Fragment Identification Method Based on DBSCAN and Its Application in Hypervelocity Impact of Whipple Shield

The mesh-free method is widely used in simulating aerospace protection structures. However, representing the continuum with discrete particles hinders the actual shape of fragments, thus limiting its capacity to support quantitative studies on the effectiveness of aerospace protection structures. In this paper, the Density-Based Spatial Clustering of Applications with Noise (DBSCAN) algorithm was applied to mesh-free method for fragments identification. The algorithm considering geometric discrimination (spatial coordinates) and physical discrimination (velocity distribution) was proposed for fragment identification. The key parameters of the DBSCAN algorithm were thoroughly discussed and validated. The method was then applied to a Whipple shield impact with an outer bumper thickness to projectile diameter ratio of 0.4 and an impact velocity of 5.29 km/s. The fragment characteristics (number, size, momentum, and kinetic energy) and damage to the Whipple shield were analyzed. Results showed that fragment identification was crucial to the mesh-free method as it prevented overly conservative estimations of the fragments damage, i.e., momentum density based on particle statistics was twice as high as that based on fragment statistics. The analysis indicated that the number and kinetic energy of the outer bumper fragments were greater than the projectile fragments and were the main cause of the severe damage to the spacecraft wall.