Experimental study on explosion dispersion process of a multi-layer composite charge under different initiation modes

The influe nce of initiation modes on the explosive dispersion process of the multi-layer co mposite charge(MCC) was studied.Overpressure sensors and high-speed photography system were used to investigate the energy release process of an MCC with a specific structure.The shock wave pressure and explosive dispersion characteristics of the MCC under different initiation modes were compared.The forming and expanding process of the shock wave of the composite charge under different initiation modes was determined.The separation position of the shock wave and fireball interface was determined.The calculation formulas of the shock radius and overpressure of the composite charge are presented.The radius of the shock wave of the composite charge was significantly affected by the initiation mode.Moreover,the development process of the composite explosive fireball under different initiation modes was analyzed,the variation rules of the composite charge dispersion radius and fireball dispersion velocity with time were obtained under the different initiation modes,the explosion energy release rate of composite charge under simultaneous initiation modes was the highest,and the peak overpressure under the simultaneous initiation mode was 1.61 times that of central single-point initiation.

Initiation Mechanism of Loess Mudflows by Flume Experiments

The structure of loess is loose,and the shear strength of loess drops sharply after contact with water.Therefore,loess mudflows have become a common geological disaster on the Chinese Loess Plateau.In order to study the initiation mode and mechanism of loess mudflows,in this study,seven sets of flume experiments were designed by controlling the slope angle and rainfall intensity.The results show that(1)when the slope angle is between 10°and 20°,there are two initiation mechanisms of loess mudflows:mudflow(large scale)and retrogressive toe sliding,and mudflow(small-scale)and retrogressive toe sliding.(2)The main method by which water infiltrates into the soil accumulation is mainly vertical infiltration,which is not affected by the slope angle and the seepage direction of the accumulation soil.(3)The liquefaction of loess is the root cause of loess mudflows.Water infiltrates into the area with an uneven density and a large amount of water accumulates in this area.Thus,the water content of the loess increases and the pore water pressure increases quickly and cannot dissipate in time,so the loess liquefies and the liquefacted area continues to spread and become larger.Thus,loess mudflows(large scale)occur.The increase in pore water pressure was captured in the seven sets of experiments.However,the order of the rising positions in the accumulation were different.This requires us to carry out tracking of the particle displacement inside the soil and the spatial changes in the internal structure of the soil in future research.

IMPLICIT NONLINEAR NORMAL MODE INITIALIZATION:A MULTIGRID APPROACH

The implicit nonlinear normal mode initialization (INMI) is applied to a tropical limited area shallow water model in spherical coordinates.The boundary condition for the INMI scheme is based on the boundary formulation of the model.The INMI scheme is found to be very efficient in suppressing spurious gravity wave oscillation and providing a well balanced initial data set for the model.The INMI scheme involves solving a number of elliptic type equations with varying complexity.and hence an efficient numerical technique is required for solving such equations.In order to make INMI computationally more attractive,we are employing the multigrid method for solving all the elliptic type equations in the INMI scheme.The numerical procedures for the development of such multigrid solvers are briefly described.