Title page for ETD etd-32998-103459

Type of Document Dissertation
Author Seward, Lori Welte
Author's Email Address lseward@cadswes.colorado.edu
URN etd-32998-103459
Title Preventive Maintenance for a Multi-task System
Degree PhD
Department Industrial and Systems Engineering
Advisory Committee
Advisor Name Title
Nachlas, Joel A. Committee Chair
Ioannou, George Committee Member
Kobza, John E. Committee Member
Rakes, Terry R. Committee Member
Schmidt, J. William Committee Member
  • Preventive Maintenance
  • Availability
  • Renewal Theory
Date of Defense 1998-04-02
Availability unrestricted
This research models the behavior of a multi-task system with respect to

time. The type of multi-task system considered here is one in which not all

system components are required to perform each task. Each component may,

however, be used for more than one task. Also, it is possible that some of the

components may be required for every task that the system performs.

The components that are required for a subset of the tasks are considered

to be intermittently demanded components and those components required for

every task are continuously demanded components. This modeling approach

assumes that the system is subject to a Modified Age Replacement Policy

(MARP.) With a MARP the intermittently demanded components are maintained

during their idle periods and the continuously demanded components are replaced

according to their age replacement times.

A renewal theory approach is used to develop an availability expression

for the multi-task sytem. Past research has focused on systems consisting of

continuously demanded components and typically does not distinguish between

elapsed clock time and elapsed operating time in the renewal density function

expressions. This research recognizes that the operational age of an intermittently

demanded component is different than the chronological age of the component. The renewal density function and availability measures are modeled using joint

density functions defined on both clock time and operating time.

The expressions are evaluated numerically using a multidimensional

numerical integration routine. The results show logical behavior of the joint

density functions used to define the availability measure. The availability

measure also displays behavior consistent with the definition of a multi-task

system. This model is an important development in the need for stochastic

models of highly complex systems. The model is also a first step in defining

performance measures for systems composed of both intermittently demanded

components and continuously demanded components.

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