We propose a simple friction model for isolated polymer chains on a solid substrate. The chains are pulled at constant velocity by one end, the other end can be trapped on the solid substrate on localised sites. We focus on the energy dissipation due to the traps. This simple model leads to non trivial friction laws, depending on the velocity and the distance between traps. Some refinements of ...

Large-eddy simulations (LES) of turbulent flow in a smoothwall pipe at Reynolds numbers based on the pipe Radius R and wall friction velocity in the range Reτ = 2,000−2,000,000 are discussed. Using a Reynolds number based on D and the bulkflow velocity, then corresponding values are ReD = 91,800 − 165,000,000. For the LES, the spectral-element code SEMTEX was used combined with the stretched-vo...

An analytical study was performed to study effects of thermo-diffusion and chemical reactions on a three-dimensional MHD mixed convective flow of dissipative fluid along an infinite vertical porous plate with transverse sinusoidal suction velocity. The parabolic partial differential equations governing the fluid flow, heat transfer, and mass transfer were solved using perturbation technique and...

We theoretically study the occurrence of magnetic friction of a nanometer-sized tip scanning a magnetic surface by studying the dynamics of a model of classical spins interacting through dipolar and exchange interactions, neglecting thermal effects. We find that for small scanning velocities, the friction force linearly scales with the velocity, with a slope proportional to the phenomenological...

Jointed exoskeletons permit rapid appendage-driven locomotion but retain the soft-bodied, shape-changing ability to explore confined environments. We challenged cockroaches with horizontal crevices smaller than a quarter of their standing body height. Cockroaches rapidly traversed crevices in 300-800 ms by compressing their body 40-60%. High-speed videography revealed crevice negotiation to be ...

Friction and wear are detrimental to engineered systems. Ultrasonic lubrication is achieved when the interface between two sliding surfaces is vibrated at a frequency above the acoustic range (20 kHz). As a solid-state technology, ultrasonic lubrication can be used where conventional lubricants are unfeasible or undesirable. Further, ultrasonic lubrication allows for electrical modulation of th...

The friction coefficient was measured for developed flow of drag-reducing polymer solutions in tubes of 2, 5, 10, 20 and 52 mm i.d. Our results were processed along with other authors' data in terms of different parameters in order to investigate the possibility of developing a simple empirical method for the prediction of the pipe diameter effect on friction. We found that the drag-reduction c...

We present a simple model for the friction of two solid bodies moving against each other. In a self consistent way we can obtain the dependence of the macro-scopic friction force as a function of the driving velocity, the normal force and the ruggedness of the surfaces in contact. Our results are discussed in the context of friction laws used in earthquake models.

  Micro scale gas flows has attracted significant research interest in the last two decades. In this research, the fluid flow of gases in the stepped micro-channel at a wide range of Knudsen number has been analyzed with using the Lattice Boltzmann (MRT) method. In the model, a modified second-order slip boundary condition and a Bosanquet-type effective viscosity are used to consider the veloci...

An analytical study of free convection flow near an impulsively started infinite vertical plate with Newtonian heating in the presence of thermal radiation and constant mass diffusion was performed. The mathematical model reduced to a system of coupled linear partial differential equations for the velocity, the temperature, and the concentration; the closed-form exact solutions were obtained by...