Subhash C. Sarin

• Doctor of Engineering
• Virginia Tech

In this paper, we address a biomass feedstock logistics problem to supply biomass from production fields to satellite storage locations (SSLs) and from there to bioenergy plants (BePs) and then to a biorefinery. It entails a new problem feature of routing load-out equipment sets among the SSLs to perform loading/unloading of biomass and/or its pre-...

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 m identical parallel machines in Stage 2. We call this problem a 1 + m T...

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 betwee...

We introduce a compact formulation for the fixed-destination multi-depot asymmetric travelling salesman problem (FD-mATSP). It consists of m salesmen distributed among D depots who depart from and return to their respective origins after visiting a set of customers. The proposed model exploits the multi-depot aspect of the problem by labelling the...

The design of a product impacts its price and end-of-life (EOL) option. In this paper, we present a two-stage model for the reverse supply chain of an original equipment manufacturer (OEM) to study this impact. In the first stage, an OEM designs and sells its new products while in the second stage, which is the end of their useful lives, the OEM co...

Covid-19 has affected the lives of people in different ways. A number of models are available in the literature to study the dynamics of a pandemic. However, there are very few models that study the impact of vaccine distribution among different population groups. In this paper, we use a modified epidemiological model which incorporates relationshi...

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 t...

In this paper, we investigate performances of different sorghum biomass feedstock logistics systems (S-BFLSs). To do so, we use a multi-period, mixed integer linear programming model to determine the optimal design for such systems. Our model prescribes strategic decisions pertaining to locations and sizes of storage facilities (called satellite st...

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...

This paper studies a multiproduct newsvendor problem with customer-driven demand substitution, where each product, once run out of stock, can be proportionally substituted by the others. This problem has been widely studied in the literature; however, because of nonconvexity and intractability, only limited analytical properties have been reported...

In this paper, we address a scheduling problem belonging to a two-stage assembly system that can also be viewed as a mass customization system. The first stage of this system consists of a set of subassembly machines, each of which produces a component type. These components are then transferred in sublots to Stage 2, where they are assembled into...

This paper addresses a biomass feedstock logistics supply chain design problem (BFL-SCDP), which comprises a multi-period facility location problem, a special case of a single-item parallel-facilities capacitated lot-sizing problem, and a network flow problem. We formulate this problem as a mixed-integer program and propose a branch-and-price-based...

A Nuclear Power Plant (NPP) outage is a planned period of time during which the plant does not produce energy and undergoes offline refueling and maintenance. For a commercial power plant, an outage window could last up to two months during which thousands of activities are performed. These activities are related by precedence thereby constituting...

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 methodologi...

This paper studies a multi-product newsvendor problem with customer-driven demand substitution, where each product, once run out of stock, can be proportionally substituted by the others. This problem has been widely studied in the literature, however, due to nonconvexity and intractability, only limited analytical properties have been reported and...

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 perio...

Dual-sourcing is a strategy of ordering the material required to process a lot (order) from two suppliers, instead of a single supplier. This strategy has been well-studied in the literature and has been shown to reduce lead time. However, the additional ordering cost incurred for dual-sourcing makes this strategy unattractive. In this paper, we co...

Abstract In this paper, we address a corn-stover harvest scheduling problem (CSHSP) that arises when a cellulosic ethanol plant contracts with farmers to harvest corn stover after the grain harvest has been completed. The plant contracts a fleet of harvesting crews, which must be assigned by the plant scheduler to harvest fields as they are called...

In this paper, we present an algorithm to solve the single and multiple asymmetric traveling salesmen problems (ATSP and mATSP) by generating violated subtour elimination constraints (SECs) from specific integer solutions. Computational results for the ATSP reveal that the proposed approach is able to solve 29 out of 33 well-known instances taken f...

In this paper, we present a single-commodity flow-based formulation for the high-multiplicity asymmetric traveling salesman problem (HMATSP), which is an extension of the asymmetric traveling salesman problem (ATSP) wherein a city can be visited multiple times. We show that even though this formulation is not as tight as the best known formulation...

We address a problem that arises for an original equipment manufacturer (OEM) who produces a product both in new and remanufactured forms. A remanufactured product is produced using the parts harvested from recovered products (cores) upon their disassembly, and it may contain some new parts while the excess good parts from cores are salvaged for pr...

Lot streaming is the process of splitting a production lot into sublots, and then processing the sublots on different machines in an overlapping manner. In this paper, we study the use of lot streaming for processing a lot in a two-machine flow shop when a sublot-attached setup time is incurred before the processing of each sublot. The objective is...

In this chapter, we address the problem of optimally routing and sequencing a set of jobs over a network of flexible machines for the objective of minimizing the sum of completion times and the cost incurred, assuming stochastic job processing times. This problem is of particular interest for the production control in high investment, low volume ma...

This paper is concerned with a hospital staff scheduling problem wherein surgical operation times are stochastic. We formulate a complete recourse, scenario-based model for this problem, and develop a branch-and-cut (B&C) algorithm that is further hybridised with the Monte Carlo method (MCM). The proposed hybrid MCM-based approach is demonstrated t...

In this paper, we address a single-lot, lot streaming problem for a two-stage hybrid flow shop, which consists of one machine at Stage 1 and two parallel (identical) machines at Stage 2. The objective is to minimize makespan. The lot is to be split into sublots each of which is processed first on the machine at Stage 1, and then, on one of the mach...

This article addresses an integrated lot-sizing and scheduling problem that arises in the primary manufacturing phase of a pharmaceutical supply chain. Multiple pharmaceutical ingredients and their intermediate products are to be scheduled on parallel and capacitated bays for production in batches. Sequence-dependent setup times and costs are incur...

In this chapter, we address a lot streaming problem for a two-stage assembly system involving multiple lots with the objective of minimizing the makespan. Each lot consists of items of a unique product type. We designate this problem as a multiple-lot, two-stage assembly, lot streaming problem (ML-TSALSP) which combines two key decisions: lot split...

In this paper, we investigate the performances of 32 formulations for the multiple asymmetric traveling salesman problem (mATSP) from the viewpoint of their tightness and solvability using commercial software. These formulations are either new or are generalizations of those proposed in the literature for the ATSP, including a transformation of the...

In this paper, we address a resource-constrained project scheduling problem involving a single resource. The resource can be applied at varying consumption rates to the activities of the project. The duration of each activity is defined by a convex, non-increasing time-resource trade-off function. In addition, activities are not preemptable (ie, th...

In this article, we address a stochastic generalized assignment machine scheduling problem in which the processing times of jobs are assumed to be random variables. We develop a branch-and-price (B&P) approach for solving this problem wherein the pricing problem is separable with respect to each machine, and has the structure of a multidimensional...

This paper introduces the use of conditional-value-at-risk (CVaR) as a criterion for stochastic scheduling problems. This criterion has the tendency of simultaneously reducing both the expectation and variance of a performance measure, while retaining linearity whenever the expectation can be represented by a linear expression. In this regard, it o...

From the Preface: This festschrift is devoted to recognize the career of a man who not only witnessed the growth of operations research from its inception, but also contributed significantly to this growth. Dr. Salah E. Elmaghraby received his doctorate degree from Cornell University in 1958, and since then, his scholarly contributions have enriche...

In this paper we present a review of the literature on lot streaming. Lot streaming is a technique that accelerates the flow of a product through a production system by splitting its production lot into sublots and then processing the sublots simultaneously over the machines, thereby reducing the work-in-process and cycle time. We divide the work p...

Recently, much attention has been devoted to research in reverse supply chain (RSC) and remanufacturing. This has been motivated both by academic interest and by the significant impact that the RSC activities, including remanufacturing, have on a nation’s economy. In 1996, remanufacturing alone accounted for 0.4% of the US economy, as a $53 billion...

In this paper, we address a multiple-lot lot streaming problem for a two-stage hybrid flow shop, which consists of one machine at Stage 1 and two parallel (identical) machines at Stage 2. Each item of a lot requires for its processing only one of the machines at Stage 2 after its processing at Stage 1. A lot can be split into sublots where the item...

In this paper, we address a two-machine flow shop scheduling problem in which a given set of jobs, each consisting of a number of wafers, is to be configured in the given number of carriers of limited capacity for transferring the wafers, and then, processing the wafers one-at-a-time on the machines, in order to minimise the makespan. First, we con...

In this paper, we investigate scenario generation methods to establish lower bounds on the optimal objective value for stochastic scheduling problems that contain random parameters with continuous distributions. In contrast to the Sample Average Approximation (SAA) approach, which yields probabilistic bound values, we use an alternative bounding me...

A high volume/high mix wafer fabrication facility processes customer orders (or lots) that are smaller in size. Because of their small sizes, a number of these lots are transported together in a carrier from one machine to another for processing. This is in contrast to transporting them individually, which would lead to an excessive number of mostl...

Given the location of a bio-energy plant for the conversion of biomass to bio-energy, a feedstock logistics system that relies on the use of satellite storage locations (SSLs) for temporary storage and loading of round bales is proposed. Three equipment systems are considered for handling biomass at the SSLs, and they are either placed permanently...

Stochastic scheduling is in the area of production scheduling. There is a dearth of work that analyzes the variability of schedules. In a stochastic environment, in which the processing time of a job is not known with certainty, a schedule is typically analyzed based on the expected value of a performance measure. This book addresses this problem a...

This paper presents a new model for a special type of traveling salesman problem called the High Multiplicity Asymmetric Traveling Salesman Problem (HMATSP). The formulation adopts a flow-based subtour elimination structure and establishes its validity for this problem. Also, we present computational results to demonstrate the efficacy of our model...

Production scheduling in semiconductor wafer fabs is a non-trivial task owing to the complexity of wafer fabrication. Dispatching rules are the most commonly used tools for shop floor control in this industry. Over the years, advanced dispatching rules, capable of impacting multiple performance measures and utilising both upstream and downstream in...

We address a single-batch lot streaming problem for a two-stage assembly system. The first stage consists of m parallel subassembly machines, each devoted to a component type. A single assembly machine at the second stage assembles a unit of a product after all m components (one each from the subassembly machines) are ready. The batch consists of U...

In this paper, we perform a detailed cost analysis of the operations pertaining to a biomass logistics problem. This involves balancing the total cost incurred for transporting raw biomass, a bulky low-value product, from the farms to the bio-crude plants, and the total cost incurred for transporting bio-crude oil, a higher-value more energy dense...

In this paper, we address a biomass logistics system that spans from the farms to a refinery. The key elements of a biomass logistics system include the hauling of biomass from the farms to satellite storage locations (SSLs) (for densification and systematic loading), transportation of biomass from the SSLs to bio-crude plants (for conversion into...

In this article, we investigate the integration of lot sizing and dispatch-related decisions for a wafer fabrication (hereafter referred to as wafer fab) facility. These decisions pertain to the operational planning and shop floor control (SFC) levels of its decision hierarchy. Our objective is to minimise output variability, which is an important...

In this paper, we address a university-timetabling problem and present a methodology that relies on Benders’ partitioning for its solution. This partitioning results from the special nature of the underlying integer programming formulation for this problem. We have used our methodology to schedule courses offered by the College of Engineering as we...

After locating a bio-energy plant for the conversion of biomass to biofuels, the logistics component associated with transporting the biomass is a nontrivial system. In this paper, we propose local storage locations throughout an area for the temporary storage and loading of round bales. Prior results of uniformly distributing storage locations ove...

In this paper, we investigate a supply chain scheduling problem involving a single manufacturer and multiple customers. Our aim is to integrate the production and shipping functions of the manufacturer so as to minimize the total cost incurred due to tardiness of customer orders and shipping of orders to customers. Since this problem is NP-hard (wh...

The inter-departure time variability is an important measure in production lines. Higher variability means added work-in-process and less predictability in output. It can be a primary obstacle towards achieving on-time delivery. The effects of line parameters (e.g., line length or buffer capacity) on inter-departure time variability have been studi...

In this paper, we address a facility layout problem involving arbitrary-shaped departments. Because of the difficulty involved in arranging arbitrary-shaped departments, this problem is rarely addressed in the literature. We present a formulation for this problem and show its validity. We also present a simulated annealing based algorithm for the s...

In this paper, we address an n-job, m-machine permutation flow shop scheduling problem for the objective of minimizing the total flow time. We propose a modification of the best-known method of Framinan and Leisten [An efficient constructive heuristic for flowtime minimization in permutation flow shops. Omega 2003;3 1:31 1-7] for this problem. We s...

In this paper, we present closed-form expressions, wherever possible, or devise algorithms otherwise, to determine the expectation and variance of a given schedule on a single machine. We consider a variety of completion time and due date-based objectives. The randomness in the scheduling process is due to variable processing times with known means...

In this paper, we address a facility layout problem involving arbitrary-shaped departments. Because of the difficulty involved in arranging arbitrary-shaped departments, this problem is rarely addressed in the literature. We present a formulation for this problem and show its validity. We also present a simulated annealing based algorithm for the s...

Lot streaming is the process of splitting a production lot into sublots, and then, scheduling the sublots in an overlapping fashion on the machines. In this paper, we present a polynomial-time procedure for determining the number of sublots of a single-lot, multiple-machine flow shop lot-streaming problem in order to minimize a unified cost-based o...

In this paper, we address the problem of allocating the work elements, belonging to the products of a lot, to the stations of an assembly line so as to minimize the makespan. The lots that are processed on the assembly line are characterized by a low overall demand for each product. There is no buffer permitted in between the stations, and the line...

This research investigates the effect of system's configuration (layout) and work allocation on the makespan of batches of different products characterised by significant learning. Frequently, in science-based industries the layout of the batch assembly could be relatively easily setup separately for each batch, where each batch contains different...

This paper addresses the problem of allocating work to the stations of an assembly line for minimising the makespan required to process a lot of products with a low overall demand. This environment is characterised by different learning slopes in the various stations (due to the nature of work). We assume small (e.g. a laser pen) to medium size pro...

Introduction Production Planning and Control Production Control in the Factory of the Future Integration in Production Control Systems Control Issues in Integrated Manufacturing Summary Bibliography

Lot streaming is the process of splitting a production lot into sublots and then scheduling the sublots in overlapping fashion on the machines in order to improve the performance of the production system. Implementation of this concept arises in several batch production environments. These include, among others, printed circuit board assembly and s...

In this paper, we address the problem of both releasing and scheduling of lots in a wafer fab. In the lot release problem, we determine the number of lots of different products to be released in each period of a planning horizon in order to minimize total tardiness. The problem of the scheduling of lots at various workstations is modeled as a mathe...

Recognizing the complexity of coal mining management, e.g., the scarcity of financial resources and a variation in the quality of coal found in different sections of a mine, in this paper, we develop a mixed-binary programming model as an aid for generating mine production schedules in order to obtain coal of the desired quality and maximize the as...

Lot streaming is a process of breaking a batch of jobs into smaller lots, and then processing these in an overlapping fashion on the machines. This important concept can significantly improve the overall performance of a production process, and thereby make the operation of a manufacturing system lean. Flow Shop Lot Streaming introduces the reader...

To comprehend the intricacies of a problem situation, it is best to represent it, if possible, as a mathematical model. A mathematical model can also help in possibly identifying some inherent structural properties of the problem and in devising an appropriate algorithm for its solution. Chapter 1 contains a brief review of work on the flow shop lo...

We consider the scenario where lots consisting of several discrete and identical items are to be processed on several machines configured as a flow shop. Instead of transferring the entire lot after all of its items have been processed on amachine, we consider transferring the items of the lot in smaller batches called sublots. This technique of sp...

The m-machine lot streaming problem is more difficult than its two- and threemachine counterparts. Even though structural properties have been identified for some versions of this problem, yet it is not uncommon to find heuristic approaches that have been proposed for its solution.

As alluded to earlier, the three-machine lot streaming problems form a stepping stone for the study of general m-machine lot streaming problems. For the case of continuous and consistent sublot sizes and makespan objective, the single lot, three-machine lot streaming problem can be modeled as a linear program for minimizing the completion time of t...

In this book, we have expounded on the concept of lot streaming in which a lot of the jobs is split into small-size sublots to enable their processing in an overlapping fashion over the machines of a production facility. This is a useful concept for implementation in a batch production environment since it can aid in reducing the makespan, work-in-...

The two-machine lot streaming problem has been investigated extensively and encompasses both the single-lot and multiple-lot scenarios. In the presence of a single lot and a given number of sublots in which to process this lot, the problem reduces to finding sublot sizes in order to optimize a criterion under consideration. For an ordinary flow sho...

In this paper, we present a new class of polynomial length formulations for the asymmetric traveling salesman problem (ATSP) by lifting an ordered path-based model using logical restrictions in concert with the Reformulation–Linearization Technique (RLT). We show that a relaxed version of this formulation is equivalent to a flow-based ATSP model, w...

In this paper, we address a product-disassembly optimization problem, which aims at minimizing the costs associated with the disassembly process (namely, the cost of breaking the joints and the sequence-dependent set-up cost associated with the disassembly operations), while maximizing the benefits resulting from the recovery of components and suba...

One of the main objectives of balancing a flowline is to achieve maximum throughput with minimum WIP. To that end, various methods have been proposed to control the loading of products (flow of material) on a flowline. However, the sequence in which the products are released is an issue that has rarely been addressed in conjunction with the materia...

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 o...

In this paper, we address the problem of loading non-intermixable products in a vehicle consisting of compartments of different sizes. The demands of the products are different but uniform over time. The objective is to meet product demands and minimize setup rate (that is, the number of deliveries per unit time). Two approaches, namely, dynamic an...

Production scheduling in semiconductor wafer fabs is a nontrivial task owing to the complexity of wafer fabrication. Dispatching rules are the most commonly used tools for shop floor control in this industry. Over the years, advanced dispatching rules capable of impacting multiple performance measures and utilizing both upstream and downstream info...

In this paper, we develop a new and effective schedule algebra based algorithm to determine the K-best solutions of a knapsack problem with a single constraint. Computational experience with this algorithm is also reported and it is shown to dominate both the dynamic programming and branch and bound based procedures when applied to this problem.

We propose a new formulation for the asymmetric traveling salesman problem, with and without precedence relationships, which employs a polynomial number of subtour elimination constraints that imply an exponential subset of certain relaxed Dantzig–Fulkerson–Johnson subtour constraints. Promising computational results are presented, particularly in...