# American Institute of Mathematical Sciences

March  2019, 8(1): 231-246. doi: 10.3934/eect.2019013

## Anti-plane shear Lamb's problem on random mass density fields with fractal and Hurst effects

 1 Department of Mechanical Science & Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA 2 Sandia National Laboratories, Albuquerque, NM 87185, USA 3 Department of Mechanical Science & Engineering, also Institute for Condensed Matter Theory and Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA

* Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energys National Nuclear Security Administration under contract DE-NA0003525

Received  October 2017 Revised  March 2018 Published  January 2019

This paper reports a study of transient dynamic responses of the anti-plane shear Lamb's problem on random mass density field with fractal and Hurst effects. Cellular automata (CA) is used to simulate the shear wave propagation. Both Cauchy and Dagum random field models are used to capture fractal dimension and Hurst effects in the mass density field. First, the dynamic responses of random mass density are evaluated through a comparison with the homogenerous computational results and the classical theoretical solution. Then, a comprehensive study is carried out for different combinations of fractal and Hurst coefficients. Overall, this investigation determines to what extent fractal and Hurst effects are significant enough to change the dynamic responses by comparing the signal-to-noise ratio of the response versus the signal-to-noise ratio of the random field.

Citation: Xian Zhang, Vinesh Nishawala, Martin Ostoja-Starzewski. Anti-plane shear Lamb's problem on random mass density fields with fractal and Hurst effects. Evolution Equations & Control Theory, 2019, 8 (1) : 231-246. doi: 10.3934/eect.2019013
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##### References:
(a) cell (i, j) and its neighbors for Cellular Automata discretization (b) the neighbor stresses acting on cell (i, j)
(a) Computational domain (b) Anti-plane triangular load
At 92$\mu$s: CA displacement and stress responses
White noise RFs with carying coarseness, mean = 1300 $\mathrm{ kg/m^{3}}$ and $\mathrm{CV_{RF}}$ = 0.124. Legends are density in $\mathrm{ kg/m^{3}}$
WN RFs responses with varying coarseness (a): mean and SD of random field responses versus theoretical solution and homogenerous results; (b) CV of response; (c) SNR of response
Cauchy RFs with $\left\langle \rho \right\rangle = 1, 300$ $\mathrm{ kg/m^{3}}$, $\mathrm{CV_{RF}}$ = 0.124. Legends are density in $\mathrm{ kg/m^{3}}$
Cauchy RFs with mean = 1300 $\mathrm{\ kg/m^{3}}$ and $CV_{RF}$ = 0.124, (a, d, g) $\beta$ = 0.2; (b, f, i) $\beta$ = 1.0; (c, f, i) $\beta$ = 1.8. (a, b, c) $\alpha$ = 1.8; (d, f, g) $\alpha$ = 1.0; (h, i, j) $\alpha$ = 0.2
Cauchy RFs with $\mathrm{CV_{RF}} = 0.124$: Comparison of $\mathrm{SNR_{R}}$ and $\mathrm{SNR_{RF}}$ for varying $\alpha$ and $\beta$. The boundary between $\mathrm{ SNR_{R}}$ less than or greater than $\mathrm{ SNR_{RF}}$ is represently by the dotted line
Dagum RFs with $\left\langle \rho \right\rangle = 1, 300$ $\mathrm{ kg/m^{3}}$, $\mathrm{CV_{RF}}$ = 0.124. Legends are density in $\mathrm{ kg/m^{3}}$
Dagum RFs responses (at $92$ $\mu s$) with $\alpha$ = 0.8 (D = 2.9) and varying $\beta$. (a): mean and SD of random fields responses versus theoretical solution and homogenerous results; (b) CV of response versus CV of RF; (c) SNR of response versus SNR of RF
Dagum RFs with $\mathrm{CV_{RF}}$ = 0.124: Comparison of $\mathrm{ SNR_{R}}$ and $\mathrm{SNR_{RF}}$ for varying $\alpha$ and $\beta$. The boundary between $\mathrm{\ SNR_{R}}$ less than or greater than $\mathrm{\ SNR_{RF}}$ is represently by the dotted line
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