33,815 research outputs found
Stochastic Optimization Models for Perishable Products
For many years, researchers have focused on developing optimization models to design and manage supply chains. These models have helped companies in different industries to minimize costs, maximize performance while balancing their social and environmental impacts. There is an increasing interest in developing models which optimize supply chain decisions of perishable products. This is mainly because many of the products we use today are perishable, managing their inventory is challenging due to their short shelf life, and out-dated products become waste. Therefore, these supply chain decisions impact profitability and sustainability of companies and the quality of the environment. Perishable products wastage is inevitable when demand is not known beforehand. A number of models in the literature use simulation and probabilistic models to capture supply chain uncertainties. However, when demand distribution cannot be described using standard distributions, probabilistic models are not effective. In this case, using stochastic optimization methods is preferred over obtaining approximate inventory management policies through simulation.
This dissertation proposes models to help businesses and non-prot organizations make inventory replenishment, pricing and transportation decisions that improve the performance of their system. These models focus on perishable products which either deteriorate over time or have a fixed shelf life. The demand and/or supply for these products and/or, the remaining shelf life are stochastic. Stochastic optimization models, including a two-stage stochastic mixed integer linear program, a two-stage stochastic mixed integer non linear program, and a chance constraint program are proposed to capture uncertainties. The objective is to minimize the total replenishment costs which impact prots and service rate. These models are motivated by applications in the vaccine distribution supply chain, and other supply chains used to distribute perishable products.
This dissertation also focuses on developing solution algorithms to solve the proposed optimization models. The computational complexity of these models motivated the development of extensions to standard models used to solve stochastic optimization problems. These algorithms use sample average approximation (SAA) to represent uncertainty. The algorithms proposed are extensions of the stochastic Benders decomposition algorithm, the L-shaped method (LS). These extensions use Gomory mixed integer cuts, mixed-integer rounding cuts, and piecewise linear relaxation of bilinear terms. These extensions lead to the development of linear approximations of the models developed. Computational results reveal that the solution approach presented here outperforms the
standard LS method.
Finally, this dissertation develops case studies using real-life data from the Demographic Health Surveys in Niger and Bangladesh to build predictive models to meet requirements for various childhood immunization vaccines. The results of this study provide support tools for policymakers to design vaccine distribution networks
A Comparison Study of Multi-Objective Metaheuristic Techniques for Continuous Review Stochastic Inventory System
Supply chain management which involves managing the flow of material andinformation from sources to customers has been one of the most challenging issuesfacing both the academicians and the practitioners for years. Inventory control is acrucial part of tactical decision level affecting the performance of supply chain indistribution and production. The main focus of this study is to compare theperformance of different multi-objective metaheuristic techniques to optimizeinventory parameters for single-product continuous review stochastic inventorysystem with transportation costs. The simulation-based optimization method is usedto solve the problem by combining the simulation model and metaheuristicalgorithms in order to determine the inventory policy taking into account twoconflicting objectives: customer service level and total inventory cost. We build adiscrete event simulation model to evaluate the objective function of the problem.The Metaheuristic techniques such as the genetic algorithm and particle swarmoptimization are applied to search the solution space. The results obtained by allthese proposed techniques are compared and the effectiveness of each technique hasbeen illustrated
Supply chain management of the Canadian Forest Products industry under supply and demand uncertainties: a simulation-based optimization approach
The Canadian forest products industry has failed to retain its competitiveness in
the global markets under stochastic supply and demand conditions. Supply chain
management models that integrate the two-way flow of information and materials under
stochastic supply and demand can ensure capacity-feasible production of forest industry
and achieve desired customer satisfaction levels. This thesis aims to develop a real-time
decision support system, using simulation-based optimization approach, for the Canadian
forest products industry under uncertain market supply and demand conditions. First, a
simulation-based optimization model is developed for a single product (sawlogs), single
industry (sawmill) under demand uncertainty that minimizes supply chain costs and finds
optimum inventory policy parameters (s, S) for all agents. The model is then extended to
multi-product, multi-industry forest products supply chain under supply and demand
uncertainty, using a pulp mill as the nodal agent. Integrating operational planning
decisions (inventory management, order and supply quantities) throughout the supply
chain, the overall cost of the supply chain is minimized. Finally, the model integrates
production planning of the pulp mill with inventory management throughout the supply
chain, and maximizes net annual profit of the pulp mill.
It was found that incorporation of a merchandizing yard between suppliers and
forest mills provides a feasible solution to handle supply and demand uncertainty.
Although the merchandizing yard increases the total daily cost of the supply chain by
17.4 million in
the multi-product, multi-industry supply chain. Under supply and demand uncertainty
without a merchandizing yard, the pulp mill is only able to operate at 10% of its full
capacity and achieve a customer satisfaction level of 9%. The merchandizing yard
ensures pulp mill running capacity of 70%, and customer satisfaction level of at least
50%. However, the merchandizing yard is economically viable only, if the sales price of
pulp is at least $680 per tonne. Efficient and effective management of inventory
throughout the supply chain, integrated with production planning not only ensures
continuous operation of forest mills, but also significantly improves the customer
satisfaction
Inventory management based on simulation of ordering process
Inventory management is one of the key operational functions of a company which, in the context of modern Supply Chain Management schemes, plays an important role both for the company itself and the coordination with the SC partners. Especially the aspect of service level and stockout probability has become critical.
Classical methods of inventory management are based on simple analytical formulae which, however, only treat special cases. In this contribution we present a tool for the optimization of inventory management which is based on a simulation of the ordering processes. The full stochastic properties of the ordering process are incorporated which allows an accurate determination of performance measures like service level. With this tool, the determination of cost-minimal inventory parameters (reorder level, reorder quantity) for given stockout probability is easily possible
Multiobjective strategies for New Product Development in the pharmaceutical industry
New Product Development (NPD) constitutes a challenging problem in the pharmaceutical industry, due to the characteristics of the development pipeline. Formally, the NPD problem can be stated as follows: select a set of R&D projects from a pool of candidate projects in order to satisfy several criteria (economic profitability, time to market) while coping with the uncertain nature of the projects. More precisely, the recurrent key issues are to determine the projects to develop once target molecules have been identified, their order and the level of resources to assign. In this context, the proposed approach combines discrete event stochastic simulation (Monte Carlo approach) with multiobjective genetic algorithms (NSGAII type, Non-Sorted Genetic Algorithm II) to optimize the highly combinatorial portfolio management problem. In that context, Genetic Algorithms (GAs) are particularly attractive for treating this kind of problem, due to their ability to directly lead to the so-called Pareto front and to account for the combinatorial aspect. This work is illustrated with a study case involving nine interdependent new product candidates targeting three diseases. An analysis is performed for this test bench on the different pairs of criteria both for the bi- and tricriteria optimization: large portfolios cause resource queues and delays time to launch and are eliminated by the bi- and tricriteria optimization strategy. The optimization strategy is thus interesting to detect the sequence candidates. Time is an important criterion to consider simultaneously with NPV and risk criteria. The order in which drugs are released in the pipeline is of great importance as with scheduling problems
Multiobjective strategies for New Product Development in the pharmaceutical industry
New Product Development (NPD) constitutes a challenging problem in the pharmaceutical industry, due to the characteristics of the development pipeline. Formally, the NPD problem can be stated as follows: select a set of R&D projects from a pool of candidate projects in order to satisfy several criteria (economic profitability, time to market) while coping with the uncertain nature of the projects. More precisely, the recurrent key issues are to determine the projects to develop once target molecules have been identified, their order and the level of resources to assign. In this context, the proposed approach combines discrete event stochastic simulation (Monte Carlo approach) with multiobjective genetic algorithms (NSGAII type, Non-Sorted Genetic Algorithm II) to optimize the highly combinatorial portfolio management problem. In that context, Genetic Algorithms (GAs) are particularly attractive for treating this kind of problem, due to their ability to directly lead to the so-called Pareto front and to account for the combinatorial aspect. This work is illustrated with a study case involving nine interdependent new product candidates targeting three diseases. An analysis is performed for this test bench on the different pairs of criteria both for the bi- and tricriteria optimization: large portfolios cause resource queues and delays time to launch and are eliminated by the bi- and tricriteria optimization strategy. The optimization strategy is thus interesting to detect the sequence candidates. Time is an important criterion to consider simultaneously with NPV and risk criteria. The order in which drugs are released in the pipeline is of great importance as with scheduling problems
The role of learning on industrial simulation design and analysis
The capability of modeling real-world system operations has turned simulation into an indispensable problemsolving methodology for business system design and analysis. Today, simulation supports decisions ranging
from sourcing to operations to finance, starting at the strategic level and proceeding towards tactical and
operational levels of decision-making. In such a dynamic setting, the practice of simulation goes beyond
being a static problem-solving exercise and requires integration with learning. This article discusses the role
of learning in simulation design and analysis motivated by the needs of industrial problems and describes
how selected tools of statistical learning can be utilized for this purpose
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Decision support for build-to-order supply chain management through multiobjective optimization
This paper aims to identify the gaps in decision-making support based on
multiobjective optimization for build-to-order supply chain management (BTOSCM).
To this end, it reviews the literature available on modelling build-to-order
supply chains (BTO-SC) with the focus on adopting multiobjective optimization
(MOO) techniques as a decision support tool. The literature has been classified based
on the nature of the decisions in different part of the supply chain, and the key
decision areas across a typical BTO-SC are discussed in detail. Available software
packages suitable for supporting decision making in BTO supply chains are also
identified and their related solutions are outlined. The gap between the modelling and
optimization techniques developed in the literature and the decision support needed in
practice are highlighted and future research directions to better exploit the decision
support capabilities of MOO are proposed
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