Study On The Shock Waves' Features Of The Structure Internal Pressure Relief Blast

Nowadays there have been a large number of large public buildings and facilities set up with the development of urbanization. The adequate utilization of the underground space makes the plenty of underground structures constantly emerge, such as the underground transportation systems. Warehouse explosion, fireworks manufacturing plants and other structures which are closely interrelated to our daily life. It is the good antiknock performance of these structures that reduces casualties and property losses. Besides, this kind of structure usually has a door, windows and other openings, so after an explosion inside the structure, the openings turn to be the pressure relief sites which influence the blast effect inside the structure. Therefore, it is of great significance to carry out the research focusing on the method of resisting internal pressure relief blast.This paper will study from the aspect of the pressure relief blast features of the square structure in different distance and different pressure relief mode features, because the pressure relief blast is related to the geometrical shape, explosives form, scaled distance, and the location, number, open way of the pressure relief site. Based on the verifying the effectiveness of ANSYS / LS-DYNA on numerical simulation of the free and confined space explosion, first, the paper investigated the propagation regularity in the free atmosphere, the semi-confined space, confined space and the relations of the peak overpressure of the shock wave under the three conditions; then, it focused on shock waves'feature of the internal pressure relief blast.The research findings indicate:â‘ Selecting appropriate parameters and using ANSYS / LS-DYNA finite element program can simulate the explosion under different conditions effectively.â‘¡After the contrastive analysis of the peak overpressure of the shock wave under the three conditions of the free atmosphere, the semi-confined space and confined space, it concluded the effect of the blast inside the confined space based quantitatively based on the current theory of free space blast: the shock wave first comes to the detonation point, its value is much higher than that in the free space, furthermore, the difference is more obvious with the decrease of the scale factor, then the shock wave spread around the structure walls and the corners, which leads to the pressure build-up in these places. In the closed structure, not only the overpressure loading of the shock wave acts on the structure walls but also the approximately stationary pressure which also raises with the decrease of the scale factor. What's more, the shape of the structure influents the inner blast distinctly, make the shockwaves superimpose after multiple reflection, and the spreading of the waves will turn more complex and make the overpressure loading even higher than the one vertical to the detonation point.â‘¢The features of shock wave in the different pressure relief ways under a small scale factor(Z=0.15m/kg^1/3--Z=1.0m/kg^1/3): around the pressure relief hole , the shock wave has several successive peaks,and the second one is much higher than the first.This kind of difference decreases with the increment of the scale factor.The relief hole can efficiently reduces the action of blast, especially the quasi static pressure load, generally speaking, the bigger of the hole,the more efficiently of its action.With the same size of vent hole,the best way to relief the pressure in a structure is to cut the vent holes in the walls nearst from the detonation point.The second one is at the corners and the third one is at borders of the walls;with the difference size of vent hole,to cut the holes both in the walls nearst from the detonation and at the corners of the structure is the best,and to cut holes in the nearst walls or at the corners is the second, to cut holes in the other parts of the structure is the third one.While the vent holes takes over 50% of the structure, the effectiveness of the pressure relief is not obvious.â‘£The features of shock wave in the different pressure relief ways under a large scale factor(Z=1.0m/kg^1/3--Z=2.0m/kg^1/3): compared with the small one,the wave peaks at the relief hole is much lower,and the following peaks are not higer than the first one; The effectiveness of the vent holes to relief pressure is no longer as obvious as under a small sacle factor and the scale plays a less important role; With the same size of vent hole,to cut the hole at the corner of the structure is the best way of vent explosion.