Showing papers on "Angular velocity published in 2003"

The Magnetorotational Instability in Core-Collapse Supernova Explosions

Abstract: We investigate the action of the magnetorotational instability (MRI) in the context of iron-core collapse. Exponential growth of the field on the timescale Ω-1 by the MRI will dominate the linear growth process of field-line "wrapping" with the same characteristic time. We examine a variety of initial rotation states, with solid-body rotation or a gradient in rotational velocity, that correspond to models in the literature. A relatively modest value of the initial rotation, a period of ~10 s, will give a very rapidly rotating proto-neutron star and hence strong differential rotation with respect to the infalling matter. We assume conservation of angular momentum on spherical shells. Rotational distortion and the dynamic feedback of the magnetic field are neglected in the subsequent calculation of rotational velocities. In our rotating and collapsing conditions, a seed field is expected to be amplified by the MRI and to grow exponentially to a saturation field. Results are discussed for two examples of saturation fields, a fiducial field that corresponds to vA = rΩ and a field that corresponds to the maximum growing mode of the MRI. We find, as expected, that the shear is strong at the boundary of the newly formed proto-neutron star and, unexpectedly, that the region within the stalled shock can be subject to strong MHD activity. Modest initial rotation velocities of the iron core result in sub-Keplerian rotation and a sub-equipartition magnetic field that nevertheless produce substantial MHD luminosity and hoop stresses: saturation fields of order 1015-1016 G can develop ~300 ms after bounce with an associated MHD luminosity of ~1052 ergs s-1. Bipolar flows driven by this MHD power can affect or even cause the explosions associated with core-collapse supernovae.

Sporting equipment provided with a motion detecting arrangement

Abstract: Method and arrangement for detecting movement-parameters in a moving object. The parameters include acceleration and angular velocity of the object, the arrangement includes an Inertial Navigation System (INS) having at least one gyroscope and accelerometer for measuring an acceleration, angular velocity and effect of attraction of gravity on the sporting equipment.

Angular velocity sensor

Abstract: The present invention aims to present an angular velocity sensor having a self diagnosis function. An angular velocity sensor of the present invention includes a driving part for stably vibrating a driving part of a sensor element having a driver part and a detector part for detecting an angular velocity and detection means for detecting the angular velocity of the sensor element and obtains a self diagnosis signal for a malfunction by detecting a mechanical coupling signal obtained at the detection means.

Unsteady mixed convection flow from a rotating vertical cone with a magnetic field

Abstract: An analysis is developed to study the unsteady mixed convection flow over a vertical cone rotating in an ambient fluid with a time-dependent angular velocity in the presence of a magnetic field. The coupled nonlinear partial differential equations governing the flow have been solved numerically using an implicit finite-difference scheme. The local skin friction coefficients in the tangential and azimuthal directions and the local Nusselt number increase with the time when the angular velocity of the cone increases, but the reverse trend is observed for decreasing angular velocity. However, these are not mirror reflection of each other. The magnetic field reduces the skin friction coefficient in the tangential direction and also the Nusselt number, but it increases the skin friction coefficient in the azimuthal direction. The skin friction coefficients and the Nusselt number increase with the buoyancy force.

Emergency Braking Control with an Observer-based Dynamic Tire/Road Friction Model and Wheel Angular Velocity Measurement

Abstract: Summary A control scheme for emergency braking of vehicles is designed. The tire/road friction is described by a LuGre dynamic friction model. The control system output is the pressure in the master cylinder of the brake system. The controller utilizes estimated states for a feedback control law that achieves a near maximum deceleration. The state observer is designed using linear matrix inequality (LMI) techniques. The analysis shows that using the wheel angular speed information exclusively is not sufficient to rapidly estimate the velocity and relative velocity, due to the fact that the dynamical system is almost unobservable with this measurement as output. Findings are confirmed by simulation results that show that the estimated vehicle velocity and relative velocity converge slowly to their true values, even though the internal friction state and friction parameters converge quickly. The proposed control system has two main advantages when compared with an antilock braking system (ABS): (1) it produ...

Dynamical bar‐mode instability of differentially rotating stars: effects of equations of state and velocity profiles

Abstract: As an extension of our previous work, we investigate the dynamical instability against nonaxisymmetric bar-mode deformations of differentially rotating stars in Newtonian gravity by varying the equations of state and velocity profiles. We performed the numerical simulation and the follow-up linear stability analysis by adopting polytropic equations of state with polytropic indices n = 1, 3/2 and 5/2, and with two types of angular velocity profiles (the so-called j-constant-like and Kepler-like laws). It is confirmed that rotating stars with a high degree of differential rotation are dynamically unstable against bar-mode deformation, even when the ratio of the kinetic energy to the gravitational potential energy β is of order 0.01. The criterion for the onset of bar-mode dynamical instability depends weakly on the polytropic index n and the angular velocity profile, as long as the degree of differential rotation is high. Gravitational waves from the final non-axisymmetric quasi-stationary states are calculated using the quadrupole formula. For proto-neutron stars of mass 1.4 M� , radius ∼30 km and β 0.1, such gravitational waves have a frequency of ∼600‐1400 Hz, and the effective amplitude is larger than 10 −22 at a distance of about 100 Mpc, irrespective of n and the angular

Gyro aided magnetic compass

Abstract: An improved method, system, and device for a compass combining an electronic magnetic compass and an angular velocity sensing gyroscope. One aspect of the invention integrates an angular velocity output signal from an angular velocity sensor or rate gyroscope to determine the angle of motion. An initial magnetic heading is obtained from a geomagnetic sensor and used as a reference for the integrated angular velocity signal. A geomagnetic heading signal is blended with the angular velocity output signal at an adaptive time interval. The adaptive time interval is increased if the reliability of the magnetic field improves and decreased if the reliability of the magnetic field degenerates. Additionally, dynamic calibration of the angular velocity sensor may be performed to correct for gyroscope bias (zero offset), and/or gyroscope scale factor or gain.

Differential rotation in rapidly rotating F-stars ,

Abstract: We obtained high quality spectra of 135 stars of spectral types F and later and derived "overall" broadening functions in selected wavelength regions utilizing a Least Squares Deconvolution (LSD) procedure. Precision values of the projected rotational velocity v sini were derived from the first zero of the Fourier transformed profiles and the shapes of the profiles were analyzed for effects of differential rotation. The broadening profiles of 70 stars rotating faster than v sini = 45 km s −1 show no indications of multiplicity nor of spottedness. In those profiles we used the ratio of the first two zeros of the Fourier transform q2/q1 to search for deviations from rigid rotation. In the vast majority the profiles were found to be consistent with rigid rotation. Five stars were found to have flat profiles probably due to cool polar caps, in three stars cuspy profiles were found. Two out of those three cases may be due to extremely rapid rotation seen pole on, only in one case (v sini = 52 km s −1 ) is solar-like differential rotation the most plausible explanation for the observed profile. These results indicate that the strength of differential rotation diminishes in stars rotating as rapidly as v sini > 50 km s −1 .

On the tidal interaction of massive extra-solar planets on highly eccentric orbit

Abstract: In this paper we develop a theory of disturbances induced by the stellar tidal field in a fully convective slowly rotating planet orbiting on a highly eccentric orbit around a central star. We show that there are two contributions to the mode energy and angular momentum gain due to impulsive tidal interaction: a) 'the quasi-static' contribution which requires dissipative processes operating in the planet; b) the dynamical contribution associated with excitation of modes of oscillation. These contributions are obtained self-consistently from a single set of the governing equations. We calculate a critical 'equilibrium' value of angular velocity of the planet \Omega_{crit} determined by the condition that action of the dynamical tides does not alter the angular velocity at that rotation rate. We show that this can be much larger than the corresponding rate associated with quasi-static tides and that at this angular velocity, the rate of energy exchange is minimised. We also investigate the conditions for the stochastic increase in oscillation energy that may occur if many periastron passages are considered. We make some simple estimates of time scale of circularization of initially eccentric orbit due to tides, using a realistic model of the planet, for orbits withperiods after circularization typical of those observed for extra-solar planets P_{obs} > 3days. We find that dynamic tides could have produced a very large decrease of the semi-major axis of a planet with mass of the order of the Jupiter mass M_{J} and final periods P_{obs} < 4.5days on a time-scale < a few Gyrs. We also discuss several unresolved issues in the context of the scenario of the orbit circularization due to dynamic tides.

Magneto-optical rotational speed sensor

Abstract: A new passive and wireless magneto-optical rotational velocity sensor is described. It is based on measuring the intensity oscillations of linearly polarized light transmitted through an orthoferrite plate and an analyzer. The plate is subjected to the action of the magnetic field of a disc whose angular velocity has to be measured. Thanks to the high velocity and smooth reproducible character of the domain wall motion in the orthoferrite plate, one can continuously measure angular velocities in a very wide range—from ultralow to the MHz range.

Three-dimensional linear machining apparatus

Abstract: At the time of execution of concurrent six-axes cylindrical interpolation instruction wherein a start point, an intermediate point, an end point and feed speed are instructed in a machining program PRO, a machining data computing portion 59 computes angular velocity of first, second, and third rotational axis directions and moving speed of first, second and third axial directions so as to correspond the feed speed of a torch with respect to a workpiece with the feed speed instructed in the machining program PRO, and the machining control portion 55 simultaneously controls the first, second and third axes and the first, second and third rotational axes on the basis of the angular velocity and the moving speed which are computed so as to rotate a chuck holding the workpiece and to move the torch, so that machining on the workpiece is executed.

Nonlinear adaptive and sliding mode flight path control of F/A-18 model

Abstract: The question of inertial trajectory control of aircraft in the three-dimensional space is discussed. It is assumed that the nonlinear aircraft model has uncertain aerodynamic derivatives. The control system is decomposed into a variable structure outer loop and an adaptive inner loop. The outer-loop feedback control system accomplishes (x,y,z) position trajectory and sideslip angle control using the derivative of thrust and three angular velocity components (p,q,r) as virtual control inputs. Then an adaptive inner feedback loop is designed, which produces the desired angular rotations of aircraft using aileron, elevator, and rudder control surfaces to complete the maneuver. Simplification in the inner-loop design is obtained based on a two-time scale (singular perturbation) design approach by ignoring the derivative of the virtual angular velocity vector, which is a function of slow variables. These results are applied to a simplified F/A-18 model. Simulation results are presented which show that in the closed-loop system asymptotic trajectory control is accomplished in spite of uncertainties in the model at different flight conditions.

Axially symmetric rotating traversable wormholes

Abstract: This paper generalizes the static and spherically symmetric traversable wormhole geometry to a rotating axially symmetric one with a time-dependent angular velocity by means of an exact solution. It was found that the violation of the weak energy condition, although unavoidable, is considerably less severe than in the static spherically symmetric case. The radial tidal constraint is more easily met due to the rotation. Similar improvements are seen in one of the lateral tidal constraints. The magnitude of the angular velocity may have little effect on the weak energy condition violation for an axially symmetric wormhole. For a spherically symmetric one, however, the violation becomes less severe with increasing angular velocity. The time rate of change of the angular velocity, on the other hand, was found to have no effect at all. Finally, the angular velocity must depend only on the radial coordinate, confirming an earlier result.

System for estimating attitude of leg type moving robot itself

Abstract: A system for estimating the attitude angular speed at a specified part, e.g. the upper body (3) or the like, of a robot (1) mounting a gyro sensor (angular speed sensor) on the upper body (3) under motion stop state of the robot when no slip is present between the robot and the floor using motion state amounts of the robot (1) including the target motion of target gait style, a detected displacement value of joint, a target displacement value of joint, and the like, and then estimating the attitude angle at the specified part by integrating the detected attitude angular speed value corrected by a drift correction value of the angular speed sensor determined based on the difference between the estimated value of attitude angular speed and the attitude angular speed value detected by the angular speed sensor.

Electronic device, signal compensation device and signal compensation method

Abstract: An electronic device that prevents a failure caused by a temperature drift of an angular velocity sensor, and a signal compensation system and a signal compensation method for compensating for the temperature drift are provided. The present invention provides a mechanism including an angular velocity sensor that outputs a first signal in accordance with a rotational angular velocity. The device stores in advance data of a second signal normally output by the angular velocity sensor while in a stationary state, detects a stationary state and extracts the difference between the first and second signals when the stationary state is detected. The device thereby compensates for the first signal based on the extracted difference signal. A display unit in the device scrolls an image based on the compensated signal. This prevents a failure caused by the temperature drift of the angular velocity sensor.

Evolutionary sequences of rotating protoneutron stars

Abstract: We investigate the evolution of rigidly and differentially rotating protoneutron stars (PNSs) during the first twenty seconds of their life. We solve the equations describing stationary axisymmetric configurations in general relativity coupled to a finite temperature, relativistic equation of state, to obtain a sequence of quasi-equilibrium configurations describing the evolution of newly born neutron stars. Our estimates show that the scale of variation of the angular velocity in a PNSs is of the order of 7-10 km. We obtain the maximum rotation frequency that can be reached as the protoneutron stars deleptonizes and cools down, as well as other relevant parameters such as total angular momentum or |T/W|. Our study shows that imposing physical constraints (conservation of baryonic mass and angular momentum) and choosing reasonable thermodynamical profiles as the star evolves gives results consistent with the energetics of more complex simulations of non-rotating PNSs. It appears to be unlikely that PNSs formed in nearly axisymmetric core collapse reach the critical angular velocity to undergo the bar mode instability. They could, however, undergo secular or low |T/W| rotational instabilities a few seconds after birth, resulting in a strong emission of gravitational waves retarded with respect to the neutrino luminosity peak. We also found that the geometry of strongly differentially rotating protoneutron stars can become toroidal-like for large values of the angular velocity, before reaching the mass shedding limit.

Minimum Velocity Dispersion in Stable Stellar Disks. Numerical Simulations

Abstract: N-body dynamical simulations are used to analyze the conditions for the gravitational stability of a three-dimensional stellar disk in the gravitational field of two rigid spherical components--a bulge and a halo whose central concentrations and relative masses vary over wide ranges. The number of point masses N in the simulations varies from 40 to 500 thousands and the evolution of the simulated models is followed over 10--20 rotation periods of the outer edge of the disk. The initially unstable disks are heated and, as a rule, reach a quasi-stationary equilibrium with a steady-state radial-velocity dispersion $c_r$ over five to eight periods of rotation. The radial behavior of the Toomre stability parameter $Q_T (r)$ for the final state of the disk is estimated. Numerical models are used to analyze the dependence of the gravitational stability of the disk on the relative masses of the spherical components, disk thickness, degree of differential rotation, and initial state of the disk. Formal application of existing, analytical, local criteria for marginal stability of the disk can lead to errors in radial velocity dispersion $c_r$ of more than a factor of 1.5. It is suggested that the approximate constancy of $Q_T \simeq 1.2 -- 1.5$ for $r\simeq (1\div 2)\times L$ (where L is the radial scale of disk surface density), valid for a wide range of models, can be used to estimate upper limits for the mass and density of a disk based on the observed distributions of the rotational velocity of the gaseous component and of the stellar velocity dispersion.

Minimum velocity dispersion in stable stellar disks. Numerical simulations

Abstract: N-body dynamical simulations are used to analyze the conditions for the gravitational stability of a three-dimensional stellar disk in the gravitational field of two rigid spherical components—a bulge and halo whose central concentrations and relative masses vary over wide ranges. The number of point masses N in the simulations varies from 40 to 500 000 and the evolution of the simulated systems is followed over 10–20 rotation periods of the outer edge of the disk. The initially unstable disks are heated and, as a rule, reach a quasi-stationary equilibrium with a steady-state radial-velocity dispersion cr over five to eight turns. The radial behavior of the Toomre stability parameter QT(r) for the final state of the disk is estimated. Simple models are used to analyze the dependence of the gravitational stability of the disk on the relative masses of the spherical components, disk thickness, degree of differential rotation, and initial state of the disk. Formal application of existing, analytical, local criteria for marginal stability of the disk can lead to errors in cr of more than a factor of 1.5. It is suggested that the approximate constancy of QT⋍1.2–1.5 for r⋍(1–2)×L (where L is the radial scale of disk surface density), valid for a wide range of models, can be used to estimate upper limits for the mass and density of a disk based on the observed distributions of the rotational velocity of the gaseous component and of the stellar velocity dispersion.

The Roles of the Horizontal Component of the Earth's Angular Velocity in Nonhydrostatic Linear Models

Abstract: Roles of the horizontal component of the earth's rotation, which is neglected traditionally in atmospheric and oceanographic models, are studied through the normal mode analysis of a compressible and stratified model on a tangent plane in the domain that is periodic in the zonal and meridional directions but bounded at the top and bottom. As expected, there exist two distinct kinds of acoustic and buoyancy oscillations that are modified by the earth's rotation. When the cos(latitude) Coriolis terms are included, there exists another kind of wave oscillation whose frequencies are very close to the inertial frequency, 2Ω sin(latitude), where Ω is the earth's angular velocity. The objective of this article is to clarify the circumstance in which a distinct kind of wave oscillation emerges whose frequencies are very close to the inertial frequency. Because this particular kind of normal mode appears only due to the presence of boundary conditions in the vertical, it may be appropriate to call these w...

Spacecraft Angular Rate Estimation Algorithms For Star Tracker-Based Attitude Determination

Abstract: In this paper, two different algorithms are presented for the estimation of spacecraft body angular rates in the absence of gyro rate data for a star tracker mission. In first approach, body angular rates are estimated with the spacecraft attitude using a dynamical model of the spacecraft. The second approach makes use of a rapid update rate of star camera to estimate the spacecraft body angular rates independent of spacecraft attitude. Essentially the image flow of the stars is used to establish a Kalman filter for estimating the angular velocity. The relative merits of both the algorithms are then studied for the spacecraft body angular rates measurements. The second approach has an advantage of being free from any bias in attitude estimates.

Determination of operational parameters of tires in vehicles from longitudinal stiffness and effective tire radius

Abstract: An apparatus and method for determining operational parameters of a tire in terrestrial vehicles are described. Velocity of a vehicle is determined, for example, by using the global positioning system. A free-rolling radius of a free-rolling wheel is determined from the velocity and angular velocity of the free-rolling wheel, which is determined with a wheel sensing unit when angular acceleration is negligible. Absolute velocity and acceleration are determined from the free-rolling radius and the angular velocity. Longitudinal stiffness and effective radius of the tire on a monitored wheel are determined. For a free-rolling wheel, these parameters may be determined separately. For a driven wheel, these parameters are determined simultaneously when the vehicle is accelerating using a nonlinear estimation algorithm. The resulting operational parameters of the tire, such as a tire pressure, temperature or wear, are determined accurately and on an absolute scale enabling real-time monitoring of performance of the tire.

A new scheme of non-gyro inertial measurement unit for estimating angular velocity

Abstract: The non-gyro inertial measurement unit (NGIMU) uses only accelerometers replacing gyroscopes to compute the motion of a moving body. To alleviate the accumulation of angular velocity error attributed to accelerometers error, a novel design scheme for a NGIMU is proposed along with its mathematic model. Based on the conventional six-accelerometer cube configuration, this scheme employs a nine-accelerometer configuration scheme and obtains the correct sign by exploiting the redundant information of the accelerometers and integrating the angular acceleration value. The accurate angular velocity can be calculated as square root of the square expression of the angular velocity. Simulation results show that the computational accuracy of angular velocity can be improved and confirm the effectiveness and feasibility of the proposed design scheme.

Belt drive control device and image forming apparatus including the same

Abstract: A belt drive control device of the present invention is constructed to sense the angular displacement or the angular velocity of a driven roller, separates from the angular displacement or the angular velocity sensed an AC component having a frequency that corresponds to the periodic thickness variation of an endless belt in the circumferential direction, and then controls the rotation of a drive roller in accordance with the amplitude and phase of the AC component.

Axle unit with slip sensor and slip measurement method

Abstract: An axle unit 210 including a rolling bearing unit attached to a knuckle of a wheel support member has a slip sensor (211) including acceleration sensors and a rotation sensor in one piece The slip sensor (211) has the rotation sensor placed on the base face, and the rotation sensor is placed facing an encoder (213) attached to a rotation member (212) At the vehicle running time, the traveling acceleration in the traveling direction of the wheel and the rotation angular speed are detected and at the vehicle running time, the ground speed of each wheel, the tire radius of each wheel, and the slip ratio of each wheel are found

Spacecraft Angular Velocity Stabilization Using a Single-Gimbal Variable Speed Control Moment Gyro

Abstract: Feedback controllers for the stabilization of the angular velocity vector of a rigid spacecraft using a single-gimbal Variable Speed Control Moment Gyro (VSCMG) are presented. Linearization of the equations of motion show that complete attitude stabilization is not possible via linear methods. Nonetheless, it is shown that the linearized angular velocity equations are controllable, and a simple LQR control law is used to locally asymptotically stabilize the angular velocity vector. A Lyapunov-based approach is subsequently used to derive a state feedback control law that globally asymptotically stabilizes the nonlinear angular velocity system.

Power steering system

Abstract: PROBLEM TO BE SOLVED: To provide a power steering system that can protect an electric motor against overheat without sacrificing a steering feeling at sudden steering. SOLUTION: A basic target rotational speed setting part 42 sets a basic target rotational speed Rb of the electric motor 27 according to a vehicle speed and a steering angular velocity. A temperature coefficient setting part 43 sets a temperature coefficient a reducing with increasing temperature. A target rotational speed setting part 44 sets a target rotational speed R of the electric motor 27 from R=α.Rb. A motor drive control part 45 controls a driving circuit 28 so that the target rotational speed R is reached. Upon a temperature rise in the electric motor 27, steering auxiliary effort is reduced over a full range of steering angular velocity.

Chaotic rotations of an asymmetric body with time-dependent moments of inertia and viscous drag

Abstract: We study the dynamics of a rotating asymmetric body under the influence of an aerodynamic drag. We assume that the drag torque is proportional to the angular velocity of the body. Also we suppose that one of the moments of inertia of the body is a periodic function of time and that the center of mass of the body is not modified. Under these assumptions, we show that the system exhibits a transient chaotic behavior by means of a higher dimensional generalization of the Melnikov's method. This method give us an analytical criterion for heteroclinic chaos in terms of the system parameters. These analytical results are confirmed by computer numerical simulations of the system rotations.