Collapse of generalized Euler and surface quasigeostrophic point vortices
- Link:
- Autor/in:
- Erscheinungsjahr:
- 2018
- Medientyp:
- Text
- Schlagworte:
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- Astrophysics
- Computational fluid dynamics
- Hamiltonians
- Finite time singularity
- Fractional Laplacian
- Geometrical interpretation
- Point vortex models
- Quasi-geostrophic point vortices
- Self-similarities
- Surface quasi-geostrophic equations
- Vortex circulation
- Vortex flow
- Beschreibung:
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- Point-vortex models are presented for the generalized Euler equations, which are characterized by a fractional Laplacian relation between the active scalar and the stream function. Special focus is given to the case of the surface quasigeostrophic (SQG) equations, for which the existence of finite-time singularities is still a matter of debate. Point-vortex trajectories are expressed using Nambu dynamics. The formulation is based on a noncanonical bracket and allows for a geometrical interpretation of trajectories as intersections of level sets of the Hamiltonian and Casimir. Within this setting, we focus on the collapse of solutions for the three-point-vortex model. In particular, we show that for SQG the collapse can be either self-similar or non-self-similar. Self-similarity occurs only when the Hamiltonian is zero, while non-self-similarity appears for nonzero values of the same. For both cases, collapse is allowed for any choice of circulations within a permitted interval. These results differ strikingly from the classical point-vortex model, where collapse is self-similar for any value of the Hamiltonian, but the vortex circulations must satisfy a strict relationship. Results may also shed a light on the formation of singularities in the SQG partial differential equations, where the singularity is thought to be reached only in a self-similar way. © 2018 American Physical Society. NZ.
- Point-vortex models are presented for the generalized Euler equations, which are characterized by a fractional Laplacian relation between the active scalar and the stream function. Special focus is given to the case of the surface quasigeostrophic (SQG) equations, for which the existence of finite-time singularities is still a matter of debate. Point-vortex trajectories are expressed using Nambu dynamics. The formulation is based on a noncanonical bracket and allows for a geometrical interpretation of trajectories as intersections of level sets of the Hamiltonian and Casimir. Within this setting, we focus on the collapse of solutions for the three-point-vortex model. In particular, we show that for SQG the collapse can be either self-similar or non-self-similar. Self-similarity occurs only when the Hamiltonian is zero, while non-self-similarity appears for nonzero values of the same. For both cases, collapse is allowed for any choice of circulations within a permitted interval. These results differ strikingly from the classical point-vortex model, where collapse is self-similar for any value of the Hamiltonian, but the vortex circulations must satisfy a strict relationship. Results may also shed a light on the formation of singularities in the SQG partial differential equations, where the singularity is thought to be reached only in a self-similar way. © 2018 American Physical Society. NZ.
- Lizenz:
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- info:eu-repo/semantics/restrictedAccess
- Quellsystem:
- Forschungsinformationssystem der UHH
Interne Metadaten
- Quelldatensatz
- oai:www.edit.fis.uni-hamburg.de:publications/513dc72d-cac2-4759-b61e-1fcf6370fc1b