PSI - Issue 81

Anandito Adam Pratama et al. / Procedia Structural Integrity 81 (2026) 58–65

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Table 2. Mesh convergence study for the critical configuration Mesh size (m)

Peak structural response

Difference from 0.015 m (%)

0.005

0.120448 0.120032 0.117991 0.118014 0.114815 0.114199

2.06 1.71 0.02 0.00 2.71 3.23

0.0075

0.01

0.015 (used mesh size)

0.0175

0.02

Sandwich Panel • S4R shell element • Plate thickness = 5 mm • Core thickness = 6 mm • Mesh size= 15 mm

Encastre

Sandwich panel

Acoustic medium

Water Domain

Water Domain • AC3D8R acoustic element • Radius = 800 mm • Mesh size = 10 mm

Explosive

Fig. 4. Boundary conditions and mesh scheme of the numerical model of the sandwich panel.

4. Parametric Study This study focuses on the performance of sandwich panels subjected to UNDEX loading using a constant SF approach. By varying the TNT charge mass ( ) and stand-off distance ( ), while keeping the SF value constant at 0.45, the blast severity remains equivalent, thereby eliminating the influence of different explosion configurations and allowing the analysis to emphasize the structural response. Three charge – distance combinations were considered: 1 kg TNT at 1 m, 2.25 kg TNT at 1.5 m, and 4 kg TNT at 2 m, applied to four sandwich panel configurations (S-core, U-core, X-core, and Y-core). For clarity, the variations are denoted as S1, S2, S3; U1, U2, U3; X1, X2, X3; and Y1, Y2, Y3, corresponding to the three charge – distance levels for each core type. The use of constant SF is intended to highlight the influence of sandwich panel core geometry on underwater blast response, independent of variations in blast energy. In this way, comparisons between cores such as X-core, Y-core, S-core, and U-core can be focused on the efficiency of stress distribution, deformation, and energy absorption. This approach also emphasizes the importance of selecting the right combination of TNT mass and stand-off distance to ensure that the SF value remains relevant to real-world operating conditions, such as ship hull structures or underwater components. 5. Results and Discussion The structural response of the sandwich panels was evaluated using two key response parameters: maximum deflection and total impulse acting on the bottom plate. Maximum deflection represents the global deformation response of the structure under UNDEX loading, where lower values indicate higher stiffness and improved structural integrity. Total impulse reflects the momentum transfer from the shock wave to the structure and serves as an indicator of the shock energy absorbed, which is closely associated with the risk of severe deformation and structural damage. The quantitative results are presented in Fig. 5(a) for maximum deflection and Fig. 5(b) for total impulse. Clear trends can be observed across the different core configurations. The S-core consistently exhibits the highest maximum deflection and total impulse, indicating the weakest resistance to UNDEX loads. In contrast, the X-core shows the lowest maximum deflection, while both X-core and U-core achieve the lowest impulse values. The Y-core displays intermediate behavior between these extremes. These results indicate that core geometry plays a dominant role in governing structural response under identical SF conditions.