S. Keerthi Raaj

Bio: S. Keerthi Raaj is an academic researcher from Indian Institutes of Technology. The author has contributed to research in topics: Torpedo & Engineering. The author has co-authored 2 publications.

Foldable Torpedo Anchor: A Novel Anchoring System for Deepwater Floaters

Abstract: Ultra-deepwater energy resources are explored very little to till date. Depletion of oil and gas in shallow water depth made the exploration into the deep and ultra-deepwater resources. The offshore floating energy extractors like wind turbines, oscillating water column, offshore oil exploration production and drilling platforms often needs an efficient anchoring system. The development in offshore gas exploration and platform construction has made use of several anchor types like vertically loaded drag anchor (VLA), Omni-Max anchor, suction embedded plate anchor (SEPLA) and dynamically embedded plate anchor (DEPLA) to withstand heavy mooring loads. In the late 1990s, torpedo anchors were made, which were inexpensive and less time-consuming to install due to the simple installation technique. The anchors penetrate the target embedment depth by the kinetic energy acquired in the process of free fall, and the installed anchor is moored to the floating structure. Even though the torpedo anchors are able to withstand ample horizontal loads, in the case of vertical load-carrying ability, their performance is poor. This is one of the main reasons the concept has not become very popular in practice despite its simplicity. Hence, there is a need to improve the conventional anchor suffering from low vertical load-carrying ability. The objective of the present study is to depict the novel foldable torpedo anchor (FOTOAN) concept, design developments and installation mechanism. The FOTOAN is similar to the conventional torpedo anchors but comprises of foldable wings and fins which extend laterally to increase the pull-out resistance. Thus, the FOTOAN can be an efficient technique for deepwater anchoring applications.

Vertical Pull-Out Capacity of Torpedo Anchors

Abstract: In recent years, the novel concept of dynamically installed anchors like torpedo-shaped anchors has a significant development in offshore gas exploration and platform construction. Torpedo anchors are those which breach to the designated embedment depth by the kinetic energy acquired in the process of free fall and develop vertical as well as horizontal pull-out resistances. The large scale of uncertainties in pull-out capacity theoretical prediction often requires a finite element analysis. Hence, this paper investigates the vertical pull-out resistance offered by torpedo pile anchors through numerical simulation using PLAXIS. The kaolin clay soil properties are assumed, and modified cam clay (MCC) soil model is assigned throughout the entire numerical simulation. The cylindrical-shaped torpedo pile anchor was modelled with “wished in place” configuration as zero fin, blunt tip with four different aspect ratios (\(l/d\) = 5, 10, 15, 30), and each anchor is analysed under four different embedment depths to anchor height ratios (\({D/l}\) = 2, 2.5, 3, 3.5). The effects of embedment ratio and aspect ratio and their influence on the anchoring capacity were studied, and the numerical results are validated through the established empirical results. The pull-out capacities of the anchors are further studied for varying disturbed zone diameter of (1D, 2D, 3D and 4D). And hence, it is concluded that the character of the remoulded soil significantly influences the vertical pull-out resistance and the extent of remoulded soil zone due to anchor penetration is between 3D to 4D.

Exploration of deep-water torpedo anchors - A review

Abstract: It is worth deliberating on torpedo anchors, a development that emerged in the offshore exploration field in recent times. The demand for ocean renewable energy exploration and this interest required developing a new sort of mooring and anchoring systems for offshore platforms. Though a vast type of anchors has been developed, the literature lacks a critical review of torpedo anchors. This critique summarizes a state-of-the-art discussion on torpedo anchors. It aims to review the developments of deep-water torpedo anchors that occurred during the last few decades. The level of growth achieved in this field is significant, economical, and reliable, making it simple and easing the anchor installation operation. This paper recapped the detailed survey of theoretical, experimental (laboratory and field-test) and numerical analysis and design of torpedo anchors and reviewed their performance. And a complete discussion of the torpedo anchor's primary factors (pullout capacity and embedment depth) influencing characteristic features is explained. In addition, it describes the soil failure process of the anchors during penetration and pullout of the anchor. A wide range of features for the application of torpedo anchors is readily enabled. In conclusion, the current challenges encountered in this field are mentioned.

Analysis of Torpedo Anchors for Mooring Operations

Abstract: A novel technique of dynamically installing torpedo-shaped anchors is investigated. A vast extent of uncertainties arises in pull-out capacity estimation due to the excessive tilt of a torpedo anchor during free-fall and subsequent embedment into the seafloor. This paper will investigate the issues encountered by the torpedo anchor during the vertical drop, which ultimately reduces the pull-out resistance. The pull-out resistance study offered by torpedo anchors is investigated using a finite element tool, PLAXIS 3D. A series of pull-out tests were conducted with anchors under four different ballast conditions (20, 40, 60 and 80%) with three chosen fin configurations (without fin, 3 fins and 4 fins). The anchors are tested for various inclinations (0°, 2.5°, 5°, 7.5° and 10°) and the effect of torpedo anchor tilt on pull-out resistance is studied, and the allowable range of anchor tilt was recommended. Thus, this study provides the benefit of ideal ballast and fins arrangements.

FOTOAN: A Novel Deepwater Anchoring System

Abstract: The lack of energy resources in shallow water depths made deepwater energy resources exploration as an important step. Deepwater energy devices like floating offshore wind turbines (FOWT), hybrid and integrated energy systems, and mobile offshore drilling units often need anchoring support, which is adaptable to all marine conditions. There are several marine anchor types like drag anchors, suction anchors and self-installing anchors, in which dynamically embedded anchors are popular due to the simple installation procedure. In the taut-leg or vertical mooring systems, these dynamically embedded anchor's performance is unsatisfactory. Also, their excess pore pressure dissipation time after installation in NC clay is higher, which made them lesser attractive. Despite its simplicity, this anchoring concept has not gained widespread acceptance for the above-mentioned reasons. Hence, the present work described the novel anchoring concept of foldable torpedo anchor (FOTOAN) and their working mechanism, theoretical capacity estimation and installation sequence in detail. A limited comparative laboratory study of the FOTOAN to the traditional torpedo anchor in soft clay shows the FOTOAN to be more efficient. In the vertical mooring systems, the performance is improved by 3.5 – 5 times. Thus, the FOTOAN has been promised as an efficient technique for deepwater anchoring applications. Also, the installation sequence of FOTOAN with the aid of two anchor handling vessels (AHV-1 & AHV-2) are presented as an example case study.