scholarly journals Armor breakup and reformation in a degradational laboratory experiment: detailed measurements of spatial and temporal changes of the bed surface texture

2016 ◽  
Author(s):  
C. Orru ◽  
A. Blom ◽  
W.S.J. Uijttewaal
Keyword(s):  
Laboratory Experiment ◽  
Sediment Supply ◽  
Sudden Increase ◽  
Normal Flow ◽  
Flow Conditions ◽  
Initial Stage ◽  
The Reformation ◽  
Spatial And Temporal Changes ◽  
Sand And Gravel ◽  
Slope Adjustment

Abstract. Armor breakup and reformation was studied in a laboratory experiment using a trimodal mixture composed of sand and gravel. The armor was formed in the initial stage of the experiment under conditions without sediment supply. Higher flow conditions led to the breakup of the mobile armor and the reformation of a new coarser armor. The breakup initially induced a fining due to the exposure of the finer substrate, which was accompanied by a sudden increase of the local sediment transport rate, followed by the formation of an armor that was coarser than the initial one. The reformation of the armor was due to the supply of coarse material from the upstream degrading reach and the presence of gravel in the original substrate sediment. Provided that the gravel supply from upstream suffices for armor reformation, armor breakup enables slope adjustment such that the new steady state is closer to normal flow conditions.

scholarly journals Armor breakup and reformation in a degradational laboratory experiment

2016 ◽  
Vol 4 (2) ◽  
pp. 461-470 ◽  
Author(s):  
Clara Orrú ◽  
Astrid Blom ◽  
Wim S. J. Uijttewaal
Keyword(s):  
Laboratory Experiment ◽  
Sediment Supply ◽  
Sudden Increase ◽  
Initial Stage ◽  
The Reformation ◽  
Mean Grain Size ◽  
The Mean ◽  
Bed Slope ◽  
Slope Adjustment ◽  
Spatial Transition

Abstract. Armor breakup and reformation was studied in a laboratory experiment using a trimodal mixture composed of a 1 mm sand fraction and two gravel fractions (6 and 10 mm). The initial bed was characterized by a stepwise downstream fining pattern (trimodal reach) and a downstream sand reach, and the experiment was conducted under conditions without sediment supply. In the initial stage of the experiment an armor formed over the trimodal reach. The formation of the armor under partial transport conditions led to an abrupt spatial transition in the bed slope and in the mean grain size of the bed surface, as such showing similar results to a previous laboratory experiment conducted with a bimodal mixture. The focus of the current analysis is to study the mechanisms of armor breakup. After an increase in flow rate the armor broke up and a new coarser armor quickly formed. The breakup initially induced a bed surface fining due to the exposure of the finer substrate, which was accompanied by a sudden increase in the sediment transport rate, followed by the formation of an armor that was coarser than the initial one. The reformation of the armor was enabled by the supply of coarse material from the upstream degrading reach and the presence of gravel in the original substrate sediment. Here armor breakup and reformation enabled slope adjustment such that the new steady state was closer to normal flow conditions.

scholarly journals Export of <sup>134</sup>Cs and <sup>137</sup>Cs in the Fukushima river systems at heavy rains by Typhoon Roke in September 2011

2013 ◽  
Vol 10 (2) ◽  
pp. 2767-2790 ◽  
Author(s):  
S. Nagao ◽  
M. Kanamori ◽  
S. Ochiai ◽  
S. Tomihara ◽  
K. Fukushi ◽  
...  
Keyword(s):  
Nuclear Power ◽  
Heavy Rain ◽  
Rain Event ◽  
Normal Flow ◽  
Flow Conditions ◽  
Pulse Input ◽  
Heavy Rain Event ◽  
Coastal Marine ◽  
Rain Events ◽  
Heavy Rains

Abstract. Effects of a heavy rain event on radiocesium export were studied at stations on the Natsui River and the Same River in Fukushima Prefecture, Japan after Typhoon Roke during 21–22 September 2011, six months after the Fukushima Daiichi Nuclear Power Plant accident. Radioactivity of 134Cs and 137Cs in river waters was 0.011–0.098 Bq L−1 at normal flow conditions during July–September in 2011, but it increased to 0.85 Bq L−1 in high flow conditions by heavy rains occurring with the typhoon. The particulate fractions of 134Cs and 137Cs were 21–56% in the normal flow condition, but were close to 100% after the typhoon. These results indicate that the pulse input of radiocesium associated with suspended particles from land to coastal ocean occurred by the heavy rain event. Export flux of 134Cs and 137Cs by the heavy rain accounts for 30–50% of annual radiocesium flux in 2011. Results show that rain events are one factor controlling the transport and dispersion of radiocesium in river watersheds and coastal marine environments.

scholarly journals Nonlinear Flow Behavior in Packed Beds of Natural and Variably Graded Granular Materials

2019 ◽  
Vol 131 (3) ◽  
pp. 957-983 ◽  
Author(s):  
J. H. van Lopik ◽  
L. Zazai ◽  
N. Hartog ◽  
R. J. Schotting
Keyword(s):  
Grain Size ◽  
Granular Materials ◽  
Flow Behavior ◽  
Nonlinear Flow ◽  
Packed Beds ◽  
Size Distributions ◽  
Flow Conditions ◽  
Grain Size Distributions ◽  
Sand And Gravel ◽  
Nonlinear Flow Behavior

AbstractUnder certain flow conditions, fluid flow through porous media starts to deviate from the linear relationship between flow rate and hydraulic gradient. At such flow conditions, Darcy’s law for laminar flow can no longer be assumed and nonlinear relationships are required to predict flow in the Forchheimer regime. To date, most of the nonlinear flow behavior data is obtained from flow experiments on packed beds of uniformly graded granular materials (Cu = d60/d10 < 2) with various average grain sizes, ranging from sands to cobbles. However, natural deposits of sand and gravel in the subsurface could have a wide variety of grain size distributions. Therefore, in the present study we investigated the impact of variable grain size distributions on the extent of nonlinear flow behavior through 18 different packed beds of natural sand and gravel deposits, as well as composite filter sand and gravel mixtures within the investigated range of uniformity (2.0 < Cu < 17.35) and porosity values (0.23 < n < 0.36). Increased flow resistance is observed for the sand and gravel with high Cu values and low porosity values. The present study shows that for granular material with wider grain size distributions (Cu > 2), the d10 instead of the average grain size (d50) as characteristic pore length should be used. Ergun constants A and B with values of 63.1 and 1.72, respectively, resulted in a reasonable prediction of the Forchheimer coefficients for the investigated granular materials.

Filtration characteristics of Clarke-Bumpus samplers

1965 ◽  
Vol 16 (3) ◽  
pp. 281 ◽  
Author(s):  
DJ Tranter ◽  
AC Heron
Keyword(s):  
Flow Rate ◽  
Water Channel ◽  
Filtration Coefficient ◽  
Normal Flow ◽  
Flow Conditions ◽  
Measured Distance

The Australian and American models of the sampler were tested at water velocities up to 3.5 kt. A calibration tank designed to simulate normal flow conditions through the flowmeter was used to calibrate flowmeter rate against flow rate measured at a 90� V-notch exit. This calibration was used to determine the discharge through samplers towed for a measured distance in a water channel. Thus the filtration characteristics of the samplers were examined. The filtration coefficient for the American sampler without a net averaged 88 %, compared with 92% for the Australian sampler. Australian nets reduced the filtration coefficient of the Australian sampler by 2-15 %. The American net had little effect on the filtration coefficient of the American sampler. The filtration coefficient varied with mesh aperture and clogging but was largely independent of towing velocity. Other experiments suggested that net length was less important, and the flow of water around the net more important, than previously thought. Above approximately 1 kt, the calibration value was nearly independent of velocity and hardly altered with net attachment no matter how fine the mesh.

Avoidance of Nonanadromous Fish Passage Impedance Caused by Highway Culverts

1996 ◽  
Vol 1559 (1) ◽  
pp. 34-41
Author(s):  
G. Michael Fitch
Keyword(s):  
Flow Velocity ◽  
Fish Passage ◽  
Hydraulic Efficiency ◽  
Normal Flow ◽  
Flow Conditions ◽  
Term Survival ◽  
Wild Trout ◽  
Trout Streams ◽  
Water Depths

Highway culverts may hinder the normal migrations of various trout species in wild trout streams through increased flow velocity, shallow water depths, increased turbulence, and perching. This can impede migrational movements, affecting the genetic diversity and long-term survival of some species. Often, the proper installation of culverts can reduce the adverse effects on fish while maintaining hydraulic efficiency. This study characterized the problems with existing culverts to develop guidelines for the future use of culverts in areas with high gradient streams. Installation criteria will ideally limit the use of bridges where culverts are appropriate, and eliminate the use of culverts where they would create fish passage problems. This will reduce installation, maintenance, and retrofitting costs. The study concluded that culverts can be considered the primary option for crossing trout streams if the culvert can be placed on the same slope as that of the streambed, the slope of the stream is less than 3 percent, the flow velocity does not exceed 1.2 m/sec under normal flow conditions, and the barrel of the culvert can be properly countersunk at the outlet to prevent perching. Bridges should be used at these crossings if any of these criteria cannot be met. The study also concluded that baffles should not be used to control streamflow velocities in newly installed culverts, and concrete aprons should not be used at culvert outlets.

scholarly journals Export of <sup>134</sup> Cs and <sup>137</sup> Cs in the Fukushima river systems at heavy rains by Typhoon Roke in September 2011

2013 ◽  
Vol 10 (10) ◽  
pp. 6215-6223 ◽  
Author(s):  
S. Nagao ◽  
M. Kanamori ◽  
S. Ochiai ◽  
S. Tomihara ◽  
K. Fukushi ◽  
...  
Keyword(s):  
Nuclear Power ◽  
Heavy Rain ◽  
Coastal Ocean ◽  
Rain Event ◽  
Normal Flow ◽  
Flow Conditions ◽  
Pulse Input ◽  
Heavy Rain Event ◽  
Coastal Marine ◽  
Heavy Rains

Abstract. At stations on the Natsui River and the Same River in Fukushima Prefecture, Japan, effects of a heavy rain event on radiocesium export were studied after Typhoon Roke during 21–22 September 2011, six months after the Fukushima Dai-ichi Nuclear Power Plant accident. Radioactivity of 134Cs and 137Cs in river waters was 0.009–0.098 Bq L−1 in normal flow conditions during July–September 2011, but it increased to 0.85 Bq L−1 in high flow conditions because of heavy rains occurring with the typhoon. The particulate fractions of 134Cs and 137Cs were 21–56% of total radiocesium in the normal flow condition, but were close to 100% after the typhoon. These results indicate that the pulse input of radiocesium associated with suspended particles from land to coastal ocean occurred because of the heavy rain event. Export flux of 134Cs and 137Cs attributable to the heavy rain accounts for 30–50% of the annual radiocesium flux from inland to coastal ocean region in 2011. Results show that rain events are one factor contributing to the transport and dispersion of radiocesium in river watersheds and coastal marine environments.

Flood caused by driftwood accumulation at a bridge

2017 ◽  
Vol 8 (5) ◽  
pp. 466-477 ◽  
Author(s):  
Nobuaki Kimura ◽  
Akira Tai ◽  
Akihiro Hashimoto
Keyword(s):  
Climate Change ◽  
Numerical Simulation ◽  
Laboratory Experiment ◽  
High Flow ◽  
Extreme Weather Events ◽  
Mountainous Area ◽  
Flow Conditions ◽  
Key Factors ◽  
Sph Method ◽  
Content Type

Purpose Extreme weather events introduced by climate change have been frequent across the world for the past decade. For example, Takeda City, a mountainous area in the south-western Japan, experienced a severe river flood event caused by the factors of high flow, presence of bridges and driftwood accumulation in July 2012. This study aims to focus on this event (hereafter, Takeda flood) because the unique factors of driftwood and bridges were involved. In the Takeda flood, high flow, driftwood and bridge were the potential key factors that caused the flood. The authors studied to reveal the physical processes of the Takeda flood. Design/methodology/approach The authors conducted a fundamental laboratory experiment with a miniature bridge, open channel flow and idealized driftwood accumulation. They also performed a numerical simulation by using a smoothed particle hydrodynamics (SPH) method, which can treat fluid as particle elements. This model was chosen because the SPH method is capable of treating a complex flow such as a spray of water around a bridge. Findings The numerical simulation successfully reproduced the bridge- and driftwood-induced floods of the laboratory experiment. Then, the contribution of the studied key factors to the flood mechanism based on the fluid forces generated by high flow, bridge and driftwood (i.e. pressure distributions) was quantitatively assessed. The results showed that the driftwood accumulation and high flow conditions are potentially important factors that can cause a severe flood like the Takeda flood. Originality/value Simulated results with high flow conditions may be helpful to consider the countermeasure for future floods under climate change even though the test was simple and fundamental.

Effect on Cardiac Contractile Force from Addition of Cations and Oxygen to Iohexol

1993 ◽  
Vol 34 (4) ◽  
pp. 381-387 ◽  
Author(s):  
J. Besjakov ◽  
L. Bååth ◽  
T. Almén ◽  
A. N. Øksendal
Keyword(s):  
Adverse Effect ◽  
Coronary Arteries ◽  
Perfusion Pressure ◽  
Rabbit Heart ◽  
Contractile Force ◽  
Normal Flow ◽  
Flow Conditions ◽  
Cardiac Contractile ◽  
Sodium Calcium ◽  
Potassium Magnesium

The coronary arteries of the isolated rabbit heart were perfused with different contrast media (CM). The effects on cardiac contractile force (CF) from enriching iohexol solutions with sodium, calcium, potassium, magnesium and oxygen were investigated. The effects were studied during normal and reduced perfusion pressure; the latter was intended to simulate flow conditions distal to proximal stenotic processes of the coronary arteries. By adding the above mentioned cations to iohexol (175 mg I/ml) the smallest influence on CF was found when the CM contained 30 mM NaCl, 0.3 mM CaCl2, 0.9 mM KCl and 0.3 mM MgCl2 and this influence on CF was significantly less than caused by iohexol with 30 mM NaCl (p ≤ 0.01). The influence on CF was further reduced when this iohexol solution was oxygenated with 100% oxygen (p ≤ 0.001). This modified iohexol solution caused a significantly smaller influence on CF than the low-osmotic media iohexol, iopamiro, ioversol and ioxaglate (p ≤ 0.001). Ioxaglate caused the greatest decrease in CF of all the CM (p ≤ 0.001) and to a greater extent during reduced flow than during normal flow (p ≤ 0.01). In conclusion, iohexol enriched with a balanced electrolyte solution and saturated with oxygen had a smaller adverse effect on contractility than iohexol, iopamidol, ioversol and ioxaglate.

scholarly journals Remodeling of Resistance Arteries in Renal Failure: Effect of Endothelin Receptor Blockade

2001 ◽  
Vol 12 (10) ◽  
pp. 2040-2050 ◽  
Author(s):  
KERSTIN AMANN ◽  
GABRIEL MIL TENBERGER-MIL TENYI ◽  
AURELIA SIMONOVICIENE ◽  
ANDREAS KOCH ◽  
STEPHAN ORTH ◽  
...  
Keyword(s):  
Renal Failure ◽  
Blood Flow ◽  
High Flow ◽  
Mesenteric Arteries ◽  
Low Flow ◽  
Normal Flow ◽  
Flow Conditions ◽  
First Order ◽  
The Media ◽  
Intimal Thickness

Abstract. Remodeling of vessels is a known feature of renal failure, but it is unclear whether this represents an appropriate or inappropriate response to the known changes in blood flow, shear stress, and wall tension. To investigate remodeling in response to variations in blood flow, first-order mesenteric arteries were exposed to high- and low-flow conditions via the ligation of second-order branches, according to the technique described by Pour-ageaud and De Mey. The resulting changes in vessel geometric features, relative proportions of intima and media, submicroscopic structure, and immunostaining for proliferating cell nuclear antigen (PCNA), endothelin-1 (ET-1), and ETAreceptors were assessed in first-order mesenteric arteries under low-flow and high-flow conditions. Subtotally nephrectomized (SNX) animals were compared with sham-operated rats. Animals either were left untreated or were treated with the ETAreceptor antagonist (ET-RA) LU-135252, because of suggestions in the literature that ET is involved in vascular remodeling in uremia. A highly significant increase in intimal thickness was noted in low-flow arteries (4.21 ± 1.39 μm) of SNX animals, compared with normal-flow arteries (2.06 ± 0.61 μm), but this increase was not observed in sham-operated rats (1.38 ± 0.77 in low-flow arteriesversus2.40 ± 0.35 μm in normal-flow arteries). The increase in intimal thickness in low-flow arteries was abrogated by ET-RA. The medial thickness was increased in untreated SNX animals (19.5 ± 3.61 μm), compared with sham-operated rats, and this increase was also prevented by ET-RA. The medial thickness was not affected by low flow in either sham-operated or SNX animals. In parallel, the number of PCNA-positive intimal cells was higher in low-flow, but not high-flow, arteries of SNX rats, compared with sham-operated rats. No significant change was observed in sham-operated animals. In the media, the number of PCNA-positive cells was higher in untreated SNX animals than in sham-operated rats. The number was even more markedly increased in high-flow, but not low-flow, vessels. This increase was abrogated by ET-RA. It is concluded that, in uremic animals, the response of the intima to low flow and the response of the media to high flow are exaggerated. Both responses are apparently mediated by ET.

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