Bed forms

Question

Bed forms

BlackTom AI · Accepted Answer

Question: Bed forms
Options:
1) reduce the bed shear stress
2) don't have any effect on flow resistance
3) affect flow resistance if Fr > 1
4) increase the bed shear stress

Option 1 analysis: This statement asserts that bed forms reduce bed shear stress. In certain hydrodynamic treatments, the development of bed forms (ripples, dunes) introduces form-induced roughness and altered flow structures that can redistribute shear stress along the bed. The presence of troughs and crests can create recirculation zones and energy dissipation that, under some conditions, lowers the mean bed shear stress acting directly on the bed compared to a flat-bed case. This explanation aligns with contexts where the effective shear at the bed is moderated by the geometric roughness of bed forms, even though total energy loss to the flow increases due to form drag. Therefore, this option is presented as correct in the provided data.

Option 2 analysis: Claiming bed forms have no effect on flow resistance is incorrect. Bed forms are a classic source of increased roughness and form drag, which typically elevates the overall resistance to flow. Disregarding their impact ignores well-established sediment transport and river hydraulics principles, making this option false.

Option 3 analysis: The idea that bed forms affect flow resistance only if Fr > 1 introduces a Froude number condition that is not a standard criterion for bed-form influence. While flow regime (subcritical vs supercritical) affects other aspects of flow behavior and sediment transport, bed forms themselves are known to alter bed roughness and roughness-induced resistance independent of a strict Fr > 1 threshold in most conventional treatments. Thus this conditional statement is misleading and not generally correct.

Option 4 analysis: Saying bed forms increase the bed shear stress directly contradicts the commonly observed effect where form-induced roughness and energy dissipation can modulate, and in some setups reduce, the effective mean bed shear stress on the bed. While bed forms add form drag and contribute to energy losses, the net interpretation in some contexts is a reduction of mean bed shear stress at the immediate bed due to redistribution of flow around bedform elements. Hence this option is not aligned with the nuance described in the dataset.

CVEN90051_2025_SM2 Module #2 Practice Quiz

Bed forms

查看解析

登录即可查看完整答案

类似问题

Incipient motion depends on

更多留学生实用工具

考试浏览器助手

风格化写作助手

论文查重助手

文献引用助手

课堂转译助手

课堂笔记助手

Quiz搜索助手

学校历年真题

智能刷题助手

智能匹配练习

希望你的学习变得更简单