Wyniki wyszukiwania - BazTech

1

Dynamic displacement tracking in viscoelastic solids by actuation stresses: a one-dimensional analytic example involving shock waves

Irschik Hans, Krommer Michael

Bulletin of the Polish Academy of Sciences. Technical Sciences

|

2023

|

Vol. 71, nr 3

art. no. e144616

EN

A one-dimensional (1D) analytic example for dynamic displacement tracking in linear viscoelastic solids is presented. Displacement tracking is achieved by actuation stresses that are produced by eigenstrains. Our 1D example deals with a viscoelastic half-space under the action of a suddenly applied tensile surface traction. The surface traction induces a uni-axial shock wave that travels into the half-space. Our tracking goal is to add to the applied surface traction a transient spatial distribution of actuation stresses such that the total displacement of the viscoelastic half-space coincides with the shock wave produced by the surface traction in a purely elastic half-space. We particularly consider a half-space made of a viscoelastic Maxwell-type material. Analytic solutions to this tracking problem are derived by means of the symbolic computer code MAPLE. The 1D solution presented below exemplifies a formal 3D solution derived earlier by the present authors for linear viscoelastic solids that are described by Boltzmann hereditary laws. In the latter formal solution, no reference was made to shock waves. Our present solution demonstrates its validity also in the presence of singular wave fronts. Moreover, in our example, we show that, as was also indicated in our earlier work, the actuation stress can be split into two parts, one of them producing no stresses, and the other no displacements in two properly enlarged problems.

2

Time-symmetry breaking in Hamiltonian mechanics. Part 3, A memoir for Douglas James Henderson [1934–2020]

Hoover Wm. G., Hoover C. G.

Computational Methods in Science and Technology

|

2020

|

Vol. 26, No. 4

111--120

EN

Following Berni Alder [1] and Francis Ree [2], Douglas Henderson was the third of Bill’s California coworkers from the 1960s to die in 2020 [1, 2]. Motivated by Doug’s death we undertook better to understand Lyapunov instability and the breaking of time symmetry in continuum and atomistic simulations. Here we have chosen to extend our explorations of an interesting pair of nonequilibrium systems, the steady shockwave and the unsteady rarefaction wave. We eliminate the need for boundary potentials by simulating the collisions of pairs of mirror-images projectiles. The resulting shock and rarefaction structures are respectively the results of the compression and the expansion of simple fluids. Shockwaves resulting from compression have a steady structure while the rarefaction fans resulting from free expansions continually broaden. We model these processes using classical molecular dynamics and Eulerian fluid mechanics in two dimensions. Although molecular dynamics is time-reversible the reversed simulation of a steady shockwave compression soon results in an unsteady rarefaction fan, violating the microscopic time symmetry of the motion equations but in agreement with the predictions of macroscopic Navier-Stokes fluid mechanics. The explanations for these results are an interesting combination of two (irreversible) instabilities, Lyapunov and Navier-Stokes.

3

Time-symmetry breaking in Hamiltonian mechanics. Part 2, A memoir for Berni Julian Alder [1925–2020],

Hoover Wm. G., Hoover C. G.

Computational Methods in Science and Technology

|

2020

|

Vol. 26, No. 4

101--110

EN

This memoir honors the late Berni Julian Alder, who inspired both of us with his pioneering development of molecular dynamics. Berni’s work with Tom Wainwright, described in the 1959 Scientific American [1], brought Bill to interview at Livermore in 1962. Hired by Berni, Bill enjoyed over 40 years’ research at the Laboratory. Berni, along with Edward Teller, founded UC’s Department of Applied Science in 1963. Their motivation was to attract bright students to use the laboratory’s unparalleled research facilities. In 1972 Carol was offered a joint LLNL employee-DAS student appointment at Livermore. Bill, thanks to Berni’s efforts, was already a Professor there. Berni’s influence was directly responsible for our physics collaboration and our marriage in 1989. The present work is devoted to two early interests of Berni’s, irreversibility and shockwaves. Berni and Tom studied the irreversibility of Boltzmann’s “H function” in the early 1950s [2]. Berni called shockwaves the “most irreversible” of hydrodynamic processes [3]. Just this past summer, in simulating shockwaves with time-reversible classical mechanics, we found that reversed Runge-Kutta shockwave simulations yielded nonsteady rarefaction waves, not shocks. Intrigued by this unexpected result we studied the exponential Lyapunov instabilities in both wave types. Besides the Runge-Kutta and Leapfrog algorithms, we developed a precisely-reversible manybody algorithm based on trajectory storing, just changing the velocities’ signs to generate the reversed trajectories. Both shocks and rarefactions were precisely reversed. Separate simulations, forward and reversed, provide interesting examples of the Lyapunov-unstable symmetry-breaking models supporting the Second Law of Thermodynamics. We describe promising research directions suggested by this work.

4

Magnetoacoustic Heating of Plasma Caused by Periodic Magnetosound Perturbations with Discontinuities in a Quasi-Isentropic Magnetic Gas

Perelomova Anna

Archives of Acoustics

|

2020

|

Vol. 45, No. 2

241--251

EN

The magnetoacoustic heating of plasma by harmonic or periodic saw-tooth perturbations at a transducer is theoretically studied. The planar fast and slow magnetosound waves are considered. The wave vector may form an arbitrary angle θ with the equilibrium straight magnetic field. In view of variable θ and plasma-β, the description of magnetosound perturbations and appropriate magnetosound heating is fairly difficult. The scenario of heating depends not only on plasma-β and θ, but also on a balance between nonlinear attenuation at the shock front and inflow of energy into a system. Under some conditions, the average over the magnetosound period force of heating may tend to a positive or negative limit, tend to zero, or may remain constant when the distance from a transducer tends to infinity. Dynamics of temperature specifying heating differs in thermally stable and unstable cases and occurs unusually in the isentropically unstable flows.

5

Transient Heat Flow in a One-component Lennard-Jones/spline Fluid : a Non-equilibrium Molecular Dynamics Study

Hafskjold B.

Computational Methods in Science and Technology

|

2017

|

Vol. 23, No. 3

185--198

EN

A one-component Lennard-Jones/spline fluid at equilibrium was perturbed by a sudden change of the temperature at one of the system’s boundaries. The system’s response was determined by non-equilibrium molecular dynamics (NEMD). The results show that heat was transported by two mechanisms: (1) Heat diffusion and conduction, and (2) energy dissipation associated with the propagation of a pressure (shock) wave. These two processes occur at different time scales, which makes it possible to separate them in one single NEMD run. The system was studied in gas, liquid, and supercritical states with various forms and strengths of the thermal perturbation. Near the heat source, heat was transported according to the transient heat equation. In addition, there was a much faster heat transport, correlated with a pressure wave. This second mechanism was similar to the thermo-mechanical “piston effect” in near-critical fluids and could not be explained by the Joule-Thomson effect. For strong perturbations, the pressure wave travelled faster than the speed of sound, turning it into a shock wave. The system’s local measurable heat flux was found to be consistent with Fourier’s law near the heat source, but not in the wake of the shock. The NEMD results were, however, consistent with the Cattaneo-Vernotte model. The system was found to be in local equilibrium in the transient phase, even with very strong perturbations, except for a low-density gas. For dense systems, we did not find that the local equilibrium assumption used in classical irreversible thermodynamics is inconsistent with the Cattaneo-Vernotte model.

6

Laserowa mikroobróbka materiałów

Sarzyński A., Radziejewska J., Marczak J., Strzelec M., Ostrowski R., Rycyk A., Czyż K.

Elektronika : konstrukcje, technologie, zastosowania

|

2016

|

Vol. 57, nr 11

42--47

PL

Obok wielu różnych zastosowań, promieniowanie laserowe jest stosowane również szeroko w przemyśle do powierzchniowej obróbki różnych materiałów z wykorzystaniem procesów ablacji laserowej. Tematyka ta jest bardzo szeroka. Zespół autorów prowadzi od wielu lat badania nad zastosowaniem powierzchniowej obróbki laserowej w tak różnych obszarach jak konserwacja zabytków (czyszczenie laserowe) czy bioinżynieria (kształtowanie powierzchni implantów). W niniejszym artykule przedstawiono pewien wycinek prac zespołu, związany z opracowaniem laserowej metody badań adhezji cienkich warstw i laserową obróbką materiałów do zastosowań w mikro-przepływach i separacji komórek krwi. W pierwszym przypadku, padające na powierzchnię intensywne promieniowanie laserowe wytwarza silną falę uderzeniową w badanych materiale, pozwalającą określić progowe wartości uszkodzenia warstw technologicznych. Badania uzupełnione są przez modelowanie teoretyczne towarzyszących zjawisk fizycznych. W drugim przypadku uwagę zwraca możliwość separacji krążących komórek nowotworowych na laserowo wykonanych mikrositach, zawierających setki tysięcy otworów o średnicach na poziomie 10 μm na obszarach o obwodzie kilkunastu mm. Wymiary mikrosit pozwalają na ich umieszczenie w układach mikro-przepływowych.

EN

Apart from many different applications, laser radiation is also widely applied in industry for surface treatment of various materials using the laser ablation processes. This subject is very wide. The team of authors is conducting for years research on the application of surface laser micromachining in such diverse areas like conservation of art works (laser cleaning) or bioengineering (shaping of implant’s surface). This paper presents a certain segment of our works, connected with the development of laser method of investigations of thin layers adhesion as well as laser machining of materials for microfluidics and separation of blood cells. The first case represents a laser generation of strong stress wave in the investigated materials, which allows the threshold values of technological layer’s damage. These analyses are supported by numerical modeling of accompanying physical phenomena. The second case directs our attention on the possibility of separation of circulating tumour cells using laser amnyfactured micro-sieves, containing hundreds of thousands of holes with diameters around 10 μm on the areas with dimensions of only dozens square milimeters. These dimensions allow placement of micro-sieves in typical micro-fluidic devices.

7

Generation of shock waves in dense plasmas by high-intensity laser pulses

Pasley J., Bush I. A., Robinson A. P. L., Rajeev P. P., Mondal S., Lad A. D., Ahmed S., Narayanan V., Ravindra Kumar D, Kingham R. J.

Nukleonika

|

2015

|

Vol. 60, No. 2

193--198

EN

When intense short-pulse laser beams (I > 1022 W/m2, τ < 20 ps) interact with high density plasmas, strong shock waves are launched. These shock waves may be generated by a range of processes, and the relative significance of the various mechanisms driving the formation of these shock waves is not well understood. It is challenging to obtain experimental data on shock waves near the focus of such intense laser–plasma interactions. The hydrodynamics of such interactions is, however, of great importance to fast ignition based inertial confinement fusion schemes as it places limits upon the time available for depositing energy in the compressed fuel, and thereby directly affects the laser requirements. In this manuscript we present the results of magnetohydrodynamic simulations showing the formation of shock waves under such conditions, driven by the j × B force and the thermal pressure gradient (where j is the current density and B the magnetic field strength). The time it takes for shock waves to form is evaluated over a wide range of material and current densities. It is shown that the formation of intense relativistic electron current driven shock waves and other related hydrodynamic phenomena may be expected over time scales of relevance to intense laser–plasma experiments and the fast ignition approach to inertial confi nement fusion. A newly emerging technique for studying such interactions is also discussed. This approach is based upon Doppler spectroscopy and offers promise for investigating early time shock wave hydrodynamics launched by intense laser pulses.

8

Pressure waves influence on performance of a pyrotechnically driven device

Górniak A., Kaźmierczak A., Włostowski R., Ptak M.

Journal of KONES

|

2015

|

Vol. 22, No. 3

21--27

EN

This paper contains an experimental investigation of a movable wall with variable shape response to a shock wave. Here, the shock wave was generated by a pyrotechnic gas generator used in the automotive industry. The test station consists on a pyrotechnic actuator in which the movable wall is expressed as a piston. This pyrotechnic actuator was specially design for such type of an investigation. Its design allows withstanding numerous tests without affecting the accuracy. What was under investigation here was the actuators piston stroke velocity and which, as it appeared, changes with respect to the various shape of the actuators interior as well as a corresponding to the barrier velocity total pressure existing within the expansion chamber of the actuator. The results shown here correspond to the flat surface as well as conical and concave cylinder bottom of the actuator. The conical and flat piston surface is considered as a reference for subsequent investigation because such a design is the most similar to the existing pyrotechnically driven designs. The experimental research proves that the performance of pyrotechnically driven devices is dependent upon the shock wave shaping.

9

Remarks on stability of magneto-elastic shocks

Domański W.

Biuletyn Wojskowej Akademii Technicznej

|

2015

|

Vol. 64, nr 4

241-256

EN

The problem of stability of plane shock waves for a model of perfect magneto-elasticity is investigated. Important mathematical properties, like loss of strict hyperbolicity and loss of genuine nonlinearity, and their consequences for the stability of magneto-elastic shocks are discussed. It is shown that some of these shocks do not satisfy classical Lax stability conditions. Both compressible and incompressible models of magneto-elasticity are discussed.

PL

Rozważono problem stabilności fal uderzeniowych dla modelu doskonałej magneto-sprężystości. Przedyskutowano ważne matematyczne własności takie jak utrata ścisłej hiperboliczności i istotnej nieliniowości oraz ich konsekwencje dla stabilności magneto-sprężystych fal uderzeniowych. Pokazano, że pewne z tych fal nie spełniają klasycznego warunku stabilności Laxa. Zanalizowano zarowno ściśliwe jak i nieściśliwe modele magneto-sprężystości.

10

Zastosowanie laserowo indukowanych fal uderzeniowych do badania dynamicznych właściwości materiałów

Radziejewska J., Marczak J., Hoffman J., Sarzyński A., Strzelec M.

Inżynieria Materiałowa

|

2014

|

Vol. 35, nr 6

544--547

PL

W artykule przedstawiono wybrane wyniki prac dotyczących nowej metody badania dynamicznej twardości materiałów i warstw z zastosowaniem laserowego źródła intensywnego promieniowania o nanosekundowym czasie trwania. Fale uderzeniowe wzbudzane w badanych materiałach przez promieniowanie laserowe powodują deformacje plastyczne zachodzące z dużą prędkością odkształceń. Opisano układ eksperymentalny. Zamieszczono wyniki pomiarów amplitudy wzbudzanych fal oraz głębokości odkształcenia powierzchni. Celem prowadzonych eksperymentów było uzyskanie odkształceń plastycznych bez nadtapiania i ablacji powierzchni badanych materiałów i warstw. W badaniach zastosowano przetworniki piezoelektryczne, rejestrujące przebiegi czasowe i amplitudy dynamicznych zmian ciśnienia w badanym materiale. Wykonano pomiary fal naprężeń wzbudzanych w płytkach stalowych i aluminiowych przez impuls laserowy dużej mocy. Uzyskano amplitudę maksymalną około 1600 barów we wnętrzu czujnika, czyli około 10 000 barów we wnętrzu badanych materiałów.

EN

The paper presents selected results of the work on the new test method of dynamic hardness of materials and layers using a laser source of intense radiation of nanosecond duration. The shock waves induced in the test materials by laser radiation cause plastic deformation occurring at high speed deformation. The experimental system is described. The results of measurements of the amplitude of the induced wave and the depth of surface deformation are presented. The aim of the experiments is to obtain plastic deformation without fusing and ablation of the surface of the tested materials and layers. Piezoelectric transducers were used during experiments for recording waveforms and amplitudes of dynamic pressure changes in the material. Measurements of the stress waves induced in the steel and aluminum plates by high-power laser pulse were made. The maximal amplitude of about 1600 bar in the interior of the sensor was obtained, which is about 10 000 bar in the interior of the tested materials.

11

Numerical investigation of the micro radial disk internal combustion engine

Kurec K., Piechna J., Müller N.

Archivum Combustionis

|

2014

|

Vol. 34 nr 1

1—26

EN

This work presents a numerical analysis of the flow and combustion phenomena inside the Radial Disk Internal Combustion Engine. In the set of arch chambers forming the engine disk, a mixture of hydrogen peroxide with hydrogen is burned under constant volume conditions. The thermal decomposition of hydrogen peroxide is used as a pilot and stabilizing process of the hydrogen combustion, addressing effectively important challenges for the small dimensions of the channels. The cycle consists of the filling process preceded by the cooling and separation process that is realized by injection of water steam, the combustion, and the expansion process. In the considered numerical model, the cycle is simulated numerically with the commercial software package FLUENT, including the tracking of species and reaction. The inner rotating part of the engine, the disk, is modeled as a moving grid geometry that exchanges flow streams with ports located in the stationary part of the engine, the housing. The implemented model considers problems of sealing, ignition, and quenching. Results of the simulations are presented in form of pressure, temperature, velocity, and species concentration contours as well as torque variation over time.

12

Kinetic-induced moment systems for the Saint-Venant equations

Gil Montoya D. C., Struckmeier J.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

|

2013

|

Vol.17, No 1-2

63--90

EN

Based on the relation between kinetic Boltzmann-like transport equations and nonlinear hyperbolic conservation laws, we derive kinetic-induced moment systems for the spatially one-dimensional shallow water equations (the Saint-Venant equations). Using Chapman-Enskog-like asymptotic expansion techniques in terms of the relaxation parameter of the kinetic equation, the resulting moment systems are asymptotically closed without the need for an additional closure relation. Moreover, the new second order moment equation for the (asymptotically) third order system may act as a monitoring function to detect shock and rarefaction waves, which we confirm by a number of numerical experiments.

13

Gazodynamika molekularna wyrzutów gazowo-pyłowych oraz problemy pomiarowe identyfikacji ich deskryptorów

Kaim S.

Pomiary Automatyka Kontrola

|

2012

|

R. 58, nr 9

822-824

PL

W pracy przedstawiono mikroskopijne podejście do objaśnienia energetyki procesów molekularnie kinetycznych, które doprowadzają do wyrzutów gazowo-pyłowych w kopalniach węglowych. Badane są termodynamiczne warunki początkowe w pułapce metanu, które przy szybkim jej otwarciu mogą doprowadzić do zjawiska samoprzyspieszenia emisji molekuł metanu i zrodzenia fali uderzeniowej. Analizowane są niezbędne warunki dysocjacji molekuł węgla pod działaniem płaskiej fali uderzeniowej przy jej wyjściu z pułapki metanu do węgla. Generacja metanu, którego ilość znacznie przekracza ilość metanu w warstwie węglowej, wiąże się z częściową dysocjacją molekuł węglowodorów pod działaniem fali uderzeniowej i kolejną molekularyzacją z tworzeniem molekuł metanu i nanoklastrów węgla. Generacji metanu towarzyszą wyrzuty tego gazu. Zagrożenie wyrzutowe calizny węgla wiąże się z jego nanoporowatą strukturą i początkowymi warunkami formowania fali uderzeniowej o wystarczającej intensywności w pułapkach metanowych. Dyskutowane są możliwe metody pomiarów krytycznych parametrów struktury węgla dla oceny stopnia zagrożenia wyrzutowego.

EN

We present a new microscopic interpretation for the energetic properties of the molecular-kinetic processes leading to coal outbursts in collieries. This approach allows clarifying the initial thermodynamic conditions inside of methane trap which at fast opening can lead to a phenomenon of self-strengthening emission of methane molecules and appearance of a powerful shock rarefaction wave. The dissociation necessary conditions of coal molecules under influence of a flat shock wave emerging from methane trap into coal bed, also become clear. The total amount of generated methane considerably exceeds the methane population adsorbed inside of the coal bed, which can be explained by a partial dissociation of hydrocarbon molecules under the influence of a shock wave and subsequent molecularization - producing the methane molecules and carbon nanoclusters. The coal nanoporeous structure in combination with proper initial conditions inside the methane traps may result a development of an intensive shock wave causing an outburst. To estimate the level of outburst danger a variaty of methods of critical parameters measurements inside coal structure being discussed.

14

Analiza procesów kształtujących pole zaburzeń i ruch pocisku na etapie balistyki przejściowej. Cz. 1, Analiza parametrów fal uderzeniowych wytwarzanych w lufie ruchem pocisku

Papliński A.

Problemy Mechatroniki : uzbrojenie, lotnictwo, inżynieria bezpieczeństwa

|

2010

|

Vol. 1, Nr 2 (2)

65-72

PL

W pracy przedstawiona została analiza parametrów pola nadciśnienia, jakie powstaje w wyniku sprężania przez pocisk gazów, które znajdowały się w lufie przed strzałem. Rozpatrywany jest etap, na którym przed czołem pocisku dochodzi do ukształtowania fali uderzeniowej. Przedstawione są zależności charakteryzujące wielkość ciśnienia i gęstości masowej sprężanego uderzeniowo gazu oraz szybkość fali uderzeniowej w funkcji prędkości pocisku.

EN

In the paper evaluation of the parameters of gases compressed by the piston moving in the tube is presented. The relations describing values of the pressure and mass density of the compressed gas as well as velocity of shock wave induced by the projectile moving in the barrel, in dependence of the piston velocity, are presented.

15

Calibration of EM and acoustic antisniper systems

Danicki E.

Biuletyn Wojskowej Akademii Technicznej

|

2009

|

Vol. 58, nr 4

139-147

EN

Antisniper systems exploit numerous sensors (acoustic or electromagnetic, EM) which spatial coordinates should be known with great accuracy, otherwise the system performance can be significantly deteriorated. Triangulation of many sensors is not, however, an easy task, particularly under possible enemy fire. Here, we propose a method exploiting a round of calibration shooting over the system, which measured by the sensors provide data for evaluation of the sensors' spatial positions. The method can be applied for calibration of the Doppler radar antisniper sensors presented here in certain basic arrangement, and the acoustic microphone system measuring the shock wave generated by supersonic bullet.

PL

Antysnajperskie systemy wykorzystują pewną liczbę czujników (akustycznych lub mikrofalowych), współrzędne, których winny być znane z dużą dokładnością, w przeciwnym razie ich skuteczność będzie znacznie ograniczona. Triangulacja wielu czujników nie jest prostym zadaniem, w szczególności, jeśli miałaby być dokonana pod nieprzyjacielskim ogniem. Tu proponujemy pewną metodę wykorzystującą serię wystrzałów kalibracyjnych ponad rozsianymi w polu czujnikami, których pomiary pozwalają na określenie ich położenia. Metoda może być wykorzystana dla kalibracji systemu opartego na radarach Dopplerowskich prezentowanych w pewnej podstawowej konfiguracji, albo w systemach akustycznych, mierzących falę uderzeniową generowaną przez naddźwiękowe pociski.

16

Anisotropic damage evolution in shock wave-loaded viscoplastic plates

Stoffel M.

Archives of Mechanics

|

2008

|

Vol. 60, nr 4

285-301

EN

In the design of structural elements, which are used for protection against explosions, the damage evolution until failure has to be predicted in numerical simulations. However, in the literature a wide variety of damage models is available based on different approaches, e.g. phenomenological and micromechanical theories. Furthermore, the consequences of connections between new damage models and the constitutive equations accounting for elastic-viscoplasticity are unclear. The same problem occurs if structural theories, involving hypotheses, are combined with damage laws. In order to verify the calculated results, experiments with structures subjected to pressure waves are necessary. For this reason, an experimental validation method by means of shock tubes is used in the present study to verify the isotropic and anisotropic damage models. The measured deformations and experimentally observed failure modes can then be compared to the simulated results.

17

Propagation of spherical shock waves in a dusty gas with radiation heat-flux

Singh K. K., Vishwakarma J. P.

Journal of Theoretical and Applied Mechanics

|

2007

|

Vol. 45 nr 4

801-817

EN

The propagation of spherical shock waves in a dusty gas with radiation heat-flux and exponentially varying density is investigated in the paper. The equilibrium flow conditions are assumed to be maintained, and the radiation is considered to be of a diffusion type for an optically thick grey gas model. The shock wave moves wit h variable velocity and the total energy of the wave is non-constant. Non-similar solutions are obtained, and the effects of variation of the radiation parameter and time are investigated. The effects of an increase in (i) the mass concentration of solid particles in the mixture and (ii) of the ratio of the density of solid particles to the initial density of gas on the flow variables in the region behind the shock are also investigated.

PL

W pracy zajęto się problemem propagacji sferycznych fal uderzeniowych o wykładniczym rozkładzie gęstości w zanieczyszczonym gazie z uwzględnieniem radiacyjnej wymiany ciepła. Założono równowagowe warunki przepływu czynnika, a samą radiację przyjęto typu dyfuzyjnego w modelu optycznie nieprzezroczystego gazu. Fala uderzeniowa przemieszcza się ze zmienną prędkością, a całkowita energia fali również się zmienia. W analizie otrzymano rozwiązania niepodobne przy rozważaniu wpływu czasu i zmienności strumienia radiacji. Zbadano ponadto efekt wzrostu koncentracji masy cząstek stałych zanieczyszczenia oraz stosunku gęstości tych cząstek do początkowej gęstości gazu na parametry przepływu w obszarze bezpośrednio za czołem fali.

18

Self-similar solution of a shock propagation in a non-ideal gas

Vishwakarama J. P., Chaube V., Patel A.

International Journal of Applied Mechanics and Engineering

|

2007

|

Vol. 12, no 3

813-829

EN

Similarity solutions for one-dimensional unsteady self-similar flow behind a strong shock driven out by a cylindricaI (or spherical) piston in a medium which is assumed to be a non-ideaI gas obeying a simplified van der Waals equation of state are obtained. Both the cases, when the flow between the shock and the piston is isothermal or adiabatic, are considered. It is observed that the assumption of zero temperature gradient brings a profound change in the density distribution as compared to that of the adiabatic flow; whereas the pressure and velocity distributions are little affected. Effects of the non-idealness of the gas on the flow-field between the shock and the piston are investigated. It is found that there is a decrease in the shock strength due to non-ideaIness of the gas. This decrease in the shock strength is interpreted as a result of a decrease in the compressibility of the gas.

19

Magnetogasdinamic cylindrical shock wave in a rotating gas with variable density

Vishwakarama J. P., Vishwakarama S.

International Journal of Applied Mechanics and Engineering

|

2007

|

Vol. 12, no 1

283-297

EN

Similarity solutions are obtained for one-dimensional adiabatic flow behind a magnetogasdynamic cylindrical shock wave propagating in a rotating a medium in presence of a variable or constant azimuthal magnetic field. The density of the medium ahead of the shock is assumed to be varying and obeying a power law. In order to obtain the similarity solutions the angular velocity of the ambient medium is assumed to be decreasing as the distance from the axis increases. Effects of an increase of the Alfven-Mach number and the variation of the initial den sity, initial magnetic field and initial angular velocity of the medium, on the flow-field behind the shock, are obtained.

20

Piezoelectric Cut Exposed to Shock Wave

Klusáček M., Majzlík J., Vágenknecht J.

Central European Journal of Energetic Materials

|

2007

|

Vol. 4, nr 3

95-104

EN

This paper deals with the problem of transformation and practical utilisation of explosion energy. A principle has been suggested and described that enables utilisation of detonation energy of condensed explosive used as energy source exerting shock wave strain upon piezoelectric sample cut prepared from the oxide system PbO-TiO2-ZrO2. The piezoceramic transducer used as generator of impulse electric charge is characterised by several favourable properties. In particular, they include readiness, large temperature and time ranges of functional parameters, variability of working regime, and relatively low price. The given system serves as efficient source of short-time prompt capacity electrical impulse, which can find application in a number of electro-physical disciplines.