Structural complexity management in sustainable engineering

Sustainable product development comprises several aspects. Beside environmental, material, and production issues, market success and design processes have to be taken into account.Methods for sustainable engineering have to address all these aspects simultaneously. Structural complexity management as a method allows for the modeling of different system aspects and their relations. Thus, it is particularly suited for sustainable engineering by providing a means of relating various concurrent perspectives onto a system. This chapter introduces the basic concepts and discusses their application. The use case illustrating the application deals with the development of a high-pressure pump. Every system, for example, a technical product composed of parts, or a project consisting of process steps, people, and documents, is characterized by dependencies among the system's parts. In practice, this collection of dependencies makes systems difficult to handle and extremely complex. Dependencies of a system form structures, such as a sequential chain of dependencies, a loop, or a hierarchical tree. Such system structures show characteristic behaviors in practical applications. System elements, interlocked by dependencies in the structure of a loop, for example, may demonstrate selfenergizing or self-impeding behavior. Thus, if system structures are identified, it is possible to predict system behavior. A key characteristic of structural complexitymanagement is the consideration of multiple aspects of dependencies. Geometric and functional dependencies between technical components, for example, can be processed jointly in order to describe the system's behavior. This possibility is addressed as the "multipledomain" approach and contrasts common "Design for X" perspectives in product design, where the X stands for a large variety of optimization targets that do not necessarily coexist simultaneously. However, focusing only on one specific objective, for example, cost or assembly, cannot provide comprehensive and sustainable system improvements. One-sided optimization of a system bears the risk of spreading single adaptations to a multitude of system elements. As system dependencies link different aspects of system behavior, they can, in fact, help to achieve the objectives of improved design by considering their combined occurrence. When considering system structures, only the existence of dependencies has to be known and not their quantified specification. This allows applying structural complexity management in the early phases of product design, where detailed system specifications are often not available. Yet, decisions in early phases possess far-reaching consequences which can be beneficial or detrimental. The approach to structural complexity management as shown here is able to deal with qualitative models and thus differs substantially from simulation approaches for complexity management. Simulation also applies system dependencies but tries to result in exact predictions of system behavior. However, the underlying computations in simulation approaches require detailed quantification of elements and dependencies. A use case illustrates the application of these concepts. It deals with the development of high-pressure pumps. The aim was to optimize existing product structures of various current pump concepts. The use case shows how multiple product views, for example, geometry, function, and production, were modeled. The different views were combined to derive proposals for modules and carryover parts.