scholarly journals Identifying finite-time coherent sets from limited quantities of Lagrangian data

2015 ◽  
Vol 25 (8) ◽  
pp. 087408 ◽  
Author(s):  
Matthew O. Williams ◽  
Irina I. Rypina ◽  
Clarence W. Rowley
Keyword(s):  
Finite Time ◽  
Lagrangian Data

scholarly journals Lagrangian Reduced Order Modeling Using Finite Time Lyapunov Exponents

Fluids ◽  
2020 ◽  
Vol 5 (4) ◽  
pp. 189
Author(s):  
Xuping Xie ◽  
Peter J. Nolan ◽  
Shane D. Ross  ◽  
Changhong Mou  ◽  
Traian Iliescu
Keyword(s):  
Finite Time ◽  
Standard Procedure ◽  
Inner Product ◽  
Reduced Order ◽  
Finite Time Lyapunov Exponents ◽  
Inner Products ◽  
Finite Time Lyapunov Exponent ◽  
Lagrangian Data ◽  
Complex Nonlinear Systems ◽  
Low Dimensional

There are two main strategies for improving the projection-based reduced order model (ROM) accuracy—(i) improving the ROM, that is, adding new terms to the standard ROM; and (ii) improving the ROM basis, that is, constructing ROM bases that yield more accurate ROMs. In this paper, we use the latter. We propose two new Lagrangian inner products that we use together with Eulerian and Lagrangian data to construct two new Lagrangian ROMs, which we denote α-ROM and λ-ROM. We show that both Lagrangian ROMs are more accurate than the standard Eulerian ROMs, that is, ROMs that use standard Eulerian inner product and data to construct the ROM basis. Specifically, for the quasi-geostrophic equations, we show that the new Lagrangian ROMs are more accurate than the standard Eulerian ROMs in approximating not only Lagrangian fields (e.g., the finite time Lyapunov exponent (FTLE)), but also Eulerian fields (e.g., the streamfunction). In particular, the α-ROM can be orders of magnitude more accurate than the standard Eulerian ROMs. We emphasize that the new Lagrangian ROMs do not employ any closure modeling to model the effect of discarded modes (which is standard procedure for low-dimensional ROMs of complex nonlinear systems). Thus, the dramatic increase in the new Lagrangian ROMs’ accuracy is entirely due to the novel Lagrangian inner products used to build the Lagrangian ROM basis.

Filtering methods for finite-time normal modes and atmospheric error growth

2000 ◽  
Vol 42 ◽  
pp. 1482
Author(s):  
Mozheng Wei ◽  
Jorgen S. Frederiksen ◽  
Steve Kepert
Keyword(s):  
Finite Time ◽  
Normal Modes ◽  
Error Growth
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