Smarter Systems Development: A systems engineering trade study to support green initiatives with model-driven development

Introduction
We know they’re an essential part of the systems engineering process. Trade studies help us fully explore the design space to ensure that a proposed solution best meets conflicting performance and cost requirements. But many of us don’t know that you can analytically and objectively conduct your trade studies well before you engineer anything. Using a model-driven approach with IBM Rational® Rhapsody® software, you can determine which solution will best capture stakeholder requirements while also justifying your engineering decisions.

This paper describes a multivariable decision problem based upon the selection of a power source for an environmentally conscious but cost-effective family-size vehicle for the European/United Kingdom (U.K.) marketplace. Stakeholders’ primary requirements for the vehicle are green credentials and low fuel costs, which are shown in U.K. pounds (£). Figure 1 captures the two primary requirements, as well as several others.

The process we’re going to follow is based on the workflow described in the third version of The Harmony Deskbook1 (a helpful guidebook to which this author also contributed). To evaluate the potential solutions, we’ll employ a technique known as the weighted objectives method,2 and we’ll automate the process using Rational Rhapsody software (as implemented by A. Lapping, a colleague to whom this author owes great thanks). Each stage of the process, apart from the task “merge solutions to form system architecture,” will be detailed in a worked example, and we’ll briefly discuss the implementation in Rational Rhapsody software. Our green vehicle example only focuses on one key system function, so the final stage in figure 2 will not be discussed.

It’s worth noting that, although the figures used in this example are sourced from published information, the final results should not be taken as definitive. Our intent is to provide an example of how to use the modeling method and the Rational Rhapsody tool; we’re not implying that electric vehicles will save the world in the very near future.

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