Beyond Normality: Estimation of Near-Bed Sediment Concentrations Accounting for Asymmetric Distribution and Spatial Influence of Turbulence Coherent Structures

2020 ◽  
Author(s):  
Christina Tsai ◽  
Kuan-Ting Wu
Keyword(s):  
Coherent Structures ◽  
Probability Distributions ◽  
Fickian Diffusion ◽  
Asymmetric Distribution ◽  
Turbulent Fluctuation ◽  
Sediment Particle ◽  
Diffusion Behavior ◽  
Fluctuation Velocity ◽  
Spatial Influence ◽  
Turbulent Coherent Structures

<p>Abstract</p><p>Recent experiments have established that the sediment particle motion, especially for particles near the bed, may not follow the normal (Fickian) diffusion behavior. To modify the diffusion equation where the fluctuation velocity is based on the normal distribution, this investigation hypothesizes that the fluctuation velocity based on bivariate probability distributions and particle-bed collision in open channel can provide some physical insight into the particle diffusion behavior. The distribution of fluctuation velocity is obtained using the Gram-Charlier expansion which considers the first four statistical moments of turbulent fluctuation velocity. The correlation between two-dimensional fluctuation velocities is modeled by performing Monte Carlo simulations. Besides, the uniform momentum zones (UMZ) are further identified and consequently the spatial locations of the edges that demarcate UMZs can be estimated. Once UMZs in the turbulent boundary layers can be characterized, the streamwise momentum deficit, and occurrences of ejection events and sweep events in the vicinity of UMZ edges under different Reynolds numbers can be simulated. The spatial influence of turbulent coherent structures on sediment particle trajectory can be demonstrated.</p>

scholarly journals Interaction of Very Large Scale Motion of Coherent Structures with Sediment Particle Exposure

Water ◽  
2021 ◽  
Vol 13 (3) ◽  
pp. 248
Author(s):  
Sencer Yücesan ◽  
Daniel Wildt ◽  
Philipp Gmeiner ◽  
Johannes Schobesberger ◽  
Christoph Hauer ◽  
...  
Keyword(s):  
Coherent Structures ◽  
Large Scale ◽  
Numerical Study ◽  
Local Maximum ◽  
Wave Number ◽  
Exposure Level ◽  
Sediment Particle ◽  
High Wave Number ◽  
Large Scale Motion ◽  
Scale Motion

A systematic variation of the exposure level of a spherical particle in an array of multiple spheres in a high Reynolds number turbulent open-channel flow regime was investigated while using the Large Eddy Simulation method. Our numerical study analysed hydrodynamic conditions of a sediment particle based on three different channel configurations, from full exposure to zero exposure level. Premultiplied spectrum analysis revealed that the effect of very-large-scale motion of coherent structures on the lift force on a fully exposed particle resulted in a bi-modal distribution with a weak low wave number and a local maximum of a high wave number. Lower exposure levels were found to exhibit a uni-modal distribution.

NONLINEAR EVOLUTION OF TURBULENT COHERENT STRUCTURES IN CHANNEL FLOWS

2005 ◽  
Vol 19 (28n29) ◽  
pp. 1539-1542
Author(s):  
ZHANG LI ◽  
DENGBIN TANG ◽  
LINLIN GUO
Keyword(s):  
Coherent Structures ◽  
Nonlinear Evolution ◽  
Three Dimensional ◽  
Channel Flows ◽  
Navier Stokes ◽  
Theoretic Model ◽  
Compact Difference Scheme ◽  
Navier Stokes Equation ◽  
Turbulent Coherent Structures ◽  
Dimensional Coupling

The generation and the development of turbulent coherent structures in channel flows are investigated by using numerical simulation of Navier-Stokes equation and the theoretic model of turbulent coherent structures built up by the flow stability theories. The three-dimensional coupling compact difference scheme with high accuracy and resolution developed can be applied to the calculative region including points near the boundary. The results computed show nonlinear evolution process and characteristics of Reynolds stress, stream-wise vortices and span-wise vorticities, especially the nonlinear interactions between different coherent structures.

Turbulent coherent structures in a long cavity semiconductor laser near the lasing threshold

2020 ◽  
Vol 45 (17) ◽  
pp. 4903
Author(s):  
Uday Gowda ◽  
Amy Roche ◽  
Alexander Pimenov ◽  
Andrei G. Vladimirov ◽  
Svetlana Slepneva ◽  
...  
Keyword(s):  
Semiconductor Laser ◽  
Coherent Structures ◽  
Lasing Threshold ◽  
Turbulent Coherent Structures

Turbulent coherent structures in a long cavity semiconductor laser near the lasing threshold: publisher’s note

2020 ◽  
Vol 45 (19) ◽  
pp. 5500
Author(s):  
Uday Gowda ◽  
Amy Roche ◽  
Alexander Pimenov ◽  
Andrei G. Vladimirov ◽  
Svetlana Slepneva ◽  
...  
Keyword(s):  
Semiconductor Laser ◽  
Coherent Structures ◽  
Lasing Threshold ◽  
Turbulent Coherent Structures

Determination of Hydrocarbons Using Sapphire Fibers Coated with Poly(Dimethylsiloxane)

2003 ◽  
Vol 57 (4) ◽  
pp. 400-406 ◽  
Author(s):  
Rhona Howley ◽  
B. D. MacCraith ◽  
Kieran O'Dwyer ◽  
Hugh Masterson ◽  
P. Kirwan ◽  
...  
Keyword(s):  
Film Thickness ◽  
Diffusion Model ◽  
Diffusion Coefficients ◽  
Molecular Size ◽  
Infrared Region ◽  
Sensor Response ◽  
Fickian Diffusion ◽  
Prototype System ◽  
Pdms Film ◽  
Diffusion Behavior

A poly(dimethylsiloxane) (PDMS) coated sapphire fiber has been investigated as a sensor for hydrocarbons (HCs) in the mid-infrared region around 3000 cm−1. In order to optimize and predict sensor response, the diffusion behavior of the analytes into the PDMS preconcentration medium has been examined. A diffusion model based on Fickian diffusion was used to quantify diffusion. The model incorporated such factors as film thickness, refractive index of the polymer and the fiber core, and principal wavelength at which the analyte absorbs. A range of hydrocarbons, from hexane to pentadecane, was analyzed at 2930 cm−1 using both fiber-coupled Fourier transform infrared spectroscopy and a modular prototype system. Diffusion coefficients were determined for these compounds and diffusion behavior examined and related to factors such as analyte polarity and molecular size. The diffusion coefficients were found to range from 6.41 × 10−11 ± 5 × 10−12 to 5.25 × 10−11 ± 9 × 10−13 cm2 s−1 for hexane and pentadecane into a 2.9 μm PDMS film, respectively. The diffusion model was also used to examine the effect of changing system parameters such as film thickness in order to characterize sensor response.

Rutherford Backscattering Spectrometry Studies on Copper and Chromium Diffusion in Polyimide

1989 ◽  
Vol 153 ◽  
Author(s):  
Kyung W. Paik ◽  
Arthur L. Ruoff
Keyword(s):  
Diffusion Coefficient ◽  
Diffusion Coefficients ◽  
Room Temperature ◽  
Rutherford Backscattering Spectrometry ◽  
Annealing Treatment ◽  
Rutherford Backscattering ◽  
Fickian Diffusion ◽  
Chromium Diffusion ◽  
Diffusion Behavior ◽  
Slight Amount

AbstractDiffusion of Cu in polyimide(PI) film was observed after Cu evaporation on PI at room temperature. Annealing treatment significantly enhanced the diffusion of Cu. The diffusion coefficient measured at 200 and 400 C using the Fickian erfc solution are 3 × 10−14 and 1 × 10−13 cm2/sec, respectively. Cu shows the Fickian diffusion behavior. In contrast to Cu, no clearly measurable diffusion had occurred for an as-deposited Cr specimen and a specimen annealed at 400 C for 1 hour. However, for longer annealing times a slight amount of Cr diffused into PI because of the growth of the intermixed region. The diffusion coefficients of Cr at 200 and 400 C for less than 20 hours are 2 × 10−15 and 7 × 10−15 cm2/sec, respectively. The diffusion of Cr in PI shows non-Fickian behavior.

scholarly journals Modulation of the turbulence regeneration cycle by inertial particles in planar Couette flow

2018 ◽  
Vol 861 ◽  
pp. 901-929 ◽  
Author(s):  
G. Wang ◽  
D. H. Richter
Keyword(s):  
Reynolds Number ◽  
Couette Flow ◽  
Coherent Structures ◽  
Large Scale ◽  
Relative Length ◽  
Dominant Factor ◽  
Inertial Particles ◽  
Streamwise Vorticity ◽  
Turbulent Coherent Structures ◽  
Regeneration Cycle

Two-way coupled direct numerical simulations are used to investigate the effects of inertial particles on self-sustained, turbulent coherent structures (i.e. the so-called regeneration cycle) in plane Couette flow at low Reynolds number just above the onset of transition. Tests show two limiting behaviours with increasing particle inertia, similar to the results from previous linear stability analyses: low-inertia particles trigger the laminar-to-turbulent instability whereas high-inertia particles tend to stabilize turbulence due to the extra dissipation induced by particle–fluid coupling. Furthermore, it is found that the streamwise coupling between phases is the dominant factor in damping of the turbulence and is highly related to the spatial distribution of the particles. The presence of particles in different turbulent coherent structures (large-scale vortices or large-scale streaks) determines the turbulent kinetic energy of particulate phase, which is related to the particle response time scaled by the turnover time of large-scale vortices. By quantitatively investigating the periodic character of the whole regeneration cycle and the phase difference between linked sub-steps, we show that the presence of inertial particles does not alter the periodic nature of the cycle or the relative length of each of the sub-steps. Instead, high-inertia particles greatly weaken the large-scale vortices as well as the streamwise vorticity stretching and lift-up effects, thereby suppressing the fluctuating amplitude of the large-scale streaks. The primary influence of low-inertia particles, however, is to strengthen the large-scale vortices, which fosters the cycle and ultimately reduces the critical Reynolds number.

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