Experimental Study Of Hopkinson Bar Based Measurement Methodology To Wall Pressure Genearted By Near-field Underwater Explosion

Not only for the design and anti-explosion study of the ship structure but also for the damage effectiveness assessment and development of the underwater weapon,the pressure measurement is of great importance.With the development of underwater guidance technology and target recognition and tracking technology,the directly hitting rate of the underwater weapon increases significantly which results in increasing the probability of the ship suffering the attack of the near-field underwater explosion in sea war or conflict greatly.Due to the extremely high amplitude of the wall pressure loading of near-field underwater explosion(WPL-NFUE)and the bad measurement circumstance,there are difficulties in the measurement of the WPL-NFUE.To this end,a Hopkinson bar based measurement methodology to the WPL-NFUE is proposed.According to the experimental condition,the design and manufacture of the experimental apparatus is carried out and the whole experimental system is set up.Through the experimental study,the calibration of the methodology and experimental system is conducted.Then the experimental study of the wall pressure generated by lower and higher voltage Spark-generated bubble,mini-charge underwater explosion and the impact of high speed water jet is carried out.Based on the results of the conducted experiments,the validity and feasibility of the proposed methodology is verified,providing a novel experimental method and approach for the study of the near-field underwater explosion and transducer.Firstly,the domestic and foreign research related to the near-field underwater explosion is reviewed and elaborated in theory,numerical computation and experiments.Specially,the composition,characteristics and the measuring environment of the WPL-NFUE are summarized,based on which the difficulties in the measurement of the WPL-NFUE are determined.Based on the analysis and summarization of the existing experimental research of assessment to the near-field underwater explosion wall pressure loading,the difficulties and shortcomings of the current measurement methodology and techniques in the measurement of the WPL-NFUE are concluded.The applications of the Hopkinson bar based pressure measurement methodology in the pressure loading assessment of the near-field explosion buried in ground,in the air and the impact of high speed sand cylinder show the advantages of the pressure measurement methodology in assessing the pressure loading with high amplitude.Taking the characteristics of the WPL-NFUE,the problems in using the Hopkinson bar based pressure loading measurement methodology to get the WPL-NFUE is summarized,laying a foundation for the following study.To meet the requirement of the experimental environment in the experimental study of the WPL-NFUE measurement,the characteristics of the low,high voltage Spark-generated bubble are investigated and summarized as well as the relationship between the size,pulsation period of the bubble and the discharge voltage and electrode.To overcome the problem that the amplitude of the shock wave pressure loading is not high enough to meet the requirement,a lab-scale mini-charge underwater explosion experimental method is proposed.Through the optimization of the synchronizing trigger signal,the requirement of the synchronizing trigger in the conjoint analysis of the pressure loading electric signal and the images of the underwater explosion procedure,which lays a foundation for the verdict of the electric signal obtained by the pressure measurement system and the study of the bubble pressure loading.Based on the principle of the pressure measurement methodology,the experimental system is designed and manufactured with the consideration of the laboratory condition.A surface sticking based Hopkinson bar fixation method is proposed.It is concluded that the proposed fixation method is able to exert a restraint on the motion of the bar without interfering the propagation of the strain wave.For the strain measurement of the experimental system,the strain measurement sub-system is improved through experiments resulting in an improvement of the signal-to-noise ratio.Based on the time analysis of the electric signal obtained by the experimental system and the conjoint analysis of the electric signal and the captured images in the preliminary tests,the proposed pressure measurement methodology and experimental system are validated to capture the pressure loading signal generated by the underwater Spark-generated bubble and mini-charge underwater explosion.Before the applied study of the proposed pressure measurement methodology and system,the accuracy of the obtained pressure should be verified.Based on the propagation of the underwater explosion shock wave,a validating experiment based on the underwater explosion between two parallel plates is proposed,designed and manufactured.The characteristics of the bubble dynamics and the pressure on the two plates are investigated.Through studying the comparison between the pressure loadings on the two plates,the experiment conditions that meet the requirement of the validating experiment are obtained.Through the validating experiments of the Hopkinson bar based pressure measurement methodology,accuracy of the proposed measurement methodology and the experimental system is verified.Based on the proposed wall pressure measurement methodology and experimental system,the pressure loading on the target plate generated by the Spark-generated bubble and mini-charge underwater explosion located below the plate is studied experimentally.The shock wave pressure of the spark discharge and the explosion is measured the changes of the variation law of the shock wave pressure with stand-off changing is investigated.Through the conjoint analysis of the bubble pressure loading and the bubble dynamics,the effects of the stand-off on the composition of the bubble pressure loading as well as the characteristics of the induced water jet and bubble collapse pressure loadings are investigated,the formation mechanisms and characteristics of the second bubble collapse pressure loading are paid investigation as well.For the pressure loading generated by high speed water impact,a high speed water impact experimental method using the explosion as the power source is proposed.The movement patterns of the high speed water is studied through experiments with different conditions,based on which the experimental study of the pressure loading generated by the impact of the high speed water.The characteristics of the high speed water impact pressure loading is obtained.According to the results,the proposed Hopkinson bar based pressure measure methodology is verified to assess the water hammer pressure.