pdf, 12 MiB - Infoscience - EPFL

More documents

Recommendations

Info

Chapter 8 - Summary, conclusions and recommendations in the second scour hole. These oscillations are reduced by half by the presence of vertical ribs on the outer wall for low discharges and they even disappear for high discharges. All the proposed formulae should be used within the domain for which they were established. The tests were performed at rather high Froude numbers (> 0.3) but at subcritical flow regimes. The radius of curvature to width ratio ( R c ⁄ B ) ranged between 2 and 6 and the flow depth to mean diameter of the substrate ( h m ⁄ d m ) was between 6.5 and 39. The study of the influence of the macro-roughness was performed at R c ⁄ B ratios of 6 and h m ⁄ d m ratios between 18 and 24, but the positive influence of the macro-roughness on scour and flow in bends can certainly be observed in a much wider range of parameters. c) The optimum rib spacing A rib spacing to rib depth ratio of 10 to 15 is recommended. The depth of the ribs was chosen in the present research study at about 2.5 to 5 times the mean diameter of the initially built-in bed material (substrate). Almost no local scour was observed at the bottom of the ribs having a depth of 2.5 times the mean diameter, whereas for the deeper ribs, some local scour was observed. Therefore a rib depth of about 2.5 times the mean diameter (or about one time d 90 ) can be recommended for engineering applications. It is important to choose an appropriate rib spacing, since the scour can be even amplified by a too small a rib spacing. In order to obtain a smooth transition with the upstream and downstream reaches next to the bend, additional ribs should be placed in a transition zone towards the bend. The laboratory tests were carried out with a transition zone having a length of about 10 times the mean flow depth. The ribs were placed with increasing spacing (factor 2 compared to the previous spacing, Fig. 5.3 on page 111) for an increasing distance from the bend with good results. page 200 / November 9, 2002 Wall roughness effects on flow and scouring
Notations Generalities Upper case characters: Lower case characters: average or global values (applied to the whole channel) local values Variables and constants A [ ] cross-section area of the channel m 2 B [m] width of the channel C [m 1/2 /s] CHEZY coefficient c [-] correction factor defined as tanφ∗ = c ⋅ tanφ c x C L C D [-] coefficient for the optimization of existing scour formulae [-] lift coefficient [-] drag coefficient d [m] characteristic grain size diameter, if not mentioned, the characteristic diameter is related to the substrate d∗ [-] dimensionless grain size diameter d∗ = ( γ s – γ w ) ⋅ d ⁄ τ 0 d∗ = (( s – 1) ⋅ d) ⁄ ( h ⋅ S e ) D [N 1 ] dynamic drag force e d e s [° or m] depth of the macro-roughness (dimension in radial direction) [° or m] spacing between the macro-roughness (from axis to axis) f [-] friction coefficient of DARCY-WEISSBACH Fr [-] FROUDE number Fr = V ⁄ ( g ⋅ h) Fr d [-] densimetric FROUDE number Fr d = V⁄ ( ( s – 1) ⋅ g ⋅ d) Fr∗ [-] particle FROUDE number Fr∗ = V∗ ⁄ ( ( s – 1) ⋅ g ⋅ d) , Fr∗ = τ 0 ⁄ γ s – γ w ⋅ d, Fr∗ = τ∗ = θ F S [N] Force due to the bed shear stress g [m/s 2 ] gravitational acceleration (9.81) G' [N] gravity force (vertical resulting force) h [m] flow depth h s [m] scour depth (water surface to ground) K [-] constant 1. N = kg ⋅ m ⁄ s 2 page 201
Page 1:
WALL ROUGHNESS EFFECTS ON FLOW AND
Page 4 and 5:
Abstract By applying vertical ribs
Page 6 and 7:
Résumé En disposant des nervures
Page 8 and 9:
Zusammenfassung • Ein markanter S
Page 10 and 11:
Acknowledgments page x / November 9
Page 12 and 13:
Table of contents 4. Smart & Jäggi
Page 14 and 15:
Table of contents 7.6 Summary and c
Page 16 and 17:
Chapter 1 - Introduction 1.1 Contex
Page 18 and 19:
Chapter 1 - Introduction page 4 / N
Page 20 and 21:
Chapter 2 - State of the art 2.1 Fl
Page 22 and 23:
Chapter 2 - State of the art 2.2.2
Page 24 and 25:
Chapter 2 - State of the art Theref
Page 26 and 27:
Chapter 2 - State of the art resolu
Page 28 and 29:
Chapter 2 - State of the art comple
Page 30 and 31:
Chapter 2 - State of the art ORLAND
Page 32 and 33:
Chapter 2 - State of the art 2.6 Me
Page 34 and 35:
Chapter 2 - State of the art page 2
Page 36 and 37:
Chapter 3 - Theoretical considerati
Page 38 and 39:
Page 40 and 41:
Page 42 and 43:
Page 44 and 45:
Page 46 and 47:
Page 48 and 49:
Page 50 and 51:
Page 52 and 53:
Page 54 and 55:
Page 56 and 57:
Page 58 and 59:
Page 60 and 61:
Page 62 and 63:
Page 64 and 65:
Page 66 and 67:
Page 68 and 69:
Page 70 and 71:
Page 72 and 73:
Page 74 and 75:
Page 76 and 77:
Page 78 and 79:
Page 80 and 81:
Page 82 and 83:
Chapter 4 - Experimental setup and
Page 84 and 85:
Page 86 and 87:
Page 88 and 89:
Page 90 and 91:
Page 92 and 93:
Page 94 and 95:
Page 96 and 97:
Page 98 and 99:
Page 100 and 101:
Page 102 and 103:
Page 104 and 105:
Page 106 and 107:
Page 108 and 109:
Page 110 and 111:
Page 112 and 113:
Page 114 and 115:
Chapter 5 - Test results 5.1 Introd
Page 116 and 117:
Chapter 5 - Test results 5.2 Prelim
Page 118 and 119:
Chapter 5 - Test results with and w
Page 120 and 121:
Chapter 5 - Test results 5.2.2 Test
Page 122 and 123:
Chapter 5 - Test results 5.3 Main t
Page 124 and 125:
Chapter 5 - Test results and 210 l/
Page 126 and 127:
Chapter 5 - Test results 5.5 Tests
Page 128 and 129:
Chapter 6 - Analysis of the test re
Page 130 and 131:
Page 132 and 133:
Page 134 and 135:
Page 136 and 137:
Page 138 and 139:
Page 140 and 141:
Page 142 and 143:
Page 144 and 145:
Page 146 and 147:
Page 148 and 149:
Page 150 and 151:
Page 152 and 153:
Page 154 and 155:
Page 156 and 157:
Page 158 and 159:
Page 160 and 161:
Page 162 and 163:
Page 164 and 165: Chapter 7 - Establishing an empiric
Page 208 and 209: Chapter 8 - Summary, conclusions an
Page 216 and 217: Notations K S [m 1/3 /s] roughness
Page 218 and 219: Notations bed b bf c cr d e g w o o
Page 220 and 221: References de Vriend H.J. (1981). S
Page 222 and 223: References Meyer-Peter, E., Favre,
Page 224 and 225: References Williams, R. (1899). Flu
Page 226 and 227: References by chapter Keulegan (193
Page 228 and 229: References by chapter page 214 / No
Page 230 and 231: Index of Authors Hoffmanns 13 Hoffm
Page 232 and 233: Index of Authors page 218 / Novembe
Page 234 and 235: Index of Figures Fig.4.19: Frame po
Page 236 and 237: Index of Figures 22] 183 Fig.7.15:
Page 238 and 239: Index of Tables Table 7.3: Table of
Page 240 and 241: Index of Keywords dimensional analy
Page 242 and 243: Index of Keywords sediment sampling
Page 244 and 245: Index of Keywords parameter 77 Pete
Page 246: Publications (continued) 1997 Hersb
show all

pdf, 12 MiB - Infoscience - EPFL

Create successful ePaper yourself

Delete template?

Save as template?