Underwater Electrical Explosion Research Articles

Underwater electrical wire explosions under different discharge types: An experimental study with high initial energy storage

In this study, underwater electrical explosions of aluminum wires of various sizes were carried out with an initial energy storage of ∼53.5 kJ. Two piezoelectric probes were adopted to record the pressure waveforms. The experiments were divided into different discharge types, and the statistical properties of the electrical and shock-wave parameters of the different discharge types were compared. The experimental results show that there are three discharge types, called type A (breakdown type), type B (transition type), and type C (matched type). The three types differ in the resistance characteristics of the plasma channel during the plasma growth process, which are determined from the average electrical field strength and the remaining energy in the circuit at the peak voltage. Shock waves from type C discharges are more likely to exhibit a higher peak pressure, a larger impulse, and a higher energy density than the other types. However, using a matched wire that matches a specific discharge type, a high peak pressure, large impulse, and high energy density can also be achieved under type A or type B discharges. For example, the maximum peak pressures at ∼33 cm under type B and type C discharges are 38.7 and 42.4 MPa, respectively. These results provide significant guidance for load selection in underwater electrical wire explosion engineering applications.

Multi frame radiography of supersonic water jets interacting with a foil target

Pulsed-power-driven underwater electrical explosion of cylindrical or conical wire arrays produces supersonic water jets that emerge from a bath, propagating through the air above it. Interaction of these jets with solid targets may represent a new platform for attaining materials at high pressure (>1010 Pa) conditions in a university-scale laboratory. However, measurements of the internal structure of such jets and how they interact with targets are difficult optically due to large densities and density contrasts involved. We utilized multi-frame x-ray radiographic imaging capabilities of the ID19 beamline at the European Synchrotron Radiation Facility to explore the water jet and its interaction with a 50 μm thick copper foil placed a few mm from the surface of water. The jet was generated with a ∼130 kA-amplitude current pulse of ∼450 ns rise time applied to a conical wire array. X-ray imaging revealed a droplet-type structure of the jet with an average density of <400 kg/m3 propagating with a velocity of ∼1400 m/s. Measurements of deformation and subsequent perforation of the target by the jet suggested pressures at the jet–target interface of ∼5 × 109 Pa. The results were compared to hydrodynamic simulations for better understanding of the jet parameters and their interaction with the foil target. These results can be used in future research to optimize the platform, and extend it to larger jet velocities in the case of higher driving currents supplied to the wire array.

Electrothermal instability in different modes of underwater electrical wire explosion

Electrothermal instability and its effect on the uniformity of discharge channels during underwater electrical wire explosions at different energy deposition rates have been investigated. According to the liquid–vapor transition mechanism, we classified underwater electrical explosion into “phase explosion mode” and “supercritical mode.” Two sets of experiments corresponding to the two modes were conducted, and the exploding wires were observed by a shadow imaging system. Results showed that a bamboo-shaped discharge channel was formed in the phase explosion mode, whereas the discharge channel in the supercritical mode was a uniform cylinder. Self-consistent magnetohydrodynamic simulation results indicated that exploding wires transfer into liquid–vapor coexistence phase in the phase explosion mode, accompanied by a rapid increase in the density perturbation and the formation of bamboo-shaped structures. Moreover, a small perturbation model was derived to analyze the electrothermal instability in different thermodynamic states. It was indicated that the density perturbation is easier to grow in the liquid–vapor coexistence state than the supercritical state, which provides a theoretical explanation for the differences between the two electrical explosion modes.

Underwater electrical explosion of metallic wire and tube: A comparison study

With an initial energy storage of approximately 53.5 kJ, experiments on underwater electrical explosions of metallic wire and thin-wall tube were conducted. Two sets of controlled experiments were designed, and the wire and tube for each set were of the same length, cross-sectional area, and material. Load voltage, circuit current, and shock wave pressure were measured and analyzed, and electric power, energy deposition, and energy deposition rate were also calculated and investigated. Experimental results indicated that the underwater electrical tube explosion (UETE) always has higher and earlier local resistance peak, voltage peak, and electric power peak, as well as faster phase transition and ionization process than the underwater electrical wire explosion (UEWE). In addition, the energy deposition rate from the beginning of discharge or the decrease in current to the voltage peak is significantly increased when replacing a wire with a tube. For the shock-wave characteristics, the peak pressure, energy density, and impulse of the shock wave generated by UETE are greater than that generated by UEWE. The peak pressure at ∼33 cm increased from 21.1 to 24.5 MPa in the first set and from 18.1 to 21.7 MPa in the second when a tube was used instead of a wire. These experimental results help us understand the physical process of UETE and provide an alternative methodology for load design in industrial applications.

Study on the shock wave generated by underwater electrical explosion of Al wire coated with CuO powder

Study on the shock wave generated by underwater electrical explosion of Al wire coated with CuO powder

Comparing magnetic pushing to underwater explosions for flyer acceleration

We present results exploring various methods of aluminum flyer acceleration. One method uses the shock wave generated by underwater electrical explosions of thin foils supplied by a pulse generator with stored energy of ∼4.7 kJ. Utilizing the shock created by an exploding foil, a maximal free flyer velocity of ∼2000 m/s is obtained. This acceleration method is compared to results exploiting only magnetic pushing to accelerate flyers using a common strip-line configuration, resulting in much lower velocities of ∼300 m/s. We also present a modified strip-line configuration, for which a significant increase in the flyer velocity to ∼1200 m/s is measured. Finally, a hybrid strip configuration, incorporating both the effects of magnetic pushing and acceleration by exploding foil and its subsequent shock wave, results in ∼1400 m/s flyer velocity. These experimental results are analyzed by numerical simulations and analytical modeling of the conservation equations of mass and momentum.

Underwater microsecond timescale electrical explosions of aluminum and copper foils

We present results on underwater electrical explosions of thin aluminum and copper foils using a generator delivering ∼200 kA current amplitude, ∼0.9 μs rise time pulses. Time-resolved shadow imaging displays the generation of a strong planar shock wave in water in the vicinity of the exploding foil. Using time-resolved spectroscopy, aluminum oxide (AlO) absorption bands were observed in a Planckian-like spectrum, indicating that aluminum combustion starts when aluminum vaporizes. It is also shown that the strongest shock wave is obtained for the largest linear energy deposition rate to the foil.

Liquid–vapor phase transition process during underwater electrical wire explosion

The liquid–vapor two-phase region has attracted the attention of various fundamental studies and applications. To explore the liquid–vapor two-phase region, underwater electrical wire explosion (UEWE) is a useful tool. In this work, we observe two different mechanisms of the liquid–vapor transition in UEWE: volume vaporization and spinodal decomposition. The main factors through which the mechanisms occur are the heating power and pressure accumulation in the system during UEWE. From the electrical properties and shadowgraph images, the phase transition process of the exploding wire is analyzed. The effects of possible instabilities during the liquid–vapor phase transition are also discussed. We expect that the thermodynamic properties of the liquid–vapor two-phase region can be explored using the UEWE technique based on the understanding of the phase transition process.

Supersonic water jets as point-like sources of extremely high pressure

Two interacting supersonic water jets and collisions of a water jet with an aluminum target are studied experimentally and by hydrodynamic simulations. Supersonic water jets form, when shocks generated by underwater electrical explosions of conical wire arrays converge. The arrays are supplied by a ∼250 kA, ∼1 μs rise time current pulse. Underwater explosion of two conical arrays placed face to face produces jets propagating in air with velocities of ∼2.5×103 m/s leading to hot plasma formation at a temperature of ∼2200–3000 K, pressure ∼1.7×1010 Pa, and density >1029 m−3. When a single array explodes underwater in front of an aluminum target, the collision of the jet with the target produces a local pressure of ∼3×1010 Pa on the surface of the target.

Molecular dynamics study of liquid–vapor transition in underwater electrical wire explosion

During underwater electrical wire explosion, liquid–vapor transitions are crucial to the energy deposition and the generation of shock waves. To explore the characteristics of liquid–vapor transition during electrical explosions in water, a large-scale molecular simulation method was designed. The modeling scales experimental exploding wires to nano-size and then tracks the motion of each atom. The surrounding water medium was simplified as an expanding wall, whose velocity was determined by experimental steak images. Using this model, the phase transition processes at different energy deposition rates were compared. The results show that high energy deposition rates can make the discontinuous liquid–vapor phase transition disappear, forming an axially uniform vapor column, while slow energy injection will change the exploding wire into a foamlike liquid–vapor mixture at a subcritical temperature. The different shapes of wire–water interfaces in the experimental shadowgraphs can be explained by these features of liquid–vapor transition.

The Influence of Discharge Mode on Morphology of Al–Ni Nanoparticles Prepared by Underwater Electrical Wire Explosion

We report the results of experiments investigating the influence of discharge mode on morphology of Al–Ni bimetallic nanoparticles prepared by underwater electrical explosion (UEE) of intertwined Al/Ni wire. The experiments were conducted using a pulsed power generator with the stored energy of [Formula: see text][Formula: see text]J (underheat mode) and [Formula: see text][Formula: see text]J (overheat mode), delivering to the intertwined Al/Ni wire a [Formula: see text][Formula: see text]kA current rising during [Formula: see text]s. By analyzing electrical signals, we conclude that there exists a competitive process between Al wire and Ni wire, and the latter always lags behind the former in various stages, duo to the difference of electrical resistivity. Using transmission electron microscope (TEM) and energy dispersive spectroscopy (EDS), the morphology and element composition of nanopowders obtained at underheat mode and overheat mode were studied. The results reveal that core-shell structured Al–Ni nanoparticles can be easily obtained at underheat mode, due to the mismatched specific surface energy and matching lattice type between aluminum and nickel. Besides, the Al–Ni powder prepared by underwater electrical wire explosion (UEWE) has a smaller particle size (less than 100[Formula: see text]nm) and more consistent particle size distribution compared with traditional preparation methods. These results show that UEWE is very attractive for the preparation of Al–Ni nanopowders, which is helpful in improving the specific surface area of Raney–Ni catalyst.

Addressing the critical parameters for overdamped underwater electrical explosion of wire

Experimental and magnetohydrodynamic numerical simulation results and analysis of a μs- and sub-μs-timescale overdamped underwater electrical explosion of copper wires having different lengths and diameters are presented. For these explosions, ∼80% of the energy stored in the pulse generator is deposited into the wire during a time comparable or shorter than a quarter period of the underdamped discharge. It was found that the threshold values of the deposited energy density, energy density rate, and energy density per unit area, which satisfy overdamped discharge, depend on the wire parameters and on the timescale of the explosion. It was shown that the mechanism responsible for this is the process during which the wire experiences phase transitions to a low-ionized plasma, the resistivity of which is determined by the electron–neutral collision rate, which, in turn, depends on the wire radial expansion velocity, current density, and temperature.

Two-dimensional simulation of microsecond-timescale underwater electrical explosion of a copper wire

Underwater electrical wire explosion (UEWE) is an efficient source of underwater shock waves (SWs). In order to efficiently simulate the interaction between the UEWE SW and structures, a coupled model that includes the electric circuit, the exploding wire and the surrounding water is established based on user-subroutines provided by the commercial explicit dynamics software ANSYS AUTODYN. The modeling starts from room temperature by using the tabular wide-range metal equation of state (EOS) and conductivity data. Experimental validation is performed with copper wires exploded by a μs-timescale pulsed discharge. The numerical results show satisfactory consistency with experiments in terms of the current and voltage waveforms, the wire expansion trajectory, the evolution of SW front, the interaction between SW and electrodes and the SW pressure profiles. The main discrepancy lies in the SW amplitude that is ∼20% higher in the calculation and the possible reasons are discussed in detail. Based on this approach and with proper modifications to the metal EOS and conductivity data, the interaction between UEWE SWs and structures can be efficiently modeled in 2D and 3D for practical applications.

Peculiarities of planar shockwave interaction with air–water interface and solid target

We present the results of the research on underwater electrical explosion of planar copper wire arrays, accompanied by the generation of a planar shock, using the synchrotron-based phase-contrast radiography imaging capabilities of the ID19 beamline at the European Synchrotron Radiation Facility. It is shown that the interaction of a strong shock with an air–water interface leads to additional acceleration of the wire expansion due to a rarefaction wave along with the emergence of micro-jets. In the case of a target placed above the array, we observed the formation of a cavity between the array and the target due to the interaction of two rarefaction waves. The results of two-dimensional hydrodynamic simulations of the wire explosion and the interaction of the generated shock with the water–air and water-target interfaces showed good agreement with experimental results.

Supersonic jet generation by underwater sub-microsecond electrical explosions of wire arrays

Experiments in which supersonic water jets are generated by underwater sub-μs timescale electrical explosions of cylindrical and conical wire arrays are presented. These are compared with previous experiments [Maler et al., Phys. Plasmas 28, 063509 (2021)] in which the generation of supersonic water jets was demonstrated using a μs timescale generator. Although in the present experiments less energy is deposited into the wire arrays, the water jets acquire higher velocities compared to when the deposited energy is higher but the timescale is slower. That is, with a higher energy density deposition rate, faster radial wire expansion is induced resulting in a stronger converging shockwave and a faster waterflow behind its front. In addition, two dimensional hydrodynamic numerical simulations show that the formation of the water jet is the result of extremely high pressure at the axis of the shockwave implosion and the cumulative edge effect realized at the array output.

Target acceleration by sub-microsecond underwater electrical explosions of wire arrays

Experiments of a target accelerated by the shockwaves and water flow generated by underwater sub-μs timescale electrical explosion of a planar wire array are presented. The results of this experiment are compared with previous results [Maler et al., J. Appl. Phys. 129, 034901 (2021)] in which efficient target acceleration by μs-timescale underwater explosions of planar wire arrays was obtained. Although less energy is deposited into the wire array in the present experiments, the target acquires similar and even higher velocities compared to the previous research. This is considered to be associated with the higher energy density deposition rate, inducing faster radial wire expansion, and, consequently, the generation of a stronger shockwave and faster water flow behind its front.

Unbalanced distribution of electric current in underwater electrical wire array explosion

The uniformity of electric current distribution in a wire array and its unstable behavior during the process of underwater electrical explosion have been investigated. Two exploding wires in parallel were used in the experiments and the current waveforms flowing through each wire were obtained using two self-integrating coils. Significant differences in the current waveforms of the two wires were observed near the melting point, which was attributed to the non-simultaneity of heating and phase transition. Unbalanced current distribution caused by the deviations of wire dimensions was analyzed based on a magneto-hydrodynamic model, and the simulation results show that thermodynamic state difference between two wires is present throughout the entire electrical explosion process. It is also found that the initial stored energy of pulse generator will affect the thermodynamic state evolution of exploding wires, resulting in different behaviors of current distribution after the explosion time. The slightly different heating rate caused by unbalanced current distribution in a wire array can break the symmetry of converging shock waves and lower the pressure peak in the vicinity of implosion axis, which was discussed based on the two-dimensional hydrodynamic simulations.

Current distribution at underwater electrical explosion of wires with different diameter connected in parallel

Underwater electrical wire explosion is usually used as a source of underwater shock waves, and the generated shock wave intensity can be regulated by adopting a wire array. In this paper, the dynamics of the electrical explosion of two wires with different diameters connected in parallel were studied. The current flowing through each wire was measured to study the current distribution, and the self-emission image and laser backlight shadow image was obtained to observe the evolution of the wires. A numerical model was built to make explanations and predictions. The results showed that due to the presence of wire inductance and contact resistance between the wire and electrode, the wires are with different current densities and undergo asynchronous heating from the beginning of the discharge. Furthermore, the variation of current distribution among the wires was divided into six stages according to the moment the wire melted and exploded, and analyzed stage by stage. The unbalanced energy deposition results in obvious differences in thermal dynamic parameters, which explains the gradual “extinguishment” of the thinner wire in the self-emission image.

Instability of cumulation in converging cylindrical shock wave

The conditions of linear instability for a converging cylindrical shock wave in an arbitrary inviscid medium are obtained. The initial continuous cylindrical symmetry of the shock wave front is exchanged on a discrete symmetry that is determined by the most unstable small azimuthal dimensionless wave numbers 0<k<kth<1 of corrugation perturbations. Due to the long azimuthal wavelengths (λ=2πRs0/k, Rs0—the radius of the shock wave) of perturbations, the shape of the resulting shock wave front is not changed significantly, but the corresponding restriction of the internal energy cumulation can be caused by the intensification of the rotation of the medium behind the front. The instability and the restriction of cumulation are also possible in the case of the exponential rapid growth of the one-dimensional perturbations with k=0, when the shape of the shock front is not changed at all. The correspondence of present theory to the experimental and simulation data on underwater electrical explosion is considered.

Underwater electrical wire explosions can destroy steel plate

By using pulsed power to explode underwater wire arrays, researchers create dense water jets with extremely high energies and velocities.