We study the deformations of elastic filaments confined within slowly-shrinking circular boundaries, under contact forces with friction. perform computations a spring-lattice model that deforms like thin inextensible filament uniform bending stiffness. Early in deformation, two lobes make contact. If friction coefficient is small enough, one lobe slides inside other; otherwise, move together or...

We present a new method to measure hydrodynamic friction forces on colloidal particles at very low (ci 10~~) Reynolds numbers with high accuracy. Exploiting magnetic field induced aggregation of microcopic paramagnetic spheres into straight chains of calibrated length, we determine the anisotropic friction coefficient of the chains, with a range from one to 100 particles, by video-microscopic o...

Viscoelastic liquids with very small amounts of polymer/surfactant additives can, as well known since B.A. Toms’ observation in 1948, provide substantial reductions in frictional drag of wall-bounded turbulence relative to the corresponding Newtonian fluid flow. Friction reductions of up to 80% compared to the pure water flow can be occasionally achieved with smooth channel/pipe flow of viscoel...

We derive an effective boundary condition for dense granular flow taking into account the effect of the heterogeneity of the force network on sliding friction dynamics. This yields an intermediate boundary condition which lies in the limit between no slip and Coulomb friction; two simple functions relating wall stress, velocity, and velocity variance are found from numerical simulations. Moreov...

This paper reviews turbulent boundary-layer control strategies for skin-friction reduction of aerodynamic bodies. The focus is placed on the drag-reduction mechanisms by two flow control techniques-spanwise oscillation and spanwise travelling wave, which were demonstrated to give up to 45 per cent skin-friction reductions. We show that these techniques can be implemented by dielectric-barrier d...

The shear rate dependence of the slip length in thin polymer films confined between atomically flat surfaces is investigated by molecular dynamics simulations. The polymer melt is described by the bead-spring model of linear flexible chains. We found that at low shear rates the velocity profiles acquire a pronounced curvature near the wall and the absolute value of the negative slip length is a...

It is known that the distribution of active earth pressure against a translating rigid wall is not triangular but nonlinear, owing to arching effects in the backfill. In the present paper, a new formulation is proposed for calculating the active earth pressure on a rigid retaining wall undergoing horizontal translation. It takes into account the arching effects that occur in the backfill (or re...

We describe a simple method for estimating wall friction which uses the fit of velocity data to the boundary layer profile in wall units all the way from the wall to the end of the log region. Two different models for the boundary layer profile are examined, the power-series interpolation scheme of Spalding and the Musker profile which is based on the eddy viscosity concept. The accuracy of the...

Algebraic explicit wall models covering the entire inner region of turbulent boundary layer are proposed to reduce computational effort for large eddy simulation wall-bounded flows. The formulas given in closed forms with either logarithmic- or power-function-based laws wall, allowing straightforward evaluation friction velocity on near grids independent their locations layer. performance is de...

Existing data for soft magnetic materials of critical current for domain-wall motion, wall speed driven by a magnetic field, and wall electrical resistance, show that all three observable properties are related through a single parameter: the wall mobility μ. The reciprocal of μ represents the strength of viscous friction between domain wall and conduction-electron gas. And μ is a function of t...