scholarly journals AstroSeis: A 3D Boundary Element Modeling Code for Seismic Wavefields in Irregular Asteroids and Bodies

2020 ◽  
Vol 91 (6) ◽  
pp. 3528-3538
Author(s):  
Yuan Tian ◽  
Yingcai Zheng
Keyword(s):  
Frequency Domain ◽  
Boundary Element ◽  
Liquid Core ◽  
Computer Code ◽  
Elastic Response ◽  
Numerical Dispersion ◽  
Moment Tensors ◽  
Direct Solution Method ◽  
Set Up ◽  
Modeling Code

Abstract We developed a 3D elastic boundary element method computer code, called AstroSeis, to model seismic wavefields in a body with an arbitrary shape, such as an asteroid. Besides the AstroSeis can handle arbitrary surface topography, it can deal with a liquid core in an asteroid model. Both the solid and liquid domains are homogenous in our current code. For seismic sources, we can use single forces or moment tensors. The AstroSeis is implemented in the frequency domain, and the frequency-dependent Q can be readily incorporated. The code is in MATLAB (see Data and Resources), and it is straightforward to set up the model to run the code. The frequency-domain calculation is advantageous to study the long-term elastic response of a celestial body due to a cyclic force, such as the tidal force, with no numerical dispersion issue suffered by many other methods requiring volume meshing. Our AstroSeis has been benchmarked with other methods such as normal-mode summation and the direct solution method. This open-source AstroSeis will be a useful tool to study the interior and surface processes of asteroids.

Wave propagation improvement in two-dimensional bond-based peridynamics model

2021 ◽  
pp. 095440622098555
Author(s):  
Reza Alebrahim ◽  
Pawel Packo ◽  
Mirco Zaccariotto ◽  
Ugo Galvanetto
Keyword(s):  
Wave Propagation ◽  
Dynamic Performance ◽  
Numerical Dispersion ◽  
Motion Modeling ◽  
Minimization Method ◽  
Irregular Wave ◽  
Point Collocation ◽  
Potential Applications ◽  
Non Local ◽  
Set Up

In this study, methods to mitigate anomalous wave propagation in 2-D Bond-Based Peridynamics (PD) are presented. Similarly to what happens in classical non-local models, an irregular wave transmission phenomenon occurs at high frequencies. This feature of the dynamic performance of PD, limits its potential applications. A minimization method based on the weighted residual point collocation is introduced to substantially extend the frequency range of wave motion modeling. The optimization problem, developed through inverse analysis, is set up by comparing exact and numerical dispersion curves and minimizing the error in the frequency-wavenumber domain. A significant improvement in the wave propagation simulation using Bond-Based PD is observed.

Regularization of the Boundary Integrals in the Bem Analysis of 3D Potential Problems

2012 ◽  
Vol 29 (3) ◽  
pp. 385-401 ◽  
Author(s):  
Y. C. Shiah ◽  
M. R. Hematiyan ◽  
Y. H. Chen
Keyword(s):  
Boundary Element ◽  
Local Coordinate System ◽  
Computer Code ◽  
Boundary Integral ◽  
Boundary Integrals ◽  
Element Analysis ◽  
Numerical Tests ◽  
Potential Problems ◽  
Boundary Element Analysis ◽  
Proper Values

AbstractIn the conventional boundary element analysis, near-singularities are present in the associated boundary integral equation for problems involving ultra-thin media. For this case, any conventional numerical schemes will fail to yield proper values for the integrals. In this paper, the boundary integrals of the boundary element method for 3D potential problems are fully regularized by the technique of integration by parts under the local coordinate system. The fully regularized integrands are expressed as very explicit formulations that can be easily programmed into a computer code. Numerical tests carried out for a typical case have verified the accuracy of the approach for any orders of small distance between the source and the element under integration.

A simple and exact acoustic wavefield modeling code for data processing, imaging, and interferometry applications

Geophysics ◽  
2013 ◽  
Vol 78 (6) ◽  
pp. F17-F27 ◽  
Author(s):  
Erica Galetti ◽  
David Halliday ◽  
Andrew Curtis
Keyword(s):  
Finite Difference ◽  
Synthetic Data ◽  
Acoustic Modeling ◽  
Numerical Dispersion ◽  
Seismic Interferometry ◽  
Numerical Errors ◽  
Matlab Code ◽  
Modeling Code ◽  
Seismic Images ◽  
Methods Numerical

Improvements in industrial seismic, seismological, acoustic, or interferometric theory and applications often result in quite subtle changes in sound quality, seismic images, or information which are nevertheless crucial for improved interpretation or experience. When evaluating new theories and algorithms using synthetic data, an important aspect of related research is therefore that numerical errors due to wavefield modeling are reduced to a minimum. We present a new MATLAB code based on the Foldy method that models theoretically exact, direct, and scattered parts of a wavefield. Its main advantage lies in the fact that while all multiple scattering interactions are taken into account, unlike finite-difference or finite-element methods, numerical dispersion errors are avoided. The method is therefore ideal for testing new theory in industrial seismics, seismology, acoustics, and in wavefield interferometry in particular because the latter is particularly sensitive to the dynamics of scattering interactions. We present the theory behind the Foldy acoustic modeling method and provide examples of its implementation. We also benchmark the code against a good finite-difference code. Because our Foldy code was written and optimized to test new theory in seismic interferometry, examples of its application to seismic interferometry are also presented, showing its validity and importance when exact modeling results are needed.

scholarly journals Bond graph based frequency domain sensitivity analysis of multidisciplinary systems

2002 ◽  
Vol 216 (1) ◽  
pp. 85-99 ◽  
Author(s):  
W Borutzky ◽  
J Granda
Keyword(s):  
Frequency Domain ◽  
Transfer Functions ◽  
Linear Time ◽  
Graph Model ◽  
Bond Graph ◽  
Sensitivity Matrix ◽  
Symbolic Form ◽  
Multidisciplinary Systems ◽  
Set Up ◽  
The Time Domain

Multidisciplinary systems are described most suitably by bond graphs. In order to determine unnormalized frequency domain sensitivities in symbolic form, this paper proposes to construct in a systematic manner a bond graph from another bond graph, which is called the associated incremental bond graph in this paper. Contrary to other approaches reported in the literature the variables at the bonds of the incremental bond graph are not sensitivities but variations (incremental changes) in the power variables from their nominal values due to parameter changes. Thus their product is power. For linear elements their corresponding model in the incremental bond graph also has a linear characteristic. By deriving the system equations in symbolic state space form from the incremental bond graph in the same way as they are derived from the initial bond graph, the sensitivity matrix of the system can be set up in symbolic form. Its entries are transfer functions depending on the nominal parameter values and on the nominal states and the inputs of the original model. The sensitivities can be determined automatically by the bond graph preprocessor CAMP-G and the widely used program MATLAB together with the Symbolic Toolbox for symbolic mathematical calculation. No particular program is needed for the approach proposed. The initial bond graph model may be non-linear and may contain controlled sources and multiport elements. In that case the sensitivity model is linear time variant and must be solved in the time domain. The rationale and the generality of the proposed approach are presented. For illustration purposes a mechatronic example system, a load positioned by a constant-excitation d.c. motor, is presented and sensitivities are determined in symbolic form by means of CAMP-G/MATLAB.

Analysis of Instability for OTSG by Using Multivariable Frequency Domain Method

2009 ◽  
Author(s):  
Su-xia Hou ◽  
Yun Tai ◽  
Fu-yu Zhao
Keyword(s):  
Frequency Domain ◽  
Hydrodynamic Instability ◽  
Computer Code ◽  
Domain Theory ◽  
Frequency Domain Method ◽  
Stable Boundary ◽  
Numerical Examples ◽  
Parametric Effects ◽  
The Stability ◽  
Good Agreement

A new method for analyzing the problem of the thermal-hydrodynamic instability of OTSG (once-through steam generator) with multiple boiling channels is presented in this paper. The mothod is based on modern frequency domain theory and is more efficient for analyzing the instability of OTSG with coupling interactions and complicated boundary conditions than the usually used single variable method. A mathematical model for a OTSG is derived from the foundamental equations by use of the small perturbation and Laplace-transform techniques. The stable boundary and parametric effects on the stability of the system are evaluated with a computer code. Numerical examples are given in the paper and the predictions of the model are in good agreement with the experimental results.

Boundary Element Analysis of Coupled Continuum and Skeletal Structures

2007 ◽  
Vol 10 (4) ◽  
pp. 415-438
Author(s):  
Youssef F. Rashed
Keyword(s):  
Boundary Element ◽  
Main Idea ◽  
Element Analysis ◽  
Skeletal Structures ◽  
Stiffness Matrices ◽  
Assembly Technique ◽  
A New Technique ◽  
Set Up ◽  
The Continuum ◽  
Element Method

This paper presents a new technique for solving coupled continuum and skeletal structures. The technique is based on employing the well-known flexibility and stiffness methods within the boundary element method (BEM). The analyzed problem is divided into: continuum parts, which are modeled using the BEM and skeletal parts which are modeled using the flexibility or stiffness methods. The main idea of the presented technique is to set up a methodology to generate flexibility or stiffness matrices for the continuum parts using the BEM. To do so, several flexibility and stiffness models are developed. The developed technique is tested on three problems. Results are compared to those obtained from the finite element method (FEM) to show the validity of the developed technique. The present technique gains both advantages of the BEM and the FEM as it allows boundary-only discretization for the continuum parts and uses the banded assembly technique of FEM for the overall structure.

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