Numerical Modeling of Suction and Trench Formation at the Touchdown Zone of Steel Catenary Riser
Bibliographic record
Abstract
Steel catenary risers (SCR) are widely used in deepwater oil and gas production. The riser–seabed–water interaction near the touchdown zone is one of the main concerns in the design of fatigue life of SCR. During upward displacement, suction develops under the riser and a trench might be formed when it separates from the seabed near the touchdown point. In the subsequent downward movement, the riser penetrates through this trench to the seabed. Therefore, modeling of suction and trench formation is very important. In the existing models available in the literature for uplift resistance, these factors are incorporated using empirical relationships. It is also recognized that the available finite-element (FE) modeling techniques for this large-deformation problem are computationally very expensive, although penetration behavior can be simulated. In the present research program, both penetration and uplift behavior are simulated using FE and computational fluid dynamics (CFD) approaches. The simulation results for penetration are presented in Hawlader et al. (2014). In this paper, CFD simulations of uplift resistance, suction and trench formation using ANSYS CFX are discussed. A new model for undrained shear strength of soft clay is proposed that is applicable to a wide range of shear strain rates. The effects of strain rate and strength degradation are incorporated properly in ANSYS CFX and simulations are performed for one penetration-uplift cycle. Comparing with empirical models developed from experimental results and also with FE results for idealized conditions, it is shown that the present CFX model can simulate the suction and uplift resistance. Moreover, the CFX model developed in this study using the subdomain approach is computationally very efficient. The suction under the riser is the main source of uplift resistance for shallow embedments. The parametric study shows that the maximum uplift resistance and depth of trench depend on uplift velocity and the undrained shear strength of clay.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.002 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".