1,169 research outputs found
A note concerning physical space occupation costs in Vendor Managed Inventory with consignment agreement models
No full textA new analytic formulation of the Vendor Managed Inventory with consignment agreement is proposed. It represents a modified and more realistic version of the model proposed in Braglia and Zavanella (2003). The evaluation of the stockholding related costs is herewith substantially revisited to consider the requirements of a standard VMI relationship with consignment agreement. In particular, the physical space occupation cost held by the buyer is introduced as a component of the overall holding cost and is referred to the maximum stock level, rather than to the average value, as proposed in the past literature. Finally, an implicit analytical solution is given and compared to the original one obtained by Braglia and Zavanella (2003)
Safety Stock Management in Single Vendor-Single Buyer Problem under VMI with Consignment Stock Agreement
No full textIn this paper a new analytical approach to safety stock management, within single buyer–single vendor framework under VMI with consignment agreement, is presented. In particular, the cost of the safety stock is evaluated adopting a logistic approximation of the standard normal cumulative distribution. The service level is put in relation to the dimension of the single shipment, to the average demand on the buyer and to the number of admissible stockouts. Once the mean joint total cost function is defined, on the basis of the model of Braglia and Zavanella, (2003. Int. J. Prod. Res. 41, 3793–3808) modified according to Braglia et al. (2014. Int. J. Logist. Syst. Manage. forthcoming 2014), a minimum cost solution (within a predefined domain) is derived. Moreover, a numerical study is carried out. First, a sensitivity analysis is shown. Then, the model of Braglia and Zavanella, (2003. Int. J. Prod. Res. 41, 3793–3808), in its original expression, is compared with both Hill (1997. Eur. J. Oper. Res. 97, 493–499), Hill (1999. Int. J. Prod. Res. 37, 2463–2475) and Hill and Omar (2006. Int. J. Prod. Res. 44, 791–800). In particular, the comparison considers the equal-sized shipments case without delayed deliveries taking into account different reciprocal values for the stockholding costs
Improving Tool-Life Stochastic Control Through a Tool-Life Model Based on Diffusion Theory
No full textIt is known that estimating the wear level at a future time instant and obtaining an updated evaluation of the tool-life density is essential to keeping machined parts at the desired quality level, reducing material waste, increasing machine availability, and guaranteeing the safety requirements. In this regard, the present paper aims at showing that the tool-life model that Braglia and Castellano [23] developed can be successfully adopted to probabilistically predict the future tool wear and to update the tool-life density. Thanks to the peculiarities of a stochastic diffusion process, the approach presented allows deriving the density of the wear level at a future time instant, considering the information on the present tool wear. This makes it therefore possible updating the tool-life density given the information on the current state. The method proposed is then experimentally validated, where its capability to achieve a better exploitation of the tool useful life is also shown. The approach presented is based on a direct wear measurement. However, final considerations give cues for its application under an indirect wear estimate
On the solutions in rational expectations models
No full textThis paper deals with the solutions to macroeconomic models with rational expectations. A first purpose is to demonstrate that two forms of the efficient-market equation commonly used in the literature may be treated as approximations of the same general equation, of different orders with respect to perturbative forces of the market. Second aim is to show how the perturbative terms can be given explicit forms. Finally, the paper addresses the question of finding contributions which can concur to explain the phenomenon usually referred to as stock price volatility
Monte-Carlo calculations of electron transport coefficients in H2. First simulations of the Townsend-Huxley experiment
No full textThe aim is to get additional evidence to assist in resolving the discrepancy between swarm-derived, theoretical and beam-measured vibrational cross sections for the case v = 0 --> 1. Good agreement between Monte-Carlo and experimental transport data is obtained with the swarm-derived cross sections. However, some simulations relevant to the Townsend-Huxley experiment call into question the accuracy of the characteristic energies used in swarm analyses. Possible reasons of the observed discrepancies between Monte-Carlo and experimental data and expected implications even on the accuracy of the cross sections in H-2 are discussed
Influence of the limited service capacity of the inspection station on the control policy of an automatized production system
No full textThe influence of the limited capacity of an inspection station on the control policy is studied for a job shop manufacturing process. The production system and the control station are described by queue models M/G/1 and G/G/1, respectively. The deterministic sampling rate is obtained which, in case of breakdown minimizes the number of defective units
Optimal replacement policy for a deteriorating production system
No full textAn optimal replacement policy for a deteriorating production system is considered. A minimal repair model is defined which assumes the system to be replaced after a specified time, during which a number of failures may occur The probability of failure can be given any arbitrary (increasing) form. The model is based on a technique which permits to deal with large repair times (non-negligible with respect to the replacement time and the interval time) and to calculate the probability of k breakdowns over the replacement interval rigorously. The average downtime relevant to k minimal repairs is obtained, on the contrary, from a semiempirical formula that appears in good agreement with the results of Monte Carlo simulations. The theory permits an accurate analysis of the error that is introduced when move conventional and approximate models are used
Optimisation of a simulated-annealing-based heuristic for single row machine layout problem using genetic algorithm
No full textWe discuss a procedure to determine the optimal set of parameters relevant to heuristics based on the Simulated Annealing technique, an algorithm which is widely applied to combinatorial problems in the field of manufacturing systems. We consider the search for the best set as a second optimisation problem that we solve by a Genetic Algorithm. The performance of our approach is tested in the particular case of backtracking minimisation in a single row machine layout problem for flexible manufacturing systems
Manufacturing cell design with size constraints: a multiperturbation simulated annealing approach
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