Abstract:
Design changes are an inevitable part of any product development process. In
complex engineered products, changes can cause a cascading effect on other
components, commonly known as the “knock-on effect of change”. Managing
changes, therefore, has become an important part of design projects. Such
changes can propagate through many facets of design and by many different
mechanisms. Of particular interest in this dissertation, margins in design
play an important role in determining whether a change propagates or gets
absorbed.
A literature review identifies the underlying concepts of change propagation
through a metamodel. The review reveals a lack of study on the mechanisms
of change propagation, which greatly dictates how the changes propagate or
whether they get absorbed. Based on the insights gained from the literature
review, empirical experiments were conducted using student participants.
Data from the experiments was collected and analysed using a modelling
approach based on a conceptual framework. The analysis of data gave rise
to a list of five change propagation mechanisms. The study concluded that
margins in a design are one of the most influential factors which determine
the nature of propagation when a change is triggered.
This dissertation introduces a method called the Margin Value Method to
analyse an engineering design, localise the excess margin, and quantify it
considering change absorption potential in relation to design performance
deterioration. Margin in design may be desirable to mitigate risk and absorb future
changes, but at the same time, may be undesirable if the over-specification
deteriorates the design’s performance. The Margin Value Method provides
guidance for improving a design by prioritising excess margin that provides
relatively little advantage at high cost, and could therefore be eliminated to
improve design performance. Two case studies using the method are presented.