Bulk flow driven by a viscous monolayer

2015 ◽  
Vol 785 ◽  
pp. 283-300 ◽  
Author(s):  
Aditya Raghunandan ◽  
Juan M. Lopez ◽  
Amir H. Hirsa
Keyword(s):  
Stokes Flow ◽  
Water Surface ◽  
Bulk Flow ◽  
Bulk Liquid ◽  
Knife Edge ◽  
Viscous Coupling ◽  
Interfacial Film ◽  
Monomolecular Film ◽  
Wide Range ◽  
Flow Inertia

The flow in the bulk driven by a viscous interfacial film set in motion by a rotating sharp circular knife edge has been examined through experiments and computations. In the experiments, the water surface is covered by an insoluble monomolecular film of dipalmitoylphosphatidylcholine (DPPC), a molecule of wide interest in biology and medicine. It is shown that the viscous coupling between the interfacial film and the bulk liquid leads to a strong bulk flow. Depending on the surface packing and corresponding surface tension, DPPC monolayers exhibit a wide range of phase morphologies. Upon shearing the monolayer, its viscous response varies from that of an essentially inviscid film at low surface packing, to that of a highly viscous non-Newtonian (shear thinning) film when the packing is dense. The more viscous the film, the stronger the driven bulk flow. We have examined this behaviour for hydrodynamic regimes straddling the Stokes flow regime and where flow inertia is important.

scholarly journals Hydromechanics of low-Reynolds-number flow. Part 2. Singularity method for Stokes flows

1975 ◽  
Vol 67 (4) ◽  
pp. 787-815 ◽  
Author(s):  
Allen T. Chwang ◽  
T. Yao-Tsu Wu
Keyword(s):  
Exact Solutions ◽  
Stokes Flow ◽  
Fundamental Solutions ◽  
The Body ◽  
Circular Cylinders ◽  
Geometrical Parameters ◽  
Flow Problems ◽  
Singularity Method ◽  
Wide Range ◽  
Body Shapes

The present study further explores the fundamental singular solutions for Stokes flow that can be useful for constructing solutions over a wide range of free-stream profiles and body shapes. The primary singularity is the Stokeslet, which is associated with a singular point force embedded in a Stokes flow. From its derivatives other fundamental singularities can be obtained, including rotlets, stresslets, potential doublets and higher-order poles derived from them. For treating interior Stokes-flow problems new fundamental solutions are introduced; they include the Stokeson and its derivatives, called the roton and stresson.These fundamental singularities are employed here to construct exact solutions to a number of exterior and interior Stokes-flow problems for several specific body shapes translating and rotating in a viscous fluid which may itself be providing a primary flow. The different primary flows considered here include the uniform stream, shear flows, parabolic profiles and extensional flows (hyper-bolic profiles), while the body shapes cover prolate spheroids, spheres and circular cylinders. The salient features of these exact solutions (all obtained in closed form) regarding the types of singularities required for the construction of a solution in each specific case, their distribution densities and the range of validity of the solution, which may depend on the characteristic Reynolds numbers and governing geometrical parameters, are discussed.

Motion of slender bodies in unsteady Stokes flow

2011 ◽  
Vol 688 ◽  
pp. 66-87 ◽  
Author(s):  
Efrath Barta
Keyword(s):  
Stokes Flow ◽  
Slenderness Ratio ◽  
Creeping Flow ◽  
Slender Body Theory ◽  
Wide Range ◽  
Unsteady Stokes Flow ◽  
Slender Bodies ◽  
Set Up ◽  
Micro Organisms ◽  
Parameter Values

AbstractThe flow regime in the vicinity of oscillatory slender bodies, either an isolated one or a row of many bodies, immersed in viscous fluid (i.e. under creeping flow conditions) is studied. Applying the slender-body theory by distributing proper singularities on the bodies’ major axes yields reasonably accurate and easily computed solutions. The effect of the oscillations is revealed by comparisons with known Stokes flow solutions and is found to be most significant for motion along the normal direction. Streamline patterns associated with motion of a single body are characterized by formation and evolution of eddies. The motion of adjacent bodies results, with a reduction or an increase of the drag force exerted by each body depending on the direction of motion and the specific geometrical set-up. This dependence is demonstrated by parametric results for frequency of oscillations, number of bodies, their slenderness ratio and the spacing between them. Our method, being valid for a wide range of parameter values and for densely packed arrays of rods, enables simulation of realistic flapping of bristled wings of some tiny insects and of locomotion of flagella and ciliated micro-organisms, and might serve as an efficient tool in the design of minuscule vehicles. Its potency is demonstrated by a solution for the flapping of thrips.

scholarly journals A reduced-complexity model for river delta formation – Part 1: Modeling deltas with channel dynamics

2015 ◽  
Vol 3 (1) ◽  
pp. 67-86 ◽  
Author(s):  
M. Liang ◽  
V. R. Voller ◽  
C. Paola
Keyword(s):  
Sediment Transport ◽  
Flow Field ◽  
Water Surface ◽  
Surface Profile ◽  
River Delta ◽  
Suspended Sediment Transport ◽  
Channel Dynamics ◽  
Wide Range ◽  
Delta Formation ◽  
Reduced Complexity

Abstract. In this work we develop a reduced-complexity model (RCM) for river delta formation (referred to as DeltaRCM in the following). It is a rule-based cellular morphodynamic model, in contrast to reductionist models based on detailed computational fluid dynamics. The basic framework of this model (DeltaRCM) consists of stochastic parcel-based cellular routing schemes for water and sediment and a set of phenomenological rules for sediment deposition and erosion. The outputs of the model include a depth-averaged flow field, water surface elevation and bed topography that evolve in time. Results show that DeltaRCM is able (1) to resolve a wide range of channel dynamics – including elongation, bifurcation, avulsion and migration – and (2) to produce a variety of deltas such as alluvial fan deltas and deltas with multiple orders of bifurcations. We also demonstrate a simple stratigraphy recording component which tracks the distribution of coarse and fine materials and the age of the deposits. Essential processes that must be included in reduced-complexity delta models include a depth-averaged flow field that guides sediment transport a nontrivial water surface profile that accounts for backwater effects at least in the main channels, both bedload and suspended sediment transport, and topographic steering of sediment transport.

LONG-RANGE CORRELATIONS IN SMALL ATOMIC CLUSTERS

1996 ◽  
Vol 03 (01) ◽  
pp. 457-461 ◽  
Author(s):  
SAROJ K. NAYAK ◽  
R. RAMASWAMY
Keyword(s):  
Potential Energy ◽  
Long Range ◽  
Solid Phase ◽  
Bulk Liquid ◽  
Rare Gas ◽  
Relaxation Processes ◽  
Long Range Correlations ◽  
Wide Range ◽  
Gas Clusters ◽  
Rare Gas Clusters

We study the power spectrum of fluctuations in the potential energy of atoms in small rare-gas clusters. At temperatures when the cluster is in a liquid-like state the spectra have a “1/f” dependence over a wide range of frequency f. This behavior is distinctly different from both the solid phase of clusters or bulk liquid, and is indicative of long-range temporal correlations. The origins of this phenomenon is explored by studying the individual potential-energy distributions in pure and mixed rare-gas clusters, Xe55 and ArXe54, via molecular dynamics simulations. Substitution of atomic impurities acts as an effective probe of the dynamics, and we observe that long-lived memory effects have their origins in hierarchical relaxation processes arising in the motion of the atoms from the surface to the core and vice-versa.

Laboratory studies of wind–wave interactions

1968 ◽  
Vol 34 (1) ◽  
pp. 91-111 ◽  
Author(s):  
Jin Wu
Keyword(s):  
Surface Roughness ◽  
Wind Stress ◽  
Water Surface ◽  
Wind Wave ◽  
Wave Drag ◽  
Average Height ◽  
Drift Current ◽  
Stress Coefficient ◽  
Wide Range ◽  
Wind Velocities

The present study consists of wind profile surveys, drift current measurements and water surface observations for a wide range of wind velocities in a wind–wave tank. It is confirmed that the velocity distribution essentially follows the logarithmic law near the water surface and the velocity-defect law toward the outer edge of the boundary layer. The wind stresses and surface roughnesses calculated from these distributions are divided into two groups separated by the occurrence of the wave-breaking phenomenon. For low wind velocities the surface roughness is dictated by ripples, and the wind-stress coefficient varies with U0−½, where U0 is the free-stream wind velocity. The surface roughness is proportional to the average height of the basic gravity wave at higher wind velocities; the stress coefficient is then proportional to U0. In addition, it is found that Charnock's expression (k ∝ u*2/g) holds only at high wind velocities, and that the constant of proportionality determined from the present experiment correlates very well with field observations. A new technique, involving the use of various-sized surface floats to determine the drift current gradient and the surface drift current, has been developed. A good agreement is shown between the gradients obtained from the measured currents and those determined from the wind stresses. Finally, the wind-stress coefficient is shown to be larger than the friction coefficient for turbulent flow along a solid rough surface; the difference is shown to be the wave drag of the wind over the water surface.

scholarly journals A FOURTH ORDER DIFFUSION MONTE CARLO ALGORITHM FOR SOLVING QUANTUM MANY-BODY PROBLEMS

2001 ◽  
Vol 15 (10n11) ◽  
pp. 1752-1755 ◽  
Author(s):  
H. A. FORBERT ◽  
S. A. CHIN
Keyword(s):  
Monte Carlo ◽  
Fourth Order ◽  
Planck Equation ◽  
Monte Carlo Algorithm ◽  
Bulk Liquid ◽  
Many Body ◽  
Diffusion Monte Carlo ◽  
Step Size ◽  
Wide Range ◽  
Gaussian Random Walk

We derive a fourth-order diffusion Monte Carlo algorithm for solving quantum many-body problems. The method uses a factorization of the imaginary time propagator in terms of the usual local energy E and Langevin operators L as well as an additional pseudo-potential consisting of the double commutator [EL, [L, EL]]. A new factorization of the propagator of the Fokker-Planck equation enables us to implement the Langevin algorithm to the necessary fourth order. We achieve this by the addition of correction terms to the drift steps and the use of a position-dependent Gaussian random walk. We show that in the case of bulk liquid helium the systematic step size errors are indeed fourth order over a wide range of step sizes.

scholarly journals Quantification of the Effect of Bridge Pier Encasement on Headwater Elevation Using HEC-RAS

Hydrology ◽  
2019 ◽  
Vol 6 (1) ◽  
pp. 25
Author(s):  
Abhijit Subedi ◽  
Suresh Sharma ◽  
Anwarul Islam ◽  
Niraj Lamichhane
Keyword(s):  
Water Surface ◽  
The United States ◽  
Concrete Cover ◽  
Surface Elevation ◽  
Water Surface Elevation ◽  
Percentage Decrease ◽  
Wide Range ◽  
Bridge Superstructure ◽  
Analysis System ◽  
Water Elevation

The deterioration of bridge substructure is a serious concern across the United States. The pier encasement is one of the most common practices for repairing and strengthening the bridge substructure. It is a rehabilitation process of existing pile piers during the repair or replacement of the bridge superstructure, which involves enclosing part of an existing pile pier with a polyethylene or PVC pipe large enough to provide at least three inches of concrete cover over the existing pier when filled. However, this process of enclosing pile piers might elevate water level due to increase in pier width, which could be hazardous in high-risk flood zones. Furthermore, it may create an adverse impact on the stability of the bridge due to scouring around the pier foundation. In order to gain knowledge on the backwater effect due to pile encasement, Hydraulic Engineering Center-River Analysis System (HEC-RAS) was used in this research to perform hydraulic simulations near the bridge sites. These simulations were carried out for various channel configurations and pier sizes with a wide range of flows, which resulted into 224 HEC-RAS models in order to investigate the effects of pile pier encasement on the headwater elevation. This study demonstrated that the water elevation measured in the upstream of the bridge showed no-rise condition, especially for wider channel sections with flatter slopes. However, the water elevation at the immediate upstream of the bridge was slightly higher, and the increasing pattern was only noticeable for a smaller channel width (20 ft), and specifically, for increased flow rate. As the area of flow was decreased resulting in increased water surface elevation due to encasement, a generic power equation in the form of Y = aXb was suggested for various channel slopes for the increased water surface elevation (Y) for each percentage decrease in channel area (X).

scholarly journals Deprotonation of formic acid in collisions with a liquid water surface studied by molecular dynamics and metadynamics simulations

2016 ◽  
Vol 18 (43) ◽  
pp. 29756-29770 ◽  
Author(s):  
Garold Murdachaew ◽  
Gilbert M. Nathanson ◽  
R. Benny Gerber ◽  
Lauri Halonen
Keyword(s):  
Molecular Dynamics ◽  
Formic Acid ◽  
Liquid Water ◽  
Water Surface ◽  
Bulk Liquid ◽  
Water Interface ◽  
Air Water Interface

Formic acid has a lower barrier to deprotonation at the air–water interface than in bulk liquid water.

Observation of capillary turbulence on the water surface in a wide range of frequencies

2002 ◽  
Vol 58 (4) ◽  
pp. 510-516 ◽  
Author(s):  
M. Yu Brazhnikov ◽  
G. V Kolmakov ◽  
A. A Levchenko ◽  
L. P Mezhov-Deglin
Keyword(s):  
Water Surface ◽  
Wide Range ◽  
Capillary Turbulence
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