Optic and X-Ray Investigation of Water Fracture in Rarefaction Wave at Later Stages

Berngardt, A. R.; Bichenkov, E. I.; Kedrinskii, V. K.; Palchikov, E. I.

doi:10.1007/978-3-642-82459-3_18

Cited by 4 publications

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“…Figure 2c shows the scheme of the magma state dynamics [13] corresponding to that described in [12]. It should be noted that this model of the transition from the cavitating state to the foam-like state of the compressed medium owing to explosive unloading agrees with experimental data obtained in accordance with the dynamic HDST scheme [2,5,14] in studying problems of cavitating disintegration of liquid media subjected to pulsed loading. Despite the identity of these processes, however, simulations (and primarily experimental modeling) of the magma state dynamics in "stationary-open" volcanic systems that differ from systems of the above-considered type involve certain difficulties.…”

Section: Hydrodynamic Shock Tubes As Analogs Of the Scheme Of The Presupporting

confidence: 77%

Gas-dynamic signs of explosive eruptions of volcanoes. 1. Hydrodynamic analogs of the pre-explosion state of volcanoes, dynamics of the three-phase magma state in decompression waves

Kedrinskii

2008

J Appl Mech Tech Phy

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Experimental data and results of numerical simulations of the magma state dynamics in explosive eruptions of volcanoes are presented. The pre-explosion state of volcanoes and the cavitation processes developed in the magma under explosive decompression are studied under the assumption that the intensity of explosive volcanoes does not exert any significant effect on the eruption mechanisms. In terms of the structural features of the pre-explosion state, a number of explosive volcanic systems are close to hydrodynamic shock-tube schemes proposed by Glass and Heuckroth. High-velocity processes initiated by shock-wave loading of the liquid may be considered as analogs of natural volcanic processes, which have common gas-dynamic features and common kinetics responsible for their mechanisms, regardless of the eruption intensity.Introduction. Explosive volcanic eruptions comprise a wide range of predictable processes, which primarily involve phase transitions induced by decompression of the liquid magma previously compressed to high pressures. As a consequence, the magma solution containing large amounts of dissolved gases becomes oversaturated. Homogeneous nucleation generates cavitation nuclei growing, in particular, by the mechanism of gas diffusion from the melt. The melt viscosity dynamically increases during the degassing process. At the same time, the mechanisms of many processes that occur in the magma and determine the magma state dynamics and the formation of the flow structure in decompression waves, as well as the character of the eruption proper, remain unclear. As the answers to these questions cannot be unambiguous because the phenomena are extremely complicated and involve many aspects and many scales, a classification of volcanic systems was obviously needed.Apparently, the first classification (in terms of the eruption character) was proposed at the end of the 19th century. In this classification, all known volcanoes were divided into three groups: 1) quiet volcanoes (which produce flowing lava); 2) explosive volcanoes; 3) intermediate volcanoes (violent eruptions followed by lava flows). A physical model was formulated for the initial state of explosive volcanoes, where the magma becomes sufficiently cooled to produce a lava plug blocking the gases and the magma in the volcanic conduit. When the pressure in the conduit reaches a value sufficient to destroy the plug, the hot gases and the magma explode out of the volcano.In 1908, Lacroix refined the notion of explosive volcanoes on the basis of the eruption intensity. In his classification, explosive volcanoes are divided into the following groups (of increasing intensity): Hawaiian (eruptions that rarely have an explosive character), Strombolian (moderate eruptions), Plinian/Vulcanian (strong eruptions), and Pelean (greatest eruptions) volcanoes. A question arises: Are these processes with many aspects governed by identical mechanisms? Obviously, the answer to this question will provide better understanding of the processes inside the magma and allow...

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Section: Hydrodynamic Shock Tubes As Analogs Of the Scheme Of The Presupporting

confidence: 77%

Gas-dynamic signs of explosive eruptions of volcanoes. 1. Hydrodynamic analogs of the pre-explosion state of volcanoes, dynamics of the three-phase magma state in decompression waves

Kedrinskii

2008

J Appl Mech Tech Phy

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“…This value of the concentration corresponds to a rather dense packing of bubbles, and the magma acquires a foam state. One of the currently accepted models of the eruption [7][8][9] predicts that the foam structure of the magma appears directly before magma fragmentation.…”

Section: Crystal Clusters In the Cavitating Magma (Experimental Modelmentioning

confidence: 99%

Gas-dynamic signs of explosive eruptions of volcanoes. 2. Model of homogeneous-heterogeneous nucleation. Specific features of destruction of the cavitating magma

Kedrinskii

2009

J Appl Mech Tech Phy

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The dynamics of state of the crystallite-containing magma is studied within the framework of the gas-dynamic model of bubble cavitation. The effect of crystallites on flow evolution is considered for two cases: where the crystallites are cavitation nuclei (homogeneous-heterogeneous nucleation model) and where large clusters of crystallites are formed in the magma in the period between eruptions. In the first case, decompression jumps are demonstrated to arise as early as in the wave precursor; the intensity of these jumps turns out to be sufficient to form a series of discrete zones of nucleation ahead of the front of the main decompression wave. Results of experimental modeling of an explosive eruption with ejection of crystallite clusters (magmatic "bombs") suggest that a cocurrent flow of the cavitating magma with dynamically varying properties (mean density and viscosity) transforms to an independent unsteady flow whose velocity is greater than the magma flow velocity. Experimental results on modeling the flow structure during the eruption show that coalescence of bubbles in the flow leads to the formation of spatial "slugs" consisting of the gas and particles. This process is analyzed within a combined nucleation model including the two-phase Iordansky-Kogarko-van Wijngaarden model and the model of the "frozen" field of mass velocities in the cavitation zone.The present paper describes the dynamics of the magma flow structure studied in model experiments and the gas dynamics of its bubble state in decompression waves. Specific Features of the Structure of the Bubble Cavitation Zone under the Conditions of Homogeneous-Heterogeneous Nucleation.As was noted in [1, 2], cavitation nuclei can form on crystallites whose volume concentration can be substantially greater than the concentration of gas nuclei; as a result, heterogeneous nucleation proceeds in the melt, in addition to homogeneous nucleation. The gas-dynamic model proposed in [3], which describes the above-mentioned processes, remains valid. The specific feature of the physical formulation of the problem is the fact that the heterogeneous mechanism is "triggered" in each layer after the homogeneous nucleation is completed; at this moment, the initial sizes of all nuclei, regardless of their nature, are assumed to be identical.It follows from calculations (see the initial conditions in [3]) that the flow structure becomes significantly different if the model of homogeneous-heterogeneous nucleation is used. As in usual bubble and cavitating media [4], the incident wave (either a shock wave or a rarefaction wave) is divided into a precursor with the front 1 [curve P (x) in Fig. 1a] propagating in a homogeneous medium with a velocity of sound c 0 and the main perturbation with the front 2 propagating in a bubble medium with a phase velocity of sound c ph . The emergence of heterogeneous nuclei in the melt leads to an increase in their total density by one or two orders, as compared with the case of homogeneous nucleation. The precursor structure becomes subs...

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“…In this case, it is logical to assume that the transformation of rarefaction waves (phases) in a real liquid with regard to inversion is similar to the propagation of shock waves in bubbly media. It also make sense to use the mathematical model of such a medium for describing cavitating liquid [6,27]. This model is a combination of conservation laws for the average density ρ, pressure p, and mass velocity v, and a subsystem describing the dynamics of the bubbly medium state.…”

Section: Mathematical Model Of Cavitating Liquidmentioning

confidence: 99%

“…Changing the right-hand part of (6.3), neglecting the compressibility of the liquid component of the medium (carrier phase), and introducing the spatial variable η = αrk 1/6 under the assumption on validity of Such a "heuristic" approach justified its validity in mathematical modeling of the transformation of shock waves in bubbly systems [29]. The simultaneous solution of (6.4) and (6.5) determines the parameters of rarefaction waves and the dynamics of the cavitation process [4,27,30]. It should be noted that comparison of these approximations with the numerical solutions of the complete system of equations and with experimental data proved that this model provides reliable estimates for the main characteristics of wave processes in cavitating liquids.…”

Section: Mathematical Model Of Cavitating Liquidmentioning

confidence: 99%

Problems of Cavitative Destruction

Hydrodynamics of Explosion

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Optic and X-Ray Investigation of Water Fracture in Rarefaction Wave at Later Stages

Cited by 4 publications

References 0 publications

Gas-dynamic signs of explosive eruptions of volcanoes. 1. Hydrodynamic analogs of the pre-explosion state of volcanoes, dynamics of the three-phase magma state in decompression waves

Gas-dynamic signs of explosive eruptions of volcanoes. 1. Hydrodynamic analogs of the pre-explosion state of volcanoes, dynamics of the three-phase magma state in decompression waves

Gas-dynamic signs of explosive eruptions of volcanoes. 2. Model of homogeneous-heterogeneous nucleation. Specific features of destruction of the cavitating magma

Problems of Cavitative Destruction

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