Date of Award

8-2016

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Industrial Engineering

Committee Member

Dr. William G. Ferrell, Jr., Committee Chair

Committee Member

Dr. Scott J. Mason

Committee Member

Dr. Kevin M. Taaffe

Committee Member

Dr. Amin Khademi

Abstract

This dissertation studies routing in storage facilities with stackable unit loads with time as the objective function. In the storage facilities, orders need to be stored as well as picked and material handling vehicles can carry more than one unit load at a time if the unit load containers are stackable on each other. In the first part of this research where the number of unit loads the vehicle can carry is limited to two and only one unit load can be stored at a location, a mathematical model was developed to find optimal paths for multi-command operations to route the unit load handling vehicle that minimizes total travel time of the vehicle and unit load handling time. Time savings from the proposed model can be over 25% compared to the single unit load handling single command heuristics. Three heuristics were also developed that give sub optimal solutions, yet can be used to get quicker solutions for larger problems. Exploring further, routing in unit load storage facilities when the number of unit loads a vehicle can carry is not limited to two and when more than one unit load can be stored at a location is studied. A mixed integer linear programming model is developed and four route construction heuristics are presented to construct routes that minimizes the total time. The heuristic that constructs routes based on operating time time and starting from the locations with longest operating time provides best routes. Routing methods in temporary storage facilities where unit loads can be shipped to alternate destinations and have limited storage capacity and operation time is studied. A construction heuristic is proposed to make internal routing, storing, and reshipping decisions.

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