Unidirectional to bidirectional subtidal sandwaves influenced by gradually decreasing steady flow velocity

1997 ◽  
Vol 134 (4) ◽  
pp. 557-561
Author(s):  
KATSUHIRO NAKAYAMA
Keyword(s):  
Grain Size ◽  
Flow Velocity ◽  
Steady Flow ◽  
Periodic Flow ◽  
Southwest Japan ◽  
Unit Thickness ◽  
Flow Components ◽  
Flow Velocities

Miocene subtidal sandwave deposits in southwest Japan were influenced by periodic flow and steady flow. The sandwave deposits can be divided into five units, based on lithofacies and thickness. In order of accretion, unit 1 consists of unidirectional sand bedforms without mud drapes, unit 2 of unidirectional sand bedforms with thin, discontinuous mud drapes, unit 3 of bidirectional sand bedforms with thin continuous mud drapes, and units 4 and 5 of relatively thinner and smaller bidirectional sand bedforms with continuous mud drapes. The thickness of units 1 to 3 increase progressively to 2.6 m, and units 4 to 5 subsequently decrease from 2.0 to 1.0 m. Variations between the units are due to differing combinations of periodic and steady flow velocities. Palaeoflow velocity is estimated from grain size and unit thickness. Depth-mean velocities of steady flow components gradually decrease from 0.72 ms−1 to 0.16 ms−1 with unit accumulation.

Intraoperative transesophageal assessment of coronary artery flow can predict 5 type myocardial infarction

2020 ◽  
Vol 41 (Supplement_2) ◽  
Author(s):  
A Zagatina ◽  
M Novikov ◽  
N Zhuravskaya ◽  
V Balakhonov ◽  
S Efremov ◽  
...  
Keyword(s):  
Myocardial Infarction ◽  
Cardiac Surgery ◽  
Coronary Artery ◽  
Flow Velocity ◽  
Coronary Flow ◽  
Index Number ◽  
Left Main ◽  
Coronary Flow Velocity ◽  
Before And After ◽  
Flow Velocities

Abstract Background Stenosis of a coronary artery results in an increase in flow velocity in the pathologic segment. Effective grafting should decrease the stenotic native coronary velocity according to hemodynamic law. The range of decreased velocity before and after cardiac surgery can hypothetically reflect the effectiveness of a graft. The aim of the study is to determine if measuring coronary flow velocity changes during coronary artery bypass grafting (CABG) can predict intraoperative myocardial infarction. Methods One hundred sixty-six (166) consecutive patients (121 men, 64±9 years old) referred for cardiac surgery, were prospectively included in the study. A standard basic perioperative transesophageal echocardiography (TEE) examination was performed with additional scans of the left main, left anterior descending (LAD), and circumflex (LCx) arteries' proximal segments. Measurements of coronary flow velocities were performed before and after grafting in the same sites of the arteries. The maximal value of cardiac troponin I (cTnI) after CABG and the additive criteria were accounted for in the analysis as it is described in the expert consensus document for Type 5 myocardial infarction (MI) definition. Results One hundred sixty-three patients (98%) had arterial hypertension, 28 patients (17%) had diabetes mellitus, 35 patients (21%) were currently smokers. The feasibility of coronary flow assessment during cardiac operations was 95%. Before grafting, the mean velocity in the left main artery was 91±49 cm/s, in LAD 101±35 cm/s, and in LCx 117±49 cm/s. There was a significant correlation between changes in coronary flow velocities during operation and the value of cTnI (R=0.34, p<0.0001). Ten patients met the criteria for Type 5 MI. There were no differences in age, body mass index, number of coronary arteries with stenoses, frequency of prior MI, ejection fraction or coronary flow velocity before surgery in patients with and without Type 5 MI. The group of patients with Type 5 MI had an increase in native artery velocities during surgery in comparison with patients without MI, who had a significant decrease in coronary flow velocity after grafting (30±48 vs. −10±30 cm/s; p<0.0006). Increases in native coronary velocities greater than 3 cm/s predicted Type 5 MI with 81% accuracy (sensitivity 88%, specificity 70%). Conclusion Coronary flow velocity assessment during cardiac surgery could predict an elevation of cardiac troponins and Type 5 MI. Funding Acknowledgement Type of funding source: None

scholarly journals Ice flow velocities over Vostok Subglacial Lake, East Antarctica, determined by 10 years of GNSS observations

2013 ◽  
Vol 59 (214) ◽  
pp. 315-326 ◽  
Author(s):  
A. Richter ◽  
D.V. Fedorov ◽  
M. Fritsche ◽  
S.V. Popov ◽  
V.Ya. Lipenkov ◽  
...  
Keyword(s):  
Flow Velocity ◽  
East Antarctica ◽  
Global Navigation Satellite Systems ◽  
Steady Increase ◽  
Lake Area ◽  
Ice Flow ◽  
Satellite Systems ◽  
Subglacial Lake ◽  
Gnss Observations ◽  
Flow Velocities

AbstractRepeated Global Navigation Satellite Systems (GNSS) observations were carried out at 50 surface markers in the Vostok Subglacial Lake (East Antarctica) region between 2001 and 2011. The horizontal ice flow velocity vectors were derived with accuracies of 1 cm a−1 and 0.5°, representing the first reliable information on ice flow kinematics in the northern part of the lake. Within the lake area, ice flow velocities do not exceed 2 m a−1. The ice flow azimuth is southeast in the southern part of the lake and turns gradually to east-northeast in the northern part. In the northern part, as the ice flow enters the lake at the western shore, the velocity decreases towards the central lake axis, then increases slightly past the central axis. In the southern part, a continued acceleration is observed from the central lake axis across the downstream grounding line. Based on the observed flow velocity vectors and ice thickness data, mean surface accumulation rates are inferred for four surface segments between Ridge B and Vostok Subglacial Lake and show a steady increase towards the north.

Experimental Study on the Piping Erosion Mechanism of Gap-Graded Soils Under a Supercritical Hydraulic Gradient

2021 ◽  
Author(s):  
Liang Chen ◽  
Yu Wan ◽  
Jian-Jian He ◽  
Chun-Mu Luo ◽  
Shu-fa Yan ◽  
...  
Keyword(s):  
Hydraulic Conductivity ◽  
Unsteady Flow ◽  
Relative Density ◽  
Flow Velocity ◽  
Steady Flow ◽  
Fine Particle ◽  
Failure Process ◽  
Hydraulic Gradient ◽  
Particle Content ◽  
Piping Erosion

Abstract Seepage-induced piping erosion is observed in many geotechnical structures. This paper studies the piping mechanism of gap-graded soils during the whole piping erosion failure process under a supercritical hydraulic gradient. We define the supercritical ratio Ri and study the change in the parameters such as the flow velocity, hydraulic conductivity, and fine particle loss with Ri. Under steady flow, a formula for determining the flow velocity state of the sample with Ri according to the fine particle content and relative density of the sample was proposed; during the piping failure process, the influence of Rimax on the rate at which the flow velocity and hydraulic conductivity of the sample increase as Ri decreases was greater than that of the initial relative density and the initial fine particle content of the sample. Under unsteady flow, a larger initial relative density corresponds to a smaller amplitude of increase in the average value of the peak flow velocity with increasing Ri. Compared with the test under steady flow, the flow velocity under unsteady flow would experience abrupt changes. The relative position of the trend line L of the flow velocity varying with Ri under unsteady flow and the fixed peak water head height point A under steady flow were related to the relative density of the sample.

scholarly journals Propulsion Performance of the Full-Active Flapping Foil in Time-Varying Freestream

2020 ◽  
Vol 10 (18) ◽  
pp. 6226
Author(s):  
Zhanfeng Qi ◽  
Lishuang Jia ◽  
Yufeng Qin ◽  
Jian Shi ◽  
Jingsheng Zhai
Keyword(s):  
Flow Velocity ◽  
Steady Flow ◽  
Navier Stokes ◽  
Time Varying ◽  
Flapping Foil ◽  
Propulsion Performance ◽  
Reduced Frequency ◽  
Motion Parameters ◽  
Volume Method ◽  
The Impact

A numerical investigation of the propulsion performance and hydrodynamic characters of the full-active flapping foil under time-varying freestream is conducted. The finite volume method is used to calculate the unsteady Reynolds averaged Navier–Stokes by commercial Computational Fluid Dynamics (CFD) software Fluent. A mesh of two-dimensional (2D) NACA0012 foil with the Reynolds number Re = 42,000 is used in all simulations. We first investigate the propulsion performance of the flapping foil in the parameter space of reduced frequency and pitching amplitude at a uniform flow velocity. We define the time-varying freestream as a superposition of steady flow and sinusoidal pulsating flow. Then, we study the influence of time-varying flow velocity on the propulsion performance of flapping foil and note that the influence of the time-varying flow is time dependent. For one period, we find that the oscillating amplitude and the oscillating frequency coefficient of the time-varying flow have a significant influence on the propulsion performance of the flapping foil. The influence of the time-varying flow is related to the motion parameters (reduced frequency and pitching amplitude) of the flapping foil. The larger the motion parameters, the more significant the impact of propulsion performance of the flapping foil. For multiple periods, we note that the time-varying freestream has little effect on the propulsion performance of the full-active flapping foil at different pitching amplitudes and reduced frequency. In summary, we conclude that the time-varying incoming flow has little effect on the flapping propulsion performance for multiple periods. We can simplify the time-varying flow to a steady flow field to a certain extent for numerical simulation.

scholarly journals Effects of Using Channelling Devices to Increase Efficiency of Hydrokinetic Devices

2015 ◽  
Vol 52 (2) ◽  
pp. 3-12
Author(s):  
A. Kalnacs ◽  
J. Kalnacs ◽  
A. Mutule ◽  
V. Entins
Keyword(s):  
Flow Control ◽  
Flow Velocity ◽  
Cross Section ◽  
Power Output ◽  
High Importance ◽  
Different Types ◽  
The Cross ◽  
Increase Efficiency ◽  
Flow Velocities

Abstract In the rivers of Latvia and of many other countries the flow velocity in the places that are most suitable for installation of hydrokinetic devices is 0.4 to 0.9 m/s. In a stream or a river the hydrokinetic devices can reach full efficiency starting from about twice higher flow velocities. It is advisable to at least double this velocity thus increasing the efficiency and power output of the hydrokinetic devices installed in such places. Since Latvia has abundance of slow rivers and almost none are fast, research in this field is of high importance. Diversified technical methods are known that allow increasing substantially the efficiency of hydrokinetic devices. These methods include the use of diffusers, concentrators, different types of other channelling devices and means of flow control. Desirable effects are achieved through changing the cross-section and/or direction of a flow, its pressure, minimizing the turbulence, etc. This work substantiates the use of such devices for increasing the efficiency of hydrokinetic devices. A method is proposed for evaluation of the effects on power output gained owing to the use of channelling devices. Results show that the efficiency of hydrokinetic devices can be increased by at least 110%.

scholarly journals Determining the Relation between Groundwater Flow Velocities and Measured Temperature Differences Using Active Heating-Distributed Temperature Sensing

Water ◽  
2019 ◽  
Vol 11 (8) ◽  
pp. 1619 ◽  
Author(s):  
Bakx ◽  
Doornenbal ◽  
Weesep ◽  
Bense ◽  
Essink ◽  
...  
Keyword(s):  
Groundwater Flow ◽  
Flow Velocity ◽  
Temperature Response ◽  
Flow Equation ◽  
Absolute Temperature ◽  
Temperature Sensing ◽  
Measured Temperature ◽  
Distributed Temperature Sensing ◽  
Plan View ◽  
Flow Velocities

Active Heating-Distributed Temperature Sensing (AH-DTS) has the potential to allow for the measurement of groundwater flow velocities in situ. We placed DTS fiber-optic cables combined with a heating wire in direct contact with aquifer sediments in a laboratory scale groundwater flow simulator. Using this setup, we empirically determined the relationship between ΔT, the temperature difference by constant and uniform heating of the DTS cable and the background temperature of the groundwater system, and horizontal groundwater flow velocity. Second, we simulated the observed temperature response of the system using a plan-view heat transfer flow model to calibrate for the thermal properties of the sediment and to optimize cable setup for sensitivity to variation in groundwater flow velocities. Additionally, we derived an analytical solution based on the heat flow equation that can be used to explicitly calculate flow velocity from measured ΔT for this specific AH-DTS cable setup. We expect that this equation, after calibration for cable constitution, is valid for estimating groundwater flow velocity based on absolute temperature differences measured in field applications using this cable setup.

scholarly journals Mechanism Underlying Flow Velocity and Its Corresponding Influence on the Growth of Euglena gracilis, a Dominant Bloom Species in Reservoirs

2019 ◽  
Vol 16 (23) ◽  
pp. 4641
Author(s):  
Yi Tan ◽  
Jia Li ◽  
Linglei Zhang ◽  
Min Chen ◽  
Yaowen Zhang ◽  
...  
Keyword(s):  
Flow Velocity ◽  
Euglena Gracilis ◽  
Environmental Changes ◽  
Algal Species ◽  
Physiological Mechanisms ◽  
Algae Growth ◽  
The Impact ◽  
Stress Hysteresis ◽  
Static Flow ◽  
Flow Velocities

The effects of hydrodynamics on algae growth have received considerable attention, and flow velocity is one of the most frequently discussed factors. For Euglena gracilis, which aggregates resources and is highly resistant to environmental changes, the mechanism underlying the impact of flow velocity on its growth is poorly understood. Experiments were conducted to examine the response of algae growth to different velocities, and several enzymes were tested to determine their physiological mechanisms. Significant differences in the growth of E. gracilis were found at different flow velocities, and this phenomenon is unique compared to the growth of other algal species. With increasing flow velocity and time, the growth of E. gracilis is gradually inhibited. In particular, we found that the pioneer enzyme is peroxidase (POD) and that the main antioxidant enzyme is catalase (CAT) when E. gracilis experiences flow velocity stress. Hysteresis between total phosphorus (TP) consumption and alkaline phosphatase (AKP) synthesis was observed. Under experimental control conditions, the results indicate that flow velocities above 0.1 m/s may inhibit growth and that E. gracilis prefers a relatively slow or even static flow velocity, and this finding could be beneficial for the control of E. gracilis blooms.

scholarly journals Quantification of the bacterial community of drinking water-associated biofilms under different flow velocities and changing chlorination regimes

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Z. Tsvetanova
Keyword(s):  
Drinking Water ◽  
Flow Velocity ◽  
Biofilm Formation ◽  
Distribution Systems ◽  
Water Distribution ◽  
Culturable Bacteria ◽  
Drinking Water Distribution Systems ◽  
Biomass Removal ◽  
Water Chlorination ◽  
Flow Velocities

Abstract Microbial growth in drinking water distribution systems (DWDS) depends on a great number of factors, and its control represents a great challenge for management of these engineering systems. The present case study assessed the influence that a pair of factors—water chlorination and flow velocity—had on the biofilms formed in a model DWDS in 626 days. The culturable bacteria number and biomass of the biofilms developed under the flow velocities of 0.3 m/s, 0.5 m/s, 0.7 m/s and 1 m/s were determined during three consecutively applied regimes of water chlorination to 0.05 mg/l (in 380 days), 0.42 mg/l (in 46 days) and 0.14 mg/l free chlorine (in 200 days). The results demonstrated that biofilm formation was a prolonged process directly depended on flow velocity at drinking water chlorination to 0.05 mg/l. The increase in the water chlorination to 0.42 mg/l chlorine resulted in both the reduction in culturable bacteria number and biomass removal, but the bacteria killing and the biofilm removal were distinct processes. The biocide action of chlorine was faster and more effective than its biomass removal effect. The chlorine decreasing from 0.42 to 0.14 mg/l resulted in increasing the biofilm HPC densities, although the biomass removal process was still continuing. The study carried out contributes for better understanding the biofilm behavior in DWDS and demonstrates that biofilm formation could be managed within a DWDS through operational decisions on parameters that can be changed and controlled as flow velocity and chlorination to safeguard drinking water quality.

Comparative study of transcranial color duplex sonography and transcranial Doppler sonography in adults

1993 ◽  
Vol 78 (5) ◽  
pp. 776-784 ◽  
Author(s):  
Martin Schöoning ◽  
Reiner Buchholz ◽  
Jochen Walter
Keyword(s):  
Flow Velocity ◽  
Doppler Sonography ◽  
Transcranial Doppler Sonography ◽  
Maximum Flow ◽  
Duplex Sonography ◽  
Color Duplex Sonography ◽  
Content Type ◽  
Maximum Flow Velocity ◽  
Fine Print ◽  
Flow Velocities

✓ To determine whether the frequency shift recorded in basal cerebral arteries corresponds to “true” flow velocities, a prospective comparative study of transcranial color duplex sonography (TCCD) and transcranial Doppler sonography (TCD) was performed. A 2.0-MHz transducer of a computerized TCCD system and a TCD device were used. The middle cerebral artery (MCA) and anterior cerebral artery (ACA) were examined by TCCD in 49 healthy volunteers (mean age 35 ± 12 years). In 45 of the same volunteers a comparative TCD examination was possible. The studies were carried out blindly by different examiners at separate appointments. Peak systolic flow velocity, end-diastolic maximum flow velocity, time-averaged maximum flow velocity, and the pulsatility index were measured by both techniques. Additionally, for TCCD, time-averaged flow velocity was assessed, the resistance index and a spectral broadening index were calculated, and the energy output required for reliable measurement was analyzed. The TCCD signals were recorded in 98% of both MCA's and ACA's; with TCD, signals were recorded in 98% of MCA's and 87% of ACA's. Although in both vessels the angle-corrected peak systolic and time-averaged maximum velocities were approximately 10% to 15% higher in TCCD than in TCD measurements, correlation of flow velocities between both techniques was significant (p < 0.0001); differences between sides and age-dependency of flow velocities corresponded as well. In a reproducibility study, TCCD was repeated in 27 subjects by a third examiner with significant correlation (p < 0.0001) of both TCCD examinations. It is concluded that the advantage of TCCD is associated more with a qualitative aspect than a quantitative one. The additional visual dimension of TCCD can open new diagnostic possibilities in cerebrovascular disorders.

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