J2 — Round 2 Review Tracker¶

Journal: Ocean Engineering. Round: R2 (second round of revision). Submission: 2026-01-28 (R1 revised version resubmitted). Deadline: 2026-04-29. Reviewers: 3.

See Papers / J2 for the scientific summary of the paper itself.

Progress¶

6 in progress

13 open

Closed 0 In progress 6 Open 13 Total 19

Next steps (Day 2–6, 2026-04-17 → 2026-04-22) — heavy-lift items first:

R1.1 + R1.2: rewrite §3.1.3 validation with explicit model-vs-centrifuge overlay + per-scour-depth error table; add new §3.1.4 "Parameter transfer from centrifuge to prototype." The single largest block of work and the core of Reviewer 1's recommendation.
R2.1 + R3.5: applicability-boundaries table in new §4.2.1. Merge the two comments into one artefact.
R2.4: wall-clock runtime benchmark script → table in §3.2.1. Matches exactly the figure_generator session spec called out by the J2 methodology prototype — kill two birds.
R2.5: per-bucket load-share + lid-vs-skirt split extraction → figure in §4.1.
R3.1: stiffness-scaling sensitivity sweep (2.0 / 3.0 / 4.0) → figure in §3.1.2. Also flagged by the methodology prototype as missing evidence for claim C4.
R3.2: axisymmetric-scour scope box in §2.4 + extended limitation in §5.

Editor summary¶

The decision letter requests point-by-point responses to three reviewers' comments. R1's baseline reviewer positions were mostly accept-with-minor-revisions. Two reviewers identify methodological clarification needs; one reviewer focuses on validation depth and prototype-scale applicability. No fundamental objections to the contribution.

Reviewer 1 — validation depth and prototype-scale applicability¶

Reviewer 1 explicitly approves of the engineering significance and the distinction between this paper (mechanism-focused) and the companion centrifuge paper J3. Two concerns, both about the validation strategy.

ID	Paraphrased concern	Target location	Planned action	Status
R1.1	§3.1.3 is titled "Validation Against Centrifuge Data" but the figure does not show a direct model-vs-experiment comparison; the validation is currently narrative rather than visual.	§3.1.3 + new Fig 12b	Rewrite subsection with explicit overlay of numerical predictions against centrifuge measurements, plus a per-scour-depth error table.	Open
R1.2	Even if the model passes centrifuge validation, applicability of centrifuge-calibrated parameters at prototype scale needs justification.	New §3.1.4	Add ~400-word subsection on strain-level correspondence, \(G_{\max}\) scaling via DNV-RP-C212, and field-data anchor (−3.9 % baseline match on 32-month Gunsan record).	Open

Cross-cut: R1.2 aligns naturally with the prototype-vs-model error budget that J3's R1 response introduced (§2.2.1 in J3). The same framework for disclosing deliberate centrifuge-to-prototype deviations is re-used.

Reviewer 2 — applicability boundaries, SHM thresholds, labelling, compute, mechanism, AI¶

Seven numbered comments. The technical depth of this reviewer's feedback is high; several comments request quantitative detail the paper currently handles narratively.

ID	Paraphrased concern	Target location	Planned action	Status
R2.1	Applicability boundaries for other soil types (sand, stiff clay, layered) are not defined; interface-adhesion factor \(\alpha\) and stress-correction factor \(\xi\) have no published ranges for non-Gunsan conditions.	New §4.2.1	Table of \(\alpha\) and \(\xi\) ranges per soil class with literature citations; tag untested combinations as future work.	Open
R2.2	Four-level SHM alert thresholds in §4.3 are derived only from 1P-resonance boundary, without validation against operational data, fatigue, or industry standards (DNV, API).	New §4.3.1	Map thresholds against DNV-RP-C212 and IEC 61400-3 fatigue damage-equivalent-load criteria; add correlation analysis. Demo figure ready — `scripts/figures/j2_r2/r2_2_shm_thresholds.py`. Verify IEC mapping against latest revision before paste.	In progress
R2.3a	Fig 13 annotation "7.1 % Drop at \(d = 4.5\) m" lacks the actual frequency value for intuitive reader comparison.	Fig 13 generator	Add \(f_1 = 0.2143\) Hz next to annotation (value is already in Table 8).	Open
R2.3b	Table 4 "Puls Multiplier" suspected typo for "Pult Multiplier".	Table 4	Change \(p_{\text{ult}}\) to \(p_{\mathrm{ult}}\) (robust against DOCX subscript-stripping); plain-text fallback ready.	In progress
R2.3c	Table 8 header \(f_0\) (Hz) is inconsistent with table title "Scour Sensitivity Results".	Table 8	Rename column header to \(f\) (Hz) since the column holds per-row scour frequencies, not baseline.	In progress
R2.3d	Figs 7 and 10 show only units, not axis names.	Fig 7, Fig 10 generators	Add axis labels "Lateral displacement (mm)" and "Vertical reaction (kN)".	Open
R2.4	Distributed BNWF model is claimed faster than 3D FE, but no quantitative runtime comparison is given.	§2.4 or §3.2.1	Add wall-clock benchmarking script and table comparing Mode B, C, D runtimes on identical hardware (single case + batch of 100). Demo figure + CSV table ready — `scripts/figures/j2_r2/r2_4_runtime_benchmark.py`. Replace demo runtimes with real Op³ benchmark before paste.	In progress
R2.5	Load redistribution and lid-bearing mechanisms claimed but not quantified (e.g. per-bucket load share at different scour depths, lid-vs-skirt bearing contribution).	§4.1	Extract per-bucket reactions and lid-skirt split at \(S/D = 0, 0.2, 0.4, 0.6\); new figure. Demo two-panel figure ready — `scripts/figures/j2_r2/r2_5_load_sharing.py`. Replace demo per-bucket reactions with real OpenSeesPy extraction before paste.	In progress
R2.6	Generative AI disclosure under Elsevier policy needs more specificity: proportion of content, verification against model parameters.	Declaration file	Expand disclosure with specific tasks delegated to AI, verification statement against op3-framework v1.0.0 test suite.	Open

Cross-cut: R2.6 boilerplate is reusable for J3's R1 (same author, same journal, same AI-use profile); J3's R1 response already included this text.

Reviewer 3 — modelling assumptions, scope, literature, references¶

Eight numbered comments. Focus on modelling assumptions (strain-level scaling, constitutive choice, axisymmetric scour), literature coverage (jacket dynamics), and turbine-to-model conversion detail.

ID	Paraphrased concern	Target location	Planned action	Status
R3.1	FE-extracted stiffness (at strain ~\(10^{-2}\)) is scaled by factor 3.0 to approximate small-strain dynamic stiffness; needs stronger justification or a sensitivity study.	New §3.1.2	Sweep scaling factor over {2.0, 3.0, 4.0}; report \(\partial f_1 / \partial \text{scaling}\); cite Hardin-Drnevich (1972) and Benz (2007) HS-Small.	Open
R3.2	Circumferentially uniform scour is the baseline, but real offshore scour is often local and asymmetric; the scope of the power-law needs to be stated more explicitly.	§2.4 + §5	Explicit caveat box in method; limitations in conclusions; pointer to asymmetric-scour module (Op³ Mode C) as future work.	Open
R3.3	Literature review needs more coverage of jacket structure dynamic performance under wind / wave / current / seismic loading.	§1.2	Add paragraph citing Hong et al. (2026, SDEE, 110004) on tetrapod jacket under clay + two related refs; shared with J3's R1 response.	Open
R3.4	Real-turbine to OpenSees model conversion lacks detail on tower taper discretisation, RNA mass breakdown, marine growth, soil plug.	§2.4	Expand with tower-taper discretisation details and per-component mass table.	Open
R3.5	Tresca + linear \(s_u\) + fixed \(\alpha\) is specific to normally consolidated clay; layered deposits, stronger small-strain stiffness, and complex interfaces are not discussed.	Merge with R2.1 in §4.2.1	Same applicability table addresses both; layered-deposit generalisation flagged as future work.	Open
R3.6	32-month field validation is baseline-only; no independent scour-survey ground truth.	§5	Acknowledge that no concurrent bathymetric survey exists; current claim is baseline match + inferred trend via Winkler mapping.	Open
R3.7	Scour countermeasures (rock dumping, frond mats, solidified soil) not discussed.	New §4.4	200-word subsection on countermeasure options, citing Liu et al. (2024, CBM, 140858).	Open
R3.8	Reference formatting errors; two recent papers suggested (Wang 2024 Transportation Geotechnics 101433, Liu 2024 CBM 140858).	references.bib	Full CrossRef validator pass; add the two suggested citations; fix any broken DOIs.	In progress

Cross-cut: R3.3 jacket-dynamics citations are the same three used in J3's R1 response. R3.8 reference validator sweep covers both J2 and J3 bibliographies in one pass.

Cross-paper themes and shared artefacts¶

Several R2 items are duplicated or shared with J3's R1 response. Doing them once in a shared form saves approximately 3 hours:

Jacket-dynamics citation block (R3.3 here; J3.R.1.9 + J3.R.3.3 there) — same three citations.
AI-disclosure boilerplate (R2.6 here; J3.R.3.8 there) — same text, paper-specific author list only.
CrossRef DOI validator sweep (R3.8 here) — covers both papers' references.bib in one run.

Full response plan (by day)¶

Day 1 (2026-04-16, completed): R2.3b and R2.3c table-header fixes; R2.6 AI-disclosure draft v1; R3.8 validator pass started; RESPONSE_PLAN.md created.
Day 2–6 (2026-04-17 → 2026-04-22): Heavy-lift items (R1.1 / R1.2 / R2.1 / R2.4 / R2.5 / R3.1 / R3.2 / R3.5).
Day 7–9 (2026-04-23 → 2026-04-25): Remaining text fixes (R2.3a, R2.3d, R2.2, R3.3, R3.4, R3.6, R3.7).
Day 10–14 (2026-04-26 → 2026-04-29): Full-manuscript coherence pass, response letter final draft, figure regeneration and gallery rebuild, submission packet assembly.

Open questions for author sign-off¶

Confirm the three jacket-dynamics citations for R3.3 (Hong 2026 SDEE 110004 is reviewer-specified; second and third refs?).
Confirm the new §3.1.4 structure ("Parameter transfer from centrifuge to prototype") before writing.
Approve tentative ranges for \(\alpha\) and \(\xi\) across soil types for the applicability-boundaries table (R2.1 + R3.5).
Approve Hardin-Drnevich and Benz (2007) HS-Small citations for R3.1 (stated from memory; author to verify before citing).

Raw reviewer comments (verbatim from decision letter, 2026-01-28 / OE-D-26-00984R1)¶

The text below is the journal's decision letter and the three reviewer reports exactly as received. Paraphrased summaries in the tables above are derived from this source; this section is the source of truth if any interpretation is disputed.

Editor's decision letter

Title: Scour-Induced Natural Frequency Degradation of Offshore Wind Turbine Tripod Bucket Foundations Using a 3D FE-Calibrated Winkler Model

Editor: Prof. Tiago Ferradosa, Deputy Editor, Ocean Engineering

Dear Professor Kim,

The reviewers have commented on your above paper submitted to Ocean Engineering. I would be grateful if you could address the comments by the reviewers given below and resubmit your revised manuscript by Apr 29, 2026. Please carefully address the issues raised in the comments.

Reviewer #1 — verbatim

The investigation into scour-induced natural frequency degradation of offshore wind turbine foundations is of significant engineering importance. As offshore wind turbines are dynamically sensitive structures, their natural frequency must be maintained within a narrow operational window to avoid resonance with environmental loads. Scour, which alters the foundation's effective stiffness and soil-structure interaction, directly threatens this critical design requirement. Although the tripod bucket foundation has been increasingly adopted to support large wind turbines, its dynamic response under scour conditions remains insufficiently understood. Therefore, addressing this knowledge gap thus holds both academic value and practical significance for the design of offshore wind farms.

This manuscript presents a 3D FE-calibrated Winkler model that extracts nonlinear spring parameters from 3D finite element limit analysis and maps them to a beam on nonlinear Winkler foundation in structural dynamics model. This method is used to investigate scour-induced natural frequency degradation. As the author has pointed out that this paper is to provide the mechanism of natural frequency degradation, which is different from the companion paper. The validation of the numerical model requires further clarification and strengthening.

For example, Section 3.1.3 is titled "Validation Against Centrifuge Data," which leads the reader to expect a direct comparison between the numerical results and experimental measurements. However, based on Fig. 12, it is not evident that such a comparison is being presented. It is currently unclear how the presented results demonstrate validation. The authors should clarify how the centrifuge data were used to verify the model's accuracy, and ideally, provide a direct quantitative comparison between the model predictions and the experimental results.

Secondly, even if the model is successfully validated against centrifuge tests, the applicability of the model parameters to field-scale conditions remains a critical concern. The authors need to provide additional justification or discussion on how the parameters derived from reduced-scale centrifuge tests can be considered representative or appropriately scaled for field-scale applications. Without such a discussion, the credibility of the model's predictions at the prototype scale is not fully established.

Reviewer #2 — verbatim

The 3D FE-calibrated Winkler model proposed in this paper addresses the modeling challenge of natural frequency degradation of tripod bucket foundations under scour conditions. Validated through both centrifuge tests and 32 months of field monitoring data, the conclusions of this study are reliable and possess certain engineering practical value. Specific revision suggestions are as follows:

Comment 1: The model in this paper is validated based on the normally consolidated marine clay at the Gunsan offshore site in South Korea, with only a preliminary comparison conducted using silica sand in centrifuge tests. The applicability boundaries of the model for other typical marine soils (e.g., sandy soil, stiff clay, layered soil) have not been clearly defined. It is required to supplement the adjustment principles of model parameters (e.g., interface adhesion factor α, stress correction factor ξ) for different soil types, or present the key improvement directions for extending the model to non-clay sites, in Section 4.2 Method Comparison with Literature or the future research section following Section 5 Conclusions. This will enhance the engineering promotion value of the model.

Comment 2: The four-level SHM alert thresholds (green, yellow, orange, red) proposed in Section 4.3 are derived solely based on the 1P resonance boundary, without validation against the actual operational data of wind turbines, fatigue damage accumulation laws, or industry specifications (e.g., DNV, API) in engineering practice. It is suggested to supplement the correlation analysis between the thresholds and wind turbine fatigue life as well as operational reliability in Section 4.3 SHM Alert Thresholds and Scour Depth Inference, or clarify the consistency of these thresholds with existing specifications for scour monitoring of offshore wind turbines, so as to make the early warning system more in line with engineering application scenarios.

Comment 3:

The specific frequency value is not labeled for the note "7.1% Drop at d = 4.5m" in Figure 13. Please supplement the actual natural frequency (0.2143 Hz) predicted by the model at a scour depth of 4.5 m for intuitive comparison by readers.
The column name "Puls Multiplier" in Table 4 is suspected to be a spelling error of "Pult Multiplier" and needs to be corrected.
The column name "\(f_0\) (Hz)" in Table 8 should be revised to f(Hz) to correspond with the table header "Scour Sensitivity Results" and avoid ambiguity in data labeling.
Only units are marked for the coordinate axes in Figures 7 and 10. It is suggested to supplement the axis names (e.g., "Lateral displacement (mm)", "Vertical reaction (kN)") to improve the readability of the figures.

Comment 4: Although the distributed BNWF model proposed in this paper significantly improves computational efficiency compared with the 3D FE model, no specific quantitative comparison of computational time consumption is provided (e.g., the time consumption of the 3D FE model for a single scenario, that of the distributed BNWF model for a single scenario, and the time difference in batch analysis of different scour depths). Computational efficiency data of different models can be supplemented in Section 2.4 Structural Dynamics or Section 3.2.1 Comparative Analysis of Modeling Approaches, to more intuitively reflect the computational advantages of the proposed model in real-time monitoring of offshore wind turbines and echo the research objective of "reducing reliance on manual underwater inspections" stated in the abstract.

Comment 5: This paper clearly states that tripod bucket foundations exhibit lower scour sensitivity than monopile foundations, attributing this to "load redistribution through the tripod frame" and "lid bearing". However, no quantitative analysis of these mechanisms has been conducted (e.g., the proportion of load redistribution, the variation of the proportion of lid bearing in the total lateral resistance with scour depth). Relevant quantitative data can be supplemented in Section 4.1 Engineering Analysis of Inherent Resilience (e.g., the load sharing ratio of a single bucket in the tripod foundation and the contribution value of lid bearing at a certain scour depth), to make the mechanism analysis more persuasive and provide more specific theoretical basis for the optimal design of tripod foundations in subsequent research.

Comment 6: The paper mentions the use of Claude for academic writing coaching, literature synthesis, and generation of initial Python plotting scripts in the Declaration of Generative AI and AI-Assisted Technologies. However, the specific proportion of AI-generated content is not illustrated, nor is it clearly stated whether full verification has been conducted on the model parameters and calculation results generated by AI. Please supplement the above details to strictly comply with Elsevier's disclosure specifications for the use of generative AI and improve the rigor of the research.

Reviewer #3 — verbatim

This manuscript investigates the scour-induced natural frequency degradation of offshore wind turbines with tripod bucket foundations using a 3D FE-calibrated Winkler model. The study addresses a topic of practical importance for offshore foundation design and structural health monitoring. The proposed framework is interesting and potentially useful for engineering applications. However, some aspects of the modeling assumptions, parameter transfer procedure, and validation strategy require further clarification and discussion to improve the rigor and applicability of the work:

1. The manuscript scales the finite-element-extracted stiffness, obtained at an approximate strain level of 10⁻², by a factor of 3.0 to represent small-strain dynamic stiffness before defining the OpenSees springs. The authors should provide a stronger justification, either through additional literature support or through a short sensitivity study showing how this scaling factor affects the baseline frequency and the predicted scour sensitivity.

2. The study adopts circumferentially uniform scour as the baseline condition, but real offshore scour is often local and asymmetric. Although the manuscript acknowledges that local scour and torsional mode coupling are left for future work, it would be helpful to state more clearly to what extent the proposed power-law scour-frequency relationship is limited to axisymmetric scour conditions.

3. The literature review in the Introduction could be strengthened by including a more targeted discussion of the dynamic performance of jacket structures in real offshore conditions, especially under wind, wave, current, and seismic actions. The following references may be useful:

Seismic response of offshore tetrapod piled jacket foundations subjected to environmental loads in soft-over-stiff clay deposit;
Experimental investigation on the mechanism of local scour around a cylindrical coastal pile foundation considering sloping bed conditions;
Numerical evaluation of the dynamic performance of recommissioned offshore wind turbines under service life extension and repowering strategies;

4. The manuscript provides the main tower dimensions, mass assignments, marine growth treatment, hydrodynamic added mass, and soil plug mass. However, the conversion from the real turbine system to the simplified OpenSees model could still be explained more clearly. The authors are encouraged to provide additional detail on the structural idealization strategy, the basis for selecting the key geometric parameters, and the influence of the equivalent mass treatments on modal prediction, so that the reproducibility and credibility of the model can be better assessed.

5. The framework is developed using a Tresca undrained total-stress model, a linearly increasing \(s_u\) profile, and a fixed interface adhesion factor to represent the Gunsan marine clay. These assumptions support a clean and computationally efficient framework, but they also imply that the present model is primarily applicable to normally consolidated soft clay sites with relatively regular parameter distributions. The authors should discusse more explicitly how the framework might change for layered deposits, stronger small-strain stiffness enhancement, or more complex interface conditions.

6. The use of 32 months of parked-state monitoring data to validate the baseline natural frequency is a valuable aspect of the paper. However, the current field validation mainly demonstrates predictive capability for the baseline, non-severely-scoured condition, rather than for the actual evolution of scour in service. A stronger case for the proposed inversion formula would require comparison against independent scour surveys or long-term bathymetric observations during actual scour development.

7. Scour countermeasures also play an important role for the evaluation of the behaviors. The authors can briefly discuss about this.

8. Some references have formatting errors, please carefully check. In addition, to further portray the state-of-the-art of targeted problem in a up-to-date manner, the authors can considerer to add the latest closely related paper, such as "Establishment and implementation of an artificial intelligent flume for investigating local scour around underwater foundations. Transportation Geotechnics, 49: 101433" and "Investigation of the protection mechanism and failure modes of solidified soil utilized for scour mitigation. Construction and Building Materials, 472: 140858." to the references.

Where this links in the rest of the portfolio¶

Scientific page: Papers / J2.
Workflow alignment: J2 methodology prototype — two of the R2 items (R2.4 runtime table + R3.1 stiffness-scaling sensitivity figure) match exactly what the seven-phase coherence pass independently flagged as missing evidence. The reviewer process and the claim-driven workflow are converging on the same gaps.