Multiple sourcing in single- and multi-echelon inventory systems

This thesis deals with stochastic inventory models that focus on the following two aspects in particular: (i) the coordination of multiple supply sources and (ii) the optimization of the inventory allocation and sizing in multi-echelon systems. Initially, single-echelon inventory models with multiple sourcing and multi-echelon inventory models with single sourcing are analyzed separately. In the former case, the goal is the identification of effective inventory control policies. In the latter case, the focus lies on the development of a new multi-echelon approach, which combines the two major frameworks currently available in the literature. Subsequently, both aspects are integrated into a multi-echelon inventory model with multiple sourcing

Resonance modes in the standard piezoceramic shear geometry: A discussion based on finite element analysis

El pdf del artículo es el manuscrito de autor.Several authors developed methods for the complex characterization of piezoceramics from complex impedance measurements at resonance. Alemany et al. developed an automatic iterative method, applied and reported in a first publication to four modes of resonance: (1) the length extensional mode of a thickness poled rectangular bar; (2) the length extensional mode of long rods or rectangular bars, length poled; (3) the thickness extensional mode of a thin plate and (4) the thickness shear mode of a thin plate. In a second publication it was reported the application of the method to (5) the radial mode of a thin disk, thickness poled, the most mathematically complex geometry. The (2), (3), (4) and (5) modes of resonance are sufficient for the purpose of the determination of the full set of complex elastic, dielectric and piezoelectric coefficients of piezoceramics, a 6mm symmetry material. This work presents the results of the FEA modeling of a thin plate based on the characterization of a commercial ceramic. The comparison of the experimental resonance spectra and the FEA results obtained for elastically, dielectrically and piezoelectrically homogeneous samples is presented and discussed. The complex characterization for the first time of the shear mode of a new lead-free piezoceramic is also shown.This work was carried out under the projects PIRAMID (G5RD-CT-2001-00456) of the GROWTH Program of the EC and MAT 2001-4819-E, MAT2002-00463 and the Ramon y Cajal Program, of the Spanish CICyT, and has benefited from the synergy provided by the POlar ELEtroCERamics, POLECER, (G5RT-CT2001-05024) Thematic Network of the EC.Peer reviewe

Комплексные геофизические исследования с целью доразведки юго-западного фланга уранового месторождения Харасан (республика Казахстан)

Цель работ: Комплексные геофизические иследования с целью доразведки юго-заподного фланга уранового месторождения Харасан (республика Казахстан) Объект работ: Участок Байкенже месторождения Харасан, локализованный в горизонте верхнего мела на глубинах от 610 м до 690м. Методы решения задач: анализ и обобщение геолого-геофизических материалов. На территории «Харасан» для решения геологических задач применяется комплекс геофизических методов исследования скважин. При этом, гамма-каротаж, электрокаротаж, инклинометрия выполнялись во всех скважинах, независимо от их целей, задач и назначения. Дополнительные геофизические методы, такие как каротаж мгновенных нейтронов деления (КНД-М), кавернометрия, проводятся выборочно.Purpose of work: Integrated geophysical isledovanija for the purpose of further exploration of the south- west- side attack Kharassan uranium deposit (Republic of Kazakhstan ) Object of work: Planning Baykenzhe Kharassan deposits localized in the Upper Cretaceous horizon at a depth of 610 m to 690m . Methods for solving problems : analysis and synthesis of geological and geophysical data . On " Kharassan " territory for solving complex geological tasks used geophysical methods for wells .At the same time , gamma ray , electric logging , directional survey carried out in all wells , regardless of their objectives , tasks and appointments . Additional geophysical methods , such as logging prompt fission neutron ( CPV -M ) , caliper , conducted selectively

Safety stock optimization in distribution systems - a comparison of two competing approaches

Contributions to multi-echelon safety stock optimisation can broadly be divided into models following either a stochastic- or guaranteed-service approach. These approaches form the basis of several commercial inventory optimisation software tools. To date, there is still a lack of a detailed comparison between the two approaches. This paper presents a cost comparison for two-stage distribution systems by means of a simulation study. The results indicate that the cost difference between the two approaches is quite small amounting to 4 at most. We observe that in most cases, the resulting (lower) internal warehouse service level is a good indicator for the superiority of an approach. The guaranteed-service approach shows a better performance for moderate flexibility costs, large warehouse processing times and high retailer service levels

Strategic Safety Stock Placement in Supply Networks with Static Dual Supply

Many real-world supply networks source required materials from multiple suppliers. Existing multiechelon inventory optimization approaches either restrict their scope to multiple supply sources in two-echelon systems or single suppliers in multiechelon systems. We develop an exact mathematical model for static dual supply in a general acyclic N-echelon network structure, which builds on the guaranteed-service framework for safety stock optimization. It is assumed that the suppliers are allocated static fractions of demand. We prove that for normally distributed demand an extreme point property holds. We present a real example from the industrial electronics industry consisting of five echelons and three dual-sourced materials. This example forms the basis for a numerical analysis. Compared with the only previously published approximate solution, our exact approach results in considerable cost savings because the exact model captures inventory pooling in a way that the approximation is unable to do. For a set of test problems, total safety stock cost savings are 9.1%, on average

Operations Research in BASF's Supply Chain Operations

In this paper, we highlight the application of operations research (OR) at BASF in the area of supply chain management (SCM) by using selected examples with annual cost savings ranging between several hundred thousand and several million euros. We address special characteristics of the process industry that should be dealt with and identify future research needs. The examples cover strategic, tactical, and operational topics encountered at BASF. We share our lessons learned, based on our experience from past OR projects in SCM, about challenges as well as benefits of standard and tailor-made OR solutions. In general, we find that the special characteristics often call for a modification or enhancement of standard OR models. Providing appropriate solutions therefore requires a joint effort of SCM, IT, and OR experts

Rail Car Fleet Design: Optimization of Structure and Size

We develop a model to determine the optimal structure and size of a rail car fleet at a chemical company under uncertainty in demand and travel times as well as substitution between rail car types. First, we formulate an MILP model that accounts for the substitution relations between the types and minimizes the total direct rail car cost under given rail car availability constraints and a predefined maximum number of types. Second, based on the fleet structure obtained by the MILP model, the fleet size is computed by using an approximation from inventory theory that considers the existing uncertainties. Compared to the current approach of the rail car fleet management team, the model produces a reduction in safety stock of 120 rail cars and thus direct cost savings of 8% as well as further indirect cost savings due to a smaller number of rail car types, which reduces the switching effort of the rail cars on the storage tracks

A Comparison of the Constant-Order and Dual-Index Policy for Dual Sourcing

We analyze a single-product, periodic-review, stochastic demand inventory model with backorders and two supply options, a regular and a more expensive expedited one, with deterministic, offsetting lead times. Since the optimal policy for such a problem is generally unknown, several simpler policies have been proposed in the literature, e.g., the single-index (SIP), dual-index (DIP), or constant-order policy (COP). In previous research the DIP has been found to perform closely to the optimal policy in specific numerical settings. The COP, on the other hand, is very appealing from a practical point of view. We explore the relative cost performance of these two policies in a numerical study to gain insights into appropriate policy choices. We find that in settings, where dual sourcing is most valuable, the simpler COP delivers satisfactory results, sometimes even better ones than the DIP, and therefore represents a legitimate policy alternative for practical situations