Mechanism of Dynamic Responses of Grillage Structures under Loads of Close-in and Contact Underwater Explosions

doi:10.12382/bgxb.2022.0037

Abstract

Abstract:

This paper designs grillage structure models based on a specific protective structure of a surface ship, and conducts close-in and contact underwater explosion experiments on 10 grillage models under 7 working conditions with various charges and distances. The velocities of typical points are measured with the Photonic Doppler Velocimetry system, the fragments of the grillage structure are gathered, and the damage forms after each experiment are recorded. The experimental results compare well with the numerical results, verifying the generality of the experiment and the accuracy of the simulation. The analyses of experimental and numerical results reveal several conclusions. The grillage structure is susceptible to shear and tear at reinforcing ribs and diaphragm plates, leading to the formation of fragments. The number and weight of fragments depend on the explosive charges, distances, and structures of the grillage. The velocities of points on the surface of the grillage decrease exponentially with increasing distance between the measuring point and center point. The center point is the projection point of the explosive charge on the grillage surface. When the ratio of the explosion distance to explosive charge radius is not less than 2, the velocity of center point remains nearly constant, even though the explosive charge mass changes.

Key words: grillage structure, close-in and contact underwater explosion, explosive load

SHEN Chao, ZHANG Lei, ZHOU Zhangtao, LIU Jianhu. Mechanism of Dynamic Responses of Grillage Structures under Loads of Close-in and Contact Underwater Explosions[J]. Acta Armamentarii, 2023, 44(4): 1050-1061.

Figures/Tables 27

Fig.1 Vertical view of tentative layout

Fig.2 Test setup

Fig.3 Engineering drawing of experimental grillage (dimensional unit: mm)

Fig.4 Back of the test grillage

Fig.5 Installation frame of test model (dimensional unit: mm)

Fig.6 Assembly drawing of grillage and installation frame

Fig.7 Assembly drawing of grillage, water tank, and installation frame

Table 1 Test conditions

工况	药量/g	爆距/mm	有效试验发数
1	125	6R₀	1
2	125	4R₀	1
3	125	2R₀	1
4	125	R₀	1
5	500	4R₀	2
6	500	2R₀	2
7	500	R₀	2

Fig.8 Explosive projection position on the grillage

Fig.9 Schematic diagram of PDV measuring points on the grillage

Fig.10 Typical damage conditions of the grillage with different charges

Fig.11 Fragments collected under test condition 7

Fig.12 Deformation and damage conditions of the grillage with different test conditions

Fig.13 Velocity curve versus time of 8 points on grillages under each test condition

Fig.14 Numerical model of grillage test

Fig.15 Comparison between test and numerical results under test condition 4

Fig.16 Comparison of velocity curves of test and numerical results under test condition 4

Table 2 Comparison of test points’ peak velocity values under test condition 4

测点编号	速度峰值/(m·s^-1)		数值计算与试验偏差/%
测点编号	试验结果	数值计算结果	数值计算与试验偏差/%
D₁	1189	1130	-5
D₂	253	162	-36
D₃	45	62	37.8
D₄	35	52	48.6
D₅	130	129	-0.8
D₆	39	42	7.7
D₇	34	37	8.8

Table 3 Comparison of D1 test point’s peak velocity value under each test condition

工况编号	速度峰值/(m·s^-1)		数值计算与试验偏差/%
工况编号	试验结果	数值计算结果	数值计算与试验偏差/%
2	286	254	-11.2
3	558	541	-3
4	1189	1130	-5
5	325	332	2.2
6	766	693	-9.5
7	1694	1507	-11

Fig.17 Damage area and velocity distribution under test condition 2

Fig.18 Damage area and velocity distribution under test condition 3

Fig.19 Damage process and velocity contours under test condition 2

Fig.20 Damage process and velocity contours under test condition 3

Fig.21 Damage process and velocity contours under test condition 4

Fig.22 Velocity distribution of points on the grillage versus the relative distance from the projection point

Table 4 Fitting parameters of test velocities of the grillage

工况编号	爆距/mm	药量/g	A₀	B₀	α
2	4R₀=106	125	328.7	-54.0	-0.125
3	2R₀=53	125	641.6	-14.9	-0.234
4	R₀=26.5	125	1214.0	-5.7	-0.384

Fig.23 Velocity distribution of points versus the relative distance from the projection point with different charges

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