arXiv subjects

Alexandre J. Chorin

Publications and source records attributed to Alexandre J. Chorin.

21 records · Page 2Linked to original sources

arXiv2001

Non-Markovian Optimal Prediction

Optimal prediction methods compensate for a lack of resolution in the numerical solution of complex problems through the use of prior statistical information. We know from previous work that in the presence of strong underresolution a good approximation needs a non-Markovian "memory", determined by an equation for the "orthogonal", i.e., unresolved, dynamics. We present a simple approximation of the orthogonal dynamics, which involves an ansatz and a Monte-Carlo evaluation of autocorrelations. The analysis provides a new understanding of the fluctuation-dissipation formulas of statistical physics. An example is given.

math.NA↗

arXiv2000

Stochastic Optimal Prediction with Application to Averaged Euler Equations

Optimal prediction (OP) methods compensate for a lack of resolution in the numerical solution of complex problems through the use of an invariant measure as a prior measure in the Bayesian sense. In first-order OP, unresolved information is approximated by its conditional expectation with respect to the invariant measure. In higher-order OP, unresolved information is approximated by a stochastic estimator, leading to a system of random or stochastic differential equations. We explain the ideas through a simple example, and then apply them to the solution of Averaged Euler equations in two space dimensions.

math.NA↗

arXiv1999

Self-Similar Intermediate Structures in Turbulent Boundary Layers At Large Reynolds Numbers

Processing the data from a large variety of zero-pressure-gradient boundary layer flows shows that the Reynolds-number-dependent scaling law, which the present authors obtained earlier for pipes, gives an accurate description of the velocity distribution in a self-similar intermediate region of distances from the wall adjacent to the viscous sublayer. The appropriate length scale that enters the definition of the boundary layer Reynolds number is found for all the flows under investigation. Another intermediate self-similar region between the free stream and the first intermediate region is found under conditions of weak free stream turbulence. The effects of turbulence in the free stream and of wall roughness are assessed, and conclusions are drawn.

math.NA↗