Explosion Models Research Articles

Light Curves of Type IIP Supernovae from Neutrino-driven Explosions of Red Supergiants Obtained by a Semianalytic Approach

Type IIP supernovae (SNe IIP) mark the explosive death of red supergiants (RSGs), evolved massive stars with an extended hydrogen envelope. They are the most common supernova type and allow for the benchmarking of supernova explosion models by statistical comparison to observed population properties rather than by comparing individual models and events. We construct a large synthetic set of SNe IIP light curves (LCs) using the radiation hydrodynamics code SNEC and explosion energies and nickel masses obtained from an efficient semianalytic model for two different sets of stellar progenitor models. By direct comparison, we demonstrate that the semianalytic model yields very similar predictions as alternative phenomenological explosion models based on 1D simulations. We find systematic differences of a factor of ∼2 in plateau luminosities between the two progenitor sets due to different stellar radii, which highlights the importance of the RSG envelope structure as a major uncertainty in interpreting the LCs of SNe IIP. A comparison to a volume-limited sample of observed SNe IIP shows decent agreement in plateau luminosity, plateau duration, and nickel mass for at least one of the synthetic LC sets. The models, however, do not produce sufficient events with very small nickel mass M Ni < 0.01 M ⊙ and predict an anticorrelation between plateau luminosity and plateau duration that is not present in the observed sample, a result that warrants further study. Our results suggest that a better understanding of RSG stellar structure is no less important for reliably explaining the LCs of SNe IIP than the explosion physics.

Helium as a signature of the double detonation in Type Ia supernovae

ABSTRACT The double detonation is a widely discussed mechanism to explain Type Ia supernovae from explosions of sub-Chandrasekhar mass white dwarfs. In this scenario, a helium detonation is ignited in a surface helium shell on a carbon/oxygen white dwarf, which leads to a secondary carbon detonation. Explosion simulations predict high abundances of unburnt helium in the ejecta, however, radiative transfer simulations have not been able to fully address whether helium spectral features would form. This is because helium can not be sufficiently excited to form spectral features by thermal processes, but can be excited by collisions with non-thermal electrons, which most studies have neglected. We carry out a full non-local thermodynamic equilibrium radiative transfer simulation for an instance of a double detonation explosion model, and include a non-thermal treatment of fast electrons. We find a clear He i λ10830 feature which is strongest in the first few days after explosion and becomes weaker with time. Initially this feature is blended with the Mg ii λ10927 feature but over time separates to form a secondary feature to the blue wing of the Mg ii λ10927 feature. We compare our simulation to observations of iPTF13ebh, which showed a similar feature to the blue wing of the Mg ii λ10927 feature, previously identified as C i. Our simulation shows a good match to the evolution of this feature and we identify it as high velocity He i λ10830. This suggests that He i λ10830 could be a signature of the double detonation scenario.

Parameterization of a ventilation network model for the analysis of mine working emergency ventilation modes

Digital simulation of mine fires and explosions is an important stage in the process of developing technical solutions and measures aimed at improving the safety of personnel involved in underground mining. Correct simulation results determine the effectiveness of decisions in the event of an actual emergency situation. In this regard, due attention should be paid to each stage of the simulation, and especially to the initial stage of model parameterization. This study formulates a general principle for determining the parameters of mine fire and explosion models, in order to assess their development using the AeroNetwork analytical package. Such parameters in the event of a fire are heat and gas (afterdamp) releases. In the event of an explosion, excessive pressure at the shock front in the explosion origin. It has been established that when simulating a fire, it is advisable to use equivalent heat and gas releases determined by the content of combustible components in the combustion origin. In the event of burning mining equipment, these parameters can be calculated on the basis of the technical characteristics of a machine. Furthermore, when simulating an unauthorized explosion of explosives, the excess pressure determined by the dimensionless length of the active combustion area is calculated taking into account the weight and specific heat of an explosive, as well as the geometric parameters of a mine working. When simulating an explosion of a methane-air mixture (firedamp), the excess pressure is calculated taking into account the gas content of rocks in terms of free combustible gases, the length of a blast cut, the size of the area of increased fracturing, and the lower explosive limit of methane. Based on the proposed principle of the parameterization of emergency models, as an example, a model of fire and explosion development in existing extended dead-end workings (more than 1000 m long) passing coaxially to each other at different heights was developed. The numerical simulation of different emergency situations in workings was carried out, taking into account performing mining in difficult mining conditions.

Application of rate sensitive plasticity-based damage model for near and contact explosions

Application of rate sensitive plasticity-based damage model for near and contact explosions

Nanosecond laser-induced filamentous modification in silicate glasses

Laser-induced filamentous modification (LIFM) has been extensively studied in transparent materials and is widely used for cutting and drilling with a high aspect ratio. However, the discussion focuses on the domain of ultra-short pulses recently, such as picosecond and femtosecond pulses. In this work, a LIFM by a short pulse in silicate glasses is demonstrated, and the physical mechanism is investigated. In the soda-lime glass, a filamentous modification with a length of >650 μm was introduced by a nanosecond pulse with an energy of 0.86 mJ. The average length of LIFM is positively correlated with the pulse energy but is not affected by the focus depth significantly. Furthermore, LIFM is also observed in borosilicate glass and K9 glass, but not in fused silica glass. Theoretical analysis shows that the contribution of the self-focusing and optical error to LIMB could be ignored in soda-lime glass. An improved Laser-induced moving breakdown (LIMB) model is proposed to describe LIFM by a nanosecond pulse, and the thermal explosion (TE) model is used to explain the micro-structures. High-density defects dominate the LIMB of nanosecond pulses in silicate glasses, which provide seed electrons for laser-induced ionization and induce a thermal explosion through enhanced absorption. The estimation result of the TE model shows that the final temperature of thermal plasma exceeds 1 × 105 K, resulting in micro-explosion and forming micro-voids and micro-crack clusters. Based on the principle of LIFM, stealth cutting was implemented by a high-frequency nanosecond laser in soda-lime glass with a thickness of 2 mm, and the cutting speed reaches 3000 mm/s.

On the Hα faintness of the North Polar Spur

ABSTRACT The ratio of Hα intensity to 1.4-GHz radio continuum intensity in the North Polar Spur (NPS) is measured to be ≲ 50, two orders of magnitude smaller than the values of ∼104 observed in the typical shell-type old supernova remnants of the Cygnus Loop and S147. The extremely low Hα-to-radio intensity ratio favours the Galactic Centre explosion model for the NPS, which postulates a giant shock wave at a distance of several kiloparsecs in the hot and low-density Galactic halo with a low hydrogen recombination rate, over the local supernova(e) remnant model.

A refined numerical investigation of a large equivalent shallow-depth underwater explosion

The large equivalent shallow-depth explosion problem is very significant in the field of naval architecture and ocean engineering, as such explosions can be used to attack and demolish ships and anti-ship missiles. In the current work, a refined numerical study of the flow-field characteristics of a large equivalent shallow-depth explosion is carried out using a self-developed Eulerian finite element solver. First, the numerical model is validated against theoretical results and a small equivalent explosion test in a tank. The numerical results are found to agree well with the theoretical and experimental results. In the next step, the cavitation cut-off effect is added to the underwater explosion model, and the cavitation phenomenon is quantitatively analyzed through the flow-field pressure. In addition, the dynamic characteristics of the bubble and water hump under various initial conditions for different stand-off parameters are analyzed. The effect of gravity on these physical processes is also discussed. The bubble pulsation period, taking into account the free surface effect, is then quantitatively studied and compared with Cole’s experimental formula for an underwater explosion. Overall, when the stand-off parameter γ &amp;gt; 2, the influence of the free surface on the empirical period of the bubble is not significant. Our investigation provides broad insights into shallow-depth underwater explosions from theoretical, experimental, and numerical perspectives.

Over 500 Days in the Life of the Photosphere of the Type Iax Supernova SN 2014dt

Type Iax supernovae (SNe Iax) are the largest known class of peculiar white dwarf SNe, distinct from normal Type Ia supernovae (SNe Ia). The unique properties of SNe Iax, especially their strong photospheric lines out to extremely late times, allow us to model their optical spectra and derive the physical parameters of the long-lasting photosphere. We present an extensive spectral timeseries, including 21 new spectra, of SN Iax 2014dt from +11 to +562 days after maximum light. We are able to reproduce the entire timeseries with a self-consistent, nearly unaltered deflagration explosion model from Fink et al. using TARDIS, an open source radiative-transfer code. We find that the photospheric velocity of SN 2014dt slows its evolution between +64 and +148 days, which closely overlaps the phase when we see SN 2014dt diverge from the normal spectral evolution of SNe Ia (+90 to +150 days). The photospheric velocity at these epochs, ∼400–1000 km s−1, may demarcate a boundary within the ejecta below which the physics of SNe Iax and normal SNe Ia differ. Our results suggest that SN 2014dt is consistent with a weak deflagration explosion model that leaves behind a bound remnant and drives an optically thick, quasi-steady-state wind creating the photospheric lines at late times. The data also suggest that this wind may weaken at epochs past +450 days, perhaps indicating a radioactive power source that has decayed away.

Quantification of spatial and seasonal trends in the atmosphere and construction of statistical models for infrasonic propagation

SUMMARY Infrasonic waves are influenced by variations in the density, pressure and temperature as well as the ambient winds. Modelling infrasonic propagation can be challenging due to the dynamic nature of the atmosphere as well as the sparseness of measurements which result in variability and notable uncertainty. A framework is presented to quantify spatial and seasonal trends in atmospheric structure via analysis of the effective sound speed profile and identification of temporal trends in the middle atmospheric waveguide produced by the circumpolar vortex winds. Seasonal definitions identifying typical atmospheric structures during the summer, winter and spring/fall transition periods are identified using atmospheric data from 2010 through 2020. Seasonal trend analysis is conducted for a number of locations across the contiguous United States to quantify spatial variations in atmospheric structure that impact infrasonic propagation. For each season and location, empirical orthogonal function analysis is used to reduce the historical archive of atmospheric data into a smaller representative set that can be analysed using numerical tools more efficiently. Infrasonic ray tracing and finite-frequency modal propagation analyses are applied to construct propagation path geometry and transmission loss statistics which are useful in localization and yield estimation for infrasonic sources, respectively. An example application is detailed in which transmission loss statistics are combined with an explosive source model and noise statistics to quantify the capability of a network to detect nearby sources.

Supernova 2020wnt: An Atypical Superluminous Supernova with a Hidden Central Engine

We present observations of a peculiar hydrogen- and helium-poor stripped-envelope (SE) supernova (SN) 2020wnt, primarily in the optical and near-infrared (near-IR). Its peak absolute bolometric magnitude of −20.9 mag (L bol, peak = (6.8 ± 0.3) × 1043 erg s−1) and a rise time of 69 days are reminiscent of hydrogen-poor superluminous SNe (SLSNe I), luminous transients potentially powered by spinning-down magnetars. Before the main peak, there is a brief peak lasting <10 days post explosion, likely caused by interaction with circumstellar medium (CSM) ejected ∼years before the SN explosion. The optical spectra near peak lack a hot continuum and O ii absorptions, which are signs of heating from a central engine; they quantitatively resemble those of radioactivity-powered hydrogen/helium-poor Type Ic SESNe. At ∼1 yr after peak, nebular spectra reveal a blue pseudo-continuum and narrow O i recombination lines associated with magnetar heating. Radio observations rule out strong CSM interactions as the dominant energy source at +266 days post peak. Near-IR observations at +200–300 days reveal carbon monoxide and dust formation, which causes a dramatic optical light-curve dip. Pair-instability explosion models predict slow light curve and spectral features incompatible with observations. SN 2020wnt is best explained as a magnetar-powered core-collapse explosion of a 28 M ⊙ pre-SN star. The explosion kinetic energy is significantly larger than the magnetar energy at peak, effectively concealing the magnetar-heated inner ejecta until well after peak. SN 2020wnt falls into a continuum between normal SNe Ic and SLSNe I, and demonstrates that optical spectra at peak alone cannot rule out the presence of a central engine.

A timescale for placental mammal diversification based on Bayesian modeling of the fossil record

The timing of the placental mammal radiation has been the focus of debate over the efficacy of competing methods for establishing evolutionary timescales. Molecular clock analyses estimate that placental mammals originated before the Cretaceous-Paleogene (K-Pg) mass extinction, anywhere from the Late Cretaceous to the Jurassic. However, the absence of definitive fossils of placentals before the K-Pg boundary is compatible with a post-Cretaceous origin. Nevertheless, lineage divergence must occur before it can be manifest phenotypically in descendent lineages. This, combined with the non-uniformity of the rock and fossil records, requires the fossil record to be interpreted rather than read literally. To achieve this, we introduce an extended Bayesian Brownian bridge model that estimates the age of origination and, where applicable, extinction through a probabilistic interpretation of the fossil record. The model estimates the origination of placentals in the Late Cretaceous, with ordinal crown groups originating at or after the K-Pg boundary. The results reduce the plausible interval for placental mammal origination to the younger range of molecular clock estimates. Our findings support both the Long Fuse and Soft Explosive models of placental mammal diversification, indicating that the placentals originated shortly prior to the K-Pg mass extinction. The origination of many modern mammal lineages overlapped with and followed the K-Pg mass extinction.

Damage mechanisms of full-scale ship under near-field underwater explosion

The near-field underwater explosion produced by the torpedo and other weapons was one of the most critical threats to naval ships. However, most underwater explosion tests were scale models, which would bring dissimilarities between the gravity and strain rate. We carried out a near-field underwater explosion test on a full-scale ship and recorded the dynamic response processes to make up for this shortcoming. The ship damage was mainly embodied in the loss of overall strength and damage of local structures. The Coupled Eulerian–Lagrangian (CEL) method was used to establish the model of the near-field underwater explosion, and the effectiveness of the calculation method was validated. Based on the analysis results, the near-field underwater explosion could be divided into three stages: shock wave and after flow, bubble pulsation, and water jet. The overall strength of the ship was lost under the combined action of these three stages. The “negative pressure” caused by bubble pulsation was the key to the sagging deformation of the ship. This study would guide the production of underwater weapons and ship protection design.

Numerical Simulations of Plasmas Generated by Air Explosion

The explosion process of explosives is very complex, often accompanied by phenomena such as luminescence, heat, and electromagnetic radiation. Many studies have shown that the electromagnetic radiation of explosive explosions is related to plasma generated by explosion. In this paper, through the thermal equilibrium ionization model, the plasma model of explosive explosion is established, the calculation formula of plasma state parameters is obtained, and the plasma dynamics program is written. The numerical simulation analysis of the air explosion conditions is carried out by using the plasma dynamics program, and the relationship between the electron density and conductivity of the air explosion plasma and the mass of explosive and distance are summarized.

Nonlinear fitting based energetic material explosive shock wave pressure action evaluation model

There are many varieties of new developed energetic materials with different capabilities of shock wave pressure action. In order to effectively evaluate the explosive damage power of diverse energetic materials and to make the evaluation model universal, the TNT is used as the basic material, and the evaluation model of the explosive pressure action of energetic materials is established in this paper based on the nonlinear fitting method. Explosion tests of TNT with different charge quantities are carried out under the same test conditions, and the shock wave surface reflection pressure data at different proportional distances are obtained. The evaluation model between the peak pressure of the TNT shock wave and the proportional distances is constructed based on the explosion similarity ratio formula using the nonlinear fitting function. The prediction accuracy of the established model is verified by the typical TNT charge test, and the proposed model is applied to evaluate the explosive pressure effect of energetic materials. Experimental results show that the predication accuracy of the evaluation model for evaluating the explosion shock wave pressure action of energetic materials based on the nonlinear fitting method is higher than 86.5067%, which can meet the requirements of the engineering applications.

Three-body fragmentation dynamics of BrCNq+ (q=3–6) induced by 1-keV electron impact

The three-body fragmentation dynamics of $\mathrm{BrC}{\mathrm{N}}^{q+} (q=3--6)$ produced by 1-keV electron impact has been investigated using the ion momentum imaging technique. Up to 11 three-body Coulomb explosion channels were identified and analyzed. The corresponding kinetic energy release (KER) distributions were obtained and compared with the predictions of the Coulomb explosion model. By means of the Dalitz plot, Newton diagram, and native frame method, we have studied the concerted and sequential fragmentation mechanisms for channels leading to ${\mathrm{Br}}^{l+}+{\mathrm{C}}^{+}+{\mathrm{N}}^{+} (l=1--3)$. The KER for the intermediate dications $\mathrm{Br}{\mathrm{C}}^{2+}$ and $\mathrm{C}{\mathrm{N}}^{2+}$ from the sequential mechanism were determined and the electronic states of the intermediate molecular ion $\mathrm{C}{\mathrm{N}}^{2+}$ were discussed. For the channels leading to higher charge states of the carbon and nitrogen ions, only the concerted fragmentation mechanism was observed.

Analysis of the response characteristics of a roadway wall under the impact of gas explosion

AbstractMine gas explosion causes serious failure (damage) to the roadway, but the research on the response characteristics of the impact load of gas explosion to the roadway wall are still very limited. In view of the shortcomings of the existing research, the LS‐DYNA software is used to establish the physical and mathematical models of gas explosion in a roadway, and the validation results show that the model is effective and reliable. Based on the model, changes of pressure, velocity, displacement of roadway walls and equivalent stress under the impact of gas explosions are measured. The response characteristics of the end and wall of roadway under the thermal impact of gas explosion are analyzed. The results show that the pressure on the closed end wall, the center and edge of the roadway is relatively large, and the wall failure is also relatively more serious. With the propagation of gas explosion, the overpressure on the closed end wall gradually attenuates, and the maximum overpressure region also retracts to the center. At the closed end, the explosion pressure is first loaded on the inner wall and gradually transferred to the outer wall. During the transfer, the pressure decays step by step, and the velocity of the measuring point at the closed end decays continuously. With the propagation of gas explosion, the displacement of each measuring point in the Z direction increases continuously. In the axial direction, the displacement near the center of the roadway is large, and then the displacement decreases in the form of regular rings. The impact load produced by the gas explosion is first loaded onto the closed end wall, resulting in wall deformation and equivalent stress. The study results can provide some theoretical basis and data support for the roadway wall design, and reduction of the wall failure.

Calibration of Impact Ignition from Shear-Band Formation on The Mesoscale

Relying on test results in [1], we proposed in [2] a macroscopic impact ignition model for low velocity impact situations, in terms of the product PD (P=pressure, D=plastic deformation rate). Here we upgrade this model by taking into account the time duration to ignition for different PD levels. Our macroscopic impact ignition model is now based on, and calibrated from, 1D simulations of pure torsion on the mesoscale. We assume that low velocity impact ignition is invoked by shear localization and formation of shear bands. We denote by (PD)L the macroscopic shear localization threshold. When PD&gt;(PD)L in a macroscopic cell, shear bands start to form there. The shear bands then develop and heat up towards the ignition temperature. We further assume that the time duration from localization to ignition h=tig-tL is also dependent on PD. Using 1D simulations of shear band formation in torsion similar to [3], we calibrate (PD)L and h(PD), which we can then use in macroscopic hydrocode simulations. Our mesoscale simulations depend on a realistic strength model for explosives. This model employs the overstress approach to dynamic viscoplasticity [4], and its main feature here is the pressure dependence of its plastic flow curve.

Modelling supernova nebular lines in 3D with extrass

ABSTRACT We present EXplosive TRAnsient Spectral Simulator (extrass), a newly developed code aimed at generating 3D spectra for supernovae in the nebular phase by using modern multidimensional explosion models as input. It is well established that supernovae are asymmetric by nature, and that the morphology is encoded in the line profiles during the nebular phase, months after the explosion. In this work, we use extrass to study one such simulation of a $3.3\, \mathrm{ M}_\odot$ He-core explosion ($M_\text{ejecta}=1.3\, M_\odot$, $E_\text{kin}=1.05\times 10^{51}\,$erg) modelled with the Prometheus-HotB code and evolved to the homologous phase. Our code calculates the energy deposition from the radioactive decay of 56Ni → 56Co → 56Fe and uses this to determine the Non-Local-Thermodynamic-Equilibrium temperature, excitation, and ionization structure across the nebula. From the physical condition solutions we generate the emissivities to construct spectra depending on viewing angles. Our results show large variations in the line profiles with viewing angles, as diagnosed by the first three moments of the line profiles; shifts, widths, and skewness. We compare line profiles from different elements, and study the morphology of line-of-sight slices that determine the flux at each part of a line profile. We find that excitation conditions can sometimes make the momentum vector of the ejecta emitting in the excited states significantly different from that of the bulk of the ejecta of the respective element, thus giving blueshifted lines for bulk receding material, and vice versa. We compare the 3.3 M⊙ He-core model to observations of the Type Ib supernova SN 2007Y.

Dynamic Process and Damage Evaluation Subject to Explosion Consequences Resulting from a LPG Tank Trailer Accident

The involvement of liquefied petroleum gas (LPG), which is highly combustible and explosive, greatly increases risk in road transport. A 3D numerical model was conducted in FLACS, which depicts the dynamic process and variation of combined effects along the multi-directions of LPG explosion under an actual case. With the simulation of scenarios, power-law explosion and fireball models were used to reproduce the results, and the dynamic evolution of specific parameters during the LPG explosion process was analyzed. The results reveal that the LPG explosion’s expansion around the expressway moved along the spaces between obstacles, while conditions at the site of the accident had an enhancement effect on LPG/air mixture accumulation. The propagation trajectory of the shock wave in the horizontal direction presented a regular circle within 623.73 ms, and the overpressure was enough to lead to extensive damage to surrounding structures. Further, shock wave-driven overpressure brought hazards to buildings further afield with multiple peak values. The influence of the LPG explosive fireball evolution is significantly reflected in the injury range of the heat flux; the maximum diameter of the on-site fireball eventually extended to 148.19 m. In addition, the physical effect indicated that the turbulence intensity induced by the surrounding buildings in the accident site significantly promoted the interaction between the shock wave and flame propagation. This research proposes a detailed analysis of damage coupling characteristics caused by an LPG tank trailer explosion integrated with a FLACS-mirrored model, which are useful for blast-resistant design and disposal planning under similar accidental circumstances.

Specific Aspects of Modeling Gas Mixture Explosions in the Atmosphere

Aspects of mathematical and physical modeling of deflagration explosions emerging during atmospheric (outdoor) accidental explosions are addressed. It has been demonstrated that when physically modeling accidental deflagration explosions, a stoichiometric mixture in the shape of a sphere or hemisphere supported by the ground should be used. This allows us to research the parameters of blast loads for the worst-case accidental scenarios or address the accident using the most conservative approach. A technique has been provided allowing one to create a mixture of a given blend composition in the shape of a sphere or hemisphere supported by the ground in outdoor conditions. It has been demonstrated that there is an ability to conduct modeling studies of accidental atmospheric explosions. We have provided examples of modeling studies of accidental atmospheric explosions; a methodology for analyzing experimental results has also been reviewed. The article discusses the mathematical modeling of outdoor (unobstructed) accidental deflagration explosions. It has been demonstrated that it is most reasonable to base computational experiments on linearized (acoustic) equations of continuum motion, as the visible flame propagation rate emerging during explosive combustion is small (compared to the speed of sound). There has been a satisfactory agreement between the numerical analysis and the experimental data.