WSC 2007 WSC 2007 Final Program

WSC 2007 Final Abstracts

Case Studies Track

Monday 10:30:00 AM 12:00:00 PM
Operations and Inventory

Chair: Christos Alexopoulos (Georgia Institute of Technology)

Arena in the Petrochemical Operations Environment
Lorraine Malherbe (Sasol Technology)

The use of discrete event simulation within Sasol, an international petrochemical company, is fast becoming an important tool for supporting strategic decision-making in the continuous operations environment. Arena models are used specifically to investigate the feasibility of new undertakings for current expansions at the Sasol Secunda site. These include the use of new gasifier technologies, the possible expansion of existing gasification capacity, and the increase of the current natural gas intake. The value of the models lies in the fact that it is possible to assess the interactions between the integrated plants dynamically, taking into account the impact of reliability, scheduled maintenance and availability of utilities on throughput. This presentation examines the use of Arena to identify capacity constraints such as to reach future production targets by optimizing the intake of natural gas in relation to the gasification process and focusing on the optimal use of current and future oxygen capacity.

Limitations in the Use of Mathematical Models to Support Investment Decisions
Mario Jorge Lima and Guilherme de Aquino Barbosa (Petrobras)

Decision making is a complex job, especially when it involves millions of dollars. Experience, intuition and other personal features are essential, but the support of a mathematical tool can help avoiding errors. This paper presents a summary of the experience acquired by the Petrobras refinery simulation team in using mathematical models to support investment decisions in tank farm problems. Real situations will be presented where limitations and risks came up along with recommendations to avoid similar problems in the future.

A Comparison of Inventory Optimization and Discrete-Event Simulation for Supply Chain Analysis
Erin Murphy (3M Company)

This 3M Company supply chain case study compares inventory optimization and discrete-event simulation methodologies, and presents an iterative approach between an optimization model and a discrete-event simulation model. We know that modeling provides value-added decision support for complex inventory management problems. The inventory optimization model assists in making the best decision in the tradeoff between cost and customer service, in specific system states. On the other hand, the discrete-event simulation model quantifies the impact, over time, of inventory management policies, thus illustrating feasibility and ranges of system performance. Is one approach "better" than the other? Could coupling the two models improve the solution? Each method has its own limitations and its own contribution to decision making, which are highlighted in this case study.

Monday 1:30:00 PM 3:00:00 PM
Check-in and Check-out Simulations

Chair: Erin Murphy (3M Company)

Security Checkpoint Optimizer Simulation Tool for Passenger Screening Prototyping
Diane Wilson and Robert Pryor (Transportation Security Administration) and S. Annie So and Eric K. Roe (Northrop Grumman Corp.)

Northrop Grumman in support of Transportation Security Administration (TSA), part of the U.S. Department of Homeland Security (DHS), began development of the Security Checkpoint Optimizer (SCO) discrete-event simulation software in 2001. Since then, a number of security screening simulation models have been developed in support of DHS Science and Technology Branch and TSA. In 2007, Northrop Grumman was tasked by the TSA Office of Security Technologies to develop a prototype system demonstrating connectivity of screening equipment with an enterprise screening control and monitoring system. To support the prototype, SCO was enhanced with network capabilities to enable device emulation. The SCO simulation software was able to act as a "stand in" for screening devices, which are not currently network-capable. The initial prototype showed the feasibility of such an interconnected system, and will serve as a basis for future testing. The study also produced valuable insights to facilitate actual implementation.

Checkout - Kroger's Store Front Simulator
John Osborne (The Kroger Co.) and Matthew Duffin (Visual8 Corp.)

The Kroger Co. is the largest grocery retailer in the United States, with store formats that include grocery and multi-department stores, convenience stores, fuel centers, pharmacies, floral, and jewelry stores. Kroger and Visual8 Corp. have created the Store Front simulator which is used in the design and analysis of store checkout configurations. This tool models regular, express and self-service checkout lanes, with staffing levels to handle different customer profiles and varying queuing behaviors by time of day. The simulator, which provides a drag-and-drop layout capability, can help determine cost-effective store front layouts and staffing plans to satisfy target customer service levels. This presentation will demonstrate how the Store Front simulator is being used to streamline staffing and re-design checkout operations in order to satisfy Krogerís mandate to provide superior customer service levels within its industry.

Passenger Simulation Modeling to Identify Optimum Customs Staffing Levels
Gareth Coville, Vandana Patidar, Debayan Sen, Brian Nadreau, and Evert Meyer (Jacobs Consultancy)

Currently over 130 international flights arrive at a major international airport in the USA on an average day. Every passenger on each of these flights needs to pass through Customs Border and Patrol (CBP) before entering the United States. These flight arrival times vary significantly on a daily basis, annual passenger levels are steadily increasing and, since September 11, 2001, there has been an increase in security measures. All of these factors have placed an increased workload on the CBP staff. There is mounting pressure on the Airport CBP management to minimize the passenger wait times, while simultaneously meeting annual staffing budgets. Jacobs Consultancy (JC) was asked to identify optimum CBP staffing levels and determine strategies for CBP to better accommodate their variable staffing needs based on the variability of flight arrival times. JC used CAST, a passenger simulation model developed by the Airport Research Center (ARC), to assist in the evaluation.

Monday 3:30:00 PM 5:00:00 PM
Successful Simulation Strategies

Chair: Gareth Coville (Jacobs Consultancy)

Using Data Mining Tools To Build Integrated Discrete-Event Simulations
David Ames Holland and Scott C. R. Henry (Computer Sciences Corporation)

Building a simulation from disparate software requires analysis to establish commonality of code. The ability of a data mining tool to extract repeating functional structures and data flows is the first essential step to reduce exploration, save development time, and re-use simulation software components. Such a tool must not only drill down to the atomic data but also roll-up to "10,000 feet" to reveal the relationships and hierarchies that allow event based simulations to interact. Computer Sciences Corporation (CSC) is developing a system for analysis of discrete event data structures defined by a set of nodes and links between those nodes. The Model Integration Application (MIA) is an integrated suite of tools that perform data mining to generate a representation in IDEF0 format, which then provides a description of the basic simulation activities and Input/Output interfaces. MIA allows for connection of the simulations along established rules and protocols in accordance with the IDEF0 standard.

Tips and Tricks for Using Simulation DOE to Assess the Complex Interactions of Your Process
Marietsa Louise McCreary (3M Company)

When studying a complex process, a Design of Experiments (DOE) using Discrete-event Simulation, is a powerful tool to determine key factors and results. A DOE is a road map for data generation and analysis that is methodical, efficient, and meaningful. This presentation highlights two manufacturing simulation case studies with emphasis on the process for creating and assessing the DOEs. DOE evolution is discussed, as well as the difference between a DOE and a DOE model. Tips and tricks for setup, visualization, and graphing are also highlighted.

Stochastic Modelling as a Decision Making Tool in an Integrated Green-Brown Fields Growth Program at the Sasol Secunda Site, South Africa
Anette Van der Merwe (Sasol)

Sasol, the world leader in coal to fuels, is embarking on a major growth program integrating new and existing technologies into its current facilities. This program will increase production capacity, improve energy efficiency, and enable compliance to expected future environmental and fuel specifications. The program will affect the entire production site and is of a very complex nature. This presentation discusses examples where the impact on the integrated refinery and propylene value chain operations are tested by means of a discrete-event simulation model to determine infrastructure and capacity constraints. Interactions between units and across value chains are taken into consideration. The presentation further discusses the use of the decision making tool for determining advantages and concerns of possible technologies for debottlenecking options for the current operating units.

Tuesday 8:30:00 AM 10:00:00 AM
Modeling Innovations and Applications I

Chair: Anette Van der Merwe (Sasol Technology)

Applying Variable Rate Processing to Queueing Simulation Models at
Paul D. Babin ( and Allen Greenwood (Mississippi State University)

In simple queueing models, the average processing rate is assumed to be constant - regardless of the number of entities in the queue. In many real systems, the effective processing rate often increases as the queue builds (by working faster or adding resources) and decreases as the queue empties (by working slower or shedding resources). Whether planned as part of the production control management, or unplanned as human nature, the effect is often causing the corresponding queueing systems to be more stable than predicted by simple queueing models. Discrete Event Simulation models can easily handle this complexity. This case study demonstrates the basics of variable rate processing, and illustrates its effective use in capacity simulation models at

A Simulation Case Study of Patient Flow at The University of South Alabama Medical Center
Donna Retzlaff-Roberts (University of South Alabama) and Sharon Ezelle (USA Medical Center)

The University of South Alabama Medical Center is a trauma hospital that serves Mobile, Alabama. Delays in the patient discharge process were preventing patient rooms from becoming available for new arrivals. The discharge decision is typically made early in the morning by the attending physician. However, delays from numerous sources would frequently result in the patient's departure not occurring until late in the day, or even being delayed until the following day. A simulation study was undertaken to identify ways to reduce the duration of the patient discharge process, thereby increasing the availability of rooms for new patients.

How Dynamic Disease Modeling Supports Strategic Marketing at Pharmaceutical & Biotech Companies
Radhesh B Nair (PA Consulting Group)

Dynamic disease models integrate disparate information sources, such as epidemiology, treatment dynamics and market behavior, to create a virtual test bed that can be used to identify leverage points and market prospects for to-be-launched drugs. These models are effective in exploring a wide scenario space that influence key strategic marketing decisions. We present a methodology for disease modeling that has been used to support strategic marketing decision making for several acute and chronic conditions.

Tuesday 10:30:00 AM 12:00:00 PM
Modeling Innovations and Applications II

Chair: Radhesh Nair (PA Consulting Group)

A Financial Simulation of an International Business Graduate School
John Stocker (FLAG International, LLC) and Conrado Gempesaw and Kliment Nachkov (University of Delaware)

Given the substantial cost involved in establishing an international business graduate school, the objective of this study is to evaluate the financial viability of starting an MBA program in a foreign location. In 2004, the University of Delaware in partnership with Flag International, LLC was awarded a contract to offer an MBA program in Bosnia and Herzegovina (BiH). Based on the experience gained in implementing this USAID project, this study develops a financial simulation model that can be used to evaluate the sustainability of foreign-based MBA programs. While the deterministic model indicates that the model may be a viable venture with minimal start-up costs, the results of the stochastic simulation indicate that significant risk does exist with the potential for negative returns if the venture is not managed properly.

Manufacturing and Distribution Integrated Solution at Votorantim Cimentos
Alain d'Audenhove (Belge Engenharia) and Rodrigo Cintra Villas Boas (Votorantim Cimentos)

After being consecrated as an important technology for decision making concerning strategic issues, simulation is increasingly applied towards tactical and operational issues. This paper shows an interesting and innovative use of simulation at Votorantim Cimentos, where logistics planning must consider distribution and manufacturing integration and constraints in order to make weekly decisions to achieve better results.

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