scholarly journals Image-Based Bed Material Mapping of a Large River

Water ◽  
2020 ◽  
Vol 12 (3) ◽  
pp. 916
Author(s):  
Alexander A. Ermilov ◽  
Sándor Baranya ◽  
Gergely T. Török
Keyword(s):  
Sampling Methods ◽  
Surface Composition ◽  
Large River ◽  
Danube River ◽  
Size Distributions ◽  
Analysis Method ◽  
Fluvial Systems ◽  
Grain Size Distributions ◽  
Material Grain Size ◽  
Bed Material

The composition or bed material plays a crucial role in the physical hydromorphological processes of fluvial systems. However, conventional bed material sampling methods provide only pointwise information, which can be inadequate when investigating large rivers of inhomogeneous bed material characteristics. In this study, novel, image-based approaches are implemented to gain areal information of the bed surface composition using two different techniques: monocular and stereo computer vision. Using underwater videos, captured in shorter reaches of the Hungarian Danube River, a comparison of the bed material grain size distributions from conventional physical samplings and the ones reconstructed from the images is carried out. Moreover, an attempt is made to quantify bed surface roughness, using the so-called Structure from Motion image analysis method. Practical aspects of the applicability of image-based bed material mapping are discussed and future improvements towards an automatized mapping methodology are outlined.

scholarly journals Experimental investigation of time-dependent local scour downstream of a stepped channel

Water SA ◽  
2019 ◽  
Vol 45 (3 July) ◽  
Author(s):  
Aysegul Ozgenc Aksoy ◽  
Mustafa Dogan
Keyword(s):  
Temporal Variation ◽  
Particle Number ◽  
Experimental Tests ◽  
Local Scour ◽  
Coefficient Of Determination ◽  
Size Distributions ◽  
Grain Size Distributions ◽  
Different Grain Size ◽  
Experimental Findings ◽  
Bed Material

In this study, temporal variation of local scour occurring at the downstream part of the stepped channel were investigated experimentally. The experimental tests were carried out in a stepped flume with a height of 2.4 m. The width of the rectangular flume was 0.10 m and the length of the stilling basin was 2.12 m. Bed material was placed in a sediment box with a height of 24 cm and length of 2.48 m, without any compaction. Experiments were carried out by using bed material of 4 different grain size distributions, 2 different sill heights and 6 different flow rates. Two empirical equations which include Shields parameter (θ) and densimetric Froude particle number (Fd) were proposed by using the experimental findings to predict the temporal variation of the scour depth. The R2 (coefficient of determination) values were computed for both proposed equations as 0.866 and 0.865. The scatter index (SI) values were also determined and computed as 8.73% and 8.25%. The fit of the equations was also determined by means of Fisher’s test.

Statistical Characterization of Grain-Size Distributions in Sandy Fluvial Systems

2010 ◽  
Vol 80 (2) ◽  
pp. 184-192 ◽  
Author(s):  
E. A. Hajek ◽  
S. V. Huzurbazar ◽  
D. Mohrig ◽  
R. M. Lynds ◽  
P. L. Heller
Keyword(s):  
Grain Size ◽  
Size Distributions ◽  
Fluvial Systems ◽  
Statistical Characterization ◽  
Grain Size Distributions

scholarly journals OBTAINING AND TESTING COARSE GRAIN SIZE DISTRIBUTIONS FROM PHOTOGRAPHIC GRID COUNTS

2017 ◽  
Vol 50 (1) ◽  
pp. 345
Author(s):  
S. Karalis ◽  
A. Aytousmis ◽  
A. Iordanou ◽  
G. Karakostas ◽  
K. Charatsis ◽  
...  
Keyword(s):  
Grain Size ◽  
Standard Method ◽  
Field Work ◽  
Coarse Grain ◽  
Size Distributions ◽  
Site Specific ◽  
Alluvial Rivers ◽  
Grid Sampling ◽  
Grain Size Distributions ◽  
Bed Material

The grain size distribution (GSD) of surface bed material in alluvial rivers is of interest in many geological, ecological and engineering applications. In this work, which is a part of our broader Ph.D research in Vouraikos river on sediment transport, we are testing the possibility of obtaining such a distribution from photographs taken at the field (grid sampling), compared with the standard method which is the “pebble count”. We have also examined and quantified the errors resulting from radial distortion of the photographs. The motive of the work was to explore the opportunity of substituting field work for laboratory work. Results show that for this method to give reliable results, a better knowledge of the site-specific conditions is needed, which, in turn, requires more field work.

scholarly journals Effect of Strain-Induced Precipitation on the Recrystallization Kinetics in a Model Alloy

2021 ◽  
Author(s):  
Mo Ji ◽  
Martin Strangwood ◽  
Claire Davis
Keyword(s):  
Grain Size ◽  
Size Distribution ◽  
Grain Size Distribution ◽  
Avrami Exponent ◽  
Model Alloy ◽  
Size Distributions ◽  
Recrystallization Kinetics ◽  
Grain Size Distributions ◽  
Recrystallized Grain Size ◽  
Nb Addition

AbstractThe effects of Nb addition on the recrystallization kinetics and the recrystallized grain size distribution after cold deformation were investigated by using Fe-30Ni and Fe-30Ni-0.044 wt pct Nb steel with comparable starting grain size distributions. The samples were deformed to 0.3 strain at room temperature followed by annealing at 950 °C to 850 °C for various times; the microstructural evolution and the grain size distribution of non- and fully recrystallized samples were characterized, along with the strain-induced precipitates (SIPs) and their size and volume fraction evolution. It was found that Nb addition has little effect on recrystallized grain size distribution, whereas Nb precipitation kinetics (SIP size and number density) affects the recrystallization Avrami exponent depending on the annealing temperature. Faster precipitation coarsening rates at high temperature (950 °C to 900 °C) led to slower recrystallization kinetics but no change on Avrami exponent, despite precipitation occurring before recrystallization. Whereas a slower precipitation coarsening rate at 850 °C gave fine-sized strain-induced precipitates that were effective in reducing the recrystallization Avrami exponent after 50 pct of recrystallization. Both solute drag and precipitation pinning effects have been added onto the JMAK model to account the effect of Nb content on recrystallization Avrami exponent for samples with large grain size distributions.

The volcanological significance of deep-sea ash layers associated with ignimbrites

1980 ◽  
Vol 117 (5) ◽  
pp. 425-436 ◽  
Author(s):  
R. S. J. Sparks ◽  
T. C. Huang
Keyword(s):  
Deep Sea ◽  
Eastern Mediterranean ◽  
Eruption Column ◽  
Size Distributions ◽  
Ash Fall ◽  
Column Collapse ◽  
Median Diameter ◽  
Grain Size Distributions ◽  
Bimodal Grain Size ◽  
Fall Deposits

SummaryMany volcanic ash layers preserved in deep-sea sediments are the products of large magnitude ignimbrite eruptions. The characteristics of such co-ignimbrite ash-fall deposits are illustrated by two layers from the Eastern Mediterranean: the Minoan ash, Santorini, and the Campanian ash, Italy. These layers are divisible into a coarse lower unit and a fine upper unit in proximal cores. Both layers also show striking bimodal grain size distributions in more distal cores. The coarser mode decreases in median diameter with distance from source whereas the finer mode shows no lateral variation. These features are interpreted in terms of a model for ignimbrite formation by eruption column collapse. Comparable volumes of ignimbrite and associated air-fall ejecta are produced.

Grain Growth in Nanocrystalline Nickel

1999 ◽  
Vol 580 ◽  
Author(s):  
G.D. Hibbard ◽  
U. Erb ◽  
K.T. Aust ◽  
G. Palumbo
Keyword(s):  
Thermal Stability ◽  
Grain Size ◽  
Grain Growth ◽  
Size Distributions ◽  
Nanocrystalline Nickel ◽  
Scanning Calorimetry ◽  
Solute Content ◽  
Grain Size Distributions ◽  
Thermal Stability Of ◽  
Total Solute Content

AbstractIn this study, the effect of grain size distribution on the thermal stability of electrodeposited nanocrystalline nickel was investigated by pre-annealing material such that a limited amount of abnormal grain growth was introduced. This work was done in an effort to understand the previously reported, unexpected effect, of increasing thermal stability with decreasing grain size seen in some nanocrystalline systems. Pre-annealing produced a range of grain size distributions in materials with relatively unchanged crystallographic texture and total solute content. Subsequent thermal analysis of the pre-annealed samples by differential scanning calorimetry showed that the activation energy of further grain growth was unchanged from the as-deposited nanocrystalline nickel.

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