Visualizing the effect of Fin length on torpedo anchor penetration and pullout using a transparent soil

The effect of torpedo shape on its penetration depth and pull out capacity is explored using laboratory-scale experiments. The study offers a number of useful practical implications for the design of full-scale torpedo anchors. Results demonstrate that the resistance to penetration and extraction of torpedo anchors is strongly affected by their fin design. A transparent soil surrogate made of Magnesium Lithium Phyllosilicate (MLPS), was employed to simulate soft marine clay. Three torpedo models having a length to diameter (L/D) ratio of eight and a similar weight (W), but different fin length to diameter ratios (L_F/D) of zero (no fins), 2.6, and 5.2, were penetrated, vertically, at an impact velocity of 4.5 m/s. It was found that fin length correlated negatively with penetration depth (P) and positively with the maximum resistance to extraction. However, the maximum extraction resistance, normalized by weight (W), increased from 2.3 for the case of no fins to 3.1 for short fins and to 3.6 for long fins. Transparent soils enabled measurement of in situ displacements within the target during penetration and pullout and correlating them to the torpedo behavior. Soil displacement increases with the increase of penetration depth till full embedment, after that displacements remain constant.