Simulation Of Propagation Research Articles

Reduced-order modeling for complex 3D seismic wave propagation

Summary Elastodynamic Green’s functions are an essential ingredient in seismology as they form the connection between direct observations of seismic waves and the earthquake source. They are also fundamental to various seismological techniques including physics-based ground motion prediction and kinematic or dynamic source inversions. In regions with established 3D models of the Earth’s elastic structure, such as southern California, 3D Green’s functions can be computed using numerical simulations of seismic wave propagation. However, such simulations are computationally expensive which poses challenges for real-time ground motion prediction and uncertainty quantification in source inversions. In this study, we address these challenges by using a reduced-order model (ROM) approach that enables the rapid evaluation of approximate Green’s functions. The ROM technique developed approximates three-component time-dependent surface velocity wavefields obtained from numerical simulations of seismic wave propagation. We apply our ROM approach to a 50 km × 40 km area in greater Los Angeles accounting for topography, site effects, 3D subsurface velocity structure, and viscoelastic attenuation. The ROM constructed for this region enables rapid computation (≈0.0001 CPU hours) of complete, high-resolution (500 m spacing), 0.5 Hz surface velocity wavefields that are accurate for a shortest wavelength of 1.0 km for a single elementary moment tensor source. Using leave-one-out cross validation, we measure the accuracy of our Green’s functions for the CVM-S velocity model in both the time domain and frequency domain. Averaged across all sources, receivers, and time steps, the error in the rapid seismograms is less than 0.01 cm/s. We demonstrate that the ROM can accurately and rapidly reproduce simulated seismograms for generalized moment tensor sources in our region, as well as kinematic sources by using a finite fault model of the 1987 MW 5.9 Whittier Narrows earthquake as an example. We envision that rapid, accurate Green’s functions from reduced-order modeling for complex 3D seismic wave propagation simulations will be useful for constructing real-time ground motion synthetics and source inversions with high spatial resolution.

Monitoring fatigue damage in aircraft fuselages using Paris Law parameters C and m

This study proposes an innovative methodology for integrating the Paris Law parameters, C and m, into the analysis, design, and maintenance of aircraft fuselages to enhance fatigue life predictions and structural integrity. The approach combines macro- and micro-scale analyses, leveraging the Boundary Element Method (BEM) to calculate internal stress fields, identify critical stress points, and guide crack propagation simulations at the micro-scale. These simulations utilize C and m to estimate remaining fatigue life under various operational scenarios. The methodology is implemented using a custom computational tool that integrates the BemLab GUI and BemCracker2D solver, automating stress evaluation, compliance calculations, and crack growth simulations. Case studies validate the approach, illustrating how variations in C and m affect fatigue life predictions and enable optimized material selection and inspection strategies. The first case examines a fuselage section under normal and shear loading, while the second includes additional stress components to evaluate their influence on damage tolerance. This methodology provides a practical alternative to traditional crack size-based evaluations by incorporating C and m into routine assessments. It enhances maintenance strategies, improves safety, reduces operational costs, and extends the service life of fuselage structures, presenting a significant advancement in aerospace engineering.

Modeling and simulation of rumor propagation and optimal control strategy based on social positive reinforcement

Modeling and simulation of rumor propagation and optimal control strategy based on social positive reinforcement

Simulation of Concrete Fracture Using ABAQUS

This paper discusses the analytical simulation of crack propagation using the Fictitious Crack Model for notched and unnotched Portland Cement Concrete beam specimens. Parameters such as those controlling the loading conditions, mesh fineness, aspect ratio in the vertical or horizontal directions, and notch to beam thickness ratio are considered. The commercial program ABAQUS is used, and simulations are compared to previous analytical and experimental results. A linear elastic investigation is first conducted to test the agreement of the results with the Timoshenko beam theory. Subsequently, an investigation is conducted to test the built-in fracture mechanics capabilities of ABAQUS for tracking crack propagation. Since these built-in capabilities are found to be inadequate, the creation of a model from basic elements is pursued. This is accomplished by introducing JOINTC elements along the crack plane to model joint interactions. Several series of tabulated results are used to illustrate the advantage of using finite element simulation over conducting laboratory experiments, reflected in the time, effort, and money saved. The application of fracture mechanics to understanding concrete pavement cracking is found to be desirable, practical and feasible. It is argued that the development of a truly mechanistic design procedure hinges on the elimination of long-held empirical concepts, including statistical transfer functions.

Coupling Fully Staggered Grids via Numerical Filtering for Wave Propagation Simulation

The fully staggered grid (FSG) combines multiple standard staggered grids (SSGs) to simulate seismic wave propagation in anisotropic elastic media. However, its accuracy is contingent upon the wavefield’s consistency and continuity across multiple sets of SSGs. In isotropic or weakly anisotropic media, decoupling or weak coupling between the SSGs can lead to wavefield discontinuities at adjacent grid points in the diagonal direction. Issues such as inconsistent source activation, medium parameter discontinuities, and different numerical treatments of boundary conditions over multiple sets of SSGs can exacerbate these problems. While previous methods, such as FD-consistent point source technique and equivalent medium parameterization methods, have partially addressed these issues, they do not completely solve the problem. This study, drawing inspiration from numerical damping techniques used in collocated-grid finite-difference schemes to eliminate odd-even oscillations, introduces an explicit filter operator along the diagonal direction of the FSG. This approach ensures wavefield consistency and continuity across multiple SSGs, improving the accuracy of the FSG scheme. Although this method increases computational costs, it is essential for reliable seismic modeling in anisotropic media.

Feasibility of electron cyclotron resonance heating for high-field and high-density tokamak COMPASS Upgrade

Abstract Electron cyclotron resonance heating is one of the additional heating systems that is going to be installed at the future high-field tokamak COMPASS Upgrade in Prague. Experimental scenarios cover a wide range of operational parameters, thus the designed heating system has to be exceptionally versatile. The simulations of wave propagation in plasma have been performed using the TORBEAM code. The obtained results yield important information about density limitations and other constraints of ECRH at COMPASS Upgrade, which are necessary for the subsequent design phase. A brief description of intended experimental scenarios is provided together with simulations of the influence of ECRH on COMPASS Upgrade plasma. Efforts should be made to prevent high-density discharges in H-mode plasma. If the high densities can be prevented, the 105/140~GHz frequency heating system provides sufficient heating in most experimental scenarios. The utilization of 170 GHz would be beneficial for intermediate magnetic field scenarios as well. In the future, the potential upgrade towards the 200+ GHz systems would help to tackle the problems with natural H-mode density.

Simulation framework for X-ray grating interferometry optimization.

Wave-front propagation simulations have been a tool to design and optimize X-ray interferometry devices. The often used plane wave approaches, however, lack the angular resolution to describe effects like system imperfections or inhomogeneous samples in conjunction with the X-ray source size. We developed a framework that allows to simulate optical components as well as samples with any source size in arbitrary configurations by inducing the mentioned effects within the wave propagation instead of adding intermediate models. The simulation results were able to predict and explain the impact of local grating defects for different focal spot sizes and provided a spectral sampling optimization for image acquisition. The simulation framework can run on GPU, do out-of-memory calculations, and is publicly available on Github.

Chained occurrences of early afterdepolarizations may create a directional triggered activity to initiate reentrant ventricular tachyarrhythmias.

It has been believed that polymorphic ventricular tachycardia (VT) such as torsades de pointes (TdP) seen in patients with long QT syndromes is triggered by creating early afterdepolarization (EAD)-mediated triggered activity (TA). Although the mechanisms creating the TA have been studied intensively, characteristics of the arrhythmogenic (torsadogenic) substrates that link EAD developments to TA formation are still not well understood. Computer simulations of excitation propagation in a homogenous two-dimensional ventricular tissue with an anisotropic conduction property were performed to characterize torsadogenic substrates that potentially form TA. We examined how the configuration of islands (clusters) of myocytes with synchronously chained occurrence of EADs within the tissue, each EAD cluster size and stimulation from different directions impact the TA creation. The presence of EAD clusters within the tissue created local regions of cardiomyocytes maintained at a depolarized membrane potential above 0 mV due to the chained occurrence of EADs. When the local area contained a concave surface border, the TA was created depending on its curvature. We found that the distance of EAD clusters was a critical factor for the development of EAD-mediated TA and polymorphic VT in long QT syndromes, that there existed a region of the distance favorable for the development of TA and VT, and that the TA was always created along the myocardial fiber orientation regardless of stimulating directions. The chained occurrences of EADs may create a directional TA. Our findings provide deeper understandings of the cardiac arrhythmogenic substrates for preventing and treating arrhythmias.

All-mirror wavefront division interferometer for Fourier transform spectrometry across multiple spectral ranges.

We report on the design of an all-mirror wavefront-division interferometer capable of spectroscopic studies across multiple spectral ranges-from the plasma frequencies of metals to terahertz wavelengths and beyond. The proposed method leverages the properties of laser sources with high spatial coherence. A theoretical framework for the interferometer scheme is presented, along with an analytical solution for determining the far-field interference pattern, which is validated through both optical propagation simulations and experimental results. The practical implementation of the spectrometer, using cost-effective off-the-shelf components (knife-edge prisms for separation and recombination), is demonstrated. The system features ultra-broad optical bandwidth, high throughput, simple architecture, dispersion-free operation, and variable arm split ratio. These unique attributes make our approach a prospective alternative to standard Fourier transform spectrometer schemes, specifically tailored to laser-based scenarios. Further, the employed design inherently enables the measurement of the sample's dispersion. In the experimental section, we demonstrate the feasibility of spectroscopic measurements by coupling the system with a supercontinuum source with more than an octave-spanning range (1.5µm - 4.4µm). As a proof-of-concept, an experimental demonstration is provided for various applied spectroscopic studies: transmission measurements of polymers (polypropylene) and gas (methane), as well as reflectance measurements of dried pharmaceuticals (insulin products on a metal surface).

How fine particles alter wave propagation in granular media: insights from micromechanical modelling

This paper presents an attempt to address an intriguing question about the role of fine particles in altering wave propagation in granular media from the micromechanical perspective. Special effort is made to examine whether the state dependency of shear wave velocity can be characterised in a unified manner and to establish micromechanical understanding on the observations from recent physical experiments. To simulate the wave propagation accurately, several novel techniques are used to build the numerical model to a scale comparable to laboratory specimens and to effectively eliminate the near-field effect and boundary reflections. It is shown that, with the presence of fines, the degradation of elastic wave velocity is directly associated with the reduction of coordination number. The dispersion relationship constructed from the space-time data of all particles reveals that even a small quantity of fines can cause severe frequency filtering and attenuation. Tied up with recent experimental work, the unified method of characterising the shear wave velocity by the state parameter in the critical state theory is confirmed by the simulations of both small-strain wave propagation and large-strain triaxial compression tests. At the microscopic level, a sound relationship is found between the mechanical coordination number and the stress-normalised shear wave velocity.

Exploring the Possibility of a Planar Tetracoordinate Boron in BXY3 (X = B, Al, Ga; Y = C, Si, Ge) Clusters: A Theoretical Study.

In this study, we investigated the potential energy surface of BXY3 (X = B, Al, Ga; Y = C, Si, Ge) clusters employing a few global optimization techniques. Remarkably, the global minimum structure obtained for most of the cases revealed a planar tetracoordinate boron atom, shedding light on the inherent stability of this motif. A comparative analysis of the performance of the different global optimization techniques employed is presented, offering insights into their efficacy. Additionally, the overall stability of the obtained global minimum structures is thoroughly examined through Atom-centered Density Matrix Propagation (ADMP) simulations spanning 20 ps at temperatures 300 and 500 K. The aromaticity of the respective clusters is also assessed via Nucleus Independent Chemical Shift (NICS) and Isochemical Shielding Surface (ICSS) calculations, providing valuable information regarding their electronic structure and stability. This comprehensive theoretical investigation contributes to our understanding of the structural properties of these clusters, with implications for their potential applications in various fields of chemistry.

Numerical simulations of fracture propagation in overlying strata for deep underground coal gasification using controlled retraction injection point technology

Numerical simulations of fracture propagation in overlying strata for deep underground coal gasification using controlled retraction injection point technology

Effect of Activation Energy on Detonation Cellular Dynamics and Reinitiation Behaviors

Two-dimensional simulations of detonation propagation in a channel filled with stoichiometric hydrogen–air mixture with unity Lewis number using the chemical-diffusive model (CDM) coupled with compressible Navier–Stokes equations are presented. Specifically, the effect of four activation energies (E=2,4,6, and 10) with CDM on detonation cell structures, cellular dynamics, and reinitiation behaviors is discussed. As E increases, detonation cell size increases and the cellular structure becomes more irregular. Spectral analysis by the auto-correlation function is performed to provide quantitative insights about detonation cell size and irregularity. Furthermore, detailed analysis on the detonation wavefront captures three distinct detonation propagation modes, including stable detonation (E=2), weakly unstable detonation (E=4,6), and highly unstable detonation (E=10). The effect of activation energy in detonation attenuation is further studied through a detonation propagation over a semicylinder obstacle, where two distinct detonation attenuation regimes are captured, including unattenuated detonation transmission (E=2,4) and critical detonation reinitiation (E=6,10). The mechanism of the critical detonation reinitiation event is further examined. It is found that a strong transverse detonation wave forms at higher activation energies after the Mach shock reflection at the bottom wall, which eventually leads to a steady detonation propagation.

Simulation of mixed-mode crack propagation in Mindlin plates by a hierarchical quadrature element method with minimal remeshing

Simulation of mixed-mode crack propagation in Mindlin plates by a hierarchical quadrature element method with minimal remeshing

The effects of jet Lorentz factor on a relativistic astrophysical jet

In this Letter, the numerical simulation of axisymmetric hydrodynamic relativistic jet propagation was performed by solving the hydrodynamic relativistic Euler equation using the computer code PLUTO [Mignone et al., Astrophys. J. Suppl. Ser. 170, 228 (2007)]. The detailed flow features involved in this relativistic jet propagation has been thoroughly discussed in this present numerical study. The effect of the jet Lorentz factor (Γj) on the shock–turbulence interaction has been studied by analyzing the divergence of the Lamb vector (L=ω×U). The strong coexistence of two layers ∇·L<0 and ∇·L>0 enhances the momentum transfer due to energy difference, causing turbulence amplification.

Linear and nonlinear resonant properties of electron gas in n-InSb and graphene layers in terahertz range in bias magnetic fields

Abstract The nonlinear conductivity of 2D electron gas in graphene and 3D electron gas in the narrow-gap n-InSb semiconductor has been simulated in terahertz (THz) range by various methods including the direct quantum approach, the quasi-classical kinetics, and the quasi-relativistic hydrodynamics. These methods yield the same results under the electron temperatures ≤100 K when the kinetic electron effective mass used in the nonlinear hydrodynamics is equal to the effective mass in n-InSb and it is equal to some nonzero mass that depends on 2D electron concentration in the graphene. The linear resonant dependencies of the complex electron conductivity are simulated both from the kinetic theory and from the hydrodynamic one. The kinetic dependencies of the resonant conductivity on frequency coincide with ones obtained from the hydrodynamic theory under realistic electron concentrations and collision frequencies. Thus, the nonlinear hydrodynamic equations are valid to describe the nonlinear dynamics of the electron gas in graphene and in n-InSb. The nonlinear hydrodynamics has been applied for simulations of nonlinear propagation of THz electromagnetic waves through the multilayer structures dielectric - graphene or n-InSb - dielectric placed in a bias magnetic field. The simplest three-layer structures demonstrate the sharp nonlinear switching of the transparency of THz waves and the bistability under relatively low values of amplitudes of the incident electromagnetic wave.

Numerical simulation of sound propagation in shear layer based on linearized lattice Boltzmann method

Numerical simulation of sound propagation in shear layer based on linearized lattice Boltzmann method

Characterisation and 3D modelling of Cast Duplex Stainless Steel microstructure: Application to ultrasonic wave propagation simulations

Characterisation and 3D modelling of Cast Duplex Stainless Steel microstructure: Application to ultrasonic wave propagation simulations

Investigation of the Thickness Effects on Three‐Dimensional Fracture Toughness in Metallic Materials via the Phase‐Field Model

ABSTRACTWith the wide application of large wall‐thickness metallic structures in engineering, there has been a growing focus on the three‐dimensional fracture issues associated with these materials. This article uses the phase‐field model to investigate the impact of thickness on elastic–plastic metallic materials. Initially, the fracture toughness of metallic materials in three dimensions is calculated under elastic deformation. The findings reveal that the outcomes obtained from the phase‐field model remain consistent regardless of thickness, thus confirming its effectiveness. Subsequently, the study delves into the three‐dimensional fracture behavior of metallic materials during plastic deformation. It illustrates how the phase–field model approach enables a thorough simulation of crack propagation within these materials, offering a comprehensive understanding of their fracture behavior. By analyzing the phase‐field contour, the thickness effects of three‐point bending specimens during crack growth are effectively captured. In addition, the dimensionless fracture toughness ratio trends with thickness are compared between phase‐field modeling and experimental results in the open literature, showing good agreement.

Coupled 4D Flow-Geomechanics Simulation to Characterize Dynamic Fracture Propagation in Tight Sandstone Reservoirs.

Although China's low-permeability and tight oil reservoir utilization and newly proven reserves are growing annually, the overall recovery of such reservoirs is generally low. One of the main factors influencing the low recovery is the effect of intricate dynamic fracture propagations on the remaining oil distribution. Constrained by the evolution of an in situ stress field and the accumulation of fluid injection volumes, the growth of dynamic fractures allows a production profile of water breakthrough. To reveal this phenomenon, this paper systematically summarized the workflow of geoengineering integration and took the target block of an oil reservoir in the Changqing oilfield as an example. The numerical simulation model and geomechanical model of the reservoir were established, respectively, by using core analysis and rock mechanics experiments, and the simulation of dynamic fracture propagation under the control of flow-geomechanical coupling mechanisms was carried out. It is found that injection-induced fractures open and propagate under propulsion pressure until they link with natural fractures when the injection pressure surpasses the formation rupture pressure. The natural fractures become effective after long-term water injection and propagate until they connect to hydraulic fractures near a producing well. The study results on the dynamic fracture propagation process have theoretical and practical implications for the characterization of fractures, residual oil production, and water control techniques in tight sandstone reservoirs.