A FIXED LEG PLATFORM
225
Figure 9.2 Stalk model of the fixed leg platform: (a) définition of coordinates; (b)
components of the modal vector ? i (c) components of the modal vector ;...
Table 9.1 Characteristics of a Fixed Platform and an Incident Wave
Platform Parameters
Wave Loading Parameters
= 4.69 x 106 kg;
— 3.13 x 106 kg
fcn = 7.35 x 107 N/m; fc22 = 3.59 x 108 N/m
^12 = &2i = —1.15 x 108 N/m
= ^2 = 38 m;
d = 61 m
Ci = <2 = 0.05
De = 5.5 m;
Dc = 4.3 m
= 4: Nc = 2
w = 30 m
H = 11.6 m
T = 15.4 s
k = 0.0201 m-1
A = 312 m
w = 0.408 rad/s
p = 1031 kg/m3
CM ^2
Frequencies
The two tmdamped structural frequencies for free vibration are computed
by solving the characteristic déterminant, équation (8.61), for the two positr.'
roots ai. The governing équation is
det(K - w2M) = 0
(9-3)
With the numerical values above, this déterminant becomes
73.5 -4.69w2
-115
x io6 = 0
-115
359-3.13w2
(9.4)