Investigation of horizontal coherent structures in a shallow open-channel flow using velocity signal decomposition
Bibliographic record
Abstract
This paper concerns the large-scale horizontal coherent structures (HCS's) in open-channel flows.In contrast to large-scale vertical coherent structures, HCS's have not yet been the focus of directed, systematic studies, and as a result the exact role they play in river morphodynamics remains elusive.This paper, which is to be viewed as an extension of da Silva and Ahmari (2009), reports some of the first measurements and results of an extensive laboratory study recently initiated by the authors as an attempt to develop an understanding of the characteristic scales, dynamics and consequences of HCS's.At these early stages of the research, our efforts, and thus this paper, are directed towards the establishment of the characteristic length-and time-scales of HCS's.The present analysis rests on a series of flow velocity measurements carried out in a 21m-long, 1m-wide laboratory channel, having a flat, sand bed.Two different techniques of signal decomposition are applied to the oscillograms of instantaneous flow velocity, collected throughout the flow domain, to reveal the aforementioned characteristic scales: "smoothening" of the velocity records through time-averaging; and Empirical Mode Decomposition (EMD) combined with Power Spectral Density (PSD) analysis.The filtered (or smoothed) oscillograms of instantaneous flow velocity were found to invariably exhibit cycles of fluctuation of velocity consistent with the presence of large-scale horizontal coherent structures, affecting (or occupying) the entire body of fluid.The average length traveled by HCS's from their "birth" location to the location of their disintegration (i.e. the horizontal burst length) was found to be 4 .5 times the flow width.In view of the present results, and given the similarity between the horizontal burst length and the average length of alternate bars and the wave-length of meanders, strongly suggesting a relationship between them, it seems particularly worthwhile to pursue further research on HCS's.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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 teacher head, 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".