VARIABLE DYNAMIC MODE DECOMPOSITION FOR ESTIMATING TIME EIGENVALUES IN NUCLEAR SYSTEMS

Abstract: An extension to the Dynamic Mode Decomposition method for calculating time eigenvalues
(also known as \(\alpha\)eigenvalues) that removes the requirement of a constant time step is derived
and demonstrated. The new method, called variable-dynamic mode decomposition (V-DMD), is
shown to be accurate when computing eigenvalues for systems that were infeasible with DMD
due to a large separation in time scales. The alpha eigenvalues of an infinite medium neutron
transport problem with delayed neutrons and consequently having multiple, very different relevant
time scales are computed. Furthermore, V-DMD is shown to be of similar accuracy to the
original DMD approach when computing eigenvalues in other systems where DMD can be used.