Electromagnetic Velocity Meter Research Articles

Boundary Influence and Flow Characteristics of Orisa and Ala Rivers in Kwara and Ondo States, Nigeria

In this study, the effects of boundary influence on flow characteristics of Rivers Ala and Orisa were investigated. Soil samples were collected from three points each from both rivers namely Glory Parish Area (GPA), Olusola Oke Area (OOA) and Fiwasaye; Aran-Orin Area (AOA), Rore and Omu-Aran on Rivers Ala and Orisa Respectively. A MGG/KL-DCB Portable Electromagnetic Velocity Meter was used to measure the in-situ readings of discharge and velocity at the various points. The sediments collected from the sampling points were placed in the Flume in the Hydraulic Laboratory of Civil Engineering Department, Landmark University. The Flume was then set with the measured parameter (Discharge) for each sampling point to apply the Flume to determine the Velocity for both Rivers at slopes of 0.008 to 0.056 respectively. The velocities obtained at the different slopes were inserted into Manning’s Coefficient equation to obtain the flow characteristics. The relationship between the velocity and Manning’s Coefficient was determined using the Spearman’s rank correlation coefficient. All analyses were done at P-value less than 0.05 level of significance. The velocity varied between 0.0237± 0.0004 and 0.0587± 0.0004 m/s; 0.0542± 0.0004 and 0.0701± 0.0003m/s and 0.0789± 0.0005 and 0.0172± 0.1323m/s for GPA, OOA and Fiwasaye for Ala River and between 0.0751± 0.0007 and 0.1008± 0.0006m/s; 0.0628± 0.0007 and 0.0839± 0.0004m/s and 0.0421± 0.0005 and 0.1076± 0.0004m/s for AOA, Rore and Omu-Aran for Orisa River. The results of the effects of soil boundary influence showed that the velocity was inversely proportional with the Mannings’ coefficient at all sampling points of both rivers if the geometry of the river channel is kept constant. This indicates that areas with high velocities are prone to flooding. Further studies should be carried out on more sampling points on the rivers to confirm flow characteristics of the rivers.

Enhancing transverse mixing by using triangular vane in the straight channel

The transport of pollutants in the large rivers especially in the lowest downstream reach of a river, in which the velocity and the intensity of flow turbulent become very low, is performed to a great extent by dispersion. Any measure to enhance the level of turbulence in the flow field will increase the mixing of pollutants. The main goal of the present study is to investigate how the transverse mixing is increased by using a triangular vane (TV). TV is a hydraulic structure used for bank protection and habitat restoration and is suitable for fish and other aquatic organisms. Experiments were carried out in a flume of 10m long and 0.8m wide. Two different conditions of with and no vane were tested under four different flow conditions. A salt solution was used as a tracer. An electronic concentration measuring equipment consisted of conductivity probes was used which can measure the concentration at 49 nodes in four cross-sections downstream simultaneously. The three-dimensional velocity components were also measured by using the electromagnetic velocity meter and the characteristics of three-dimensional flow patterns including turbulent kinetic energy (TKE) and the vertical distribution of the transverse velocity were analyzed. The result showed that the TV by deviating the velocity vectors to the transverse direction, by developing the secondary flows and by displacing the position of the rotating cells in different transverse sections, causes the transverse mixing to increase 3.2 times and to reduce the complete mixing length by as much as 76% compare to the case of no vane. The average values of the TKE found to be increased by as much as 3 times. Finally, a new dimensionless parameter has been proposed to correlate dimensionless transverse mixing to the flow parameters.

An experimental study on the secondary flows and bed shear stress at a 90-degree mild bend with and without triangular vanes

River outer bank erosion and associated inner bank sedimentation cause river morphological and environmental changes. Triangular vanes are eco-friendly structures used for protection of river bank from erosion and morphological changes, fish passage improvement, and also fish habitat enhancement. In the present study, the 3D velocity components at a mild 90-degree channel bend were measured via an electromagnetic velocity meter with and without installed triangular vane. These tests were conducted at a Froude number of Fr = 0.214. The analysis of data showed that the triangular vane decreased the bed shear stress near the outer bank at the upstream and downstream sections of the vane for a distance of about 11 times the effective length of the vane. The maximum reduction at the upstream and downstream of the structure was calculated to be 67% and 80%, respectively. The strength of the vane-induced secondary flow was greater than that of the bend-induced secondary flow. At the position of 0.8L in the structure's downstream, the strength of the vane-induced secondary flow was maximum, after which started reducing and reached the strength of the bend-induced secondary flow at the position of 7L in the structure's downstream.

Bed-mounted electro magnetic meters: Assessment of the (missing) technical parameters

Flow measurements in Urban Drainage Systems (UDS) are essential for pollution control and system management. Since the accuracy of, today the most popular, Acoustic Doppler Velocimeters is impeded by several factors, this research is focused on the alternative, or a supplemental, Electro-Magnetic Velocity (EMV) meters. EMV meters are more robust and can provide accurate low flow measurements, even when covered with porous sediment. However, the downside of EMV is the small control volume (CV) where the flow velocities are integrated in a non-linear manner to obtain a single, one-dimensional measured velocity. For a better understanding of the sensor output and measured mean flow velocity with quantified uncertainty, it is necessary to determine the size of the CV and to understand the non-linear integration principle within the CV. Valuable technical parameters, needed for describing these EMV properties, are typically not provided by the manufacturers. Fundamentally, they could be defined with the magnetic field and “virtual” current distributions. To allow for a more practical interpretation of the EMV operating principle, a simplified model of an EMV sensor is proposed here. The suggested model describes the EMV operating principle with only two technical parameters, one-dimensional weighting function w and the reach of the CV, the τmax. Furthermore, a methodology is proposed for defining these two parameters, using two lab flume experiments. The first one is focused on the investigation of the EMV output, when the EMV is covered by the porous sediment with different depths. The second experiment involves the determination of the longitudinal velocity distribution within the lab flume and the CV of the EMV meter. A backward analysis is suggested to formulate a minimization problem, from which the unknown technical parameters are assessed. The proposed procedure was applied on the examined Flat DC-2 EMV meter. Derived one-dimensional weighting function w exponentially drops with the distance from the electrodes, while the reach of the CV was found to be τmax = 8.7 cm. These parameters, and the simplified model, were validated against the EMV outputs acquired in the lab flume, without sediment presence.

Bed-mounted Electro Magnetic meters: Implications for robust velocity measurement in Urban Drainage systems

Flow monitoring in Urban Drainage Systems (UDS) is required for a successful system control and operational assessment. Commonly used methods can lead to erroneous results in partially filled pipes and hostile environmental conditions, normally encountered in UDS. Recent studies focused on the flow rate measurements in UDS revealed that the capability of acoustic Doppler velocimeters to estimate mean flow velocity is impeded by several factors. Most prominent issues are the operation under low flow depths and velocities, as well as in the case of the sedimentation at low flow velocities. This study is focused on an alternative method for the velocity measurements in the UDS, based on Electro-Magnetic Velocity (EMV) meters. The study also determines the sensor’s capacity to operate when covered by a porous sediment layer, using a newly developed procedure. A brief theoretical background is given to support the idea behind the usage of EMV in UDS. Measurement uncertainties were firstly benchmarked in the laboratory flume without sediment. After local, site-specific (re)calibration, EMV operated with combined uncertainty of only few cm/s. Furthermore, the EMV measured the flow rates with depths low as 4 cm and velocities bellow 5 cm/s. Additionally, a series of tests were performed with sediment layers above the EMV meter, varying in height from 0 to 80 mm. Observational uncertainty analysis showed that EMV meter can be used even in these conditions. Since the bias uncertainty increased with the rise of the sediment depth, a correction function model was derived for the transformation of the output signal, reducing the observational uncertainties below 5 cm/s. Subsequently, practical implications of the EMV usage in the UDS are considered.

Development and installation of bedload monitoring systems with submerged load cells

Bedload governs riverbed channel variations and morphology,it isnecessarytodeterminebedload discharge through an arbitrary cross sectionin a mountain river. A new system with submerged load cells has been developed to directly measure bedload discharge. The system consists of:(1) anironbox which is 1 m long, 0.5 m wide and 0.1 m in depth, (2) two submerged load cells 0.7 m apart, (3) a pressure sensor and,(4) an electromagnetic velocity meter. This system has been designed to exclude the effect of the hydraulic pressure of water on direct measurements ofbedload particle weight. Initialtestsin a laboratorywere conducted to examine the accuracy of measurements with the system underaerial conditions. The system has beeninstalled in the supercritical flume in Ashi-arai-dani River of the Hodaka Sedimentation Observatory of the Disaster Prevention Research Institute (DPRI) of Kyoto Universityto obtain bedload dischargeunder natural conditions. Flume tests were conductedin this channelby artificial supply of uniform sediment particles ofseveral grain sizes.The averagevelocity of the sediment particles near the bed wasestimated usingcross-correlation functions forweightwaves obtained bythe two load cells.Bedload dischargecalculations were based ontime integration oftheproduct of sediment velocity andsedimentweight obtained bythe twoload cells. Thisstudyclarifies thereasons whybedload measurements are difficult, and providessomesolutions using the monitoring systems with submerged load cells through the field measurements. Additionally, the applicabilityofbedload measurement with the submerged load cellsis explained based onexperimental artificial sediment supplydata.

Optimising round-edged entrance of 55° river water intake

An experimental study was undertaken to optimise a 55° round-edged entrance irrigation water intake. The tests were carried out under different flow conditions in a laboratory flume with a rectangular cross-section under close-ended and open-ended flow conditions. To improve the efficiency of water intake, its entrance was rounded with three different radii (r): 100, 150 and 200 mm. Two components of flow velocity in transverse and flow directions were measured using an electromagnetic velocity meter. The flow velocity inside the water intake was measured at 390 regular grid points, across three horizontal layers at 30, 60 and 120 mm heights from the bed. The streamlines were drawn from the captured flow velocity, and hence the separation width and length were determined for the different depth levels, from the bed to the water surface. The discharge ratios (Qr) of the main channel to the lateral channel were set equal to 0·25, 0·67, 1·5 and 4. It was found that a 55° water intake with the radius of curvature of r/Wb = 0·8 produced minimum separation size. It was therefore selected as the optimum 55° round-edged entrance water intake.

Mathematical modeling of processes in an electromagnetic velocity meter for liquids

A method is proposed for mathematically modeling the hydrodynamic and electromagnetic processes that take place in different electromagnetic velocity meters designed for use on liquids.

An analysis of the characteristics of rough bed turbulent shear stresses in an open channel

Entrainment of sediment particles from channel beds into the channel flow is influenced by the characteristics of the flow turbulence which produces stochastic shear stress fluctuations at the bed. Recent studies of the structure of turbulent flow has recognized the importance of bursting processes as important mechanisms for the transfer of momentum into the laminar boundary layer. Of these processes, the sweep event has been recognized as the most important bursting event for entrainment of sediment particles as it imposes forces in the direction of the flow resulting in movement of particles by rolling, sliding and occasionally saltating. Similarly, the ejection event has been recognized as important for sediment transport since these events maintain the sediment particles in suspension. In this study, the characteristics of bursting processes and, in particular, the sweep event were investigated in a flume with a rough bed. The instantaneous velocity fluctuations of the flow were measured in two-dimensions using a small electromagnetic velocity meter and the turbulent shear stresses were determined from these velocity fluctuations. It was found that the shear stress applied to the sediment particles on the bed resulting from sweep events depends on the magnitude of the turbulent shear stress and its probability distribution. A statistical analysis of the experimental data was undertaken and it was found necessary to apply a Box-Cox transformation to transform the data into a normally distributed sample. This enabled determination of the mean shear stress, angle of action and standard error of estimate for sweep and ejection events. These instantaneous shear stresses were found to be greater than the mean flow shear stress and for the sweep event to be approximately 40 percent greater near the channel bed. Results from this analysis suggest that the critical shear stress determined from Shield's diagram is not sufficient to predict the initiation of motion due to its use of the temporal mean shear stress. It is suggested that initiation of particle motion, but not continuous motion, can occur earlier than suggested by Shield's diagram due to the higher shear stresses imposed on the particles by the stochastic shear stresses resulting from turbulence within the flow.

Experimental Investigation of Flow in Embayment

This study reports the results of flow visualization and velocity measurements in embayment. Flow visualization was done using aluminum powder as tracer and velocity measurements were carried out with electromagnetic velocitymeter. Visualized flow shows the formation of large organized eddies at the embayment-main channel interface and the existence of primary recirculation, secondary recirculation and flow separation. Measured velocity reveals that the mean velocities vary little with depth for low flow condition. Flow becomes more complex for flood flow condition and then, depth averaging is meaningless.

Input impedance of the systemic circulation in man.

To determine the systemic input impedance, pulsatile pressure and flow were measured in the ascending aorta in 16 human subjects who were undergoing diagnostic cardiac catheterization. Blood flow was measured with a catheter-tip electromagnetic velocity meter, and pressure with an external transducer connected with the fluid-filled lumen of the catheter. Five subjects were found to have no evidence of cardiovascular disease (group A, mean age 32 +/- 2 years, mean aortic pressure 97 +/- 4 mm Hg). Seven had clinical and angiographic signs of coronary arterial disease, and mean pressures less than 100 mm Hg (group B, mean age 48 +/- 2 years). Four subjects had signs of coronary disease and mean pressures greater than 100 mm Hg (group C, mean age 48 +/- 3 years). The frequency spectra of impedance were qualitatively similar in all three groups and resembled those previously observed in the canine aorta. Characteristic impedance was lower in the normal subjects (group A, average 53 dyn sec cm-5) than in the subjects with coronary artery disease (groups B and C, average 129 dyn sec cm-5). Among the subjects with coronary disease, characteristic impedance was higher in the hypertensive subjects (group C, average 202 dyn sec cm-5) than in those with lower mean pressures (group B, average 95 dyn sec cm-5). External left ventricular work per unit time (hydraulic power) averaged 1715 milliwatts (mW) in group A, 1120 mW in group B, and 2372 mW in group C. Cardiac outputs were within normal limits in all subjects, but tended to be lower in group B than in group C. These results suggest that the subjects of group C were better able to meet the increased energy demands imposed by an abnormally high aortic input impedance. Further investigation is needed to learn whether the high impedances in subjects with coronary disease represent an increase with age and transmural pressure alone, or whether some additional factor is involved. The data on relatively normal subjects permit a tentative definition of the normal limits for aortic input impedance in man: 26-80 dyn sec cm-5.

Use of a catheter tip electromagnetic velocity meter to determine the cardiovascular effects of glucagon.

The cardiovascular effects of glucagon were determined in anaesthetized dogs. Glucagon increased heart rate and myocardial contractility. Aortic, renal, and mesenteric flow increased. Neither the cardiac nor vascular dilating actions of glucagon were prevented by β-adrenergic blockade. Glucagon had a biphasic effect on carotid artery flow; an initial increase followed by a decrease. With femoral flow the initial response was variable, but the late response was usually a decrease in flow. These results were seen with intravenous injection. Intra-arterial injection of glucagon produced an increase in mesenteric, renal, carotid, and femoral flow. Results obtained with the intravascular catheter tip electromagnetic velocity probe were similar to those obtained with the external electromagnetic cuff flowmeter. An important advantage of the catheter tip probe over the cuff probe was that the former could be manipulated into various arteries via a small incision in a peripheral artery, thus avoiding extensive surgical dissection.