Rateand state-dependent friction laws for velocity-step and healing are analysed from a thermodynamic point of view. Assuming a logarithmic deviation from steady-state, a unification of the classical Dieterich and Ruina models of rock friction is proposed.

The unsteady two-dimensional laminar g-Jitter mixed convective boundary layer flow of Cu-water and Al2O3-water nanofluids past a permeable stretching sheet in a Darcian porous is studied by using an implicit finite difference numerical method with quasi-linearization technique. It is assumed that the plate is subjected to velocity and thermal slip boundary conditions. We have considered tempera...

Experimental investigation of the sliding-velocity dependence of friction in rock is necessary to understand slip instability and earthquake phenomena, but a capability to conduct sliding friction experiments at high normal loads and at earthquake slip rates (1 m/s) must be developed. Velocitydependent friction is ideally studied by imposing step-wise changes in rate of sliding. Velocity steps ...

We present molecular dynamics friction calculations for confined hydrocarbon "polymer" solids with molecular lengths from 20 to 1400 carbon atoms. Two cases are considered: (a) polymer sliding against a hard substrate and (b) polymer sliding on polymer. We discuss the velocity dependence of the frictional shear stress for both cases. In our simulations, the polymer films are very thin (approxim...

Accelerating displacements preceding some catastrophic landslides have been found empirically to follow a time-to-failure power law, corresponding to a finite-time singularity of the velocity v ∼ 1/(tc − t) [Voight, 1988]. Here, we provide a physical basis for this phenomenological law based on a slider-block model using a state and velocity dependent friction law established in the laboratory ...

An exact analysis of heat and mass transfer past an oscillating vertical plate with Newtonian heating is presented. Equations are modelled and solved for velocity, temperature, and concentration using Laplace transforms. The obtained solutions satisfy governing equations and conditions. Expressions of skin friction, Nusselt number, and Sherwood number are obtained and presented in tabular forms...

The velocity and humidity dependence of nanoscopic sliding friction has been studied on CrN and diamondlike carbon surfaces with an atomic force microscope. The surface wettability is found to be decisive. Partially hydrophilic surfaces show a logarithmic decrease of friction with increasing velocity, the slope of which varies drastically with humidity, whereas on partially hydrophobic surfaces...

Flat plate skin friction calculations over a range of Mach numbers from 0.4 to 3.5 at Reynolds numbers from 16 million to 492 million using a Navier Stokes method with advanced turbulence modeling are compared with incompressible skin friction coefficient correlations. The semi-empirical correlation theories of van Driest; Cope; Winkler and Cha; and Sommer and Short T’ are used to transform the...

A dynamic model is presented for omnidirectional wheeled mobile robots, including wheel/motion surface slip. We derive the dynamics model, experimentally measure friction coefficients, and measure the force to cause slip (to validate our friction model). Dynamic simulation examples are presented to demonstrate omnidirectional motion with slip. After developing an improved friction model, compar...