Currently, Dr. Jae-Gon Kim and Prof. Marc Goetschalckx are studying an integrated layout design methodology for physical layout design of manufacturing and service systems.  The three main issues in the facility layout problem are determining shapes and locations of departments within the floor (a block layout), locations of input and output (I/O) points, and flow paths.  Although these three issues are closely related with each other, usually they are considered as isolated problems for computationally tractable formulations.  This motivated us to develop an integrated layout design methodology to consider them concurrently.  The considered problem in this study is summarized as follows.

Objective
To determine a block layout, locations of I/O points and flow paths simultaneously minimizing the total transportation distance based on the contour distance metric.

Assumptions
· Dimension of the floor where departments are placed is given.
· Departments have rectangular shapes but different sizes.
· Each department has one input point and one output point.
· Materials are moved along boundaries of the departments, which are considered as candidates for flow path segments.
· Capacity of a flow path segment is finite and predetermined.  (Here, the capacity of a flow path segment is defined as a maximum amount of material flows that go through the path segment in a unit time period.)
· Spaces for material flow paths are not considered since areas of departments are usually inflated to take into account the need for flow paths.
· Cost of constructing material flow paths is not considered.

Constraints
· All departments should be placed within a given floor.
· Area of each department in a layout should be greater than or equal to its given value.
· Aspect ratio of each department should be within a its given range.
· Departments should not overlap with each other.
· I/O points should be placed on the boundaries of the departments.

In this study, we use the sequence-pair to represent relative positions of departments in a block layout, which was originally used for the physical design of VLSI layout.  A linear programming model is presented to generate a block layout from a sequence-pair and the obtained block layout is transformed to a graph using a suggested graph generation method.  To determine locations of I/O points and flow paths, heuristic methods are developed, respectively.  All these methods are embedded into a simulated annealing algorithm to obtain the best layout design.

Although the above methodology is suggested for the (general) facility layout problem, it may be applied to the warehouse layout design after proper modifications since the warehouse layout problem is a special case of the facility problem.  The warehouse layout problem has special characteristics in that a warehouse has a typical pattern of layout structure due to the storage system and the layout decision is highly interrelated with the warehouse operation processes and policies such as order picking process/policy and storage process/policy.  These characteristics should be considered when generating a layout design.  We can consider shipping area, receiving areas, storage area, forward picking area (if exist), sorting/consolidation area (if exist) as departments of a warehouse and generate a block layout with locations of docks, aisles and I/O points where pickers perform various administrative and start-up tasks such as collecting a pick device, obtaining a picking list etc.  Usually, the storage area consists of multiple pallet racks and crossing aisles and has the largest area among the departments.  Therefore, a layout within the storage area itself is also very important.  However, the storage area layout has been generated separately with the warehouse block layout to avoid complexities of the layout problem.  Using the suggested layout methodology, we could try to generate warehouse block layout and storage layout simultaneously by splitting up the storage area in smaller departments such as pallet racks and crossing aisle.

Contact:  marc.goetschalckx@isye.gatech.edu