A Test of Wagner’s Heuristics for the Spare Parts Inventory Control Problem

Author(s):  
Ibrahim S. Kurtulus

Over the years, Wagner’s (1975) heuristic rules appealed to the practitioners because they had simple data requirements, were easy to understand and hence easy to apply. In his algorithmic solution, Wagner assumes that the exact distribution of demand (during lead time) is known. If such a distribution is not available, he recommends using the normal distribution. The author’s purpose is to compare the cost of the solutions provided by Wagner’s (1975) heuristics to optimal (Archibald & Silver, 1978) and determine their quality. Their second goal is to perform sensitivity analysis on the results with respect to demand’s skewness, the ratio of ordering cost to carrying cost. The author’s third goal is to use as much actual data as they possibly can.

2017 ◽  
Vol 2017 ◽  
pp. 1-12 ◽  
Author(s):  
Jing Cai ◽  
Yibing Yin ◽  
Li Zhang ◽  
Xi Chen

Under the background of the wide application of condition-based maintenance (CBM) in maintenance practice, the joint optimization of maintenance and spare parts inventory is becoming a hot research to take full advantage of CBM and reduce the operational cost. In order to avoid both the high inventory level and the shortage of spare parts, an appointment policy of spare parts is first proposed based on the prediction of remaining useful lifetime, and then a corresponding joint optimization model of preventive maintenance and spare parts inventory is established. Due to the complexity of the model, the combination method of genetic algorithm and Monte Carlo is presented to get the optimal maximum inventory level, safety inventory level, potential failure threshold, and appointment threshold to minimize the cost rate. Finally, the proposed model is studied through a case study and compared with both the separate optimization and the joint optimization without appointment policy, and the results show that the proposed model is more effective. In addition, the sensitivity analysis shows that the proposed model is consistent with the actual situation of maintenance practices and inventory management.


Author(s):  
Leila Ladani ◽  
Lalit Roy

Additive Layer Fabrication, in particular Electron Beam Additive Fabrication (EBAF), has recently drawn much attention for its special usability to fabricate intricately designed parts as a whole. It not only increases the production rate which reduces the production lead time but also reduces the cost by minimizing the amount of waste material to a great extent. Ti6Al4V is the most common type of material that is currently being fabricated using EBAF technique. This material has been used in aerospace industry for several reasons such as excellent mechanical properties, low density, great resistance to corrosion, and non-magnetism. The effects of build direction of layers (namely, addition of layers along one of the x, y & z directions with respect to the build table) and the anisotropy effect caused by it has not been explored vigorously. This anisotropy effect has been investigated in this work. Different mechanical properties such as Yield Strength (YS), Ultimate Tensile Strength (UTS), and Modulus of Elasticity (E) of these three types of Ti6Al4V are determined using tensile tests and are compared with literature. The tensile test results show that YS and UTS for flat-build samples have distinguishably higher values than those of the side-build and top-build samples.


Author(s):  
Michael M. French

Abstract The Weather Surveillance Radar - 1988 Doppler (WSR-88D) network has undergone several improvements in the last decade with the upgrade to dual-polarization capabilities and the ability for forecasters to re-scan the lowest levels of the atmosphere more frequently through the use of Supplemental Adaptive Intra-volume Scanning (SAILS). SAILS reduces the revisit period for scanning the lowest 1 km of the atmosphere but comes at the cost of a longer delay between scans at higher altitudes. This study quantifies how often radar Volume Coverage Patterns (VCPs) and all available SAILS options are used during the issuance of 148,882 severe thunderstorm and 18,263 tornado warnings, and near 10,474 tornado, 58,934 hail, and 127,575 wind reports in the dual-polarization radar era. A large majority of warnings and storm reports were measured with a VCP providing denser low-level sampling coverage. More frequent low-level updates were employed near tornado warnings and reports compared to severe thunderstorm warnings and hail or wind hazards. Warnings issued near a radar providing three extra low-level scans (SAILSx3) were more likely to be verified by a hazard with a positive lead time than warnings with fewer low-level scans. However, extra low-level scans were more frequently used in environments supporting organized convection as shown using watches issued by the Storm Prediction Center. Recently, the number of mid-level radar elevation scans is declining per hour, which can adversely affect the tracking of convective polarimetric signatures, like ZDR columns, which were found above the 0.5° elevation angle in over 99% of cases examined.


2021 ◽  
Vol 2021 (23) ◽  
pp. 20-30
Author(s):  
Taras Pechonchyk ◽  
◽  
Vitaliy Ivanchenko ◽  

AbstractIntroduction. Effective management of road indstry is particularly important in conditions of limited funding, as it is not possible to provide adequate funding of the economic entity that has the functions of a customer service. The cost of the customer service maintenance depends directly on the compliance with applicable regulations for these works cost determination. One of the aspects that form a considerable part of the costs of customer service is the maintenance of service vehicles.Problem Statement. Road services in the regions (hereinafter RSR) are the recipients and managers of the funds from the State Budget of Ukraine that are directed for the development and maintenance of public roads of state importance, being as well the asset holders of these roads. To perform their functions, the RSR have vehicles on their balance, the use of which involves a number of costs, including fuel and lubricants, repair, maintenance, replacement of tires, etc. The most important of the steps involved in setting the costs of vehicle maintenance is the process of cost planning. Planning has to be based on the structure of the vehicle fleet (own or leased), functional responsibilities and scope of road works.Planning is carried out for vehicles on the balance of the RSR, as well as for leased vehicles. In the case of leasing, the costs mentioned above are added by the vehicles leasing costs. These costs must be forecasted, justified and performed within the approved cost estimates of the customer service expenses.Purpose. The purpose of the article is to highlight the theoretical and methodological approaches to the calculation of planned costs for the maintenance of service vehicles of the road works customer.Materials and methods. Dialectical methods of knowledge, such as analysis and synthesis of fleet composition characteristics and approaches to cost planning methods, as well as induction, were used in writing the article to explore some aspects of the process of calculating the planned cost of maintenance of the road works customer's service vehicles.Results. The study highlights and describes the main approaches to the calculation of planned costs for the maintenance of service vehicles of the road works customer. The methodology of calculation of planned costs for the maintenance of service vehicles is explored.Conclusions. The introduction of a clear methodology and analytical toolkit for calculating all necessary expenditure items for the maintenance of the road works customer's vehicles in the cost planning process will establish the implementation of a clear mechanism for calculating the planned costs of maintenance of the road works customer's vehicles. It will also provide an automated information-analytical complex for planning of cost estimates, with information entry and reporting in standard forms and possibility of prompt response to changes in fleet composition, needs for spare parts, repairs or other expenses for the maintenance of service vehicles and making changes in cost estimates.Keywords: motor vehicles, costs, cost planning, customer service, maintenance of service vehicles


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