56
STRUCTURE-ENVIRONMENTAL FORCE INTERACTIONS
both flows are in the same direction. If the wind velocity is offset by an angle
6 to the tidal current, what is the équation for the total velocity in terms of 8.
2.9 A relatively isolated, vertical cylindrical pile is fully submerged and
subjected to a steady tidal current of magnitude 4 knots. The pile has diameter
D = 0.3 m and height h = 5 m. Compute the total current-induced drag force
on this pile. State ail assumptions you make in arriving at your answer.
2.10 Based on studies reported in the most recent literature (for instance,
The Proceedings of the Offshore Technology Conférence), discuss briefly both
the advantages and dangers of using onshore seismic data for ground motion in
the design of fixed-bottom offshore structures for earthquake résistance.
2.11 The coefficient Ci of équation (2.37), which is used to predict the
horizontal impact of ice on structures, varies by more than a factor of two.
Investigate the physical reasons for this variability.
2.12 After Consulting the recent literature on the subject, write a summary
report comparing the particular design features that allow the offshore platforms
near Alaska to resist ice hazards. How do these platforms differ from the jackettemplate structures in the Gulf of Mexico?
2.13 For the case of two opposing cables shown in Figure 2.19, where the
equilibrium angle 9r is 45 deg, calculate fcj and >:s for a best fit to équation
(2.69). If w = 39 Ib/ft and zg = 1000 ft, what is q(y)?
2.14 Assume that the floating structure of Figure 2.19 is supported by four
identical, symmetrically arranged cables, 90 deg apart. Assume that the only
motion is horizontal and along the line of two opposing cables. Show that the
restoring force as a function of deflection as given by the curves of Figure 2.21 is
still quite accurate because the cables perpendicular to the direction of motion
contribute very little résistance to this motion. For what range of initial angles
0r is this approximation not a good one?
2.15 Assume that N pairs of identical cables are arranged at equal angles
.3, as shown in Figure 2.19. Dérivé a general expression for the restoring force
along the line of one of these pairs. State ail your assumptions. Then plot the
antisymmetric curve in the nondimensional form of Figure 2.21 for N = 6, f)T
= 45 deg, and 0 = 30 deg.
2.16 Based on the analysis of Kocsis (1976), calculate le, the équivalent
length of a solid concrète pile submerged in medium stiff sand. Use the following
data: t = 30 ft, D = 4 ft, E = 3000 kips/in2, and No = 14 tons/ft3. (Hint:
First couvert to a consistent set of units.)
REFERENCES
Adrezin. R., Bar-Avi, P., and Benaroya, H., Dynamic Response of Compilant Offshore
Sructures-Review, Journal of Aerospace Engineering, 1996.
STRUCTURE-ENVIRONMENTAL FORCE INTERACTIONS
both flows are in the same direction. If the wind velocity is offset by an angle
6 to the tidal current, what is the équation for the total velocity in terms of 8.
2.9 A relatively isolated, vertical cylindrical pile is fully submerged and
subjected to a steady tidal current of magnitude 4 knots. The pile has diameter
D = 0.3 m and height h = 5 m. Compute the total current-induced drag force
on this pile. State ail assumptions you make in arriving at your answer.
2.10 Based on studies reported in the most recent literature (for instance,
The Proceedings of the Offshore Technology Conférence), discuss briefly both
the advantages and dangers of using onshore seismic data for ground motion in
the design of fixed-bottom offshore structures for earthquake résistance.
2.11 The coefficient Ci of équation (2.37), which is used to predict the
horizontal impact of ice on structures, varies by more than a factor of two.
Investigate the physical reasons for this variability.
2.12 After Consulting the recent literature on the subject, write a summary
report comparing the particular design features that allow the offshore platforms
near Alaska to resist ice hazards. How do these platforms differ from the jackettemplate structures in the Gulf of Mexico?
2.13 For the case of two opposing cables shown in Figure 2.19, where the
equilibrium angle 9r is 45 deg, calculate fcj and >:s for a best fit to équation
(2.69). If w = 39 Ib/ft and zg = 1000 ft, what is q(y)?
2.14 Assume that the floating structure of Figure 2.19 is supported by four
identical, symmetrically arranged cables, 90 deg apart. Assume that the only
motion is horizontal and along the line of two opposing cables. Show that the
restoring force as a function of deflection as given by the curves of Figure 2.21 is
still quite accurate because the cables perpendicular to the direction of motion
contribute very little résistance to this motion. For what range of initial angles
0r is this approximation not a good one?
2.15 Assume that N pairs of identical cables are arranged at equal angles
.3, as shown in Figure 2.19. Dérivé a general expression for the restoring force
along the line of one of these pairs. State ail your assumptions. Then plot the
antisymmetric curve in the nondimensional form of Figure 2.21 for N = 6, f)T
= 45 deg, and 0 = 30 deg.
2.16 Based on the analysis of Kocsis (1976), calculate le, the équivalent
length of a solid concrète pile submerged in medium stiff sand. Use the following
data: t = 30 ft, D = 4 ft, E = 3000 kips/in2, and No = 14 tons/ft3. (Hint:
First couvert to a consistent set of units.)
REFERENCES
Adrezin. R., Bar-Avi, P., and Benaroya, H., Dynamic Response of Compilant Offshore
Sructures-Review, Journal of Aerospace Engineering, 1996.