The motivation of the thesis is to develop a new type of dynamically installed anchor concept and experimentally analyze the novel foldable torpedo anchor (FOTOAN). The FOTOAN has been proposed as an efficient technique for deepwater anchoring applications, especially for offshore floating energy extractors like wind turbines, oscillating water columns, offshore oil exploration production and drilling platforms made of FPS, SPAR, TLP etc. The FOTOAN is similar to the conventional torpedo-shaped dynamically installing anchors (DIA’s) but comprises foldable wings and fins, which extend laterally to increase the pullout resistance. The FOTOAN is installed to the target embedment depth into the seabed by free fall in the water column (similar to the conventional DIA anchors). After the embedment, the central shaft is tensioned, making the anchor wings extend perpendicularly in the soil with minimal loss in the embedment depth. The wings consist of fins and hinges, which act as an inclined plated anchor and support the load eventually. Thus the FOTOAN combines the functions of DIA for easier installation and plate anchor for increased load-bearing resistances.
This study aimed to assess the geotechnical performance of the novel FOTOAN through 1g laboratory experimental studies. The 1g laboratory study was conducted with 1:50 scale-down models to verify the proof of concept, the anchor folding mechanism and the failure phenomenon. All the 1g laboratory tests are performed in the Department of Ocean Engineering at IIT Madras. The reduced scale-down model anchor is instrumented with the Inertial Measuring Unit (IMU) to record the anchor acceleration profile during the free fall and subsequent penetration into the soil. The drop test is conducted with the instrumented anchors in a 4.5m deep water pit to study the hydrodynamic behavior of the anchor. From the drop test in a deep water pit, the anchor terminal velocity, drag coefficient, and drag force variation due to the change in the ballast weight, nose shape, and fin length was estimated experimentally. In the drop test in kaolin test beds, the anchors are made to fall freely into the prepared test tanks at different drop heights and ballast weights, the corresponding anchor embedment depth, loss in the embedment depth during the keying process and the ultimate pullout capacity are studied in detail. Accounting the following parameters like nose shape, fin numbers, extension angles and setup period to study their effects on embedment depth and pullout resistance. Based on the experimental results, key observations are made, and FOTOAN has been proposed as an efficient technique for deepwater anchoring applications.