Evgeny A. Novikov

Numerical simulation of the wake of a towed sphere in a weakly stratified fluid

We present some preliminary results from using large-eddy simulation to compute the late wake of a sphere towed at constant speed through a non-stratified and a uniformly stratified fluid. The wake is computed in each case for two values of the Reynolds number: Re = 10 4 , which is comparable to that used in laboratory experiments, and Re = 10 5 . An important aspect of the simulation is the use of an iterative procedure to relax the initial turbulence field so that the normal and shear turbulent stresses are properly correlated and the turbulent production and dissipation are in equilibrium. For the lower Reynolds number our results compare well with existing laboratory experimental results. For the higher Reynolds number we find that even though the turbulence is more developed and the wake contains finer structure, most of the similarity properties of the wake are unchanged compared with those observed at the lower Reynolds number

On Markov modelling of turbulence

We consider Lagrangian stochastic modelling of the relative motion of two fluid particles in the inertial range of a turbulent flow. Eulerian analysis of such modelling corresponds to an equation for the Eulerian probability distribution of velocity-vector increments which introduces a hierarchy of constraints for making the model consistent with results from the theory of locally isotropic turbulence. A nonlinear Markov process is presented, which is able to satisfy exactly, in the statistical sense, incompressibility, the exact results on the third-order structure function, and the experimental second-order statistics. The corresponding equation for the Eulerian probability density of velocity-vector increments is solved numerically. Numerical results show non-Gaussian statistics of the one-dimensional Lagrangian probability distributions, and a complex shape of the three-dimensional Eulerian probability density function. The latter is then compared with existing experimental data.

Chaotic capture of vortices by a moving body. I. The single point vortex case.

The study of the dynamical properties of vortex systems is an important and topical research area, and is becoming of ever increasing usefulness to a variety of physical applications. In this paper, we present a study of a model of a rotational singularity which obeys a logarithmic potential interacting with a bluff body in a uniform inviscid laminar flow, e.g., a line vortex interacting with a cylinder in three dimensions or a point vortex with a circular boundary in two dimensions. We show that this system is Hamiltonian and simple enough to be solved analytically for the stagnation points and separatrices of the flow, and a bifurcation diagram for the relevant parameters and classification of the various types of motion is given. We also show that, by introducing a periodic perturbation to the body, chaotic motion of the vortex can be readily generated, and we present analytic criteria for the generation of chaos using the Poincare-Melnikov-Arnold method. This leads to an important dynamical effect for the model, i.e., that the possibility exists for the vortex to be chaotically captured around the body for periods of time which are extremely sensitive to initial conditions. The basic mechanism for this capture is due to the chaotic dynamics and is similar to that of other chaotic scattering phenomena. We show numerically that cases exist where the vortex can be captured around an elliptic point external to (and possibly far from) the body, and the existence of other very complicated motions are also demonstrated. Finally, generalizations of the problem of the vortex-body interaction are indicated, and some possible applications are postulated such as the interaction of line vortices with aircraft wings.

Ultralight Gravitons with Tiny Electric Dipole Moment Are Seeping from the Vacuum

Mass and electric dipole moment (EDM) of graviton, which is identified as dark matter particle (DMP), are estimated. This change the concept of dark matter and can help to explain the baryon asymmetry of the universe. The calculations are based on quantum modification of the general relativity (Qmoger) with two additional terms in the Einstein equations, which takes into account production/absorption of gravitons. In this theory, there are no Big Bang in the beginning (some local bangs during the evolution of the universe are probable), no critical density of the universe, no dark energy (no need in cosmological constant) and no inflation. The theory (without fitting) is in good quantitative agreement with cosmic data.

CONDITIONALLY AVERAGED DYNAMICS OF TURBULENCE

The conditionally averaged Navier-Stokes equations with fixed vorticity in a point are considered. It is found in particular that the conditionally averaged rates of vortex stretching and dissipation increase exponentially with the vorticity magnitude. The local imbalance of these effects leads to the formation and destruction of twisted vortex strings.

Similarity regime in the brain activity

The spectral analysis of multi-channel magnetoencephalographic data from a group of adults is performed. This analysis revealed a local similarity regime in brain activity, which is analogous to similarity regimes in other systems with strong interaction of many degrees of freedom (turbulence etc., see E. A. Novikov, Phys. Rev. E 50, R3303 (1994) and reference therein).

Velocity circulations in free-surface flows

Abstract The equations of balance between horizontal and vertical accelerations on a free surface are derived from the Euler equations for vertical flows with arbitrary distribution of density. From these equations it follows that the velocity circulations on a free surface are invariants of motion. Application of these invariants to the problem of persistence of ship wakes over long distances is discussed. The effects of surface tension and molecular viscosity on velocity circulations are also considered.