Showing papers on "Displacement (vector) published in 1991"

Full-field representation of discretely sampled surface deformation for displacement and strain analysis

Abstract: A detailed evaluation of the feasibility of determining displacements and displacement gradients from measured surface displacement fields is presented. An improved methodology for both the estimation and elimination of noise is proposed. The methodology is used to analyze the gradients for three tests: (1) uniform rotation, (2) uniform strain, and (3) crack-tip displacement fields. Results of the study indicate that the proposed methodology can be used to extract the underlying two-dimensional displacements and their corresponding gradients from the noisy data with reasonable accuracy. Specifically, it is shown that (a) the digital correlation method for acquiring displacement fields has an error in strain of approximately 150 μ strain at each point, (b) the average strain in a region of uniform strain has much less error, typically on the order of 20 μ strain, (c) the displacement ‘nolse’ present in digital correlation is very small, approximately 0.01 pixels, (d) the proposed methodology for reducing noise in the data is essential to the accurate evaluation of displacement gradients and (e) the successful evaluation of displacement and displacement gradients for all three cases indicates that the proposed methodology can be used both to quantify the displacement fields and to reasonably estimate the overall gradient trends.

On the sufficiency of the velocity field for perception of heading

Abstract: All models of self-motion from optical flow assume the instantaneous velocity field as input. We tested this assumption for human observers using random-dot displays that simulated translational and circular paths of movement by manipulating the lifetime and displacement of individual dots. For translational movement, observers were equally accurate in judging direction of heading from a "velocity field" with a two-frame dot life and a "direction field" in which the magnitudes of displacement were randomized while the radial pattern of directions was preserved, but at chance with a "speed field" in which the directions were randomized, preserving only magnitude. Accuracy declined with increasing noise in vector directions, but remained below 2.6° with a 90° noise envelope. Thus, the visual system uses the radial morphology of vector directions to determine translational heading and can tolerate large amounts of noise in this pattern. For circular movement, observers were equally accurate with a 2-frame "velocity field", 3-frame "acceleration" displays, and 2-frame and 3-frame "direction fields", consistent with the use of the pattern of vector directions to locate the center of rotation. The results indicate that successive independent velocity fields are sufficient for perception of translational and circular heading.

Global zoom/pan estimation and compensation for video compression

Abstract: An algorithm is presented for estimating and compensating camera zooms and pans. It models the global motion in each frame with just two parameters: a zoom factor and a two-dimensional pan vector both based on local displacement vectors found by conventional means (such as block matching). Since motion by objects in the scene obscures global motion, the algorithm can iterate to refine its estimate. Simulations suggest the algorithm is robust and accurate, and can significantly reduce both the energy of the motion compensated residual image as well as the zeroth-order entropy of the local displacement vector field. >

Finite element with inner softening band

Abstract: A new technique for modeling localized deformations within a softening band is described, where softening is attributed to a displacement discontinuity within an element. Concepts such as fracture strain are not included in the formulation of the model, and consequently nonlocal parameters such as internal length measures are not needed. It is shown that the shape functions within the element provide the necessary information normally given with internal length. In this manner, objectivity with regard to element configuration seems to be automatically satisfied, which is demonstrated by numerical studies in which Rankine failure criterion is employed. It is also noted that the displacement field rather than the strain field is additively decomposed into elastic and inelastic parts. This additivity is valid independently of the magnitude of displacement continuity in the softening band, which implies that the technique can be extended in a straight‐forward fashion to finite displacements.

Interferometer for measuring displacement and distance

Abstract: A simple interferometer for measuring both relative displacement and absolute distance is fabricated that uses a laser diode. The sign of the displacement is detected by means of a λ/8 plate, and the distance is measured by a FM radar technique of modulating the laser-diode frequency. Measurement accuracies of 0.02 μm for displacement and 100 μm for distance are obtained over a range of a few meters.

Displacement and strain measurement with automated grid methods

Abstract: An image-processing-based automated grid method is investigated to determine the method's displacement and strain accuracy limits, and how these limits are influenced by the choice of camera-calibration models A CCD camera and a PC-based frame grabber are used to record grid spot motion, then ordering and centroiding are used to identify each spot and calculate their individual displacements The displacements are fitted with a moving biquadratic surface, and the strains are obtained by analytical differentiation of that surface Camera-calibration models which are considered include various combinations of image-perspective transformation, image stretching, and elliptical-lens distortion The strain and displacement accuracy are explored through rigid-body motion and uniaxial tension tests In the process, sensitivity to in-plane and out-of-plane rigid-body translation, and extreme sensitivity to in-plane rigid-body rotation (for non-synchronized frame grabbers) are confirmed It is found that under the best conditions the displacement accuracy is 015 pixels and that the strain accuracy is 120 microstrain Finally, the automated grid method is used to investigate the strains developed in an aluminum perforated strip subjected to uniaxial tension

Iterative motion estimation method using triangular patches for motion compensation

Abstract: In order to overcome the drawback of the conventional block-based motion compensation, a new triangle-based method which utilizes triangular patches instead of blocks has recently been proposed. Compared to conventional methods which represent the motion of scene objects by translational displacements of blocks, the new method can cope with a wider range of motions since is allows for rotation and deformation of the triangular patches. In the block- based motion compensation, a simple local minimization algorithm (i.e., block matching) is applied to obtain the displacement vector of each block. However, it is inappropriate to apply this algorithm in the triangle-based motion compensation because of the complicated linkage between the deformation of the triangular patches and the displacement of the grid points (vertices of triangles). Consequently, the primary issue is to find an optimal way to estimate motion of the grid points. In this paper, we present a new motion estimation algorithm called hexagonal matching which iteratively refines the estimated displacement vectors. Simulation results show that the motion estimation algorithm produces less prediction error than the previously proposed triangle-based method or the block-based method. We also propose another algorithm with similar function but less computational complexity.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Efficient and accurate front tracking for two‐dimensional groundwater flow models

Abstract: Four new algorithms are presented to cost-effectively delineate displacement fronts and capture zones via particle tracking in complex flow fields. These algorithms include methods of (1) defining path lines using “mixed distance and time particle tracking”; (2) computing displacement fronts and capture zones using “dynamic particle allocation front tracking” allowing insertion/deletion of particles to optimize front definition; (3) obtaining accurate breakthrough curves by using simultaneous “mass redistribution,” reallocating particle mass among particles defining the displacement front; and (4) determining production well breakthrough curves using “optimized sorting algorithms” when backward tracking to map capture zones. Examples are shown for capture zones and aquifer remediation applications. Comparisons are made to conventional algorithms. Results show that the number of particles required to define displacement fronts and breakthrough curve is a function of time, position, and How field complexity. Dynamic front tracking results in significant savings of storage and computational expense, even for relatively simple velocity fields. A corresponding increase in the accuracy of breakthrough curves is obtained.

A 3-D raytracer for teleseismic body-wave arrival times

Abstract: In this article, we present a method for determining the minimum time ray path from a planar wavefront at depth to a fixed point at the surface through a 3-D heterogeneous velocity structure. The program is based on the two point raytracer of Prothero et al. (1988), with a modification to use odd quarter-cycles of sinusoids to distort the rays. These functions produce zero displacement at the fixed receiver but non zero displacement at the wavefront. This allows the raytracer to explore a wide variety of ray paths starting at different points on the wavefront, while the rays leaving the wavefront remain normal to it. To find the minimum time path, amplitudes of these functions are systematically perturbed using the simplex algorithm. The approach is analogous to using a Fourier series to fit a curve with specific properties at each end. Development of this raytracer was motivated by the desire to model our observations of large perturbations in the bearings and phase velocities of teleseismic P waves recorded in Long Valley caldera, California. These observations clearly show the inadequacy of 1-D raytracing in regions having complex, three-dimensionally varying velocity structure. This raytracer provides a basic tool with which to study the effects of ray bending on tomographic results from these kinds of environments.

An ultrasonic ranging system for structural vibration measurements

Abstract: An ultrasonic ranging system (URS) that can be used to measure vibratory displacements in structures is described. A pair of ultrasonic transducers is used in a transmit-receive mode to acquire the motion of a point on a flexible structure. The structure's oscillating motion modulates the phase angle between the transmitted and received acoustic signals. A simple phase detector and low-pass filter combination demodulate the phase signal, thus extracting information about the motion of the point on the structure. The results reported concentrate on some design issues of the URS and its use as a potential displacement measuring device for flexible structures. The URS accurately distinguished four vibration frequencies of a simple cantilevered aluminum beam, with the highest frequency near 50 Hz. >

Measuring residual stresses by hole-drilling and coherent optics techniques: a numerical calibration

Abstract: This paper reports the displacement calibration constants derived from the results of an extensive numerical analysis. The constants proposed enable a uniform residual stress field to be determined, whatever the displacement component detected

Thin‐Walled Space Frames. I: Large‐Deformation Analysis Theory

Abstract: A finite element formulation for the large‐deformation analysis of space‐frame structures is presented The formulation is based on second‐order geometric nonlinear theory and Vlasov's theory for thin‐walled beams (ie, large displacement of members with small strains, which includes the warping deformation influence) The influence of member‐distributed loading on the geometric nonlinear response of space‐frame structures also is included An updated Lagrangian formulation is used to model large joint translations and rotations Prismatic beams of arbitrary cross section are considered Rodriguez's modified rotation vector is used to represent angular deformations, which avoids rotational discontinuities at the joints of deformed space‐frame structures Numerical results and algorithmic details are presented in a companion paper

Base Excitation of Rigid Bodies. II: Periodic Slide‐Rock Response

Abstract: An approximate closed‐form solution is developed for a single‐mode, steady‐state slide‐rock response resulting from a harmonic ground acceleration. The approximate solution is developed using the method of slowly varying parameters and is valid for a rectangular block undergoing small angles of rotation at the frequency of base excitation. Impacts with the foundation are assumed to be perfectly plastic and frictional impulses are included. Periodic solutions are found to exist in general only for relatively high amplitudes of ground acceleration and friction less than the inverse aspect ratio of the block. The rock component of the response is sensitive to changes in aspect ratio and friction and insensitive to changes in ground acceleration. The slide component of response is approximately equal to the amplitude of ground displacement and is insensitive to changes in friction and aspect ratio. Results compare favorably to those obtained by numerical integration. The accuracy of the approximate solution i...

Measuring Residual Stresses by Hole-Drilling and Coherent Optics Techniques: A Numerical Calibration

Abstract: This paper reports the displacement calibration constants derived from the results of an extensive numerical analysis. The constants proposed enable a uniform residual stress field to be determined, whatever the displacement component detected

Magnetostriction type actuator

Abstract: A magnetstriction type actuator is capable of reducing an input power loss and increasing an output, which actuator is reduced in size and is applicable to a vibrator. The actuator comprises: displacement generating means formed of a magnetic substance having magnetostriction; a movable member fixed to the displacement generating means, which movable member is movable in the direction of displacement of the displacement generating means; first magnetic field generating means, provided around the displacement generating means, for applying a magnetic field to the displacement generating means and second magnetic field generating means for applying a magnetic bias; a magnetic circuit component for constituting, along with the movable member, a main part of a closed magnetic circuit, within which magnetic circuit component the displacement generating means and the magnetic field generating means are stored; and an elastic member, disposed within the magnetic circuit component, for applying a compression force to the displacement generating means via the movable member in the direction of displacement of the displacement generating means.

An ultrasonic method for measuring tissue displacement: technical details and validation for measuring myocardial thickening

Abstract: The authors developed a method for measuring myocardial thickening from a single ultrasonic transducer attached to the epicardium. Displacement of the underlying myocardial tissue is measured by following the phase of the echoes within a sample volume range-gated across the myocardium. The output is in the form of an analog signal. To verify the accuracy, resolution, and limitations of the system, the authors derived the equations relating the position of a reflector to the phase of its echo and compared the system output in vitro to a known input using a single moving target and a random distribution of scatterers, and in vivo to that of an ultrasonic transit-time dimension gauge. The results demonstrate that the 10 MHz system can accurately follow the motion of single or multiple targets with a resolution of 0.02 mm. In 25 dogs myocardial thickening measured with the displacement system compared favorably in both waveform and magnitude with thickening measured by the two-crystal transit-time method. Applications for the displacement method are discussed. >

Method for measuring three-dimensional motion with tagged MR imaging.

Abstract: Recent methods of magnetic resonance imaging involve the placement of a grid of planes of saturation over the imaging plane; distortion of the grid corresponds to tissue displacement in two dimensions. An extension to this method that allows measurement of motion in the third dimension involves a second acquisition that tilts the grid, allowing analysis of motion normal to the imaging plane. A rotating phantom was used to verify the accuracy of the motion measurements, and the technique was applied to the heart wall and skeletal muscle. Phantom results show that the measure of z motion can be as accurate as that of x and y motion. Three-dimensional displacements of heart-wall and skeletal muscle are shown. With an accurate measure of three-dimensional motion, more complete analysis of heart-wall motion and contraction is possible.

On the finite element analysis of non-linear vibration for cylindrical shells with high-order shear deformation theory

Abstract: The development of an existing 36 degrees-of-frcedom (dof), curved, quadrilateral, thin shell element, for large displacement/rotation static analysis of shell structures, is extended for the study of non-linear vibration of a cylindrical shell. Parabolic transverse shear strains are assumed to vary through the shell thickness and vanish at the top and bottom surface. The equations of motion are based on a total Lagrangian frame of reference, and the applied dynamic loads are assumed conservative. A beta- m method, which is a generalization of Newmark's time marching integration scheme, and the Newton-Raphson iterative method, are both applied in order to numerically solve the set of non-linear equations of motion. An algorithm based on the above numerical procedures is developed. The isotropic or composite structures comprising laminates of orthotropic or multilayered anisotropic materials are considered to be elastic. Comparisons with several existing solutions demonstrate the validity and accuracy of the present development.

Flutter control system for aircraft wings

Abstract: A flutter control system of an aircraft wing comprising an actuator mounted on the aircraft wing to control a control surface, flight control command unit for outputting an actuation command signal for actuating the actuator, wing-displacement measurement unit for measuring an actual displacement of a predetermined point on the wing and outputting an actual displacement signal corresponding to the measured actual displacement, normal-wing-displacement prediction unit for predicting a normal displacement of the wing during normal flight in which no disturbance occurs, on the basis of the actuation command signal and of an information signal representing information about atmospheric density, flight speed and actuation position of the actuator and for outputting a predicted normal displacement signal representing the predicted displacement during the normal flight, disturbance-component estimation unit for receiving the actual displacement signal and the predicted normal displacement signal and for outputting a difference signal between these signals, and command-signal correction unit for correcting the actuation command signal so that a wing displacement by disturbance is cancelled out, on the basis of the difference signal.

Displacement detecting apparatus

Abstract: A magnetic scale (3) formed by arranging a non-magnetic material (2) at a predetermined pitch (P) in the direction of motion of a piston rod (1), and a pair of magnetic sensors (5) which output two sine waves with a phase difference of 90° corresponding to the pitch (P) of said magnetic scale (3), are provided. The peak voltages of the sensor output at each pitch of the magnetic scale are updated and stored. Center voltages are computed from the peak voltages at each pitch, and a coarse displacement is computed based on the result of comparing the center voltages and sensor outputs. Correction coefficeints of the sensor outputs are computed from the peak voltages and center voltages, and the sensor outputs are compensated based on these correction coefficients. A fine displacement is then computed by an inverse trigonometric function from the two corrected signals, and a displacement signal is output by adding the coarse displacement to the fine displacement.

Process and device for measuring the variation in internal pressure in the cylinder of a piston engine.

Abstract: In order to determine the course of a varying internal pressure in the cylinder of a piston-type internal combustion engine using measurement sensors which are in interaction with the outside of the cylinder; an acceleration, velocity or displacement signal (X(t)) is produced and a transfer function (H(ω)) between the internal pressure (Y(t)) and the acceleration, velocity or displacement signal (X(t)) is determined once and thereafter an output signal representing the internal pressure is derived only from the acceleration, velocity or displacement signal X(t)) and the transfer function.