Research and experiment on the wave-dissipation performance of rapidly assembled explosion-proof walls

Abstract:The wave suppression performance of the rapid assembly explosion-proof wall is mainly based on the static explosion test of the shell, and the overpressure peak of the shock wave before and after the explosion-proof wall under different proportions of the explosion-proof wall is compared, and the improved overpressure effect coefficient can reflect the wave suppression ability of the explosion-proof wall. Based on the relevant data of the test, the effects of proportional burst distance, proportional wall height and scale distance behind the wall on the dissipation performance are analyzed. The results show that the reflective overpressure acting on the blast-proof wall surface is generally one order of magnitude larger than the maximum diffraction overpressure behind the wall. The wave-dissipation effect of the explosion-proof wall can reach more than 50%, and the free field overpressure when there is no wall is higher than the shock wave after the wall when there is an explosion-proof wall; the reflective overpressure acting on the explosion-proof wall explosion-proof surface is generally an order of magnitude larger than the maximum diffraction overpressure behind the wall, and the proportional burst distance and the distance of the measuring point behind the wall affect the diffraction overpressure to a large extent. Both the height of the proportional wall and the proportional burst distance have an impact on the dissipation performance of the wall, and the coefficient of the sinking effect gradually increases as the proportional distance behind the wall decreases.

Keywords: wave suppression performance Explosion mechanics experimental study explosion-proof wall

At present, explosion-proof walls are a research hotspot in the field of protective engineering, and have become an effective measure for temporary protection on the battlefield and anti-terrorism explosion protection for important targets. The installation of an explosion-proof wall at a certain distance outside the important target will effectively reduce the destructive effect of the explosion shock wave and fragmentation, and reduce the loss of equipment and the probability of casualties. The rapid assembly explosion-proof wall can quickly build a protective barrier around the target periphery, and achieve the purpose of protection by directly reflecting the air shock wave generated by the explosion, its own deformation and the scattering of the filler, friction absorption and consumption of the explosion shock wave energy.

In recent years, scholars at home and abroad have conducted a lot of research on explosion-proof walls using experimental research, theoretical analysis and numerical calculations. Mu Chaomin and others. By combining numerical simulation and testing, the load and shock wave circulation law of the explosion shock wave acting on the explosion-proof wall are studied, and the internal mechanism of the explosion shock wave circulation and the distribution law of the shock wave flow field around the explosion-proof wall are obtained. Zhang Yao et al. used AUTODYN software to simulate the weakening effect of water explosion-proof wall and reinforced concrete explosion-proof wall on the ground explosion shock wave, compared the wave-dissipation performance of the two explosion-proof walls, and analyzed the law of energy conversion of various substances when the shock wave acts on the two explosion-proof walls. Hongwu and others. AutoDYN software was used to study the overpressurization distribution of shock waves behind non-upright rigid explosion-proof walls, and it was pointed out that the wall suppression effect of different tilting conditions was comparable; Ding Nana et al. used LS-DYNA program to numerically simulate the propagation law of the explosion shock wave when it encountered the cantilever explosion-proof wall, and compared it with the absence of the explosion-proof wall, and obtained the attenuation rate of the overpressure behind the explosion-proof wall. Most of the previous studies have used numerical simulation methods, and the explosion tests that have been carried out have mostly been scale-down or small-equivalent close-range tests, and there are currently few prototype explosion tests on rapidly assembled explosion walls. In this paper, the static explosion test of shells for rapid assembly explosion-proof walls of different assembly forms is carried out, and the distribution law of shock wave overpressure after explosion-proof walls is measured, and the dissipation performance of fast assembled explosion-proof walls is analyzed by comparing the calculation value of the CONWEP program of free field overpressure when there is no wall.

1. Test overview

1.1 Test components

The rapid assembly type explosion-proof wall wall structure unit is welded by low carbon steel wire to form a skeleton, assembled and connected into a detachable and reusable steel mesh by spiral hinge, and lined with high tensile high-quality geotextile, and then filled with sand, soil and stone to form a wall, as shown in Figure 1. The shells adopt 122mm, 130mm and 152mm explosive warheads, and their explosive types are TNT, and the charge is 3.2kg, 3.5kg and 5.8kg respectively, as shown in Figure 2.

1.2 Measurement systems and equipment

Pressure sensors are used to measure the shock wave overpressure on the blast-proof wall and on the ground behind the wall, as shown in Figures 3(a) and (b). Reflective overvoltage sensor using Kistler sensors of different ranges, the output signal is voltage, the pressure sensor has the advantages of frequency bandwidth, high sensitivity, simple follow-up circuit, zero drift, stable performance. The TRIOC SC56671 portable data acquisition device is selected as the acquisition instrument (as shown in Figure 4), and the sampling rate is 2MHz, the negative delay is 250ms, and the sampling time is 2S. During the test, the data acquisition system adopts the external trigger method of breaking the target, winding the broken target line on the warhead, and the broken target line is broken after the warhead explodes, and the data acquisition equipment obtains a step signal (0 ~ 5V), and then data acquisition.

1.3 Test layout

The explosion-proof walls of different specifications are laid out according to Figure 5. The test adopts the method of one explosion and multiple uses, and the static explosion test of each shell is tested on the explosion-proof wall 5in, 10nl and 15In from the explosion center, and the wall arrangement ensures that the center of each wall wall and the center of the explosion are in a straight line, and the explosion wave is transmitted to the blasting surface of all walls. The dimensions of the explosion-proof walls are shown in Table 1.

During the static explosion of each shell, the shock wave overpressure at the center of the blasting surface of the explosion-proof wall and the horizontal interval of the positive center of the explosion-proof wall are tested respectively, and the ground shock wave overpressure at the 0.5nl, 1.5in and 3.0in behind the wall is tested, and the position of the overpressure measurement point is shown in Figure 5. The test sequentially detonated 1 round of 122mm explosive bomb, 1 round of 130mm killing bomb, 2 rounds of 152mm explosive bomb in the form of detonator and detonation column detonation at the center of the explosion, of which 1 round of 152 killing bomb was shallow burial, the projectile was placed horizontally, the bullet shaft was parallel to the 1}} wall, the topmost part of the projectile body was 0.08ITI from the ground, and the rest of the explosive bombs were placed vertically on the bomb rack, and the explosion center was 11 meters from the ground.

2. Test results and analysis

At present, researchers mainly use parameters such as shock wave pressure and overpressure peak to describe the propagation law of the explosion shock wave, and these parameters are generally expressed by proportional burst distance. Proportional burst distance is defined as: (1) In the formula: R is the distance between the measurement point and the question of the burst heart, in; C is the equivalent TNT dosage, kg.

2.1 Test data

The test data of the explosion-proof wall and the test point after the wall in the static explosion test are analyzed, and the shock wave overpressure time course curve under different proportions of explosion distance is obtained, and Figure 6 and Figure 7 give the shock wave overpressure time range curve under some proportional explosion distances, where (a), (b), (C), (d) respectively indicate 1# wall under the static explosion condition of 122mm anti-explosive bomb, 2# wall under the static explosion condition of 130mm anti-explosive bomb, 5# wall under the static explosion condition of 152mm anti-explosive bomb, 5# wall under the static explosion condition of 122mm anti-explosive bomb, 5}} under the static explosion condition of 122mm anti-explosive bomb. The shockwave timeframe curve of the wall.

2.2 Analysis of results

2.2.1 Blast wave flow field around the explosion-proof wall

Table 2 gives the results of the overpressure peak test under the proportional explosion distance, of which the four proportional explosion distance test results indicate the peak of the shock wave under the static explosion of the 122mm explosive bomb, the 2# wall under the static explosion of the 130mm explosive bomb, the 5# wall under the static explosion of the 152mm explosive bomb, and the peak of the shock wave of the 5# wall under the static explosion of the 122mm explosive bomb.

As can be seen from Table 2, due to the existence of the explosion-proof wall, the shock wave reflection overpressure acting on the explosion-proof wall facing surface is 1 order of magnitude larger than the maximum diffraction overpressure of the shock wave behind the wall, indicating that the wave-dissipation effect of the explosion-proof wall is more significant. The distribution law of the shock wave flow field after the explosion-proof wall wall is obviously different from the free field, in the test measurement range, when the proportional burst distance R is larger, the peak of the shock wave overpressure increases with the increase of the distance R: behind the wall, which is significantly different from the attenuation of the shock wave overpressure peak in the free field with the increase of the distance. However, when the proportional burst distance R is small, the distribution law of the flow field behind the wall changes again, and the larger value of the overpressure peak of the shock wave after the wall has a tendency to approach the wall, and the overpressure peak of the measurement point near the wall is not much different. It can be seen that the existence of the explosion-proof wall will change the propagation law of the air shock wave and the distribution law of the flow field, and the distribution law of the flow field changes according to the difference of the proportional burst distance.

2.2.2 Explosion-proof wall dissipation effect

The weakening effect of the explosion-proof wall on the shock wave directly determines the quality of its protective performance, which is of great significance for the safety fortification research of important targets behind the wall. Therefore, the definition of rapid assembly explosion-proof wall overpressure effect coefficient muscle, in order to analyze the rapid assembly of explosion-proof wall dissipation performance, the calculation formula of the suppression effect coefficient is: (2) formula: △P. Indicates that there is a shock wave overpressure behind the wall when there is an explosion-proof wall, and △P0 indicates a free-field shock wave overpressure without an explosion-proof wall. From the test results, it can be seen that the shock wave overpressure behind the explosion-proof wall wall is related to the proportional distance behind the wall. Now the scale distance behind the wall is defined as: (3) in the formula: R: is the distance between the measuring point behind the wall and the back explosion surface of the explosion-proof wall, m; C is the explosive charge, kg.

It can be seen from the formula (2) that when there is an explosion-proof wall, the shock wave behind the wall exceeds the pressure △P. The smaller, the greater the sinking effect coefficient of the rapidly assembled explosion-proof wall, indicating that the better the wave-suppression performance of the explosion-proof wall. If the change law of the extinction effect coefficient muscle is found through the explosion test, combined with the overpressure and impulse empirical formula of the explosion shock wave in the free field, the shock wave overpressure △ P behind the explosion-proof wall can be calculated according to the calculation formula of the extinction effect coefficient. , thus providing a basis for determining the fortification safety distance of important targets and personnel behind the wall. In order to study the subtraction effect of the explosion-proof wall on the shock wave overpressure, the CONWEP program calculates the explosion shock wave free field overpressure corresponding to the same measurement point in the explosion-proof test without the explosion-proof wall, and Table 3 gives the peak shock wave overpressure of the post-wall measurement point of the shell static explosion test without the explosion-proof wall, where the explosion distance is R. from the explosive to the explosion-proof wall. Comparing the data in Table 2 and Table 3, it can be obtained that the peak of the shock wave after the wall when there is an explosion-proof wall is significantly smaller than the free field overpressure peak at the same location when there is no explosion-proof wall. According to the data in the table, combined with formula (2), the overpressure extinction effect coefficient of different assembled explosion-proof walls (that is, different proportions of explosion distance) under each static explosion test is calculated, and Figure 8 shows the overpressure extinction effect coefficient under each proportion of the explosion distance with the scale distance behind the wall: the change curve. As can be seen from Figure 8, under different proportions of burst distance, with the ratio behind the wall from Figure 9 can be obtained, when only the explosive equivalent is changed, the wave-sinking effect coefficient of the three measurement points behind the wall does not change much, and the proportional burst distance R under this condition. The impact on the eyelid is small, and the overpressure extinction effect of the three measurement points behind the explosion-proof wall wall with a burst distance of 5m is basically maintained at about 91%, 87% and 80%. According to the data in Table 2 and Table 3, formula (2) is used to calculate the overpressure extinction effect coefficient of each measurement point behind the wall in the shell test with the proportional burst distance R. The change graph, as shown in Figure 10, where the change in the proportional burst pitch is achieved by changing the burst pitch only and other conditions unchanged.

It can be seen from Figure 10 that when only the burst distance is changed, the overpressure extinction effect coefficient of the three measurement points behind the wall changes greatly, and the proportional burst spacing is greatly affected. With the increase of the proportional burst distance R, the overpressure extinction effect coefficient decreases, taking the explosive equivalent of 3.2kg as an example, when the proportional burst spacing (m/kg3) increases from 2.78 to 5.57, the three measurement points behind the wall are reduced from 90%, 86%, 80% to 078%, 77%, 69% respectively, which shows that the extinction effect of the explosion-proof wall on the shock wave overpressure is significantly weakened. When the proportional explosion distance is fixed, R: the smaller, the shape of the explosion-proof wall, the larger, indicating that the wave-killing effect near the back explosion surface of the explosion-proof wall is better, and the explosion-proof wall can give full play to the protective role.

Synthesizing the above analysis, it is found that the overpressure elimination effect coefficient behind the wall described in Figure 9 and Figure 10 varies with the proportional burst distance R, and the reason is that when the explosive equivalent is changed, the proportional wall height of the explosion-proof wall also changes, and the muscle is affected by the proportional wall height in addition to the explosive equivalent, and with the increase of the proportional burst distance, the proportional wall height also increases accordingly. Literature [16] the study found that when the proportional burst distance is fixed, as the height of the proportional wall increases, the shock wave overpressure behind the explosion-proof wall gradually decreases. Corresponding to Figures 9 and 10, it can be seen that the proportional burst distance and the proportional wall height both affect the change of muscle and cancel each other out to a certain extent, so the change of muscle at this time is not large, and the experimental conclusions in this paper are consistent with the literature. The proportional wall height behind the wall is defined as: (4) In the formula: H is the height of the explosion-proof wall, m; C is the explosive charge, kg.

3. Conclusion

(1) The reflective overpressure acting on the explosion-proof wall facing surface is generally an order of magnitude larger than the maximum diffraction overpressure behind the wall, and the proportional blast distance and the measurement point distance behind the wall have a greater impact on the diffraction overpressure of the explosion-proof wall; (2) the wave-dissipation effect of the rapid assembly explosion-proof wall can reach more than 50%, but with the increase of the proportional distance behind the wall R, the explosion-proof wall overpressure effect coefficient muscle gradually decreases, the wave-killing performance of the explosion-proof wall gradually weakens, and the wave-killing effect of the explosion-proof wall on the far field is reduced; (3) The wave suppression performance of the explosion-proof wall is affected by the proportional burst distance and the proportional wall height, and the wall suppression ability cannot be judged solely by the proportional burst spacing.