Measurement of Fluctuating Pressures on Coarse Bed Material

Hofland, Bas; Battjes, J.A.; Booij, R.

doi:10.1061/(asce)0733-9429(2005)131:9(770)

Cited by 63 publications

(65 citation statements)

References 26 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…, where F D is the estimated drag force, F L is the lift force and A is the area of the spherical test grain projected in both horizontal and vertical planes [Einstein and El-Samni, 1949;Hofland et al, 2005; see the definition sketch and the insets in Figure 1a]. For the analysis hereafter, we consider F L as the effective lift force that excludes the buoyancy force acting on the submerged 12.7 mm diameter grain.…”

Section: Impulse Detectionmentioning

confidence: 99%

“…Recently, experimental studies of Hofland et al [2005] and Dwivedi et al [2010] using conventional quadrant analysis estimated the contributions from the four quadrants to the pressures acting on bed material and pointed out the importance of Q IV flow events. We note however that prior work by Heathershaw and Thorne [1985] and later by Nelson et al [1995] demonstrated quantitatively that Q I events are equally effective, compared to Q IV, in moving sediment.…”

Section: Impulse Events and Quadrant Characterizationmentioning

confidence: 99%

“…[4] More recently, technological advancements have allowed for direct measurements of time-resolved forces (lift and drag) on an instrumented immobile grain [e.g., Schmeeckle et al, 2007;Dwivedi et al, 2011aDwivedi et al, , 2011b or of time-resolved grain surface pressures [Hofland et al, 2005;Smart and Habersack, 2007;Dwivedi et al, 2010;Detert et al, 2010;Celik, 2011]. To capture the grain/flow interaction, the force or pressure measurements were synchronized with simultaneous time-resolved velocity measurements.…”

Section: Introductionmentioning

confidence: 99%

“…To capture the grain/flow interaction, the force or pressure measurements were synchronized with simultaneous time-resolved velocity measurements. Hofland et al [2005] and Dwivedi et al [2010Dwivedi et al [ , 2011a report, in addition to pressure or force measurements, separate mobile grain experiments with simultaneously recorded particle image velocimetry (PIV) measurements. A number of other investigations report simple grain entrainment observations simultaneously with flow velocity (via either LDV or PIV) without providing separate force or pressure measurements, notably Balakrishnan [1997], Cameron [2006], and Celik et al [2010].…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Instantaneous turbulent forces and impulse on a rough bed: Implications for initiation of bed material movement

Çelik

Diplas

Dancey

2013

Water Resources Research

View full text Add to dashboard Cite

[1] The overall objective of this study is to identify the physical mechanisms responsible for the entrainment of an exposed particle subject to rapidly fluctuating hydrodynamic forces in the case of channel flow with a fully rough boundary. This is pursued here by examining particle dislodgment under uniform and cylinder wake-flow experiments. The critical impulse concept is investigated more rigorously by measuring directly the pressures at four points on the surface of a fixed test grain. The number of impulse events determined from these experiments increases by more than an order of magnitude, over a modest change of roughness Reynolds number. Furthermore, they are well described by a lognormal probability density function. Both results are consistent with those obtained from similar experiments via indirect (velocity-based) impulse calculations and reported in a prior contribution. This comparison supports the use of the velocity record for determining instantaneous hydrodynamic forces and impulses instead of the more difficult approach of measuring the pressure fluctuations directly. The present results demonstrate the dominant role the local, streamwise velocity component plays on particle dislodgment. This is attributed to the large impulse content and occasionally strong positive lift force associated with flow events, exhibiting pronounced positive streamwise velocity fluctuations. The majority ($70%) of these events occur in the fourth quadrant, while a significant number ($22%) appear as first-quadrant episodes. It was also determined that wake flows can increase substantially particle entrainment via enhanced lift and increased turbulence intensity.Citation: Celik, A. O., P. Diplas, and C. L. Dancey (2013), Instantaneous turbulent forces and impulse on a rough bed: Implications for initiation of bed material movement, Water Resour.

show abstract

Section: Impulse Detectionmentioning

confidence: 99%

Section: Impulse Events and Quadrant Characterizationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Instantaneous turbulent forces and impulse on a rough bed: Implications for initiation of bed material movement

Çelik

Diplas

Dancey

2013

Water Resources Research

View full text Add to dashboard Cite

show abstract

“…More recently, Vollmer and Kleinhans [7] point out the importance of "vertical pressure gradients in the upper sediment layer", which are directly connected to a certain lift force acting on the bed surface. Further studies investigate the pressure fluctuations in and above gravel beds and link their results to incipient motion of single particles [8,9]. In addition numerical investigations such as Derksen and Larsen [10] report strong lift forces, while others [11] still argue that lift forces can be neglected.…”

Section: Introductionmentioning

confidence: 99%

Dynamic Lift on an Artificial Static Armor Layer During Highly Unsteady Open Channel Flow

Spiller

Rüther

Friedrich

2015

Water

View full text Add to dashboard Cite

Abstract:The dynamic lift acting on a 100 mm × 100 mm section of a static armor layer during unsteady flow is directly measured in a series of physical experiments. The static armor layer is represented by an artificial streambed mold, made from an actual gravel bed. Data from a total of 190 experiments are presented, undertaken in identical conditions. Results show that during rapid discharge increases, the dynamic lift on the streambed repeatedly exhibits three clear peaks. The magnitude of the observed lift depends on the following hydrograph characteristics: (1) the initial flow depth; (2) the ramping duration and therefore the ramping rate; and (3) the total discharge increase. An adjusted unsteadiness parameter combines those three hydrograph characteristics for rapid discharge increases. Direct correlations between the unsteadiness parameter and the measured dynamic lift during unsteady flow are presented. In addition, the armor layer porosity showed a major impact on the observed effects. It is shown that increasing bed porosity leads to decreasing dynamic lift.

show abstract

A mechanistic-stochastic formulation of bed load particle motions: From individual particle forces to the Fokker-Planck equation under low transport rates

Fan

Zhong

Wang

et al. 2014

J. Geophys. Res. Earth Surf.

View full text Add to dashboard Cite

Bed load transport is a highly complex process. The probability density function (PDF) of particle velocities results from the local particle momentum variability in response to fluid drag and interactions with the bed. Starting from the forces exerted on a single particle under low transport rates (i.e., rolling and sliding regimes), we derive here the nonlinear stochastic Langevin equation (LE) to describe the dynamics of a single particle, accounting for both the deterministic and the stochastic components of such forces. Then, the Fokker-Planck equation (FPE), which describes the evolution of the PDF of the ensemble particle velocities, is derived from the LE. We show that the theoretical PDFs of both streamwise and cross-stream velocities obtained by solving the FPE under equilibrium conditions have exponential form (PDFs of both positive and negative velocities decay exponentially), consistent with the experimental data by Roseberry et al. (2012). Moreover, we theoretically show how the exponential-like PDF of an ensemble of particle velocities results from the forces exerted on a single particle. We also show that the simulated particle motions using the proposed Langevin model exhibit an emergent nonlinear relationship between hop distances and travel times (power law with exponent 5/3), in agreement with the experimental data, providing a statistical description of the particles' random motion in the context of a stochastic transport process. Finally, our study emphasizes that the motion of individual particles, described by the LE, and the behavior of the ensemble, described by the FPE, are connected within a statistical mechanics framework.

show abstract

Measurement of Fluctuating Pressures on Coarse Bed Material

Cited by 63 publications

References 26 publications

Instantaneous turbulent forces and impulse on a rough bed: Implications for initiation of bed material movement

Instantaneous turbulent forces and impulse on a rough bed: Implications for initiation of bed material movement

Dynamic Lift on an Artificial Static Armor Layer During Highly Unsteady Open Channel Flow

A mechanistic-stochastic formulation of bed load particle motions: From individual particle forces to the Fokker-Planck equation under low transport rates

Contact Info

Product

Resources

About