Dynamic Source Model Research Articles

Three‐Dimensional Numerical Modeling of Coseismic Atmospheric Dynamics and Ionospheric Responses in Slant Total Electron Content Observations

AbstractDespite routine detection of coseismic acoustic‐gravity waves (AGWs) in Global Navigation Satellite System (GNSS) total electron content (TEC) observations, models of the earthquake‐atmosphere‐ionosphere dynamics, essential for validating data‐driven studies, remain limited. We present the results of three‐dimensional numerical simulations encompassing the entire coupling from Earth's interior to the ionosphere during the 7.8 2016 Kaikoura earthquake. Incorporating the impact of data/model uncertainties in estimating the ionospheric state, the results show a good agreement between observed and simulated slant TEC (sTEC) signals, assessed through a set of metrics. The signals exhibit intricate waveforms, resulting from the integrated nature of TEC and phase cancellation effects, emphasizing the significance of direct signal comparisons along realistic line‐of‐sight paths. By comparing simulation results initialized with kinematic and dynamic source models, the study demonstrates the quantifiable sensitivity of sTEC to AGW source specifications, pointing to their utility in the analysis of coupled dynamics.

A Detailed Understanding of Slow Self‐Arresting Rupture

AbstractRecent numerical simulation studies suggest the existence of a seismic type that is distinct from regular earthquakes—the slow self‐arresting rupture (SSAR). Unlike regular earthquakes that propagate dynamically following the initiation, The SSARs automatically arrest within the nucleation zone without interference. Additionally, numerical simulations indicate that SSARs exhibit a significantly lower energy release compared to regular earthquakes, while also exhibiting a relatively long source duration. Given these distinctive properties, comprehending the source processes of SSARs assumes great strategic importance. However, our current understanding of SSARs, particularly regarding their response to different frictional conditions and their correlation with natural phenomena, remains limited in scope. To further explore the intricacies of SSARs, we employ a three‐dimensional fully dynamic source model to simulate SSARs under various slip‐weakening frictional conditions. The findings indicate that SSARs occur in frictional environments characterized by large normalized critical slip distances, with the seismic source process being primarily influenced by this parameter. Apart from displaying significantly smaller average slip and stress drop, which are two to three orders of magnitude lower than those of regular earthquakes of comparable magnitude, SSARs also showcase a decrease in duration, seismic moment, slip rate, and stress drop as the normalized critical slip distance increases. The moment‐duration scaling law of SSARs exhibits a linear pattern. Moreover, the observation of slow earthquakes offers further implications for the presence of SSARs, indicating their potential association with a wider range of intricate seismic phenomena.

Numerical analysis of static and dynamic heat source model approaches in laser micro spot welding

Numerical analysis of static and dynamic heat source model approaches in laser micro spot welding

Analysis on friction stir welding process of 7022 aluminum alloy

The state of the simulation technology widely used in friction stir welding (FSW) studies requires greater and greater accuracy. An analysis is made of an FSW dynamic heat source model and related information. The model is combined with results from FSW experiments and the welding temperature field. A relationship is obtained for the friction coefficient between the tool and welding materials with temperature. By incorporating tool force measurements and analysis, a simulation model which is much more in line with actual FSW results is thus established. In the simulation process, the temperature of each part of the tool, the material model, fixture constraints, and the role of tool–material forces are analyzed and discussed in detail. In the new model, the different input heats on the advancing and retreating sides on the shoulder, the pin surround, and top of the pin are distinguished. The mechanical properties of the materials with change in temperature and the constitutive equations for the welding, before and after, are obtained. The contact relationship between the fixture and workpiece was built. In the welding process, the forces of the tool toward the welding material were applied. The 7022 aluminum alloy FSW process was simulated by the constructed simulation model. The temperature field, residual stress, and deformation in the simulations were in good agreement with the experiment results.

Modeling of microstructure evolution coupled with molten pool oscillation during electron beam welding of an Al-Cu alloy

The physical understanding of electron beam welding (EBW) and prediction of the weld microstructure are valuable but challenging. In this work, a multi-physics modeling framework is adopted to simulate the microstructure evolution during the EBW process. A molten pool model incorporating multiple driving forces and a dynamic heat source model provides the temperature field as the input for the microstructure simulation. Both the temperature and chemical concentration are considered in the grain growth process. Additionally, an efficient method is adopted to track the second phase in the solidification process, and a practical algorithm is proposed to identify the complex weld shapes. The mechanism of microstructure evolution under the effect of molten pool oscillation is elaborated. Based on the simulated results, the effects of the process parameters on the grain morphology, grain size, segregation and second phase are quantified. These predicted results are compared to experimental observations and measurements. This study could be helpful for both understanding microstructure evolution and optimizing the actual welding process to tailor the microstructure.

Modeling and ex vivo experimental validation of liver tissue carbonization with laser ablation

ObjectiveThe purpose of this study was to model the process of liver tissue carbonization with laser ablation (LA). MethodsA dynamic heat source model was proposed and combined with the light distribution model as well as bioheat transfer model to predict the development of tissue carbonization with laser ablation (LA) using an ex vivo porcine liver tissue model. An ex vivo laser ablation experiment with porcine liver tissues using a custom-made 1064 nm bare fiber was then used to verify the simulation results at 3, 5, and 7 W laser administrations for 5 min. The spatiotemporal temperature distribution was monitored by measuring the temperature changes at three points close the fiber during LA. Both the experiment and simulation of the temperature, tissue carbonization zone, and ablation zone were then compared. ResultsFour stages were recognized in the development of liver tissue carbonization during LA. The growth of the carbonization zone along the fiber axial and radial directions were different in the four stages. The carbonization zone along the fiber axial direction (L2) grew in the four stages with a sharp increase in the initial period and a minor increase in Stage 4. However, the change in the carbonization zone along the fiber radial direction (D2) increased dramatically (Stage 1) to a long-time plateau (Stages 2 and 3) followed by a slow growth in Stage 4. An acceptable agreement between the computer simulation and ex vivo experiment in the temperature changes at the three points was found at all three testing laser administrations. A similar result was also obtained for the dimensions of coagulation zone and ablation zone between the computer simulation and ex vivo experiment (carbonization zone: 2.99± 0.10 vs. 2.78 mm2, 67.39± 0.09 vs. 63.53 mm2, and 90.53± 0.11 vs. 85.15 mm2; ablation zone: 68.95± 0.28 vs. 65.29 mm2, 182.11± 0.24 vs. 213.81 mm2, and 244.80± 0.06 vs. 251.79 mm2 at 3, 5, and 7 W, respectively). ConclusionThis study demonstrates that the proposed dynamic heat source model combined with the light distribution model as well as bioheat transfer model can predict the development of liver tissue carbonization with an acceptable accuracy. This study contributes to an improved understanding of the LA process in the treatment of liver tumors.

Volumetric heat source model for laser-based powder bed fusion process in additive manufacturing

Laser-based powder bed fusion (L-PBF) is one of the most widely used additive manufacturing methods. Its most striking feature is the melt pool in the powder bed, which is formed by a laser heat source. Many physical phenomena occur as a result of the interaction of the heat source with metal powders. Spattering, melting and sintering to each other of the metal powders (phase and shape change), liquid metal movement induced by buoyancy force and surface tension gradient, high evaporation and resulting recoil pressure, fluctuations and deteriorations on the liquid metal surface, plume type structures can be given as examples. The most important point in terms of L-PBF and similar methods is to predict the melt pool dimensions and temperature distribution in the powder bed. However, the phenomena mentioned above complicate the process considerably and require high calculation costs. Volumetric heat sources are a frequently used prescription in terms of simplifying the modeling of the process and reducing the calculation cost. However, such heat source models may contain many non-standard parameters and do not always produce reasonable results. In this study, a dynamic heat source model is presented for use in powder bed systems. Some discussions related to the problems such as uncertainties in absorptivity ratios used in L-PBF are also presented.

General Learning Equilibrium Optimizer: A New Feature Selection Method for Biological Data Classification

ABSTRACT Finding relevant information from biological data is a critical issue for the study of disease diagnosis, especially when an enormous number of biological features are involved. Intentionally, the feature selection can be an imperative preprocessing step before the classification stage. Equilibrium optimizer (EO) is a recently established metaheuristic algorithm inspired by the principle of dynamic source and sink models when measuring the equilibrium states. In this research, a new variant of EO called general learning equilibrium optimizer (GLEO) is proposed as a wrapper feature selection method. This approach adopts a general learning strategy to help the particles to evade the local areas and improve the capability of finding promising regions. The proposed GLEO aims to identify a subset of informative biological features among a large number of attributes. The performance of the GLEO algorithm is validated on 16 biological datasets, where nine of them represent high dimensionality with a smaller number of instances. The results obtained show the excellent performance of GLEO in terms of fitness value, accuracy, and feature size in comparison with other metaheuristic algorithms.

Modelling sagittal and vertical phase differences in a lumped and distributed elements vocal fold model

The quality and timbre of disordered voices heavily rely on the vibration properties of the vocal folds. We discuss the representation of sagittal phase differences in vocal fold oscillations through a numerical biomechanical model involving lumped elements as well as distributed elements, i.e., delay lines. A dynamic glottal source model is proposed in which the fold displacement along the vertical and the sagittal dimensions is modelled using delay lines. In contrast to other models, with which the reproduction of sagittal phase differences is impossible (e.g., in two-mass models) or not easy to control (e.g., in 3D 16-mass and multi-mass models in general), the one proposed here provides direct control over the amount of phase delay between folds’ oscillations at the posterior and anterior part of the glottis, i.e., the sagittal axis, and at the superior and inferior part of the glottis, i.e., the vertical axis, while keeping the dynamic model simple and computationally efficient. The model is assessed by addressing the reproduction of oscillatory patterns observed in high-speed videoendoscopic data, in which sagittal phase differences are observed. Also, timing asymmetry parameters observed in hemi glottal area waveforms (GAWs) are used for fitting.

Numerical Investigation on Molten Pool Dynamics and Defect Formation in Electron Beam Welding of Aluminum Alloy

Penetration depth fluctuations and spiking defects, which appear almost simultaneously during partial penetration electron beam welding (EBW) of aluminum alloy, lead to weakened joint strength. In this study, a novel dynamic heat source model, which can be used to understand the coupling behavior between the electron beam and keyhole wall, is proposed to simulate the EBW process. While studying molten pool patterns, the formation mechanism of weld defects is also discussed in detail. In addition, a corresponding experimental test is carried out as verification. The weld bead profile and dimensions predicted by simulations agree well with the experimental data. The periodic oscillation of the molten pool is the root cause of the penetration depth fluctuations. The simulation results show that spiking defect formation has four crucial steps: keyhole collapse, liquid metal backfilling, cutting by the molten pool boundary and liquid metal backfilling. The findings from this work provide a fundamental understanding of the formation mechanism of the penetration depth fluctuations and spiking defects during EBW of aluminum alloy to improve the weld bead quality.

Modeling dynamic behavior of volatile organic compounds in a zero energy building

With increasing building airtightness, the design of an adequate ventilation system gains importance. The first generation of ventilation systems, based on continuous supply of the nominal airflow rate, are now being replaced by demand controlled ventilation (DCV). These systems, often H2O and/or CO2 controlled, typically do not take into account the emissions of volatile organic compounds (VOCs) to the indoor environment. A small, airtight, zero energy building that has been designed as the Belgian submission to the international Solar Decathlon competition (2011) was rebuilt afterwards in Ostend, Belgium. This building will be used as test facility for the development and validation of a holistic VOC source model. In this study, results are obtained from thermal, airflow and contaminant simulation models of the test facility to check the potential of this facility for research concerning VOCs. The different models and modeling assumptions are discussed. A dynamic VOC source model, derived from literature, is used as proxy to obtain possible VOC concentrations. The results show an important influence of temperature and humidity on the indoor VOC levels with VOC concentrations exceeding health guidelines. It is therefore important to design DCV systems and controls taking into account possible elevated VOC levels and while doing so, incorporate the dynamic behavior (influence of temperature and humidity) of the VOC emissions.

Adaptive model selection in photonic reservoir computing by reinforcement learning

Photonic reservoir computing is an emergent technology toward beyond-Neumann computing. Although photonic reservoir computing provides superior performance in environments whose characteristics are coincident with the training datasets for the reservoir, the performance is significantly degraded if these characteristics deviate from the original knowledge used in the training phase. Here, we propose a scheme of adaptive model selection in photonic reservoir computing using reinforcement learning. In this scheme, a temporal waveform is generated by different dynamic source models that change over time. The system autonomously identifies the best source model for the task of time series prediction using photonic reservoir computing and reinforcement learning. We prepare two types of output weights for the source models, and the system adaptively selected the correct model using reinforcement learning, where the prediction errors are associated with rewards. We succeed in adaptive model selection when the source signal is temporally mixed, having originally been generated by two different dynamic system models, as well as when the signal is a mixture from the same model but with different parameter values. This study paves the way for autonomous behavior in photonic artificial intelligence and could lead to new applications in load forecasting and multi-objective control, where frequent environment changes are expected.

A Dynamic Rupture Source Model for Very Low‐Frequency Earthquake Signal Without Detectable Nonvolcanic Tremors

AbstractA very low‐frequency earthquake is a type of seismic event that is rich in low frequencies and depleted in higher frequencies compared to regular fast local earthquakes of similar magnitude. The source process behind very low‐frequency earthquakes is still poorly understood. Here we present a dynamic rupture source model for very low‐frequency earthquake signal without detectable associated tremors. We show that a single asperity model with sudden stress drop followed by a rate strengthening effect damps the seismic radiation and increases event duration. We compute synthetic seismograms for our source model. The synthetic signal successfully reproduces the features of observed very low‐frequency earthquakes. Moreover, the synthetic very low‐frequency earthquake signal in 0.02–0.05 Hz is not accompanied by detectable tremor signals at 2–8 Hz. Our results help explain why in some cases we observe very low‐frequency earthquakes without accompanying tremor.

Dynamic Rupture Simulations of the 1920 Ms 8.5 Haiyuan Earthquake in China

Abstract The Haiyuan fault is a major seismogenic fault on the northeastern edge of the Tibetan–Qinghai plateau. The 16 December 1920 Ms 8.5 Haiyuan, China, earthquake is the largest and most recent event along the eastern Haiyuan fault (the Haiyuan fault in the article). Because only a few near‐field seismic recordings are available, the rupture process remains unclear. To understand the source process and intensity distribution of the 1920 Haiyuan earthquake, we simulated the dynamic rupture and strong ground motion of said earthquake using the 3D curved‐grid finite‐difference method. Considering the differences in epicenter locations among various catalogs, we constructed two models with different source points. For each model, three versions with different fault geometries were investigated: one continuous fault model and two discontinuous fault models with different stepover widths (1.8 and 2.5 km, respectively). A dynamic rupture source model with a final slip distribution similar to that observed on the ground surface was found. The maximum displacement on the ground surface was ∼6.5 m. Based on the dynamic rupture model, we also simulated the strong ground motion and estimated the theoretical intensity distribution. The maximum value of the horizontal peak ground velocity occurs near Haiyuan County, where the intensity reaches XI. Without considering the site conditions, the intensity values in most regions, based on the dynamic scenarios, are smaller than the values from field investigation. In this work, we present physically based insights into the 1920 Haiyuan earthquake, which is important for understanding rupture processes and preventing seismic hazards on the northeastern boundary of the Tibetan plateau.

Dynamic Source Model for the 2011 Tohoku Earthquake in a Wide Period Range Combining Slip Reactivation with the Short-Period Ground Motion Generation Process

This paper describes a validated dynamic rupture model of the 2011 Tohoku earthquake that reproduces both long-period (20–100 s) and short-period (3–20 s) ground motions. In order to reproduce the observed large slip area (slip asperity), we assign a large Dc (slip critical distance) area following kinematic source inversion results. Sufficiently large slip is achieved through rupture reactivation by the double-slip-weakening friction model. In order to reproduce the strong-motion generation areas (SMGAs), we assign short Dc and large stress-drop areas following empirical Green’s function (EGF) simulation results, which indicate that, although more distant from the hypocenter, SMGA1 ruptured earlier than SMGA2 or SMGA3, which are closer to the hypocenter. This observation is confirmed by the backprojection method. In order to reproduce this important feature in dynamic simulation results, we introduce a chain of small high stress-drop patches between the hypocenter and SMGA1. By systematic adjustment of stress drops and Dc, the rupture reproduces the observed sequence and timing of SMGA ruptures and the final slip derived by kinematic models. This model also reproduces the multiseismic wavefront observed from strong ground motion data recorded along the Pacific coast of the Tohoku region. We compare the velocity waveforms recorded at rock sites along the coastline with one-dimensional (1D) synthetic seismograms for periods of 20–100 s. The fit is very good at stations in the northern and central areas of Tohoku. We also perform finite-difference method (FDM) simulations for periods of 3–20 s, and confirm that our dynamic model also reproduces wave envelopes. Overall, we are able to validate the rupture process of the Tohoku earthquake.

Seismic shaking in the North China Basin expected from ruptures of a possible seismic gap

AbstractA 160 km long seismic gap, which has not been ruptured over ~8000 years, was identified recently in North China. In this study, we use a dynamic source model and a newly available high‐resolution 3‐D velocity structure to simulate long‐period ground motion (up to 0.5 Hz) from possibly worst case rupture scenarios of the seismic gap. We find that the characteristics of the earthquake source and the local geologic structure play a critical role in controlling the amplitude and distribution of the simulated strong ground shaking. Rupture directivity and slip asperities can result in large‐amplitude (i.e., >1 m/s) ground shaking near the fault, whereas long‐duration shaking may occur within sedimentary basins. In particular, a deep and closed Quaternary basin between Beijing and Tianjin can lead to ground shaking of several tens of cm/s for more than 1 min. These results may provide a sound basis for seismic mitigation in one of the most populated regions in the world.

Seismological asperities from the point of view of dynamic rupture modeling: the 2007 Mw6.6 Chuetsu-Oki, Japan, earthquake.

We study the ground motion simulations based on three finite-source models for the 2007 Mw6.6 Niigata Chuetsu-oki, Japan, earthquake in order to discuss the performance of the input ground motion estimations for the near-field seismic hazard analysis. The three models include a kinematic source inverted from the regional accelerations, a dynamic source on a planar fault with three asperities inferred from the very-near-field ground motion particle motions, and another dynamic source model with conjugate fault segments. The ground motions are calculated for an available 3D geological model using a finite-difference method. For the comparison, we apply a goodness-of-fit score to the ground motion parameters at different stations, including the nearest one that is almost directly above the ruptured fault segments. The dynamic rupture models show good performance. We find that seismologically inferred earthquake asperities on a single fault plane can be expressed with two conjugate segments. The rupture transfer from one segment to another can generate a significant radiation; this could be interpreted as an asperity projected onto a single fault plane. This example illustrates the importance of the fault geometry that has to be taken into account when estimating the very-near-field ground motion.

A dynamic welding heat source model in pulsed current gas tungsten arc welding

A time-dependent welding heat source model, which is defined as the dynamic model, was established according to the characteristic of PCGTAW. The parabolic model was proposed to describe the heat flux distribution at the background times. The recommended Gaussian model was used at the peak times due to the bell-shaped temperature contour. The dynamic welding heat source was composed of these two models with a function of time.To assess the validity of the dynamic model, an experiment was conducted in which the pulsed current gas tungsten arc deposits on the plate. From the comparison of the experimental and the simulated values, it can be concluded that the dynamic heat source model, which uses the parabolic model at the background time, is more realistic and accurate under the same welding conditions.

Dynamic simulation of the 1999 Chi‐Chi, Taiwan, earthquake

We apply a modified three‐dimensional finite difference method to investigate the dynamics of the 1999 Chi‐Chi earthquake. We determine the dynamic source rupture process and simulate the strong ground motions over a frequency range of 0.05–0.5 Hz. Our dynamic source model reveals that the rupture process of the Chi‐Chi earthquake is much more complex than that described in the classical propagation rupture models. The Chi‐Chi earthquake rupture process includes the jumping phenomenon. The northern parts on the fault plane have a longer slip duration than the southern parts. The motions on the hanging wall are larger than those on the footwall side, which is a consequence of the asymmetry of the fault with respect to the free surface. In general, the synthetics calculated by the dynamic source model agree well with the observed data. Our dynamic source model reproduces distinctive velocity pulses at stations located in the forward rupture direction and at stations close to the fault surface breaks. The apparent rupture directivity, propagating from south to north, then produces noticeably larger peak ground velocity to the north. These results demonstrate that the dynamic rupture model reproduces the main features of long‐period ground motions. These results may lead to improved understanding of rupture processes accompanying large earthquakes. The dynamic modeling scheme may produce more reasonable and reliable strong ground motion predictions for assessment of seismic hazard.

Correlation Between Local Slip Rate and Local High-frequency Seismic Radiation in an Earthquake Fault

For any earthquake, the slipping fault and the source of high-frequency seismic waves, by and large, coincide. On a more local scale, however, the areas of high seismic slip rate and of increased high-frequency radiation output (seismic luminosity) need not match. To study in some detail how slip rate and seismic luminosity are interrelated, a systematic study is performed that uses 251 records of teleseismic P waves from 23 intermediate-depth earthquakes of magnitude 6.8 and above. From a broadband trace we extract two time histories: (1) displacement and (2) 0.5–2.5 Hz band-passed and squared velocity, or ``HF power'', and calculate correlation coefficient, ρ between the two. To reduce the bias related to formation of P coda, a special procedure is applied to data. We estimated the average value ρ = 0.52 (range of event averages 0.35 to 0.65) for the correlation coefficient between the radiated time histories for displacement and ``HF power'', which is considerably below the ``ideal'' value of unity. We argue that the same or even lower value characterizes the degree of slip rate - seismic luminosity correlation at the fault. Two factors may contribute to the revealed decorrelation: (1) random fluctuations of observed HF power (inevitable for a signal with a limited bandwidth), and (2) the genuine mismatch of slip rate and mean luminosity. We show that these factors, acting separately, would result in the ρ values equal to, correspondingly, 0.72 and 0.80. We also show that genuine decorrelation is statistically significant. We conclude that the observed values of ρ indicate genuine differences between the distributions of the slip rate and the seismic luminosity over the fault area. These results provide important constraints both for the accurate wide-band simulation of strong ground motion and for theoretical dynamic source models.