Coupling fluid-elastic

Fluid-Elastic Coupling Fluid flowing over tubes causes them to vibrate with a whirling motion. The mechanism of fluid-elastic coupling occurs when a critical velocity is exceeded and the vibration then becomes self-excited and grows in amplitude. This mechanism frequently occurs in process heat exchangers which suffer vibration damage. 

If pulses can be generated and detected whose length is short compared with the time difference between reflections from the top and the bottom surfaces of a layer, then the elastic properties of the layer can be deduced from the amplitude and timing of the two echoes. The return pulses from such a situation are illustrated in Fig. 8.10. Figure 8.10(a) is an oscilloscope trace of the reference echo from the substrate at defocus z0 and with nothing on it except the coupling fluid. We can choose to write the reference signal as... 

The fourth and last solution is a pressure-porosity wave in which fluid flow at the incompressible limit of fluid motions is coupled to elastic deformations of the matrix. The attenuation of this wave is highly frequency dependent, but it is quite conservative at low frequencies. Unlike the previous three solutions which each exist as an independent process, this solution is always coupled to porosity diffusion. It can leave behind an increase in pressure as it propagates, converting some of the inertial energy associated with the... 

The first finite element schemes for differential viscoelastic models that yielded numerically stable results for non-zero Weissenberg numbers appeared less than two decades ago. These schemes were later improved and shown that for some benchmark viscoelastic problems, such as flow through a two-dimensional section with an abrupt contraction (usually a width reduction of four to one), they can generate simulations that were qualitatively comparable with the experimental evidence. A notable example was the coupled scheme developed by Marchal and Crochet (1987) for the solution of Maxwell and Oldroyd constitutive equations. To achieve stability they used element subdivision for the stress approximations and applied inconsistent streamline upwinding to the stress terms in the discretized equations. In another attempt, Luo and Tanner (1989) developed a typical decoupled scheme that started with the solution of the constitutive equation for a fixed-flow field (e.g. obtained by initially assuming non-elastic fluid behaviour). The extra stress found at this step was subsequently inserted into the equation of motion as a pseudo-body force and the flow field was updated. These authors also used inconsistent streamline upwinding to maintain the stability of the scheme. 

Many of the new plastics, blends, and material systems require special, enhanced processing features or techniques to be successfully injection molded. The associated materials evolution has resulted in new plastics or grades, many of which are more viscoelastic. That is, they exhibit greater melt elasticity. The advanced molding technology has started to address the coupling of viscoelastic material responses with the process parameters. This requires an understanding of plastics as viscoelastic fluids, rather than as purely viscous liquids, as is commonly held... 

Figure 8 Left Schematic graph of the setup for the simulation of rubbing surfaces. Upper and lower walls are separated by a fluid or a boundary lubricant of thickness D. The outermost layers of the walls, represented by a dark color, are often treated as a rigid unit. The bottom most layer is fixed in a laboratory system, and the upper most layer is driven externally, for instance, by a spring of stiffness k. Also shown is a typical, linear velocity profile for a confined fluid with finite velocities at the boundary. The length at which the fluid s drift velocity would extrapolate to the wall s velocity is called the slip length A. Right The top wail atoms in the rigid top layer are set onto their equilibrium sites or coupled elastically to them. The remaining top wall atoms interact through interatomic potentials, which certainly may be chosen to be elastic.

Typical of this class of viscometer is the coaxial or Couette type of instrument described in Volume l, Section 3.7.4. The sample fluid is contained within the annular space between two coaxial cylinders, either of which may be rotated by a motor with the remaining cylinder suspended elastically in such a way that the torsional couple exerted on the latter can be measured. If the outer cylinder of radius r2 rotates with an angular velocity cou and the inner cylinder of radius r, is stationary, and the torque (or viscous drag) per unit length of cylinder exerted on the inner cylinder is T, then, for a Newtonian fluid(49) ... 

Abstract We formulate the balance principles for an immiscible mixture of continua with micro structure in the broadest sense for include, e.g., phenomena of diffusion, adsorption and chemical reactions. After we consider the flow of a fluid/adsorbate mixture through big pores of an elastic solid skeleton and propose suitable constitutive equations to study the coupling of adsorption and diffusion under isothermal conditions. 

The tubule is a spatially extended structure, and it presents both elastic properties and resistance to the fluid flow. The dynamic pressure and flow variations in such a structure can be represented by a set of coupled partial differential equations [11]. An approximate description in terms of ordinary differential equations (a lumped model) consists of an alternating sequence of elastic and resistive elements, and the simplest possible description, which we will adopt here, applies only a single pair of such elements. Hence our model [12] considers the proximal tubule as an elastic structure with little or no flow resistance. The pressure P, in the proximal tubule changes in response to differences between the in- and outgoing fluid flows ... 

Fig. 5 Wave motion at maximum damping and infinite dilational elasticity. A Motion at the maximum damping coefficient where optimal resonant mode coupling implies that a surface fluid element moves at a 45° angle to the direction of wave propagation. B Wave Motion at infinite dilational elasticity, where the same element is only able to move in the transverse direction...

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