Offshore Technology Research Center

 

OTRC Project Summary

Project Title:

Numerical Modeling of Torpedo Anchors

Prinicipal Investigators:

John Tassoulas

Sponsor:

Minerals Management Service and Industry Consortium

Completion Date:

August, 2008

Final Report ID#

B174 Year One Report(Click to view final report abstract)

OBJECTIVE:

This Research Project is aimed at development and application of numerical models for the analysis of installation, behavior and strength of torpedo anchors. The Project will utilize and extend earlier developments at OTRC on suction caissons. Studies will be conducted to establish the relative significance of factors affecting the performance of torpedo anchors and variants, thus contributing toward improved design of these deep-water foundations.

APPROACH:

The computational techniques to be developed in the course of this work will be based on the finite-element method and will take into account the nonlinear behavior of clayey and sandy soils where torpedo anchors may be installed. Procedures used in earlier work on suction caissons will require modifications to reflect the dynamics of torpedo entry and subsequent trajectory into the soil, the three-dimensional features stemming from off-vertical penetration and the presence of flukes, and rate-dependent aspects of soil behavior.

DEPLOYMENT OF RESULTS:

By virtue of ease of installation, torpedo anchors appear to be promising foundations for deep-water applications. The proposed work will explore the mechanics underlying the performance of these anchors and will thereby seek to contribute to design improvements. Results of the work will be disseminated through presentations, dissertations, theses, reports and conference and journal articles.

PROJECT PLAN FOR YEAR 1 (2005 -2006):

Scope and Plan: The literature on torpedo anchors or piles, also known as “rocket” anchors, and several variants installed by release from some depth, “free” fall through the seawater and penetration into the seabed, will be reviewed in order to fully understand the current state of the art in the design and practice of such anchoring systems. Alongside the literature review, a database of available experimental evidence and measured-performance records will be compiled. Our activities will then focus on the development and demonstration of numerical models that can be used effectively in simulating the installation and subsequent behavior of torpedo anchors. The following Tasks are envisioned during Phase 1 of the Project:

Task 1: A thorough examination of the literature will be conducted in this Task. Preliminary search suggests that current torpedo-pile technologies, although reportedly already in use, are not documented in widely available comprehensive reports, or easily retrievable journal articles. The most likely sources of information appear to be relatively few conference articles and progress reports of limited circulation. Therefore, we expect that our review of the literature will involve not only traditional information mining but, in addition, personal communications with engineers and other industry representatives.

Task 2: An up-to-date database of available measurements and experience related to installation, behavior and performance of torpedo anchors will be compiled in this Task. We are already familiar with other academic research efforts with regard to small-scale rocket-anchor model testing. Other important records of tests, especially full-scale, are only partially described in easily accessible conference articles or reports. Success in this Task will require, as in Task 1, communications, exchanges and discussions of ideas and, possibly, collaborations with engineers and researchers active in using and further developing torpedo piles.

Task 3: Numerical models of torpedo piles based on the finite-element method and built on our earlier extensive modeling experience with suction caissons will be developed in this Task. Various levels of sophistication and detail will be explored until reasonable balance between model fidelity and model practical effectiveness can be achieved. Nonlinear behavior of clayey and sandy soils where torpedo anchors may be installed will be taken into account, including consideration of rate-dependent effects of soil behavior, especially during installation. The models will be capable of simulating penetration into the seabed at arbitrary angle of torpedo-pile incidence. However, it is expected that, during Phase 1 of the Project, attention will be focused on the relatively more straightforward case of vertical incidence. As in our previous work on suction caissons, the computational procedure that will be formulated in this Project will provide information not only on the state of stress in the soil immediately after installation but, as well, on the dissipation of the pore-water pressure field and the accompanying changes in soil behavior and strength during, relatively long-term, reconsolidation of the soil-pile system, and estimates of the pull-out capacities of torpedo piles at various times after installation.

Task 4: Simulations of vertical torpedo-anchor installation will be pursued in this Task. The objectives will be twofold, to demonstrate the effectiveness of the numerical models in this relatively simple case, from the viewpoints of modeling and computational effort, and to obtain a baseline that can be used later in this Project in exploring off-vertical incidence, an issue of concern in torpedo-pile performance.

Task 5: A Report of our work and progress during Phase 1 will be prepared in this Task. It is expected that parts of the Report will be ready relatively early and will be made available as soon as possible thereafter, upon completion of the literature review and compilation of the test and performance database.

Anticipated Results: The knowledge available on torpedo anchors will be compiled. The procedure for nonlinear, dynamic finite-element analysis of vertical torpedo anchor penetration into the soil will be described along with examples of simulations.

PROJECT PLAN FOR YEAR 2 (2006 - 2007):

Scope and Plan: Off-vertical torpedo entry, penetration and extraction: finite-element modeling; preliminary computations and comparisons with available laboratory test data on torpedo anchor models.

Anticipated Results: The procedure for nonlinear, dynamic finite-element analysis of torpedo anchor response will be described and preliminary computational results will be reported.

PROJECT PLAN FOR YEAR 3 (2007 - 2008):

Scope and Plan: Parametric studies of torpedo anchor installation and holding axial and lateral capacities; effects of entry angle, speed, rate-dependence of soil behavior, flukes and other features.

Anticipated Results: The parametric studies along with the computational tools will be documented.

 

©2013 All Rights reserved Offshore Technology Research Center