Browsing by Author "White, John A."

Now showing 1 - 4 of 4

Citation - WoS: 1
Citation - Scopus: 2
Comparison of Expected Distances in Traditional and Non-Traditional Layouts
(World Scientific Publ Co Pte Ltd, 2024) Tutam, Mahmut; White, John A.
The performance of a unit-load warehouse depends on numerous parameters such as storage area, layout, aisle configuration, width-to-depth ratio, the number and locations of dock doors, storage policy, etc. These parameters typically relate to the layout configuration, which can be either traditional (rectangle-shaped) or non-traditional (contour-line-shaped). In this paper, we analyze the performance of rectangle-shaped and contour-line-shaped storage areas within a unit-load warehouse having multiple dock doors. Expected distances traveled in rectangle-shaped storage areas are compared with expected distances in their counterpart contour-line-based storage areas when an ABC class-based storage policy is used to assign unit-loads. For a single product class, the expected-distance for a rectangle-shaped storage area is at most 6.07% greater than it is for the corresponding contour-line-shaped storage area. Depending on the skewness of the ABC curve or storage areas for multiple classes, the expected distance for rectangle-shaped storage areas can be no more than 0.59% greater than it is for the corresponding contour-line shaped storage areas when multiple dock doors are distributed with a specified distance between them.
Citation - WoS: 8
Citation - Scopus: 10
Consideration of Skewness in Designing Robotic Compact Storage and Retrieval Systems
(Pergamon-Elsevier Science Ltd, 2024) Tutam, Mahmut; Liu, Jingming; White, John A.
A relatively new goods-to-person order picking system (robotic compact storage and retrieval system, RCS/RS) has been implemented within order fulfillment centers. In such a system, robots move in x- and y-dimensions on top of a grid-based storage area to retrieve bins from stacks by "digging" in z-dimension. To transport a requested bin to a port, robots (or a robot) remove(s) all blocking bins above the requested bin and place(s) them around neighboring stacks. Defining the throughput of an RCS/RS as the number of bins processed per unit time, we analyze the time required for bins to be removed from stacks, transported to ports, returned to stacks, and placed in stacks. In making a case for considering skewness among activity levels for bins, we develop closed-form expressions to calculate the expected operation time for the movement of bins, validate the closed-form expressions using simulation, and obtain the system configuration that maximizes throughput performance (or minimizes operation time for bins) based on current practice. Then, with an objective of having an optimal RCS/ RS design based on activity levels of bins, we show the significant impact on throughput when different skewness values for activity levels of the bins are incorporated into the design.
Citation - WoS: 7
Citation - Scopus: 8
Multi-Dock Unit-Load Warehouse Designs with a Cross-Aisle
(Pergamon-Elsevier Science Ltd, 2019) Tutam, Mahmut; White, John A.
This study develops discrete formulations of expected distance traveled in a unit-load warehouse with a middle-cross-aisle. Defining optimal shape factor as the width-to-depth ratio of a rectangle-shaped warehouse minimizing expected distance traveled, our results reveal the number of dock doors and the number of storage/retrieval locations significantly affect the optimal shape factor regardless of the orientation of storage/retrieval locations. Providing computational results based on realistic parameter values, configurations are compared based on the number of storage/retrieval locations. Based on the results, recommendations are provided regarding conditions in which each layout configuration minimizes expected distance traveled.
Citation - WoS: 11
Citation - Scopus: 12
A Multi-Dock, Unit-Load Warehouse Design
(Taylor & Francis Inc, 2019) Tutam, Mahmut; White, John A.
Expected distance formulations are developed for a rectangle-shaped, unit-load warehouse having dock doors along one warehouse wall. Based on dock-door configurations treated in the literature and/or used in practice, three scenarios are considered: (i) equally spaced dock doors spanning a wall; (ii) equally spaced dock doors with a specified distance between adjacent dock doors, and an equal number of dock doors located on each side of the wall's centerline; and (iii) equally spaced dock doors with a specified distance between adjacent dock doors and the first dock door located a given distance to the right of the left wall. Defining the shape factor as the warehouse width divided by its depth, the shape factor minimizing expected distance is determined. Single- and dual-command travel results from discrete formulations are compared with results from closed-form expressions using continuous approximations. The optimal shape factor depends on the number and locations of dock doors. When the distance between adjacent dock doors is a function of the warehouse's width, previous research results are confirmed. However, when distances between adjacent dock doors are specified, our results differ from a commonly held belief the optimal shape factor is always less than or equal to 2.0.