Showing papers on "Displacement (vector) published in 2008"

Empirical Predictive Models for Earthquake-Induced Sliding Displacements of Slopes

Abstract: Earthquake-induced sliding displacement is the parameter most often used to assess the seismic stability of slopes The expected displacement can be predicted as a function of the characteristics of the slope (yield acceleration) and the ground motion (eg, peak ground acceleration), yet there is significant aleatory variability associated with the displacement prediction Using multiple ground motion parameters to characterize the earthquake shaking can significantly reduce the variability in the prediction Empirical predictive models for rigid block sliding displacements are developed using displacements calculated from over 2,000 acceleration–time histories and four values of yield acceleration These empirical models consider various single ground motion parameters and vectors of ground motion parameters to predict the sliding displacement, with the goal of minimizing the standard deviation of the displacement prediction The combination of peak ground acceleration and peak ground velocity is the tw

Three dimensional image correlation from X-Ray computed tomography of solid foam

Abstract: A new methodology is proposed to estimate 3D displacement fields from pairs of images obtained from X-ray computed microtomography (XCMT). Contrary to local approaches, a global approach is followed herein that evaluates continuous displacement fields. Although any displacement basis may be considered, the procedure is specialized to finite element shape functions. The method is illustrated with the analysis of a compression test on a polypropylene solid foam (independently studied in a companion paper). A good stability of the measured displacement field is obtained for cubic element sizes ranging from 16 to 6 voxels.

Efficient Dense Scene Flow from Sparse or Dense Stereo Data

Abstract: This paper presents a technique for estimating the three-dimensional velocity vector field that describes the motion of each visible scene point (scene flow). The technique presented uses two consecutive image pairs from a stereo sequence. The main contribution is to decouple the position and velocity estimation steps, and to estimate dense velocities using a variational approach. We enforce the scene flow to yield consistent displacement vectors in the left and right images. The decoupling strategy has two main advantages: Firstly, we are independent in choosing a disparity estimation technique, which can yield either sparse or dense correspondences, and secondly, we can achieve frame rates of 5 fps on standard consumer hardware. The approach provides dense velocity estimates with accurate results at distances up to 50 meters.

Nanohole Array as a Lens

Abstract: We demonstrate that a quasi-crystal array of nanoholes in a metal screen can mimic a function of the lens: one-to-one imaging of a point source located a few tens of wavelengths away from the array to a point on the other side of the array. A displacement of the point source leads to a linear displacement of the image point. Complex structures composed of multiple point sources can be faithfully imaged with resolutions comparable to those of high numerical aperture lenses.

Assessment of Speed and Position during Human Locomotion Using Nondifferential GPS

Abstract: Purpose: To validate a nondifferential global positioning system (GPS) to measure speed, displacement, and position during human locomotion. Methods: Three healthy participants walked and ran over straight and curved courses for 59 and 34 trials, respectively. A nondifferential GPS receiver provided speed data by Doppler shift and change in GPS position over time, which were compared with actual speeds determined by chronometry. Displacement data from the GPS were compared with a surveyed 100-m section, and static positions were collected for 1 h and compared with the known geodetic point. Results: GPS speed values on the straight course were closely correlated with actual speeds (Doppler shift: r = 0.9994, P < 0.001, ? GPS position/time: r = 0.9984, P < 0.001). Actual speed errors were lowest using the Doppler shift method (90.8% of values within ± 0.1 m·s-1). Speed was slightly underestimated on a curved path, though still highly correlated with actual speed (Doppler shift: r = 0.9985, P < 0.001, ? GPS distance/time: r = 0.9973, P < 0.001). Distance measured by GPS was 100.46 ± 0.49 m, and 86.5% of static points were within 1.5 m of the actual geodetic point (mean error: 1.08 ± 0.34 m, range 0.69-2.10 m). Conclusions: Nondifferential GPS demonstrated a highly accurate estimation of speed across a wide range of human locomotion velocities using only the raw signal data with a minimal decrease in accuracy around bends. This high level of resolution was matched by accurate displacement and position data. Coupled with reduced size, cost, and ease of use, this method offers a valid alternative to differential GPS in the study of overground locomotion

Large Scale Dynamics of the Persistent Turning Walker Model of Fish Behavior

Abstract: This paper considers a new model of individual displacement, based on fish motion, the so-called Persistent Turning Walker (PTW) model, which involves an Ornstein-Uhlenbeck process on the curvature of the particle trajectory. The goal is to show that its large time and space scale dynamics is of diffusive type, and to provide an analytic expression of the diffusion coefficient. Two methods are investigated. In the first one, we compute the large time asymptotics of the variance of the individual stochastic trajectories. The second method is based on a diffusion approximation of the kinetic formulation of these stochastic trajectories. The kinetic model is a Fokker-Planck type equation posed in an extended phase-space involving the curvature among the kinetic variables. We show that both methods lead to the same value of the diffusion constant. We present some numerical simulations to illustrate the theoretical results.

Tilting Touch Control Panel

Abstract: A control panel for controlling a device in response to user indications, the control panel comprising, a position sensing element (60) having a sensing surface, and a position interface circuit (76). The position interface circuit (76) is operable to determine a position of an object (100) on the sensing surface, when the object (100) is applied to the sensing surface of the position sensing element (60). At least one pressure sensing device (54, 66) and the sensing surface of the position sensing element (60) are arranged with the effect that a displacement of the sensing surface with respect to the pressure sensing device in response to the pressure applied by the object is detectable by the pressure sensing device. As such, in one example, the position interface circuit (76) is operable to identify one or more of a plurality of user indicated signals by correlating the position of the object on the sensing surface with a pressure detected by the pressure sensing device. The sensing surface may include pre-designated and pre-determined locations representing virtual buttons so that by determining whether the object is at one of a plurality of pre-determined locations on the sensing surface of the position sensing element, the position interface circuit (76) can identify the user indicated signal by correlating the position of the object at one of the predetermined locations with the detected pressure, each of the pre-determined location corresponding to one of the plurality of user indicated signals.

Robot-to-Robot Relative Pose Estimation From Range Measurements

Abstract: In this paper, we address the problem of determining the 2-D relative pose of pairs of communicating robots from (1) robot-to-robot distance measurements and (2) displacement estimates expressed in each robot's reference frame. Specifically, we prove that for nonsingular configurations, the minimum number of distance measurements required for determining all six possible solutions for the 3 degree-of-freedom (3-DOF) robot-to-robot transformation is 3. Additionally, we show that given four distance measurements, the maximum number of solutions is 4, while five distance measurements are sufficient for uniquely determining the robot-to-robot transformation. Furthermore, we present an efficient algorithm for computing the unique solution in closed form and describe an iterative least-squares process for improving its accuracy. Finally, we derive necessary and sufficient observability conditions based on Lie derivatives and evaluate the performance of the proposed estimation algorithms both in simulation and via experiments.

Probabilistic Seismic Hazard Analysis for the Sliding Displacement of Slopes: Scalar and Vector Approaches

Abstract: Sliding block displacements often are used to evaluate the potential for ground failure due to slope instability. The procedures used to assess sliding block displacement typically use deterministic or pseudoprobabilistic approaches, in which the uncertainties in the expected ground motion and resulting displacement are either ignored or not treated in a rigorous manner. Thus, there is no concept of the actual hazard associated with the computed displacement. This paper presents a fully probabilistic framework for assessing sliding block displacements. The product of this analysis is a displacement hazard curve, which provides the annual rate of exceedance, λ, for a range of displacement levels. The framework considers two procedures that will yield a displacement hazard curve: (1) a scalar hazard approach that utilizes a single ground motion parameter and its associated hazard curve to compute permanent displacements; and (2) a vector hazard approach that predicts displacements based on two (or more) ground motion parameters and the correlation between these parameters. The vector approach reduces the displacement hazard significantly, as compared with the scalar approach, because of the reduction in the variability in the displacement prediction. Comparison of the fully probabilistic approach with an approach using probabilistically derived ground motions reveals that using a ground motion for a given hazard level does not produce a displacement level with the same hazard.

Nontarget Image-Based Technique for Small Cable Vibration Measurement

Abstract: In this paper, a proof-of-concept image-based technique is proposed for measuring small cable vibration. The technique analyzes an image sequence of a vibrating cable segment captured by a camera. An optical flow method is used to calculate variation of optical intensity of an arbitrary selected region of interest ROI on the cable image sequence. The obtained optical flow vector provides the direction of vibration for the ROI on the cable segment, which then can be used to estimate displacement of the ROI on the image plane. Furthermore, actual displacement of the ROI can be extracted when some conditions are met. The proposed technique is validated both in the laboratory using a rigid pipe and in the field on a small pedestrian bridge cable. Results show that the technique is able to measure the pipe motion and the cable vibration accurately. The proposed technique requires only one commercial camera, and no prior camera calibration is needed. In addition, the use of an optical flow method eliminates the need to attach any target to the cable and makes the technique very easy to implement. Despite these advantages, the technique still needs further development before it can be applied to long-span bridge cables.

A new laser displacement sensor based on triangulation for gauge real-time measurement

Abstract: A new laser displacement sensor has been designed, constructed, and used in a train running at a speed of 64 km/h. The laser displacement sensor is insensitive to ambient light and to temperature. The parameters of the laser displacement sensor are as follows: the measurement range is 20 mm, and the laser displacement sensor resolution is 0.3 mm. All the results show that this new displacement sensor meets the requirement for real-time gauge measurement.

Development of digital image correlation method to analyse crack variations of masonry wall

Abstract: The detection of crack development in a masonry wall forms an important study for investigating the earthquake resistance capability of the masonry structures. Traditionally, inspecting the structure and documenting the findings were done manually. The procedures are time-consuming, and the results are sometimes inaccurate. Therefore, the digital image correlation (DIC) technique is developed to identify the strain and crack variations. This technique is non-destructive for inspecting the whole displacement and strain field. Tests on two masonry wall samples were performed to verify the performance of the digital image correlation method. The phenomena of micro cracks, strain concentration situation and nonuniform deformation distribution which could not have been observed preciously by manual inspection are successfully identified using DIC. The crack formation tendencies on masonry wall can be observed at an earlier stage by this proposed method. These results show a great application potential of the DIC technique for various situations such as inspecting shrinkage-induced cracks in fresh concrete, masonry and reinforced concrete structures, and safety of bridges.

Estimating Displacement of Periodic Motion With Inertial Sensors

Abstract: Inertial sensors, like accelerometers and gyroscopes, are rarely used by themselves to measure displacement. Accuracy of inertial sensors is greatly handicapped by the notorious integration drift, which arises due to numerical integration of the sensors zero bias error. A solution is proposed in this paper to provide drift free estimation of displacement from inertial sensors.

Displacement and interaction of normal fault segments branched at depth: Implications for fault growth and potential earthquake rupture size

Abstract: We present field data from segmented normal faults having particular displacement and overlapping geometries that may be related to down-dip branching of the fault segments. Based on a 3-D numerical modeling study of computed displacement and stress fields around different geometries of down-dip branched normal fault segments, we show that the bends of fault surfaces that coalesce at depth exert a significant influence on (I) the displacement distribution on the fault segment branches and (2) the quasi-static stress fields around the relay zones. The asymmetry in the displacement profiles and low fault interaction at relay zones modeled are consistent with the fault segment geometries observed in field data. As an application, we model the geometry and interaction of the Vallo di Diano normal fault which is segmented at the Earth's surface and which produced an earthquake of magnitude 6.4 along a single fault surface at depth. Numerical modeling of the segmented fault produces an asymmetric displacement profile and low shear stress at the relay zone consistent with the profile and fault interaction inferred from the held. We conclude that asymmetry of the displacement profile and large overlap/separation ratio of the unlinked relay zone can be indicators of the presence of a continuous fault surface underneath. These geometrical attributes are therefore important to consider in the probabilistic analysis of seismic hazard along segmented normal faults.

A State‐Space Approach for Deriving Bridge Displacement from Acceleration

Abstract: : The dynamic response (i.e., acceleration and displacement) of a bridge under vehicular load is an important component of design and evaluation. Field measurement of girder displacement, however, is generally nontrivial. Traditional sensors often require a stationary reference such as temporary scaffolds or a suspended cable. In either form, there are added costs, restrictions, and labor. As a result, there are both economic and practical incentives for developing methods that can use an accelerometer to measure both acceleration and displacement. One difficulty of this, however, is the presence of small low-frequency errors in the measured signal, which become sufficiently large through successive integrations and lead to a significantly distorted displacement profile. The objective of this article is to examine an analytical model based on the state-space approach for minimizing such errors and to compare results with two time domain correction methods. Field measurements from a three-span continuous bridge are used to assess the accuracy of each routine.

Estimation of the strain field from full-field displacement noisy data: Comparing finite elements global least squares and polynomial diffuse approximation

Abstract: In this study, the issue of reconstructing strain fields from corrupted full-field displacement data is addressed. Two approaches are proposed, a global one based on Finite Element Approximation (FEA) and a local one based on Diffuse Approximation (DA). Both approaches are compared on a case study which is supposed difficult (open-hole tensile test). DA provides more stable results, but is more CPU time consuming. Eventually, it is proposed to monitor locally the filtering effect of both approaches, the prospects being an impending improvement of the reconstruction for both approaches.

Dynamic force control with hydraulic actuators using added compliance and displacement compensation

Abstract: A new approach to dynamic force control of mechanical systems, applicable in particular to frame structures, over frequency ranges spanning their resonant frequencies is presented. This approach is implemented using added compliance and displacement compensation. Hydraulic actuators are inherently velocity sources, that is, an electrical signal regulates their velocity response. Such systems are therefore by nature high-impedance (mechanically stiff) systems. In contrast, for force control, a force source is required. Such a system logically would have to be a low-impedance (mechanically compliant) system. This is achieved by intentionally introducing a flexible mechanism between the actuator and the structure to be excited. In addition, in order to obtain force control over frequencies spanning the structure's resonant frequency, a displacement compensation feedback loop is needed. The actuator itself operates in closed-loop displacement control. The theoretical motivation, as well as the laboratory implementation of the above approach is discussed along with experimental results. Having achieved a means of dynamic force control, it can be applied to various experimental seismic simulation techniques such as the effective force method and the real-time dynamic hybrid testing method. Copyright © 2008 John Wiley & Sons, Ltd.

Human Motion Tracking with a Kinematic Parameterization of Extremal Contours

Abstract: This paper addresses the problem of human motion tracking from multiple image sequences. The human body is described by five articulated mechanical chains and human body-parts are described by volumetric primitives with curved surfaces. If such a surface is observed with a camera, an extremal contour appears in the image whenever the surface turns smoothly away from the viewer. We describe a method that recovers human motion through a kinematic parameterization of these extremal contours. The method exploits the fact that the observed image motion of these contours is a function of both the rigid displacement of the surface and of the relative position and orientation between the viewer and the curved surface. First, we describe a parameterization of an extremal-contour point velocity for the case of developable surfaces. Second, we use the zero-reference kinematic representation and we derive an explicit formula that links extremal contour velocities to the angular velocities associated with the kinematic model. Third, we show how the chamfer-distance may be used to measure the discrepancy between predicted extremal contours and observed image contours; moreover we show how the chamfer distance can be used as a differentiable multi-valued function and how the tracker based on this distance can be cast into a continuous non-linear optimization framework. Fourth, we describe implementation issues associated with a practical human-body tracker that may use an arbitrary number of cameras. One great methodological and practical advantage of our method is that it relies neither on model-to-image, nor on image-to-image point matches. In practice we model people with 5 kinematic chains, 19 volumetric primitives, and 54 degrees of freedom; We observe silhouettes in images gathered with several synchronized and calibrated cameras. The tracker has been successfully applied to several complex motions gathered at 30 frames/second.