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1 Markets I: The Ecosystem and Exchange-Traded Marketsবাজার অনলাইন 2 Markets II: Rates, FX and Creditবাজার অনলাইন 3 Markets III: Commodities, Energy and Cryptoবাজার অনলাইন 4 Quantitative Methodsপদ্ধতি অনলাইন 5 Derivatives and Volatilityডেরিভেটিভস অনলাইন 6 Rates, Credit, XVA and Riskসুদহার, ঋণ ও ঝুঁকি অনলাইন 7 Research Craft: Predictors, Backtests, Measurement, Portfoliosগবেষণা অনলাইন 8 Strategies I: Equities and Futuresকৌশল অনলাইন 9 Strategies II: Volatility, Relative Value, Macro and the Bank Desksকৌশল অনলাইন 10 Microstructure and Executionএক্সিকিউশন অনলাইন 11 Market Making and High-Frequency Tradingমার্কেট মেকিং অনলাইন 12 Machine Learning for Marketsমেশিন লার্নিং অনলাইন 13 Low-Latency Softwareপ্রযুক্তি অনলাইন 14 Networks, Hardware and Trading Infrastructureপ্রযুক্তি অনলাইন 15 Research, Data and Risk Platformsপ্রযুক্তি অনলাইন 16 The Desk and the Firmপ্রতিষ্ঠান অনলাইন 17 The Industry: Firms, Roles and Careersক্যারিয়ার অনলাইন 18 Interviews I: Maths, Probability and Speedক্যারিয়ার অনলাইন 19 Interviews II: Markets, Trading Games and the Final Roundক্যারিয়ার অনলাইন 20 Interviews III: Codeক্যারিয়ার অনলাইন
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Earth and Space Sciences · পরিভাষা

Bedform, ripple, dune কী?

অন্য নাম: bedform · ripple · dune

Definition 21.6 University Earth and Space Sciences — Year 1 · অধ্যায় 21 — Clastic Sediments and Their Environments

A bedform is a regular relief moulded by a current on a bed of loose grains, repeated along the flow. A ripple is a small bedform, a few centimetres high and 10 to 20 cm20\,\mathrm{cm} from crest to crest, with a gentle upstream (stoss) side and a steep downstream (lee) side; a dune has a similar shape but is at least ten times larger, from decimetres to metres high under water.

(a) The succession of bed configurations in medium sand as the flow strengthens, from bottom to top, with the water surface above each (schematic, heights exaggerated). Ripples and dunes move downstream, antidunes upstream, their surface waves in phase with the bed. (b) The fields in which each bed phase is stable, against the grain size and the flow velocity, for a flow a few decimetres deep (schematic, after the flume compilations of Southard; the solid curve at the bottom is the threshold of motion). The two dots are the triple points near 0.2\, mm and 0.8\, mm: ripples form only in finer sand, dunes only in coarser.
(a) The succession of bed configurations in medium sand as the flow strengthens, from bottom to top, with the water surface above each (schematic, heights exaggerated). Ripples and dunes move downstream, antidunes upstream, their surface waves in phase with the bed. (b) The fields in which each bed phase is stable, against the grain size and the flow velocity, for a flow a few decimetres deep (schematic, after the flume compilations of Southard; the solid curve at the bottom is the threshold of motion). The two dots are the triple points near 0.2 mm0.2\,\mathrm{mm} and 0.8 mm0.8\,\mathrm{mm}: ripples form only in finer sand, dunes only in coarser.
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