brazil-2014ugm-torpedo-anchor-in-seabed.pdf

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FEM Modelling of the Torpedo Anchor

Penetration in the Seabed

Pedro Henrique Epichin Cheroto

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Topics

General Idea

Motivation

Overview

Geometry

Material

Meshing

Solution

Results

Final Remarks

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What is a Torpedo Anchor?

What is its use?

Torpedo Anchor General Idea

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Torpedo Anchor modelling in Ansys

Goal: correctly predict the anchor pull-out capacity

Torpedo Anchor Motivation

The soil displacement during the

penetration causes an increased stress

and pore pressure on the regions near

the anchor, resulting in a reduced pull-

out resistance. Subsequent soil

reconsolidation will provide a recovery

of the pull-out capacity.

The pullout resistance is mostly

caused by the shear strength in the

soil-anchor interface which is greatly affected by the reconsolidation time

after the installation.

Today we focuse on the

stationary solution, were the

pore pressure field is

consolidated. Pore pressure

relaxed to stationary condition

result in larges effective stress

in the soil and the largest pull

out capacity.

We do not model the

interface capacity. The

anchor pull-out capacity

is limited by the soil

material limits.

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Analysis Overview

Model Based on paper from Sturm H. and Andresen L (2010)

Automated model in Ansys APDL to generate the geometry, mesh,

contacts, loads and solution config.

Model with ineherent Ansys material models for soil - drucker

prager.

Model with multiPlas materials for soil

Tresca

Mohr Coulomb

Torpedo Anchor Overview

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Geometry

Axissimetric Model

Small gap between axissimetric axis and geometry, to prevent mesh distortion problems, based on assumption of Cudmani and

Sturm (2006)

Torpedo Anchor Geometry

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Material

The material model used for the soil in this case is Tresca, from the multiPlas material library

A region with reduced stiffness was created to simulate an infinite domain, based on a proposal from Burd and Houslby (1990)

The torpedo anchor was modelled with as a rigid line

Torpedo Anchor Material

Region with reduced

stiffness.

Torpedo

anchor

modelled as

rigid line.

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Meshing

Initially mapped mesh, with rezoning after initial penetration

Torpedo Anchor Meshing

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Solution

Quasistatic solution, with many substeps for stability and accuracy

Rezoning to solve convergence issues

Large strains create large mesh distortions

Torpedo Anchor Solution

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Results

With mises and tresca failure: Radial stress results comparison.

Similar contours.

Torpedo Anchor Results

Radial Stress contours in

Abaqus model Radial Stress Contours in Ansys

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Results

With mises and tresca failure: Normalised Stress Components.

Very similar results, with small differences near the torpedo anchor

interface with the soil.


Normalised Stress Components -

Abaqus Normalised Stress Components - Ansys

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Results

With mises and tresca failure: Residual stresses and Strains.

Same behavior on both models, the stresses on the near wall region

after the installation of the anchor are higher on Ansys models


Strain at midheight of the anchor and Radial above the

anchor, after installation - Abaqus

Strain at midheight of the anchor and Radial above the

anchor, after installation - Ansys

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Results

With mises and tresca failure: Normalized stress results over time

at depth 5.8m, 0.3 meters away from the anchor

Again, very similar results, with slightly different values after the anchor

insertion.


Normalized stresses during penetration -

Abaqus Normalized stresses during penetration - Ansys

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Additional remarks

Although the mohr-coulomb and drucker prager material models

can be used to model more realistic materials, on this particular

case, experimental data would be required to define the material

parameters.

The normalized results of ansys and abaqus are almost the same,

but the paper used does not give the exact material parameters, so

the actual results will differ.

The results from simulations using Tresca and Mises failure were

almost the same. For that reason, the images in this report are

from only one of the simulations the one using tresca failure

criteria.


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Cudmani, R. and H. Sturm (2006).An investigation of the tip resistance in granular and soft soils during static, alternating

and dynamic penetration. In H. Gonin, A. Holeyman, and F.

Rocher-Lacoste (Eds.), TransVib 2006: International

Symposium on vibratory pile driving and deep soil compaction,

pp. 221231.

Burd, H. and G. Houlsby (1990). Finite Element Analysis of two Cylindrical Expansion Problems involving nearly Incompressible

Material Behaviour. International Journal for Numerical and

Analytical Methods in Geomechanics 14(5), 351366.

Sturm, H. and Andresen, L. (2010). Large deformation analysis of the installation of Dynamic Anchor. Numerical Methods in

Geotechnical Engineering Benz & Nordal (eds) 2010 Taylor & Francis Group

References

Documents

brazil-2014ugm-torpedo-anchor-in-seabed.pdf