ASME V&V Authors: Marcus Gamino Samuel Abankwa Ricardo Silva Leonardo Chica Paul Yambao

Transcription

1 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 Authors: Marcus Gamino Samuel Abankwa Ricardo Silva Leonardo Chica Paul Yambao Raresh Pascali Egidio Marotta, Carlos Silva Alberto Rivas

2 Motivation 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).

3 Objective 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.

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

5 Background 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

6 Background 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

7 Overview Overview of the Methodology DOE

8 Assumptions Assumptions single mode response (1 st mode) uniform current flow no affect from seabed distance an empty pipeline even seabed topology zero axial tension

9 Methodology 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 meters (10 inches), and a thickness of 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

10 Modal Analysis ASME V&V 2013 Methodology 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

11 Methodology 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 cosimulation, 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.

12 Methodology FSI Results Mode 1 of the Free Span Free Span Deformation Results from Two-Way FSI Studies Mode 1 of the Jumper Jumper Deformation Results from Two-Way FSI Studies

13 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. ASME V&V 2013 Methodology

14 Methodology Choosing the Correct Pipe-Soil Model Pure Lagrangian ALE (Arbitrary Lagrangian Eulerian) CEL (Coupled Eulerian- Lagrangian) Used Mohr-Coulomb Plasticity ALE CEL

15 Methodology 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 Resulting Stress Locations CEL FE Free Span Model Setup CEL FE Free Span Model Pipe-Soil Effects

16 Computational DOE Design of Experiments Variables: Length of Contact with Soil (a) Entrenched Depth of span (b) Soil Density itl.nist.gov a b

17 DOE Results Screening within JMP Software Pipe depth has the biggest influence on the stress response of the free span.

18 DOE Results Design of Experiments

19 DOE Results JMP Prediction Profiler Lowest stress response at: Pipe fully entrenched Longest Pipe-Soil Contact Soil density is at highest or lowest value

20 DOE Results (Comparison) Without Soil Results: Max Stress = 1600psi With Soil Results: Max Stress = 1050psi

21 Conclusions 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.

22 Future Work ASME V&V 2013 Future Work To model the soil during the FSI simulations: -Abaqus -STAR-CCM+ -ANSYS

23 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 ASME V&V 2013 Future Work

24 References References Abaqus Version 6.7 Extended Functionality Documentations, 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, 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): 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, 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, Standard Practices for Cycle Counting in Fatigue Analysis. ASTM E (2011)e1. Star CCM+ Training. Lectures CCM+. CD-Adapco offices. Houston, TX 15 Jul

25 Thank You

26 Questions Questions?