Resultant Velocity Vector Research Articles

PIV Investigations of the Flow Field in the Volute of a Rotary Blood Pump

A full-size acrylic model of a rotary blood pump was developed in order to utilize Particle Image Velocimetry (PIV) to make measurements of the fluid velocities and turbulent stresses throughout the device. The development of an understanding of the hemodynamics within the blood pump is critical to the development and validation of computational models. A blood analog solution, consisting of sodium iodide solution and glycerin, was developed to match physiological kinematic viscosity. The refractive indecies of the fluid, the pump casing, and the impeller were matched to facilitate the use of PIV to make velocity measurements. Velocity measurements made in the volute exit/diffuser region are presented for pumps speeds of 3000–3850 rpm. At each speed data were obtained at a physiological pressure of 12 kPa and at a maximum flow condition. Four hundred data pairs were used for each resultant mean velocity vector value, representing greater than an order of magnitude more data pairs than reported previously in the literature on similar devices and resulting in velocity uncertainty levels of approximately ±2.9%.

Centro instantâneo de movimento, na avaliação ex-vivo da reconstrução extra-articular fabelo-tibial, após transecção do ligamento cruzado cranial em cães

Este estudo comparou o efeito na biomecânica articular de dois fios de sutura, aço e polipropileno, na estabilização do joelho após transecção do ligamento cruzado cranial de cães, utilizando-se a técnica extra-articular de sutura fabelo-tibial. O centro instantâneo de movimento e o vetor velocidade resultante, foram calculados por meio de análise radiográfica das articulações fêmur-tíbio-patelares de doze cães, antes e após a desestabilização e estabilização articular. Todas as articulações apresentavam centro instantâneo e vetor velocidade normais antes da transecção do ligamento. Após a mesma, observou-se o posicionamento anormal do vetor velocidade em onze articulações. Na análise radiográfica posterior à estabilização articular, quatro articulações do grupo nos quais foi empregado o fio de aço continuaram apresentando posicionamento anormal do vetor velocidade, enquanto todas as articulações do grupo em que foi utilizado o fio de polipropileno apresentaram vetor velocidade em posição tangente às superfícies ósseas. Conclui-se que o fio de polipropileno é mais indicado na estabilização extra-articular por manter a biomecânica articular inalterada.

A weighted least squares solution for space intersection of spaceborne stereo SAR data

The use of stereoscopic SAR images offers an alternative to interferometric SAR for the generation of digital elevation models (DEMs). The stereo radargrammetric method is robust and can generate DEMs of sufficient accuracy to geocode SAR images. Previous work has shown that ground coordinates with accuracy of four times the resolution cell can be obtained from ERS data without using any ground control points (GCPs), where the high accuracy of the orbit and satellite position of the order of metres introduce insignificant errors into the intersection procedure. The orbit data for RADARSAT is not as accurate as that for ERS, and the perpendicular relationship between the resultant velocity vector and the resultant range vector is uncertain in terms of image geometry. Hence, it is necessary to refine the method to allow for possible errors. This paper introduces a weighted space intersection algorithm based on an analysis of the predicted errors. A radargrammetric error model for observation errors is also formulated to predict the accuracy of the algorithm. The revised method can be used without any GCPs, but this can lead to systematic errors due to less accurate orbit data, and it has been found that the use of two GCPs provides a reasonable solution. The method is insensitive to the spatial distribution of GCPs, which is often critical in traditional methods. The error statistics of the results generated from 32 independent check points, distributed through the entire SAR image, approach the predicted errors and give positional accuracy of 38 m in three dimensions.

207回転像静止法を用いた円形羽根周り流れのPIV計測

This paper presents the PIV measurement results for the flow around a circular blade revolving in a circular channel. This flow is a model of the flow in a tea-spoon type pump, model that is employed to examine the effect of the motion of the circular blade on the flow characteristic. The flow visualization is carried out under the derotating observation with a reflecting prism that rotates at the half speed of that of a rotating object. The visualization images are digitized into a personal computer to obtain velocity vectors maps using a PIV algorithm, direct cross-correlation method. From the resulting velocity vectors maps, we estimate the time-averaged velocity, the velocity fluctuation and vorticity distributions around the circular blade.

Comparison of the kinematics of the full-instep and pass kicks in soccer.

The goal of this study was to gain a better understanding of the mechanics of the inside-of-the-foot passing shot used in soccer ("pass kick"). The motions of the pass kick were compared with those of the full-instep kick ("full kick"). The study followed an inverse dynamics approach, using three-dimensional cinematographic techniques. At impact, the pelvis and the thigh-shank plane pointed more toward the right in the pass kick; the shank-foot plane also pointed further outward relative to the thigh-shank plane. Knee extension accounted for most of the speed of the foot in both kicks (86% in the full kick; 67% in the pass kick). In the pass kick, pelvis tilt toward the right and hip adduction contributed to a medial component of foot velocity (8.4 m.s-1) normal to the thigh-shank plane, which made the resultant foot velocity vector more oblique to the plane than in the full kick. This facilitated ball impact with the medial aspect of the foot. The slower ball speed in the pass kick was because of a slower foot speed (18.3 m.s-1 vs 21.6 m.s-1). Limitations in the maximum medial velocity that can be generated may force players to restrain the within-plane (and therefore also the resultant) velocity of the foot to be able to impact the ball squarely with the medial aspect of the foot. To impact the ball with the medial aspect of the foot in the pass kick, the player orients the pelvis, the right leg, and the foot more toward the right and introduces a medial component of foot velocity. However, most of the speed of the foot is still generated through knee extension.

Comparison of the kinematics of the full-instep and pass kicks in soccer

Comparison of the kinematics of the full-instep and pass kicks in soccer. Med. Sci. Sports Exerc., Vol. 30, No. 6, pp. 917-927, 1998. Purpose: The goal of this study was to gain a better understanding of the mechanics of the inside-of-the-foot passing shot used in soccer ("pass kick"). Methods: The motions of the pass kick were compared with those of the full-instep kick ("full kick"). The study followed an inverse dynamics approach, using three-dimensional cinematographic techniques. Results: At impact, the pelvis and the thigh-shank plane pointed more toward the right in the pass kick; the shank-foot plane also pointed further outward relative to the thigh-shank plane. Knee extension accounted for most of the speed of the foot in both kicks (86% in the full kick; 67% in the pass kick). In the pass kick, pelvis tilt toward the right and hip adduction contributed to a medial component of foot velocity (8.4 m·s−1) normal to the thigh-shank plane, which made the resultant foot velocity vector more oblique to the plane than in the full kick. This facilitated ball impact with the medial aspect of the foot. The slower ball speed in the pass kick was because of a slower foot speed (18.3 m·s−1 vs 21.6 m·s−1). Limitations in the maximum medial velocity that can be generated may force players to restrain the within-plane (and therefore also the resultant) velocity of the foot to be able to impact the ball squarely with the medial aspect of the foot. Conclusions: To impact the ball with the medial aspect of the foot in the pass kick, the player orients the pelvis, the right leg, and the foot more toward the right and introduces a medial component of foot velocity. However, most of the speed of the foot is still generated through knee extension.

Telerobotic Master Reflected Force Adjustment with Local Feedback

Efficient telerobotic operation requires an intuitive transmission of forces and velocities between the master and slave manipulators. However, due to friction in the joints of each kinematic chain, the associated Cartesian space impedance matrices are not diagonal. The result is a misalignment between the applied force and resulting velocity vectors. While a force sensor on the slave is often used to provide an internal feedback to eliminate the problem for this manipulator, the same is not UBually true for the master. A local feedback of available velocity and force sensory information to the master is proposed which would diagonalize its effective mechanical damping to allow a correct display of force direction information from the slave.

On the positioning of control sources in active noise control of three-dimensional interior space

Locations of secondary sources in three-dimensional active noise control influence greatly on final control result. To find efficient secondary source sites for given primary source layout, an acoustic analysis of a three-dimensional interior space is done for low frequency ranges with low modal density. By using the boundary element method, magnitude and phase of optimum velocities of boundaries are evaluated for underdetermined system with an example of a rectangular box. Because the potential energy at mutiple field points depends on boundary velocity field, “good” sites for control sources can be determined by investigating the distribution of resultant velocity vectors. Results show a general tendency that the dipole positioning is most effective and the source should be placed at antinodes of related modes for maximum noise reduction, and this agrees with previous ones. With this method, positions of control sources for maximum noise attenuation can be determined for a variety of primary source configurations and for irregular boundary shapes.

Inertial representation of angular motion in the vestibular system of rhesus monkeys. I. Vestibuloocular reflex

1. The spatial organization of the vestibuloocular reflex (VOR) was studied in six rhesus monkeys by applying fast, short-lasting, passive head and body tilts immediately after constant-velocity rotation (+/- 90 degrees/s) about an earth-vertical axis. Two alternative hypotheses were investigated regarding the reference frame used for coding angular motion. 1) If the vestibular system is organized in head-centered coordinates, postrotatory eye velocity would decay invariably along the direction of applied head angular acceleration. 2) Alternatively, if the vestibular system codes angular motion in inertial, gravity-centered coordinates, postrotatory eye velocity would decay along the direction of gravity. 2. Horizontal VOR was studied with the monkeys upright. Pitch (roll) tilts away from upright elicited a transient vertical (torsional) VOR and shortened the time constant of the horizontal postrotatory slow phase velocity. In addition, an orthogonal torsional (after pitch tilts) or vertical (after roll tilts) response gradually built up. As a result, the eye velocity vector transiently deviated in the roll (pitch) plane and then gradually rotated in the same direction as gravity in the pitch (roll) head plane until the orthogonal component reached a peak value. Subsequently, the residual postrotatory eye velocity decayed along a line parallel to gravity. 3. The time constant of the horizontal postrotatory response was maximal in upright position (21.5 +/- 5.7 s, mean +/- SD) and minimal after tilts to prone (3.8 +/- 0.7 s), supine (4.5 +/- 1.2 s), and ear-down (5.2 +/- 1.6 s) positions. A similar dependence on head orientation relative to gravity characterized the dynamics of the resultant eye velocity vector in the pitch and roll planes. 4. Torsional VOR was studied with the monkeys in supine or prone position. Pitch (yaw) tilts from the supine or prone position toward upright (ear-down) position elicited a transient vertical (horizontal) VOR and shortened the time constant of the torsional postrotatory response while a horizontal (vertical) orthogonal component slowly built up. As a result the eye velocity vector gradually rotated in the pitch (yaw) plane until the orthogonal component reached a peak value. Subsequently residual postrotatory eye velocity decayed along a line parallel to gravity. 5. The time constant of the torsional postrotatory response in supine/prone positions was 16.5 +/- 6.8 s. After tilts from supine/prone positions toward upright position, time constants decreased and were minimal after tilts to upright position (2.7 +/- 0.7 s).(ABSTRACT TRUNCATED AT 400 WORDS)

Comparison of Stifle Biomechanics after Two Different Techniques of Cranial Cruciate Ligament Repair

SummaryStifle joint biomechanics were evaluated by analysis of instant centre of motion, after cranial cruciate ligament transection and after stifle joint stabilization, using either the fibular head transposition or the under-and-over fascial strip technique. The instant centres of motion and resulting velocity vectors were determined by radiographic evaluation of the stifle of twelve fresh cadavers before and after cranial cruciate ligament transection, and after stabilization of the stifle joint by either the fibular head transposition or the under-and-over fascial strip technique. All 12 stifles had normal instant centres of motion before transection of the cranial cruciate ligament, and 10 of 12 were normal after transection. All six stifles repaired by fibular head transposition retained normal instant centre of motion. Abnormal instant centres of motion were present in three of six stifles repaired by the under-and-over technique. These differences were not statistically significant.Stifle joint biomechanics were evaluated by analysis of instant centre of motion after cranial cruciate ligament transection and after stifle joint stabilization using either the fibular head transposition or the underand-over fascial strip technique. Neither surgical technique consistently resulted in abnormal instant centres of motion.

Particle image velocimetry measurements of wave-current interaction in a laboratory flume

The hydrodynamics of wave-current interaction is of interest to those concerned with marine and offshore structures. In particular the fluid loading characteristic may be radically altered in a sea state consisting of a mean current flow mixed with freely propagating gravity waves. The present paper describes water flume experiments, using Particle Image Velocimetry (PIV), executed to examine hydrodynamics of wave-current interaction. A variety of wave and current conditions were investigated to determine the major influences on the combined flow. This paper describes the experimental procedures used to obtain simultaneous measurements of the resulting wave velocity vectors over an extended region of the wave. It also describes how the directional ambiguity inherent in the basic PIV method was resolved by ‘pulse tagging’ technique. Velocity vectors under waves at various phase points for different current and wave conditions are presented and compared in some cases with measurements derived using Laser Doppler Anemometry (LDA). The resulting velocity vectors are used to estimate how the mutual interaction, between wave and current, effect the calculation of structural loads using Morrison's equation.

A modified skew upwind scheme for fluid flow and heat transfer computations

Conventional skew upwind differencing (SUD) substantially reduces numerical diffusion but produces oscillations for convection-dominated flows. The present study describes a modified skew upwind weighted differencing (SUWD) scheme which produces less numerical diffusion and oscillations than SUD. The convected quantity at a cell face is approximated by a weighted average of two quantities. These two quantities are obtained by using linear interpolation at two successive locations upstream of the resultant velocity vector at the cell face. Three laminar flow test cases are used to evaluate the scheme. Comparison of the results obtained by SUD and SUWD schemes are presented.

Effect of Suture Type on Stifle Joint Biomechanics After Extra-Articular Repair of Cranial Cruciate Ligament Transection in the Dog

SummaryThe effect of two suture types, monofilament polybutester and braided polyester, on stifle joint biomechanics after extra-articular repair of cranial cruciate ligament rupture was evaluated by analysis of the instant centre of motion. The instant centres of motion and resulting velocity vectors were determined radiographically on both stifles of eight fresh canine cadavers before and after cranial cruciate ligament transection. After ligament transection, all 16 stifles were repaired with an extra-articular technique utilizing a double strand of suture placed between the lateral fabella and the tibial tuberosity. One stifle on each cadaver was repaired with each suture type. The instant centres of motion and resulting velocity vectors were re-evaluated post repair. All stifles had normal instant centres of motion prior to transection of the cranial cruciate ligament. Neither ligament transection nor extra-articular repair with either suture type resulted in an abnormal change in the instant centre of motion.

Effect of roll and pitch on flash-induced nystagmus: Support for involvement of retinal direction-selective elements?

The direction of eye movement (i.e., the angle of the resultant velocity vector calculated from the horizontal and vertical components) during flash-induced nystagmus was evaluated in static roll and pitch positions. It appeared that this direction coincided with the orientation of the visual streak, as influenced by the ocular countertorsion which is known to occur in the various body positions. This supports the hypothesis that flash-induced nystagmus results from stimulation of direction-selective retinal elements. The intensity of flash-induced nystagmus, evaluated either by measuring slow-phase velocity (i.e., magnitude of resultant vector) or by beat frequency, was minimal in approximately 90 and 270° roll or pitch positions, presumably because the total combined (utricular and saccular, left and right) excitatory otolith stimulation was maximal in these positions, the effect of this stimulation being inhibitory to the flash-induced nystagmus.

LARM Two-Dimensional Model: An Evaluation

Center Hill Lake in Tennessee has been the object of several water quality and fisheries management studies over the past decade. The flow regimes of Center Hill Lake were investigated with a numerical, two-dimensional, laterally averaged, hydrodynamic model. This laterally averaged reservoir model (LARM) couples the mass continuity, momentum, and energy equations (with the equation of state) to compute resultant temperatures and flow velocity vectors The LARM model is reviewed, summarizing the model validation process, presenting a summary of the hydrodynamic predicitions, and showing the results of management techniques simulations. Since this was one of the very first uses of the LARM model, the conclusions should be of interest to reservoir water quality managers and modelers.

An Investigation of Vertical Structure in Shelf Circulation

Abstract Recording current meter data from four levels are used to describe the vertical structure of the circulation of mid shelf waters 33 m deep off the central Texas Gulf coast. Resultant current velocity vectors for the 41-day study indicate a strong onshore mass flux past the study site, with the cross-isobath deflection increasing with height above the bottom. Both the resultant current speed and direction vary approximately linearly when plotted against the natural log of the depth. Statistically significant coherences are computed for time scales in excess of one day for longshore motion through the lowest three-fourths of the water column, and for both longshore and cross-shelf motion in a layer 7 m thick just above mid depth.

Qualification of optimal strategies and singular surfaces of a class of differential games

At each point of a regular region, there exist two tangent cones which are complementary to each other. The two vectograms defined by the pair of optimal strategies must be contained separately in the two tangent cones. The velocity vector resulting from the selection of the optimal strategies consequently must represent a semipermeable direction. These conditions, which reveal a fundamental separating property of the optimal velocity vector, are weaker than that of Isaacs' main equation. However, they hold even on singular surfaces. A singular surface arises only when the resulting velocity vector of the previous optimal strategies cannot continuously represent a semipermeable direction after the optimal path crosses over the surface. This observation yields a necessary condition for a singular surface to occur. The localization of singular surfaces is then possible. Finally, a smooth condition with respect to optimal paths is given.

A Theory for Rectangular Wings of Small Aspect Ratio

T theory for flow about wings of large aspect ratio has been worked out rather completely along the lines suggested by Prandtl. This flow is of interest for the main lifting surfaces of present day airplanes. However, for some unconventional airplane wings and especially for the control surfaces of dirigibles, the lifting surfaces have generally a very small aspect ratio and the existing theories have so far been inadequate. Moreover, the dirigible as a whole exhibits very much the same behavior, at least as far as the dynamic lift is concerned, as a wing of small aspect ratio. In view of this, Th. von Karman suggested to the author making a theoretical analysis of wings of small aspect ratio. The first step was the limiting case of a rectangular wing of zero aspect ratio, that is, finite span but infinite chord. Such a wing is hydrodynamically equivalent to a constant distribution of bound vortices whose axes lie along the span (Fig. 1). At the ends of the span these vortices separate, the flow downstream following the resultant velocity vector. The inclination of the vortices to the wing was found to be about half the angle of attack. As an approximation, in order to simplify the calculation of the induced velocities, it was assumed that the trailing vortices formed straight lines at some effective inclination to the wing. This effective inclination was taken equal to the initial angle at which the vortices separate, on the assumption that the part of the vortex nearest the wing is the most influential in inducing downwash at the wing. With this approximation, three important results were obtained for the wing of zero aspect ratio: