Sweep Type Research Articles

The Effect of Frequency Sweeping and Fluid Flow on Particle Trajectories in Ultrasonic Standing Waves

Particle concentration and separation in ultrasonic standing waves through the action of the acoustic radiation force on suspended particles are discussed. The acoustic radiation force is a function of the density and compressibility of the fluid and the suspended particles. A two-dimensional theoretical model is developed for particle trajectory calculations. An electroacoustic model is used to predict the acoustic field in a resonator, driven by a piezoelectric transducer. Second, the results of the linear acoustic model are used to calculate the acoustic radiation force acting on a particle suspended in the resonator. Third, a particle trajectory model is developed that integrates the equation of motion of a particle subjected to a buoyancy force, a fluid drag force, and the acoustic radiation force. Computational fluid dynamics calculations are performed to calculate the velocity field that is subsequently used to calculate fluid drag. For a fixed frequency excitation, the particles are concentrated along the stable node locations of the acoustic radiation force. Through a periodic sweeping of the excitation frequency particle translation is achieved. Two types of frequency sweeps are considered, a ramp approach and a step-change method. Numerical results of particle trajectory calculations are presented for two configurations of flow-through resonators and for two types of frequency sweeping. It is shown that most effective particle separation occurs when the fluid drag force is orthogonal to the acoustic radiation force.

Frequency sweeping and fluid flow effects on particle trajectories in ultrasonic standing waves

Particle concentration in ultrasonic standing waves by the acoustic radiation force is discussed. The acoustic radiation force is a function of the density and compressibility of the fluid and the suspended particles. A two-dimensional theoretical model is developed for particle trajectory calculations. An electro-acoustic model is used to predict the acoustic field in a resonator. The results of the linear acoustic model are used to calculate the acoustic radiation force acting on a particle suspended in the resonator. A particle trajectory model is developed that integrates the equation of motion of a particle subjected to a buoyancy force, a fluid drag force, and the acoustic radiation force. Computational fluid dynamics calculations are performed to calculate the velocity field. For a fixed frequency excitation, the particles are concentrated along the stable node locations of the acoustic radiation force. Through a periodic sweeping of the excitation frequency particle translation is achieved. Two types of frequency sweeps are considered, a ramp approach and a step-change method. Numerical results of particle trajectory calculations in a resonator with dimensions much larger than a typical wavelength are presented. A movie of experimental observations of particle trajectories is shown to illustrate the method.

The $\kappa-\mu$ Distribution Applied to the Analysis of Fading in Body to Body Communication Channels for Fire and Rescue Personnel

In this letter, we perform a novel characterization of the fading experienced in body to body communications channels for fire and rescue personnel using the recently proposed kappa - mu distribution. A transmitter positioned on the lead fire person and four strategically placed, time-synchronized 2.45-GHz receivers situated on the protective helmet and shoulders of another team member allowed small-scale signal variation to be recorded while a rescue team of four persons performed a building sweep and search type operation. A general kappa - mu model with parameters kappa=2.31 and mu=1.19 was obtained using maximum likelihood estimation and shown to provide a good fit to measured data. Level crossing rates for these channels are also presented.

Two-Dimensional Scour Hole Problem: Role of Fluid Structures

An experimental program was carried out to understand scour caused by a plane wall jet. A two-dimensional laser Doppler anemometer was used to characterize the velocity field at various locations in the scour hole region. Observations indicate that different types of flow structures influence scour at different time periods. Based on the present tests, the entire test duration is divided into five time zones. Following vigorous scour caused principally by jet shear forces and impingement at the start of the test and during early time periods, the flow was characterized by the presence of longitudinal axial vortices, turbulent bursts, and movement of the jet impingement point during the later stages. Attempts were made to distinguish the fluid structures at asymptotic conditions. The scour hole region was characterized by the presence of randomly forming and disappearing streaks, laterally located concave shaped depressions, rolling and ejection of the bed material. Through analysis of higher order moments and quadrant decomposition, sweep and ejection type events were observed, which can potentially contribute to scour.

Turbulent transport in the outer region of rough-wall open-channel flows: the contribution of large coherent shear stress structures (LC3S)

Acoustic Doppler velocity profiler (ADVP) measurements of instantaneous three-dimensional velocity profiles over the entire turbulent boundary layer height, δ, of rough-bed open-channel flows at moderate Reynolds numbers show the presence of large scale coherent shear stress structures (called LC3S herein) in the zones of uniformly retarded streamwise momentum. LC3S events over streamwise distances of several boundary layer thicknesses dominate the mean shear dynamics. Polymodal histograms of short streamwise velocity samples confirm the subdivision of uniform streamwise momentum into three zones also observed by Adrian et al. (J. Fluid Mech., vol. 422, 2000, p. 1). The mean streamwise dimension of the zones varies between 1δ and 2.5δ. In the intermediate region (0.2<z/δ<0.75), the contribution of conditionally sampled u'w' events to the mean vertical turbulent kinetic energy (TKE) flux as a function of threshold level H is found to be generated by LC3S events above a critical threshold level Hmax for which the ascendant net momentum flux between LC3S of ejection and sweep types is maximal. The vertical profile of Hmax is nearly constant over the intermediate region, with a value of 5 independent of the flow conditions. Very good agreement is found for all flow conditions including the free-stream shear flows studied in Adrian et al. (2000). If normalized by the squared bed friction velocity, the ascendant net momentum flux containing 90% of the mean TKE flux is equal to 20% of the shear stress due to bed friction. In the intermediate region this value is nearly constant for all flow conditions investigated herein. It can be deduced that free-surface turbulence in open-channel flows originates from processes driven by LC3S, associated with the zonal organization of streamwise momentum. The good agreement with mean quadrant distribution results in the literature implies that LC3S identified in this study are common features in the outer region of shear flows.

A Novel Economic-Based Scheduling Heuristic for Computational Grids

In the economic-based computational grids we need effective schedulers not only to minimize the makespan but also to minimize the costs that are spent for the execution of the jobs. In this work, a novel economy driven job scheduling heuristic is proposed and a simulation application is developed by using GridSim toolkit to investigate the performance of the heuristic. The simulation-based experiments demonstrate the effectiveness of the proposed heuristic both in terms of parameter sweep and sequential workflow type of applications.

Lateralization of linear and logarithmic frequency-modulated (FM) sweeps at high frequencies

The ability to lateralize linear and logarithmic frequency‐modulated (FM) sweeps at high frequencies was investigated using a 2IFC adaptive block design. The FM stimulus swept from 3 kHz to 8 kHz with the onset frequency roved by 15% on each presentation. The cue to be detected was an interaural delay in the waveform’s fine‐structure (i.e., delay in instantaneous frequency) that varied on each trial according to a 2‐down 1‐up adaptive rule. The waveforms to the left and right channels had simultaneous onset/offset envelopes. The stimulus duration (0.5, 1, 5, 10, 25, or 50 ms) and thus the sweep rate, as well as the sweep direction (up or down), were additional parameters of the study. Thresholds were higher than expected from studies of sinusoidal FM and ranged from approximately 100 μs for the 0.5 ms sweep to near chance for durations exceeding 10 ms. Sweep direction and type (log versus linear) did not substantially affect thresholds. Implications of these findings for models of binaural interaction at high frequencies and within‐channel mechanisms of FM‐to‐AM transduction will be discussed. [Work supported by NSF.]

Method for the evaluation of optical encoders performance under vibration

Optical encoders are the preferred choice for position measurement, both linear and angular, when high accuracy is required. Their performance is widely affected by deformation, temperature and vibration. This last aspect is analysed, showing the limitations found in conventional methods of performance evaluation. The determining parameters, such as sweep type, sampling rate, trigger etc. are examined and a final diagram of measuring accuracy versus frequency is presented, where aspects as resonance effects and measuring uncertainty are identified and discussed. Experimental analyses have been made in a commercial linear optical encoder and show that its measuring error is three times its precision, and wide areas of large measuring uncertainty are present in the frequency span. The information obtained through this method can be used to improve encoder design and mounting conditions in the machine, reducing the total error.

Soil Movement resulting from Sweep Type Liquid Manure Injection Tools

Knowledge of soil movement is important for the design and selection of injection tool to minimise agronomic and environmental concerns associated with liquid manure injection. Laboratory studies were conducted in an indoor soil bin to investigate soil movement in three directions resulting from sweep type injection tools. The first study was carried out to select point tracers. Three tracer sizes (10, 15 and 20 mm) and four tracer materials [wood, polyvinyl chloride (PVC), aluminium and steel] were tested for measurements of soil movement resulting from a sweep at constant injection depth and tool forward speed. The test results led to the selection of the 10 mm PVC tracers for the subsequent soil movement study. In the soil movement study, three sweeps (small, medium and large) were tested at three injection depths (50, 100 and 150 mm), two tool forward speeds (0·6 and 1·4 m s−1), and two soil moisture contents (14 and 18%). The selected tracers were used to measure soil movement in forward, upward and lateral directions. Increasing injection depth from 50 to 150 resulted in a 39% increase in the soil forward movement and a 37% increase in the upward movement. The higher tool forward speed produced a 31% higher forward movement and a 56% higher lateral movement. The higher soil moisture content increased the soil upward movement by 17%. The large sweep resulted in a 27 and 48% greater forward movement than the medium and small sweeps, respectively.

Laboratory investigation of cutting forces and soil disturbance resulting from different manure incorporation tools in a loamy sand soil

Injection of manure is becoming more popular than surface spreading due to its agronomical and environmental benefits. In this study, four different existing tools (two sweep types and two disc types) for liquid manure incorporation were tested in an indoor soil bin located in the Department of Biosystems Engineering at the University of Manitoba with loamy sand, to investigate the effects of working depth (50, 100 and 150 mm) and speed (0.57 and 1.4 m/s) on soil cutting forces and soil disturbance. Draft forces and soil disturbance for all tools significantly increased with working depth, but not with working speed. Owing to its wider soil cutting width, sweep B required 80% more draft force than sweep A. For the same reason, sweep B disturbed a 44% wider soil surface along the tool passage, compared to sweep A. On the average, sweep type tools created 27% new soil pores, which would be available for containing injected manure. For the discs, vertical forces decreased with increased working depth. As compared with disc A, wider surface disturbances along the tool passage were observed for disc B due to its two concave disc design. Comparing soil disturbance for different depths, disc B may not be suitable for manure incorporation at shallow depths (50 and 100 mm). At greater depths (150 mm) both disc-type tools will favor manure coverage.

Inner Workings of Aerodynamic Sweep

The recent trend in using aerodynamic sweep to improve the performance of transonic blading has been one of the more significant technological evolutions for compression components in turbomachinery. This paper reports on the experimental and analytical assessment of the pay-off derived from both aft and forward sweep technology with respect to aerodynamic performance and stability. The single-stage experimental investigation includes two aft-swept rotors with varying degree and type of aerodynamic sweep and one swept forward rotor. On a back-to-back test basis, the results are compared with an unswept rotor with excellent performance and adequate stall margin. Although designed to satisfy identical design speed requirements as the unswept rotor, the experimental results reveal significant variations in efficiency and stall margin with the swept rotors. At design speed, all the swept rotors demonstrated a peak stage efficiency level that was equal to that of the unswept rotor. However, the forward-swept rotor achieved the highest rotor-alone peak efficiency. At the same time, the forward-swept rotor demonstrated a significant improvement in stall margin relative to the already satisfactory level achieved by the unswept rotor. Increasing the level of aft swept adversely affected the stall margin. A three-dimensional viscous flow analysis was used to assist in the interpretation of the data. The reduced shock/boundary layer interaction, resulting from reduced axial flow diffusion and less accumulation of centrifuged blade surface boundary layer at the tip, was identified as the prime contributor to the enhanced performance with forward sweep. The impact of tip clearance on the performance and stability for one of the aft-swept rotors was also assessed.

A comparison between a rotavator and conventional tillage equipment for wheat-soybean rotations on a vertisol in Central India

Timeliness of seedbed preparation is important in achieving higher crop yields. The performance of a tractor-operated rotavator was compared with that of conventional tillage equipment for seedbed preparation under a wheat ( Triticum aestivum L. emend. Flori & Paol) and soybean ( Glycine max (L.) Merr.) crop rotation. The study comprised four treatments with five replications. The four tillage treatments consisted of two operations of a sweep type cultivator followed by one operation of a disc harrow (T1), mouldboard ploughing followed by two operations of a disc harrow (T2), one operation of a rotavator (T3) and two operations of a rotavator (T4). For soybean, two sub-treatments included chemical followed by mechanical weed control and mechanical weed control only. In the winter wheat crop, soil bulk density after tillage in treatments T3 and T4 was significantly lower in comparison with T1 and T2 in 1986, although soil bulk densities in T1 and T2 as well as T3 and T4 were similar. However, no significant difference in soil bulk density was observed during 1987. There was no significant effect of various tillage treatments on soil bulk density for the soybean crop. There was a significant improvement in soil pulverisation with the use of the rotavator. The mean mass diameter of clods in seedbeds of wheat in treatments T3 and T4 was significantly smaller than in T1. However, there were no significant differences between T2, T3 and T4. For soybean, the mean mass diameter in T3 and T4 was significantly smaller than in T1 and T2. Neither wheat nor soybean yield was affected by tillage treatment. The yield of soybean was increased significantly when weeds were controlled by a combination of chemical and mechanical methods rather than when mechanical methods only were used. The specific energy utilised in seedbed preparation for both the crops was low with one pass of the rotavator (T3) compared with conventional tillage treatments T1 and T2.

Vortex reynolds number in turbulent boundary layers

The effects of vortex Reynolds number on the statistics of turbulence in a turbulent boundary layer have been investigated. Vortex Reynolds number is defined as the ratio of circulation around the vortex structure to the fluid viscosity. The vortex structure of the outer region was modeled and a full numerical simulation was then conducted using a high-order spectral method. A unit domain of the outer region of a turbulent boundary layer was assumed to be composed of essentially three elements: a wall, a Blasius mean shear, and an elliptic vortex inclined at 45° to the flow direction. The laminar base-flow Reynolds number is roughly in the same range as that of a turbulent boundary layer based on eddy viscosity, and the vortex-core diameter based on the boundary-layer thickness is nearly the same as the maximum mixing length in a turbulent boundary layer. The computational box size, namely, 500, 150, and 250 wall units in the streamwise, surface-normal, and spanwise directions, respectively, is approximately the same as the measured quasi-periodic spacings of the near-wall turbulence-producing events in a turbulent boundary layer. The effects of vortex Reynolds number and the signs of the circulation on the moments of turbulence were examined. The signs mimic the ejection and sweep types of organized motions of a turbulent boundary layer. A vortex Reynolds number of 200 describes the turbulence moments in the outer layer reasonably well.

Conditional Reynolds stress on a V-grooved surface

Measurements of both mean and turbulent dynamic fields over a ribbed wall show the existence of a minute zone in which the boundary layer characteristics are strongly altered. The turbulent kinetic energy (k+), deduced from the three velocity standard deviations, is strongly increased above the ridge, and reduced over the valley. A similar effect is also visible on the Reynolds stress (−〈uv〉+) profiles, but the relative variations of k+ and −〈uv〉+, with respect to the flat plate case, are not of the same magnitude. Close to the ridge plane, contributions to the Reynolds shear stress from ejection and sweep types of motions are seen to be larger and more frequent above the ridge than over the smooth wall, whereas they are reduced above the valley. Comparison of the respective productions of turbulence above a riblet and above smooth walls, inferred at the distance y+=9 above the ridge plane, indicates a reduction of about 5% in the manipulated flow.

Narrow-band frequency analysis using a [formula omitted] real-time analyser

A technique is presented that yields a narrow-band frequency-sweep analysis by making use of the ability of the Norwegian Electronics RTA830 analyser to store in its transient mode hundreds of consecutive 1 3 - octave-band spectra. The narrow-band analysis is performed by the computer program that transforms the data while transmitting it from the analyser into the computer. The technique simulates a 2 3 - octave-band tracking filter and thus eliminates overtones of the signal and part of the background noise. The time-to-frequency conversion and the synchronization of the tracking filter are solely based on information in the received spectra; precise information about the signal produced or about the transmission path is not needed. By selecting the speed and type of the frequency sweep, a wide range of analysis band widths can be realized. The technique has been used successfully to measure sound transmission in forests under varying weather conditions.

SIGNAL DESIGN IN THE “VIBROSEIS”® TECHNIQUE

After more than twenty years of field practice, the most widely used signal in the Vibroseis technique remains the original so‐called linear sweep. To many, it seems that substantial improvement should be expected from taking advantage of more sophisticated signal design techniques. The purpose of this paper is to present a tutorial survey of the basic concepts involved in signal design, tying together the known features of the linear sweep with those of the more general type. Several particular types of nonlinear sweeps are analyzed and the results of a field test seem to confirm the conclusions drawn from the conceptual analysis. After a brief consideration of still another type of nonlinear signals, a particular variety of pseudorandom sweeps, the author concludes by giving his views of what might be the role of nonlinear signal design in the future development of the Vibroseis technique.

Detection of acrolein in engine exhaust with microwave cavity spectrometer of stark voltage sweep type

Acrolein in automobile engine exhaust is detected using a microwave cavity spectrometer of Stark voltage sweep type. The cavity operates in the TE/sub 1,0,20/ mode at a fixed microwave frequency in the X-band region. The exhaust gas is collected through a glass tube packed with phosphorus pentoxide and trapped on a cold adsorbent in a dry ice-acetone cold bath. A sample of the engine exhaust is found to contain about 5 ppm of acrolein.

A sensitive microwave cavity spectrometer: Direct detection of formaldehyde in automobile exhaust

Abstract A newly constructed sensitive microwave cavity spectrometer of the Stark-dc-voltage sweep type has revealed that formaldehyde in concentrations as small as 0.2 ppm can be directly detected by using the 725 ← 726 rotational line. The cavity resonator is operated in the rectangular TE1,0,20 mode. A sample of automobile-engine exhaust showed a strong spectrum indicating a concentration of 24 ppm of formaldehyde.

A stark-sweep microwave cavity spectrometer for Zeeman effect studies and for pollutant monitoring

A microwave cavity spectrometer of the Stark-dc-voltage sweep type with a fixed resonance frequency in the X-band region is described. The spectrometer was applied to the study of the Zeeman effect in molecules as well as to pollutant monitoring.

On solution of boundary value problems in an infinite interval for some non-linear sets of ordinary differential equations involving singularities

The behaviour with respect to the set of variables ( x, t) of the one-dimensional manifold of solutions, tending to zero at infinity, of the set of two non-linear equations t −rx′ = A (t)x + ƒ (t, x), t 0 ⩽ t < ∞ , was investigated in [1], The results obtained enabled us to propose a method for solving the boundary value problem for such a set of equations in the interval [ t 0, ∞) with any given condition at the point t 0 and the limiting condition x( t) → 0 as t → ∞ at the right-hand end. The method consists in replacing [ t 0, ∞) by an interval [ t 0, T], taking as the boundary condition at the point T the equation of the entire stable manifold, and solving the boundary value problem in this finite interval. The present paper extends the results of [1] to a set of n equations. The condition x( t) → 0 as t → ∞ is removed from infinity to a finite point by means of the equation of the k-dimensional stable manifold, effectively defined by utilizing a convergent and asymptotic series. This type of sweep is justified here under the assumption that all k eigenvalues of the matrix A(∞), lying in the left-hand half-plane, are simple. We use the following notation: x = colon ( x i , …, x n ) is a real or complex vector column, diag ( D i , …, D s ) is a quasi-diagonal matrix, Ω x(c) is a closed region of the x-space, ¦x j¦⩽ c , j = 1, …, n; I t is a real semiinfinite interval T ⩽ t < ∞; Ω x, y(c) is the Cartesian product of the sets Ω x(c) × Ω y(c); ω x, t(c, T) = ω x(c) × I t ; ƒχƒ′ = ∑ j=1 n ƒχjƒ, where χ = (χ,…,χ n); ƒAƒ = ∑ i,j,=1 n ƒa ijƒ, where A = ( a i j ) is an n-th order square matrix, E = ( δ i j ) is the unit matrix, and [ x] m is a vector whose components are power series in the coordinates x, the powers of whose initial terms are not less than m. In addition, let l = ( l i , …, 1 n ) be a row-vector of non-negative integers, and x = colon ( x i , …, x n ). We take x l = x l 1 … x n l n , by definition, and define the length ¦l¦ of the vector l by the equation ƒlƒ = ∑ j=1 n lj . Then, for example, the series S = ∑ l 1…,l n=0 ∞ a l 1 … l n (t)χ l t 1…χ l n n ∑ j=1 n l j⩾1 may be written in the form S = ∑ ƒlƒ⩾1 a l(t)χ l . Throughout, we take T to be a large positive constant.