Displacements of Multiblock Geotechnical Structures Subjected to Seismic Excitation

A method is presented for calculations of irreversible displacements of multiblock structures subjected to seismic excitation. Use is made of the kinematic approach of limit analysis. To make the analysis tractable a hodograph representing distribution of accelerations in the structure is introduced. Distinction is made between soils conforming to the associative and nonassociative flow rules, and the importance of this distinction is demonstrated. The yield acceleration calculated for slopes comprised of soils conforming to the nonassociative flow rule is lower than that for a soil with the same strength parameters, but its deformation governed by the associative flow rule. Consequently, the displacements predicted for the former are larger. An example of a slope is demonstrated, but the method presented is applicable to other structures, such as retaining walls and embankments.     

Simplified Procedure for Estimating Earthquake-Induced Deviatoric Slope Displacements

A simplified semiempirical predictive relationship for estimating permanent displacements due to earthquake-induced deviatoric deformations is presented. It utilizes a nonlinear fully coupled stick-slip sliding block model to capture the dynamic performance of an earth dam, natural slope, compacted earth fill, or municipal solid-waste landfill. The primary source of uncertainty in assessing the likely performance of an earth/waste system during an earthquake is the input ground motion. Hence, a comprehensive database containing 688 recorded ground motions is used to compute seismic displacements. A seismic displacement model is developed that captures the primary influence of the system’s yield coefficient (ky), its initial fundamental period (Ts), and the ground motion’s spectral acceleration at a degraded period equal to 1.5Ts. The model separates the probability of “zero” displacement (i.e., ? 1?cm) occurring from the distribution of “nonzero” displacement, so that very low values of calculated displacement do not bias the results. The use of the seismic displacement model is validated through reexamination of 16 case histories of earth dam and solid-waste landfill performance. The proposed model can be implemented rigorously within a fully probabilistic framework or used deterministically to evaluate seismic displacement potential.     

An overview of a hybrid crack element and determination of its complete displacement field

The hybrid crack element (HCE) is one of the most accurate and convenient finite elements for the direct calculation of the stress intensity factor (SIF) and coefficients of the higher order terms of the Williams expansion. It is formulated from a simplified variational functional using truncated asymptotic crack tip displacement and stress expansions and interelement boundary displacements compatible with the surrounding regular elements. However, the exclusion of the rigid body modes in the truncated asymptotic displacements creates jumps between these displacements and element compatible boundary displacements. In this study, an overview of the HCE is given. Furthermore, the rigid body modes excluded in its formulation are recovered by minimizing the jumps via a least squares method. Limitations of the boundary collocation method (BCM) widely used for predicting these terms, as well as the complete displacements are also investigated.     

Optical flow estimation for motion-compensated compression

The computation of optical flow within an image sequence is one of the most widely used techniques in computer vision. In this paper, we present a new approach to estimate the velocity field for motion-compensated compression. It is derived by a nonlinear system using the direct temporal integral of the brightness conservation constraint equation or the Displaced Frame Difference (DFD) equation. To solve the nonlinear system of equations, an adaptive framework is used, which employs velocity field modeling, a nonlinear least-squares model, Gauss–Newton and Levenberg–Marquardt techniques, and an algorithm of the progressive relaxation of the over-constraint. The three criteria by which successful motion-compensated compression is judged are 1.) The fidelity with which the estimated optical flow matches the ground truth motion, 2.) The relative absence of artifacts and “dirty window” effects for frame interpolation, and 3.) The cost to code the motion vector field. We base our estimated flow field on a single minimized target function, which leads to motion-compensated predictions without incurring penalties in any of these three criteria. In particular, we compare our proposed algorithm results with those from Block-Matching Algorithms (BMA), and show that with nearly the same number of displacement vectors per fixed block size, the performance of our algorithm exceeds that of BMA in all the three above points. We also test the algorithm on synthetic and natural image sequences, and use it to demonstrate applications for motion-compensated compression.     

大排量线性调节液压泵的开发与应用

本文论述了BPV泵功能特性以及泵在液压系统中的应用。     

Displacement threshold and Frenkel pair formation energy in ionic systems

Displacement threshold energies (E_d) and Frenkel pair formation energies (E_Fp) are investigated in detail by molecular dynamics computer simulation for three different ionic systems with the same crystal structure, MgO, SrO and NaCl in order to see if there is a functional relationship between them. It is found that there are wide variations in the values of E_d depending on the direction in which energy is imparted to a static atom in the lattice. Large values of E_d are found along the major crystallographic directions and lower values elsewhere. Typically these thresholds are between 5 and 9 times bigger than the Frenkel pair formation energies E_Fp with no observable dependence on mass or ion charge. The differences in the interaction potentials also means that for any given direction, there is only limited correlation between values of E_d in the different systems studied and no quantifiable relationship with E_Fp.     

牙齿松动位移测量仪的研究

本文针对牙齿松动位移测量仪的研制，就其位移传感原理，信号处理以及相关的机械结构进行了理论分析，整机实验结果与临床试用表明，本测量仪的性能指标达到了临床应用的标准。     

Atomic-scale simulation of displacement cascades and amorphization in β-SiC

Molecular dynamics (MD) methods with a modified Tersoff potential have been used to simulate Si displacement cascades with energies up to 50 keV and to compare clustering behavior for Si and Au recoils in β-SiC (3C). The results show that the lifetime of the thermal spike is very short compared to that in metals, and that the surviving defects are dominated by C interstitials and vacancies for Si displacement cascades. Only 19% of the interstitial population is contained in clusters, with the largest cluster containing only four interstitial atoms for energetic Si recoils. The energy dependence of stable defect formation exhibits a power-law relationship. The high energy Si recoil generates multiple sub-cascades and forms dispersed defect configurations. These results suggest that in-cascade amorphization in SiC does not occur with any high degree of probability during the lifetime of Si cascades. On the other hand, large disordered domains are created in the cascades produced by 10 keV Au recoils. Structure analysis indicates that these highly disordered regions have amorphous characteristics. The data for the cluster spectra have been used to calculate the relative cross-sections for in-cascade amorphization (or clustering) and defect-stimulated amorphization. The ratios of these cross-sections for Si and Au are in excellent agreement with those derived from a fit of the direct-impact/defect-stimulated model to experimental data.     

Three-Dimensional Green’s Functions for a Multilayered Half-Space in Displacement Potentials

To advance the mathematical and computational treatments of mixed boundary value problems involving multilayered media, a new derivation of the fundamental Green’s functions for the elastodynamic problem is presented. By virtue of a method of displacement potentials, it is shown that there is an elegant mathematical structure underlying this class of three-dimensional elastodynamic problems which warrant further attention. Constituted by proper algebraic factorizations, a set of generalized transmission-reflection matrices and internal source fields that are free of any numerically unstable exponential terms common in past solution formats are proposed for effective computations of the potential solution. To encompass both elastic and viscoelastic cases, point-load Green’s functions for stresses and displacements are generalized into complex-plane line-integral representations. An accompanying rigorous treatment of the singularity of the fundamental solution for arbitrary source-receiver locations via an asymptotic decomposition of the transmission-reflection matrices is also highlighted.