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TECHNICAL PAPERS

Torpedo Anchor Installation Hydrodynamics

[+] Author and Article Information
Antonio Carlos Fernandes

COPPE/UFRJ

Jairo Bastos de Araujo, José Carlos Lima de Almeida, Rogério Diniz Machado, Vinicius Matos

Petrobras

J. Offshore Mech. Arct. Eng 128(4), 286-293 (Jun 06, 2006) (8 pages) doi:10.1115/1.2355514 History: Received June 30, 2005; Revised June 06, 2006

The installation procedure of a torpedo anchor is the release of the torpedo from a high enough position from the sea bottom to allow the device to reach the terminal velocity. A sufficient kinetic energy at the bottom is essential for the penetration. Besides this, the anchor has to reach the bottom in an upright position to maximize the final holding power in all directions. The present work addresses two hydrodynamic aspects for the installation design and analysis. The first is the drag evaluation and the second is the directional stability. If the drag is to be kept small, then the terminal velocity should be high. The work shows that parameters like the mass and the shape are essential for this. On the other hand, the shape and mass distribution have a strong influence on the directional stability. One important parameter is the rear line length connected to the anchor. This line is necessary for further connection with the final mooring line and influences both the terminal velocity and the directional stability. The work addresses all these aspects under the light of an innovative model test setup to be performed in a deep ocean basin. This kind of model testing has been conceived specifically to attend the torpedo anchor evaluation.

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Copyright © 2006 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Example of a torpedo anchor; this version of the torpedo is a pile with fin nose with large fins

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Figure 2

Starting arrangements for the torpedo anchor installation

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Figure 3

Torpedo free-body diagram during installation launching

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Figure 4

Extrapolation mathematical model (EMM) applied with the data from the tests in the ocean basin; at the time about 1.2s the safety spring starts to act, the extrapolation follows then analytically using the EMM formulas 11,6,12; F1C2 torpedo anchor case

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Figure 5

Vertical rear line free-body diagram

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Figure 6

Test setup for the rear line; two pulleys were used to support the lines before and during the torpedo anchor release; two positions for the cameras were used

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Figure 7

Hydrodynamic forces and moment and the definition of the hydrodynamic center (CH); point O is an arbitrary pole and A is the center of the transverse force (FN)

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Figure 8

Position of the hydrodynamic center (CH) and the center of gravity (CG) for the torpedo anchors F1C2 tested in the ocean basin; XCH is the case without fins neither vertical rear line; XCH′ is the case with fins; XCH″ is the case with fins and vertical rear line

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Figure 9

Arrangement in the ocean basin for the vertical launching of the 1:15 torpedo anchor model; a safety spring together with a cable have been introduced; the camera was used for a video tracking system to obtain the trajectory; the launching was made above the ocean basin extra 10m pit

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Figure 10

Safety spring used during the test in the ocean basin

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