Linear and non linear rheology of a wormlike micellar system in presence of sodium tosylate

In this experimental work, we investigate the influence of an organic counterion, sodium tosylate, on the rheological properties of an aqueous solution of CTAB at the concentration of 0.05M. With this system we can clearly see shear thickening for small salt concentrations C _s and only shear thinning behavior at higher C _s characterized by a linear evolution of η=f(γ) in a log-log representation. In these evolutions it is only in a very small domain of concentrations of the salt (near C _s =0.035M) that we can observe a nearly constant plateau of the shear stress against shear rate. The values of σ₀ (characterizing the stress plateau), G ₀ (the plateau modulus) and τ_R (the relaxation time) obtained by dynamical rheological measurements, allow to compare experimental results obtained to predicted values of the theory of Cates corresponding to the occurrence of shear induced banding structures. Received: 22 July 1997 Accepted: 3 February 1998     

Model reference adaptive control of a nonsmooth dynamical system

In this paper a modified model reference adaptive control (MRAC) technique is presented which can be used to control systems with nonsmooth characteristics. Using unmodified MRAC on (noisy) nonsmooth systems leads to destabilization of the controller. A localized analysis is presented which shows that the mechanism behind this behavior is the presence of a time invariant zero eigenvalue in the system. The modified algorithm is designed to eliminate this zero eigenvalue, making all the system eigenvalues stable. Both the modified and unmodified strategies are applied to an experimental system with a nonsmooth deadzone characteristic. As expected the unmodified algorithm cannot control the system, whereas the modified algorithm gives stable robust control, which has significantly improved performance over linear fixed gain control.     

Behavior of a pulsating rigid body in a viscous fluid in the presence of gravity

The paper considers the motion of a rigid sphere due to specified pulsations of the sphere and gravity in a viscous fluid which is at rest away from the sphere.     

Heat exchange between a selectively emitting liquid and a laminar gas flow in the presence of an external source of radiation

An investigation is conducted in the solution of a number of practical problems of the radiative and combined heat exchange in nonuniform systems having widely different physical properties. The processes of thermal interaction between the ocean and the atmosphere have been treated in the paper [1], the effect of thermal radiation on the melting and solidification of semitransparent crystals has been investigated in [2], the flow of a selectively emitting gas around the lateral surface of an object evaporating under the action of radiative heating has been discussed in [3], and heat transfer from a jet to the molten mass of glass in a glassmaking furnace tank has been investigated in [4]. The radiative and combined heat exchange between a selectively emitting liquid and a transparent heat-conducting laminar gas flow in the case of a specified external thermal radiation field is discussed in this paper. The energy conservation equations are set up taking into account the heat transfer by radiation, convection, and molecular thermal conduction. A differential approximation is used in calculating the values of the radiation fluxes. A system of fundamental computational equations is solved by the method of finite differences and iterations and by the Runge-Kutta method. The results of the calculations are presented in the form of graphs.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 3, pp. 116–122, May–June, 1976.     

Application of nonsmooth transformations to analyze a vibroimpact duffing system

The forced vibrations of an impact Duffing oscillator with one degree of freedom are studied using Zhuravlev's nonsmooth transformation and the multiple-scales method. Detailed consideration is given to the forced vibrations in the domain of resonance family. The stability and bifurcations of periodic vibrations are analyzed Translated from Prikladnaya Mekhanika, Vol. 44, No. 10, pp. 114–121, October 2008.     

Mechanisms of strange nonchaotic attractors in a nonsmooth system with border-collision bifurcations

Nonlinear Dynamics - It is not very clear to understand genesis and mechanisms for the creation of strange nonchaotic attractors (SNAs) due to the nonsmooth bifurcations in the nonsmooth systems. A...     

On two-dimensional laminar flows of a particulate suspension in the presence of gravity field

Three simple two-dimensional streaming motions of a mixture of solid particles with a continuous carrier fluid, or gas, in the presence of the gravity field are considered. These include flow of a mixture over an infinite stationary rigid plane perpendicular to the direction of the gravity field, flow near an oscillating rigid plane and flow in a mixture induced by a suddenly accelerated plane. The nature of the boundary conditions at the interface between a layer of sediment settling on the rigid boundary and the mixture above it suggests an introduction of the independent variables that enable simple analytical expressions for the solutions of the first two flows and a numerical solution by means of a Laplace transform in the last case.     

Vibration reduction evaluation of a linear system with a nonlinear energy sink under a harmonic and random excitation

The nonlinear behaviors and vibration reduction of a linear system with a nonlinear energy sink(NES) are investigated. The linear system is excited by a harmonic and random base excitation, consisting of a mass block, a linear spring, and a linear viscous damper. The NES is composed of a mass block, a linear viscous damper, and a spring with ideal cubic nonlinear stiffness. Based on the generalized harmonic function method,the steady-state Fokker-Planck-Kolmogorov equation is presented to reveal...     

Flow of a fully ionized gas with finite time for energy exchange between electrons and ions

The flow of a jet of a fully ionized gas with velocity ~5·10⁶ cm/sec is examined; the finite time of energy exchange between the electrons and ions is considered.The derived solution agrees well with experimental data on the behavior of the electron and ion temperatures in the zone behind the shock wave which forms in the ionized gas jet issuing from a channel.     

Capillary wave gas exchange in the presence of surfactants

 The effect of surfactants on gas exchange across an air/water interface populated with capillary waves, is considered. Experiments were conducted on capillary waves having a wavelength of 2.87 mm in the presence of oleyl alcohol and stearic acid, as well as on surfaces which were surfactant-free. The presence of these surfactants decreased the gas exchange rate by at most a factor of two when the energy delivered to the tank was held constant. Thus, even in the presence of surfactants, pure capillary waves still caused significant gas exchange, indicating that partially damped capillary waves may play an important role in air/sea gas exchange. When the gas exchange coefficient was plotted as a function of mean square slope, the presence of surfactants was found to negligibly affect the gas exchange rate, with the possible exception of the high wave slope regime for stearic acid. This result suggests that it is principally the kinematics of wave motion which accounts for the enhancement of transport due to the capillary waves investigated here. Moreover, these results agree with those obtained from polychromatic, wind-generated waves, suggesting that, for non-breaking waves, knowledge of the statistics of the wave field may be all that is required to parameterize the gas exchange coefficient. Received: 10 June 1998/Accepted: 3 November 1998     

On energy transfer between vibrating systems under linear and nonlinear interactions

The present study deals with energy transfer in a dissipative mechanical system. Numerical results are given by considering two different potentials and periodical excitation. Specifically, we show energy transfer from linear oscillator to another one, depending on initial conditions. Also, energy transfer from linear to nonlinear (energy pumping), as well as from nonlinear to linear, oscillator is analyzed, under linear and nonlinear interactions.     

Effect of pressure on the exchange of energy in a vortex tube

Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 4, pp. 72–74, July–August, 1989.     

Dispersion of linear gravity waves on a viscoelastic fluid in an horizontal canal

A characteristic equation is derived that describes the spatial decay of linear surface gravity waves on Maxwell fluids. Except at small frequencies, the derived dispersion relation is different from the temporal decay dispersion relation which is normally studied within fluid mechanics. The implications for waves on viscous Newtonian fluids using the two different dispersion relations is briefly discussed. The wave number is measured experimentally as function of the frequency in a horizontal canal. Seven Newtonian fluids and four viscoelastic liquids with constant viscosity have been used in the experiments. The spatial decay theory for Newtonian fluids fits well to the experimental data. The model and experiments are used to determine limits for the Maxwell fluid time numbers for the four viscoelastic liquids. As a result of low viscosity it was not possible within this study to obtain these time numbers from oscillatory experiments. Therefore, a comparison of surface gravity wave experiments with theory is applicable as a method to evaluate memory times of low viscosity viscoelastic fluids.