The cascade to complexity:modeling the evolution of first-of-a-kind systems in problem-solving design processes

First-of-a-kind engineered systems often burst with complexitya major cause of project budget and time overruns.Our particular concern is the structural complexity of nuclear fusion devices, which is determined by the amount and entanglement of components.We seek to understand how this complexity rises during the development phase and how to manage it.This paper formulates a theory around the interplay between a problem-solving design process and an evolving design model.The design process introduces new elements that solve problems but also increase the quantifiable complexity of the model.Those elements may lead to new problems, extending the design process.We capture these causal effects in a hierarchy of problems and introduce two metrics of the impact of design decisions on complexity.By combining and incorporating the Function-Behavior-Structure (FBS) paradigm, we create a new problem-solving method.This method frames formulation, synthesis and analysis activities as transitions from problems to solutions.We demonstrate our method for a nuclear fusion measurement system.Exploring different design trajectories leads to alternative design models with varying degrees of complexity.Furthermore, we visualize the time-evolution of complexity during the design process.Analysis of individual design decisions emphasizes the high impact of early design decisions on the final system complexity.