Normal Flow Conditions Research Articles

Analysis of flow characteristics around islands due to semi-diurnal currents in the Han River, Korea

In this study, an unsteady 2D depth-averaged flow model by Petrov-Galerkin stabilization was developed to investigate flow characteristics caused by semi-diurnal current at the tidal reach of the Han River. In order to analyze the velocity field around islands located in the mid-course of the Han River, simulations of the transient flow were conducted with principal lunar and solar semidiurnal constituent conditions. In addition, the influence of an artificial island construction located at the tributary confluence was quantitatively examined. The results show that, under normal flow condition, around Bam Island, main flow was inclined to the left half of the river span, and the velocity reversal was occurred during the flood tide which would result in the deposition sediment to form the Island. Under bank-full flood condition, velocities around No-deul Island were higher than those around Seon-yu Island reaching 3.5 m/s in maximum. The construction of the artificial island at the Jung-nang Stream confluence caused the significant reduction in the flood conveyance of the Han River and 90% increase in maximum velocity during the bank-full flood flow condition.

Migration behavior of 134Cs and 137Cs in the Niida River water in Fukushima Prefecture, Japan during 2011–2012

Total radioactivity of 137Cs in water samples from the Niida River was 0.025–4.18 Bq/L during May 2011–November 2012. Higher radioactivity was found during May–September 2011 and after a high flow condition caused by a rain event in 2012. The particulate phase of 134Cs and 137Cs was 47–48 % for May–September 2011, 75–93 % in normal flow conditions and 86–91 % in high flow conditions after December 2011. These results indicate that the supply of 134Cs and 137Cs from the watershed differs from the early stage up to September 2011 and from the last stage.

Rapid assessment of flood susceptibility in urbanized rivers using digital terrain data: Application to the Arno river case study (Firenze, northern Italy)

As a result of the recent acquisitions of detailed geographic data in fluvial environments this study proposes an analytical procedure in a GIS environment for an easy, rapid and cost-effective evaluation of flood susceptibility within urban and sub-urban areas. The method, based on data gathering in various public offices and possibly integrating missing geomorphologic information with new records, has been tested in a real case study in central Italy from which operational instructions could be extrapolated for other similar areas in the world. A long reach of the Arno river, which is currently the most important national hydraulic emergency area in terms of civil protection, was selected for this purpose. The measured dike heights, extrapolated from a geographic database previously created by the authors on behalf of the Provincia di Firenze administration, were compared with the results of hydraulic modeling conducted by the Arno River Basin Authority in which water flood levels were simulated for various return periods. This data comparison has allowed us to identify critical points for overflow hazard. In addition, the flood discharges provided by the same model were related to the freeboard typically used in river hydraulics for the major Italian watercourses (1.00 m for a 200-year flood). A deeper analysis of the flood susceptibility was subsequently carried over to the urban area of Firenze. A model of the surface hydrological flows concentrated on the historic center has provided a comprehensive response of this area to the sudden appearance of abundant surface-water flows. The behavior of the urban water circulation in terms of path and areas involved were promptly identified with great precision during normal flow conditions of the Arno in the event of river obstruction at bridges and in case of undifferentiated runoff out from the riverbed.

Characteristics and behavior of dissolved organic matter in the Kumaki River, Noto Peninsula, Japan

Dissolved organic matter (DOM) in river water was studied to understand the transport behavior of DOM in a small watershed with forest and paddy fields. Field experiments were conducted under normal flow conditions in the Kumaki River, which is located in the central part of the Noto Peninsula in Japan, during the period 2009–2010. The concentrations and structural properties of fulvic acid-like components, which are the major components of DOM, were determined using three-dimensional excitation–emission matrix spectroscopy and high-performance size-exclusion chromatography. The relative fluorescence intensity for fulvic acid-like components at an excitation wavelength of 305–335 nm and an emission wavelength of 425–440 nm increased from the upper forest area to the lower paddy field area and increased seasonally in this river system in the following order: winter, autumn, spring, summer. Fulvic acid-like components with a higher molecular weight were observed in the summer samples. These results suggest that higher precipitation and agricultural activity in the summer season increase the amount of fulvic acid-like components with higher molecular weight that are transported from the watershed into the river.

SWIRLING FLOW CAN SUPPRESS MONOCYTES ADHESION IN END-TO-END ARTERIAL ANASTOMOSIS

To test the hypothesis that the monocytes adhesion would be suppressed by intentionally inducing swirling flow in end-to-end arterial anastomosis to inhibit the flow disturbance, the comparing experimental and numerical investigation under both normal flow condition and swirling flow condition were executed, in which the sudden expanded tube and U-937 cells were used. The numerical results reveal that, comparing to normal flow, the swirling flow could reduce the size of flow disturbed zones and enhance the wall shear stress (WSS) in the closed downstream of sudden expanded tube. The experimental results show that there are disturbed flow zones in the sudden expanded tube, where the adhesion number of U-937 cells is larger than other zones. More importantly, comparing to the normal flow, the swirling flow could reduce the adhesion of U-937 cells, in which the adhesion number become smaller with the increasing of the swirling intensity. Therefore, the present study suggests that intentionally introducing swirling flow in end-to-end arterial anastomosis may be a solution to solve the problem of intimal hyperplasia (IH) by suppressing the flow disturbance and restraining the adhesion of monocytes to keep the favorably unimpeded flow.

Improvement of the Variable Storage Coefficient Method with Water Surface Gradient as a Variable

<abstract> <bold><sc>Abstract.</sc></bold> The variable storage coefficient (VSC) method has been used for streamflow routing in continuous hydrological simulation models such as the Agricultural Policy/Environmental eXtender (APEX) and the Soil Water Assessment Tool (SWAT) for more than 30 years. APEX operates on a daily time step and offer options for simulating processes on shorter time steps (e.g., hourly). However, APEX is not adequate for applications such as designing flood control structures or estimating flood damages because of a fundamental assumption in the VSC method: the normal flow condition. The storage with variable slope (SVS) method and an enhanced variable storage coefficient (VSCe) method are proposed as new routing methods for continuous simulation models that will improve flow routing and water quality simulation at subdaily time scales. This study describes the principle of the SVS method and the VSCe method and their performances against HEC-RAS unsteady flow results for various hydraulic and geometric conditions. Results show that the peak flow and the time to peak flow improved by up to 20% with SVS and VSCe on mild slopes (less than 0.0005 m m^-1) and small time steps of less than 1 h when compared to the conventional VSC method, although the difference narrowed as the channel slope and time interval increased. A case study on a small agricultural watershed in Texas indicates that both VSCe and VSC are reliable in watershed applications, but the improvement in streamflow prediction can be marginal in watersheds with steep slopes.

Influence of second-order random wave kinematics on the design loads of offshore wind turbine support structures

The impact of wave model nonlinearities on the design loads of wind turbine monopile foundations is delineated based on a second-order nonlinear random wave model that satisfies the boundary conditions at the free surface and by including the effects of convective acceleration in the inertial loads. The second-order nonlinear water kinematics is developed based on a Gram Charlier series expansion using the first four stochastic moments of the wave process. The wave surface velocities and accelerations are expressed using a Taylor series expansion about the mean sea level, which satisfies to the second-order, the unsteady Bernoulli equation and normal flow condition at the free surface. The operating design loads on the monopile are computed using fully coupled and uncoupled methods. The computation of the mud level loads based on the inclusion of nonlinear wave surface kinematics is compared with those obtained when using linear waves and Wheeler stretching. The effect of the spatial derivatives of the wave velocity on the wave surface kinematics is quantified and shown to determine the wave spectral cut-off frequency limit. The spatial derivatives of wave velocity also participate in the expression for the wave convective acceleration, whose effect is demonstrated on the inertial loads on the foundation in the presence of ocean currents. The effect of nonlinear water kinematics on the monopile design load reveals the large frequency bandwidth of wave structure interaction, but the phase differences between the hydrodynamic loads with the rotor loads tend to lower the probability of joint simultaneous extreme peaks in hydrodynamics and rotor loads.

Effect of [18F]FMISO stratified dose-escalation on local control in FaDu hSCC in nude mice

ObjectiveTo investigate the effect of radiation dose-escalation on local control in hypoxic versus non-hypoxic hypoxic tumours defined using [18F]fluoromisonidazole ([18F]FMISO) PET. Materials and methodsFaDu human squamous cell carcinomas (hSCCs) growing subcutaneously in nude mice were subjected to [18F]FMISO PET before irradiation with single doses of 25 or 35Gy under normal blood flow conditions. [18F]FMISO hypoxic volume (HV) and maximum standardised uptake value (SUVmax) were used to quantify tracer uptake. The animals were followed up for at least 120days after irradiation. The endpoints were permanent local tumour control and time to local recurrence. ResultsHV varied between 38 and 291mm3 (median 105mm3). Non-hypoxic tumours (HV below median) showed significantly better local control after single dose irradiation than hypoxic tumours (HV above median) (p=0.046). The effect of dose was significant and not different in non-hypoxic and in hypoxic tumours (HR=0.82 [95% CI 0.71; 0.93], p=0.002 and HR=0.86 [0.78; 0.95], p=0.001, respectively). Dose escalation resulted in an incremental increase of local tumour control from low-dose hypoxic, over low-dose non-hypoxic and high-dose hypoxic to high-dose non-hypoxic tumours. SUVmax did not reveal significant association with local control at any dose level. ConclusionsThe negative effect of [18F]FMISO HV on permanent local tumour control supports the prognostic value of the pre-treatment [18F]FMISO HV. Making the assumption that variable [18F]FMISO uptake in different FaDu tumours which all have the same genetic background may serve as an experimental model of intratumoural heterogeneity, the data support the concept of dose-escalation with inhomogeneous dose distribution based on pre-treatment [18F]FMISO uptake. This result needs to be confirmed in other tumour models and using fractionated radiotherapy schedules.

Dynamic CT Myocardial Perfusion Imaging: Detection of Ischemia in a Porcine Model with FFR Verification.

Dynamic cardiac CT perfusion (CTP) is a high resolution, non-invasive technique for assessing myocardial blood flow (MBF), which in concert with coronary CT angiography enable CT to provide a unique, comprehensive, fast analysis of both coronary anatomy and functional flow. We assessed perfusion in a porcine model with and without coronary occlusion. To induce occlusion, each animal underwent left anterior descending (LAD) stent implantation and angioplasty balloon insertion. Normal flow condition was obtained with balloon completely deflated. Partial occlusion was induced by balloon inflation against the stent with FFR used to assess the extent of occlusion. Prospective ECG-triggered partial scan images were acquired at end systole (45% R-R) using a multi-detector CT (MDCT) scanner. Images were reconstructed using FBP and a hybrid iterative reconstruction (iDose 4, Philips Healthcare). Processing included: beam hardening (BH) correction, registration of image volumes using 3D cubic B-spline normalized mutual-information, and spatio-temporal bilateral filtering to reduce partial scan artifacts and noise variation. Absolute blood flow was calculated with a deconvolution-based approach using singular value decomposition (SVD). Arterial input function was estimated from the left ventricle (LV) cavity. Regions of interest (ROIs) were identified in healthy and ischemic myocardium and compared in normal and occluded conditions. Under-perfusion was detected in the correct LAD territory and flow reduction agreed well with FFR measurements. Flow was reduced, on average, in LAD territories by 54%.

Erosion Protection by Calcium Lactate/Sodium Fluoride Rinses under Different Salivary Flows in vitro

This study investigated the effect of a calcium lactate prerinse on sodium fluoride protection in an in vitro erosion-remineralization model simulating two different salivary flow rates. Enamel and dentin specimens were randomly assigned to 6 groups (n = 8), according to the combination between rinse treatments - deionized water (DIW), 12 m<smlcap>M</smlcap> NaF (NaF) or 150 m<smlcap>M</smlcap> calcium lactate followed by NaF (CaL + NaF) - and unstimulated salivary flow rates - 0.5 or 0.05 ml/min - simulating normal and low salivary flow rates, respectively. The specimens were placed into custom-made devices, creating a sealed chamber on the specimen surface connected to a peristaltic pump. Citric acid was injected into the chamber for 2 min, followed by artificial saliva (0.5 or 0.05 ml/min) for 60 min. This cycle was repeated 4×/day for 3 days. Rinse treatments were performed daily 30 min after the 1st and 4th erosive challenges, for 1 min each time. Surface loss was determined by optical profilometry. KOH-soluble fluoride and structurally bound fluoride were determined in specimens at the end of the experiment. Data were analyzed by 2-way ANOVA and Tukey tests (α = 0.05). NaF and CaL + NaF exhibited significantly lower enamel and dentin loss than DIW, with no difference between them for normal flow conditions. The low salivary flow rate increased enamel and dentin loss, except for CaL + NaF, which presented overall higher KOH-soluble and structurally bound fluoride levels. The results suggest that the NaF rinse was able to reduce erosion progression. Although the CaL prerinse considerably increased F availability, it enhanced NaF protection against dentin erosion only under hyposalivatory conditions.

Export of &amp;lt;sup&amp;gt;134&amp;lt;/sup&amp;gt; Cs and &amp;lt;sup&amp;gt;137&amp;lt;/sup&amp;gt; Cs in the Fukushima river systems at heavy rains by Typhoon Roke in September 2011

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.

Stroke Propensity Is Increased under Atrial Fibrillation Hemodynamics: A Simulation Study

Atrial fibrillation (AF) is the most common sustained dysfunction in heart rhythm clinically and has been identified as an independent risk factor for stroke through formation and embolization of thrombi. AF is associated with reduced cardiac output and short and irregular cardiac cycle length. Although the effect of AF on cardiac hemodynamic parameters has been reported, it remains unclear how the hemodynamic perturbations affect the potential embolization of blood clots to the brain that can cause stroke. To understand stroke propensity in AF, we performed computer simulations to describe trajectories of blood clots subject to the aortic flow conditions that represent normal heart rhythm and AF. Quantitative assessment of stroke propensity by blood clot embolism was carried out for a range of clot properties (e.g., 2–6 mm in diameter and 0–0.8 m/s ejection speed) under normal and AF flow conditions. The simulations demonstrate that the trajectory of clot is significantly affected by clot properties as well as hemodynamic waveforms which lead to significant variations in stroke propensity. The predicted maximum difference in stroke propensity in the left common carotid artery was shown to be about 60% between the normal and AF flow conditions examined. The results suggest that the reduced cardiac output and cycle length induced by AF can significantly increase the incidence of carotid embolism. The present simulations motivate further studies on patient-specific risk assessment of stroke in AF.

Inhibition of Patched-1 Prevents Injury-Induced Neointimal Hyperplasia

To determine the role of patched receptor (Ptc)-1 in mediating pulsatile flow-induced changes in vascular smooth muscle cell growth and vascular remodeling. In vitro, human coronary arterial smooth muscle cells were exposed to normal or pathological low pulsatile flow conditions for 24 hours using a perfused transcapillary flow system. Low pulsatile flow increased vascular smooth muscle cell proliferation when compared with normal flow conditions. Inhibition of Ptc-1 by cyclopamine attenuated low flow-induced increases in Notch expression while concomitantly decreasing human coronary arterial smooth muscle cell growth to that similar under normal flow conditions. In vivo, ligation injury-induced low flow increased vascular smooth muscle cell growth and vascular remodeling, while increasing Ptc-1/Notch expression. Perivascular delivery of Ptc-1 small interfering RNA by pluronic gel inhibited the pathological low flow-induced increases in Ptc-1/Notch expression and markedly reduced the subsequent vascular remodeling. These results suggest that pathological low flow stimulates smooth muscle cell growth in vitro and vascular remodeling in vivo via Ptc-1 regulation of Notch signaling.

Turbulent Flow Characteristics and Dynamics Response of a Vertical-Axis Spiral Rotor

The concept of a vertical-axis spiral wind rotor is proposed and implemented in the interest of adapting it to air flows from all directions and improving the rotor’s performance. A comparative study is performed between the proposed rotor and conventional Savonius rotor. Turbulent flow features near the rotor blades are simulated with Spalart-Allmaras turbulence model. The torque coefficient of the proposed rotor is satisfactory in terms of its magnitude and variation through the rotational cycle. Along the height of the rotor, distinct spatial turbulent flow patterns vary with the upstream air velocity. Subsequent experiments involving a disk generator gives an in-depth understanding of the dynamic response of the proposed rotor under different operation conditions. The optimal tip-speed ratio of the spiral rotor is 0.4–0.5, as is shown in both simulation and experiment. Under normal and relative-motion flow conditions, and within the range of upstream air velocity from 1 to 12 m/s, the output voltage of the generator was monitored and statistically analyzed. It was found that normal air velocity fluctuations lead to a non-synchronous correspondence between upstream air velocity and output voltage. In contrast, the spiral rotor’s performance when operating from the back of a moving truck was significantly different to its performance under the natural conditions.

Correlation between freshwater discharge and salinity intrusion in the Han River Estuary, South Korea

Yoon, B.I. and Woo, S.B., 2013. Correlation between freshwater discharge and salinity intrusion in Han River Estuary, South Korea In: Conley, D.C., Masselink, G., Russell, P.E. and O'Hare, T.J. (eds.)The salinity distributions of estuaries and tidal rivers exhibit unique characteristics due to the effects of various external forces, such as tides, freshwater discharge, wind, and topographic effects. The interpretation and understanding of the structure of salinity profiles in coastal and estuarine areas is necessary for addressing issues related to oceanography, water quality, ecology, and engineering. To identify the salinity distribution of Han River Estuary (HRE), South Korea the surface salinity of the southern and northern regions of Yeomha Channel were observed from May to June, 2007. Variations in the salinity were clearly correlated with long- and short-term tidal fluctuations. Furthermore, the salinity strongly decreased when additional freshwater was discharged relative to the dry period, and more than 25 days were required following a high-discharge period to restore the salinity to that of the normal flow conditions. The characteristics of the axial salinity distribution in the Yeomha Channel of the HRE were studied using data from the National Marine Monitoring Network of the National Fisheries Research and Development Institute, and the length of the salinity intrusion relative to the tidal range, the amount of freshwater discharge, and topographic effects were expressed using an empirical equation. A correlation between the saltwater intrusion limit at the HRE and the freshwater discharge rate was expressed using an empirical equation. Based on this simple analytical approach, we believe that the structural characteristics of the salinity distribution in estuaries and tidal rivers vary not only due to freshwater discharge and tidal mechanisms but also due to topographic effects.

An experimental study of turbulence in a heterogeneous channel

This paper examines the velocity field in an idealised heterogeneous open channel during normal flow conditions, corresponding to two different subcritical flow conditions (discharges of 0·040 m3/s and 0·056 m3/s, with corresponding Froude numbers 0·51 and 0·57). The bed of the channel is formed of two full-length, longitudinal strips of equal width, a smooth section constructed from polyvinyl chloride and a rough section constructed from gravel (d72 = 10 mm). The results indicate that the turbulence appears to propagate vertically from the rough bed and horizontally over the rough–smooth boundary. There is also evidence to suggest that the turbulent momentum transfer is maximised at the rough–smooth boundary. Secondary flow structures are seen to exist due to the rough–smooth boundary and provide another mechanism for momentum transfer. These transfer mechanisms are important in understanding the effect of a heterogeneous channel bed on open-channel flow.

Theoretical study on the constricted flow phenomena in arteries

The present study is dealt with the constricted flow characteristics of blood in arteries by making use of an appropriate mathematical model. The constricted artery experiences the generated wall shear stress due to flow disturbances in the presence of constriction. The disturbed flow in the stenosed arterial segment causes malfunction of the cardiovascular system leading to serious health problems in the form of heart attack and stroke. The flowing blood contained in the stenosed artery is considered to be non-Newtonian while the flow is treated to be two-dimensional. The present pursuit also accounts for the motion of the arterial wall and its effect on local fluid mechanics. The flow analysis applies the time-dependent, two-dimensional incompressible nonlinear Navier-Stokes equations for non-Newtonian fluid representing blood. An extensive quantitative analysis presented at the end of the paper based on large scale numerical computations of the quantities of major physiological significance enables one to estimate the constricted flow characteristics in the arterial system under consideration which deviates significantly from that of normal physiological flow conditions.

Cardiovascular drift during low intensity exercise with leg blood flow restriction

Previous studies reported that aerobic-type exercise such as walking or cycling with blood flow restriction (BFR) has been shown to elicit increases in leg muscle hypertrophy and strength, as well as improved aerobic capacity. Although previous studies investigated cardiovascular responses during a relatively short duration of exercise (∼5 min), the effects of prolonged leg muscular BFR have remained unknown. The purpose of this study was to examine the cardiovascular effects of longer duration low intensity exercise combined with BFR. Eight men performed 30 min of exercise at 40% of a predetermined maximal oxygen uptake under both BFR and normal flow (CON) conditions. Cardiovascular parameters were measured at rest and every 10 min during exercise. The main findings were that 1) the SV and HR did not change significantly between 10 to 30 min of exercise in BFR and CON conditions, although BFR-induced reduction of SV and increased HR were found at 10 min exercise compared with normal flow, 2) blood pressure was increased at 10 min of exercise in BFR compared to the CON, however the blood pressure decreased gradually with BFR from 10 to 30 min of exercise, and 3) blood lactate and RPE increased gradually during exercise with BFR. In conclusion, our results suggest that the BFR-induced reduction of SV and increased HR within the first 10 min of exercise are representative of changes in these parameters.

Analysis of flood‐reduction capacity of hydropower schemes in an Alpine catchment area by semidistributed conceptual modelling

AbstractThe simulation of run‐off in Alpine catchment areas is essential for the optimal operation of high head storage hydropower plants (HPPs) under normal flow conditions, but also in case of flood events. A conceptual semidistributed numerical approach is presented, combining hydrologic modelling and operation of hydraulic works. Spatial rainfall and temperature distributions were taken into account for simulating the dominant hydrologic processes, such as glacier melt, snowpack constitution and melt, soil infiltration and run‐off. The object‐oriented modelling tool allowed run‐off generation, simulation of the operating mode of complex HPP and its impact on the downstream river network for different scenarios. The paper briefly presents the hydrologic model and then the application for the upper Aare catchment in Switzerland, where about half of the area is operated by the Oberhasli hydropower scheme. The development, calibration and validation of the hydrologic model are discussed. Finally, the retention effect of the existing reservoirs and their management, including preventive turbine operations, on flood routing in the Aare River upstream of Lake Brienz is presented for the 2005 historical flood event.

A Methodological Approach for Estimating Temporal and Spatial Extent of Delays Caused by Freeway Accidents

Given that reliable prediction of such relatively rare-and random-events as accident occurrence will remain elusive, the most important potentially soluble factor in the development of accident management strategies is to identify and quantify the conditions affecting the nonrecurrent congestion caused by accidents once they have been known to have occurred. The objective of the research reported in this paper is to develop a method of quantifying the delay due to accidents on urban freeways, as well as to identify the causal factors affecting the total delay caused by such accidents. Binary integer programming (BIP) is applied in estimating the temporal and spatial extent of delay caused by freeway accidents, based solely on commonly available inductance loop detector data. The basic idea behind the method is to estimate the most likely temporal and spatial extent of the region of congestion caused by an accident by solving a BIP problem that is consistent with the topology of the spatio-temporal region that defines candidate speed differences between normal flow conditions and accident conditions. The procedures developed in this paper will be useful for the performance evaluation of accident management systems by quantifying accident congestion in terms of the total delay to evaluate the benefit of accident management systems accrued from efficient traffic operations. The procedures are demonstrated by a case study using accident data collected from six major freeways in Orange County, CA.