Showing papers on "Acceleration published in 1975"

Calculation of nonlinear ground response in earthquakes

Abstract: A method is presented for calculating the seismic response of a system of horizontal soil layers. The essential element of the method is a rheological model suggested by Iwan which takes account of the nonlinear hysteretic behavior of soils and has considerable flexibility for incorporating laboratory results on the dynamic behavior of soils. Finite rigidity is allowed in the underlying elastic medium, permitting energy to be radiated back into the underlying medium. Three alternate ways of integrating the equations of motion are compared, an implicit technique, an explicit technique, and integration along characteristics. An example is set up for comparing the different methods of integration and for comparing the nonlinear solution with a solution based on the widely used equivalent linear assumption. The example consists of a 200-m section of firm alluvium excited at its base by the N21E component of the Taft accelerogram multiplied by four to produce a peak acceleration of 0.7 g and a peak velocity of 67 cm/sec. The three techniques of integration give very similar results, but integration along characteristics has the advantage of avoiding spurious high-frequency oscillations in the acceleration time history at the surface. For the chosen example, which has a thick soil column and a strong input motion, the equivalent linear solution underestimates the intensity of surface motion for periods between 0.1 and 0.6 sec by factors exceeding two. The discrepancies, however, would probably be less for input motion of lower intensity. At longer periods the equivalent linear solution is in essential agreement with the nonlinear solution. For the same example both solutions show that, compared to a site with rock at the surface, motion at the surface of the soil is amplified for periods longer than 1.5 sec by as much as a factor of two. At shorter periods the amplitude is reduced.

Perception and extrapolation of velocity and acceleration.

Abstract: A moving target disappeared behind a screen and subjects predicted when the target passed behind a marker on the screen. When the target moved with constant velocity, predictions were extremely accurate, regardless of the spatial and temporal exposure and concealment of the target and regardless of its rate of velocity. When the target accelerated, accuracy of prediction decreased with increasing acceleration and with increasing target concealment. Analyses of the results suggest that the perception of velocity and acceleration is direct and accurate and that extrapolation of velocity and acceleration incorporates concrete and abstract characteristics of the motion that was seen. It is proposed that the motion perception system is tuned to accelerated rather than to constant velocity movement. Language: en

Eye movements due to linear accelerations in the rabbit.

Abstract: 1. Compensatory vertical or torsional eye movements of rabbits caused by linear accelerations along the transverse or sagittal axis were measured. Sinusoidal accelerations (parallel swing) in a frequency range of 0-068--1-22 Hz and acceleration steps (linear track) of 0-02--0-11 g were applied. 2. On the parallel swing, properties of the maculo-ocular reflexes were similar for transverse and sagittal acceleration. Gain (rotation of eye/rotation of the resultant linear vector) proved to be very low: about 0-1 for 0-3 Hz and smaller than 0-01 for frequencies above 1-0 Hz. The decrease in gain was accompanied by an increase in phase lag to about 180degrees. No non-linearity was revealed by the use of different amplitudes (10--30 cm). 3. On the linear track, eye deviation after an acceleration step took many seconds to develop fully. Gain increased with time and was about 0-65 after 5 sec. 4. The results indicate that the responses of the otoliths, as reflected in maculo-ocular reactions, are very slow. Fluctuations in the direction of gravity seem to be averaged over several seconds by the system. This may explain that erratic linear accelerations(frequency greater than 1 Hz) during locomotion or transport do not lead to eye movements or disorientation.

Automatic stability control system with strain gauge sensors

Abstract: An automatic stability control system is provided which senses the lateral acceleration of a vehicle by way of strain gauge sensors, or the like, to provide lateral acceleration signals to an amplifier. Since strain gauge sensors which operate on the piezoelectric effect provide very weak signals, special amplifier circuits must be employed. The amplified signals control a brake assembly on the vehicle to simultaneously, continuously and gradually apply the right and left brakes with a force proportional to the lateral acceleration signals in order to eliminate swerving or swaying of the vehicle. The amplifier is mounted in the vehicle and includes a sensitivity adjustment for setting a threshold point corresponding to a minimum lateral acceleration force to which the system will respond. Sensor configurations are also used which have strain gauges to sense the regular brake fluid pressure of the vehicle in combination with the lateral force sensing sensors. Additional sensitivity adjustments are provided for the amplifiers of these configurations. The control system is primarily adapted for use in a trailing or towed vehicle in combination with a leading or towing vehicle although it is equally effective when used in a single vehicle.

The effect of the initial position of the head and neck on the dynamic response of the human head and neck to -Gx impact acceleration

Abstract: Thirteen human volunteer subjects ranging from the 5th to the 97th percentile in sitting height were exposed to -Gx impact acceleration at peak sled accelerations of 6G and 10G. Two angles of the neck relative to chair and two angles of the head relative to the neck for a total of four conditions were tested for each subject for the 2 peak acceleration levels giving a total of 104 experiments. Instrumentation consisted of 6 accelerometers and two-axis rate gyro at the posterior spinous process of the first thoracic vertebral body, 6 accelerometers at the mouth, and a two-axis rate gyro at the top of the head. Three-dimensional photography from two orthogonally mounted onboard cameras was used also. The input data at T//1 along with the differential effects of initial head position relative to T//1 on the linear acceleration at the origin of the head anatomical coordinate system and on the angular acceleration and angular velocity of the head are presented along with the implications for modeling the response and a statistical comparison. Language: en

Theory of ion acceleration by drifting intense relativistic electron beams. I. Theory

Abstract: A theory that describes the collective acceleration of ions by an intense relativistic electron beam injected into a metallic guide tube filled with neutral gas at low pressure is presented. The acceleration mechanism is shown to be of electrostatic origin (although it is different from those employed in previous electrostatic theories), and its many parametric dependences are identified and discussed. In the theory, ion acceleration occurs in the electrostatic fields of a two‐dimensional, time‐dependent, potential well, which is described by the self‐consistent coupling of the beam dynamics with the ionization processes of the neutral gas. The theory divides into the cases (i) I0 ≳ Il, and (ii) I0 ≪ Il, where I0 is the peak injected beam current and Il is the space‐charge limiting current. For case (i), the beam initially stops at the anode and creates a deep potential well. At roughly the charge neutralization time, a nonadiabatic transition occurs, the beam begins to propagate, and an ion bunch is acce...

Acceleration controlled fluidic shock absorber

Abstract: The invention provides a shock absorber for wheeled and track type vehicles in which the conventional compression valve is replaced by an acceleration controlled vortex throttle. A beam deflection amplifier introduces fluid radially, tangentially or at an intermediate position into a vortex chamber under control of an accelerometer. The vortex throttle is controlled such that in the presence of acceleration of a wheel relative to the ground shock motion is lightly resisted while long term movement of the wheel toward the vehicle is strongly resisted so that the wheel more closely follows the terrain contour with reduced energy delivered by the wheel to the vehicle body.

Relationships between maximum acceleration, maximum velocity, distance from source and local site conditions for moderately strong earthquakes

Abstract: The paper presents the results of a study to determine the influence of local geological conditions on the attenuation of peak accelerations and peak velocities, with increasing distance from the source of energy release, for earthquakes with a magnitude of about 6.5 occurring in the western part of the United States. While the results can only be considered to be strictly applicable to these conditions, it is hoped that they can also serve as a guide to possible relationships between peak accelerations and peak velocities which may be expected for earthquakes of higher magnitudes occurring in different locations and thereby serve a useful purpose in the difficult task of predicting the likely characteristics of earthquake ground motions in different geological settings.

Electronic fuel control for a gas turbine engine

Abstract: An electronic gas turbine fuel control of the slave datum type, i.e. one including a circuit which generates a speed error signal, an electronic integrator which integrates that error signal to produce a speed datum signal and a difference amplifier comparing the speed datum signal with the actual engine speed to produce a fuel error signal, incorporates a surge detection and recovery circuit. For detection the rate of change of the fuel error signal is derived and compared with a reference value varying with engine conditions. For recovery, if the rate of change exceeds the reference value for a predetermined time during acceleration, the speed error signal is caused to go negative for a fixed period to ramp the integrator output downwards, after which acceleration is allowed to recommence.

Minimum-fuel rocket trajectories involving intermediate-thrust arcs

Abstract: The optimal trajectories in the neighborhood of an optimal intermediate-thrust arc are investigated for the minimum-fuel orbit rendezvous problem with fixed specific impulse. Since such an arc is singular, the thrust acceleration magnitude being the singular control component, a second-variation analysis leads to the identification of a field of neighboring, singular arcs in a state space of dimension four rather than six, provided that a suitable Jacobi condition is met. A given neighboring initial six-dimensional state vector does not generally lie on a neighboring singular arc, and junction onto the appropriate singular arc must be accomplished by a short period of strong variations in the acceleration. The neighboring singular arc meets the final condition in 4 dimensions, rather than 6 dimensions, and rendezvous must be completed by another, terminal short period of strong variations in the acceleration. Implications for midcourse guidance near a singular arc are discussed.

Dynamic response of an isothermal static corona to finite-amplitude disturbances

Abstract: The velocity evolution of sprays, surges and fast ejections is characterized by a rapid acceleration followed by a slowdown. In contrast, eruptive prominences show a velocity evolution with a slow increase followed by a rapid acceleration. We examine the physical causes which differentiate these two characteristic velocity evolutions, and study the dynamic responses of the solar corona. For simplicity, the ascending disturbances are modelled as purely radial adiabatic flows caused by finite-amplitude perturbations (pulses) in an initially isothermal, static corona. It is shown that the resultant flow depends strongly on the nature of the disturbing causes. In particular, the coronal response to sprays and fast ejections can be identified with temperature and velocity pulses at the bottom of the corona, with surges related to shorter pulses, while the slow moving eruptive prominences are correlated with density pulses. It is shown that for large flare sprays 5 × 1039 particles can be injected into the solar wind.

Adaptive anti-lock brake control system

Abstract: An anti-lock brake control system especially suited to heavy duty trucks with air brakes senses the wheel speeds on a given axle and cyclically releases and applies the brakes on that axle as required to avoid undesirable wheel slip during braking. In one control channel, a deceleration switch responsive to a wheel speed signal produces a brake release signal when wheel deceleration exceeds a predetermined threshold. A second parallel channel, also responsive to wheel speed, derives a velocity error signal representing the difference between wheel speed and an estimated vehicle speed and produces a release signal when the velocity error exceeds a value which varies as a function of wheel speed. The velocity error is determined by comparing the wheel deceleration with a vehicle deceleration and integrating the difference. The estimated vehicle deceleration is determined in large part by a wheel acceleration sensing circuit to determine the rate of wheel spinup during brake release. The second channel also includes an acceleration switch connected to the release integrator to quickly remove the velocity error signal when a predetermined wheel acceleration occurs to effect brake reapplication. A self-check circuit includes a timer producing an output signal which increases with time and a synchronous reapply circuit connected to the second channel to effect brake reapplication when a preset time has expired. The timer is operative when a self-check accelerometer indicates that the wheels are near synchronous speed and when a self-check logic circuit indicates that the control circuit calls for a brake release. A comparator and latch circuit responsive to the timer output signal is actuated when a second larger preset time has expired and is effective to illuminate a warning lamp and to disable the control circuit.

Adaptive anti-lock brake control apparatus

Abstract: An anti-lock brake control apparatus especially suited to heavy duty trucks with air brakes senses the wheel speeds on a given axle and cyclically releases and applies the brakes on that axle as required to avoid undesirable wheel slip during braking. In one control channel, a deceleration switch responsive to a wheel speed signal produces a brake release signal when wheel deceleration exceeds a predetermined threshold. A second parallel channel, also responsive to wheel speed, derives a velocity error signal representing the difference between wheel speed and an estimated vehicle speed and produces a release signal when the velocity error exceeds a value which varies as a function of wheel speed. The velocity error is determined by comparing the wheel deceleration with an estimated vehicle deceleration and integrating the difference. The second channel also includes an acceleration switch connected to the release integrator to quickly remove the velocity error signal when a predetermined wheel acceleration occurs to effect brake reapplication. A self-check circuit includes a timer producing an output signal which increases with time and a synchronous reapply circuit connected to the second channel to effect brake reapplication when a time period has expired. The timer is operative when a self-check accelerometer indicates that the wheels experience low positive or negative acceleration and when a self-check logic circuit indicates that the control circuit calls for a brake release. A comparator and latch circuit responsive to the timer output signal is actuated when a second larger time period has expired and is effective to illuminate a warning lamp and to disable the control circuit. The timer is retarded when a large velocity error signal is present to extend the time periods for brake reapplication and disabling of the circuit.

Energy spectrum of particles accelerated in the neighborhood of a line of zero magnetic field

Abstract: A study is made of the acceleration of charged particles in a hyperbolic magnetic field and uniform electric field, these fields arising from the decay of a neutral current sheet. The acceleration process consists of direct acceleration by the electric field in the nonadiabatic region near the zero line and betatron acceleration in the drift region. The characteristic energy of the accelerated particles is found in the nonrelativistic and ultrarelativistic limits. At high energies, the spectra are exponential. (AIP)

Theory of ion acceleration by drifting intense relativistic electron beams. II. Comparison with experiments

Abstract: Predictions of a theory together with a detailed comparison of that theory with data obtained over the past six years at several laboratories are presented, and good agreement is shown for a wide variety of measurable quantities This agreement includes the ion energy and its dependence on ion charge state, beam current, beam energy, neutral gas perameters, and guide tube and beam dimensions It also includes the ion number and pulse shape and their variation with pressure; the acceleration characteristics including the delay time near the anode, the acceleration region length, and the acceleration time; and the location of the ion bunch relative to the beam front The beam front velocity and propagating beam risetime behavior are also in agreement Effects of an external magnetic field and a plasma‐filled guide are considered In addition, radially accelerated ions, the effects of ν/γ, and possible multiple pulse mechanisms are discussed

Method and apparatus for numerical control

Abstract: Method and apparatus for numerical control to produce contouring by simultaneous coordinated motions along two or more axes, characterized by the creation of desired velocity signals supplied as the primary inputs to velocity servos coupled to drive a member relatively along the respective axes. Although capable of practice by and susceptible of embodiment in other apparatus, a digital computer is physically organized and conditioned by a master program, and associated with an adjustable interrupt clock which measures off successive time periods ΔT, so as to supply a changeable velocity command number signal to each servo proportional to the distance per ΔT through which motion along the associated axis is to occur. This velocity command number is algebraically added to a theoretical position number to signal dynamically during each period ΔT the axis position at which the member should reside; and the latter number is used with a dynamically signaled actual position number to re-compute and signal during each period the position error. The position errors are used as a trimming or adjusting term in the signals applied to the respective axis servos. When the signaled error exceeds a first threshold on any axis, the periods ΔT are lengthened to reduce all axis velocities; when it exceeds a second threshold, the system is put into a holding mode. On the other hand, as the error is reduced below the second threshold, the system returns to the running mode and as the error is reduced below the first threshold the periods ΔT are reduced to increase all axis velocities back to programmed values. The input signal applied to each axis servo includes a further historical adjustment term incrementally changed during any period when the error exceeds a predetermined value --all to the objective of making the axis servos (a) operate with substantially zero following error, (b) correct themselves if the position error becomes at all appreciable, or (c) stop if that error becomes intolerable. Because of the accuracy of velocity control, the system terminates any path segment for one block of command data when the number of elapsed periods ΔT equals a precomputed number of time periods ΔT required for the controlled member to travel the segment length at the commanded velocity expressed in distance per period. No comparison of command end point coordinates with actual end point coordinates is required. Automatic acceleration and deceleration is performed by starting the execution of a block of command data at the commanded velocity, and beginning an incrementing of the velocity command number during each period ΔT after the number of elapsed periods becomes equal to the total of the periods for the entire block less the quantity required for the velocity to change from one block velocity to the next at the chosen incrementing or acceleration value.

Vibration isolator with integral non-amplifying seismic restraint

Abstract: The force transmitted to vibration-isolated equipment during a seismic event can be essentially limited to the force generated by the floor input acceleration by a combination of friction restraining devices and energy-absorbing stops constructed into the vibration isolators which support the equipment. The friction restraint devices permit essentially undamped vibration of the equipment during normal operation but provide a frictional force which restrains vibration of the equipment at amplitudes greater than a selected value. Any movement of the equipment in excess of the selected amplitude that results from a floor input force that exceeds the frictional restraining force of the friction restraint devices is limited by the energy-absorbing stops, which transmit to the equipment with a small amplification only the residual of the input force over the frictional force.

Scaling Studies of Collective Ion Acceleration with Intense Relativistic Electron Beams

Abstract: Recent experimental observations1 of collective ion acceleration produced when an intense relativistic electron beam was iniected into a low pressure neutral gas have firmly established a threshold beam current for the process which was predicted by Olson2; for this geometry ion acceleration does not occur unless the electron beam current (I) exceeds the space-charge limiting current (Il). In this paper we report additional observations of ion acceleration obtained in two series of experiments. In the first series, the guide tube and diode were configured to provide a large ratio of injected beam current to space charge limiting current, and drift tube endplate effects were examined. When the separation between the anode and tube endplate become less than the drift tube diameter the efficiency of the collective acceleration process is strongly reduced. In the second series of experiments the scaling of accelerated ion energy with electron beam kinetic energy was investigated using two electron beam machines which differ in stored energy by a factor of approximately 20. Using the larger machine proton energies in excess of 16.5 MeV have been attained. In addition, we also present an expression for the optimum pressure for ion acceleration in the drifting beam neutral gas geometry.

Circuit arrangement for controlling the propulsion, braking and station stopping function for a rapid transit train

Abstract: A propulsion, braking, and station stopping control circuit for a rapid transit train including a first summing and amplifying apparatus for producing a velocity signal which is a function of the desired and actual velocity of the train and including a second summing and amplifying apparatus for producing a propulsion error signal which is a function of the velocity signal and an actual acceleration signal. An absolute value and sign determining apparatus for receiving the propulsion error signal and for producing an up-down signal which is to be supplied to an advanced train line register and propulsion train line encoder and for producing an analog signal which is supplied to a clock for generating pulses which are applied to the advanced train line register. Apparatus for producing a speed control braking error signal which is a function of the velocity signal and an actual acceleration signal. First gate apparatus for applying the speed control error signal to an output amplifying apparatus which provides a brake error signal to a train line wire driver. Third summing apparatus for producing a station stop brake error signal which is a function of the actual acceleration and calculated deceleration signals. Second gating apparatus for receiving the station stop brake error signal and comparing apparatus for enabling the second gating apparatus when the calculated deceleration and desired acceleration signals are equal so that the station stop brake error signal is applied to the output amplifying apparatus for providing a brake error signal on the train line wire driver.

Electronic watch generator

Abstract: An electronic watch generator in which the wrist of the wearer is turned until the angle of inclination of the watch and, thus, the rotor, is sufficient to enable gravity to overcome a magnetic latching force which holds the rotor in place. The rotor is a pendulum with gravity and subsequent acceleration activating its position change to generate a voltage due to relative movement between coils located on the stator and the magnetic pole pieces on the rotor. The magnetic latching force holds the rotor against rotation until the desired angle of inclination of the wrist is sufficient to provide rapid acceleration and, accordingly, a large voltage output. The voltage generated by this action is stored in a rechargeable storage cell and is utilized to operate the watch module and display.

Experimental studies of collective ion acceleration

Abstract: This paper briefly treats the history of linear collective acceleration experiments, describes several configurations in which collective ion acceleration has been observed at Sandia Laboratories, and outlines experimental techniques used and results obtained to date. Short explanations of the acceleration process are included, so that similarities in results of ions accelerated in diodes and in drift tubes can be appreciated. (MOW)

Railway vehicle derailment detection system

Abstract: In order to detect derailment of a railway vehicle each vehicle in a train is provided with an acceleration responsive device which, in response to the vehicle acceleration resulting from derailment of the vehicle transmits a short range radio signal to a receiver installed in the engine to provide a visual or audio alarm. In one practical arrangement requiring no routine maintenance each transmitter unit has a resonant circuit which is energized as a result of the stressing of a piezo-electric crystal upon vehicle derailment, avoiding the need for any separate electrical power source on the vehicle.

Device for measurement of the speed of a helicopter

Abstract: Apparatus for measurement of the velocity of a helicopter with reference to the air comprises two measurement systems that are substantially identical, associated with a double indicator. The measurements are effected with reference to the longitudinal axis and the transverse axis of the helicopter. Each measurement system comprises a position detector for detecting the position of the cyclic rotor pitch command member along one axis, and a detector of the acceleration component along the same axis, with a substantially identical measurement system associated with the other axis. Computing means effect integration of the algebraic sum of the measured values, and pass signals to the double indicator which indicates velocity of the helicopter along the axes. The acceleration detectors include pendular levels, and all detectors incorporate measurement potentiometers. The apparatus is especially useful in the measurement of the air speed of a helicopter close to hovering conditions.

On the dynamical process of the Process of the Parkfield earthquake of June 28, 1966.

Abstract: The seismic acceleration recorded at the Parkfield, Cholame No.2 station in California at the time of the Parkfield earthquake of June 28, 1966, is analysed to determine the focal parameters on the dynamical process of faulting. A direct comparison of the calculated accelerations with the recorded one yields focal parameter estimates of 0.5-0.7sec for the rise time of the source time function, 50-70cm for the average dislocation and 50cm/sec for the particle velocity of the fault motion. The effective stress is determined from the particle velocity to be 25-50bars by the dynamic faulting models recently developed. The wave form of the calculated acceleration shows a good peak-to-peak correspondence with the recorded one, only when the source time function is assumed to be of a ramp type. This suggests that the ramp function is a good approximation for the source time function of this earthquake. We obtain an amplitude of about 7cm for the perpendicular component of the theoretical ground displacement if the values of 50-70cm for the average dislocation and of 0.5-0.7sec for the rise time as estimated above are used. The value of 30cm for the amplitude of displacement, obtained by previous investigators from numerical integration of the record acceleration, seems to be too large. The integrated displacements may not be good approximations for the true ground displacements.

Head movement induced by angular oscillation of the body in the pitch and roll axes.

Abstract: The transmission of angular acceleration to the head of the human subject has been investigated during sinusoidal angular oscillation of the body in either pitch or roll about an axis through the upper lumbar vertebrae The results indicated that angular acceleration of the skull was induced in all three axes of the head by both pitch and by roll motion At frequencies below 1-2 Hz the head moved with the body, but in the frequency range 2-8 Hz the amplitude of head acceleration was augmented indicating that oscillation about a centre of rotation low in the body may induce large angular movements in this frequency range because of the linear component of acceleration delivered at the cervical vertebrae At higher frequencies, the acceleration at the head was attenuated with an associated increase in phase lag, probably due to the absorption of input acceleration by the upper torso

Nutation damping in dual-spin stabilized devices

Abstract: A motor active nutation damping system employing a rotor mounted accelerometer, a platform/rotor relative rate sensor, a despin motor and a controller. In the presence of nutation, the accelerometer senses a sinusoidal acceleration whose amplitude is proportional to nutation angle and whose frequency is rotor nutation frequency, i.e., the rate at which the transverse angular momentum vector appears to rotate in rotor fixed coordinates. The controller multiplies the filtered accelerometer signal by a square wave at relative rate generated by the relative rate sensor to obtain a signal consisting of sinusoids at platform nutation frequency and higher order frequencies. Since platform nutation frequency is the rate at which the transverse angular momentum vector appears to rotate in platform fixed coordinates, spin axis torque appropriately phased at this frequency and applied to a dynamically imbalanced platform generates a transverse reaction torque that reduces the transverse angular rate associated with nutation. The controller accomplishes this function by appropriately filtering and amplifying the modulated signal, and then commanding a torque to the despin motor proportional to the resulting signal.