A Method Using Epoch-Era Analysis to Identify Valuable Changeability in System Design

Changeability is a means of creating value robustness in engineering systems that is currently less understood and correspondingly less utilized than more traditional passive robustness. This paper presents a new approach for investigating system changeability using Epoch-Era Analysis, with an emphasis on tradespace exploration using an illustrative case study. Epoch-Era Analysis is an approach for describing systems over time as existing in a series of static contexts (epochs) that change stochastically. A five-step method is used to generate an intuitive and accessible set of data and graphs describing the abstract concept of changeability, which is difficult to grasp due to its intrinsically time-dependent nature. Ideas for future changeability metrics are discussed. Motivation and Previous Research Changeability in Engineering. Changeability is an abstract design concept that is experiencing increased interest as engineering systems grow, both in cost commitment and system lifetime. The perceived potential performance advantages of changeable systems, the difficulty of designing a system fully robust to changes over decades, and the increased cost of failure are driving the increased level of interest in changeability and related “ilities”. However, imprecision in the usage of the word “changeability” and the other “ilities” has created a barrier that must be surmounted to properly understand the concept. The basic understanding is simple and universal: changeability is nothing more than the ability of a system to change. However, the meaning of that phrase is subject to a wide range of interpretations, largely based on the system application it is being used to describe. For example, a term with many similarities to changeability is flexibility; indeed, the words are used interchangeably quite often in the literature. Saleh et al. (2009) performed a survey of the use of the word “flexibility” in the literature for different fields, mainly managerial, manufacturing, and engineering design, while cataloguing the different meanings of the usage. Focusing here on the meaning for engineering systems, Saleh finds two distinct uses: one for flexibility in the design process and another for flexibility in the design itself. Even these subcategories of flexibility have been used differently, with design process flexibility being applied to both customers (flexibility in requirements 9th Conference on Systems Engineering Research Los Angeles, CA, April 2011 Pre-print