Showing papers on "Displacement (vector) published in 1983"

Displacement vectors derived from second-order intensity variations in image sequences

Abstract: A local approach for interframe displacement estimates is developed by minimization of the squared differences between a second-order Taylor expansion of gray values from one frame and the observed gray values within the same window from the next frame. If the second-order terms in the Taylor expansion are significant, a system of two coupled nonlinear equations for the two unknown components of the displacement vector can be derived. In the special case of “gray value corners,” these equations can be simplified to facilitate a closed form solution. An iterative refinement procedure is developed to extend these estimates for image regions which do not exhibit exactly the properties of “gray value corners.” The minimization approach is generalized in such a way that the approach of Horn and Schanck (Artif. Intell. 17, 1981, 185–203) can be recognized as a special case of this generalized form which should be applicable even across occluding edges. It thus appears to be an interesting model for the local computation of optical flow.

A Coordinate Reduction Technique for Dynamic Analysis of Spatial Substructures with Large Angular Rotations

Abstract: A substructuring technique is presented for transient dynamic analysis of systems composed of interconnected rigid and elastic bodies that undergo large angular displacements. Displacement of elastic bodies is represented by superposition of local linear elastic deformation on large displacement of body reference coordinate systems. Elastic bodies are thus represented by combined sets of reference and local elastic generalized coordinates. Modal analysis and substructuring of individual elastic components allow for elimination of insignificant modes. Equations of motion and constraint are formulated in terms of mixed sets of modal and reference generalized coordinates. Planar and spatial linkages with flexible elements are presented to illustrate use of the method developed.

Processing translational motion sequences

Abstract: A procedure for processing real world image sequences produced by relative translational motion between a sensor and environmental objects is presented. In this procedure, the determination of the direction of sensor translation is effectively combined with the determination of the displacement of image features and environmental depth. It requires no restrictions on the direction of motion, nor the location and shape of environmental objects. It has been applied successfully to real-world image sequences from several different task domains. The processing consists of two basic steps: feature extraction and search. The feature extraction process picks out small image areas which may correspond to distinguishing parts of environmental objects. The direction of translational motion is then found by a search which determines the image displacement paths along which a measure of feature mismatch is minimized for a set of features. The correct direction of translation will minimize this error measure and also determine the corresponding image displacement paths for which the extracted features match well.

Seismically Induced Movement of Retaining Walls

Abstract: In recent years, new seismic design methods for gravity retaining walls, based on the earthquake-induced permanent displacement of the wall, have been proposed. These methods generally ignore the effects of ground motion amplification in the backfill on the seismic behavior of the wall. In the present paper, results obtained with a finite element model capable of taking into account the amplification of ground motion in the backfill, while computing permanent distortions, are presented. Implications of these results for design are also considered.

The anisotropic reflectivity technique: theory

Abstract: Summary. The reflectivity technique for the calculation of synthetic seismograms from a point source in a horizontally stratified isotropic structure is extended to include weakly anisotropic layers. The formulation is in terms of displacement excitation factors rather than potential functions, which have not yet been specified for wave propagation in anisotropic media. Coupling between vertical, radial and transverse components of motion increases the number of plane-wave reflection and transmission coefficients which must be computed for any problem. These coefficients are calculated by extending Kennett’s iterative scheme for the computation of isotropic coefficients to

The Differential Method for Image Motion Estimation

Abstract: Small variations of the apparent velocity of objects imaged by television cameras can be efficiently measured comparing the frame differences with the spatial variations of the luminance. The main lobe of the autocovariance of a block of picture elements of an image is first modeled as a paraboloid; afterwards, the comparison with the mutual covariance between two successive video frames, allows to determine their relative displacement. The curvatures of the autocovariance taken at the origin are proportional to the m.s. slopes of the image along the coordinate axes; it can be shown that the slopes should be calculated using a centered differentiation, rather than a non centered one, to avoid bias in the estimation of the displacement. To be able to precisely measure the displacement along a given direction, it is necessary that the m.s. slope in that direction be high enough; in fact, the measure of temporal and spatial image derivatives only constrains the projection of the actual displacement along the image gradient. More complex, but continuous, motion fields can be estimated with simple extensions of the original formulation of the differential method. A stochastic model for the motion field is therefore introduced, in order to derive a recursive estimation technique. The component of the motion paralel to the local image gradient is updated, on a pel by pel basis, while the other one is approximately kept constant. The practical results are sufficient for image coding, but not good enough to get a nicely smooth velocity field in real situations.

A spatio-temporal gradient method for estimating the displacement field in time-varying imagery

Abstract: The displacement between successive frames of each picture element in an image sequence forms a two-dimensional vector field called the displacement field (or optical flow). This paper presents an algorithm for estimating the displacement field, based on a constraint equation relating the spatial gradient to a temporal directional derivative for a moving object. The estimate for a given picture element is obtained by updating the estimate for the corresponding picture element in the previous frame, using information in a three-dimensional block centered on the picture element of interest, The performance of this estimator has been tested on a number of sequences of real imagery, both with artificial displacements and with natural motion, and the main parameters of the estimator have been optimized. It has been found to be accurate, and robust in the presence of noise. A number of simplifications to reduce the computational complexity of the algorithm have been proposed, and their effects on performance have been studied.

A stable and accurate numerical method to calculate the motion of a sharp interface between fluids

Abstract: On met au point une methode pour le calcul du mouvement d'une interface fluide. Etude de l'instabilite numerique typique des algorithmes de ce probleme

Apparatus for measuring velocity of a moving image or object

Abstract: Apparatus for measuring the velocity of a moving image or object including a first array of sensors extending in a first direction transverse to image motion for sensing a primary set of image elements; a second array of sensors extending generally in the first direction and spaced a known distance from the first array for sensing successive sets of image elements; a device for correlating the primary set of image elements with each of the successive sets of image elements and for producing a correlation level indicating the level of correlation of the primary set with each of the successive sets; means for selecting one of the correlation levels which indicates an optimal level of correlation; and means for determining the time interval between the sensing of the first array of the primary set and the sensing by the second array of the successive set corresponding to the selected correlation level; in addition, the means for correlating may include means for comparing with the primary set each successive set in a plurality of different positions along the first direction and for producing a comparison level indicating the level of comparison of the primary set with each of the successive sets in each of the different positions along the first direction; and means for determining the displacement between the position in which the successive set is sensed and the position corresponding to the indicated comparison level.

Elastic Stability of Curved Members

Abstract: A general solution method of a system of coupled differential equations governing the elastic buckling of thin-walled curved members is presented. The finite element displacement method is formulated based on a variational principle. The stiffness and stability properties of the finite elements are consistent and are obtained within the bounds of linearized displacement theories. Included are the warping contributions to the buckling loads and the effects of antisymmetry of the cross section which were found to be significant.

A finite element for vibration analysis of twisted blades based on beam theory

Abstract: A finite element method of discretizing beam segments of pretwisted rotating blades is presented. Employing the matrix displacement method, stiffness and mass properties are developed from basic mechanics of a pretwisted beam theory. By introducing the proper displacement functions, the effect of rotor blade rotational motion on the stiffness matrix is obtained systematically from the kinetic energy expression. Comparing with other beam elements the derivation of this element is more fundamental. This allows one to apply the same approach to more complicated problems including nonlinear effects or complex dynamic motions. Illustrative examples are given comparing numerical results with available data and other numerical solutions from rotating and nonrotating force fields. These examples show that accurate prediction of vibration frequencies for pretwisted blades can be obtained by employing a quite modest number of degrees of freedom.

On the Off-Axis Tension Test for Unidirectional Composites

Abstract: The off axis tensile test was examined experimentally to obtain actual displacement fields over the surface of graphite polyimide coupon specimens. The experimental results were compared with approximate analytical solutions and generated finite element results. An optical method of high sensitivity moireinterferometry was used to determine the actual displacements to high precision. The approximate analytical solution and the finite element results compare very favorably with the measured centerline displacements in the test section, and the finite element displacement fields provide excellent agreement with the moiredisplacements throughout the specimen. A 15 degree fiber orientation and coupon aspect ratios of 5 and 15 are presented. Previously announced in STAR as N82-23553

High-resolution rotation-angle measurement of a cylinder using speckle displacement detection.

Abstract: A new method for measuring the rotation angle of a cylinder is described, based on the speckle displacement detection caused by the cylinder surface rotation. It is shown that this method is effective for measuring the small rotation angle with high resolution. The accuracy, sensitivity, and resolution of this method are determined by the speckle size, detector pitch, and magnification of the speckle displacement. The configuration to obtain an accurate, sensitive, stable measuring system is discussed. The usefulness of this method is confirmed by experiments.

The use of moiré techniques to measure rigid body displacements

Abstract: Summary The relative advantages and disadvantages of a variety of experimental electron microscopical techniques for the measurement of rigid body displacements are considered The principles of the application of a moire method of great simplicity and high potential accuracy are then further discussed as are the experimental difficulties associated with the superposition of suitable reference latices on a substrate The method is then applied to obtain an upper limit for the rigid body displacement at {111} Σ3 twin boundaries in stainless steel

Computer processing of New Zealand strong-motion accelerograms

Abstract: Recently implemented modifications to the computer processing of earthquake accelerograms are described. The main extensions to the system include dynamic instrument correction, robust band-pass filtering and accurate integration, all implemented in the frequency domain. The processed records now provide accurate representations of strong ground motion within the frequency band from 0.25 Hz to 24.5 Hz: full accuracy is maintained in the computed velocity and displacement signals. The use of the new processing system is demonstrated using two previously recorded accelerograms.

Displacement measurement of speckles using a 2-D level-crossing technique.

Abstract: This paper proposes a new displacement method for measuring speckles using a 2-D level-crossing technique. The crossing points in space of the speckle intensity traversing a specified level are analyzed two-dimensionally by using a TV-computer system. In an actual analysis, an occurrence rate histogram of the distance vectors determined by connecting the crossing points obtainable before and after displacement of speckles is investigated. It is found that the vectorial displacement of speckles can be measured from the position of the maximum occurrence in the bivariate histogram with respect to the magnitude and angle by which the displacement vector is characterized. The vectorial displacement of speckles is related to the movement of an object.

A linear uncoupling numerical scheme for the nonlinear coupled thermoelastodynamics equations

Abstract: A numerical scheme for computing approximate solutions to the non-linear equations of coupled thermoelastodynamics is proposed. The discretization is made in such a way that the algebraic system to be solved at each time level is a linear one, the displacement and temperature fields being uncoupled for the calculations.

Free vibrations of an isotropic nonhomogeneous infinite plate of linearly varying thickness

Abstract: The free transverse vibrations of an isotropic nonhomogeneous infinite plate of variable thickness have been studied on the basis of classical plate theory. The governing differential equation of motion has been solved by Frobenius method by expressing the transverse displacement as an infinite series. The frequencies corresponding to the first two modes of vibration are computed for different values of thickness variation constant, nonhomogeneity parameter, and different combinations of boundary conditions.

Detector of displacement quantity

Abstract: PURPOSE:To obtain a precise differential output and to detect a displacement quantity more precisely by arraying at least two magnetic resistance effect elements (MR elements) in the direction intersected with the displacement direction so as to be opposed to magnetic recording tracks forming their magnetic patterns with different phases each other CONSTITUTION:A magnetic recording medium 10 is composed of two recording tracks 11a, 11b and records a magnetic pattern by shifting it by a half of a pitch P When the magnetic recording medium 10 is displaced, the resistance values R of the MR elements are changed as shown by curves 13a, 13b The differential output voltage shown by the curve 14 is obtained by finding the difference between the output signals of the MR elements 12, 12b Since the MR elements 12a, 12b are arrayed in the direction intersected with the displacing direction, the detection does not depend upon the pitch P of the magnetic pattern and the magnetic sensor can be used in common also for the magnetic patterns with different pitches P

Flow measuring system including a venturi

Abstract: A fluid flow measuring system composed of: a venturi connected to conduct the fluid whose flow is to be measured and having two outlet ports between which a pressure differential proportional to such fluid flow is created; a movably mounted measuring element having a selected zero position and connected to the venturi to be subjected to a displacement force corresponding to the pressure differential; a transducer unit associated with the measuring element for producing an electrical signal representative of the displacement of the measuring element from its zero position; a regulating device having a signal input connected to receive the electrical signal, and a signal output, and presenting a transfer characteristic having an integrating component such that the signal at the signal output is representative of the magnitude and duration of displacement of the measuring element from its zero position; a signal squaring circuit connected to the regulating device for generating a control signal dependent on the square of the signal at the output of said regulating device; and a hysteresis-free electromagnetic system connected to apply to the measuring element, in response to the control signal, a magnetic displacement force of a magnitude and direction to cause the measuring element to reach its zero position.

Method for controlling the articulation stability of road vehicles having at least two vehicle parts which are connected by an articulation unit and an articulation unit for carrying out the method

Abstract: The invention relates to a method for controlling the articulation stability of road vehicles having at least two vehicle parts which are connected by means of a joint and can be in a stationary, non-stationary, stable or unstable driving state and an articulation unit with a joint which can be actuated by means of hydraulic actuation means and a hydraulic control device which can be actuated by means of an electronic processor and has stop valves arranged in the hydraulic circuit and at least one damping valve. For the steering angles possible in a stable driving state, the respectively associated articulation angle is initially determined and then in travelling mode it is tested in a repetitive manner after a predetermined route in each case whether the articulation angle predetermined at the start of the route as a function of the respective steering angle corresponds to the articulation angle actually present at the end of the route and then in the event of a deviation of the respective actual value of the articulation angle from the reference value of the change in the articulation angle the joint is adjusted until the actual value of the articulation angle corresponds to the reference value of the articulation angle taking into account the admissible tolerance range. In the articulation unit, the actuation means are constructed as hydraulically double-acting cylinders (36, 37) and the electronic control device (31) has a microprocessor (33) or a microprocessor circuit which is in an operative connection with a non-volatile memory (32) for storing the characteristic diagram DELTA beta =f( beta , alpha ) where beta equals the articulation angle, alpha is the steering angle and DELTA beta is the change in the articulation angle beta after a route DELTA s for a specific steering angle alpha at the start of the route. The microprocessor (33) or the microprocessor circuit is clocked by means of a frequency generator at a frequency corresponding to a multiple of the displacement pulse DELTA s.

Optimization for Vibration Isolation.

Abstract: : Algorithms have been developed which minimize the forced vibrational response of structural systems. The constraints which can be used are displacements or accelerations and natural frequencies. The design variables are linear changes to mass, stiffness or damping matrices. The constraints can be expressed in either the time or frequency domain and the cumulative constraint is used to measure the amount of constraint violation. It is shown that the variation of the displacement or acceleration constraints are shallow in reciprocal design variables. The objective function is a design variable which represents a value that keeps either displacements or acceleration less than a specified maximum value. A sequence of linear programs is formulated to take advantage of the almost linear character of the vibration isolation problem. The algorithms used in the displacement or acceleration constraints are general and consistent with algorithms that have been developed for weight minimizations, but have not been used for this purpose in the study. These algorithms have been studied for transient response, frequency response and stationary random. The results shown for the minimization of vibration response are very robust. Only passive vibration isolation has been studied and no attempt was made to consider ill conditioned problems.

A method for mapping localized displacement fields in boundaries

Abstract: SUMMARY A new method is described for the initial characterization of the displacement fields of defects on boundaries. This approach can be applied to defects and boundaries which cannot easily be modelled, since it involves the comparison of known with unknown fields. An application of the technique to the study of a bcc/fcc phase boundary in a steel is also described.