scholarly journals Influence of boundary conditions on time-reversal focusing through heterogeneous media

1998 ◽  
Vol 72 (20) ◽  
pp. 2511-2513 ◽  
Author(s):  
Mickaël Tanter ◽  
Jean-Louis Thomas ◽  
Mathias Fink
Keyword(s):  
Boundary Conditions ◽  
Time Reversal ◽  
Heterogeneous Media

Photoacoustic tomography of heterogeneous media using a model-based time reversal method

2008 ◽  
Author(s):  
Hubert Grün ◽  
Robert Nuster ◽  
Günther Paltauf ◽  
Markus Haltmeier ◽  
Peter Burgholzer
Keyword(s):  
Time Reversal ◽  
Heterogeneous Media ◽  
Photoacoustic Tomography ◽  
Model Based

VOLUME CLUTTER ELIMINATION, ROUGH INTERFACE REVERBERATION SUPPRESSION, AND TARGET RESONANCE CONVERGENCE IN HETEROGENEOUS MEDIA USING AN ITERATIVE TIME REVERSAL MIRROR

2010 ◽  
Vol 18 (03) ◽  
pp. 227-243 ◽  
Author(s):  
YINGZI YING ◽  
LI MA
Keyword(s):  
Time Reversal ◽  
Finite Difference Time Domain ◽  
Small Volume ◽  
Heterogeneous Media ◽  
Resonance Mode ◽  
Rough Interface ◽  
Acoustic Signature ◽  
Time Harmonic ◽  
Time Reversal Mirror ◽  
Difference Time

The presence of the clutter of volume scattering and the echo return from rough interface hinders the detection of target in heterogeneous media. This work investigates the application of an iterative time reversal mirror to mitigate the difficulties. Numerical simulations based on pseudospectral finite-difference time-domain method are performed in one and two layered media. A wideband probe pulse is launched to initiate the process, and the time-reversed echo received at the same position is retransmitted as the renewed input signal for next iteration, and repeat the procedures iteratively. The results illustrate as the number of iteration increases, small volume clutter is eliminated, interface reverberation is suppressed relatively, and the echoes will converge to a time-harmonic waveform that corresponds to an object's dominant resonance mode. The detection of target is achieved by extracting this important acoustic signature.

3D finite-difference dynamic-rupture modeling along nonplanar faults

Geophysics ◽  
2007 ◽  
Vol 72 (5) ◽  
pp. SM123-SM137 ◽  
Author(s):  
Víctor M. Cruz-Atienza ◽  
Jean Virieux ◽  
Hideo Aochi
Keyword(s):  
Finite Difference ◽  
Boundary Conditions ◽  
Heterogeneous Media ◽  
Slip Rate ◽  
Quantitative Agreement ◽  
Boundary Integral ◽  
Boundary Integral Method ◽  
Weight Functions ◽  
Dynamic Rupture ◽  
Fault Surface

Proper understanding of seismic emissions associated with the growth of complexly shaped microearthquake networks and larger-scale nonplanar fault ruptures, both in arbitrarily heterogeneous media, requires accurate modeling of the underlying dynamic processes. We present a new 3D dynamic-rupture, finite-difference model called the finite-difference, fault-element (FDFE) method; it simulates the dynamic rupture of nonplanar faults subjected to regional loads in complex media. FDFE is based on a 3D methodology for applying dynamic-rupture boundary conditions along the fault surface. The fault is discretized by a set of parallelepiped fault elements in which specific boundary conditions are applied. These conditions are applied to the stress tensor, once transformed into a local fault referenceframe. Numerically determined weight functions multiplying particle velocities around each element allow accurate estimates of fault kinematic parameters (i.e., slip and slip rate) independent of faulting mechanism. Assuming a Coulomb-like slip-weakening friction law, a parametric study suggests that the FDFE method converges toward a unique solution, provided that the cohesive zone behind the rupture front is well resolved (i.e., four or more elements inside this zone). Solutions are free of relevant numerical artifacts for grid sizes smaller than approximately [Formula: see text]. Results yielded by the FDFE approach are in good quantitative agreement with those obtained by a semianalytical boundary integral method along planar and nonplanar parabola-shaped faults. The FDFE method thus provides quantitative, accurate results for spontaneous-rupture simulations on intricate fault geometries.

scholarly journals Analysis of an observer strategy for initial state reconstruction of wave-like systems in unbounded domains

2020 ◽  
Vol 26 ◽  
pp. 45
Author(s):  
S. Imperiale ◽  
P. Moireau ◽  
A. Tonnoir
Keyword(s):  
Boundary Conditions ◽  
Time Reversal ◽  
Unbounded Domains ◽  
Reconstruction Algorithm ◽  
Initial Condition ◽  
Transparent Boundary Conditions ◽  
Initial State ◽  
Domain Configuration ◽  
Robustness To Noise ◽  
Consistency Error

We are interested in reconstructing the initial condition of a wave equation in an unbounded domain configuration from measurements available in time on a subdomain. To solve this problem, we adopt an iterative strategy of reconstruction based on observers and time reversal adjoint formulations. We prove the convergence of our reconstruction algorithm with perfect measurements and its robustness to noise. Moreover, we develop a complete strategy to practically solve this problem on a bounded domain using artificial transparent boundary conditions to account for the exterior domain. Our work then demonstrates that the consistency error introduced by the use of approximate transparent boundary conditions is compensated by the stabilization properties obtained from the use of the available measurements, hence allowing to still be able to reconstruct the unknown initial condition.

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