Average Stream Velocity Research Articles

Raft on a Highline: Loads and Trim

This study examines the loads associated with the positioning of a 4.5m raft on a high line in moving water. Testing was conducted within a flow-calibrated channel demonstrating representative stream velocities typical (0.6 – 5.4ms/ also MPH) of those encountered during water related rescues. The raft was positioned from a high line mid-stream, and a load cell was utilised to collect force/time data. The independent variables of trim (relative positioning of the load within the boat) and average stream velocity were investigated. The findings challenge assumptions regarding the impact of trim on the loads within a highline, the relationship between flow rate and loads on highline and make recommendation for training and practice. The study contributes to understanding the loads placed on high lines by representative rafts during operational rescues. KEY WORDS: High line, trim, force, current vector, water rescue training.

Scaling Analysis and Its Implication for Asphaltene Deposition in a Wellbore

Summary The study presented here uses order-of-one—or o(1)—scaling analysis to identify dimensionless groups specific to asphaltene deposition along production tubing. The precipitation and subsequent deposition of asphaltene can lead to significant complications related to oilfield production. Aside from the many complications within a reservoir as well as surface equipment, the reduction in cross-sectional area caused by its deposition leads to increased pressure losses, reductions in volumetric flow capacity, and possible flow perturbations within a wellbore. Attempts to mitigate these adverse effects have focused on both hindering the precipitation of asphaltene and preventing its deposition after precipitated. The study used here attempts to quantify various hydrodynamic controls specific to asphaltene deposition. With o(1) scaling analysis, four independent dimensionless groups were generated from momentum and mass-balance equations relating hydrodynamic effects to the rate of asphaltene deposition. The dimensionless group π4 was of particular interest because of its inherent relationship to the rate of deposition. This group was compared with both data and existing correlations taken from literature, and noticeable trends in the deposition rate with respect to average stream velocity were observed. One of the most important trends discerned by these comparisons was a clear distinction whereby the rate of asphaltene deposition, related through π4, decreases with increasing Reynolds numbers (Re) in lower ranges, but actually increases in higher ranges. Although the data did not cover the specific region of transition, various correlations suggest a clear cutoff between what was deemed a favorable regime, or Regime I, and a nonfavorable regime, or Regime II.

POWER SPECTRUM OF AN INTERFEROMETER SIGNAL IN EXPERIMENTS ON SOUNDING OF A TURBULENT WATER STREAM WITH PULSATING VELOCITY

The paper is related to studies of a turbulent medium by the sounding method with the interferometric reception. We performed a theoretical analysis of a multiplicative interferometer response to noise quasi-monochromatic emission, disturbed by a turbulent water stream. The effect of turbulent pulsations of the stream velocity on output interferometer signal was considered. Spectral analysis of the output interferometer signal allowed to perform the diagnostics of the propagation media. Particularly, it was shown, that the interferometer power spectrum carries information on the spatial spectrum of fluctuations of cavity bubbles concentration and on the average stream velocity. The theoretical evidence has been compared with the results of interferometric experiments on ultrasonic sounding of the water stream inside a pipe.

Estimation of Average Stream Velocity

Stream tracer studies provide information supporting diverse applications in environmental research and management. Average stream velocity through a reach is often estimated from tracer temporal profiles. This Technical Note addresses the calculation of average reach velocity. It is shown here that, under steady flow, average reach velocity over a fixed distance equals the spatial harmonic mean velocity. Similarly, the average reach velocity from the point of tracer injection to a fixed downstream measurement site is equal to downstream distance divided by the harmonic mean tracer time-of-travel, rather than the commonly used temporal centroid.

Predicting changes in hydrologic retention in an evolving semi-arid alluvial stream

Hydrologic retention of solutes in hyporheic zones or other slowly moving waters of natural channels is thought to be a significant control on biogeochemical cycling and ecology of streams. To learn more about factors affecting hydrologic retention, we repeated stream-tracer injections for 5 years in a semi-arid alluvial stream (Pinal Creek, Ariz.) during a period when streamflow was decreasing, channel width increasing, and coverage of aquatic macrophytes expanding. Average stream velocity at Pinal Creek decreased from 0.8 to 0.2 m/s, average stream depth decreased from 0.09 to 0.04 m, and average channel width expanded from 3 to 13 m. Modeling of tracer experiments indicated that the hydrologic retention factor ( R h), a measure of the average time that solute spends in storage per unit length of downstream transport, increased from 0.02 to 8 s/m. At the same time the ratio of cross-sectional area of storage zones to main channel cross-sectional area ( A s/ A) increased from 0.2 to 0.8 m 2/m 2, and average water residence time in storage zones ( t s) increased from 5 to 24 min. Compared with published data from four other streams in the US, Pinal Creek experienced the greatest change in hydrologic retention for a given change in streamflow. The other streams differed from Pinal Creek in that they experienced a change in streamflow between tracer experiments without substantial geomorphic or vegetative adjustments. As a result, a regression of hydrologic retention on streamflow developed for the other streams underpredicted the measured increases in hydrologic retention at Pinal Creek. The increase in hydrologic retention at Pinal Creek was more accurately predicted when measurements of the Darcy–Weisbach friction factor were used (either alone or in addition to streamflow) as a predictor variable. We conclude that relatively simple measurements of channel friction are useful for predicting the response of hydrologic retention in streams to major adjustments in channel morphology as well as changes in streamflow.

Effect of free-stream fluctuations on laminar forced convection from a straight tube

The effect of free-stream fluctuations on forced convection heat transfer from a straight tube of circular cross-section is investigated. The tube is assumed to have an isothermal surface and is placed in an unsteady but uniform cross stream. The free-stream fluctuations are represented by periodic (sinusoidal) fluctuations superimposed on the average stream velocity. The resulting unsteady velocity and thermal fields are obtained by solving the conservation equations of mass, momentum and energy. The main parameters involved are Reynolds number, Strouhal number, Prandtl number and the relative amplitude of fluctuations. The paper focuses on the effects of the amplitude and frequency of free-stream fluctuations on the local and average Nusselt numbers while keeping Prandtl number unchanged ( Pr = 0.7). The average flow Reynolds number ranges from 50 to 500, the Strouhal number ranges from π 4 to π and the amplitude ranges from 20 to 50% of the free-stream average velocity. The study revealed that the effect of fluctuations on the time-average Nusselt number becomes more pronounced with increasing Reynolds number. It also revealed that the rate of heat transfer increases with the increase of the amplitude but decreases with the increase of frequency. The time-average Nusselt number is tabulated for all cases studied and the details of flow and thermal fields are presented in the form of local Nusselt number and surface vorticity distributions as well as streamline and temperature contours for some selected cases.

A stack dust monitor based on particle counting and sizing

A dust monitor based on forward light scattering has been developed for continuous measurement of suspended particulates in stack gas. The number and height of the scattered light pulses by small particles corresponds to the number and size of particles, respectively. The following technique has been adopted: a forward light scattering optical system to obtain hign sensitivity, an iso-kinetic sampling probe to keep the velocity of sampled gas the same as the average stream velocity in the stack or the flue, a direct and diluent sampling to attain accurate measurement in a wide range of mass concentrations, and an air-curtain to prevent the contamination of the optical system. The instrument is able to determine mass concentration and particle size distribution simultaneously. The instrument has been used in field tests at oil- and coal-fired power stations, oil-fired industrial boilers, cement kilns and so on, and reproducible and good results have been obtained.

Comparison of formulas without roughness coefficients for determining the average stream velocity in rivers

As long ago as in the 19th Century various investigators proposed several empir ica l formulas for determining the average stream veloci ty in rivers which did not include roughness coeflicient~ (the formulas of Hessle, Hermanek. Greger, Matakevich, e t al . , [1, 2]). The exclusion of these coefficients is possible owing to the circumstance that in a natural flow roughness is closely related with the character of the flow: its discharge rate, slope, width, depth, etc, The empir ica l formulas for the Chezy coefficient which do not include the roughness coefficient have a complete ly different structure, which hampers their comparison with each other. However, i f we use the morphomet~ic relations which include the main geometric and hydraulic elements of the flow, such a comparison is possible. Of the large number of such relations proposed, we used the formulas of N. V. Lapturev [3] based on treatment of ex tensive data of ful l-scale observations on lowland rivers: h=0.52Q~ s~*, B = 4,66Q ~ = 12.5h t ,5 i=0.00028Q-O,= =0.00057h-O.,.

A salt tracing method for measuring channel velocities in small mountain streams

Measuring or calculating channel velocities in small mountain streams is very difficult due to the high variability of the channel geometry parameters and roughness characteristics. A salt tracing procedure has been examined for small streams. The technique is simple and quick, using materials that are commonly available at most research watersheds and water resource centers. The velocity through the channel reach using the salt tracing method was found to be a better representation of the average stream velocity than that computed by the continuity equation at three channel cross sections.

A Method for Measuring Interplanetary Plasma Streams Using Bistatic Radar

A method of measuring interplanetary plasmastream velocities using bistatic-radar transmissions from earth to a spacecraft is proposed. Nonrelativistic plasma velocities are considered, and the presence of a uniform interplanetary magnetic field is included. The effect of the streaming motion of the plasma medium is shown to introduce a second-order Faraday polarization change on a linearly polarized transmitted wave. Furthermore, this small second-order effect can in principle be conveniently measured using twoway propagation between the two transmission termini. This method represents an improvement over existing means of velocity measurement using plasma probes since the radar measurements establish the average stream velocity over the straight-line propagation path as opposed to the point samples of the plasma probe.

Deduction of flow regime from bedding character in conglomerates and sandstones

Deduction of flow regime from bedding character in conglomerates and sandstones

Self-Focusing Streams

Streams consisting of a mixture of ions and electrons in which the average velocity of the electrons in the direction of the stream is different from the average stream velocity of the ions can be magnetically self-focusing. The random velocities of the electrons and ions about their respective average stream velocities do not need to be Maxwellian. The only condition which must be met is that the total electric current in stream must exceed a critical value which can be calculated in terms of the stream velocities and the average kinetic energies of the particles due to components of velocity transverse to the axis of the stream. Streams containing both slow and fast particles of like kind tend to eject the slow particles and keep the fast ones. Streams of particles of one kind only, entering an ionized or ionizable region can be self-focusing. Axial asymmetries grow in arcs but disappear in low-density self-focusing streams.