Drag Reduction of Filaments and Poroelastic Bodies by Non-Linear Deformation

2010 ◽  
Author(s):  
Fre´de´rick P. Gosselin ◽  
Emmanuel de Langre
Keyword(s):  
Flow Velocity ◽  
Bluff Body ◽  
Flat Plates ◽  
Linear Deformation ◽  
Theoretical Understanding ◽  
Significant Difference ◽  
Proper Scaling ◽  
Present Experimentation ◽  
Simple Systems ◽  
Parameter Values

Because of their flexibility, trees and other plants deform with great amplitude (reconfigure) when subjected to fluid flow. Hence the drag they encounter does not grow with the square of the flow velocity as it would on a classical bluff body, but rather in a less pronounced way. The reconfiguration of actual plants has been studied abundantly in wind tunnels and hydraulic canals, and recently a theoretical understanding of reconfiguration has been brought by combining modelling and experimentation on simple systems such as filaments and flat plates. These simple systems have a significant difference with actual plants in the fact that they are not porous: fluid only flows around them, not through them. We present experimentation and modelling of the reconfiguration of a simple poroelastic system. Proper scaling of the drag and the fluid loading allows comparing the reconfiguration regimes of porous systems to those of simple systems. It is found that in the large reconfiguration regime, the scaling of the drag with flow velocity is independent of the porosity for a range of parameter values.

scholarly journals Effects of Wrist Posture and Fingertip Force on Median Nerve Blood Flow Velocity

2017 ◽  
Vol 2017 ◽  
pp. 1-8 ◽  
Author(s):  
Katherine E. Wilson ◽  
Jimmy Tat ◽  
Peter J. Keir
Keyword(s):  
Blood Flow ◽  
Flow Velocity ◽  
Median Nerve ◽  
Blood Flow Velocity ◽  
Nerve Blood Flow ◽  
Occupational Risk Factors ◽  
Early Evaluation ◽  
Fingertip Force ◽  
Significant Difference ◽  
Healthy Participants

Purpose. The purpose of this study was to assess nerve hypervascularization using high resolution ultrasonography to determine the effects of wrist posture and fingertip force on median nerve blood flow at the wrist in healthy participants and those experiencing carpal tunnel syndrome (CTS) symptoms. Methods. The median nerves of nine healthy participants and nine participants experiencing symptoms of CTS were evaluated using optimized ultrasonography in five wrist postures with and without a middle digit fingertip press (0, 6 N). Results. Both wrist posture and fingertip force had significant main effects on mean peak blood flow velocity. Blood flow velocity with a neutral wrist (2.87 cm/s) was significantly lower than flexed 30° (3.37 cm/s), flexed 15° (3.27 cm/s), and extended 30° (3.29 cm/s). Similarly, median nerve blood flow velocity was lower without force (2.81 cm/s) than with force (3.56 cm/s). A significant difference was not found between groups. Discussion. Vascular changes associated with CTS may be acutely induced by nonneutral wrist postures and fingertip force. This study represents an early evaluation of intraneural blood flow as a measure of nerve hypervascularization in response to occupational risk factors and advances our understanding of the vascular phenomena associated with peripheral nerve compression.

scholarly journals Doppler Flow Velocity Indices (RI, PI, S/D & PSV) of Fetal Middle Cerebral Artery in Normal Pregnancies: Correlation with Gestational Age of 20 to 40 Weeks

2012 ◽  
Vol 2 (2) ◽  
pp. 77-80
Author(s):  
Md Abu Taher ◽  
Nuzhat Tasmin ◽  
AS Mohiuddin ◽  
Md Mohit Ul Alam ◽  
Md Mofazzal Sharif ◽  
...  
Keyword(s):  
Middle Cerebral Artery ◽  
Flow Velocity ◽  
Cerebral Artery ◽  
Gestational Age ◽  
Resistance Index ◽  
Peak Systolic Velocity ◽  
Doppler Flow ◽  
Significant Difference ◽  
Before And After ◽  
Doppler Indices

This observational type of descriptive study was carried out in the Department of Radiology and Imaging, BIRDEM selecting 70 Bangladeshi pregnant babies with the aim to find out the normogram of foetal middle cerebral artery Doppler flow velocity indices and correlation between Doppler flow velocity indices [Resistance Index (RI), Pulsatility Index (PI), Systolic/Diastolic ratio (S/D) & Peak Systolic Velocity (PSV)] of foetal middle cerebral artery and gestational age in normal pregnancies of 20 to 40 weeks. It was observed that RI, PI and S/D were decreased with the advance of gestational age but PSV was increases with the advance of gestational age. Statistical analyses showed there were significant difference between mean PSV, RI and PI before and after 25 weeks of gestation. No significant difference was found between mean S/D before and after 25 weeks of gestation. It was observed from Correlation analysis between Doppler indices with independent gestational age that all the Doppler indices of foetal middle cerebra artery was positively correlated with the whole gestation period. The statistical analysis showed only PSV and RI were significantly correlated with the gestational age. Simple regression analysis between dependent Doppler index with independent gestational age before and after 25 weeks revealed that all the Doppler indices had positive relationship with the corresponding gestational age but relationship between PSV and PI (before 25 weeks) with their corresponding gestational ages were only statistically significant.DOI: http://dx.doi.org/10.3329/birdem.v2i2.12306 Birdem Med J 2012; 2(2) 77-80

scholarly journals Relation between Fetal Renal Artery Doppler ‎Indices and Non-PROM Oligohydramnios in ‎Third Trimester of Pregnancy

2021 ◽  
pp. 1-8
Author(s):  
Asmaa Ibrahim Laag ◽  
Nareman Mahmoud Elhamamy ◽  
Amr‏ ‏Mohamed Tawfek Elbadry ◽  
Atef Hammad Teama
Keyword(s):  
Amniotic Fluid ◽  
Renal Artery ◽  
Flow Velocity ◽  
Pulsatility Index ◽  
Resistance Index ◽  
Normal Amount ◽  
Amniotic Fluid Index ◽  
Group I ◽  
Significant Difference ◽  
Artery Flow

Background: Amniotic fluid is the liquid which surround the fetus after the first few weeks of gestation. Amniotic fluid is derived mostly from the fetus and has many functions that are essential for normal growth and development. The aim of this work is to study the relation between fetal renal artery flow velocity waveforms and amniotic fluid volume in normal pregnancies and those complicated by oligohydramnios. Methods: This prospective observational study was carried out on 40pregnant women (10) of them were with normal amount of amniotic fluid (group I), while (30) of them suffered from oligohydramnios (group II).By using color doppler ultrasound imaging, the fetal renal circulation can be assessed. Intermittent assessment of renal artery flow velocity waveforms during the early stages of pregnancy may help in predicting changes in amniotic fluid dynamics. Results: There was a non-significant difference between cases with normal amount of amniotic fluid and cases with oligohydramnios in Gestational age, Maternal age, fetal femur length, bi parietal diameter, abdominal circumference and Fetal weight. There were increased values of fetal renal artery Resistance index (RI) and Pulsatility index (PI) in cases of oligohydramnios than cases with normal amount of amniotic fluid. There was no correlation between Peak systolic velocity (PSV) and Amniotic fluid index (AFI). There was a significant difference in End diastolic velocity (EDV) between cases with normal amount of amniotic fluid and cases with oligohydramnios. Also, there was a significant difference in Systolic diastolic ratio (S/D) and Amniotic fluid index (AFI) between cases with normal amount of amniotic fluid and cases with oligohydramnios. Conclusions: There is a relation between renal artery flow velocity waveforms and oligohydramnios using Pulsed wave Doppler Ultrasonography. There are higher values of renal artery Resistance index and Pulsatility index in cases of oligohydramnios more than cases with normal amount of amniotic fluid.

The Effect of Intermittent Fasting and Exercise on Some Physiological Parameters

2021 ◽  
Vol 15 (9) ◽  
pp. 2793-2798
Author(s):  
Yunus Berk ◽  
Şaban Ünver ◽  
Hasan Avlayan
Keyword(s):  
Physiological Parameters ◽  
Favorable Effect ◽  
Physiological Parameter ◽  
Control Group ◽  
Intermittent Fasting ◽  
Significant Difference ◽  
Post Test ◽  
Mean Differences ◽  
Parameter Values ◽  
Experimental Group

Background: In this study, the effect of recently popular intermittent fasting on weight loss and the role of exercise combined with intermittent fasting on some physiological parameters were investigated. Aim: This study was conducted to investigate the effect of intermittent fasting combined with exercise and intermittent fasting alone on some physiological parameters. Methods: A total of 36 healthy individuals between 20 and 24 years of age, including 18 in the experimental group (exercising) and 18 in the control group (non-exercising), who were assigned by the random selection method, participated in the study. The individuals in the experimental group exercised 36 minutes a day, 5 days a week, along with intermittent fasting for 30 days. On the other hand, the control group did not exercise during this period. Results: When the within-group pre-test and post-test physiological parameter values were compared, a significant difference was found in all values of the experimental group (p<0.05). Similarly, a significant difference was found in the physiological parameter values of the control group (p<0.05) too, with the exception of body mass index and body fluid ratio. A statistically significant difference was found between the two groups in terms of the mean differences between the pre-test and post-test physiological parameter values (p < 0.05). Conclusion: Based on the findings, it could be concluded that intermittent fasting is an effective method for losing weight and reducing body fat and that adding low-intensity exercise to this routine ensures more effective weight reduction. Hence, starving for a certain period of time has a favorable effect on the physiological parameters, and the practice of exercising in addition to dieting further improves these values. Keywords: Intermittent fasting, Exercise, Health

Electroacoustic Calibration for Sound Field Warble Tone Thresholds

1987 ◽  
Vol 52 (4) ◽  
pp. 388-392 ◽  
Author(s):  
Robyn M. Cox ◽  
Virginia A. McCormick
Keyword(s):  
Sound Pressure ◽  
Sound Field ◽  
Critical Distance ◽  
Sound Fields ◽  
Significant Difference ◽  
Sound Pressure Levels ◽  
Modulation Parameter ◽  
Test Position ◽  
Parameter Values

Walker, Dillon, and Byrne (1984) suggested reference equivalent threshold sound pressure levels (RETSPLs) for warble tones with specific modulation parameter values audited from a test position at the critical distance in a semireverberant sound field. This study evaluated these RETSPLs in two typical audiometric rooms and with typically encountered FM tones. Thresholds were measured under earphones and in two sound fields for 6-11 normal hearers at six test frequencies. Results indicated that there was a small but statistically significant difference between earphone and sound field thresholds in 4 of 24 comparisons. However, in both sound fields, 99% of the sound field thresholds were within 10 dB of the earphone thresholds. It is concluded that these RETSPLs are appropriate for electroacoustic calibration of sound field warble tones similar to those used in this study.

Flow Characteristics of a Bluff Body Cut From a Circular Cylinder

1997 ◽  
Vol 119 (2) ◽  
pp. 453-454 ◽  
Author(s):  
S. Aiba ◽  
H. Watanabe
Keyword(s):  
Circular Cylinder ◽  
Drag Coefficient ◽  
Flow Velocity ◽  
Bluff Body ◽  
Pressure Coefficient ◽  
Angular Position ◽  
Flow Characteristics ◽  
Uniform Flow ◽  
Base Pressure ◽  
Singular Flow

This is a report on an investigation of the flow characteristics of a bluff body cut from a circular cylinder. The volume removed from the cylinder is equal to d/2(1 − cos θs), where d and θs are the diameter and the angular position (in the case of a circular cylinder, θs, = 0 deg), respectively. θs, ranged from 0 deg to 72.5 deg and Re (based on d and the upstream uniform flow velocity U∞) from 2.0 × 104 to 3.5 × 104. It is found that a singular flow around the cylinder occurs at around θs = 53 deg when Re > 2.5 × 104, and the base pressure coefficient (−Cpb,) and the drag coefficient CD take small values compared with those for otherθs.

Deterministic and probabilistic approaches to geologic hazard assessment

2000 ◽  
Vol 6 (3) ◽  
pp. 209-226 ◽  
Author(s):  
William C. Haneberg
Keyword(s):  
Hazard Assessment ◽  
Probabilistic Models ◽  
Driving Mechanism ◽  
Rock Falls ◽  
Deterministic Models ◽  
Geologic Hazard ◽  
Random Behavior ◽  
Significant Difference ◽  
Simple Systems ◽  
Deterministic And Probabilistic Approaches

Abstract The occurrence of potentially hazardous geologic events such as landslides, rock falls, earthquakes, floods, and debris flows can be predicted using two fundamentally different approaches: deterministic and probabilistic. The most significant difference between the two approaches to geologic hazard assessment is whether a process is envisioned to be the result of an exact causal relationship or if some element of random behavior is assumed to be part of the system. Although the assumption of random behavior may seem self-defeating, it can provide a useful tool for the solution of important problems as long as the randomness can be quantified using statistical models. Each of these two methods can be approached either rationally (sing models derived from accepted physical or chemical principles) or empirically (by studying the occurrence of events without explicit regard to their driving mechanism). The complexity of the geologic process commonly dictates which approach is used for a particular problem, ranging from rational deterministic models for relatively simple systems such as small landslides to empirical probabilistic models for complicated processes such as floods and earthquakes. Examples of each type of model are discussed throughout the paper, primarily within the context of slope stability and the recurrence of extreme events such as floods.

Convective and Absolute Instabilities in Reacting Bluff Body Wakes

2011 ◽  
Author(s):  
Benjamin Emerson ◽  
Julia Lundrigan ◽  
Jacqueline O’Connor ◽  
David Noble ◽  
Tim Lieuwen
Keyword(s):  
Reynolds Number ◽  
Bluff Body ◽  
Flow Behavior ◽  
Density Ratio ◽  
Intermittent Flow ◽  
Flow Problems ◽  
High Reynolds ◽  
Bluff Body Flow ◽  
Density Ratios ◽  
Parameter Values

This paper describes the variation of bluff body wake structure with flame density ratio. It is known that the bluff body flow structure at “high” and “low” flame density ratios is fundamentally different, being dominated by the convectively unstable shear layers or absolutely unstable Von Karman vortex street, respectively. This paper characterizes the aforementioned transition and shows that the bifurcation in flow behavior does not occur abruptly at some ρu/ρb value. Rather, there exists a range of transitional density ratios at which the flow exists intermittently in both flow states, abruptly shifting back and forth between the two. The fraction of time that the flow spends in either state is a monotonic function of ρu/ρb. This behavior is to be contrasted with lower Reynolds number, laminar flow problems where the convective/absolute instability transition occurs at a well defined value of bifurcation parameter. With this distinction in mind, however, this paper also shows that local parallel stability analyses developed for laminar base wake flows can capture many of the observed flow dependencies. These results have important implications on the dynamics of high Reynolds number, vitiated flows, where typical parameter values fall into the highly intermittent flow regime characterized in this study. This suggests that such flows exhibit two co-existing dynamical states, intermittently jumping between the two.

scholarly journals Nitric oxide is not obligatory for radial artery flow-mediated dilation following release of 5 or 10 min distal occlusion

2010 ◽  
Vol 298 (1) ◽  
pp. H119-H126 ◽  
Author(s):  
Kyra Pyke ◽  
Daniel J. Green ◽  
Cara Weisbrod ◽  
Matthew Best ◽  
Lawrence Dembo ◽  
...  
Keyword(s):  
Nitric Oxide ◽  
Blood Flow ◽  
Shear Rate ◽  
Flow Velocity ◽  
Radial Artery ◽  
Blood Flow Velocity ◽  
Reactive Hyperemia ◽  
Area Under The Curve ◽  
Flow Mediated Dilation ◽  
Significant Difference

This study investigated the nitric oxide (NO) dependence of radial artery (RA) flow-mediated dilation (FMD) in response to three different reactive hyperemia (RH) shear stimulus profiles. Ten healthy males underwent the following three RH trials: 1) 5 min occlusion (5 trial), 2) 10 min occlusion (10 trial), and 3) 10 min occlusion with cuff reinflation at 30 s (10–30 trial). Trials were performed during saline infusion and repeated during NG-monomethyl-l-arginine (l-NMMA) infusion in the brachial artery. RA blood flow velocity was measured with Doppler ultrasound, and B-mode RA images were analyzed using automated edge detection software. Shear rate estimation of shear stress was calculated as the blood flow velocity/vessel diameter. l-NMMA decreased baseline vascular conductance by 35%. l-NMMA infusion did not affect the peak shear rate stimulus ( P = 0.681) or the area under the curve (AUC) of shear rate to peak FMD ( P = 0.088). The AUC was significantly larger in the 10 trial vs. the 10–30 or 5 trial ( P < 0.001). Although percent FMD (%change in diameter) in the 10 trial was larger than that in the 5 trial ( P = 0.035), there was no significant difference in %FMD between the saline and l-NMMA conditions in any trial: 5 trial, 5.62 ± 1.48 vs. 5.63 ± 1.27%; 10 trial, 9.07 ± 1.16 vs. 11.22 ± 2.21%; 10–30 trial, 6.52 ± 1.43 vs. 7.98 ± 1.51% for saline and l-NMMA, respectively ( P = 0.158). We conclude the following: 1) RH following 10 min of occlusion results in an enhanced stimulus and %FMD compared with 5 min of occlusion. 2) When the occlusion cuff is reinflated 30 s postrelease of a 10 min occlusion, it does not result in an enhanced %FMD compared with that which results from RH following 5 min of occlusion. 3) The lack of effect of l-NMMA on FMD suggests that NO may not be obligatory for radial artery FMD in response to either 5 or 10 min of occlusion in healthy volunteers.

A Free-Streamline Model for Bluff Bodies in Confined Flow

1977 ◽  
Vol 99 (3) ◽  
pp. 585-592 ◽  
Author(s):  
V. J. Modi ◽  
S. E. El-Sherbiny
Keyword(s):  
Potential Flow ◽  
Bluff Body ◽  
Flow Model ◽  
Circular Cylinders ◽  
Bluff Bodies ◽  
Two Dimensional ◽  
Flat Plates ◽  
Surface Loading ◽  
Confined Flow ◽  
Potential Flow Model

A potential flow model is presented for two-dimensional symmetrical bluff bodies under wall confinement. It provides a procedure for predicting surface loading on a bluff body over a range of blockage ratios. Experimental results with normal flat plates and circular cylinders for blockage ratios up to 35.5 percent substantiate the validity of the approach.

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