Browsing by Author "White, J.A."

Now showing 1 - 2 of 2

Designing Unit-Load Warehouses: Use Deterministic or Probabilistic Models
(Institute of Industrial and Systems Engineers, IISE, 2021) Tutam, M.; Liu, J.; White, J.A.; Liao, H.
Designing a warehouse can be quite challenging because of the variability and uncertainty of operations performed. Although deterministic models can be developed and solved easily, they do not capture the random variation inherent in travel distances. In determining the optimal shape of a unit-load warehouse, will the designs be different if the shape is determined to minimize the average travel distance versus minimize the expected number of requests for storage and retrieval (S/R) waiting or being served? To answer this question, we compared the optimal shape factor and resulting expected travel distance for a multi-dock, unit-load warehouse under a new dwell-point policy. Compared to previous research, the performance of the system is increased approximately nine percent by using a specific dwell-point policy for S/R equipment. The impact of minimizing the variance of travel time on the optimal warehouse shape was also examined. Although queueing model provide additional information, the optimal shape factor for unit-load warehouse based on deterministic analysis is not significantly different from the optimal shape factor based on probabilistic analysis. © 2021 IISE Annual Conference and Expo 2021. All rights reserved.
Performance Analysis of a Class-Based Robotic Compact Storage and Retrieval System
(Institute of Industrial and Systems Engineers, IISE, 2023) Tutam, M.; Liu, J.; White, J.A.
Warehouses are often characterized by low cube utilization, which becomes an issue with land scarcity and increasing land prices. Robotic Compact Storage and Retrieval Systems (RCS/RS) have been developed to increase space utilization. They do not require traditional picking- and cross-aisles. In such a system, a grid-based storage space contains bins stacked on each other. Moreover, robots operate on the roof of the system to lift or lower bins in stacks while transporting them between storage locations and ports. The question is what the dimensions of an RCS/RS should be because operation times for the system differ based on the speed of robots, as well as the x-, y- and z-dimensions and the number of bins. To minimize the expected operation time of a robot to complete storage/retrieval operations, we embed a discrete formulation of the generalized assignment problem in an enumeration over the z-direction to determine the optimum allocation of bins to locations in a three-dimensional class-based storage space and the best dimensions of an RCS/RS with the proposed algorithm in a reasonable time frame. We consider three classes of bins based on different skewness values for activity levels. Our optimization model can be used to design a new RCS/RS or analyze an existing RCS/RS based on its current system parameters. © IISE and Expo 2023.All rights reserved.