use of components because these are either not known beforehand or make the problem intractable. In this paper we propose a rolling-horizon approach that takes a long-term tentative plan as a basis for a subsequent adaptation according to information that becomes available on the short term. This yields a dynamic grouping policy that assists the maintenance manager in his planning job. We present a fast approach that allows interactive planning by showing how shifts from the tentative planning work out. We illustrate our approach with examples

An efficient optimal solution method for the joint replenishment problem

During the last two decades, many heuristic procedures for the joint replenishment problem have appeared in the literature. The only available optimal solution procedure was based on an enumerative approach and was computationally prohibitive. In this paper we present an alternative optimal approach based on global optimisation theory. By applying Lipschitz optimisation one can find a solution with an arbitrarily small deviation from an optimal value. An efficient procedure is presented which uses a dynamic Lipschitz constant and generates a solution in little time. The running time of this procedure grows only linearly in the number of items

Practical reflections on combining workshops and mentorships to build capacity in demand and use of evidence in government organisations

Decision makers’ capacity to use evidence is a key component of evidence-informed decision making (EIDM) at a policy level. This paper describes a unique combination of EIDM workshops and mentoring to build decision makers’ capacity to use evidence. It reflects how the deliberate design of sequential workshop and mentoring capacity-building activities enhanced programme effects and reports on the design features that we believe have most contributed to the observed effects. We have found that this combined approach is most effective when it is underpinned by a relationship-building theory of change and remains flexible and responsive to delivering on the needs of participants, and when it is delivered in a timely manner by partners who have been carefully paired with participants based on required expertise

Approximation algorithms and hardness results for the joint replenishment Problepm with constant demands

19th Annual European Symposium, Saarbrücken, Germany, September 5-9, 2011. ProceedingsIn the Joint Replenishment Problem (JRP), the goal is to coordinate the replenishments of a collection of goods over time so that continuous demands are satisfied with minimum overall ordering and holding costs. We consider the case when demand rates are constant. Our main contribution is the first hardness result for any variant of JRP with constant demands. When replenishments per commodity are required to be periodic and the time horizon is infinite (which corresponds to the so-called general integer model with correction factor), we show that finding an optimal replenishment policy is at least as hard as integer factorization. This result provides the first theoretical evidence that the JRP with constant demands may have no polynomial-time algorithm and that relaxations and heuristics are called for. We then show that a simple modification of an algorithm by Wildeman et al. (1997) for the JRP gives a fully polynomial-time approximation scheme for the general integer model (without correction factor). We also extend their algorithm to the finite horizon case, achieving an approximation guarantee asymptotically equal to √9/8

The Determination of Hydrogen Distribution in High-Strength Steel Weldments Part 2: Opt o-Electronic Diffusible Hydrogen Sensor

ABSTRACT. In Part 1, methods for measurement of hydrogen distributions in high-strength welded steel using laser ablation were described. Part 2 will elaborate on an advanced design for a diffusible hydrogen sensor that utilizes the optoelectronic properties of a hydrogensensitive material such as tungsten (Vl) oxide, WO~. The sensor generates the necessary analytical signal in less than one hour and has been calibrated to yield results in mL/100 g weld metal. The sensor is extremely sensitive to hydrogen and relatively inexpensive. An array of sensors could conceivably be used to measure diffusible hydrogen distributions across the weld face with a resolution of approximately one millimeter. The sensor shows excel lent promise as an advanced hydrogen measurement technique, and research is continuing to establish procedures for transfer to industry

The future of isosorbide as a fundamental constituent for polycarbonates and polyurethanes

Isosorbide is a biobased compound which could become in the near future an advantageous competitor of petroleum-derived components in the synthesis of polymers of different nature. When the reactivity of isosorbide is not enough, it can be successfully transformed into secondary building blocks, such as isosorbide bis(methyl carbonate), which provides extra functionalities for polymerization reactions with diols or diamines. The present review summarizes the possibilities for isosorbide as a green raw material to be used in the synthesis of polycarbonates and polyurethanes to obtain products of similar or enhanced properties to the commercial equivalents.This paper is a part of the research carried out within the VIPRISCAR project which has received funding from the Bio-Based Industries Joint Undertaking (JU) under the European Union’s Horizon 2020 research and innovation programme under grant agreement No 790440. The JU receives support from the European Union’s Horizon 2020 research and innovation programme and the Bio-Based Industries Consortium