Land and ocean-bottom spatial gradient-based seismic wavefield separation

In the last 20 years, seismologists have recognized that a better sensing of the seismic wavefield is obtained by considering the rotational ground motions in addition to the translation measurements usually provided by seismometers. Even though recent technological developments have resulted in new portable rotation sensors with a sensitivity and a bandwidth suited to seismological applications requirements, the ground rotations have for a long time been estimated indirectly by dense seismic arrays.The Low Noise Underground Laboratory (LSBB) includes a dense 3D seismic antenna composed of 6 STS2 broad-band seismometers since March 2005. From 2016, this array has been upgraded by the installation of about 10 new seismometers at the surface and inside the galleries of the laboratory. Thanks to these dense and small aperture seismic networks, the vertical and horizontal rotations of the ground motion have been estimated by finite difference approximation of the spatial derivatives of the local ground motions. These measurements provide the opportunity to conduct six degree of freedom (6DOF) analysis (3C translations and 3C rotations) to find out the direction of the wave propagation and to estimate the seismic wave local phase velocity. The performance of this seismic array in deriving the local spatial gradient of the seismic wavefield, as well as the rotation tensor, will be illustrated by several selected seismic records such as the 2016 central Italy crisis (Amatrice and Norcia events) as well as the recent local Teil earthquake. In addition, the Array Derived Rotations (ADR) from the LSBB antenna are compared with the rotations measured by different kinds of rotation sensors including 2 prototypes of the new BlueSeis3A and a Lily Borehole Tiltmeter.

Download Full-text

A consistent approach for image de-noising using spatial gradient based bilateral filter and smooth filtering

10.1117/12.2242273 ◽

2016 ◽

Cited By ~ 1

Author(s):

Mayank Tiwari ◽

Bhupendra Gupta

Keyword(s):

Bilateral Filter ◽

Spatial Gradient ◽

Gradient Based ◽

Consistent Approach

Download Full-text

A Density Gradient Approach to Topology Optimization Under Design-Dependent Boundary Loading

Volume 2B: 44th Design Automation Conference ◽

10.1115/detc2018-85960 ◽

2018 ◽

Author(s):

Cunfu Wang ◽

Xiaoping Qian

Keyword(s):

Topology Optimization ◽

Density Gradient ◽

Optimization Method ◽

Spatial Gradient ◽

Computationally Efficient ◽

Physical Density ◽

Gradient Based ◽

Design Dependent Loads ◽

Previous Iteration ◽

Gradient Approach

The paper proposes a density gradient based approach to topology optimization under design-dependent boundary loading. In the density-based topology optimization method, we impose the design dependent loads through spatial gradient of the density. We transform design-dependent boundary loads into a volume form through volume integral of density gradient. In many applications where loadings only need to be exerted on partial boundary, we introduce an auxiliary loading density to keep track of the loading boundary. During the optimization, the loading density is updated by tracking the changes of the physical density in the vicinity of the loading boundary at previous iteration. The proposed approach is easy to implement and computationally efficient. In addition, by adding more auxiliary density fields, the proposed approach is applicable to multiple design-dependent loads. To prevent the intersection of different loading boundaries, a Heaviside projection based integral constraint is developed. Both heat conduction problems under convection loading and elastic problems under hydrostatic pressure loading are presented to illustrate the effectiveness and efficiency of the method.

Download Full-text