The dynamics and stability of thin liquid films have fascinated scientists over many decades: the observations of regular wave patterns in film flows down a windowpane or along guttering, the patterning of dewetting droplets, and the fingering of viscous flows down a slope are all examples that are familiar in daily life. Thin film flows occur over a wide range of length scales and are central to numerous areas of engineering, geophysics, and biophysics; these include nanofluidics and microfluidics, coating flows, intensive processing, lava flows, dynamics of continental ice sheets, tear-film rupture, and surfactant replacement therapy. These flows have attracted considerable attention in the literature, which have resulted in many significant developments in experimental, analytical, and numerical research in this area. These include advances in understanding dewetting, thermocapillary- and surfactant-driven films, falling films and films flowing over structured, compliant, and rapidly rotating substrates, and evaporating films as well as those manipulated via use of electric fields to produce nanoscale patterns. These developments are reviewed in this paper and open problems and exciting research avenues in this thriving area of fluid mechanics are also highlighted.

Dynamics and stability of thin liquid films

Recent advances in nonlinear passive vibration isolators

This article presents an overview of the acoustics of friction by covering friction sounds, friction-induced vibrations and waves in solids, and descriptions of other frictional phenomena related to acoustics. Friction, resulting from the sliding contact of solids, often gives rise to diverse forms of waves and oscillations within solids which frequently lead to radiation of sound to the surrounding media. Among the many everyday examples of friction sounds, violin music and brake noise in automobiles represent the two extremes in terms of the sounds they produce and the mechanisms by which they are generated. Of the multiple examples of friction sounds in nature, insect sounds are prominent. Friction also provides a means by which energy dissipation takes place at the interface of solids. Friction damping that develops between surfaces, such as joints and connections, in some cases requires only microscopic motion to dissipate energy. Modeling of friction-induced vibrations and friction damping in mechanical systems requires an accurate description of friction for which only approximations exist. While many of the components that contribute to friction can be modeled, computational requirements become prohibitive for their contemporaneous calculation. Furthermore, quantification of friction at the atomic scale still remains elusive. At the atomic scale, friction becomes a mechanism that converts the kinetic energy associated with the relative motion of surfaces to thermal energy. However, the description of the conversion to thermal energy represented by a disordered state of oscillations of atoms in a solid is still not well understood. At the macroscopic level, friction interacts with the vibrations and waves that it causes. Such interaction sets up a feedback between the friction force and waves at the surfaces, thereby making friction and surface motion interdependent. Such interdependence forms the basis for friction-induced motion as in the case of ultrasonic motors and other examples. Last, when considered phenomenologically, friction and boundary layer turbulence exhibit analogous properties and, when compared, each may provide clues to a better understanding of the other.

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Acoustics of friction.

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TOPICAL REVIEW: Superconducting bearings

This two-part review article presents an overview of mechanics of pipes conveying fluid and related problems such as the fluid-elastic instability under conditions of turbulence in nuclear power plants. In the first part, different types of modeling, dynamic analysis, and stability regimes of pipes conveying fluid restrained by elastic or inelastic barriers are described. The dynamic and stability behaviors of pinned-pinned, clamped-clamped, and cantilevered pipes conveying fluid together with curved and articulated pipes will be discussed. Other problems such as pipes made of viscoelastic materials and active control of severe pipe vibrations are considered. This part will be closed by conclusions highlighting resolved and nonresolved controversies reported in literature. The second part will address the problem of fluid-elastic instability in single- and two-phase flows and fretting wear in process equipment such as heat exchangers and steam generators. Connors critical velocity will be discussed as a measure of initiating fluid-elastic instability. Vibro-impact of heat exchanger tubes and the random excitation by the cross-flow can produce a progressive damage at the supports through fretting wear or fatigue. Antivibration bar supports used to limit pipe vibrations are described. An assessment of analytical, numerical, and experimental techniques of fretting wear problem of pipes in heat exchangers will be given. Other topics related to this part include remote impact analysis and parameter identification, pipe damage-induced by pressure elastic waves, the dynamic response and stability of long pipes, marine risers together with pipes aspirating fluid, and carbon nanotubes conveying fluid.

Overview of Mechanics of Pipes Conveying Fluids—Part I: Fundamental Studies

The purpose of this paper is to study the nonstationary vibration of a string with time-varying length and a mass-spring system attached at the lower end. The string is hung vertically and excited sinusoidally by a horizontal displacement at its upper end. The mass is supported by a guide spring horizontally and has two-degrees-of-freedom, vertical and horizontal. It is shown analytically that axial velocity of the string influences the peak amplitude of the string vibration at the passage through resonances. Moreover, it is shown numerically that the amplitudes of both the string and the mass vibrations depend on the sign of the axial velocity, when the natural frequency of the mass-spring system is close to the frequency of the excitation. The above two theoretical results are confirmed experimentally with a simple experimental setup.

Nonstationary Vibrations of a String with Time-Varying Length and a Mass-Spring Attached at the Lower End

This research deals with dynamics of a permanent magnet freely levitated above an excited high-T/sub c/ superconductor. Vertical restoring forces acting on the magnet were evaluated by analysis based on the critical state and flux flow models. The results show nonlinearity and frequency-dependence of the forces, which were observed in experiments. Vertical vibration properties of the system were also evaluated analytically by considering the above properties of the restoring forces. The results show good agreement with experimental ones, which include effect of the frequency-dependent stiffness on the resonant frequency, the primary resonance characteristics, stability of the steady-state motions and so on.

Mechanical stability of a high-T/sub c/ superconducting levitation system

This research deals with a kind of parametric excitation of a permanent magnet freely levitated above a high-T/sub c/ superconductor excited in the vertical direction. We find the magnet has two vibration modes of linearly coupled horizontal translation and roll motion. These two modes are coupled nonlinearly with the vertical motion by the magnetic force and torque. Through nonlinear analysis and numerical simulation, this research discusses parametric resonance of each mode caused by vertical excitation at the frequency in the neighborhood of twice the natural frequency of that mode. Analytical and numerical results show qualitative agreement with experimental ones.

Parametrically excited horizontal and rolling motion of a levitated body above a high-T/sub c/ superconductor

Asymptotic analysis of the formation of thin liquid film in spin coating

http://asmedigitalcollection.asme.org/IDETC-CIE/proceedings-pdf/doi/10.1115/DETC1993-0092/6666177/63_1_detc1993-0092.pdf

Masatsugu Yoshizawa

Papers

Nonstationary Vibrations of a String with Time-Varying Length and a Mass-Spring Attached at the Lower End

Mechanical stability of a high-T/sub c/ superconducting levitation system

Parametrically excited horizontal and rolling motion of a levitated body above a high-T/sub c/ superconductor

Asymptotic analysis of the formation of thin liquid film in spin coating

Nonstationary Vibrations of a String With Time-Varying Length and a Mass-Spring System Attached at the Lower End