The effect of the bend radius on the impulse transfer characteristics of V-hulls: Numerical simulations

Abstract

A study was performed to investigate the effects of geometry on impulse transfer to V-plates subjected to localised air-blast loading. The V-plates were designed to be 1:8 scale compared to the full-scale V-hulls used in landmine-protected vehicles. Simulations were performed using LS-DYNA and validated using results from blast experiments on scaled rigid V-plated structures of varying internal angle. The validated numerical models were then used to ascertain the influence of including the clamp, varying the stand-off distance, internal angle and V-tip radius on impulse transfer. The simulations showed that, in general, the impulse increased as V-tip radius increased. For the 90° and 120° V-plates, the impulse transferred was observed to plateau for bend radii greater than 160 mm. The increase in impulse was attributed to changes in the spatial and temporal load distribution due to the higher V-tip radius. There was no significant variation in the pressure distributions for larger bend radii (above 160 mm). For both the 90° and 120° V-plates, a dip in impulse was observed when the V-tip radii was between 0 and 20 mm. This was caused by reduced peak pressures and an increase in gas flow. Fixing the clearance height and increasing the V-tip radius (and therefore the stand-off distance) had no discernible effect on impulse transfer. However, it was shown to increase the arrival time and load duration, while decreasing the peak total force.

Attempts to improve on the V‐hull structural design for air‐blast loading applications

“…The impulses transferred to the mono V120 structures were similar in the 19-20 g detonations, regardless of bend radius, indicating that there was little difference between the global impulse transfer characteristics of the R4 and R32 mm tip radii structures. This is consistent with the predictions from rigid V-structure numerical modelling presented by Langdon and Shekhar [7].…”

“…In general, there was a trend of increasing impulse transfer with increasing charge mass within a design type, as might be expected from previous work [2][3]7]. The impulses measured in the current experiments were approximately 10% lower than those reported by Yuen et al [2] due to improvements in the clamp frame design in the present work.…”

“…Ultimately, mono V-structure MRAP hull design history has shown that operational constraints must be of primary importance during selection of underbelly protection systems [6]. A 45° internal angle would result in the lowest impulse transfer and the lowest deformation but would require a very high ground clearance, and so mono V-structures usually have internal angles in the 105-120° range, such as the Casspir [6][7]. In the new designs considered herein, ground clearance was removed as a factor by ensuring all designs fitted into the same envelope as the mono 120° V-structure baseline design.…”

“…Computational modelling of the clamp frame design used in reference [2] showed that it produced impulse recirculation along its clamped edge that would not be representative of a real MRAP vehicle hull [7]. Thus, the clamping system was redesigned such that the clamps were attached along the straight vertical edges, as shown in Figure 2.…”

“…Several designs are proposed and evaluated by comparing the deformation, rupture and impulse transfer characteristics to those of a conventional mono 120° V-structure subjected to the same air-blast loading conditions. The results are compared to previous experimental work on more traditional V-structures at the same scale [2][3]7]. Some practical considerations for the design of steel V-structures are discussed using the experimental results.…”