Roll Orientation Research Articles

A magnetic field system using implanted sensors to track limb movements in the monkey

This paper describes the design and construction of a magnetic field system with implanted sensors, capable of tracking limb orientation during unconstrained movements of awake, behaving monkeys. Tiny sensors (approximately 5 mm diameter) made from two orthogonal coils of wire are implanted in the monkey's upper arm, forearm, and hand. Three mutually orthogonal magnetic fields are detected by each sensor, providing sufficient information to determine the orientation of each limb segment. The use of implanted sensors and magnetic fields overcomes the two main difficulties associated with the use of existing tracking systems with monkeys. (1) It is impossible for the monkey to interfere with the sensors. (2) The sensors are never obscured because the body is permeable to magnetic fields. The tracking system provides highly accurate yaw, pitch, and roll orientation information for each limb segment within a cubical workspace approximately 50 cm on a side. Noise is less than 0.3 degrees, and long-term drift is on the order of 0.2 degrees/h. The system is insensitive even to large pieces of steel within the field, provided the sensors remain at least 10–15 cm from the metal.

Electrohydrodynamic Convection in Nematics: Hybrid and Tilted Alignment

We calculate the threshold of electrohydrodynamic convection (EHC) for nematic liquid crystals with negative dielectric anisotropy, where one allows for different director orientations at the upper and lower confining plates (hybrid cells). Besides the planar versus homeotropic case we present for the first time an analysis of continuous tilt at one plate. The predistorted ground state strongly influences the EHC character and the roll orientation. One observes a generic nonstationary behaviour and in particular the interesting scenario of drifting oblique rolls.

Convection for Prandtl numbers near 1: Dynamics of textured patterns.

Rayleigh-Benard convection in a cylindrical geometry with radius-to-height ratio {Gamma}=40 was studied with the shadowgraph imaging method. The working fluid was CO{sub 2} at 32 bars and at temperatures near 34 {degree}C, with a Prandtl number {sigma}=0.98. The onset pattern of largely straight, parallel rolls went through successive qualitative changes as {epsilon}{equivalent_to}{Delta}{ital T}/{Delta}{ital T}{sub {ital c}}{minus}1 was increased. Quantitative measurements of wave numbers, of spatially averaged roll curvature, and of sidewall roll orientation as functions of {epsilon} are presented. As {epsilon} was increased, pattern dynamics induced by the skewed-varicose instability were first observed at {epsilon}{approx}0.09, and roll-nucleating sidewall foci were seen for {epsilon}{approx_gt}0.15. Spiral defects appeared intermittently at {epsilon}{approx}0.55. The number of spirals fluctuated with time, but the average number increased with {epsilon} until, at {epsilon}{approx}0.8, spirals were present at all times. Coincident with the increase in spiral-defect activity was a decrease in the average wave number, a marked increase in the sidewall-foci roll-nucleation frequency and average roll curvature, and a distinct shape change in the structure factor {ital S}({ital k}). The oscillatory instability was observed at {epsilon}{approx}3.0, in agreement with the stability analysis for straight rolls.

“Granular” Convection in a Vibrated Fluid

Numerical simulation of the Navier-Stokes equation in a continuously vibrated box demonstrates the formation of convection rolls. These rolls circulate with the opposite orientation to those found in granular flows. By introducing a negative-slip boundary condition, we recover the roll orientation and roll reversal with increasing side wall angle that have been obtained in experiments on granular convection.

Chaotic domains: A numerical investigation.

We study the chaotic domain state in rotating convection using a model equation that allows for a continuous range of roll orientations as in the experimental system. Methods are developed for extracting the domain configuration from the resulting patterns that should be applicable to a wide range of domain states. Comparison with the truncated three mode amplitude equation description is made. (c) 1994 American Institute of Physics.

Spatiotemporal Dynamics of Optical Parametric Oscillators

Abstract The coupling of diffraction and the x (2) nonlinearity is shown to lead to pattern formation in parametric oscillators in optical cavities. In particular the threshold for the generation of signal and idler waves is lowered by an off-axis emission for negative detunings. The output intensity is spatially modulated just above threshold while more complicated patterns appear for larger values of the pump amplitude. Competition between domains of rolls with different orientations leads to long transients until boundary effects prevail. In the case of finite-size input beams, the roll orientation is locally perpendicular to the boundary and the pattern tends to rotate. Finally, the effect of spatial structures on the spectrum of quantum fluctuations of the vacuum is considered and discussed.

Pattern formation in a rotating fluid: Küppers-Lortz instability

We propose a model similar to a generalized Swift-Hohenberg equation that includes coupling to mean flow field to describe the Küpper-Lortz instability. The derivation assumes free-free boundary conditions at the top and the bottom. We present a numerical solution of this dynamical model near onset, which yields results that are in good agreement with recent experimental observations. In particular, we observe the reorientation of rolls for frequencies less than a critical frequency, as well as the disordered pattern comprised of several different roll orientations for frequencies greater than the critical frequency.

The kinematics and performance of escape responses of the knifefish Xenomystus nigri

The kinematics and performance of the escape responses of the knifefish Xenomystus nigri, a fish specialized for low-speed, undulatory median-fin propulsion, were recorded by means of high-speed cinematography. Two types of escape were observed, one involving the formation of a C-shape along the longitudinal axis of the fish (stage 1), followed by a slow recoil of the body (single bend); the other (double bend) involved stage 1 followed by a contralateral bend (stage 2). The pectoral fins were extended throughout escapes of both types. The average maximum acceleration for double bend escapes was 127.98 m∙s−2; acceleration was usually greatest in stage 1. In double bend escapes, turning angles for stages 1 and 2 were not correlated. Pitch and roll orientations change during escapes. In stage 1, the average roll and average pitch were linearly correlated, suggesting that roll was partly responsible for establishing pitch. Knifefish achieved high maximum acceleration relative to other fish. Therefore, performance was not compromised by morphological specialization for low-speed swimming; however, a negative correlation of pitch with acceleration in stage 1 suggested that escapes involve a trade-off between acceleration and confusing a predator by changing planar orientation.

Pattern dynamics and heat transport in rotating Rayleigh-Benard convection.

Pattern dynamics and heat transport in moderate aspect ratio (Gamma=10) rotating Rayleigh-Benard convection are discussed. Patterns are obtained from shadowgraph visualization of the temperature field. Using 2-D Fourier transform analysis of the patterns, it is demonstrated that organized patterns with one dominant roll orientation produce greater thermal heat transport than do more disordered patterns generated by the Kuppers-Lortz instability and consisting of combinations of different roll orientations.

Attitude based trackers for airplane, helicopter and ground targets

Abstract A class of aircraft and ground‐vehicle trackers is described that uses imaging sensors and image processing techniques to increase the tracking and prediction accuracy of target tracking systems. The image information is used to obtain the roll, pitch and yaw orientation angles of the target, and this aspect data is shown to be a significant supplement to the position data used by present‐day systems. This paper demonstrates that target aspect angle information as obtained from an image processing system is important in target tracking for the following reasons: for aircraft targets, aspect angle information is directly related to the magnitude and direction of the target acceleration vector; for ground targets, aspect angle gives direct information about the direction of the target velocity vector. Equations of motion are presented that specifically show the relationships between aspect angles and vehicle motion for fixed‐wing aircraft, helicopters, and ground vehicles. Sample results show that ...

The role of balance dynamics in the active perception of orientation.

The Stoffregen and Riccio (1988) hypothesis that perceived orientation is determined primarily by balance dynamics was tested. Perception of orientation was evaluated in the context of a task that required Ss to control the roll orientation of a device in which they were seated. The device's direction of balance was manipulated across trials and thus was independent of gravity. Eighteen Ss participated in the investigation. After each trial, Ss estimated their mean tilt with respect to upright. Correlations of perceived tilt with tilt from balance were consistently higher than the correlations with gravity tilt. The dominance of balance over gravity depended on the magnitude of tilt from balance.

Asymmetric Vortices on a Slender Body of Revolution

The symmetric and asymmetric leeward-side flow fields on an inclined ogive-cylinder have been investigated using a number of experimental techniques. Naturally occurring and perturbed flow fields were studied at a moderate Reynolds number and at many incidence angles. By close examination of the steady side force behavior at different roll orientations of the tip, it has been established that micro-variations in the tip geometry of the model have a large influence on the downstream development of the flow field. Under certain conditions, a bistable flow field was observed.

Large-Eddy Simulation of Turbulent Sheared Convection

Abstract A series of large-eddy simulators of free and sheared convective flow between moving flat plates is presented. Results for free convection are compared with laboratory data. The ratio of friction velocity to the convective velocity sale,u*/w*,is identified as an important parameter in sheared convective flow determining the formation of longitudinal rolls. Rolls are found for u*/w* ≥ 0.35, with aspect ratio decreasing as this parameter increases. It is shown that, in this regime, two-dimensional simulations with a proper choice of roll orientation and turbulence length-scale can produce correct velocity variances and roll aspect ratio.

Orientation technology and commercial products from a unique roll orientation process

AbstractIt is well known that orientation can produce, at a minimum, an order of magnitude improvement in physical properties of low cost plastic resins. A unique, large‐scale, commercial rolling mill process for continuous orientation of plastic sheet has been developed, A number of oriented materials have been commercially produced by this rolling mill process with a wide variety of physical properties attained. This has resulted in large volume sales of many interesting commercial products. Over the last thirty years, numerous researchers have conducted studies to evaluate the theoretical aspects of the rolling process, and the resultant properties. Most commercial oriented products are of relatively small cross sectional size such as fibers and film. The process reported herein produces heavy cross section oriented sheet. A new class of high strength thermoplastic materials is now available for design engineers to use. Long‐term strength properties are often 10 to 100 times better than with unoriented thermoplastics.

Horizontal Roll and Boundary-Layer Interrelationships Observed over Lake Michigan

Abstract On 7, 9 and 10 January 1981 some 35 hours of organized horizontal roll convection in the boundary layer over lake Michigan were probed with two airplanes and two radars from the University of Chicago Lake Snow Project. During this time, roll wavelength varied from 1.5 to 13.7 km, roll depth from 0.9 to 2.1 km, and roll aspect ratio from 1.0 to 9.1; the roll axes changed orientation to remain within ±10° of the inversion-level geostrophic wind direction, and the maximum transverse wind speed varied from 1 to 2 m s−1. Boundary-layer parameters such as wind speed, wind direction, over-water fetch, surface-layer instability, and upstream stability, also varied over the same period. The roll orientations, and the variations of roll wavelength and maximum roll transverse wind speed with Rayleigh number and Richardson number, are examined with reference to theoretical models of roll convection. The observations suggest that roll orientation, roll wavelength, and roll transverse wind speed depend primari...

Pressures Around an Inclined Ogive Cylinder with Laminar, Transitional, or Turbulent Separation

This paper reports results From comprehensive pressure tests on an ogive cylinder in the low-turbulence 12-ft pressure wind tunnel at Ames Research Center. The results consist of detailed pressure distributions over a wide range of Reynolds numbers (0.2 x 10(exp 6) to 4.0 x 10(exp 6)) and angles of attack (20 to 90 deg). Most important, the tests encompassed a complete coverage of different roll orientations. This variation of roll orientation is shown to be essential in order to fully define all the possible flow conditions. When the various roll-angle results are combined, it is possible to interpret correctly the effects of changing angle of attack or Reynolds number. Two basic mechanisms for producing asymmetric flow are identified. One mechanism operates in both the laminar and the fully turbulent separation regimes; this mechanism Is the one qualitatively described by the impulsive flow analogy. The other mechanism occurs only in the transitional separation regime. This asymmetric flow has the same form as that found in the two-dimensional cross flow on a circular cylinder in the transitional flow regime. Finally, these results make it possible to draw up critical Reynolds number boundaries between the laminar, transitional, and fully turbulent separation regimes throughout the angle-of-attack range from 20 to 90 deg.

Development of New Lifting-Parachute Designs with Increased Trim Angle

The trim angle of attack of a high-strength ribbon lifting parachute has been increased by a combination of modifications including increased liner area, increased slanted ribbon area, and the addition of flow-directin g side vents. Ram air inflated leading-edge chambers were used to prevent canopy collapse at high angles of attack. Small-scale wind-tunnel models with the most beneficial combination of modifications had trim angles as high as at =46 deg. Full-scale parachutes had trim angles greater than at =40 deg in wind-tunnel and flight tests. Yawroll interaction was identified as a source of aerodynamic roll moment which would probably necessitate active control of roll orientation.

A two‐dimensional numerical study of horizontal roll vortices in an inversion capped planetary boundary layer

AbstractThe dynamics of large‐scale horizontal roll vortices in an inversion‐capped planetary boundary layer subject to surface heating are investigated by means of a numerical model. The rolls are assumed to be twodimensional and calculated explicity, while small scale turbulence is parametrized using a buoyancy‐dependent mixing length hypothesis. The assumptions of the model are based upon atmospheric observations which show the occurrence of large eddies highly elongated in a direction close to that of the geosstrophic wind and a partitioning of turbulence energy between these large eddies and smaller scales. The model produces realistic turbulence statistics and provides information on the sensitivity to various assumptions and parameters. Apart from the generation of internal gravity waves in the stable region above the boundary layer the results are insensitive to the details of the parametization. The internal gravity wave generation is sensitive to most parameterss and in particular to the roll orientation.

Simulation of skew domain wall bowing in SiFe laminations with asymmetric roll orientation

Cyclic motion of 180° domain walls spanning perfect monocrystalline laminations with first-order positive cubic anisotropy (like 3% SiFe) has been simulated using a finite segment technique. Only drive field, eddy field, and surface tension forces on the domain wall were considered. Calculations were made for various crystal orientations over the range between (110) [001]. At intermediate orientations the profile of a rapidly moving domain wall suffers shearing and bowing distortion; this is very different from the symmetric bowing reported in earlier work on the symmetric

Comparison of Analytical and Experimental Supersonic Aerodynamic Characteristics of a Forward Control Missile

Techniques to predict the aerodynamic characteristics of slender cruciform missiles have been developed and are constantly being updated and improved. This paper presents comparisons between analytical and experimental supersonic aerodynamic data for a class of canard-controlled missile configurations similar to the sidewinder missile. Three aerodynamic prediction computer codes, including program MISSILE2, a recently improved version of program MISSILE, are evaluated by comparison with the test data to assess their accuracy. The major emphasis is placed on the roll control characteristics. In addition, tail span optimization, longitudinal and lateral control, induced roll, and missile roll orientation effects are addressed.