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1 Markets I: The Ecosystem and Exchange-Traded Markets市场在线 2 Markets II: Rates, FX and Credit市场在线 3 Markets III: Commodities, Energy and Crypto市场在线 4 Quantitative Methods方法在线 5 Derivatives and Volatility衍生品在线 6 Rates, Credit, XVA and Risk利率、信用与风险在线 7 Research Craft: Predictors, Backtests, Measurement, Portfolios研究在线 8 Strategies I: Equities and Futures策略在线 9 Strategies II: Volatility, Relative Value, Macro and the Bank Desks策略在线 10 Microstructure and Execution交易执行在线 11 Market Making and High-Frequency Trading做市在线 12 Machine Learning for Markets机器学习在线 13 Low-Latency Software技术在线 14 Networks, Hardware and Trading Infrastructure技术在线 15 Research, Data and Risk Platforms技术在线 16 The Desk and the Firm公司运营在线 17 The Industry: Firms, Roles and Careers职业发展在线 18 Interviews I: Maths, Probability and Speed职业发展在线 19 Interviews II: Markets, Trading Games and the Final Round职业发展在线 20 Interviews III: Code职业发展在线

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Earth and Space Sciences · 术语表

什么是 Bedform, ripple, dune？

又称： bedform · ripple · dune

Definition 21.6 University Earth and Space Sciences — Year 1 · 第 21 章 — 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 $20\,\mathrm{cm}$ 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 $0.2\,\mathrm{mm}$ and $0.8\,\mathrm{mm}$ : ripples form only in finer sand, dunes only in coarser.

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