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Dr. François Hemez, Lawrence Livermore National Laboratory
High-consequence decision-making is increasingly being supported by numerical simulations. Examples include predicting the trajectories of hurricanes; anticipating the consequences of terrorist threats; and managing complex, inter-dependent infrastructure in urban environments. Attempting to forecast the future or predict conditions that cannot be observed experimentally raises into question the veracity of numerical models and the quantification of prediction uncertainty. We provide a high-level overview of the three classes of uncertainty (randomness, numerical uncertainty, assumption-making) in modeling and simulation. Due to their different natures, quantifying these uncertainties and aggregating them are daunting tasks (still today!). Communicating to decision-makers what the uncertainty represents is another serious roadblock. We contend that these challenges can be addressed by focusing on answering “what if” questions for scenarios that the decision-makers care about and establishing confidence in these answers. Confidence comes from assessing the extent to which our predictions, and the decisions they support, are not adversely affected by our information gaps (what we do not know or cannot control). The discussion is illustrated with examples that range from simple engineering design to training emergency personnel to respond to large-scale incidents in urban environments.
Speaker biosketch
François Hemez is a scientist at Lawrence Livermore National Laboratory (LLNL) where he contributes to assessments of the U.S. nuclear deterrent and supports non-proliferation efforts of the Intelligence Community. Before joining LLNL, he spent twenty-one years at Los Alamos National Laboratory with responsibilities in various programs for computational engineering and physics, and was adjunct professor at the University of California San Diego (Structural Engineering Department). François graduated from Ecole Centrale Paris, France in 1989 and earned a doctoral degree in aerospace engineering from the University of Colorado Boulder in 1993. François is recognized for his expertise in model verification and validation, uncertainty quantification and decision-making. Since 2001, he has authored 430+ technical reports, peer-reviewed manuscripts and book chapters; given 162 invited lectures, including 9 international keynotes; and taught short-courses to 938 graduate students and practicing engineers around the world.
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