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The work objective. The paper deals with the issues of modeling biologically inspired movement of an unmanned flying platform (UFP) equipped with flapping wings. Special attention is paid to modeling the interaction of a flapping wing with a resisting air medium. Therefore, the study aim is mathematical modeling of the force which occurs when the wings interact with the resisting medium. The problem to which the paper is devoted. To solve the problem is to make the mathematical model of the rotational motion of drone wing taking into account kinematic and dynamic features of two-coordinate rotation for various angle changing relative to the longitudinal and transverse axes. Research methods. Methods of classical mechanics, theory of motion stability, optimal control, observations, parametric optimization were used to solve the problem. The novelty of the work lies in the algorithms for changing the angles of wings rotation relative to the longitudinal and transverse axes, presented as smooth functions. A method for defining the reduced force arising during the wing movement is proposed. The dependences of the reduced force of wing-air interaction are obtained which provide the development of lifting and traction forces. These forces allow the drone to move in space along a given trajectory. The study results. The modes of flapping wing motion are simulated and the dependences of instantaneous force values which the wing creates during movement are obtained. These forces allow the drone to move in space along a given trajectory. It is shown that the drone movement is controlled by changing the frequency and amplitude of the wing vibrations, as well as by changing the angle of theneutral line inclination relative to which the wing rotates. Conclusions: a model of the reduced force arising from the flapping wing movement is proposed. Dependence graphs of the effective wing area (frontal area) for various parameters of changing rotation angles from time are constructed. Flapping wing motions of the aircraft is simulated. The range of parameters is defined at which the wing movement projections create horizontal F1x and lifting F1z forces at different values of area projections S1x, S1y, S1z.

Peptides play a critical role in the life of organisms, performing completely different functions. The biological activity of some peptides, such as cyclosporins, can be determined by the degree of membrane permeability. Thus, it becomes important to study how the molecule interacts with lipid bilayers. Cyclosporins C, E, H and L were characterised molecular dynamics simulation; NMR spectroscopy studies were also carried out for cyclosporins C and E. The comparison of one- and two-dimensional spectra revealed certain similarities between spatial structures of the studied cyclosporin variants. Upon dissolving in water containing DPC micelles, which serve as model membranes, subtle changes in the NMR spectra appear, but in a different way for different cyclosporins. In order to understand whether observed changes are related to any structural modifications, simulation of the interaction of the peptide with the phospholipid micelle was performed. The onset of the interaction was observed, when the peptide is trapped to the surface of the micelle. Simulations of this kind are also of interest in the light of the well-known membrane permeability of cyclosporin, which is important for its biological action.

Transcriptional regulators select their targets from a large pool of similar genomic sites. The binding of the Drosophila dosage compensation complex (DCC) exclusively to the male X chromosome provides insight into binding site selectivity rules. Previous studies showed that the male-specific organizer of the complex, MSL2, and ubiquitous DNA-binding protein CLAMP directly interact and play an important role in the specificity of X chromosome binding. Here we studied the highly specific interaction between the intrinsically disordered region of MSL2 and the N-terminal zinc-finger C2H2-type (C2H2) domain of CLAMP. We obtained the NMR structure of the CLAMP N-terminal C2H2 zinc finger, which has a classic C2H2 zinc-finger fold with a rather unusual distribution of residues typically used in DNA recognition. Substitutions of residues in this C2H2 domain had the same effect on the viability of males and females, suggesting that it plays a general role in CLAMP activity. The N-terminal C2H2 domain of CLAMP is highly conserved in insects. However, the MSL2 region involved in the interaction is conserved only within the Drosophila genus, suggesting that this interaction emerged during the evolution of a mechanism for the specific recruitment of the DCC on the male X chromosome in Drosophilidae.

Zeipel–Lidov–Kozai cycles is the name given to long-term interrelated changes in the inclinations and eccentricities of the orbits of natural and artificial celestial bodies. They were discovered independently by H. von Zeipel (1910), M. Lidov (1961), and Y. Kozai (1962). Originally, the existence of Zeipel–Lidov–Kozai cycles was established for nonresonant motions of celestial bodies. Approaches to studying such secular effects in the case of resonance of orbital movements appeared much later. It turned out that, at resonance, the Zeipel–Lidov–Kozai cycles may not have the symmetry that these cycles always have in nonresonant situations within the framework of the restricted three-body problem. Moreover, results of numerical studies indicate the presence of asymmetric Zeipel–Lidov–Kozai cycles in the dynamics of a number of Kuiper belt objects moving in resonance with Neptune.

Mefenamic acid has been used as a non-steroidal anti-inflammatory drug for a long time. However, its practical use is quite limited due to a number of side effects on the intestinal organs. Conformational polymorphism provides mefenamic acid with unique properties regarding possible modifications obtained during the micronization process, which can improve pharmacokinetics and minimize side effects. Micronization can be performed by decompression of supercritical fluids; methods such as rapid expansion of the supercritical solution have proven their efficiency. However, this group of methods is poorly applicable for compounds with low solubility, and the modification of the method using a pharmaceutically suitable co-solvent may be useful. In our case, addition of only 2 mol% dimethyl sulfoxide increased the solubility remarkably. Information on the conformational state may be critically important for carrying out micronization. In this work, structural analysis and estimate of conformational preferences of mefenamic acid in dimethyl sulfoxide-d6 (at 25 °C and 0.1 MPa) and in a mixed solvent supercritical carbon dioxide + dimethyl sulfoxide-d6 (45 °C, 9 MPa) were performed based on nuclear Overhauser effect spectroscopy. Results show changes in the conformation fractions depending on the medium used. The importance of allowing for hidden conformers in estimating the conformational state was demonstrated in the analysis. Obtained results may be useful for improving micronization parameters.

Studies of the equation of states (EOS) of different materials at extreme pressures and densities are of great importance for various fields of research. A commonly used method to achieve extreme conditions is shock compression. Shock compression can be achieved by numerous techniques, one of them is the flyer plate which can be accelerated using either explosives, gas guns or pulse magnetic field gradients. In our presentation we will describe the experimental setup and results of accelerating flyer plates using a strong shock wave generated by the underwater electrical explosion of a planar wire array. Explosion of a planar Cu wire array was produced using a µs and sub-µs-timescale generators with stored energies of up to ~6 kJ, delivering to the array a current pulse with amplitudes of up to ∼500 kA with rise time of ~400 ns and ~1 µs, respectively. A Photonic Doppler Velocimetry (PDV) is applied for determining the velocity of a free moving target.

Studies of matter at extreme pressures and densities is the subject of High Energy Density Physics (HEDP) which is of great importance for basic physics, including physics of astrophysical objects and various applications. To conduct such studies in a laboratory environment, different systems with stored energy of >10 5 J are used, namely Z-pinch, plasma focus, powerful pulsed laser system, multistage gas guns, high energy heavy ion beams and chemical explosives.

The article presents a space-time analysis of the seismic wave from a distributed career explosion. The method of direct measurement based on the dynamic model of the wave field is used to form an image of the seismic wave field in the field of quarry explosions. The efficiency of the proposed method is shown by the example of experimental seismic recording processing. The program "Nelumbo" is used to visualize the seismic field, which on the basis of experimental seismic records allows to form an image of the wave field in the space of the hemisphere, the center of which corresponds to the position of the seismometer (registration point). The algorithm of the program "Nelumbo" is based on the Huygens – Fresnel principle and Kirchhoff's theorem. The algorithm of the program allows to allocate from record of a seismic signal frames of a certain duration and to form the image of a wave field in space of a solid angle dimension π. This approach can be used as a tool to analyze the nature of the development of disturbances in the environment and the analysis of environmental risks in the production of blasting.

We present the design and parameters of a compact and mobile high-current pulse generator, which can be applied in the study of warm dense matter in university laboratories. The generator dimensions are 550 × 570 × 590 mm3, the weight is ∼70 kg, and it consists of four “bricks” connected in parallel. Each brick, made up of 2 × 40 nF, 100 kV low-inductance capacitors connected in parallel, has its own multi-gap and multichannel ball gas spark switch, triggered via a capacitively coupled triggering by a positive polarity pulse of ∼80 kV amplitude and ∼15 ns rise time. At a charging voltage of ∼70 kV, the generator produces a ∼155 kA current pulse with a rise time of ∼220 ns on a ∼15 nH inductive short-circuit load and a ∼90 kA amplitude current pulse in the underwater electrical explosion of a copper wire.

This paper contains the description and results of modeling a miniature autonomous underwater robot (MUUV) with an intelligent control system for monitoring reservoirs. The article shows a structural diagram of a prototype robot equipped with a number of sensors. Human-machine interaction described in combined mode when the operator monitors and controls the underwater robot periodically at certain times, while the robot carries out the movements set by the operator, but otherwise the operator does not control the position. Diagrams of the robot's movement when monitoring reservoirs are shown and optimal control algorithms are synthesized. A method for monitoring reservoirs using a mobile underwater robot has been formalized.

Two-dimensional

We examine a 2-DOF Hamiltonian system modeling some previously unexplored dynamical effects in first-order mean motion resonances in the spatial circular restricted three-body problem “star-planet-asteroid.” In distinction from the well-known integrable model of Sessin and Ferraz-Mello (Celest Mech Dyn Astron 32:307–332, 1984) and Wisdom (Celest Mech Dyn Astron 38:175–180, 1986), in our analysis, we kept more terms in the expansion for the disturbing function. This allowed us to study the phenomena caused by coexisting resonant modes, that were lost in the integrable model. In addition, we identified the areas of dynamical chaos in the phase space of the considered system. Despite the non-integrability of our model, we were able to compute analytically many quantities characterizing its dynamical behavior. Finally, we illustrate some of our results through the examples of the known resonant Kuiper belt objects.

The motion of an ornithopter, a flying robot, consisting of a body and two symmetric twolink wings, is considered. The device moves in a vertical plane perpendicular to the longitudinal axis of the robot. All the links of the object form a chain through cylindrical joints with parallel axes. A mathematical model of the ornithopter is developed based on a bird’s flight analysis taking into account the aerodynamic interaction of all the links with the environment. Sequences of flight phases are considered, each of which differs in the direction of motion of the wing links. As a result of numerical simulation, diagrams of the robot’s modes of motion are constructed (ascent, hovering, and descent) and the effect of the amplitude and frequency of oscillation of the wing links, as well as their area, is determined (the same wing area was achieved by varying the length and width of the wings).

Climate change simulation based on 30-member ensemble of Voeikov Main Geophysical Observatory RCM (resolution 25 km) for northern Eurasia is used to drive hydrological model CaMa-Flood. Using this modeling framework, we evaluate the uncertainties in the future projection of the peak river discharge and flood hazard by 2050–2059 relative to 1990–1999 under IPCC RCP8.5 scenario. Large ensemble size, along with reasonably high modeling resolution, allows one to efficiently sample natural climate variability and increase our ability to predict future changes in the hydrological extremes. It has been shown that the annual maximum river discharge can almost double by the mid-XXI century in the outlets of major Siberian rivers. In the western regions, there is a weak signal in the river discharge and flood hazard, hardly discernible above climate variability. Annual maximum flood area is projected to increase across Siberia mostly by 2–5% relative to the baseline period. A contribution of natural climate variability at different temporal scales to the uncertainty of ensemble prediction is discussed. The analysis shows that there expected considerable changes in the extreme river discharge probability at locations of the key hydropower facilities. This suggests that the extensive impact studies are required to develop recommendations for maintaining regional energy security.

This paper focuses on environmental preventive measures aimed at protecting the health of city residents. To achieve this goal it is necessary to improve the efficiency of remote contact monitoring. The paper offers the use of smallsized unmanned aerial vehicles (UAVs) equipped with environmental hazard sensors to improve the efficiency and accuracy of detecting pollution sources of a target zone in real time. A method of high-precision determination of coordinates of the pollution sources has been developed with the use of a combined method of measuring the CO concentration by a mobile gas analyzer and an algorithm for finding the sources of pollution. A model of the flying mobile platform has been simulated taking into account a combined control strategy that includes the use of PID and Fuzzy logic controllers.

The article approaches the issues of application of a group of robots consisting of unmanned aerial systems (UAS), on board of which mobile gas analyzers (MGA) are installed, and a ground-based robotic platform (GRP), on board of which fire extinguishing appliances are located. A method of planning the trajectory of motion of a flying complex to the source of combustion, and modeling its modes of motion associated with the early detection of sources of combustion based on the space sensing and determining the concentration of CO, are proposed. Flight algorithms to the source of combustion have been developed, combining both motions along straight lines and circles, as well as joint interaction of a group of robots, realizing the calculation of control voltages during the movement of a robotic platform depending on the deviation from a given trajectory. The regularities of the guided motion controlled by various methods along a given s-shaped trajectory are revealed; the analysis of the latter showed that fuzzy control under the signal of an optocoupler matrix in comparison with the “deterministic” control in response to a signal of an optocoupler provides an increase in the quality of motion by the criterion “action speed-accuracy”.

The article approaches the use of the unmanned aerial complex application for fire safety systems on the basis of a mobile gas analyzer (MGA), installed on a flying platform. A method is proposed for planning the trajectory of movement of the aerial complex, based on a convertiplane, toward a source of combustion and modeling its modes of motion associated with early detection of combustion sources attributed to sensing the space and estimating the CO concentration scope. A method for determining the coordinates of the source of combustion, implemented with reference to a mobile gas analyzer, has been described. A flight algorithm in the direction of the source of combustion has been developed, combining both types of movement along straight lines and motion in circles.

The results of experimental studies together with numerical and analytical modeling showed that the acceleration of a target by employing the shock compression and water flow generated by the underwater electrical explosion of a wire array can be considered an efficient (up to ∼20%) approach. In experiments, a pulse generator with stored energy of ∼6.5 kJ, current amplitude of ∼380 kA, and rise time of ∼1.2 μs was used for underwater electrical explosion of a copper wire planar array. Streak shadow imaging and photonic Doppler velocimetry were applied to study the time-resolved velocity of the shock in water and an aluminum target in air, respectively. The targets, having different thicknesses and designs, were positioned at variable distances from the array. Experimental results showed that the target velocity evolution is characterized by an ns-timescale rise time peak with a subsequent decrease, which transfers to a μs-timescale increase up to its saturated value. Target velocities of up to 1360 m / s were measured. The experimental, numerical, and analytical modeling results showed that a temporally unmovable barrier, located between the exploding array and the target, allows one to increase the pressure in that location, which leads to higher shock velocity in the target.

We report the results of experiments investigating the implosion of a shock generated by the electrical explosion of a cylindrical aluminum wire array immersed in a >80% hydrogen peroxide/water solution. This solution was chosen as an additional energy source to the supplied electrical energy to generate the imploding flow with higher velocity. The experiments were conducted using a generator with the stored energy of ∼4.8 kJ, delivering to the array a ≤280 kA current rising during ∼1 μs. The backlighted images of the imploding shocks were recorded using a streak camera. Using different diameter wires, the explosion of arrays, characterized by critically damped and under-damped discharges, was studied. The experiments revealed that an array explosion in a 92% H2O2/H2O solution results in the second strong shock generated after the peak of the deposited electrical power, a solid indication of H2O2 detonation. This second shock converges ∼40% faster than the first strong shock generated by the wire explosion. One-dimensional hydrodynamic simulations of the shock convergence in H2O2/H2O solutions support this proposition.

Spectroscopic studies of plasma formed inside a capillary and compressed by a shockwave (SW) generated by the underwater electrical explosion of a spherical wire array (SWA) showed density evolution to be in agreement with those of the model considering the adiabatic compression caused by the SW with a pressure predicted by HD modeling assuming uniformity of the converging SW.1 Studies of converging SW generated by underwater cylindrical wire arrays exploded on ns- and μs timescales, showed that that even in the case of initial azimuthal non-symmetry, the SW self-repairs in the final stages of its motion, leading to a uniform implosion down to the r=30μm.2 To increase liquid compression, the experiments and 1D HD simulations of electrical explosions of SWA arrays in water and glycerol for various stored energy of the pulse generator and sphere diameters were carried out. It was found that the convergence of the SW generated by an exploding array in glycerol is significantly faster than in water. Increasing the initially stored energy (for identical array diameters) or decreasing the sphere diameter (for identical stored energy) leads to an increase in parameters of compressed liquid in the vicinity of the implosion.3 These results are compared with the underwater electrical explosions of SWA on the sub-us-timescale. The time-of-flight of the SW convergence was found to be the same, despite the almost 4 times faster energy density deposition for the shorter timescale. This phenomenon is reproduced by HD modeling showing that the exploding wires' expansion on both timescales results in identical radii when the convergence of the SW becomes self-similar. Thus, to increase the parameters of the compressed water, instead of increasing the energy deposition rate, one must increase the stored energy.

Low Earth orbits (LEO) are known as a region of high space activity and, consequently, space debris highest density. Launcher upper stages and defunct satellites are the largest space debris objects, whose collisions can result in still greater pollution, rendering further space missions in LEO impossible. Thus, space debris mitigation is necessary, and LEO region is a primary target of active debris removal (ADR) projects. However, ADR planning requires at least an approximate idea of the candidate objects' attitude dynamics, which is one of the incentives for our study. This paper is mainly focused on modeling and simulating defunct satellites. The model takes into account the gravity gradient torque and the torque due to eddy currents induced by the interaction of conductive materials with the geomagnetic field. A better understanding of the intermediate phase of the exponential deceleration is achieved owing to a more accurate model of the eddy currents torque than in most prior research. We also show the existence of other important factors in the studied dynamics such as evolution of the orbit itself and the residual magnetic moment, which both contribute to the overall attitude motion evolution and the variety of the final regimes., Comment: A post-conference paper on "Near-Earth Astronomy" submitted to "Open Astronomy" (De Gruyter Open). 10 pages, 24 figures

The results of experimental and numerical research of shockwaves generated by the underwater electrical explosion of a single wire and a planar wire array are reported. Experiments were conducted using a microsecond time scale pulse power generator delivering a 2 × 107 A/cm2); (c) the planar shock velocity can be accelerated using the combustion properties of the Al wires efficiently, and (d) the shock velocity can be enhanced using a metal reflector placed below the array.The results of experimental and numerical research of shockwaves generated by the underwater electrical explosion of a single wire and a planar wire array are reported. Experiments were conducted using a microsecond time scale pulse power generator delivering a 2 × 107 A/cm2); (c) the planar shock velocity can be accelerated using the combustion properties of the Al wires efficiently, and (d) the shock velocity can be enhanced using a metal reflector placed below the array.

We report a direct observation of the microsecond time scale combustion of aluminum realized in underdamped electrical explosions of aluminum wires in the water environment. Experiments were conducted using a pulse power generator delivering a ≤200 kA current amplitude within an ∼1 μs rise-time. Time-resolved spectroscopy was applied to obtain the spectrum of AlO oxide absorption bands, and the temperature of oxides was determined. The results show that decreasing the wire diameter and increasing the discharge current density allow one to decrease the time delay in the appearance of AlO absorption bands to ≤1 μs with respect to the beginning of the wire explosion and significantly increase the rate of aluminum combustion up to ∼1.3 × 103 g/s.

The results of an experimental, analytical, and numerical study of the cylindrical shock wave generated by the underwater electrical explosion of copper and aluminum wires are reported. Experiments were conducted using a microsecond timescale generator delivering ∼180 kA pulses with a 1.2 μs rise time. Shadow streak images were used to study the radial expansion of the exploding wire and the generated shock wave. It was found that the shock wave expansion velocity decreases to the velocity of sound in two stages: a fast stage and then a gradual stage. The fast stage occurs during ∼1.5 μs after the maximum of the resistive voltage is reached, and then, a gradual decrease occurs during several tens of microseconds. It was shown that the duration of the fast stage corresponds to the period of time when the main energy deposition into the wire occurs. Hydrodynamic simulations show that the fast decrease in the shock velocity is related to the evolution of the exploded wire's subsonic expansion, which leads to time/spatial compression of the adjacent water layer. For the gradual decrease stage of the shock wave velocity, we developed a simplified model, which considers uniform water density between the wire boundary and the shock wave front. The results of this model agree satisfactorily with the experimentally obtained shock wave trajectory and radial expansion of the wire.

We present X-ray radiography images showing the propagation of shock waves generated by electrical explosion of a cylindrical arrangement of wires in water driven by pulsed power. In previous experiments [S. N. Bland et al., Phys. Plasmas 24, 082702 (2017)], the merger of shock waves from adjacent wires has produced a highly symmetrical, cylindrical shock wave converging on the axis, where it is expected to produce a high density, strongly coupled plasma ideal for warm dense matter research. However, diagnostic limitations have meant that much of the dynamics of the system has been inferred from the position of the front of the cylindrical shock and timing/spectra of light emitted from the axis. Here, we present a synchrotron-based radiography of such experiments—providing direct quantitative measurements on the formation of the convergent shock wave, the increased density of water on the axis caused by its arrival, and its “bounce” after arrival on the axis. The obtained images are compared with two-dimensional hydrodynamic simulations, which reproduce the observed dynamics with a satisfactory agreement in density values.

(Experimental studies of a spherical converging shock wave (SW) interaction with preliminary formed plasma are presented. The SW was generated by an underwater electrical explosion of a spherical Cu wire array (radius of 15 mm, number of wires of 40, and wire diameter of 0.1 mm) supplied by 240 kA amplitude current pulse with rise time of ∼0.8 μs. The plasma was formed by a 40 Pa propane discharge between the cathode and anode electrodes, placed at the distance of 1.5 mm apart, inside of 2 mm inner diameter quartz capillary located at the equatorial plane of the array. The light emission from the plasma was transferred to the inputs of two spectrometers by optical fiber installed from the one side of the capillary and beam splitter with lenses. The spectral lines intensities at the output of spectrometers were recorded prior and during the SW interaction with plasma by intensified framing 4QuikE cameras and by a photomultiplier tube when one of the spectrometers was used as a monochromator.

Underwater electrical explosion of wire arrays is a promising method of obtaining extreme states of water (T > 1 eV, P > 1010 TPa). These extreme states are obtained in the vicinity of implosion of strong converging shock waves generated by the array explosion. Explosions of cylindrical and spherical wire arrays were studied in which the latter results in higher water parameters due to the shock wave convergence to a smaller region (origin of a sphere as opposed to an axis of a cylinder). Latest results obtained in our laboratory show that one can achieve even higher water parameters with the same amount of stored energy than with the spherical wire array. This is achieved by introducing parabola shaped boundaries (super-spherical geometry) in the space where the generated strong shock wave is propagating. The experimental and numerical results of this recent research will be reported.

The generation of strong (≥30 T) magnetic fields is important for basic research and different applications. The generation of such strong magnetic fields involves high energy (>100 kJ) pulse generators and magnetic fields >100 T are usually obtained by destructive methods. The measurement of such strong magnetic fields involves either Hall probes or B-dots or fiber optic probes. Here we present the results of measuring a pulsed magnetic field of up to 50 T generated by single/three turns coils. The coils were placed in water and supplied by a ∼230 kA current with pulse with rise time of ∼1 μs produced by a pulse generator with stored energy of ∼3 kJ. Due to high Verdet constant of water, the Faraday rotation of the electric field of the laser beam propagating along the axis of the coil was used to measure the time evolution of the magnetic field. In addition, it was shown that this method can be applied to measure the magnetic field's diffusion enhanced due to the fast heating of the metal.

The results of experiments on the ignition of aluminum micro-particles’ combustion by underwater electrical wire explosion (UEWE) are reported. A compact sub-microsecond timescale duration high-current (240 kA) pulsed power generator was used to explode copper and aluminum wires electrically in different aluminum powder suspensions. The combustion of the aluminum micro-particles was characterized by a target time-of-flight method and optical measurements of the exploding wire and aluminum suspension light emission. It was shown that, by using a proper solution and type of aluminum powder, this method allows aluminum micro-particle combustion in the estimated range of 32–79 % efficiency.

The results of experiments involving underwater electrical explosion of different wire arrays using an outer metallic cylinder as a shock reflector are presented. A pulse generator with a stored energy of about 6 kJ, current amplitude ≤ 500 kA, and rise time of 350 ns was used for the wire array explosion. The results of the experiments and of hydrodynamic simulations showed that in the case of a Cu wire array explosion, the addition of the reflector increases the pressure and temperature of the water in the vicinity of the implosion axis about 1.38 and about 1.33 times, respectively. Also, it was shown that in the case of an Al wire array explosion with stainless steel reflector, Al combustion results, and, accordingly, additional energy is delivered to the converging water flow generating about 540 GPa pressure in the vicinity of the explosion axis. Finally, it was found that microsecond time scale light emission that appears with microsecond time scale delay with respect to the nanosecond time scale self-light emission of the compressed water in the vicinity of the implosion axis is related to water bubbles formation which scattered light of exploded wires.

Results of one-dimensional numerical simulations of the parameters of the converging strong shock wave generated by electrical underwater explosions of a cylindrical wire array with different array radii and different deposited energies are presented. It was shown that for each wire array radius there exists an optimal duration of the energy deposition into the exploding array, which allows one to maximize the shock wave pressure and temperature in the vicinity of the implosion axis. The simulation results agree well with the 130-GPa pressure in the vicinity of the implosion axis that was recently obtained, which strongly indicates the azimuthal symmetry of the converging shock wave at these extreme conditions. Also, simulations showed that using a pulsed power generator with a stored energy of ~200 kJ, the pressure and temperature at the shock wave front reaches ~220 GPa and 1.7 eV at 0.1 mm from the axis of implosion in the case of a 2.5 mm radius wire array explosion. It was found that, in spite of the complicated equation of state of water, the maximum pressure at the shock wave front at radius r can be estimated as P ≈ (P*(r*/r)α, where P* is the known value of pressure at the shock wave front at radius r* ≥ r and α is a parameter that equals 0.62±0.02. A rough estimate of the implosion parameters of the hydrogen target after the interaction with the converging strong shock wave is presented as well.

Using streak images of underwater electrically exploding copper, aluminum, and tungsten wires (current densities of 107–108 A/cm2 and energy density deposition of 10–50 kJ/g) and generated weak shocks, the onset of each phase transition, its duration, and the time when the wire explosion occurred were determined. The measured discharge current and resistive voltage were used to calculate the energy and energy density deposition. Using the discharge current waveform and the onset of the strong shock wave, the specific action integral was calculated and compared with published data. The thermodynamic parameters during the wire explosion were calculated using one-dimensional magneto-hydrodynamic simulations coupled with equations of state for water, copper, and aluminum. It was shown that the onset times of weak shocks, in general, cannot be related to the melting or the evaporation of the entire wire.Using streak images of underwater electrically exploding copper, aluminum, and tungsten wires (current densities of 107–108 A/cm2 and energy density deposition of 10–50 kJ/g) and generated weak shocks, the onset of each phase transition, its duration, and the time when the wire explosion occurred were determined. The measured discharge current and resistive voltage were used to calculate the energy and energy density deposition. Using the discharge current waveform and the onset of the strong shock wave, the specific action integral was calculated and compared with published data. The thermodynamic parameters during the wire explosion were calculated using one-dimensional magneto-hydrodynamic simulations coupled with equations of state for water, copper, and aluminum. It was shown that the onset times of weak shocks, in general, cannot be related to the melting or the evaporation of the entire wire.

Results of underwater electrical explosions of spherical wire arrays in water and glycerol on the sub-microsecond timescale are presented and compared to those obtained on the microsecond timescale [Rososhek et al., Phys. Plasmas 24, 122705 (2017)]. The time-of-flight of the converging shockwave was found to be approximately the same, despite almost three times faster energy density deposition into the exploding wires for sub-microsecond timescale explosions. This phenomenon was reproduced by numerical modeling, which showed that the exploding wires' expansion on both timescales results in almost identical radii when the convergence of the shockwave becomes self-similar. Thus, to increase the shockwave convergence velocity and consequently, the parameters of the compressed water near the shockwave implosion origin, instead of increasing the energy deposition rate, one must increase the initially stored energy.

The results of a study of shock wave (SW) generation by means of underwater electrical wire explosion with different exploding wire configurations and two high-current microsecond and submicrosecond timescale generators are presented. By using aperiodical generator discharge, a ~85% and ~15% of the stored electrical energy was transferred to the exploding wire and energy of the generated water flow, respectively. The energy of the water flow is distributed between its internal (~25%) and kinetic (~75%) energies. It was shown that the exploding wire zigzag configuration, confinement of the SW propagation region, and an increase in the rate of the energy deposition into the exploding wire allow one to increase the SW pressure ges10 times that attained with microsecond timescale straight wire explosion. The averaged thermophysical properties of nonideal and weakly degenerated plasma formed as a result of the wire explosion were obtained and summarized.

Results of an investigation of underwater electrical wire explosions using high-power microsecond and nanosecond generators are reported. Different diagnostics, including electrical, optical, and spectroscopic, together with hydrodynamic and magnetohydrodynamic simulations, were used to characterize parameters of the discharge channel and generated strong shock waves. It was shown that the increase in the rate of the energy input into exploding wire allows one to increase wire temperature and amplitude of shock waves. Estimated energy deposition into Cu and Al wire material of up to 200 eV/atom was achieved. The spectroscopic analysis of the emitted radiation has unveiled no evidence for the formation of a shunting plasma channel. Analysis of the generated shock waves shows that ~15% of the deposited energy is transferred into the mechanical energy of the water flow. Also, it was shown that converging shock waves formed by underwater explosion of cylindrical wire arrays can be used to achieve extremely high pressure at the axis of implosion. A pressure up to 0.25 Mbar at 0.1 mm distance from the axis of the implosion at a stored energy of ~4 kj was demonstrated. A model explaining the nature of similarity parameters, which have been phenomenologically introduced in earlier research, was suggested.

Converging strong shock wave, generated by underwater electrical explosion of a spherical wire array, was used to generate plasma inside a copper tube (3 mm outer diameter and 1.4 mm inner diameter) placed at the equatorial plane. The diameter of a spherical wire array consisting of 40 wires each of 100 μm diameter, was 30 mm. The explosion of this array by the current pulse of ∼200 kA in amplitude and rise time of ∼1μs supplied by high-current generator charged up to 27 kV, results in an aperiodic discharge when almost all stored energy was deposited to the exploding wires during ∼0.5 μs. The light emission from the plasma formed inside preliminary evacuated tube was guided by an optical fiber placed inside the tube towards the beam splitter and further to a photomultiplier tube and an imaging spectrometer (2400 grooves/mm) coupled with fast framing 4QuikE camera (the spectral resolution at the CCD of the camera was ∼0.14 A/pixel for λ= 6328 A). The Stark broadening of Cu I spectral lines obtained was used for determination of the plasma electron density and the plasma electron temperature was calculated by the ratio of Cu I spectral lines intensity.

Different methods for measurement of strong underwater shock waves pressure pulses with peak pressures of up to 200 MPa and rise time of tens to hundreds of nanoseconds are described and compared. The experimental techniques include direct methods of pressure measurement using various electromechanical gauges such as quartz, carbon-based, and commercially available PCB gauges, and nondirect methods based on measurement of the velocity of the shock wave such as time-of-flight and fast-streak photography. Advantages and disadvantages of the used gauges and methods are discussed. The shock waves were produced by underwater electrical discharge (discharge current amplitude ≤100 kA, pulse duration ≤5 μs) initiated by an exploding wire. A good correspondence between the pressure amplitudes measured by the various gauges and methods was observed. The obtained dependence of the shock wave pressure on the distance from the discharge channel was found to be best fitted by a r −0.7 law. It is also shown that none of these methods can be used to determine the time evolution of the pressure behind the front of the shock wave.

An electron diode having a ferroelectric plasma cathode (FPS) controlled by optic fibers was operated at a repetition rate of 0.5 Hz during 1 hour, when an accelerating pulse of ~250 kV in amplitude and ~250 ns in duration is applied. The application of the fiber optic decoupling allows easy control and synchronization of the FPS operation with the firing of the HV generator. It was shown that the use of the FPS with fast fall time of the driving pulse allows reproducible generation of an electron beam having a current amplitude of ~1 kA and uniform cross-sectional current density distribution. It was shown also that in the case of the driving pulse ringing, the application of the accelerating pulse during the fall in the negative ringing leads to a plasma pre-filled mode of diode operation due to intense ion emission from the FPS. When the accelerating pulse is applied during the rise in the positive driving pulse ringing, one obtains diode operation with limited plasma emission ability. Only when the accelerating pulse is applied during the fall in the positive ringing of the driving pulse does one obtain diode operation in space-charge limited mode. This dependence of the diode operation on the timing of the accelerating pulse application with respect to the driving pulse is explained by processes related to the screening of ferroelectric bounded surface charges by the plasma charged particles.

Investigation of underwater electrical wire explosions occurring in the time scale of few microseconds requires a measurement of pressure waves with nanosecond rise time and microsecond fall time. Various types of pressure gauges are used for this purpose, however, none of them seems to be suitable for the task since the frequency range of the pressure waves lies between 107 and 109 Hz, whereas all types of mechanical gauges have a bandwidth below 107 Hz. Therefore, a mathematical processing of measurements is required for reconstruction of the actual pressure wave forms. In this article, a signal processing algorithm, based on energy conservation requirements and Fourier analysis, for reconstruction of the wave form of the pressure wave generated under water by electrical explosion of wires is proposed. The gauge used in the experiments is a PCB 119A12 type pressure gauge with a bandwidth below 1 MHz produced by Piezo-Electronics, Inc. Pressure waves were produced by underwater electrical explosion of a thin wire made of Cu by a current pulse with an amplitude of 30–60 kA having a rise time of a 3 μs. It is shown that the error of the gauge in the measurement of the peak pressure is more than 100%, which leads to an error in the estimation of the energy of almost 300%.