scholarly journals Surface Waves Enhance Particle Dispersion

Fluids ◽  
2019 ◽  
Vol 4 (1) ◽  
pp. 55 ◽  
Author(s):  
Mohammad Farazmand ◽  
Themistoklis Sapsis
Keyword(s):  
Free Surface ◽  
Single Particle ◽  
Wave Motion ◽  
Quadratic Function ◽  
Particle Dispersion ◽  
Diffusive Behavior ◽  
Linear Waves ◽  
Tracer Particles ◽  
Passive Tracers

We study the horizontal dispersion of passive tracer particles on the free surface of gravity waves in deep water. For random linear waves with the JONSWAP spectrum, the Lagrangian particle trajectories are computed using an exact nonlinear model known as the John–Sclavounos equation. We show that the single-particle dispersion exhibits an unusual super-diffusive behavior. In particular, for large times t, the variance of the tracer ⟨ | X ( t ) | 2 ⟩ increases as a quadratic function of time, i.e., ⟨ | X ( t ) | 2 ⟩ ∼ t 2 . This dispersion is markedly faster than Taylor’s single-particle dispersion theory which predicts that the variance of passive tracers grows linearly with time for large t. Our results imply that the wave motion significantly enhances the dispersion of fluid particles. We show that this super-diffusive behavior is a result of the long-term correlation of the Lagrangian velocities of fluid parcels on the free surface.

scholarly journals Method to characterize directional changes in Arctic sea ice drift and associated deformation due to synoptic atmospheric variations using Lagrangian dispersion statistics

2017 ◽  
Vol 11 (4) ◽  
pp. 1707-1731 ◽  
Author(s):  
Jennifer V. Lukovich ◽  
Cathleen A. Geiger ◽  
David G. Barber
Keyword(s):  
Sea Ice ◽  
Single Particle ◽  
Weather Forecasting ◽  
Particle Dispersion ◽  
Arctic Sea Ice ◽  
Maximum Pressure ◽  
Dynamical Regime ◽  
Scaling Exponent ◽  
Ice Drift ◽  
Sea Ice Drift

Abstract. A framework is developed to assess the directional changes in sea ice drift paths and associated deformation processes in response to atmospheric forcing. The framework is based on Lagrangian statistical analyses leveraging particle dispersion theory which tells us whether ice drift is in a subdiffusive, diffusive, ballistic, or superdiffusive dynamical regime using single-particle (absolute) dispersion statistics. In terms of sea ice deformation, the framework uses two- and three-particle dispersion to characterize along- and across-shear transport as well as differential kinematic parameters. The approach is tested with GPS beacons deployed in triplets on sea ice in the southern Beaufort Sea at varying distances from the coastline in fall of 2009 with eight individual events characterized. One transition in particular follows the sea level pressure (SLP) high on 8 October in 2009 while the sea ice drift was in a superdiffusive dynamic regime. In this case, the dispersion scaling exponent (which is a slope between single-particle absolute dispersion of sea ice drift and elapsed time) changed from superdiffusive (α ∼ 3) to ballistic (α ∼ 2) as the SLP was rounding its maximum pressure value. Following this shift between regimes, there was a loss in synchronicity between sea ice drift and atmospheric motion patterns. While this is only one case study, the outcomes suggest similar studies be conducted on more buoy arrays to test momentum transfer linkages between storms and sea ice responses as a function of dispersion regime states using scaling exponents. The tools and framework developed in this study provide a unique characterization technique to evaluate these states with respect to sea ice processes in general. Application of these techniques can aid ice hazard assessments and weather forecasting in support of marine transportation and indigenous use of near-shore Arctic areas.

scholarly journals Assumptions about footprint layer heights influence the quantification of emission sources: a case study for Cyprus

2017 ◽  
Vol 17 (18) ◽  
pp. 10955-10967 ◽  
Author(s):  
Imke Hüser ◽  
Hartwig Harder ◽  
Angelika Heil ◽  
Johannes W. Kaiser
Keyword(s):  
Mixing Layer ◽  
Particle Dispersion ◽  
Reasonable Assumption ◽  
Night Time ◽  
Meteorological Model ◽  
Source Contributions ◽  
Time Sensitivity ◽  
Tracer Particles ◽  
Constant Height ◽  
The Impact

Abstract. Lagrangian particle dispersion models (LPDMs) in backward mode are widely used to quantify the impact of transboundary pollution on downwind sites. Most LPDM applications count particles with a technique that introduces a so-called footprint layer (FL) with constant height, in which passing air tracer particles are assumed to be affected by surface emissions. The mixing layer dynamics are represented by the underlying meteorological model. This particle counting technique implicitly assumes that the atmosphere is well mixed in the FL. We have performed backward trajectory simulations with the FLEXPART model starting at Cyprus to calculate the sensitivity to emissions of upwind pollution sources. The emission sensitivity is used to quantify source contributions at the receptor and support the interpretation of ground measurements carried out during the CYPHEX campaign in July 2014. Here we analyse the effects of different constant and dynamic FL height assumptions. The results show that calculations with FL heights of 100 and 300 m yield similar but still discernible results. Comparison of calculations with FL heights constant at 300 m and dynamically following the planetary boundary layer (PBL) height exhibits systematic differences, with daytime and night-time sensitivity differences compensating for each other. The differences at daytime when a well-mixed PBL can be assumed indicate that residual inaccuracies in the representation of the mixing layer dynamics in the trajectories may introduce errors in the impact assessment on downwind sites. Emissions from vegetation fires are mixed up by pyrogenic convection which is not represented in FLEXPART. Neglecting this convection may lead to severe over- or underestimations of the downwind smoke concentrations. Introducing an extreme fire source from a different year in our study period and using fire-observation-based plume heights as reference, we find an overestimation of more than 60  % by the constant FL height assumptions used for surface emissions. Assuming a FL that follows the PBL may reproduce the peak of the smoke plume passing through but erroneously elevates the background for shallow stable PBL heights. It might thus be a reasonable assumption for open biomass burning emissions wherever observation-based injection heights are not available.

scholarly journals Deceleration of droplets that glide along the free surface of a bath

2016 ◽  
Vol 803 ◽  
pp. 313-331 ◽  
Author(s):  
Jacob Hale ◽  
Caleb Akers
Keyword(s):  
Free Surface ◽  
Wave Motion ◽  
Droplet Diameter ◽  
Reynolds Numbers ◽  
Viscous Drag ◽  
Bath Surface ◽  
Exponential Rate ◽  
Viscous Coupling ◽  
Air Film ◽  
O 10

A droplet obliquely impacting a bath surface of the same fluid can traverse along the interface while slowing at an exponential rate. The droplet rests on a thin film of air, deforms the bath surface creating a dimple and travels along the surface similarly to a wave pulse. Viscous coupling of the droplet and bath surfaces through the air film leads to viscous drag on the bath and perturbs the wave motion of the otherwise free surface. Even though the Reynolds numbers are greater than unity ($\mathit{Re}\,O(10{-}100)$), we show that the droplet’s deceleration is only due to viscous coupling through the air gap. The rate of deceleration is found to increase linearly with droplet diameter.

Hydrodynamic Analysis of Submarine of the Wave Glider

2013 ◽  
Vol 834-836 ◽  
pp. 1505-1511 ◽  
Author(s):  
Li Juan Jia ◽  
Xuan Ming Zhang ◽  
Zhan Feng Qi ◽  
Yu Feng Qin ◽  
Xiu Jun Sun
Keyword(s):  
Wave Motion ◽  
Inflection Point ◽  
Design Parameters ◽  
Hydrodynamic Characteristics ◽  
Hydrodynamic Analysis ◽  
Critical Design ◽  
Ocean Wave Energy ◽  
Lift Curve ◽  
Wave Glider

Wave glider harvests the abundant ocean wave energy for long term ocean cruising due to its particular two-part architecture. Its submerged part named glider converts vertical fluctuation of waves to horizontally forward propulsion. Because of the uncertainty of the ocean condition and irregularity of its wave motion, the design parameters of the submerged glider vary in a confined range in the state of art design models. In order to indicate the hydrodynamic characteristics and summarize the dynamic law of the submerged glider with different design parameters, this paper concentrates on three critical design details: profile of the wings, interval space of the arrayed multiple flapping wings and maximum rotating angle of wings, and performs the corresponding CFD analysis. Finally, we conclude that the lift curve of NACA0006 and plate profile is almost the same with small waves at sea, but NACA0006 profile can generate much larger forward lift than the plate profile with seawater velocity up to 0.5m/s; Decreasing space of intermittent causes more obvious decrement of forward lift while space of intermittent overpasses the inflection point at 20cm; With the decrement of the maximum rotating angle, the forward lift occurs to take a sharp decline if the angle strides the inflection point.

Parameterization of dispersion in two-dimensional turbulence

2001 ◽  
Vol 439 ◽  
pp. 279-303 ◽  
Author(s):  
C. PASQUERO ◽  
A. PROVENZALE ◽  
A. BABIANO
Keyword(s):  
Velocity Distribution ◽  
Single Particle ◽  
Stochastic Models ◽  
Particle Dispersion ◽  
Turbulent Dispersion ◽  
Two Dimensional ◽  
Component Process ◽  
Velocity Autocorrelation ◽  
Coherent Vortices ◽  
Non Gaussian

We investigate the performance of standard stochastic models of single-particle dispersion in two-dimensional turbulence. Owing to the presence of coherent vortices, particle dispersion in two-dimensional turbulence is characterized by a non-Gaussian velocity distribution and a non-exponential velocity autocorrelation, and it cannot be properly captured by either linear or nonlinear stochastic models with a single component process. Based on physical and dynamical considerations, we introduce a family of two-process stochastic models that provide a better parameterization of turbulent dispersion in rotating barotropic flows.

scholarly journals Atmospheric mercury observations from Antarctica: seasonal variation and source and sink region calculations

2012 ◽  
Vol 12 (7) ◽  
pp. 3241-3251 ◽  
Author(s):  
K. A. Pfaffhuber ◽  
T. Berg ◽  
D. Hirdman ◽  
A. Stohl
Keyword(s):  
Southern Hemisphere ◽  
Dispersion Model ◽  
Particle Dispersion ◽  
Atmospheric Mercury ◽  
The Arctic ◽  
Research Station ◽  
The Mean ◽  
The Antarctic ◽  
Source And Sink

Abstract. Long term atmospheric mercury measurements in the Southern Hemisphere are scarce and in Antarctica completely absent. Recent studies have shown that the Antarctic continent plays an important role in the global mercury cycle. Therefore, long term measurements of gaseous elemental mercury (GEM) were initiated at the Norwegian Antarctic Research Station, Troll (TRS) in order to improve our understanding of atmospheric transport, transformation and removal processes of GEM. GEM measurements started in February 2007 and are still ongoing, and this paper presents results from the first four years. The mean annual GEM concentration of 0.93 ± 0.19 ng m−3 is in good agreement with other recent southern-hemispheric measurements. Measurements of GEM were combined with the output of the Lagrangian particle dispersion model FLEXPART, for a statistical analysis of GEM source and sink regions. It was found that the ocean is a source of GEM to TRS year round, especially in summer and fall. On time scales of up to 20 days, there is little direct transport of GEM to TRS from Southern Hemisphere continents, but sources there are important for determining the overall GEM load in the Southern Hemisphere and for the mean GEM concentration at TRS. Further, the sea ice and marginal ice zones are GEM sinks in spring as also seen in the Arctic, but the Antarctic oceanic sink seems weaker. Contrary to the Arctic, a strong summer time GEM sink was found, when air originates from the Antarctic plateau, which shows that the summertime removal mechanism of GEM is completely different and is caused by other chemical processes than the springtime atmospheric mercury depletion events. The results were corroborated by an analysis of ozone source and sink regions.

The stability of unsteady axisymmetric incompressible pipe flow close to a piston. Part 2. Experimental investigation and comparison with computation

1971 ◽  
Vol 50 (4) ◽  
pp. 645-655 ◽  
Author(s):  
M. D. Hughes ◽  
J. H. Gerrard
Keyword(s):  
Free Surface ◽  
Pipe Flow ◽  
Critical Reynolds Number ◽  
Reynolds Numbers ◽  
Radial Component ◽  
Tube Diameter ◽  
Ring Vortex ◽  
Tracer Particles ◽  
The Stability ◽  
Cylindrical Reservoir

Flow visualization has been used quantitatively to determine the flow relative to a piston and a free surface started from rest. The discharge of water from a cylindrical reservoir was investigated. Flow with a free surface started from rest was found to have a critical Reynolds number (based on tube diameter and surface speed) of about 450 above which a ring vortex was produced just below the surface.Measurements at Reynolds numbers of 525 and 1200 were compared with computations made by the methods described in Part 1. The computed drift of tracer particles agreed well with observed values. The largest discrepancies occurred in the radial component of the drift in the early stages of the motion and amounted to 2½% of the tube diameter.

Use of various functions to analyse the fertiliser responses of maize ( Zea mays L.) hybrids in long-term experiments

2006 ◽  
Vol 54 (1) ◽  
pp. 1-14 ◽  
Author(s):  
Z. Berzsenyi ◽  
Q. L. Dang
Keyword(s):  
Analysis Of Variance ◽  
Response Pattern ◽  
Root Function ◽  
Quadratic Function ◽  
Maize Yield ◽  
Maximum Point ◽  
Square Root ◽  
Maize Hybrids ◽  
Year Effect

The effect of various fertiliser treatments on the yield of maize hybrids was studied on the basis of 26 years of data obtained in a long-term bifactorial split-plot experiment set up in 1967. The seven treatments (NPK ratio 2:1:1) applied were as follows (rates per hectare): 1. Control (no fertiliser), 2. 100 kg NPK, 3. 200 kg NPK, 4. 300 kg NPK, 5. 400 kg NPK, 6. 600 kg NPK, 7. 800 kg NPK. The maize was grown with the conventional cultivation techniques in continuous cropping. The results of analyses carried out with three different methods (analysis of variance, cumulative yield analysis and regression analysis) all indicated that under the given conditions the yield of maize hybrids was highest at an NPK fertiliser rate of 200-400 kg ha -1 . The effect of fertilisation on the maize yield was significant in 21 of the 26 years. Combined analysis of variance for the years showed that the year effect (quantity of rainfall) had the greatest effect on the maize yield, but although the year effect had a fundamental effect on the yield level it did not influence the fertiliser response pattern. The fertiliser responses of the maize hybrids were described by fitting four types of functions (quadratic, square root, inverse exponential, linear-plateau) to the yield data. It was found that when selecting the best function a consideration of the regression deviations (measured yield - calculated yield) was just as important as the coefficient of determination (R 2 ). In 12 of the 26 years the fitting of the quadratic function was not significant and overestimated the fertilisation optimum. The fertiliser response curve generally has a broad maximum which is far better described by the square root function than by the quadratic. If the fertiliser response pattern includes a depressive phase, a square root function should definitely be used in place of the quadratic function. If the maximum of the response surface forms a plateau (as opposed to a maximum point) a linear-plateau function or an inverse exponential function can be recommended. In the present work the linear-plateau function gave the best results.

Long-Term Genomic Instability in Human Lymphocytes Induced by Single-Particle Irradiation

2001 ◽  
Vol 155 (1) ◽  
pp. 122-126 ◽  
Author(s):  
M. A. Kadhim ◽  
S. J. Marsden ◽  
A. M. Malcolmson ◽  
M. Folkard ◽  
D. T. Goodhead ◽  
...  
Keyword(s):  
Genomic Instability ◽  
Single Particle ◽  
Human Lymphocytes ◽  
Particle Irradiation
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