Lot streaming is a strategy of splitting a production lot into several sublots so that completed sublots can be transferred to a downstream machine before the entire lot has been completely processed ...at a current machine. Such a strategy increases the velocity of material flow through a system. However, an increase in the number of transfers between stages also increases material handling cost. In this paper, we address the problem of minimizing a weighted sum of the makespan and handling costs when multiple lots are produced in an assembly system consisting of
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suppliers in the first stage and a single assembly machine in the second stage. We exploit a relationship between an optimal solution for this problem and that for a related single-lot, two-machine makespan minimization problem in developing a polynomial-time algorithm to obtain the optimal number and sizes of sublots for each lot when a sequence for processing the lots on the assembly machine is given. We also provide novel integer programming formulations to simultaneously determine an optimal production sequence for the lots and the number of sublots and sublot sizes for each lot, and present a polynomial-time method to obtain valid inequalities for this problem. Experimental results are presented to demonstrate the effectiveness of this formulation over the traditional linear-ordering-based formulations.
A multi-bale handling unit offers an advantage for the efficient hauling of round bales. Two empty racks on trailers are left at a satellite storage location for loading while a truck tractor ...delivers two loaded racks to the biorefinery, thus uncoupling the loading and hauling operations and increasing the efficiency of both. The projected 10 min trailer exchange time equals the projected 10 min unload time at the biorefinery achieved by lifting off the two full racks and replacing them with two empties, a technology adapted from the container shipping industry. A concept is presented for a bale loader that latches onto the rack/trailer and loads bales into the bottom tier chambers. This machine will load 10 bales into the rack on the front trailer by attaching on to the front of the trailer and 10 bales into the rear trailer by attaching onto the rear. A telehandler removes bales from single-layer storage and places them in the bale loader to load the bottom tier compartments. The top tier compartments are loaded directly from the top. Expectations are that an experienced operator can average 9 loads in a 10 h workday, and load-out cost is estimated as 3.61 USD/Mg, assuming the average achieved load-out productivity over annual operation is 60% of optimum productivity (24 Mg/h) equal to 14.4 Mg/h. Cost increases to 4.81 USD/Mg when the productivity factor drops to 45%, and cost is 3.09 USD/Mg for a factor of 70%.
•Develop exact and approximation algorithms to solve the model.•Derived closed-form solutions for the three special cases.•Conservative algorithm dominates the large-scale instances.•Seek the best ...budget of uncertainty by cross validation method.
This work studies a Robust Multi-product Newsvendor Model with Substitution (R-MNMS), where the demand and the substitution rates are stochastic and are subject to cardinality-constrained uncertainty sets. The goal of this work is to determine the optimal order quantities of multiple products to maximize the worst-case total profit. To achieve this, we first show that for given order quantities, computing the worst-case total profit, in general, is NP-hard. Therefore, we derive the closed-form optimal solutions for the following three special cases: (1) if there are only two products, (2) if there is no substitution among different products, and (3) if the budget of demand uncertainty is equal to the number of products. For a general R-MNMS, we formulate it as a mixed-integer linear program with an exponential number of constraints and develop a branch and cut algorithm to solve it. For large-scale problem instances, we further propose a conservative approximation of R-MNMS and prove that under some certain conditions, this conservative approximation yields an exact optimal solution to R-MNMS. The numerical study demonstrates the effectiveness of the proposed approaches and the robustness of our model.
In this paper, we consider an application of lot-streaming for processing a lot of multiple items in a hybrid flow shop (HFS) for the objective of minimizing makespan. The HFS that we consider ...consists of two stages with a single machine available for processing in Stage 1 and
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identical parallel machines in Stage 2. We call this problem a 1 +
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TSHFS-LSP (two-stage hybrid flow shop, lot streaming problem), and show it to be NP-hard in general, except for the case when the sublot sizes are treated to be continuous. The novelty of our work is in obtaining closed-form expressions for optimal continuous sublot sizes that can be solved in polynomial time, for a given number of sublots. A fast linear search algorithm is also developed for determining the optimal number of sublots for the case of continuous sublot sizes. For the case when the sublot sizes are discrete, we propose a branch-and-bound-based heuristic to determine both the number of sublots and sublot sizes and demonstrate its efficacy by comparing its performance against that of a direct solution of a mixed-integer formulation of the problem by CPLEX
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•Impact of sharing or of not sharing advertising cost on the total profit.•Centralized case performs better than the other cases under cost sharing.•Advertising provides positive economic and ...environmental benefits.•Used-product collection and channel profit in CLSC are increased by advertising.
Advertising plays an important role in contributing to the supply of returned items and market expansion. In this paper, advertising is considered as a means to entice consumers to return used-items in a remanufacturing environment. We investigate the impact of sharing or of not sharing advertisement cost on the total profit gained and the quantity of used-items acquired under the uncertain demand of remanufactured/new products and uncertain returns. For analysis, we develop mathematical models for the following closed-loop supply chain configurations: (i) advertising by manufacturer with cost-sharing, (ii) advertising by retailer with cost-sharing, (iii) individual advertising with cost-sharing, (iv) centralized advertising, and finally, (v) advertising without cost-sharing. These models have been illustrated through a numerical study, and the results reveal that the closed-loop supply chain model with “centralized advertising configuration” performs better over other models, and also, that advertising provides positive economic and environmental benefits.
In this paper, we address a Stochastic-Demand Assembly Job Shop Scheduling Problem (SD-AJSSP) in the presence of the commonality of sub-assemblies across products. We propose a new production ...methodology, named Assemble-to-Order with Commonality of Sub-Assemblies (ATO-CS) to not only solve the SD-AJSSP, but also, achieve a successful implementation of a mass customisation system by collectively aiming to (1) keep the production costs low by leveraging upon commonality of sub-assemblies in products' BOM and producing sub-assemblies on a mass scale during one of the two stages of production, (2) minimise the loss due to excess inventory build-up in anticipation of stochastic demand of products by postponing the production of certain apex sub-assemblies in products' BOM until the actual demand is realised, and (3) reduce the time of the products' delivery to customers. The ATO-CS method determines optimum production levels as well as schedules assembly operations/jobs over the machines at each stage of production, where the second stage is an assembly job shop and is shown to outperform commonly-used production methodologies. We also develop an algorithm for its implementation and show its efficacy over the use of the state-of-the-art commercial solver CPLEX® in obtaining a lower solution cost and smaller optimality gap.
This paper deals with the problem of allocating work to the stations of an assembly line to minimize the makespan of a lot of products with a low overall demand. There is no buffer permitted in ...between the stations, and the line operates under homogeneous learning (i.e., under the same learning rate for all stations). We show that in the presence of learning, the optimal makespan requires imbalanced allocation of work to stations. The level of savings in the optimal makespan value due to the imbalanced loading of work over the balanced loading case are demonstrated as a function of the value of the learning constant, number of stations on the line as well as lot size. These savings can be quite significant under the case of low overall demand.
Due to growing regulations, competition, and a changing corporate culture, original equipment manufacturers (OEMs) are now increasing their extended producer responsibility (EPR). In this paper, we ...explore how this trend of EPR affects product design when an OEM decides to lease their products and then remanufacture them at the end of a lease period. In this context, we investigate the level of durability to be built into the parts of a product. Our analysis reveals that, assuming a linear cost/durability tradeoff, there are discrete durability levels for each part to select from, and that, the optimal durability level for a part depends on: (1) the quantity of products remanufactured, (2) the profit margin of remanufactured products, and (3) the recovery rate of leased products. Also, we show how our analysis can be extended to: (1) accommodate various forms of nonlinear cost/durability trade-off functions, and (2) address cannibalization of new product leases by remanufactured products.
The assembly line balancing problem consists of assigning tasks to an ordered sequence of stations such that the precedence relations among the tasks are satisfied and some performance measure is ...optimized. Due to the complexity of the problem, heuristic procedures appear to be more promising than the optimum-seeking algorithms. For the single-model, deterministic version, there are numerous exact and heuristic algorithms developed, while for the other more complex but more realistic versions, the research published consists mainly of heuristic procedures. In this paper, the heuristic procedures are critically examined and summarized in sufficient detail to provide a state-of-the-art survey. An evaluation of the procedures and some further research topics have also been presented.
In this paper, we present a taxonomic review of the literature devoted to the use of operations research approaches for the design and operation of biomass feedstock supply chains (BFSCs). A total of ...185 publications that have appeared from 1989 to 2017 are classified based on (1) the embedded optimisation subproblems; (2) the modelling methodologies used for their formulations; and (3) the methods employed for their solution. Our objective of using this classification scheme is to highlight the presence of some useful substructures in a BFSC problem that can, then, be exploited in developing its solution procedure. We illustrate this idea on some generic BFSC problems and present a Dantzig-Wolfe decomposition-based methodology for developing customised approaches to effectively tackle these difficult and large-sized BFSC problems. Finally, we suggest several promising future research directions.
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