Influence of plasma channel impedance model on electrohydraulic shockwave simulation

Self Cite

The application of repetitive electrohydraulic shock waves (EHSs) is a developing underwater discharge technology; however, its cracking characteristics on rock under different loading modes are rarely studied. In this paper, an experimental platform of electrohydraulic discharge is built, and test results show that repetitive EHSs can cause obvious macroscopic cracks on samples. A fitting method is proposed for the time-domain waveform of the EHS. The mechanism of the EHS cracking process (liquid–solid interface transmission process, cracking process in rock) is analyzed, and the cracking criterion and fracture zone range of a single EHS on rock are given. In addition, PFC3D simulation is used to establish a three-dimensional numerical model of the test sample under the experimental conditions, and the development characteristics of the damage shape and crack density inside the rock under the action of repetitive EHSs are deeply analyzed. Under different repetitive loading modes with the same loading total energy, the simulation results show the following cracking characteristics: in single-level mode, the crack density is mainly related to the energy of the single loading. The higher the single-loading energy, the more conducive it is to the growth of the number of main cracks, but it will form a crushing zone to cause energy loss; lower single-loading energy is more favorable to the length of main cracks. In the multi-level loading mode, the degraded loading mode has a higher crack density than the upgraded loading mode. Compared to the single-level loading mode, the multi-level loading mode can effectively promote the development of the number and length of main cracks, and effectively reduce the range of the crushing zone. This paper provides theoretical and simulation guidance for the research and application of repetitive EHSs.

Section: Test Results Of Ehsmentioning

confidence: 99%

“…Based on σ r and σ θ , the normal stress σ n and shear stress τ acting on the microcrack unit can be calculated as shown in equation (19) [25]:…”

Section: Cracking Criterionmentioning

confidence: 99%

Experimental and numerical study on the cracking characteristics of repetitive electrohydraulic discharge shock waves

Xiong¹,

Liu²,

Yuan³

et al. 2020

Self Cite

“…The electrical energy that is provided by a high voltage pulse is generally dissipated in a spark plasma channel in aqueous solutions by UV light emission, radiated electromagnetic fields, the generation of reactive species, temperature increase, and the formation of shockwaves [20,21]. A quantitative analysis of the energy partitioning into each phenomenon is difficult and strongly depends on the specifications of the investigated system and especially on the parameters of the applied high-voltage pulses [22]. For microsecond pulses, it was suggested that the energy in the electromagnetic radiations can be about 30% of the input energy [23] and light emission may account for less than 5% [24,25].…”

Section: Discussionmentioning

confidence: 99%

Mechanism of microalgae disintegration by spark discharge treatment for compound extraction

Zocher

Rataj

Weltmann

et al. 2020

Microalgae possess a cell wall with remarkable physical and chemical strength, which has proved to be a bottleneck for extraction techniques. With the application of spark discharges instigated by 100-ns high voltage pulses, a novel method was established that was found to be effective and yet gentle for the extraction of sensitive, especially heat-sensitive, compounds. The spark, which was ignited directly in the submerged algae suspension, is characterised by several physical and chemical processes that might promote a successful disintegration of the cells. Among other characteristics, the conceivably most destructive mechanism, i.e. strong shockwaves, was examined with schlieren diagnostics to evaluate associated pressures. The results were compared with the tensile strength, determined by atomic force microscopy, of Chlorella vulgaris, which was chosen as model organism. A shockwave pressure of 500 MPa in the close vicinity of the discharge by far exceeded the elasticity modulus of the algae with 13.95 MPa, confirming the potential of mechanically breaking the cell wall. At the same time, bulk temperatures could be maintained close to room temperature by adjusting the operating parameters for the spark-application, hence, especially encouraging the extraction of thermally unstable intracellular substances.

“…Mach number M a is easy to calculate for different breakdown voltages U B according to figure 6 and equation (15). When working distance D is 10 mm, M a is 1.12 at the breakdown voltage of 30 kV, M a is 1.09 at the breakdown voltage of 25 kV and M a is 1.08 at the breakdown voltage of 25 kV.…”

Section: Ehd Shockwavesmentioning

confidence: 99%

“…The shockwave of the near-field is similar to the uniform spherical wave and propagates rapidly after the formation. The mechanical energy of the spherical shock generated by the discharge in water is calculated, and the energy efficiency of EHD shockwave is obtained [15]. It is difficult to directly measure the near-field pressure curve and its peak value of the EHD shockwave.…”

Section: Introductionmentioning

confidence: 99%

Cyclic shock damage characteristics of electrohydraulic discharge shockwaves

Xiong¹,

Liu²,

Yuan³

et al. 2020

Self Cite

To improve the quality of electrohydraulic discharge (EHD) shockwaves cracking effect and reduce its damage, the study examines the cumulative damage characteristics of rock induced by shockwaves generated by EHD. Voltage, current, energy, efficiency, wave velocity, and peak value of incident and transmission shockwave of a liquid–solid interface at different discharge energies are given based on the observation of the shockwaves of established discharge platform. The cyclic impact cracking test is conducted on cement samples. The cement samples are effectively cracked, and the surface formed several cracks. The tests results indicate that the cumulative effects of different cyclic loading modes exist under the action of EHD shockwaves. An upper limit exists on the cumulative effect, and the breakdown voltage affects the maximum effective number of discharges and affects the depth of action. Particle flow code 2D (PFC2D) simulation is used to simulate the cement samples under the same experimental conditions. The development process and shape distribution of the internal microcracks under different loading energies and loading times are analyzed. The results indicate that there are three cumulative effects of microcrack development stages (i.e. microcrack accumulation, cracks development, and slowing down and cessation of crack development). Simultaneously, the results suggest that the cumulative damage effect of EHD shockwave on rock materials can be divided into three zones (i.e. crushing zone, crack zone, and elastic zone), which can be effectively adjusted via controlling the loading voltage, loading times, and working distance. Finally, an experiment-simulation combined control strategy is proposed to avoid the crushing zone and raise the crack zone. The study provides theoretical, experimental and simulation guidance for the application of EHD shockwaves.