| Samriddhi Sankar Ray (ICTS Bangalore) |
WPI Seminar room, 8th floor Fak.Math. Univ. Wien |
Sat, 10. Oct 26, 10:55 |
| Dynamical slowdown, bottlenecks, and multiscaling in Voigt-regularised turbulence |
Dynamical slowdown, bottlenecks, and multiscaling in Voigt-regularised turbulence are studied using the Voigt-SABRA shell model and Navier-Stokes-Voigt simulations.
Voigt regularisation introduces a scale-dependent slowdown of nonlinear interactions without directly increasing dissipation.
Three spectral regimes are observed: a Kolmogorov inertial range, an intermediate equilibrium-like range, and a high-wavenumber equilibrium range.
The bottleneck develops due to the progressive weakening of the forward energy cascade at smaller scales.
The high-wavenumber crossover occurs at a scale proportional to alpha^(-1).
Increasing alpha delays cascade completion and enhances energy accumulation at intermediate and small scales.
The study finds reduced intermittency and increasingly Gaussian statistics with stronger Voigt regularisation.
Dynamic multiscaling in the turbulent regime changes to simple scaling in the equilibrium-like regimes.
Both shell-model and DNS results show bottleneck formation, delayed cascade, and reduced small-scale intermittency.
The findings suggest that bottlenecks are associated with scale-dependent dynamical slowdown and incipient thermalisation rather than purely dissipative effects. |
- Thematic program: Modeling Earth, Fluids, Plasmas and Space (2026/2027)
- Event: Uriel85Fest: Workshop "Around Burgers";
in honour of the 85th birthday of Uriel Frisch (2026)
|
| Rahul Pandit (Indian Inst. of Science) |
WPI Seminar room, 8th floor Fak.Math. Univ. Wien |
Fri, 9. Oct 26, 15:10 |
| Uncovering finite-time singularities in incompressible 3D magnetohydrodynamics |
We provide compelling numerical evidence for the development of (potential) finite-time singularities in the three-dimensional axisymmetric, ideal, incompressible magnetohydro- dynamic (IMHD) equations, in a wall-bounded cylindrical domain, starting from smooth initial data, for the velocity and magnetic fields. We demonstrate that the nature of the singularity depends crucially on the relative strength C of the velocity and magnetic fields at the time of initialization. If time permits, we will examine the implications of the OpenAI preprint on a 3D Navier-Stokes singularity for 3D MHD. |
- Thematic program: Modeling Earth, Fluids, Plasmas and Space (2026/2027)
- Event: Uriel85Fest: Workshop "Around Burgers";
in honour of the 85th birthday of Uriel Frisch (2026)
|
| Cornelius Rampf (Inst. Ruder Boskovic) |
WPI Seminar room, 8th floor Fak.Math. Univ. Wien |
Fri, 9. Oct 26, 14:00 |
| Cosmological fluid flow: from singularities to optimized numerical schemes |
On large cosmological scales, cold dark matter can accumulate efficiently in regions of gravitational collapse, giving rise to the highly nonlinear, filamentary network of cosmic large-scale structure. Traditionally, the dynamics of dark matter have been studied primarily through numerical simulations, while analytical approaches were often regarded as approximate tools for obtaining qualitative insights.
In this talk, I show how Uriel’s methods on singularities and their detection have helped transform our understanding of cosmic structure formation. In particular, I discuss how singularity analysis led to the first blow-up solutions in three dimensions and, ultimately, to improved numerical schemes for cosmological fluid dynamics. |
- Thematic program: Modeling Earth, Fluids, Plasmas and Space (2026/2027)
- Event: Uriel85Fest: Workshop "Around Burgers";
in honour of the 85th birthday of Uriel Frisch (2026)
|
| Oliver Hahn (U. Wien) |
WPI Seminar room, 8th floor Fak.Math. Univ. Wien |
Fri, 9. Oct 26, 11:50 |
| Reconstructing the Universe’s Devil’s Staircase |
Uriel Frisch made important contributions to large-scale structure cosmology, including Burgers dynamics in the adhesion model of cosmic structure, optimal-transport reconstruction of the early Universe, and the time-analyticity of Lagrangian trajectories. I will give a brief visual review of the first two, then discuss how aspects of all three connect to the most recent efforts in large-scale structure cosmology, as it confronts data of unprecedented quantity and quality.
|
- Thematic program: Modeling Earth, Fluids, Plasmas and Space (2026/2027)
- Event: Uriel85Fest: Workshop "Around Burgers";
in honour of the 85th birthday of Uriel Frisch (2026)
|
| Francois Golse (École Polytechnique) |
WPI Seminar room, 8th floor Fak.Math. Univ. Wien |
Fri, 9. Oct 26, 10:10 |
| A Nonlinear Regularization Mechanism for the Inviscid Burgers Equation |
It is well-known that the nonlinearity in the inviscid Burgers equation
is the reason for the onset of shock waves in finite time starting from
smooth, compactly supported initial data.
On the other hand, it is known since the work of Lax in 1954 that the
semigroup of entropies solutions to the inviscid Burgers equations is L^1
compact, which suggests that this equation also has some regularizing effect based on the nonlinearity and the entropy condition. The talk will discuss some ideas explaining this
mechanism.
|
- Thematic program: Modeling Earth, Fluids, Plasmas and Space (2026/2027)
- Event: Uriel85Fest: Workshop "Around Burgers";
in honour of the 85th birthday of Uriel Frisch (2026)
|