pdf, 12 MiB - Infoscience - EPFL
pdf, 12 MiB - Infoscience - EPFL
pdf, 12 MiB - Infoscience - EPFL
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Analysis of the final scour<br />
10° 25° 40°<br />
1300<br />
Water− and bedlevel B01 Q=210 10°<br />
1300<br />
Water− and bedlevel B01 Q=210 25°<br />
1300<br />
Water− and bedlevel B01 Q=210 40°<br />
<strong>12</strong>00<br />
<strong>12</strong>00<br />
<strong>12</strong>00<br />
1100<br />
1100<br />
1100<br />
Level [mm]<br />
1000<br />
900<br />
Level [mm]<br />
1000<br />
900<br />
Level [mm]<br />
1000<br />
900<br />
800<br />
no macro-roughness<br />
800<br />
800<br />
700<br />
Water level<br />
Bed level<br />
Mean water level<br />
Mean bed level<br />
Initial mean bed level<br />
700<br />
Water level<br />
Bed level<br />
Mean water level<br />
Mean bed level<br />
Initial mean bed level<br />
700<br />
Water level<br />
Bed level<br />
Mean water level<br />
Mean bed level<br />
Initial mean bed level<br />
600<br />
6500<br />
1300<br />
6400<br />
6300 6200 6100 6000 5900 5800 5700<br />
Distance to center of bend [mm]<br />
Water− and bedlevel B02 Q=210 10°<br />
5600<br />
600<br />
5500 6500<br />
1300<br />
6400<br />
6300 6200 6100 6000 5900 5800 5700<br />
Distance to center of bend [mm]<br />
Water− and bedlevel B02 Q=210 25°<br />
5600<br />
600<br />
5500 6500<br />
1300<br />
6400<br />
6300 6200 6100 6000 5900 5800 5700<br />
Distance to center of bend [mm]<br />
Water− and bedlevel B02 Q=210 40°<br />
5600<br />
5500<br />
<strong>12</strong>00<br />
<strong>12</strong>00<br />
<strong>12</strong>00<br />
1100<br />
1100<br />
1100<br />
Level [mm]<br />
1000<br />
900<br />
800<br />
700<br />
600<br />
6500<br />
ribs spaced every 4°<br />
6400<br />
6300<br />
6200 6100 6000 5900 5800<br />
Distance to center of bend [mm]<br />
Level [mm]<br />
1000<br />
900<br />
800<br />
Water level<br />
Bed level<br />
700<br />
Mean water level<br />
Mean bed level<br />
Initial mean bed level<br />
600<br />
5700 5600 5500 6500<br />
6400<br />
6300<br />
6200 6100 6000 5900 5800<br />
Distance to center of bend [mm]<br />
Level [mm]<br />
1000<br />
900<br />
800<br />
Water level<br />
Bed level<br />
700<br />
Mean water level<br />
Mean bed level<br />
Initial mean bed level<br />
600<br />
5700 5600 5500 6500<br />
6400<br />
6300<br />
Water level<br />
Bed level<br />
Mean water level<br />
Mean bed level<br />
Initial mean bed level<br />
6200 6100 6000 5900 5800<br />
Distance to center of bend [mm]<br />
Water level<br />
Bed level<br />
Mean water level<br />
Mean bed level<br />
Initial mean bed level<br />
5700 5600 5500<br />
Figure 6.9: Development of the line bend in the first scour (test B1d on top and B2d at the bottom)<br />
Without macro-roughness, the line bend starts at about 10° at a distance around 20% of the channel<br />
width from the outer bank to finally disappear between 50% and 80% from the outer bank. In<br />
the maximum scour cross-section, the line bend is attenuated and the profile becomes s-shaped.<br />
The same process can be observed for the second scour. At 55° the bed has flattened again partially<br />
(between the two scour holes). Downstream this point (70°), up to the end of the bend, the<br />
development of the line bend can be observed a second time.<br />
Figure 6.10: Scheme of the development of the line bend<br />
This process can be explained in a schematic way with the development of the secondary current<br />
(Figure 6.10). Between 10° and the first maximum scour, the secondary current grows (the inclination<br />
of the radial water surface slope also increases slightly which is exaggerated on the schematic<br />
view) and leads progressively to a more pronounced scour hole. At the final state, the shape of the<br />
scour hole is more s-shaped. This can be explained by the fact that the main secondary current<br />
does not “attack” the bed at the outer wall anymore, shifts towards the center, but remaining in<br />
the outer half of the channel.<br />
<strong>EPFL</strong> Ph.D thesis 2632 - Daniel S. Hersberger November 9, 2002 / page <strong>12</strong>5