CU06997 Exercise lecture 5 ; computation

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) = 1:3Basis_exercise ditch bedslopeQuestions:

  1. 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
  2. Calculate Reynolds number
    u = Q/A = 21/12.75 = 1.65 m/s
    ν = 10-6 =kinematic viscosity
    Re = 6270000 > 4000 so turbulent
  3. Is the flow laminar or turbulent?
    Re = 6270000 > 4000 so turbulent
  4. 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
  5. 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) = 1:3Basis_exercise ditch bedslope=0Questions:

  1. 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
  2. Calculate Reynolds number at P2
  3. Is the flow laminar or turbulent?

Exercise 3 plus answer
Calculate the hydraulic radius for the following cross-sections:
sloot

 

 

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

 

 

 

Exercise 4 plus answer
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

buis

 

 

 

 

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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