Type of Document	Master's Thesis
Author	Zhang, Lin
URN	etd-06242007-154228
Title	Large-Scale Simulations Using First and Second Order Adjoints with Applications in Data Assimilation
Degree	Master of Science
Department	Computer Science
Advisory Committee	Advisor Name Title Sandu, Adrian Committee Chair Borggaard, Jeffrey T. Committee Member Cao, Yang Committee Member Ribbens, Calvin J. Committee Member
Keywords	Sensitivity Analysis Second Order Adjoints 4D-Var Data Assimilation Optimization
Date of Defense	2007-06-09
Availability	unrestricted
Abstract In large-scale air quality simulations we are interested in the influence factors which cause changes of pollutants, and optimization methods which improve forecasts. The solutions to these problems can be achieved by incorporating adjoint models, which are efficient in computing the derivatives of a functional with respect to a large number of model parameters. In this research we employ first order adjoints in air quality simulations. Moreover, we explore theoretically the computation of second order adjoints for chemical transport models, and illustrate their feasibility in several aspects. We apply first order adjoints to sensitivity analysis and data assimilation. Through sensitivity analysis, we can discover the area that has the largest influence on changes of ozone concentrations at a receptor. For data assimilation with optimization methods which use first order adjoints, we assess their performance under different scenarios. The results indicate that the L-BFGS method is the most efficient. Compared with first order adjoints, second order adjoints have not been used to date in air quality simulation. To explore their utility, we show the construction of second order adjoints for chemical transport models and demonstrate several applications including sensitivity analysis, optimization, uncertainty quantification, and Hessian singular vectors. Since second order adjoints provide second order information in the form of Hessian-vector product instead of the entire Hessian matrix, it is possible to implement applications for large-scale models which require second order derivatives. Finally, we conclude that second order adjoints for chemical transport models are computationally feasible and effective.
Files	Filename       Size       Approximate Download Time (Hours:Minutes:Seconds)     28.8 Modem   56K Modem   ISDN (64 Kb)   ISDN (128 Kb)   Higher-speed Access    thesis.pdf 10.17 Mb 00:47:04 00:24:12 00:21:10 00:10:35 00:00:54

If you have questions or technical problems, please Contact DLA.