SUBJECT: Ph.D. Dissertation Defense
BY: Roxanne Moore
TIME: Monday, April 30, 2012, 1:00 p.m.
PLACE: MRDC Building, 4211
TITLE: Value-Based Global Optimization
COMMITTEE: Dr. Chris Paredis, Chair (ME)
Dr. Bert Bras (ME)
Dr. Michael Leamy (ME)
Dr. Jeff Wu (ISYE)
Dr. David Romero (ME, University of Toronto)


Computational models and simulations are essential system design tools that allow for improved decision making and cost reductions during the design process. However, the most accurate models are often computationally expensive and can therefore only be used sporadically. Consequently, designers are often forced to choose between exploring many design alternatives with less accurate, inexpensive models and evaluating fewer alternatives with the most accurate models. To achieve both broad exploration of the alternatives and accurate determination of the best alternative with reasonable costs incurred, surrogate modeling and variable accuracy modeling are used widely. A surrogate model is a mathematically tractable approximation of a more expensive model based on a limited sampling of that model, while variable accuracy modeling involves a collection of different models of the same system with different accuracies and computational costs. Designers can determine the best solutions more efficiently using surrogate and variable accuracy models because poor solutions can be eliminated inexpensively by using only less accurate models. The most accurate models are then reserved for discerning the best solution from the set of good solutions. In this thesis, a Value-Based Global Optimization (VGO) algorithm is introduced. The algorithm uses kriging-like surrogate models and a sequential sampling strategy based on Value of Information (VoI) to optimize an objective characterized by multiple analysis models with different accuracies. It builds on two primary research contributions. The first is a novel surrogate modeling method that accommodates data from any number of analysis models with different accuracies and costs. The second contribution is the use of Value of Information (VoI) as a new metric for guiding the sequential sampling process for global optimization. In this manner, the cost of further analysis is explicitly taken into account during the optimization process.