Hydraulic Structures: Fourth Edition

organisms on the surface of the cylinder will undoubtedly affect the rough-
ness and also the effective diameter of the cylinder. The presence of cur-
rents also affects the coefficients. The choice of suitable values of CDand
CMis therefore not easy. Muir Wood and Fleming (1969) suggest values of
CMandCDas functions of ReandKc. Figures 14.16 and 14.17 show the
experimental results of Sarpkaya (1976) concerning the coefficients CM
andCDwith respect to ReandKc. Different certifying agencies such as the
British Standards Institution, Det Norske Veritas and the American Petro-
leum Institute suggest values of CDandCMfor design.

FORCES ON CYLINDRICAL STRUCTURES 605

CM

3.0

0.4

3. 200
   KC


4. 
   
   
   
   5. 6.7.8.9. 10 20 30 40 50 100 150
   
   
   
   

0.5

1.0

1.5

2.0 R^103  60 80^100150200

40

30

20 20

30 40 60 80

Fig. 14.16 CMvsKCnumber for various values of Reynolds number (Re)
for smooth circular cylinder (Sarpkaya, 1976a)

CD

3.0

0.3

2.5 200

KC

4. 5.6.7.8.9. 10 20 30 4050 100 150

0.5

1.0

1.5

2.0 Re^103 ^10

0.4

3. 15

(^1520)
(^304050)
(^6080)
100
150
Fig. 14.17 CDvsKCnumber for various values of Reynolds number (Re)
for smooth circular cylinder (Sarpkaya, 1976a)