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.
Highlights
Direct measurement of the wall pressure loading of the spherical boundary subjected to the near-field underwater explosion is a great difficulty
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. e semiconductor strain gauges which stick on Hopkinson bar are used to convert the pressure-based signal to the strain wave signal. e bubble in the experiments is formed by a discharge of 400 V high voltage
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 c from 0.17 to 2.00
Summary
To investigate the wall pressure on the hemispheric boundary caused by an underwater electric spark bubble, an experimental setup using a HPB as the sensing element is designed. E diameter of the hemispheric target is 50 mm In this experiment, the material of HPB is steel. Is section first defines a dimensionless parameter to represent the distance between electric spark explosion source and the bottom of hemispheric target. Based on the spherical hypothesis of shock wave, the dimensionless distance from the initial bubble to the bottom of the hemispheric target is defined as c d/2Rm. e dimensionless stand-off distance c is a predominant factor in determining the effects of a nearby boundary on bubble. Seal rings Hopkinson bar Figure 1: Detailed schematic of the apparatus
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