On the estimation of the falling velocity and drag coefficient of torpedo anchor during acceleration

Torpedo anchor installation is a new kind of anchoring system which is much more economical than other conventional anchoring methods. However, there are few studies on the falling velocity and drag coefficient of the torpedo anchors. In this study, seven torpedo anchors with different densities, aspect ratios, scale ratios and fin sizes were utilized to investigate their influence on the falling velocity of the anchor during acceleration. Anchors were released in a water tank and the falling process was recorded using a fast speed video camera. Accordingly, the corresponding drag coefficients against the Reynolds numbers during acceleration were calculated. The Reynolds numbers varied between 4.8 x 10(5) and 2.16 x 10(6) and the drag coefficients varied between 0.2 and 1.2. The differences between the falling velocities and the drag coefficient for anchors with different shapes, sizes, densities and directional stability were illustrated and the reasons for the differences were explained. The final drag coefficients versus the Reynolds numbers were compared with other representative models found in the literature. The influence of acceleration on the drag coefficient or falling velocity was emphasized. Finally, an Extrapolation Mathematical Model for the motion of the anchor in the fluid was proposed and the results were compared to the experimental data. (C) 2012 Elsevier Ltd. All rights reserved.