# CU06997 Exercise lecture 5 ; computation Link to exercise lecture 5 Exercise 1 plus answer Water-depth (D) = 1,5 m at P1 and P2 Discharge Q = 21 m3/s Bed width ditch (W) = 4 m Slope ditch (S) = 1:3 Questions: Calculate the Hydraulic Radius for the cross-section A = 1.5 x (4 + 3*1.5) = 12.75 m2 P = 4 + 2 * (1.52 + 4.52)0.5= 13.5 m2 R=12.75/13.5=0.95 m Calculate Reynolds number u = Q/A = 21/12.75 = 1.65 m/s ν = 10-6 =kinematic viscosity Re = 6270000 > 4000 so turbulent Is the flow laminar or turbulent? Re = 6270000 > 4000 so turbulent From which velocity will the flow be laminar, assuming the cross-section stays the same. Re should be less then so V<0.5 mm/s From which velocity will the flow be turbulent, assuming the cross-section stays the same. Re should be more them so V>1 mm/s Exercise 2 plus answer Water-depth (D) = 1,5 m at P1 Water-depth (D) = 1,2 m at P2 Discharge Q = 21 m3/s Bed width ditch (W) = 4 m Slope ditch (S) = 1:3 Questions: Calculate the Hydraulic Radius for the cross-section at P2 A = 1.2 x (4 + 3*1.2) = 9.12 m2 P = 4 + 2 * (1.52 + 3.62)0.5= 11.6 m2 R=9.12/11.6=0.79 m Calculate Reynolds number at P2 Is the flow laminar or turbulent?

Calculate the hydraulic radius for the following cross-sections: bed width b [m] water depth y [m] slope [-] A[m2] P[m] R[m] 4 1.45 1:3 12.11 13.17 0.92 3 1.37 1:2 7.86 9.13 0.86 5 2.98 1:4 50.42 29.57 1.71 400 3.2 1:0 1280 406.4 3.15

Calculate the hydraulic radius for the following partially filled pipes
I used the next table, calculate h/D look en table en find R/D Diameter D [m] Water depth h [m] h/d table R/D R [m] 0.8 0.7 0.875 0.3014 0.24 0.7 0.3 0.429 0.2243 0.16 3.4 1.7 0.5 0.25 0.85 2.8 2.0 0.714 0.2979 0.83

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