Viscous Coupling Research Articles

Optimisation of AWD off-road vehicle performance using visco-lock devices

A comprehensive computer model is devised for the simulation of AWD off-road vehicle dynamics. Particular attention has been paid to the modelling of various visco-lock devices, including the viscous couplings and visco-lock limited-slip differentials. These devices are represented by fully parameterised physical models which capture the torque transmission mechanism represented by various thermodynamic, hydrodynamic, structural and mechanical modules. The characteristics of these devices can easily be altered so that comparisons can be made between different types. In addition, the influence of a wide range operating conditions, vehicle design parameters and tyre characteristics can also be made over various deformable soils.

An Improved Sharp Interface Method for Viscoelastic and Viscous Two-Phase Flows

We introduce a robust method for computing viscous and viscoelastic two-phase bubble and drop motions. Our method utilizes a coupled level-set and volume-of-fluid technique for updating and representing the air-water interface. Our method introduces a novel approach for treating the viscous coupling terms at the air-water interface; these improvements result in improved stability for computing two-phase bubble formation solutions. We also present an improved, positive-preserving discretization technique for updating the configuration tensor for viscoelastic flows, in the context of computing two-phase bubble and drop motion.

Analysis of the unconventional behavior of oil relative permeability during depletion tests of gas-saturated heavy oils

The description of two-phase flow in porous media is traditionally based on Darcy’s equation. Accordingly, effective permeabilities to each phase are expected to be smaller than absolute permeabilities, and also they determine each phase mobility. A typical behaviors such as oil relative permeabilities values larger than one, can be obtained during depressurization experiments of heavy oil saturated porous media when the data is analyzed under the conventional Darcean approach. Such an unconventional behavior is physically possible considering that the Darcean approach disregard several flow sources such as viscous coupling derived from the momentum transfer between the phases. Oil relative permeabilities larger than one, which actually are apparent values, could represent one of the most convincing evidence of the role of viscous coupling on two-phase flow in porous media. In this paper we present experimental indication of such unconventional behavior and show how it can be properly understood when taking into account the viscous coupling contribution on each phase mobility. Pore network simulations are used to complement the analysis and evaluate the effect of the capillary number on the transport parameters involved in the generalized flow equations.

Viscous boundary value problems for symmetric systems with variable multiplicities

Extending investigations of Métivier and Zumbrun in the hyperbolic case, we treat stability of viscous shock and boundary layers for viscous perturbations of multidimensional hyperbolic systems with characteristics of variable multiplicity, specifically the construction of symmetrizers in the low-frequency regime where variable multiplicity plays a role. At the same time, we extend the boundary-layer theory to “real” or partially parabolic viscosities, Neumann or mixed-type parabolic boundary conditions, and systems with nonconservative form, in addition proving a more fundamental version of the Zumbrun–Serre–Rousset theorem, valid for variable multiplicities, characterizing the limiting hyperbolic system and boundary conditions as a nonsingular limit of a reduced viscous system. The new effects of viscosity are seen to be surprisingly subtle; in particular, viscous coupling of crossing hyperbolic modes may induce a destabilizing effect. We illustrate the theory with applications to magnetohydrodynamics.

High Viscosity Sensing Using a Love Wave Acoustic Platform Combined with a PDMS Microfludic Chip

This paper exhibits a microsensor solution to allow Love wave acoustic oscillators working under highly viscous liquid environments. Microfluidic techniques are employed to limit attenuation caused by viscous coupling using a poly(dimethylsiloxane) (PDMS) chip bonded on the Love wave device. Fabrication of PDMS chips is detailed. Several microfluidic chip geometries have been realized. Liquid flows of aqueous glycerol solutions up to 0.939 Pa.s (939cP, 98% glycerol) have been tested. Thanks to insertion losses diminution, we were able to observe the Newtonian to Maxwellian behaviour transition in an oscillator mode. Modelisation using the classical perturbation theory is discussed.

The Frequency (or Time) -Temperature Equivalence of Relaxation in Saturated Rocks

Laboratory data on dry and saturated rocks show that pore fluid has the most important effect on rock attenuation. It is known that viscous and inertial coupling between the frame of a porous rock and its pore fluid dissipates seismic energy by conversion to heat and hence cause attenuation. We show that attenuation peaks, in saturated rock have the same property as that of typical thermally activated relaxations. In the frequency domain, a plot of attenuation versus frequency shows an obvious systematic shift to higher frequencies with increasing temperatures. Similarly, the attenuation versus temperature curve moves to higher temperature with increasing frequencies. The attenuation peaks are somewhat broader than that for a Zener relaxation. A Cole-Cole distribution of relaxation times closely matches the attenuations. This behavior can be explained theoretically by local flow mechanisms.

Experimental Study of Phase-Transformation Effects on Relative Permeabilities in Fractures

Summary Phase transformation affects multiphase flow in geothermal and gas/condensate reservoirs owing to the same substance occurring in different phases. These effects change the phase behavior and the flow characteristics. The goals of this research were to compare the flow behavior and relative permeability differences between two-phase flow with and without phase-transformation effects in smooth-walled and rough-walled fractures. During this research, an experimental apparatus was built to capture the unstable nature of the two-phase flow in fractures and to display the flow structures in real time. Two-phase-flow experiments with phase-transformation effects (steam/water flow) and without phase-transformation effects (nitrogen/water flow) were conducted. The porous-medium approach was used to calculate two-phase relative permeabilities. From the results in this study, steam/water relative permeabilities are different from nitrogen/water relative permeabilities. The enhanced steam-phase relative permeability is caused by the effects of phase transformation. This shows consistency with some earlier studies in porous media. The nitrogen/water relative permeability is described most appropriately by using the viscous coupling model. However, steam/water flow in the rough-walled fracture, which is coupled with strong phase-transformation effects, seems to be represented better by Brooks-Corey relative permeability functions for fractured media (λ→∞). The results from this study suggest that relative permeabilities accounting for phase-transformation effects must be used in simulations of geothermal and solution-gas reservoirs to represent two-phase interactions adequately.

Solved and unsolved questions in the non-rigid Earth nutation study

AbstractAt the IAU 26th GA held in Prague in 2006, a new precession model (P03) was recommended and adopted to replace the old one, IAU1976 precession model. This new P03 model is to match the IAU2000 nutation model that is for anelastic Earth model and was adopted in 2003 to replace the previous IAU1980 model. However, this IAU2000 nutation model is also not a perfect one for our complex Earth, as stated in the resolution of IAU nutation working group. The Earth models in the current nutation theories are idealized and too simple, far from the real one. They suffer from several geophysical factors: the an-elasticity of the mantle, the atmospheric loading and wind, the oceanic loading and current, the atmospheric and oceanic tides, the (lateral) heterogeneity of the mantle, the differential rotation between the inner core and the mantle, and various couplings between the fluid outer core and its neighboring solids (mantle and inner core). In this paper, first we give a very brief review of the current theoretical studies of non-rigid Earth nutation, and then focus on the couplings near the core-mantle boundary and the inner core-outer core boundary, including the electro-magnetic, viscous, topographic, and gravitational couplings. Finally, we outline some interesting future studies.

Magnetic and viscous coupling at the core-mantle boundary: inferences from observations of the Earth's nutations

We consider the Kirchhoff equation $$ \partial_{tt} u - \Delta u \Big( 1 + \int_{\mathbb T^d} |\nabla u|^2 \Big) = 0 $$ on the $d$-dimensional torus $\mathbb T^d$, and its Cauchy problem with initial data $u(0,x)$, $\partial_t u(0,x)$ of size $\varepsilon$ in Sobolev class. The effective equation for the dynamics at the quintic order, obtained in previous papers by quasilinear normal form, contains resonances corresponding to nontrivial terms in the energy estimates. Such resonances cannot be avoided by tuning external parameters (simply because the Kirchhoff equation does not contain parameters). In this paper we introduce nonresonance conditions on the initial data of the Cauchy problem and prove a lower bound $\varepsilon^{-6}$ for the lifespan of the corresponding solutions (the standard local theory gives $\varepsilon^{-2}$, and the normal form for the cubic terms gives $\varepsilon^{-4}$). The proof relies on the fact that, under these nonresonance conditions, the growth rate of the "superactions" of the effective equations on large time intervals is smaller (by a factor $\varepsilon^2$) than its a priori estimate based on the normal form for the cubic terms. The set of initial data satisfying such nonresonance conditions contains several nontrivial examples that are discussed in the paper.

Acoustic Love wave platform with PDMS microfluidic chip

This paper exhibits a microfluidic solution to allow Love wave acoustic oscillators working under highly viscous liquid environments. Attenuation caused by viscous coupling is limited by using a poly(dimethylsiloxane) (PDMS) chip bonded on the Love wave device. Liquid volume required for a measurement is thus minimized to the microliter order. Thanks to insertion losses decrease, the non-Newtonian behavior of silicone oils up to 30 Pa s can be observed in oscillator mode. Numerical simulations based on the transfer matrix method have been performed to modelize the sensor response.

Numerical analysis of 1‐D compression wave propagation in saturated poroelastic media

AbstractA numerical procedure is presented for the simulation of 1‐D compression wave propagation in saturated poroelastic media. The media are modelled as a two‐phase system consisting of compressible fluid and solids. Viscous coupling forces resulting from the relative motion between phases are characterized as Darcy type. The numerical procedure can account for effects of axial strain, nonlinear material behaviour, and various drained and undrained boundary conditions. Time integration is carried out explicitly and isothermal conditions are assumed. The method is capable of modelling shock wave fronts without introducing artificial viscosity. Numerical results are in close agreement with analytical solutions for several simplified cases and indicate that mass coupling may have important effects on fluid velocity and wave speed. Corresponding effects on solid velocity and wave speed are much smaller. Numerical results also indicate that damping occurs in a saturated poroelastic column and is dependent on the value of hydraulic conductivity. Copyright © 2007 John Wiley & Sons, Ltd.

Stress, strain, and B‐type olivine fabric in the fore‐arc mantle: Sensitivity tests using high‐resolution steady‐state subduction zone models

Shear‐wave splitting observations at several subduction systems show trench‐parallel fast directions in the fore‐arc mantle. The presence of B‐type olivine fabric in the mantle wedge may provide an explanation for this pattern of anisotropy under low‐temperature and hydrated conditions. Sensitivity tests are shown that provide insights into the distribution and magnitude of B‐type fabric using two‐dimensional, high‐resolution, kinematic‐dynamic subduction zone models. These models include a wet olivine rheology and a simulated aseismic creep zone in the fore‐arc mantle with parameterized viscous coupling between the slab and mantle wedge. The calculated thermal structure is in reasonable agreement with heat flow observations and Q tomography for small amounts of coupling and moderate amounts of shear heating in the seismogenic and aseismic creep zones. These small amounts of viscous coupling give rise to a slowly flowing fore‐arc mantle with thermal, stress, and strain conditions suitable for significant B‐type fabric development. The minimum shear stress necessary to drive geologically significant flow in the predicted B‐type region is sensitive to the magnitude of shear heating along the aseismic creep zone and ranges from less than 100 to 300 MPa. The minimum time required to generate sufficient finite strain for fabric development in the B‐type region is around 10 Myr depending on the amount of coupling and shear heating. The predicted distribution of olivine fabric is consistent with a pattern of shear wave anisotropy with trench‐parallel fast polarization directions above the fore arc and a rapid rotation to trench‐perpendicular in the arc and back arc.

Pattern Formation in Draining Thin Film Suspensions

We demonstrate the emergence of complexity from remarkably simple and ubiquitous systems: draining thin-film suspensions exhibiting a striking transition between two classes of self-organizing patterns. Vertical channels form when attractive forces lead to transient gelation, while horizontal bands result from granular mixtures. We propose an explanation whereby the generic physical mechanisms require only the existence of viscous and excluded-volume couplings among the particles, solvent, and substrate. System-specific, small inhomogeneities trigger large-scale pattern formation, through collective dynamics, where jamming plays a crucial role. Our results shed light on emergent complexity in bio- and geophysical processes and have implications for coatings and food industries.

Does active mantle upwelling help drive plate motions?

Earth's lithospheric plates are driven partly by shear tractions exerted on their base by viscous coupling to convective mantle flow. While downwelling flow associated with descent of subducted lithosphere has been well established as a driver of plate motions, the plate-driving role of upwelling flow is more controversial. We used a numerical mantle flow model to predict present-day plate motions driven by various combinations of upwelling and downwelling flow. We obtain a good fit to observed plate motions using flow driven only by downgoing mantle slabs, whose densities can be inferred either from the tectonic history of subduction or from positive velocity anomalies extracted from mantle tomography. Introducing upwelling flow (driven by negative density anomalies inferred from slow seismic velocity anomalies) to this slab-driven flow field generally degrades the fit to plate motions, and an acceptable fit that includes active upwelling requires amplitudes of mantle density heterogeneity that are at the low end of the accepted range (tomography to density conversion factor = 0.05 g cm −3 km −1 s). Because such small amplitudes lead to a deficit of slab material in the mantle, we infer that downwelling flow is a more significant driver of plate motions than upwelling flow. This conclusion can be reconciled with the presence of low-velocity anomalies in the lower mantle if upwelling flow does not couple effectively to plate motions, or if these low-velocity anomalies represent chemical differentiation of the lower mantle and thus do not drive upwelling flow.

On the fate of thermally buoyant mantle plumes at density interfaces

The 660-km depth endothermic phase transition is expected to delay upwelling plumes and modify their morphology. The interaction of thermal starting plumes with a density boundary is investigated experimentally by using simultaneous visualizations of temperature, composition and velocity fields. In a tank initially stratified with two viscous fluids with different densities and viscosities, a thermal starting plume was generated by using a circular plate heater at the bottom of the tank. Its interaction mode with the inner interface depends on the local buoyancy number (BL: the ratio of the stabilizing chemical buoyancy to the plume thermal buoyancy at the interface), the Rayleigh number (Ra), the viscosity contrast between the chemical layers (γ), and the local viscosity ratio of the ambient material to the plume head (γp). For BL<0.6, the “pass-through mode” develops, whereby a large volume of the lower material rises through the upper layer and reaches the top surface, since the plume head has a large thermal buoyancy compared to the stabilizing density contrast between the two layers. When BL>0.6, the “rebirth mode” occurs, where the thermal plume ponds and spreads under the chemical boundary and secondary thermal plumes are generated from the interface. Depending on the magnitude of BL, these plumes can entrain upwards by viscous coupling a significant amount of lower layer material. Scaling laws are determined for the onset of secondary plumes, their number and wavelength, the amount of entrainment and the topography of the interface. Our results could explain the hotspots' distribution above superswells and the peculiar time evolution of La Réunion hotspot.

Effects of forced convection and roughness of surface on viscous coupling unit of crossover utility vehicles

An experiment was conducted to analyse the local heat transfer and flow characteristics in the viscous coupling unit (VCU) of a crossover utility vehicle (CUV). Heat is transferred by free convection and forced convection, and affected by the lubrication effect of the smooth wall and the embedded circumferential ribs, at various rotational speeds. In the simulation of the practical operational range of VCU of CUV under experimental conditions, both rotational speed and geometric parameters must correspond closely to the real situation. In addition, the test section is designed such that the cooling characteristics of the power transmission system of the CUV of actual size could be investigated. The overall temperature distribution is measured and the local heat transfer coefficient is analysed. The impact of the centrifugal force upon the Taylor vortex is clarified with reference to the flow-field distribution. Finally, some empirical formulae by CUV designers are obtained from the experimental results.

A lattice Boltzmann study of viscous coupling effects in immiscible two-phase flow in porous media

In the present paper we study the immiscible two-phase flow in porous media using the lattice Boltzmann model proposed by He et al. [X. He, R. Zhang, S. Chen, G.D. Doolen, Phys. Fluids 11 (1999) 1143–1152]. By considering a set of appropriate boundary conditions for the density distribution function defined in that model, we account for the effect of wettability at solid–fluid interfaces and capillarity in the pores where the fluid–fluid interfaces reside. Different contact angles of the fluid–fluid interface at solid walls can be realized by taking appropriate values for the density distribution function at the solid sites of the porous domain. It is shown that the steady state contact angle is a linear function of the density value assigned to the solid sites. The model is then applied to the study of viscous coupling effects in immiscible two-phase flow in irregular pore networks, with respect to the overall wetting saturation, the viscosity ratio and the wetting angle. Our results show that when the wetting fluid is less viscous than the non-wetting fluid then the apparent relative permeability of the non-wetting phase may take values greater than unity due to the “lubricating” effect of the wetting films that cover the solid walls. The proposed model is an ideal tool for modeling immiscible two-phase flow in porous media, due both to its ability to incorporate complicated boundary conditions at the pore walls and also capture the physical aspects of the flow in the bulk and the interfaces. Furthermore, the width of the fluid–fluid interfaces is kept less than 3–4 lattice units allowing for simulations in relatively low resolution porous lattices.

Properties of Structure and Dynamics of a Two-DimensionalDissipative Yukawa Dusty Plasma

In this paper, the structural and single-particle motiveproperties of a two-dimensional dusty plasmas are investigatednumerically by molecular dynamics simulation within the frameworkof a dissipative Yukawa model. The pair correlation function, themean square displacement, the static structure factor, and the bondangle correlation function characterizing the structural properties,and the velocity autocorrelation function with Fourier spectrumfunction characterizing the single-particle motion have beencalculated for different values of coupling constant Γ andviscous damping constant νf. The results show that thesystem will coagulate quickly with increasing viscous dampingconstant and coupling constant, and the critical value of frictionparameter decreases with increasing the coupling constant in the system.

Theoretical Analysis of Viscous Coupling in Two-phase Flow through Porous Media

Theoretical analysis is presented to quantify the viscous coupling effect in two-phase flow through porous media. The analysis is based on the principle of potential difference equations as well as on the interfacial contact area and partition concept. The analysis shows that viscous coupling effect is negligible throughout the normalized saturation range. The expression, Xϕ 2, was developed for the quantification of the parameter that controls the amount of viscous coupling, where X was theoretically found to have a maximum value of 2.

MR fluid viscous coupling and its torque delivery control

A torque controllable viscous coupling is presented. The coupling consists of two types of discs with slits. One is connected to a housing (follower discs) and the other is connected to a shaft (driving discs). The driving discs and follower discs are arranged by turns and they are sandwiched. MR fluid is filled in the housing. Magnetic fields freeze the fluid, so that the shear torque is generated between the diving discs and follower discs due to shears between the slits in the discs under the magnetic fields. The torque is controlled by electromagnets. In order to have large torque with small electric power, coil turns have to be large, so that response delays due to inductance of the coil. A controller which improves response is presented. A method of control is presented which controls distribution of torque of rear wheel and front wheel.