Chapter 8 Modeling Entity Movement

LEARNING OBJECTIVES

  • To be able to model constrained entity transfer with resources

  • To be able to model constrained entity transfer with movable resources

Section 7.2.3.1 of Chapter 7 introduced the concept entity movement by computing a movement time from a velocity and a known distance. The entities can be imagined as “having little feet” that allow them to move from one location to another. That is, the entity is able to move itself. For example, in the test and repair example of Section 7.1.3, the parts moved between stations with a time delay. But how did they physically move?

One way to think about this is that there were workers always available to move the parts between the stations. If there is always a worker available, then it is as if there is an infinite supply of workers. Thus, whenever a part must be moved from one location to another the part uses one of the workers to make the movement. Since there is an infinite supply of workers, this is the same as the part moving itself (i.e. having little feet) and only the time delay for moving between the locations is relevant. If the entity is a person (e.g. a patient in a clinic), this analogy makes sense; however, if the entity is a part in a manufacturing system, this analogy begins to lose its appeal.

In many situations, modeling transfers with a delay is perfectly reasonable, especially if you are not interested in how the entities moved (only that they moved). However, in many situations, the movement of entities can become constrained by the lack of availability of the transfer mechanism. For example, the movement of parts may require that the parts be placed on a pallet and that a fork lift be used to move the parts. At any point in time, there may not be enough fork lifts available and thus the parts may have to wait for a fork lift to become available. When the potential for waiting for transport is significant, including the details the “how” behind the entity transfer becomes important. In addition, since movement can be a significant part of an operation, the design of the material movement system may be the main focus of the simulation modeling effort.

This chapter explores the various KSL constructs available to facilitate the modeling of the physical movement of entities between locations. The chapter begins by describing how to model transfers using resources. In this case, the transfer delay is accompanied by the use of a resource. Then, Section 8.2 presents how the KSL facilitates resource constrained movement using resources that can move. Since not all movement is as freely moving through space as people walking or fork trucks moving, the KSL provides constructs for modeling entity movement when the space between the locations becomes an important aspect of the modeling.

NOTE! This chapter provides a series of example Kotlin code that illustrates the use of KSL constructs for implementing the modeling of entity movement. The full source code of the examples can be found in the accompanying KSLExamples project associated with the KSL repository. The files for each example of this chapter can be found here.