Showing papers on "Angular velocity published in 2002"

Young tracks of hotspots and current plate velocities

Abstract: SUMMARY Plate motions relative to the hotspots over the past 4 to 7 Myr are investigated with a goal of determining the shortest time interval over which reliable volcanic propagation rates and segment trends can be estimated. The rate and trend uncertainties are objectively determined from the dispersion of volcano age and of volcano location and are used to test the mutual consistency of the trends and rates. Ten hotspot data sets are constructed from overlapping time intervals with various durations and starting times. Our preferred hotspot data set, HS3, consists of two volcanic propagation rates and eleven segment trends from four plates. It averages plate motion over the past ≈5.8 Myr, which is almost twice the length of time (3.2 Myr) over which the NUVEL-1A global set of relative plate angular velocities is estimated. HS3-NUVEL1A, our preferred set of angular velocities of 15 plates relative to the hotspots, was constructed from the HS3 data set while constraining the relative plate angular velocities to consistency with NUVEL-1A. No hotspots are in significant relative motion, but the 95 per cent confidence limit on motion is typically ±20 to ±40 km Myr −1 and ranges up to ±145 km Myr −1 . The uncertainties of the new angular velocities of plates relative to the hotspots are smaller than those of previously published HS2-NUVEL1 (Gripp & Gordon 1990), while being averaged over a shorter and much more uniform time interval. Nine of the fourteen HS2-NUVEL1 angular velocities lie outside the 95 per cent confidence region of the corresponding HS3NUVEL1A angular velocity, while all fourteen of the HS3-NUVEL1A angular velocities lie inside the 95 per cent confidence region of the corresponding HS2-NUVEL1 angular velocity. The HS2-NUVEL1 Pacific Plate angular velocity lies inside the 95 per cent confidence region of the HS3-NUVEL1A Pacific Plate angular velocity, but the 0 to 3 Ma Pacific Plate angular velocity of Wessel & Kroenke (1997) lies far outside the confidence region. We show that the change in trend of the Hawaiian hotspot over the past 2 to 3 Myr has no counterpart on other chains and therefore provides no basis for inferring a change in Pacific Plate motion relative to global hotspots. The current angular velocity of the Pacific Plate can be shown to differ from the average over the past 47 Myr in rate but not in orientation, with the current rotation being about 50 per cent faster (1.06 ± 0.10 deg Myr −1 ) than the average (0.70 deg Myr −1 ) since the 47-Myr-old bend in the Hawaiian‐Emperor chain.

The aerodynamic effects of wing rotation and a revised quasi-steady model of flapping flight.

Abstract: We used a dynamically scaled model insect to measure the rotational forces produced by a flapping insect wing. A steadily translating wing was rotated at a range of constant angular velocities, and the resulting aerodynamic forces were measured using a sensor attached to the base of the wing. These instantaneous forces were compared with quasi-steady estimates based on translational force coefficients. Because translational and rotational velocities were constant, the wing inertia was negligible, and any difference between measured forces and estimates based on translational force coefficients could be attributed to the aerodynamic effects of wing rotation. By factoring out the geometry and kinematics of the wings from the rotational forces, we determined rotational force coefficients for a range of angular velocities and different axes of rotation. The measured coefficients were compared with a mathematical model developed for two-dimensional motions in inviscid fluids, which we adapted to the three-dimensional case using blade element theory. As predicted by theory, the rotational coefficient varied linearly with the position of the rotational axis for all angular velocities measured. The coefficient also, however, varied with angular velocity, in contrast to theoretical predictions. Using the measured rotational coefficients, we modified a standard quasi-steady model of insect flight to include rotational forces, translational forces and the added mass inertia. The revised model predicts the time course of force generation for several different patterns of flapping kinematics more accurately than a model based solely on translational force coefficients. By subtracting the improved quasi-steady estimates from the measured forces, we isolated the aerodynamic forces due to wake capture.

Turbulent Convection under the Influence of Rotation: Sustaining a Strong Differential Rotation

Abstract: The intense turbulence present in the solar convection zone is a major challenge to both theory and simulation as one tries to understand the origins of the striking differential rotation profile with radius and latitude that has been revealed by helioseismology. The differential rotation must be an essential element in the operation of the solar magnetic dynamo and its cycles of activity, yet there are many aspects of the interplay between convection, rotation, and magnetic fields that are still unclear. We have here carried out a series of three-dimensional numerical simulations of turbulent convection within deep spherical shells using our anelastic spherical harmonic (ASH) code on massively parallel supercomputers. These studies of the global dynamics of the solar convection zone concentrate on how the differential rotation and meridional circulation are established. We have addressed two issues raised by previous simulations with ASH. First, can solutions be obtained that possess the apparent solar property that the angular velocity Ω continues to decrease significantly with latitude as the pole is approached? Prior simulations had most of their rotational slowing with latitude confined to the interval from the equator to about 45°. Second, can a strong latitudinal angular velocity contrast ΔΩ be sustained as the convection becomes increasingly more complex and turbulent? There was a tendency for ΔΩ to diminish in some of the turbulent solutions that also required the emerging energy flux to be invariant with latitude. In responding to these questions, five cases of increasingly turbulent convection coupled with rotation have been studied along two paths in parameter space. We have achieved in one case the slow pole behavior comparable to that deduced from helioseismology and have retained in our more turbulent simulations a consistently strong ΔΩ. We have analyzed the transport of angular momentum in establishing such differential rotation and clarified the roles played by Reynolds stresses and the meridional circulation in this process. We have found that the Reynolds stresses are crucial in transporting angular momentum toward the equator. The effects of baroclinicity (thermal wind) have been found to have a modest role in the resulting mean zonal flows. The simulations have produced differential rotation profiles within the bulk of the convection zone that make reasonable contact with ones inferred from helioseismic inversions, namely, possessing a fast equator, an angular velocity difference of about 30% from equator to pole, and some constancy along radial lines at midlatitudes. Future studies must address the implications of the tachocline at the base of the convection zone, and the near-surface shear layer, on that differential rotation.

Method for recognising a change in lane of a vehicle

Abstract: The invention relates to a method for recognising a change in lane of a vehicle (20). Said device comprises an angular resolution locating device (10) for locating vehicles (VEH1, VEH2, VEH3) travelling in front and a device (44) for determining the individual yaw rate (φ0). The invention is characterised in that the angular speed (φI) of at least one vehicle travelling in front of the first vehicle is measured in relation to the said individual vehicle (20) with the aid of the locating device (10) and a lane change signal (LC) indicating the lane change is formed by comparing the measured angular speed (φi) with the individual yaw rate (φ0).

Effect of high rotation rates on the laminar flow around a circular cylinder

Abstract: A two-dimensional numerical study on the laminar flow past a circular cylinder rotating with a constant angular velocity was carried out. The objectives were to obtain a consistent set of data for the drag and lift coefficients for a wide range of rotation rates not available in the literature and a deeper insight into the flow field and vortex development behind the cylinder. First, a wide range of Reynolds numbers (0.01⩽Re⩽45) and rotation rates (0⩽α⩽6) were considered for the steady flow regime, where α is the circumferential velocity at the cylinder surface normalized by the free-stream velocity. Furthermore, unsteady flow calculations were carried out for one characteristic Reynolds number (Re=100) in the typical two-dimensional (2D) vortex shedding regime with α varying in the range 0⩽α⩽2. Additionally, the investigations were extended to very high rotation rates (α⩽12) for which no data exist in the literature. The numerical investigations were based on a finite-volume flow solver enhanced by multi...

Molecular line study of the very young protostar IRAM 04191 in Taurus: infall, rotation, and outflow

Abstract: We present a detailed millimeter spectroscopic study of the circumstellar environment of the low-luminosity Class 0 protostar IRAM 04191+1522 in the Taurus molecular cloud. Molecular line observations with the IRAM 30 m telescope demonstrate that the14 000 AU radius protostellar envelope is undergoing both extended infall and fast, dierential rotation. Radiative transfer modeling of multitransition CS and C 34 S maps indicate an infall velocityvinf 0:15 km s 1 at r 1500 AU andvinf 0: 1k m s 1 up to r 11 000 AU, as well as a rotational angular velocity 3:9 10 13 rad s 1 , strongly decreasing with radius beyond 3500 AU down to a value 1:5 3 10 14 rad s 1 at11 000 AU. Two distinct regions, which dier in both their infall and their rotation properties, therefore seem to stand out: the inner part of the envelope (r < 2000 4000 AU) is rapidly collapsing and rotating, while the outer part undergoes only moderate infall/contraction and slower rotation. These contrasted features suggest that angular momentum is conserved in the collapsing inner region but eciently dissipated due to magnetic braking in the slowly contracting outer region. We propose that the inner envelope is in the process of decoupling from the ambient cloud and corresponds to the eective mass reservoir (0:5 M) from which the central star is being built. Comparison with the rotational properties of other objects in Taurus suggests that IRAM 04191 is at a pivotal stage between a prestellar regime of constant angular velocity enforced by magnetic braking and a dynamical, protostellar regime of nearly conserved angular momentum. The rotation velocity profile we derive for the inner IRAM 04191 envelope should thus set some constraints on the distribution of angular momentum on the scale of the outer Solar system at the onset of protostar/disk formation.

Disk drive having a sector clock that is synchronized to the angular speed of the spindle motor

Abstract: The present invention compensates for variations in the angular velocity of the drive's spindle motor by periodically dropping clocks to a counter based upon the previous servo wedge-to-wedge timing. This enables a substantially constant count to be maintained between servo wedges and allows a more predictable generation of the data sector pulses. A more predictable generation of the data sector pulses enables the size of the guard band preceding each data sector to be decreased and the capacity of the disk to be correspondingly increased.

Molecular line study of the very young protostar IRAM 04191 in Taurus: Infall, rotation, and outflow

Abstract: We present a detailed millimeter line study of the circumstellar environment of the low-luminosity Class 0 protostar IRAM 04191+1522 in the Taurus molecular cloud. New line observations demonstrate that the ~14000 AU radius protostellar envelope is undergoing both extended infall and fast, differential rotation. Radiative transfer modeling of multitransition CS and C34S maps indicate an infall velocity v_inf ~ 0.15 km/s at r ~ 1500 AU and v_inf ~ 0.1 km/s up to r ~ 11000 AU, as well as a rotational angular velocity Omega ~ 3.9 x 10^{-13} rad/s, strongly decreasing with radius beyond 3500 AU down to a value Omega ~ 1.5-3 x 10^{-14} rad/s at ~ 11000 AU. Two distinct regions, which differ in both their infall and their rotation properties, therefore seem to stand out: the inner part of the envelope (r ~< 2000-4000 AU) is rapidly collapsing and rotating, while the outer part undergoes only moderate infall/contraction and slower rotation. These contrasted features suggest that angular momentum is conserved in the collapsing inner region but efficiently dissipated due to magnetic braking in the slowly contracting outer region. We propose that the inner envelope is in the process of decoupling from the ambient cloud and corresponds to the effective mass reservoir (~0.5 M_sun) from which the central star is being built. Comparison with the rotational properties of other objects in Taurus suggests that IRAM 04191 is at a pivotal stage between a prestellar regime of constant angular velocity enforced by magnetic braking and a dynamical, protostellar regime of nearly conserved angular momentum. The rotation velocity profile we derive for the inner IRAM 04191 envelope should thus set some constraints on the distribution of angular momentum on the scale of the outer Solar system at the onset of protostar/disk formation.

Suppression of vortex shedding for flow around a circular cylinder using optimal control

Abstract: Adjoint formulation is employed for the optimal control of flow around a rotating cylinder, governed by the unsteady Navier-Stokes equations. The main objective consists of suppressing Karman vortex shedding in the wake of the cylinder by controlling the angular velocity of the rotating body, which can be constant in time or time-dependent. Since the numerical control problem is ill-posed, regularization is employed. An empirical logarithmic law relating the regularization coefficient to the Reynolds number was derived for 60 ≤ Re ≤ 140. Optimal values of the angular velocity of the cylinder are obtained for Reynolds numbers ranging from Re = 60 to Re = 1000

On the feasibility of the detection of differential rotation in stellar absorption profiles

Abstract: Stellar differential rotation invokes subtle effects on line absorption profiles which can be best studied in the Fourier domain. Detailed calculations of the behavior of Fourier transformed profiles with respect to varying differential rotation, limb darkening and inclination angles are presented. The zero positions of the Fourier transform are found to be very good tracers of differential rotation. The ratio of the first two zero positions σ 2 /σ 1 can be easily measured and is a reliable parameter to deduce the amount of differential rotation. It is shown that solar-like differential rotation (equatorial regions have larger angular velocity then polar regions) has an unambigious signature in the Fourier domain and that in certain cases it can easily be distinguished from limb darkening effects. A simple procedure is given allowing the determination of the amount of differential rotation by the knowledge of the first two zero positions of a line profile's Fourier transform alone (i.e., without the need for thorough atmospheric modelling), under the assumption of a linear limb darkening law with a limb darkening coefficient of e = 0.6.

Analytical Expressions for Spiral Arm Gravitational Potential and Density

Abstract: When modeling the three-dimensional hydrodynamics of interstellar material rotating in a galactic gravitational potential, it is useful to have an analytic expression for gravitational perturbations due to stellar spiral arms. We present such an expression for which changes in the assumed characteristics of the arms can be made easily and the sensitivity of the hydrodynamics to those characteristics examined. This analytic expression also makes it easy to rotate the force field at the pattern angular velocity with little overhead on the calculations.

On the Nature of Angular Momentum Transport in Nonradiative Accretion Flows

Abstract: The principles underlying a proposed class of black hole accretion models are examined. The flows are generally referred to as "convection-dominated" and are characterized by inward transport of angular momentum by thermal convection and outward viscous transport, vanishing mass accretion, and vanishing local energy dissipation. In this paper, we examine the viability of these ideas by explicitly calculating the leading-order angular momentum transport of axisymmetric modes in magnetized, differentially rotating, stratified flows. The modes are destabilized by the generalized magnetorotational instability, including the effects of angular velocity and entropy gradients. It is explicitly shown that modes that would be stable in the absence of a destabilizing entropy gradient transport angular momentum outward. There are no inward-transporting modes at all, unless the magnitude of the (imaginary) Brunt-Vaisala frequency is comparable to the epicyclic frequency, a condition requiring substantial levels of dissipation. When inward-transporting modes do exist, they appear at long wavelengths, unencumbered by magnetic tension. Moreover, very general thermodynamic principles prohibit the complete recovery of irreversible dissipative energy losses, a central feature of convection-dominated models. Dissipationless flow is incompatible with the increasing inward entropy gradient needed for the existence of inward-transporting modes. Indeed, under steady conditions, dissipation of the free energy of differential rotation inevitably requires outward angular momentum transport. Our results are in good agreement with global MHD simulations, which find significant levels of outward transport and energy dissipation, whether or not destabilizing entropy gradients are present.

Transient and Steady-State Dynamic Finite Element Modeling of Belt-Drives

Abstract: In this study, a dynamic finite element model is developed for pulley belt-drive systems and is employed to determine the transient and steady-state response of a prototypical belt-drive. The belt is modeled using standard truss elements, while the pulleys are modeled using rotating circular constraints, for which the driver pulley's angular velocity is prescribed. Frictional contact between the pulleys and the belt is modeled using a penalty formulation with frictional contact governed by a Coulomb-like tri-linear friction law. One-way clutch elements are modeled using a proportional torque law supporting torque transmission in a single direction. The dynamic response of the drive is then studied by incorporating the model into an explicit finite element code, which can maintain time-accuracy for large rotations and for long simulation times. The finite element solution is validated through comparison to an exact analytical solution of a steadily-rotating, two-pulley drive. Several response quantities are compared, including the normal and tangential (friction) force distributions between the pulleys and the belt, the driven pulley angular velocity and the belt span tensions. Excellent agreement is found. Transient response results for a second belt-drive example involving a one-way clutch are used to demonstrate the utility and flexibility of the finite element solution approach.

The subsurface radial gradient of solar angular velocity from MDI f -mode observations

Abstract: We report quantitative analysis of the radial gradient of solar angular velocity at depths down to about 15 Mm below the solar surface for latitudes up to 75° using the Michelson Doppler Imager (MDI) observations of surface gravity waves (fmodes) from the Solar and Heliospheric Observatory (SOHO) A negative outward gradient of around −400 nHz/R ⊙, equivalent to a logarithmic gradient of the rotation frequency with respect to radius which is very close to −1, is found to be remarkably constant between the equator and 30° latitude Above 30° it decreases in absolute magnitude to a very small value at around 50° At higher latitudes the gradient may reverse its sign: if so, this reversal takes place in a thin layer extending only 5 Mm beneath the visible surface, as evidenced by the most superficial modes (with degrees l>250) The signature of the torsional oscillations is seen in this layer, but no other significant temporal variations of the gradient and value of the rotation rate there are found

Carbon-Oxygen White Dwarfs Accreting CO-Rich Matter I: A Comparison Between Rotating and Non-Rotating Models

Abstract: We investigate the lifting effect of rotation on the thermal evolution of CO WDs accreting CO-rich matter. We find that rotation induces the cooling of the accreting star so that the delivered gravitational energy causes a greater expansion with respect to the standard non-rotating case. The increase in the surface radius produces a decrease in the surface value of the critical angular velocity and, therefore, the accreting WD becomes gravitationally unbound (Roche instability). This occurrence is due to an increase in the total angular momentum of the accreting WD and depends critically on the amount of specific angular momentum deposited by the accreted matter. If the specific angular momentum of the accreted matter is equal to that of the outer layers of the accreting structure, the Roche instability occurs well before the accreting WD can attain the physical conditions for C-burning. If the values of both initial angular velocity and accretion rate are small, we find that the accreting WD undergoes a secular instability when its total mass approaches 1.4 Msun. At this stage, the ratio between the rotational and the gravitational binding energy of the WD becomes of the order of 0.1, so that the star must deform by adopting an elliptical shape. In this case, since the angular velocity of the WD is as large as 1 rad/s, the anisotropic mass distribution induces the loss of rotational energy and angular momentum via GWR. We find that, independent of the braking efficiency, the WD contracts and achieves the physical conditions suitable for explosive C-burning at the center so that a type Ia supernova event is produced.

Oxidation of organic contaminants in a rotating disk photocatalytic reactor: reaction kinetics in the liquid phase and the role of mass transfer based on the dimensionless Damköhler number

Abstract: The photocatalytic degradation of a model non-volatile chlorinated aromatic compound 4-chlorobenzoic acid (4-CBA) was investigated as a function of disk angular velocity, contaminant concentration, and incident light intensity using a rotating disk photocatalytic reactor (RDPR). The study was designed to investigate the effect of all three parameters on the degradation rate as well as their importance on unveiling the existence of mass transfer limitations in the liquid phase under specific conditions. The results showed that the reaction rate increased with disk angular velocity in accordance with a saturation-type dependency. In the range of 2–6 rpm the degradation rate increased almost linearly with disk angular velocity. Above 6 rpm, however, the influence of disk angular velocity was not significant. The initial increase in the reaction rate with disk angular velocity was attributed to the longer time available per rotation resulting in higher down flow of liquid carried by the disk and to the increase in the overall mass transfer coefficient. The rates of 4-CBA acid decomposition and Cl− mineralization at 6 rpm as a function of initial 4-CBA concentration followed Langmuir–Hinshelwood kinetics. At 6 rpm, the rates of 4-CBA degradation followed a linear dependency with incident light intensity. This was attributed to the existence of low local values of incident light intensity on the illuminated disk. With respect to the effect of these three parameters on the degradation rate, the obtained results suggested the absence of significant mass transfer limitations at disk angular velocities higher than 6 rpm. The latter was verified by additional calculations of the Damkohler (Da) number based on dimensionless analysis. The Da number was found to decrease significantly with disk angular velocity and at high disk angular velocities (ω>15 rpm), Da was much lower than 0.1, even when the concentration of the contaminant in the bulk was extremely small (i.e. 1 μmol/l).

Angular Velocity Determination Directly from Star Tracker Measurements

Abstract: Introduction Star trackers are increasingly used on modern day spacecraft. With the rapid advancement of imaging hardware and high-speed computer processors, current trackers are small and routinely achieve arc-second attitude accuracy. Typical sampling rates for these trackers range from 1 to 10 Hz. As computer processor technology advances these frequencies will increase, leading to filter designs that provide even more accurate results. The body angular velocity can be derived using a derivative approach in the attitude kinematics model. For example, if the attitude quaternion q and it’s derivative q (which is usually approximated by a finite-difference) are known, then the angular velocity ω can be computed from the kinematics equations, with ω = 2 Ξ (q) q, where Ξ(q) is a 4× 3 matrix function of the quaternion (see Ref. [2] for more details). However, this approach requires knowledge of the attitude, which is determined from the star reference and body measurement vectors. In this note a new and simple approach to determine the angular velocity is shown that depends only on knowledge of the body vector measurements, which are obtained directly from the star tracker. Therefore, angular velocities can still be determined in the event of star pattern recognition anomalies, which may be used to control the spacecraft in the event of gyro failures.

The influence of limit cycle topology on the phase resetting curve

Abstract: Understanding the phenomenology of phase resetting is an essential step toward developing a formalism for the analysis of circuits composed of bursting neurons that receive multiple, and sometimes overlapping, inputs. If we are to use phase-resetting methods to analyze these circuits, we can either generate phase-resetting curves (PRCs) for all possible inputs and combinations of inputs, or we can develop an understanding of how to construct PRCs for arbitrary perturbations of a given neuron. The latter strategy is the goal of this study.We present a geometrical derivation of phase resetting of neural limit cycle oscillators in response to short current pulses. A geometrical phase is defined as the distance traveled along the limit cycle in the appropriate phase space. The perturbations in current are treated as displacements in the direction corresponding to membrane voltage. We show that for type I oscillators, the direction of a perturbation in current is nearly tangent to the limit cycle; hence, the projection of the displacement in voltage onto the limit cycle is sufficient to give the geometrical phase resetting. In order to obtain the phase resetting in terms of elapsed time or temporal phase, a mapping between geometrical and temporal phase is obtained empirically and used to make the conversion. This mapping is shown to be an invariant of the dynamics. Perturbations in current applied to type II oscillators produce significant normal displacements from the limit cycle, so the difference in angular velocity at displaced points compared to the angular velocity on the limit cycle must be taken into account. Empirical attempts to correct for differences in angular velocity (amplitude versus phase effects in terms of a circular coordinate system) during relaxation back to the limit cycle achieved some success in the construction of phase-resetting curves for type II model oscillators. The ultimate goal of this work is the extension of these techniques to biological circuits comprising type II neural oscillators, which appear frequently in identified central pattern-generating circuits.

2.5-dimensional Nonsteady Magnetohydrodynamic Simulations of Magnetically Driven Jets from Geometrically Thin Disks

Abstract: We have performed self-consistent 2.5-dimensional nonsteady MHD numerical simulations of jets from geometrically thin disks including the dynamics of accretion disks. For the initial rotational velocity of the disk, we consider two cases, the Keplerian case and the sub-Keplerian case. We compare our results with the thick-disk case in detail. The characteristics of nonsteady jets from geometrically thin disks in our Keplerian case are similar to those of the steady theory and thick-disk cases: (1) The ejection point of the jets corresponds to the slow magnetosonic point, which is determined by the effective potential made by the gravitational and centrifugal forces along the magnetic field. (2) The dependences of the velocity (Vjet) and the mass outflow rate (w) on the initial magnetic field strength (B0) are w ∝ B0 and Vjet ∝ 1/3, therefore Vjet ∝ B, where ΩF is the angular velocity of a field line. Although this dependence of the velocity corresponds to Michel's scaling law, the velocity of our simulated jets still does not reach the fast magnetosonic velocity. In the sub-Keplerian case, the relation Vjet ∝ B is satisfied, but the other dependences are not necessarily equal to those of the Keplerian case. The velocity of the jets is larger when the initial rotational velocity of the disk is smaller. The initial acceleration force on the jets is the magnetic pressure when the initial magnetic field is weak, while the centrifugal force is dominant when the initial magnetic field is strong. Finally, we found two interesting phenomena in the sub-Keplerian cases: one is knotlike structures around the rotational axis, and the other is outflow along the disk surface.

Robust speed control system considering vibration suppression caused by angular transmission error of planetary gear

Abstract: This paper proposes a new robust speed control to suppress vibration caused by angular transmission error of planetary gears. For this purpose, this paper first constructs a new numerical simulation model of angular transmission error of planetary gear, which is confirmed by experimental data from a robot arm. Next, in order to suppress the vibration caused by angular transmission error, we propose a robust speed control system based on disturbance observer and coprime factorization. Numerical simulation results show that the proposed system regulates the angular speed of motor satisfactorily, and it suppresses the vibration caused by angular transmission error.

Tracking rigid body motion using thrusters and momentum wheels

Abstract: Tracking control laws are developed for a rigid spacecraft using both thrusters and momentum wheels. The model studied comprises a rigid body with external thrusters and with rigid axisymmetric wheels controlled by axial torques. Modified Rodrigues parameters (MRPs) are used to describe the kinematics. The thruster torques and the axial motor torques are computed to track given attitude motions, using the angular velocity error and MRP error to develop linear and nonlinear control laws. Three different controllers are developed. The first controller uses thruster torques based on a bang-bang control law, while momentum wheels are used to correct tracking errors. The second controller is similar, but is designed to use the thruster torques in such a way that the momentum wheels are not used at all unless there are initial condition errors. The third controller uses linear feedback for the wheels and nonlinear feedback for the thrusters. In all three cases, the controllers are shown rigorously to result in globally asymptotically stable closed-loop systems.

Rate of change of angular bearing as the relevant property in a horizontal interception task during locomotion.

Abstract: The authors ran 3 experiments to investigate how catchers deal with the horizontal component of the ball's trajectory in an interception task during locomotion. The experiments were built upon the finding that velocity adaptations are based upon changes in the horizontal angular position or velocity of the ball with respect to the observer (M. Lenoir, M. Janssens, E. Musch, E. Thiery, & J. Uyttenhove, 1999); a potential underlying information source for that strategy is described. In Experiment 1, actor (N = 10 participants) and ball approached each other along the legs of a V-shaped track. When the velocity and the initial angular bearing of the ball were varied, the observed behavior fitted with nulling the horizontal angular velocity of the ball: A positive or negative angular velocity was compensated by a velocity change. Evidence was obtained that those adaptations are modulated by a critical change in, rather than by a critical state of, the environment-actor system. In Experiment 2, the di...

MEMS gyroscope having mass vibrating vertically on substrate

Abstract: X type MEMS gyroscope has a first mass vertically vibrating on a substrate and a second mass horizontally vibrating on the substrate. A driving electrode is disposed on the same surface with the first mass. When the first mass vertically vibrates, the second mass vibrates vertically together with the first mass. When angular velocity that is at a right angle to a movement direction of the first mass and the second mass is applied while the first mass is vertically vibrating, the second mass moves as Coriolis force is added to the second mass in a horizontal direction, and a sensing electrode measures displacement of the second mass in the horizontal direction. All moving electrodes and stationary electrodes are disposed on the same surface, and all elements are manufactured by using one mask. Therefore, adhesion between the moving and stationary electrodes is prevented and the manufacturing process is simplified.

Controlling angular oscillations through mass reconfiguration: a variable length pendulum case

Abstract: The control of angular oscillations or energy of a system through mass reconfiguration is examined using a variable length pendulum. Control is accomplished by sliding the end mass towards and away from the pivot as the pendulum oscillates. The resulting attenuation or amplification of the angular oscillations are explained using the Coriolis inertia force and by examining the energy variation during an oscillation cycle. Simple rules relating the sliding motion to the angular oscillations are proposed and assessed using numerical simulations. An equivalent viscous damping ratio is introduced to quantify the attenuation/amplification phenomena. Sliding motion profiles for achieving attenuation have been simulated with the results being discussed in detail.

Determining Subject-Specific Torque Parameters for Use in a Torque-Driven Simulation Model of Dynamic Jumping

Abstract: This paper describes a method for defining the maximum torque that can be produced at a joint from isovelocity torque measurements on an individual. The method is applied to an elite male gymnast in order to calculate subject-specific joint torque parameters for the knee joint. Isovelocity knee extension torque data were collected for the gymnast using a two-repetition concentric-eccentric protocol over a 75° range of crank motion at preset crank angular velocities ranging from 20 to 250°s–1. During these isovelocity movements, differences of up to 35° were found between the angle of the dynamometer crank and the knee joint angle of the participant. In addition, faster preset crank angular velocities gave smaller ranges of isovelocity motion for both the crank and joint. The simulation of an isovelocity movement at a joint angular velocity of 150°s–1 showed that, for realistic series elastic component extensions, the angular velocity of the joint can be assumed to be the same as the angular velocity of th...