A New Measurement Based on HPB to Measure the Wall Pressure of Electric-Spark-Generated Bubble near the Hemispheric Boundary

Abstract

Direct measurement of the wall pressure loading of the spherical boundary subjected to the near-field underwater explosion is a great difficulty. To investigate the wall pressure caused by electric-spark-generated bubble near a hemispheric boundary, an experiment system is developed. In the method of this experiment, a Hopkinson bar (HPB), used as the sensing element, is inserted through the hole drilled on the hemisphere target and the bar’s measuring end face lies flush with the loaded face of the hemisphere target to detect and record the pressure loading. The semiconductor strain gauges which stick on Hopkinson bar are used to convert the pressure-based signal to the strain wave signal. The bubble in the experiments is formed by a discharge of 400 V high voltage. To validate the pressure measurement technique based on the HPB, an experimental result from pressure transducer is used as the validating system. To verify the capability of this new methodology and experimental system, a series of electric-spark-generated bubble experiments are conducted. From the recorded pressure-time profiles coupled with the underwater explosion evolution images captured by the high-speed camera (HSV), the shock wave pressure loading and bubble collapse pressure loadings are captured in detail at different dimensionless stand-off distances γ from 0.17 to 2.00. From the results of the experiments conducted in this paper, the proposed experiment system can be used to measure the pressure signal successfully, giving new way to study the bubble collapse pressure when the bubble is near a hemispheric boundary. Through the experimental results, the bubbles generated by different dimensionless stand-off distance γ are divided into four categories, and the bubble load characteristics are also discussed.

Experimental Research on the Influence of Different Curved Rigid Boundaries on Electric Spark Bubbles

“…Cui et al [ 25 ] used a high-voltage electric discharge to generate bubbles. Ma et al [ 19 ] improved upon the equipment of Cui et al by adding a replaceable target to realize bubble experiments under different curved surface boundaries. A voltage of 400 V discharged by the capacitor was transmitted to a thin copper tube through a wire, and bubbles were generated at the intersection of the two thin copper tubes.…”

“…This research showed that the established numerical method can accurately represent the morphological evolutionary characteristics of bubbles near the sphere boundary and also provided many detailed morphological characteristics. Ma Chunlong et al [ 19 ] gave the explosion distance parameter that affects the bubble load characteristics near the hemisphere boundary using the Hopkinson bar (HPB). However, few scholars have provided the load characteristics of bubbles near a curved surface boundary from an experimental research perspective, as most only provide some flow field characteristics in numerical terms.…”

“…Our previous paper [ 19 ] studied the design of a new wall pressure load measurement system based on the work of Yao and Cui [ 26 , 27 ]. By changing the shape of the target plate, the morphology and load characteristics of bubbles produced by near-field underwater explosions were studied and analyzed under curved surface boundary conditions.…”

Experimental Research on the Electric Spark Bubble Load Characteristics under the Oblique 45 Degree Curved Surface Boundary

“…C. GL. et al [7], Fong et al [8], Gong et al [9], Luo et al [10], Ma et al [11], Zhang et al [12], and Ma et al [13] used the same method. Klaseboer et al [14] used the same method.…”

“…Jayaprakash et al [25] used a pressure sensor to measure the wall pressure load generated by the spark bubble in the vertical direction. Cui et al [26], Yao et al [27,28], and Ma et al [13] used Hopkinson rods to measure spark bubble loads and micro-explosive bubble loads. Through previous research results, it is known that the explosion distance is an important cause of damage to surrounding structures due to the cavitation bubble load.…”