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Title: Reduced order model updating
Author: Griffiths, Laurence
ISNI:       0000 0004 5923 8072
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2014
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Across all engineering disciplines, the differences found between experimental results and computational simulations gives rise to various degrees of uncertainty in the solutions. In fluid dynamics these differences can be broadly split into issues of boundary conditions and numerical accuracy. Within the computational fluid dynamics (CFD) community a great deal of effort has been invested in reducing numerical error, yet large discrepancies with experimental data persist. The nature of experimental and computational studies often dictates the application of different boundary conditions applied in each. Furthermore, for aerospace applications often both experimental and computational methods are attempting to model a free flying aircraft but doing so by applying fundamentally different conditions. Model updating provides the opportunity to modify the behaviour of the system to reduce these discrepancies. Initially this research concentrates on the update of reduced order models (ROMS). These models are a major area of research in CFD and promise the accuracy of CFD with much reduced computational cost. A novel framework is developed by which the steady state gradients of an unsteady eigenvalue based ROM may be updated. The new updating process is applied to remove tunnel wall interferences for Euler and RANS (Spalart-Allmaras) ROMS and to add the effects of viscosity to an inviscid Euler based ROM. Multistage updates are also demonstrated whereby a ROM is updated for both viscous and wind tunnel wall interference. A novel method is developed whereby the pulse input sizing for the production of ROMS from the nonlinear Euler and RANS equations equations may be automated. The method is proved accurate for a range of test cases. Finally a parameter study, investigating the suitability of a viscous-inviscid interactive model for updating, is performed. The study demonstrated that the equations in their original form are not sufficiently robust for an automated model updating process.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available