Displacement (vector)

About: Displacement (vector) is a research topic. Over the lifetime, 24669 publications have been published within this topic receiving 264944 citations.

Accurate measurement of three-dimensional deformations in deformable and rigid bodies using computer vision

Abstract: Recently, digital-image-correlation techniques have been used to accurately determine two-dimensional in-plane displacements and strains. An extension of the two-dimensional method to the acquisition of accurate, three-dimensional surfacedisplacement data from a stereo pair of CCD cameras is presented in this paper. A pin-hole camera model is used to express the transformation relating three-dimensional world coordinates to two-dimensional computer-image coordinates by the use of camera extrinsic and intrinsic parameters. Accurate camera model parameters are obtained for each camera independently by (a) using several points which have three-dimensional world coordinates that are accurate within 0.001 mm and (b) using two-dimensional image-correlation methods that are accurate to within 0.05 pixels to obtain the computer-image coordinates of various object positions. A nonlinear, least-squares method is used to select the optimal camera parameters such that the deviations between the measured and estimated image positions are minimized. Using multiple orientations of the cameras, the accuracy of the methodology is tested by performing translation tests. Using theoretical error estimates, error analyses are presented. To verify the methodology for actual tests both the displacement field for a cantilever beam and also the surface, three-dimensional displacement and strain fields for a 304L stainless-steel compact-tension specimen were experimentally obtained using stereo vision. Results indicate that the three-dimensional measurement methodology, when combined with two-dimensional digital correlation for subpixel accuracy, is a viable tool for the accurate measurement of surface displacements and strains.

A hierarchical approach to interactive motion editing for human-like figures

Abstract: This paper presents a technique for adapting existing motion of a human-like character to have the desired features that are specified by a set of constraints This problem can be typically formulated as a spacetime constraint problem Our approach combines a hierarchical curve fitting technique with a new inverse kinematics solver Using the kinematics solver, we can adjust the configuration of an articulated figure to meet the constraints in each frame Through the fitting technique, the motion displacement of every joint at each constrained frame is interpolated and thus smoothly propagated to frames We are able to adaptively add motion details to satisfy the constraints within a specified tolerance by adopting a multilevel Bspline representation which also provides a speedup for the interpolation The performance of our system is further enhanced by the new inverse kinematics solver We present a closed-form solution to compute the joint angles of a limb linkage This analytical method greatly reduces the burden of a numerical optimization to find the solutions for full degrees of freedom of a human-like articulated figure We demonstrate that the technique can be used for retargetting a motion to compensate for geometric variations caused by both characters and environments Furthermore, we can also use this technique for directly manipulating a motion clip through a graphical interface CR Categories: I37 [Computer Graphics]: Threedimensional Graphics—Animation; G12 [Numerical Analysis]: Approximation—Spline and piecewise polynomial approximation

On the displacement height in the logarithmic velocity profile

Abstract: The displacement height appears in the logarithmic velocity profile for rough-wall boundary layers as a reference height for the vertical co-ordinate. It is shown that this height should be regarded as the level at which the mean drag on the surface appears to act. The equations of motion then show that this also coincides with the average displacement thickness for the shear stress.A simple analytical model, experimental results and dimensional analysis are all used to indicate how the displacement height depends upon the detailed geometry of the roughness elements.

Submicron deformation field measurements: Part 2. Improved digital image correlation

Abstract: This is the second paper in a series of three devoted to the application of scanning tunneling microscopy (STM) to mechanics problems. In this paper, improvements to the digital image correlation method are outlined, a technique that compares digital images of a specimen surface before and after deformation to deduce its two-dimensional surface displacement field and strains. The necessity of using the framework of large deformation theory for accurately addressing rigid body rotations to reduce associated errors in the strain components is pointed out. In addition, the algorithm is extended to compute the three-dimensional surface displacement field from STM data; also, significant improvements are achieved in the rate as well as the robustness of the convergence. For (STM) topographs, the resolution yields 4.8 nm for the in-plane and 1.5 nm for the out-of-plane displacement components spanning an area of 10 μm×10μm.

The field and radiation impedance of mechanical radiators on the free surface of a semi-infinite isotropic solid

Abstract: The problem of wave-motion in a semi-infinite solid has been studied by several workers in connexion with seismological disturbances. In a classic paper (1904), Lamb investigated the propagation of vibrations over the surface of a semi-infinite isotropic solid, due to the application of force at a point or along a line in the free surface. A related problem is studied by Lapwood (I 949) who considers the case of an infinitely long dilating line-source situated parallel to and just below the free surface. Both authors obtain solutions in the form of definite integrals which they evaluate asymptotically to obtain the various components of the field at points on or near the surface at large distances from the source. In a more recent paper by Margery Newlands (I 952) this work has been extended to include the case of a source situated in a thin surface layer and propagating into a semi-infinite solid. The static problem of the distortion of a semi-infinite solid by stresses on the free surface was investigated by Boussinesq in a series of papers (1878-83) and by Love (1929). In the present paper Lamb's method has been adapted to furnish definite-integral representations of the field at an arbitrary point in a semi-infinite isotropic solid, due to prescribed periodic stresses on the free surface, the particular stress distributions considered here being such as would be produced by certain types of electro-mechanical transducer. Asymptotic formulae are obtained for the field at infinity, and the results for the various displacement components are presented in the form of polar diagrams. To obtain the radiation impedance integral expressions are derived for the mean displacement over the part of the surface which lies beneath the source; these expressions have been evaluated by numerical quadrature in a number of cases and a table shows the corresponding values of the radiation impedance.