Filter by type:

Sort by year:

1- Non-traditional warehouse layout optimization and their effects on order picking operations

Working Paper
S.G. Ozden, A. E. Smith, and K. R. Gue
IIE Transactions

Non-traditional layouts decrease the average travel distance for unit-load operations compared to traditional warehouse (i.e, straight rows with pick aisles and perpendicular cross aisles that reduce the travel distance between pick locations). Gue and Meller (2009) propose the fishbone layout that decreases average travel distance up to 20%. Ozturkoglu et. al. (2012) relax the assumption of Gue and Meller (2009) so that the pick aisles can take any angle, and achieve up to 22% improvement over traditional layout. Moreover, they prove that these designs are optimal for unit-load operations. However, the optimal warehouse designs for order picking operations are unknown. Here we describe an approach that optimizes layouts with up to 4% improvement over traditional layouts. For small pick list sizes, because of the higher importance of depot location in travel cost, near optimal layouts are creating a vertical cross aisles. As the pick list size increases these cross aisles become horizontal allowing better access between storage locations. We anticipate our approach to be a starting point for more detailed research for warehouse layout optimization. For example, analytical models can be created for the near-optimal layouts we present. Furthermore, layout optimization is a major target for retail industry, and a well-defined encoding and routing approach will be relevant for such optimizations.

2- Calculating the Length of an Order Picking Path

Working Paper
S.G. Ozden, A. E. Smith, and K. R. Gue
European Journal of Operational Research

We introduce the visibility graph as a new way of estimating the length of a route traveled by order pickers in a warehouse. Following aisle centers leads to longer travel distances when an order picker picks items within picking aisles which have angles other than 90 degrees between cross aisles. Details of the visibility graph implementation are given in the context of warehouse design. We present and compare results for traditional and fishbone layouts. Our results show that the visibility graph method changes the assessment of fishbone layout compared to traditional counterpart. Moreover, it also changes the rank order of three most common traditional layouts.

3- Environmental improvement of operating supply chains: A heuristic optimization approach for the cement industry

Conference Paper
S. G. Ozden, M. C. Velez-Gallego
IISE Annual Conference 2017, Pittsburgh, PA

The   problem   of   improving   the   environmental performance of a supply chain without entailing excessive cost is becoming a frequent problem as
companies face an increasing pressure from governments and customers for reducing the environmental impact of their activities. As the environmental improvement of an operating supply chain implies not only technology upgrading decisions, but also decisions regarding the structure of the supply chain itself; deciding on what strategy to follow is a complex task. The aim of this work is to provide a bi- objective solution approach for finding such strategy so that both the environmental and financial goals are best met.

4- Solving large batches of traveling salesman problems with parallel and distributed computing

Journal Paper
S.G. Ozden, A. E. Smith, and K. R. Gue
Computers & Operations Research, Volume 85, Issue C, Pages 87-96, 2017

In this paper, we describe and compare serial, parallel, and distributed solver implementations for large batches of Traveling Salesman Problems using the Lin-Kernighan Heuristic (LKH) and the Concorde exact TSP Solver. Parallel and distributed solver implementations are useful when many medium to large size TSP instances must be solved simultaneously. These implementations are found to be straightforward and highly efficient compared to serial implementations. Our results indicate that parallel computing using hyper-threading for solving 150- and 200-city TSPs can increase the overall utilization of computer resources up to 25 percent compared to single thread computing. The resulting speed-up/physical core ratios are as much as ten times better than a parallel and concurrent version of the LKH heuristic using SPC3 in the literature.  We illustrate our approach with an application in the design of order picking warehouses.

5- WEBASRS – A Web-Based Tool for Modeling and Design of Abstract Unit-Load Picking Systems

Conference Paper
Jeffrey S. Smith and Sabahattin Gokhan Ozden
11th International Material Handling Research Colloquium

This paper describes a web-based tool that supports the modeling and design of abstract unit-load picking systems.  The term “abstract” implies that the model is not specific to any equipment or vendors’ products, but, instead, focuses on the generic system components such as pallets, racks, slots, forklifts, cranes, etc. that comprise typical unit load picking systems.  The objectives of the tool are to support the design of an AS/RS based or a manual forklift-based picking system based on a set of design parameters and to be able to convert from an AS/RS design to a flat warehouse design and vice versa.  The research objective is to design the formal model (the data structure and operational description) that supports the conversion from one type to the other and supports the generation of static and dynamic analysis models and the recording of the analysis results.  The web implementation uses a mix of XML, HTML, JavaScript and PHP and implements two existing analysis methodologies from the literature.