A development of logistics management models for the Space Transportation System

A new analytic queueing approach was described which relates stockage levels, repair level decisions, and the project network schedule of prelaunch operations directly to the probability distribution of the space transportation system launch delay. Finite source population and limited repair capability were additional factors included in this logistics management model developed specifically for STS maintenance requirements. Data presently available to support logistics decisions were based on a comparability study of heavy aircraft components. A two-phase program is recommended by which NASA would implement an integrated data collection system, assemble logistics data from previous STS flights, revise extant logistics planning and resource requirement parameters using Bayes-Lin techniques, and adjust for uncertainty surrounding logistics systems performance parameters. The implementation of these recommendations can be expected to deliver more cost-effective logistics support

A review of asset management literature on multi-asset systems

This article gives an overview of the literature on asset management for multi-unit systems with an emphasis on two multi-asset categories: fleet (a system of homogeneous assets) and portfolio (a system of heterogeneous assets). As asset systems become more complicated, researchers have employed different terms to refer to their specific problems. With an objective to facilitate readers in searching conducive studies to their interests, this paper establishes a novel classification scheme for multi-unit systems in accordance with essential features such as diversity of assets and intervention options. Moreover, discerning differences in characteristics between cross-component and cross-asset interactions, we select three types of potential multi-component dependencies (performance, stochastic, and resource) and extend their notions to be applicable to multi-asset systems. The investigation into these dependencies enables the identification of problems that could exist in real industrial settings but are yet to be determined in academia. Ultimately, we delve into modelling approaches adopted by previous researchers. This comprehensive information allows us to offer the insights into the current trends in multi-asset maintenance. We expect that the output of this review paper will not only stress research gaps on multi-asset systems, but more importantly help systematise future studies on this aspect

Theory and Practice of Supply Chain Synchronization

In this dissertation, we develop strategies to synchronize component procurement in assemble-to-order (ATO) production and overhaul operations. We focus on the high-tech and mass customization industries which are not only considered to be very important to create or keep U.S. manufacturing jobs, but also suffer most from component inventory burden. In the second chapter, we address the deterministic joint replenishment inventory problem with batch size constraints (JRPB). We characterize system regeneration points, derive a closed-form expression of the average product inventory, and formulate the problem of finding the optimal joint reorder interval to minimize inventory and ordering costs per unit of time. Thereafter, we discuss exact solution approaches and the case of variable reorder intervals. Computational examples demonstrate the power of our methodology. In the third chapter, we incorporate stochastic demand to the JRPB. We propose a joint part replenishment policy that balances inventory and ordering costs while providing a desired service level. A case study and guided computational experiments show the magnitudes of savings that are possible using our methodology. In the fourth chapter, we show how lack of synchronization in assembly systems with long and highly variable component supply lead times can rapidly deteriorate system performance. We develop a full synchronization strategy through time buffering of component orders, which not only guarantees meeting planned production dates but also drastically reduces inventory holding costs. A case study has been carried out to prove the practical relevance, assess potential risks, and evaluate phased implementation policies. The fifth chapter explores the use of condition information from a large number of distributed working units in the field to improve the management of the inventory of spare parts required to maintain those units. Synchronization is again paramount here since spare part inventory needs to adapt to the condition of the engine fleet. All needed parts must be available to complete the overhaul of a unit. We develop a complex simulation environment to assess the performance of different inventory policies and the value of health monitoring. The sixth chapter concludes this dissertation and outlines future research plans as well as opportunities

OPTIMAL MAINTENANCE PROGRAM OF A WASTE-TO-ENERGY PLANT : Case Study: wasteWOIMA®

Waste-to-energy (WtE) plant is a complex system which requires different maintenances to be reliable and available in its full functionalities. Maintenance has a crucial impact on the performance, availability and reliability of the WTE plant. The inadequacies of WTE plant lifetime maintenance may increase the production costs, and more it negatively affects the competitiveness, makes the downtime longer and the Mean-Time-Failure is bigger. The thesis focuses on the maintenance of WtE plant and it reviews the existing literature about Waste-to-Energy maintenance program and then find the best combination that better suits a Waste-to-Energy plant. This thesis has into two parts: the first part identifies the critical factors that enable high availability of Waste-to-Energy plant and the second addresses the identification of the right criteria for spare part selection. Both parts are aimed at enhancing the availability of Waste-to-Energy plant. A survey was sent to Waste-to-Energy professionals to collect data and compare that data to the findings in literature. DEMATEL method is chosen over the other methods for the pragmatic methodology used to construct and analyze the structural model involving causal relationship between multiple factors. It also integrates different expert knowledge that helps to investigate internal relationship and significance degrees of all the chosen factors. One advantage is that it can present a derived relationship through a cause-effect diagram. Critical factors through a visual structural model can be found, as well as the interdependent relationship amount factors are identified and evaluated while using DEMTEL. Key findings of the study revealed that human, economic, equipment and tools, management and environment factors have important impact of the effectiveness of the maintenance and the availability of the WtE plant, whatever the maintenance strategies from preventive to corrective maintenance through the condition maintenance. Quality, Lead time, Price and severity of spare part failure are keys criteria to consider while selecting spare part for WtE plant. The main limitation is that, the sample was a bit small since only few responds to the survey. Limitation of the thesis is related to the amount of the data collected. The findings cannot be generalized as it is affected by the limitation. The survey encounters probably the lack of cooperation from respondents as the study was not directly requested and done from their companies. It would be interesting to do further research of the topic by using data from different plants operated by the case company, to make the research more objective. This will help the case company knowing real issues their plants face. It could be interesting to do further research by focusing for instance on different locations and population because different climatic and environment factors may influence the failure rate of the plants items; dust, humidity, cultural factors

Electricity transmission: an overview of the current debate

Electricity transmission has emerged as critical for successfully liberalising powermarkets. This paper surveys the issues currently under discussion and provides a framework for the remaining papers in this issue. We conclude that signalling the efficient location of generation investment might require even a competitive LMP system to be complemented with deep connection charges. Although a Europe-wide LMP system is desirable, it appears politically problematic, so an integrated system of market coupling, possibly evolving by voluntary participation, should have high priority. Merchant investors may be able to increase interconnector capacity, although this is not unproblematic and raises new regulatory issues. A key issue that needs further research is how to better incentivize TSOs, especially with respect to cross-border issues