Examining the Dampening Effect of Pipe-Soil Interaction at the Ends of a Subsea Pipeline Free

Span Using Coupled Eulerian-Lagrangian Analysis and Computational Design of Experiments

ASME V&V 2013

Authors: • Marcus Gamino• Samuel Abankwa• Ricardo Silva• Leonardo Chica• Paul Yambao

• Raresh Pascali• Egidio Marotta,• Carlos Silva• Alberto Rivas

ASME V&V 2013

Motivation

• To validate assumptions made in current recommended practices (e.g. DNV-RP-F105) by developing advanced computational models.

“Boundary Conditions applied at the ends of the pipeline section modeled shall adequately represent the pipe-soil interaction and

the continuity of the pipeline” (DNV-RP-F105).

Motivation

ASME V&V 2013

Objective

• To develop a new methodology for free span VIV assessment that accounts for the effects of factoring in pipe-soil interaction at the ends of the span.

Objective

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Outline– Background– Overview of the Methodology– Assumptions– Methodology– Computational Design of Experiments (DOE)– DOE Results– Conclusions– Future Work– References– Questions

Outline

ASME V&V 2013

Free Span• A free span is a section of

subsea pipeline that is not supported by the seabed.

• Caused by:– Seabed unevenness– Change in seabed topology

caused by the environment

• Susceptible to fatigue damage from vortex induced vibration

www.formshore.com

Background

http://www.neo.no/research/pipeline/xplisit.html

ASME V&V 2013

Vortex-Induced Vibration• Alternate vortices develop

behind the structure as the underwater current moves past the pipe

• This alternate vortex shedding results in structural vibrations of subsea piping components including free spans and jumpers

• Maximum amplitude of displacement occurs when the structure’s natural frequency is the same as the vortex shedding frequency behind the structure

Background

ASME V&V 2013

Overview of the Methodology

DOE

Overview

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Assumptions• single mode response

(1st mode)

• uniform current flow

• no affect from seabed distance

• an empty pipeline

• even seabed topology

• zero axial tension

Assumptions

ASME V&V 2013

Free Span Geometry and Properties• The geometry used for both

FSI and CEL simulations was a pipeline free span with a length of 10.2 meters (400 inches), an outside diameter of 0.254 meters (10 inches), and a thickness of 0.0254 meters (1 inch). The material of the free span is carbons steel grade X65.

Visualization of Free Span for FSI and CEL Simulations

Carbon Steel X65 Properties

Methodology

ASME V&V 2013

Modal Analysis• Modal analysis is used in this research to find the natural

frequencies of the pipeline free span. The component’s natural frequency depends on various factors including the span length, thickness of the pipe, contents within, and insulation.

Mode 1 of the Free Span Mode 1 of the Jumper

Methodology

ASME V&V 2013

Fluid-Structure Interaction (FSI) Overview• When a fluid flow interacts with a solid structure• STAR-CCM+, the CFD software, can perform fluid-structure

interaction with ABAQUS, the FEA software. During two-way FSI co-simulation, the CFD code and the FEM code run simultaneously, and data is mapped back and forth automatically between STAR-CCM+ and ABAQUS at each iteration.

Methodology

ASME V&V 2013

FSI ResultsMode 1 of the Free Span

Mode 1 of the Jumper

Jumper Deformation Results from Two-Way FSI Studies

Free Span Deformation Results from Two-Way FSI Studies

Methodology

ASME V&V 2013

Determining Displacement vs. Time Histories• At least one segments of the

length equivalent to one outside diameter of the free span to have their displacement amplitude defined along the span

• More segments may need to be defined pending on the mode response and the length of the free span.

Methodology

ASME V&V 2013

Choosing the Correct Pipe-Soil Model

• Pure Lagrangian

• ALE (Arbitrary Lagrangian Eulerian)

• CEL (Coupled Eulerian-Lagrangian)– Used Mohr-Coulomb

Plasticity

ALE

CEL

Methodology

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The CEL Model and Results• The free span model for the CEL

simulations included the 400 inch free span section and two additional 20 inch pipe sections supported by the seabed.

CEL FE Free Span Model Setup CEL FE Free Span Model Pipe-Soil Effects

CEL FE Free Span Model Resulting Stress Locations

Methodology

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Design of Experiments• Variables:

– Length of Contact with Soil (a)

– Entrenched Depth of span (b)

– Soil Density

ba

Computational DOE

itl.nist.gov

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Screening within JMP Software

• Pipe depth has the biggest influence on the stress response of the free span.

DOE Results

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Design of Experiments

DOE Results

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JMP Prediction Profiler

• Lowest stress response at:– Pipe fully entrenched

– Longest Pipe-Soil Contact

– Soil density is at highest or lowest value

DOE Results

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Without Soil Results:• Max Stress = 1600psi

With Soil Results:• Max Stress = 1050psi

DOE Results (Comparison)

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Conclusions• By taking into account the effect of pipe-soil interaction at the end of the free

span beyond the effective length, it was found that the soil reduces the magnitude of the stresses at the location of the effective free span’s ends.

• Maximum stress at the ends of the effective length of the pipe within the finite element (FE) model decreased as the pipe’s embedment within the soil increased and the pipe’s contact with the soil along its length increased.

• This newly found mitigation of stresses due to the free span’s interaction with the soil at its ends could prove cost effective in the design of subsea pipelines and the assessment of free span corrective action.

• To accomplish the combining of the two FSI and CEL analyses for this case, the CEL soil response has to be calculated at every iteration of the FSI coupling between STAR-CCM+ and ABAQUS. Future analysis should focus on combining the FSI and CEL simulations to more accurately determine the stress results.

Conclusions

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Future Work• To model the soil during the FSI simulations:

-Abaqus

-STAR-CCM+

-ANSYS

Future Work

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Future Work• Different computational DOE

models to validate results

• Fatigue life analysis based on ASTM standards (e.g. ASTM E1049) may be performed in combination with the Palmgren-Miner rule to estimate the fatigue life.

• Combined FSI Analysis of External Flow, Pipe-Soil Interaction and Internal Flow on Subsea pipelines

Future Work

ASME V&V 2013

References• Abaqus Version 6.7 Extended Functionality Documentations, 2007.• Abdalla, B., Pike, K., Eltaher, A., Jukes, P., and Duron B. Development and Validation of a Coupled Eulerian

Lagrangian Finite Element Ice Scour Model. Proceedings of the ASME 28th International Conference on Offshore Mechanics and Artic Engineering. (2009): 1-9.

• Blevins, R.D. Formulas for Natural Frequency and Mode Shape. New York: Van Nostrand Reinhold, 1979.• Chica, L., Pascali, R., Jukes, P., Ozturk, B., Gamino, M., and Smith, K. Detailed FSI Analysis Methodology for Subsea

Piping Components. Proceedings of the ASME 31st International Conference on Offshore Mechanics and Artic Engineering. (2012): 1-11.

• Hesar, M. Pipeline-Seabed Interaction in Soft Clay. Proceedings of the ASME 23rd International Conference on Offshore Mechanics and Artic Engineering. (2004): 1-9.

• Palmer, Andrew Clennel, and Roger A. King. Subsea Pipeline Engineering. Tulsa, Okla: PennWell, 2008.• Recommended practice DNV-RP-F105. (2002). Free Spanning Pipelines. Hovik, Norway: Det Norske Veritas. • Silling, S. A. (1993). Simulation of Penetration and Perforation with CTH, Advances in Numerical Simulation

Techniques for Penetration and Perforation of Solids. American Society of Mechanical Engineers, Applied Mechanics Division, 57-66.

• “Standard Practices for Cycle Counting in Fatigue Analysis.” ASTM E1049 - 85(2011)e1. • Star CCM+ Training. “Lectures CCM+.” CD-Adapco offices. Houston, TX 15 Jul. 2011.

References

ASME V&V 2013Thank You

ASME V&V 2013

Questions?

Questions