For analytic work in support of capital investment decisions the ultimate measure of success is not always clear. Plants and distribution systems that perform as expected in terms of throughput and uptime do validate the results of technical components of the simulation. Making such comparisons in detail is, however, costly and time consuming. In addition, changes in market and business conditions tend to have a very large impact on the economic value of infrastructure and the uncertainty around those is extremely high.
Many capital investment decisions are addressed using detailed discrete event simulations. Continuously formulated Vensim models can be used to address the same issues and offer some improved transparency. We developed a model to look at reliability and maintainability of a Liquid Natural Gas (LNG) plant using different assumptions on sizing and configuration. While this model was not that much different conceptually from its discrete event counterparts, Vensim does have some advantages for presentation and analysis and we believe this is a worthwhile approach to developing models in support of investment decisions. More information on this is available in a paper presented at the 2002 System Dynamics Conference, and the model is also available.