2,027 research outputs found
A stochastic Lagrangian representation of the 3-dimensional incompressible Navier-Stokes equations
In this paper we derive a representation of the deterministic 3-dimensional
Navier-Stokes equations based on stochastic Lagrangian paths. The particle
trajectories obey SDEs driven by a uniform Wiener process; the inviscid Weber
formula for the Euler equations of ideal fluids is used to recover the velocity
field. This method admits a self-contained proof of local existence for the
nonlinear stochastic system, and can be extended to formulate stochastic
representations of related hydrodynamic-type equations, including viscous
Burgers equations and LANS-alpha models.Comment: v4: Minor corrections to bibliography, and final version that will
apear in CPAM. v3: Minor corrections to the algebra in the last section. v2:
Minor changes to introduction and refferences. 14 pages, 0 figure
Universal Nonlinear Filtering Using Feynman Path Integrals II: The Continuous-Continuous Model with Additive Noise
In this paper, the Feynman path integral formulation of the
continuous-continuous filtering problem, a fundamental problem of applied
science, is investigated for the case when the noise in the signal and
measurement model is additive. It is shown that it leads to an independent and
self-contained analysis and solution of the problem. A consequence of this
analysis is Feynman path integral formula for the conditional probability
density that manifests the underlying physics of the problem. A corollary of
the path integral formula is the Yau algorithm that has been shown to be
superior to all other known algorithms. The Feynman path integral formulation
is shown to lead to practical and implementable algorithms. In particular, the
solution of the Yau PDE is reduced to one of function computation and
integration.Comment: Interdisciplinary, 41 pages, 5 figures, JHEP3 class; added more
discussion and reference
Computing aspects of problems in non-linear prediction and filtering
Imperial Users onl
Gaining Insights into Denoising by Inpainting
The filling-in effect of diffusion processes is a powerful tool for various
image analysis tasks such as inpainting-based compression and dense optic flow
computation. For noisy data, an interesting side effect occurs: The
interpolated data have higher confidence, since they average information from
many noisy sources. This observation forms the basis of our denoising by
inpainting (DbI) framework. It averages multiple inpainting results from
different noisy subsets. Our goal is to obtain fundamental insights into key
properties of DbI and its connections to existing methods. Like in
inpainting-based image compression, we choose homogeneous diffusion as a very
simple inpainting operator that performs well for highly optimized data. We
propose several strategies to choose the location of the selected pixels.
Moreover, to improve the global approximation quality further, we also allow to
change the function values of the noisy pixels. In contrast to traditional
denoising methods that adapt the operator to the data, our approach adapts the
data to the operator. Experimentally we show that replacing homogeneous
diffusion inpainting by biharmonic inpainting does not improve the
reconstruction quality. This again emphasizes the importance of data adaptivity
over operator adaptivity. On the foundational side, we establish deterministic
and probabilistic theories with convergence estimates. In the non-adaptive 1-D
case, we derive equivalence results between DbI on shifted regular grids and
classical homogeneous diffusion filtering via an explicit relation between the
density and the diffusion time
Review of CFD for wind-turbine wake aerodynamics
This article reviews the state of the art of the numerical calculation of wind-turbine wake aerodynamics. Different CFD techniques for modeling the rotor and the wake are discussed. Regarding rotor modeling, recent advances in the generalized actuator approach and the direct model are discussed, as far as it attributes to the wake description. For the wake, the focus is on the different turbulence models that are employed to study wake effects on downstream turbines
Review of computational fluid dynamics for wind turbine wake aerodynamics
This article reviews the state-of-the-art numerical calculation of wind turbine wake aerodynamics. Different computational
fluid dynamics techniques for modeling the rotor and the wake are discussed. Regarding rotor modeling, recent advances
in the generalized actuator approach and the direct model are discussed, as far as it attributes to the wake description. For
the wake, the focus is on the different turbulence models that are employed to study wake effects on downstream turbines
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