CFD model estimates of the airflow distortion over research ships and the impact on momentum flux measurements
Bibliographic record
Abstract
Wind velocity and air–sea turbulent flux measurements made from shipborne instruments are biased due to the effect of the ship on the flow of air to the instruments. The presence of the ship causes the airflow to a particular instrument site to be either accelerated or decelerated, displaced vertically, and sometimes deflected slightly in the horizontal. Although recognized for some time, it is only recently that the problem has been addressed using three-dimensional computational fluid dynamics (CFD) models to simulate the flow over particular ships, quantify the effects of flow distortion, and hence correct the ship-based measurements. It has previously been shown that this improves the calculated momentum fluxes by removing disparities between data from different ships, or from instruments in different locations on the same ship. This paper provides validation of the CFD model simulations. Two research ships were instrumented with multiple anemometers located in both well-exposed and badly exposed sites. Data are compared to the results of model simulations of the flow at various relative wind directions and wind speeds. Except when the anemometers are in the wake of an upwind obstruction, the model and the in situ wind speed estimates typically agree to within 2%. Direct validation of the model-derived estimates of the vertical displacement of the flow was not possible due to the extreme difficulty of obtaining such measurements in the field. In this study, simulations of flows at 0° and 90° from the bow of the ship were made and displacements of about 1 and 5 m were found, respectively. These results were used to correct the in situ momentum flux data. In one case, the application of the different bow-on and beam-on corrections for vertical displacement successfully removed the disparity seen in the uncorrected data. In a second case, the beam-on vertical displacement overcorrected the flux results. This overcorrection could be caused either by uncertainties in the in situ estimate of the relative wind direction or by partial adjustment of the turbulence during the vertical displacement. The effects of flow distortion are found to vary only slightly with wind speed, but are very sensitive to the relative wind direction and, if uncorrected, can cause large biases in ship-based meteorological measurements (up to 60% for the drag coefficient). Model results are given for bow-on flows over 11 research ships (American, British, Canadian, French, and German).
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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 | 0.001 | 0.004 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.001 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 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".