A wide-range thermodynamically consistent constitutive model for dynamic loading of partially saturated porous media

Underwater pulsed spark discharge (UPSD) shock wave focusing is widely used in marine exploration and lithotripsy. However, research on partial elliptical reflectors within restricted space remains limited. This study developed a fluid–structure interaction model using multi-material arbitrary Lagrangian–Eulerian that had been experimentally validated, substituting the arc expansion process generated by spark discharge with an explosive detonation. We compared the effects of spherical and cylindrical explosion sources with different aspect ratios on shock wave propagation, focusing gain, and energy transmission. We analyzed the axial and radial shock wave behaviors of cylindrical explosion sources and assessed their energy conversion efficiency. The results showed that spherical explosion sources had the highest energy conversion efficiency, whereas the transfer efficiency of cylindrical explosion sources decreased with increasing aspect ratios. The paper concludes with an explanation of the directional characteristics of energy propagation from cylindrical explosive sources based on observed energy change trends in water and the elliptical focusing reflector.

To investigate the changes in conditions within a blind roadway when multiple gas explosion sources are simultaneously detonated, the fluid dynamics software Fluent14.0 was used to conduct numerical simulation experiments with different numbers (2 and 3) and varying intervals (5 m, 10 m, and 15 m) of explosion sources. The results revealed that multiple explosion sources in gas explosions generate shock waves that propagate in opposite directions, creating pressure overlap zones within the roadway. The pressure waves and shock waves in these overlap zones continuously couple within the roadway. The number of overlap zones decreases incrementally with each encounter of opposing shock waves in the roadway. Unlike single explosion source models, the pressure at various positions within the roadway in multiple explosion source models oscillates due to the coupling of multiple shock waves, with significant peak pressures occurring at the closed end of the roadway and in the pressure overlap zones. Additionally, the propagation patterns of shock waves and flames within the roadway are not associated with the interval distance between explosion sources, whereas the encounter time, speed, and pressure of shock waves increase with the interval distance.

Antiknock research of reinforced concrete (RC) slabs is often carried out with spherical or nearly spherical explosives, although many explosives used in engineering and military are cylinder shaped. It is known that the shock wave caused by cylindrical explosives varies in different directions, which is quite different from the spherical charge. In this paper, the shock wave propagation characteristics of spherical and cylindrical explosives with different aspect ratios are compared and analyzed. The 2D numerical results show the peak overpressure from the cylindrical explosive is significantly affected by the L/D (length/diameter) ratio. Subsequently, the damage features of RC slabs under spherical and cylindrical explosives with a certain L/D ratio are investigated through an explosion experiment. Finally, the influence of the L/D ratio on the dynamic response of RC slabs under cylindrical explosives is studied by the fully coupled Euler–Lagrange method. The accuracy and reliability of the coupled model are verified by comparing the numerical with experimental results. Based on the experimental and numerical studies, it can be concluded that the explosive shape directly determines the shape of upper surface crater damage, and the spall damage area of RC slabs becomes larger as the L/D increases. For the L/D increases to a certain value, the cylindrical explosive will induce larger spall damage than that induced by spherical charge with the same amount of explosives. Hence, the effect of the cylindrical charge should be considered in the antiknock design of the RC structure.

Underwater explosion is a severe threat to nearby ocean structures, such as underwater construction, floating vessels. The pressure load produced by underwater explosion of explosives consists of shock wave load and the explosion bubble pulsation pressure load. After the detonation, there will be a shock wave propagating radially outwards and it’s followed by a large oscillating bubble. The shock wave has the first damaging effect on adjacent structures. Then, the collapse and high-speed jet of oscillating bubbles will cause the second damage to structures. When there are double explosive sources near a rigid structure, the mutual superposition of shock waves and the interaction between two bubbles may improve the explosive damage. If the distance between one explosive source and the rigid structure is fixed, the damage force produced by double underwater explosions is related to many factors, like the detonation time difference and the distance between two explosive sources. At first, the pressure field in single explosive source case is numerically simulated by using the AUTODYN in this paper. Next, pressure fields of underwater explosion detonated by double sources at the same time and with time difference are calculated, respectively. The flow fields in double explosive sources case are compared with that in single explosive source case. The effect of the detonation time difference and the distance between explosive sources on the damage force is investigated and analysed in detail.

In order to approximate the free-surface motion of an Earth-sized planet subjected to a giant impact, we have described the excitation of body and surface waves in a spherical compressible fluid planet without gravity or intrinsic material attenuation for a buried explosion source. Using the mode summation method, we obtained an analytical solution for the surface motion of the fluid planet in terms of an infinite series involving the products of spherical Bessel functions and Legendre polynomials. We established a closed form expression for the mode summation excitation coefficient for a spherical buried explosion source, and then calculated the surface motion for different spherical explosion source radii a (for cases of a/R= 0.001 to 0.035, R is the radius of the Earth) We also studied the effect of placing the explosion source at different radii r_0 (for cases of r_0/R= 0.90 to 0.96) from the centre of the planet. The amplitude of the quasi-surface waves depends substantially on a/R, and slightly on r_0/R. For example, in our base-line case, a/R= 0.03, r_0/R= 0.96, the free-surface velocity above the source is 0.26c, whereas antipodal to the source, the peak free surface velocity is 0.19c. Here c is the acoustic velocity of the fluid planet. These results can then be applied to studies of atmosphere erosion via blow-off caused by asteroid impacts.

Previous studies examining the response of magnetoelastic materials to shock waves have predominantly focused on applications involving pulsed power generation, with limited attention given to the actual wave propagation characteristics. This study provides detailed magnetic and mechanical measurements of magnetoelastic shock wave propagation and dispersion. Laser generated rarefacted shock waves exceeding 3 GPa with rise times of 10 ns were introduced to samples of the magnetoelastic material Galfenol. The resulting mechanical measurements reveal the evolution of the shock into a compressive acoustic front with lateral release waves. Importantly, the wave continues to disperse even after it has decayed into an acoustic wave, due in large part to magnetoelastic coupling. The magnetic data reveal predominantly shear wave mediated magnetoelastic coupling, and were also used to noninvasively measure the wave speed. The external magnetic field controlled a 30% increase in wave propagation speed, attributed to a 70% increase in average stiffness. Finally, magnetic signals propagating along the sample over 20× faster than the mechanical wave were measured, indicating these materials can act as passive antennas that transmit information in response to mechanical stimuli.

The two-phase model of dry aqueous foam dynamic behavior under the strong shock wave influence is presented under assumption that the foam structure under shock loading is destroyed into a suspension of monodispersed microdrops with the formation of a gas-droplet mixture. The system of equations for the model of aqueous foam includes the laws of conservation of mass, momentum and energy for each phase in accordance with the single-pressure, two-speed, two-temperature approximations in a three-dimensional formulation, taking into account the Schiller–Naumann interfacial drag force and the Ranz–Marshall interfacial contact heat transfer. The thermodynamic properties of air and water forming a gas-droplet mixture are described by the Peng–Robinson and Mie–Grueneisen equations of state. The presence of non-uniform process in height of aqueous foam syneresis, which is due to gravitational forces, is taken into account by setting the distribution of the liquid volume fraction in the foam. An additional consideration of the syneresis process during calculating the intensity of interphase drag forces according to the Schiller–Naumann model was controlled by introducing the parameter depending on the spatial distribution of the initial liquid volume fraction of the foam. The spherical explosion is modeled in the form of the shock wave pulse whose energy coincided with the charge energy of the HE used in the experiments. The problem numerical solution is implemented using the OpenFOAM free software package based on the two-step PIMPLE computational algorithm. The numerical solution of the problem, obtained on the basis of the proposed gas-droplet mixture model, is in satisfactory agreement with the experimental data on a spherical explosion in aqueous foam. The analysis of the spherical shock wave dynamics while its propagation through aqueous foam is given. The causes of the significant decrease in the amplitude and velocity shock waves propagation in the medium under study are investigated.

Spall, the tensile failure of a material due to high stress loading, has been observed in a number of contained and surface explosions. The phenomenon results in a repartition of the initial spherical explosion energy source, yielding a second energy source which is cylindrical and delayed in time. Recent spall models by Day et al. (1983) demanding conservation of momentum have shown the phenomenon to have little contribution to 20-sec surface waves. These models are extended to include the effect of the process on near-source seismograms. The spall model is constrained by observations within the nonlinear regime of the source which bound the mass, momentum, and timing of the process. Comparison of these forward models with the inverse vertical point force source inferred from seismic recordings of a bermed surface explosion yields excellent agreement. The spall model developed from the contained explosion, CHEAT, is used to create synthetic seismograms. Comparisons of these waveforms with those from a Mueller-Murphy contained explosion indicate that the waveform contribution from spall is similar in size to the spherical explosion waveform. The complete synthetic composed of the spall and explosion contribution compares favorably with observational data from the CHEAT experiment in both amplitude and energy distribution.

The nonlinear evolution of hydrodynamically unstable flames is studied numerically within the context of a hydrodynamic model, where the flame is confined to a surface separating the fresh mixture from the hot combustion products. The numerical scheme uses a variable-density Navier–Stokes solver in conjunction with a level-set front-capturing technique for the numerical treatment of the propagating front. Unlike most previous studies that were limited to the weakly nonlinear Michelson–Sivashinsky equation valid for small density changes, the present work places no restriction on the density contrast and thus elucidates the effect of thermal expansion on flame dynamics. It is shown that the nonlinear development leads to corrugated flames with a transverse dimension that is significantly larger than the wavelength corresponding to the most amplified disturbance predicted by the linear theory, and which is determined by the overall size of the system. The flame structure consists of wide troughs and relatively narrow cusp-like crests, and propagates ‘steadily’ at a constant speed, larger than the speed of a planar flame. The propagation speed increases as the cells widen, but eventually reaches a constant value that remains independent of the mixture's composition and of the transverse length. The dependence of the incremental increase in speed on thermal expansion is found to be nearly linear; for realistic values of thermal expansion it may be as large as 15% to 20%. In sufficiently large domains the dynamics is found to be extremely sensitive to background noise that may result, for example, from weak turbulence. Small-scale wrinkles appear sporadically on the flame surface and travel along its surface, causing a significant increase in the overall speed of propagation, up to twice the laminar flame speed.

Evolution of underwater shock wave in far-field regime of electrical wire explosion system over wide range of electric pulse energy

By using the AUTODYN, the study of numerical simulation on pressure field characteristics of underwater explosion detonated by the double explosive sources at the same time shows that a coupled zone with increased pressure appears after the two initial shock waves transmit through each other and at the intersection of the two initial shock waves, the mach wave appears. The transmitted waves diffract around bubbles with a reflected rarefaction wave. The peak pressure in the central area between the two explosive sources is caused by transmitted wave and has dishing isosurface. And the peak pressure outside the two explosive sources is caused by initial shock wave and has spherical isosurface. Coupled peak pressure in the plane of symmetry is two times more than incident peak pressure and with the propagation of shock wave, the ratio of coupled peak pressure and incident peak pressure gradually increases.

Safety of Buried Pressurized Gas Pipelines near Explosion Sources

The dynamic response of polymethyl methacrylate (PMMA) is well understood for one-dimensional planar impact shocks, but limited research has been performed on the response of PMMA under spherical shock loading. In this work, the shock decay of an explosively-driven shock wave into PMMA was experimentally measured. PMMA cubes of various geometries were explosively loaded with an RP-80 detonator to produce the explosive shock wave. High-speed schlieren imaging was implemented to measure the explosively-driven shock wave velocity throughout the PMMA cubes. Photon Doppler velocimetry (PDV) was used to measure the particle velocity imparted by the shock wave at the surface of the cubes. The material shock response was studied at distances from 21.91 to 133.3 mm from the explosive source. The particle velocity history measured by PDV was compared to the wave profile visualized in the high-speed images. The shock wave pulse amplitude decreased with increased distance from the source. The conducted experiments extend the PMMA shock Hugoniot relating to the lower shock and particle velocity regime.

A new method to determine fluid flux at high pressures and temperatures has been developed and used to study serpentinites at subduction zone conditions. Drill cores of a natural antigorite‐serpentinite with a strong foliation were used in multi‐anvil experiments in the range of 2–5 GPa and 450–800°C. Fluids released upon dehydration are fixed by the formation of brucite in an adjacent fluid sink. The amount and distribution of brucite serves as a proxy for fluid flow. In our specific setup the sample reacted with the surrounding fluid sink to form an additional layer of olivine, which has the potential to limit fluid flux within our experiments. For conditions prior to serpentine dehydration we used Al(OH)3 as fluid source. Fluid in this experiment did not migrate through the serpentinite, indicating that serpentine has a low diffusivity. The experiments also show that small deviatoric stresses have an influence on the fluid flux and can cause an anisotropic fluid flux. Comparison between the time scales of the determined fluid flux with fluid production rates indicates fluid pressure buildup during dehydration reactions. Adjacent less permeable layers can inhibit fluid flux and cause fluid pressure buildup even at conditions when an interconnected pore space formed.

The characteristics and parameter dependences of blast loading on solid and porous structures subject to explosions in a confined space are numerically investigated based on a shock tube configuration wherein the explosive source is approximated by a section at the closed end of the tube filled with high pressure gases. Using a four-way coupling compressible gas–solid numerical method, this work reveals the explicit correlations between the wave dynamics and the characteristic features of blast loading during the shock impinging transient state and the long-time steady state. Upon the shock impingement, the blast loading on the solid and porous structures both exhibits impulsive features caused by the reciprocating shock and rarefaction waves with moderate and considerable amplitude declines, respectively. The imprints of first several impulses manifest the complex wave propagations between the closed end of the tube and the surfaces of solid or porous structures. The pressure profile on the solid structure soon transitions into a shape consisting of periodic triangular waves with sharp jump fronts and unvaried amplitudes. In contrast, the peak overpressure and amplitude of impulses experienced by the porous structure undergo a significant decay so that a gradual declining loading defines the long-term blast loading. The differences of blast loading between the solid and porous structure can be attributed to the substantial energy loss due to the gas filtration inside the porous structure which becomes more intensive as the porosity is increased. Compaction of the porous structure also plays a significant role since the receding porous surface contributes to the marked dissipation of reflected waves. We further investigate the parameter dependences of the defining features of the blast loading on the solid and porous structure, including the explosion energy, the space between explosion source and the structure, and the porosity as well.