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A pantograph receives aerodynamic force while a train is traveling. As the aerodynamic force increases in proportion to the square of the flow velocity relative to the pantograph, its influence on the pantograph becomes apparent, ...
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A pantograph receives aerodynamic force while a train is traveling. As the aerodynamic force increases in proportion to the square of the flow velocity relative to the pantograph, its influence on the pantograph becomes apparent, especially for high-speed trains. When a high-speed train runs in a tunnel, the flow velocity relative to the pantograph is faster than that in an open section. In this study, we measured the flow velocity around a train model running in a tunnel using a rake of total-pressure tubes mounted on the train model. The measured waveforms were distorted owing to the influence of the frequency characteristics of the measurement system. Therefore, we developed a restoration method and applied it to the measured waveforms to obtain the restored waveforms of the flow velocity. With the restored waveforms, we obtained several statistical values, such as the average flow velocity and standard deviation of the fluctuating flow velocity around the train model. Furthermore, we proposed a method for predicting the flow velocity around the train model, including fluctuating components in a frequency range of a pantograph contact performance. The proposed method can predict the flow velocity at the panhead of a pantograph by considering the average flow velocity profile and turbulence component profile in the tunnel cross section, which could not be taken into account so far.
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Precise estimation of mean flow velocity (U _(mean)) is imperative for accurate prediction of hydrographs and sediment yield. For overland flow, U _(mean) is normally estimated by multiplying the dye or salt based velocity measure...
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Precise estimation of mean flow velocity (U _(mean)) is imperative for accurate prediction of hydrographs and sediment yield. For overland flow, U _(mean) is normally estimated by multiplying the dye or salt based velocity measurement with a correction factor (α). A wide range of correction factors is available in the literature, all of which were derived under different experimental conditions. The selection of a suitable α has become a main challenge for accurate mean flow calculations. This study aimed to assess the variability of α with grain size (D _(50)) and slope (S), and to evaluate the dependency of U _(mean) on flow rate (Q), D _(50) and S by regression analysis. Flume experiments were performed at Q varying from 33 to 1033×10 ~(-6)m ~3s ~(-1), S ranging from 3° to 10°, and D _(50) ranging from 0.233 to 1.022mm. Flow velocities were measured directly with the dye tracing technique (U _(dye)), and derived indirectly from flow depth measurements (U depth). The U depth measurements were considered as U _(mean). The derived α (U _(depth)/U _(dye)) values did not remain constant with sediment size and increase significantly with the increase of D _(50). The mean α values for 0.230, 0.536, 0.719 and 1.022mm sands were 0.44, 0.77, 0.82 and 0.82, respectively. Hence, due to the substantial variation of α with D _(50), no absolute α value is applicable to all hydraulic and sedimentary conditions. However, mean α values for 0.230, 0.536 and 0.719mm sands were found comparable with α values available in the literature for similar grain sizes. The influence of Q, S, and D _(50) on U _(mean) was studied by regression analysis. Regression analysis depicted the significant influence of Q and D _(50) on U _(mean), while the effect of slope was found to be non-significant. Comparison of the derived regression equation with five literature datasets showed that the model can predict mean flow velocities in overland flow at a reasonable accuracy as long as the mean velocity is below 0.4ms ~(-1). At higher velocities the error becomes unacceptably large.
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Speckle tracking methods overcome the major limitations of current Doppler methods for flow imaging and quantification: angle dependence and aliasing. In this paper, we review the development of speckle tracking, with particular a...
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Speckle tracking methods overcome the major limitations of current Doppler methods for flow imaging and quantification: angle dependence and aliasing. In this paper, we review the development of speckle tracking, with particular attention to the advantages and limitations of two-dimensional algorithms that use a single transducer aperture. Ensemble tracking, a recent speckle tracking method based upon parallel receive processing, is described. Experimental results with ensemble tracking indicate the ability to measure laminar flow in a phantom at a beam-vessel angle of 600, which had not been possible with previous 2D speckle tracking methods. Finally, important areas for future research in speckle tracking are briefly summarized.
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Measurement of complex natural flows, especially those occurring in rivers due to man-made structures, is often hampered by the limitations of existing flow measurement methods. Furthermore, there is a growing need for new measure...
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Measurement of complex natural flows, especially those occurring in rivers due to man-made structures, is often hampered by the limitations of existing flow measurement methods. Furthermore, there is a growing need for new measurement devices that are capable of measuring the hydrodynamic characteristics of complex natural flows required in environmental studies that often use fish as an indicator of ecological health. In this paper, we take the first step toward natural flow measurements with a new biologically inspired probe design in conjunction with signal processing methods. The device presented in this paper is a dedicated hydrodynamically sensitive sensor array following the fish lateral line sensor modality. Low-level multidimensional sensor signals are transformed to the two key hydrodynamic primitives, bulk flow velocity and bulk flow angle. We show that this can be achieved via canonical signal transformation and kernel ridge regression, allowing velocity estimates with a less than 10 cm/s error. The approach provides robust velocity estimates not only when the sensor is ideally oriented parallel to the bulk flow, but also across the full range of angular deviations up to a completely orthogonal orientation by correcting the pressure field asymmetry for large angular deviations. Furthermore, we show that their joint estimation becomes feasible above a threshold current velocity of 0.45 m/s. The method demonstrated an error of 14 cm/s in velocity estimation in a river environment after training in laboratory conditions.
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In intermediate and large scale fire test applications, a bi-directional low-velocity pressure probe is used to obtain the volume flow. The probe was presented by McCaffrey and Heskestad in 1976 and has found its way to several in...
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In intermediate and large scale fire test applications, a bi-directional low-velocity pressure probe is used to obtain the volume flow. The probe was presented by McCaffrey and Heskestad in 1976 and has found its way to several international standards including the Room Corner test and the Single Burning Item test (SBI). The probe is considered 'state of the art' for measuring flow rate in fire test applications. The main disadvantage however is that the probe factor changes with pitch and/or yaw angle variations. The modified SBI pressure probe is less sensitive to angular variations but then again is Reynolds dependent. A new pressure probe design has been developed that combines a low angular sensitivity with a Reynolds independency over a wide range. Although the probe has been developed for intermediate and large scale fire test applications, its use is not limited thereto.
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Water flow has been widely accepted as a target to suppress algae blooms. However, the effectiveness of the flow regulation is unclear due to lack of hard evidences to illuminate the direct cause-effect relationship between hydrod...
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Water flow has been widely accepted as a target to suppress algae blooms. However, the effectiveness of the flow regulation is unclear due to lack of hard evidences to illuminate the direct cause-effect relationship between hydrodynamic forces and algae growth. In this study, a field observation at a freshwater lake was conducted weekly or biweekly from July 2007 to December 2009. Phytoplankton biomass and composition were investigated at flow velocities of 0.03 m/s, 0.06 m/s, 0.10 m/s, 0.15 m/s and 0.30 m/s in field enclosure experiments. The results from the field observation indicated that phytoplankton biomass and spatial distribution largely depend on the flow condition. A strong negative correlation (R~2 = -0.618, n = 222, P<0.001) was found between Chl-a concentration and flow velocity. The results of enclosure experiments showed that turbulent flow has the inhibition effect on phytoplankton biomass, but less impact on composition. The average Chl-a concentrations in the flowing enclosures were 20.3%-37.5% lower than that in their corresponding still water enclosures during the entire experiment period. Shear stress within pumps might have caused up to 10% of cell damage. The present study highlights that a universal critical velocity for suppressing algae growth probably does not exist in freshwater bodies, for each has its unique physical, chemical and ecological characteristics. It is therefore suggested that sufficient experiments should be conducted for each water body before a critical flow condition is applied to reduce the algae bloom occurrence.
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The linear entropic relation between mean flow velocity u and maximum velocity u_(max) is defined through a dimensionless entropy parameter M, which is found constant for gauged river sections. This entropic relation has been test...
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The linear entropic relation between mean flow velocity u and maximum velocity u_(max) is defined through a dimensionless entropy parameter M, which is found constant for gauged river sections. This entropic relation has been tested for many rivers and has been found to be fundamental to addressing velocity measurements during high floods when sampling can be carried out only in the upper portion of flow area where the maximum velocity u_(max) occurs. It is therefore of considerable interest to investigate the possible dependence of M on hydraulic and geometric characteristics so that it can be determined for ungauged river sites. Thus, this study attempts to define the dependence of M on the geometric and hydraulic characteristics of river cross sections by coupling Manning's equation expressing u with the equation for u_(max) obtained through a logarithmic velocity distribution, which takes into account the possibility that u_(max) may occur below the water surface. Analysis shows that M does not depend on the energy or water surface slope S_f, thus justifying why its mean value at a gauged site is always nearly the same, whatever the flood condition. Moreover, the hydraulic and geometric characteristics that permit the determination of M mainly include Manning's roughness, hydraulic radius, and locations where u_(max) occurs and the hypothetical zero velocity. Then, a formulation relating Manning's roughness to M is proposed. Velocity measurements carried out in the past 20 years at two gauged sections along the Tiber River, Italy are used to test the analysis.
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This paper describes a novel dual-frequency inductive flow tomography (IFT) system, which relies on the use of a multi-electrode electromagnetic flow meter (EMFM). This flow meter is currently capable of imaging the velocity profi...
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This paper describes a novel dual-frequency inductive flow tomography (IFT) system, which relies on the use of a multi-electrode electromagnetic flow meter (EMFM). This flow meter is currently capable of imaging the velocity profile of the conducting continuous phase of both single phase and highly asymmetric multiphase flows ten times every second. Uniform and anti-Helmholtz magnetic fields are simultaneously applied to the cross section of the flow tube of the EMFM. This enables flow induced potentials to be measured, at an array of electrodes, flush mounted on the inner wall of the EMFM, ten times every second using a multi-channel analogue signal conditioning system. These measured flow induced potentials are then used in an image reconstruction algorithm to reconstruct the water velocity profile in the flow cross section at 0.1 s time intervals.
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Understanding the velocity distribution of shallow water flow along hill-slope is of great significance in soil erosion studies. This study proposes a method to estimate the steady flow velocity and the distance when water flow re...
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Understanding the velocity distribution of shallow water flow along hill-slope is of great significance in soil erosion studies. This study proposes a method to estimate the steady flow velocity and the distance when water flow reaches stability, using hill-slope flow velocity distribution data along a simulated rill measured by the electrolyte tracer pulse method. Laboratory experiments were performed using a flume of 12 m long, 0.1 m wide and 0.3 m height under five slope gradients (5, 10, 15, 20 and 25) and four flow discharges (2, 4, 8 and 16 L min(-1)). The electrolyte tracer pulse method was employed to measure the flow velocities at locations of 1, 2, 3, 4, 6, 8, 10 and 12 m from the inlet of the flowing water. The flow velocities measured by the dye tracer method served as a control. The results showed that the flow velocities measured by the electrolyte tracer pulse method initially accelerated and then reached a steady value. An equation for estimating flow velocity on the basis of the measurement distance was established. The flow velocities calculated by the equation agreed well with those measured by the electrolyte tracer pulse method. The determination (R-2) and the Nash-Sutcliffe model efficiency (NSE) were greater than 0.800, except for a few cases. In addition, the equation established in this study was shown to successfully predict flow velocities measured in other studies. The steady flow velocities and the distances when water flow reached stability under different slope gradients and flow discharges were determined by this equation. When the differences between the measured flow velocity and the steady flow velocity were very small, that is, 5% and 10%, the steady distances ranged from 2.239 m to 4.772 m and from 2.843 m to 6.059 m, respectively. By comparing the steady flow velocities with the flow velocities measured by the dye tracer method, the results indicated that the steady flow velocities were 0.702-0.735 times that of the flow velocit
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Эффективность управления вентиляцией угольных шахт во многом определяется точностью анемометрических измерений. Перспекти...
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Эффективность управления вентиляцией угольных шахт во многом определяется точностью анемометрических измерений. Перспективным направлением обеспечения безо- . пасности горных работявляется разработка устройств пространственного интегрального анемометрического контроля.В данной работе получено общее выражение для траектории акустического луча в анемометрическом канале. Проведена оценка степени отклонения этой траектории от прямолинейной для случаев ламинарного и турбулентного потока воздуха и выведены соответствующие аналитические зависимости. Полученные уравнения отклонений траекторий акустического пучка в аэродинамическом поле от прямолинейных позволяют устранить соответствующие погрешности измерений и вычислений при разработке аппаратуры интегральной акустической анемометрии.
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