Measurement of Fluctuating Pressures on Coarse Bed Material

Bed protections are usually characterized by low-mobility transport conditions and nonequilibrium turbulence profiles. As the present knowledge of the influence of turbulence on stability of cover layer units is minimal, an in-depth investigation was undertaken regarding the influence of turbulence on the stability of rough granular beds. Detailed measurements of (fluctuating) pressures on a bed element are used to evaluate certain concepts that are often used in modeling the entrainment of bed material from hydraulically rough beds. Three pressure transducers are placed in a cube that is part of a rough granular bed under open-channel flow, and velocities are measured using laser Doppler velocimetry. The measurements show that the magnitude of the fluctuating pressure at a certain point of the cube is a function of the exposure relative to the stones upstream of the cube. A quadrant analysis reveals that the drag force is not only directly dependent on the horizontal near-bed velocity, but on the vertical velocity as well. Further, the effect of small-scale eddies shedding from the stone during large-scale increases of longitudinal velocity is shown. The fact that large-scale velocity fluctuations create a large part of the pressure (or force) variance indicates that downstream of a roughness transition these fluctuations have to be taken into account in order to evaluate the stability of the bed.

• Availability:
  • Find a library where document is available. Order URL: http://worldcat.org/oclc/8672558
• Authors:
  • Hofland, Bas
  • Battjes, Jurjen A
  • Booij, Robert
• Publication Date: 2005-9

Language

• English

Media Info

• Media Type: Print
• Features: Figures; References; Tables;
• Pagination: pp 770-781
• Serial:
  • Journal of Hydraulic Engineering
  • Volume: 131
  • Issue Number: 9
  • Publisher: American Society of Civil Engineers
  • ISSN: 0733-9429
  • Serial URL: http://scitation.aip.org/hyo/

Subject/Index Terms

• TRT Terms: Air entrainment; Coarse grained materials; Drag; Pressure waves; Streambeds; Turbulence; Velocity
• Subject Areas: Geotechnology; Highways; Hydraulics and Hydrology; I26: Water Run-off - Freeze-thaw; I42: Soil Mechanics;

Filing Info

• Accession Number: 01003898
• Record Type: Publication
• Files: TRIS
• Created Date: Sep 13 2005 6:13AM