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Femtosecond laser with pulse duration of 35 fs is used to introduce optical breakdown in water and ethanol. The initial dynamics of the laser-introduced break down is investigated with a time resolved shadow imaging method. The motion of the shock wave front at 600 ps, 4 ns, 12 ns, 16 ns, and 20 ns are observed. Experimental results indicate that under the same laser energy, the initial velocity of the shock wave generated in ethanol is slightly lower than that in water. This is mainly determined by liquid properties (viscosity coefficient, density, molecular weight, breakdown threshold). The evolution of the shock wave also indicates that the velocity decreases with time, and the decrease in ethanol is faster than that in water. [ABSTRACT FROM AUTHOR]

The variation of shock-wave velocity with time induced by a millisecond-nanosecond combined pulse laser (CPL) on silicon is investigated. The convolution neural network (CNN) is used to predict the shock-wave velocity induced by a single ns laser and CPL with a ns laser energy density of 6, 12 and 24 J/cm2, ms laser energy density of 0 and 226.13 J/cm2, and pulse delay of 0, 0.4 and 0.8 ms. The four-layer CNN model was applied, ns laser energy density, ms laser energy density, pulse delay and time were set as the input parameter, while the shock-wave velocity was set as the output parameter. The correlation coefficient (R2), mean absolute error (MAE) and root mean square error (RMSE) of the CNN model on the test data set was 0.9865, 3.54 and 3.01, respectively. This indicated that the CNN model shows a high reliability in the prediction of CPL-induced shock-wave velocity with limited experimental data. [ABSTRACT FROM AUTHOR]

Detonation metrology is essential for the development of energetic materials, to characterize existing explosives, and to characterize materials behavior under high pressures. The optical active method (OAM), based on PMMA optical fibers (250 μm diameter) and their radiation transmission loss when shocked, was used to characterize the detonation wave (DW) and shock wave (SW) in inert barriers and applied to measure the detonation pressure in condensed explosives. The detonation velocity and detonation pressure of a PBX based on PETN (86 % PETN, 14 % Sylgard), known as Seismoplast were measured. The OAM with protected optical probes (POP) was used to determine the mean detonation velocity (7337 m s−1), whereas the OAM with bare optical probes (BOP) was used to measure the induced shock velocities generated by Seismoplast on different thicknesses of PMMA (1–9 mm), aluminum and copper (1–7 mm). Based on the shock velocities at the interfaces between the explosive and the inert barriers, the CJ pressure of Seismoplast was determined as 21.2 GPa. [ABSTRACT FROM AUTHOR]

Time-resolved visualisation of shock wave motion within a powered resonant tube (PRT) is presented for the regurgitant mode of operation. Shock position and velocity are measured as functions of both time and space from ultra-high-speed schlieren visualisations. The shock wave velocity is seen to vary across the resonator length for both the incident and reflected waves. Three mechanisms are explored as explanations for the variation in velocity: change in local fluid velocity, variation in shock strength and variations in local temperature. For the incident wave, local fluid velocity and shock strength are extracted from the data and both are demonstrated to contribute to the observed variation, with a non-trivial remainder likely explained by variation in temperature. [ABSTRACT FROM AUTHOR]

Three heat integrated air separation columns (HIASCs) with different purities (low purity, moderate purity and high purity) are presented, and the open-loop dynamic behaviors are studied. A shock wave velocity is derived for HIASC, and based on that a nonlinear wave model of the HIASC is further established. Combined with the proposed wave model, a novel model predictive control scheme (SWMPC) is carried out, which is compared with a conventional model predictive control scheme (MPC). The comparison simulation results show that SWMPC can work better than MPC, especially for the high-purity HIASC. [ABSTRACT FROM AUTHOR]