Effect of anomalously low friction in block media

We study mechanical conditions under which the effect of anomalously low friction in block media from various geomaterials, which was revealed by the authors, is realized. It is shown that the maximum transverse (horizontal) displacements of the blocks occur only in the case of canonical coordination of the delay intervals between the vertical and horizontal pulse effects on the block system and the working block, respectively. In the case of static horizontal actions on the working blocks, significant displacements of the latter occur at absolute values of these actions, which are much smaller than the corresponding friction forces. Mining Institute, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 40, No. 6, pp. 133–138, November–December, 1999.     

Dynamic behavior of piles embedded in transversely isotropic layered media

Dynamic behavior of single pile embedded in transversely isotropic layered media is investigated using the finite element method combined with dynamic stiffness matrices of the soil derived from Green's function for ring loads. The influence of soil anisotropy on the dynamic behavior of piles is examined through a series of parametric studies     

Dynamic analysis of discontinuous plant disease models with a non-smooth separation line

Nonlinear Dynamics - Based on the aim to minimize losses and maximize returns, we present a discontinuous plant disease model incorporating a threshold policy control. This control is represented...     

Squeeze flow of Bingham fluids under slip with friction boundary condition

This paper develops a theoretical analysis of a Bingham fluid in slipping squeeze flow. The flow field decomposition consists in combining a central extensional flow zone in the plane of symmetry and shear flow zones near the plates. It is also considered that the slipping zone is located around a central sticking zone as previously shown from experiments. It is assumed that the shear stress at the plates is constant in the slipping zone and equals a fixed friction yield value. The squeeze force required to compress a Bingham fluid under the slipping behaviour as well as the radial evolution of the transition point between both sticking and slipping zones are finally determined.     

动滑动摩擦因数的测试与应用

导出动滑动摩擦因数的计算公式,用自制的动态智能测试仪,可测试各种物料之间的动滑动摩擦因数. 以不同的衬衫面料与不同的西装夹里之间的动滑动摩擦因数的测试为例,介绍其测试原理、测试仪器和测试方法.     

Interaction and separation in internal flows with low skin friction

High-Reynolds-number plane steady flow of a viscous incompressible fluid past small distortions on straight-line walls intersecting at a point source is considered. The flow regimes are investigated in detail for a near-critical diffuser opening half-angle, when the skin friction is small. Solutions with local separation zones are obtained. The dependence of the skin friction on the Reynolds number is determined for transition to streams with a large region of reversed flow.Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 5, pp. 98–111, September–October, 1996.     

Multicomponent models of friction

The problem of motion of a homogeneous ball on a horizontal plane is considered. It is assumed that the contact patch is of spherical shape, whereas the pressure center does not coincide with the center of the contact patch and is displaced in the sliding direction of the ball. The friction force has two components that are parallel and perpendicular to the sliding velocity; the friction force moment has a vertical component and two horizontal components being parallel and perpendicular to the sliding velocity.     

On models of dynamic systems with dry friction

An approach to the design of models of dynamical systems with high dry friction in the kinematic pair is developed. The members of the kinematic pair are represented by parts of rigid bodies. The system as a whole is considered to have a variable structure. According to this assumption, two modes of motion with different dissipative characteristics are possible. The states in which the modes exchange and the motion switches over into critical modes with dynamic self-locking are established. A system with a variable transfer function between members that form a nonideal constraint is described __________ Translated from Prikladnaya Mekhanika, Vol. 43, No. 5, pp. 97–105, May 2007.     

Interface models coupling adhesion and friction

Interface models coupling friction and adhesion, where adhesion is regarded as interface damage, are briefly reviewed. The most widely used cohesive zone models are presented and discussed. A general framework for these laws, recently developed by Del Piero and Raous in the form of a unified model, is outlined. As an example, it is here established that the RCCM (Raous–Cangémi–Cocou–Monerie) model is a specific case in this general framework. The variational formulation and some associated solvers are briefly recalled in the context of non-smooth mechanics in the cases of both quasi-static and dynamic problems. A few examples in various fields of application are given. Lastly, some open problems and ongoing researches in this field are presented and discussed.     

Bi-linear reduced-order models of structures with friction intermittent contacts

The dynamic analysis of structures with localized nonlinearities, such as intermittent contacts of cracked structures, is a computationally demanding task because of the large size of the models involved. Thus, high-resolution finite element models are often reduced using a variety of specialized techniques which exploit spatial coherences in the dynamics. In addition, when a steady-state forced response analysis is performed, direct time integration can be replaced with multi-harmonic balance methods. Recently, a technique based on bi-linear normal modes has been successfully applied to piecewise-linear oscillators. The key idea of that approach is to represent the spatial coherences in the system dynamics with two sets of normal modes with special boundary conditions, referred to as bi-linear modes. In this paper, the bi-linear modal representation is extended to the case of intermittent contacts with friction. Furthermore, a novel reduced order modeling method is developed for the 0th order harmonic used in multi-harmonic balance methods. The forced response of a cracked structure is used to demonstrate the proposed methods.     

Temperature separation and friction losses in vortex tube

The process of energy separation and friction losses in a vortex tube is studied in detail. The hot and cold exit air temperatures were measured. Experiments have been conducted at inlet pressure of 3.5, 5, 7.5 and 9 bar, at inlet temperature of 292.15 and 298.15 K and at cold air mass ratio from 0 to1. The results demonstrate that the hot air temperature reaches its maximum value at a cold air mass ratio of nearly 0.82, while the minimum value of cold air temperature is found at a cold air mass ratio of 0.3. Based on energy and mass balances as well as on the definition of internal energy and on experimental results a new model for the determination of hot and cold exit gas temperature has been developed. The model includes the relevant primary parameters and predicts the experimental results as well as the data published in the literature sufficiently accurate for engineering purposes.A cross-section area m³ - D diameter of the pipe m - F model parameter - f friction factor - L length of the tube m - m mass flow rate kg/s - y cold air mass ratio - P static pressure Pa - T temperature K - t thickness of the orifice m - R gas constant J/kg K - v velocity of fluid m/s - density of the fluid kg/m³ - friction factor for pipe - friction factor for orifice and tee junction - 1 inlet of compressed gas - 2 exit of hot gas - 3 exit of cold gas - atm atmospheric pressure - c cold exit gas - f friction - h hot exit gas - o orifice plate - T tee junction     

Plane waves in porous or cracked media with internal friction

Asymmetry of compression and shear in porous media is considered. Since the shear causes infinite stresses across the contacts, the models of partial creep in shear are used to exclude the infinite stresses. The inelastic behavior in the shear nonlinear equations of motion corresponding to the Korteweg–de Vries (KdV) equations in one-dimension lead to purely imaginary nonlinear term. This causes absorption and dispersion of P and especially S waves.     

Penetration of rigid bodies into loose and layered media

Penetration and motion of rigid bodies in ground media attracts the researchers’ attention because of various problems arising as the technology evolves. In fact, there are two independent directions of studies in this field: (1) the problem of earth excavation when a rigid body of a definite shape slowly moves along a given trajectory in the ground; (2) an impact of a rapidly flying free rigid or deformable body against the ground. In the latter case, to which the proposed studies pertain, it is sometimes of interest to study the medium behavior and the motion of the free body, which moves in the medium after the impact owing to the kinetic energy of itself. In this field, a majority of studies deal with collision and penetration of bodies of various shapes into clay media. An extensive survey of these studies is given in [1]. After this survey appeared, numerous paper dealing with complicated collision conditions have been published [2]. Penetration in loose media has been studied much more rarely. The direct collision with fractured rock was studied in connection with the expected landing of spacecraft on other planets [3, 4]. In this case, the influence of grain dimensions and the density of the filling and vacuum on the penetration was studied for the initial velocities in the range of 1.7–10 m/s. On the other hand, in [5], the results of investigating the penetration of conic bodies in sand at entry velocities of 700–900 m/s are given; these velocities significantly exceed the speed of sound in this medium, which lies in the range of 100–200 m/s for dry sand. Analyzing the experimental results, the author came to the conclusion that it is necessary to use different representations of the drag force in the supersonic and subsonic modes. In the present paper, we do not consider the influence of the grain distribution, sand density, and filling methods on the penetration. But, as follows from the experiments whose results are described in [6] and [7], to represent the results of penetration of rigid bodies at velocities up to several hundreds of meters per second, in addition to the characteristics listed above, it is also required to describe the technology of the experiment preparation, because such media have the property of shape “memory.”     

Active slip-band separation and the energetics of slip in single crystals

This research supports recent efforts to provide an energetic approach to the prediction of stress–strain relations for single crystals undergoing single slip and to give precise formulations of experimentally observed connections between hardening of single crystals and separation of active slip-bands. Non–classical, structured deformations in the form of two-level shears permit the formulation of new measures of the active slip-band separation and of the number of lattice cells traversed during slip. A formula is obtained for the Helmholtz free energy per unit volume as a function of the shear without slip, the shear due to slip, and the relative separation of active slip-bands in a single crystal. This formula is the basis for a model, under preparation by the authors, of hardening of single crystals in single slip that is consistent with the Portevin-Le Chatelier effect and the existence of a critical resolved shear stress.     

Statistical theory of radiative transfer in layered media

An equation for the probability density of the wave intensity which takes into account absorption, is obtained with a help of the invariant imbedding method. The limiting case when the medium occupies a half-space, is considered. The field intensity is found for the case of a source inside the medium. The conditions of applicability of the linear theory or radiative transfer are obtained. Numerical solutions of the equations corresponding to the statistical theory of radiative transfer in a layered medium with random inhomogeneities are discussed.     

Two-dimensional transient dynamic response of orthotropic layered media

In this study, two-dimensional transient dynamic response of orthotropic plane layered media is investigated. The plane multilayered media consist of N different generally orthotropic, homogeneous and linearly elastic layers with different ply angles. In the generally orthotropic layer, representing a ply reinforced by unidirectional fibers with an arbitrary orientation angle, the principal material directions do not coincide with body coordinate axes. The solution is obtained by employing a numerical technique which combines the use of Fourier transform with the method of characteristics. The numerical results are displayed in curves denoting the variations of stress and displacement components with time at different locations. These curves clearly reveal, in wave profiles, the scattering effects caused by the reflections and refractions of waves at the boundaries and at the interfaces of the layers, and also the effects of anisotropy caused by fiber orientation angle. The curves properly predict the sharp variations in the response at the neighborhood of the wave fronts, which shows the power of the numerical technique employed in the study. By suitably adjusting the elastic constants, the results for multilayered media with transversely isotropic layers, or layers with cubic symmetry, or isotropic layers can easily be obtained from the general formulation. Furthermore, solutions for some special cases, including Lamb’s problem for an elastic half-space, are obtained and compared with the available solutions in the literature and very good agreement is found. Preliminary version presented at the Second International Congress on Mechatronics (MECH2K3), Graz, Austria, July 14-17, 2003.