Energy transmission through grain-to-grain contacts: The role of bulk and Rayleigh waves

abstract The predominant seismic energy input into structures is from Rayleigh waves. These attenuate rapidly with distance from the surface and are partially reflected and partially transmitted by a hole in the ground. A structure founded in such a hole may anticipate a smaller seismic input than a surface-founded structure. Estimates of such a reduction are given which indicate that only short buildings and material with low shear-wave velocities will provide the proper conditions for this beneficial effect.

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Theoretical study of the excitation, spectral characteristics, and geometrical attenuation of regional seismic phases

Bulletin of the Seismological Society of America ◽

10.1785/bssa0740010079 ◽

1984 ◽

Vol 74 (1) ◽

pp. 79-90

Author(s):

Michel Campillo ◽

Michel Bouchon ◽

Bernard Massinon

Keyword(s):

Rayleigh Waves ◽

Wave Amplitude ◽

Theoretical Study ◽

Epicentral Distance ◽

Spectral Characteristics ◽

Source Depth ◽

Source Mechanisms ◽

Lg Wave ◽

Two Phases

Abstract We present a theoretical study of the generation and geometrical attenuation of regional crustal phases. We do this through the computation of seismograms in the epicentral distance range from 60 to 500 km. The geometrical attenuation of Lg waves with epicentral distance is of the form r−0.83. Pg wave amplitudes display a much stronger decay of the form r−1.5. The spectral density of the crustal transfer function for Pg waves is relatively flat for frequencies between 0.1 and 5 Hz while Lg wave spectra strongly fall off beyond 2 to 3 Hz. The excitation of Pg wave is insensitive to the depth of the source within the crust while the Lg amplitude is about 50 per cent higher for a source in the upper and middle crust than in the lower crust. The amplitudes of these two phases drastically decrease when the source is below the Moho. These results illustrate the important role of wave guide played by the crust for the propagation of Lg and Pg. We find that the geometrical attenuation of Pg and Lg waves is independent of source mechanisms. In the case of an explosion, the excitation of Pg is insensitive to the source depth. The Lg wave amplitude is small in comparison to Pg and Rayleigh waves and depends on the closeness of the source to an interface or to the free surface.

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Computational Analysis for Validation of Blast Induced Traumatic Brain Injury and Protection of Combat Helmet

Volume 3: Biomedical and Biotechnology Engineering ◽

10.1115/imece2018-87689 ◽

2018 ◽

Author(s):

X. Gary Tan ◽

Amit Bagchi

Keyword(s):

Traumatic Brain Injury ◽

Brain Injury ◽

Shock Tube ◽

Blast Wave ◽

High Fidelity ◽

Blast Loads ◽

Next Generation ◽

Energy Transmission ◽

The Brain

Current understanding of blast wave transmission and mechanism of primary traumatic brain injury (TBI) and the role of helmet is incomplete thus limiting the development of protection and therapeutic measures. Combat helmets are usually designed based on costly and time consuming laboratory tests, firing range, and forensic data. Until now advanced medical imaging and computational modeling tools have not been adequately utilized in the design and optimization of combat helmets. The goal of this work is to develop high fidelity computational tools, representative virtual human head and combat helmet models that could help in the design of next generation helmets with improved blast and ballistic protection. We explore different helmet configurations to investigate blast induced brain biomechanics and understand the protection role of helmet by utilizing an integrated experimental and computational method. By employing the coupled Eulerian-Lagrangian fluid structure interaction (FSI) approach we solved the dynamic problem of helmet and head under the blast exposure. Experimental shock tube tests of the head surrogate provide benchmark quality data and were used for the validation of computational models. The full-scale computational NRL head-neck model with a combat helmet provides physical quantities such as acceleration, pressure, strain, and energy to blast loads thus provides a more complete understanding of the conditions that may contribute to TBI. This paper discusses possible pathways of blast energy transmission to the brain and the effectiveness of helmet systems at blast loads. The existing high-fidelity image-based finite element (FE) head model was applied to investigate the influence of helmet configuration, suspension pads, and shell material stiffness. The two-phase flow model was developed to simulate the helium-air shock wave interaction with the helmeted head in the shock tube. The main contribution was the elucidation of blast wave brain injury pathways, including wave focusing in ocular cavities and the back of head under the helmet, the effect of neck, and the frequency spectrum entering the brain through the helmet and head. The suspension material was seen to significantly affect the ICP results and energy transmission. These findings can be used to design next generation helmets including helmet shape, suspension system, and eye protection.

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