Search

Various construction activities (such as piling) often generate high-intensity ground vibrations that adversely affect the surrounding environment. A common way of assessing vibration impact is to conduct on-site ground vibration monitoring at several selected locations. However, as vibration sources are often not pinpointed in the construction process, this approach cannot predict the vibration intensities at locations other than those monitored points. Therefore, the localization of vibration sources (e.g., vibratory sheet pile driving location) is crucial to quantify the corresponding vibration intensities in a broad area. This paper investigates a time-based source localization method based on wave propagation characteristics derived via three-dimensional finite element modeling of vibratory sheet pile driving in an infinite half-space soil domain. Satisfactory accuracy in the localization of the vibratory driving sources was achieved in all investigated numerical examples. Field validation tests were also conducted on a construction site with ongoing vibratory sheet pile driving work. A site-specific empirical formula was adopted to model the attenuation of measured vibration intensities with the increasing distance from the localized vibration source. As such, the combined utilization of the estimated vibration source location and the adopted empirical formula can achieve vibration intensity assessment in a broad surrounding area rather than being confined to a few monitored points. [ABSTRACT FROM AUTHOR]

Various construction activities (such as piling) often generate high-intensity ground vibrations that adversely affect the surrounding environment. A common way of assessing vibration impact is to conduct on-site ground vibration monitoring at several selected locations. However, as vibration sources are often not pinpointed in the construction process, this approach cannot predict the vibration intensities at locations other than those monitored points. Therefore, the localization of vibration sources (e.g., vibratory sheet pile driving location) is crucial to quantify the corresponding vibration intensities in a broad area. This paper investigates a time-based source localization method based on wave propagation characteristics derived via three-dimensional finite element modeling of vibratory sheet pile driving in an infinite half-space soil domain. Satisfactory accuracy in the localization of the vibratory driving sources was achieved in all investigated numerical examples. Field validation tests were also conducted on a construction site with ongoing vibratory sheet pile driving work. A site-specific empirical formula was adopted to model the attenuation of measured vibration intensities with the increasing distance from the localized vibration source. As such, the combined utilization of the estimated vibration source location and the adopted empirical formula can achieve vibration intensity assessment in a broad surrounding area rather than being confined to a few monitored points.

Highlights • A novel variant of the Newton-Raphson method within a time integration scheme tailored for nonlinear 3D mesoscale mechanical model of CNT nanocomposite. • An optimized numerical solution scheme suitable for damping material optimizations via Differential Evolution, usually requiring thousands of cyclic analyses. • Efficiency, while retaining numerical accuracy, obtained by a unique iteration (elastic stiness) matrix. • Both serial and parallel computations numerically tested to assess performance. • Performance further improved by a caching mechanism coupled with parallel execution of numerical simulations. Abstract The accuracy and efficiency of a numerical strategy for sequential nonlinear cyclic analyses of carbon nanotube nanocomposites are investigated. The computational approach resorts to a nonlinear 3D finite element implementation that seeks to solve the cyclic hysteretic response of the nanocomposite. A variant of the Newton-Raphson method within a time integration scheme is proposed whereby the elastic tangent matrix is chosen as iteration matrix without paying the price of its iterative update. This is especially rewarding in the context of the employed mechanical model which exhibits hysteresis manifested through a discontinuous change in the stiffness at the reversal points where the loading direction is reversed. Key implementation aspects – such as the integration of the nonlinear 3D equations of motion, the numerical accuracy/efficiency as a function of the time step or the mesh size – are discussed. In particular, efficiency is regarded as performing fast computations especially when the number of cyclic analyses becomes large. By making use of laptop CPU cores, a good speed of computations is achieved not only through parallelization but also employing a caching procedure for the iteration matrix. [ABSTRACT FROM AUTHOR]

Abstract: A study is made of longitudinal “channel” cracking in tooth enamel from axial compressive loading. The cracks simulate those generated in the molar and premolar teeth of humans and animals by natural tooth function. Contact loading tests are made on extracted human molars with hard and soft indenting plates to determine the evolution of such cracks with increasing load. Fracture is largely stable, with initial slow growth followed by acceleration as the cracks approach completion around an enamel side wall. A simple power law relation expresses the critical load for full fracture in terms of characteristic tooth dimensions—base radius and enamel thickness—as well as enamel toughness. Extended three-dimensional finite element modeling with provision for growth of embedded cracks is used to validate this relation. The cracks leave “fingerprints” that offer valuable clues to dietary habits, and provide a basis for a priori prediction of bite forces for different animals from measured tooth dimensions. [Copyright &y& Elsevier]