Tower Design and Manufacture - Small Wind Turbines: Analysis, Design, and Application - page 215

The minimum tower mass for d 0 = 0.17 m is 45 kg or 8.4% below that for the
original tower in Table 10.2 , due mainly to the reduced d h and thickness of the
topmost section. It is worth pointing out that restrictions on material supply forced
the same thickness steel to be used for the top two sections of the actual 18 m
tower. This accounts for about 10 kg of the difference.
Repeated runs for d min = 0.10, and 0.14 produced closely equal results, but
Table 10.5 shows some variability in the results for d min = 0.17 due to trade-offs
between base diameter and section thickness which did not cause large changes to
the mass and none to CF max or d 0 . In practice, as hinted above, there will only be a
finite range of available thickness so this variability is unlikely to be significant
(Table 10.5 ).
When using some ''local codes'' like AS 1170.2 [ 12 ], it may be advantageous to
include n 1 in the optimisation to decide whether to have a ''static'' or ''dynamic''
tower. For example, by setting a n1 = a CF = a m = 1/3, and d min = 0.17 m, the
evolved m t was 600 kg, d 0 = 0.172 m, d h = 0.494 m, and t 1 , t 2 , t 3 = 4.2, 3.4, and
4.2 mm respectively. Method B gave n 1 = 1.53 Hz. Judging from Table 10.2 , this
should ensure the actual n 1 exceeds the 1 Hz limit in AS 1170.2 [ 12 ] for the use of
a static analysis with lower wind loads. Whether increasing the mass to lower the
loads is justified is yet another optimisation problem.

Table 10.4 Input parameters
for blade design for the
optimisation of the 18 m
monopole tower. Values not
given here are in Table 10.2

Parameter and value Parameter and value

Ns = 3 CF max = 0.6

a m = 0.5 a CF = 0.5

Maximum t = 50 mm Minimum t = 2mm

Maximum d = 0.5 m Crossover factor, CR = 0.1

Population = 2000 Max. blade age = 20 generations

No. generations = 200

Fig. 10.6 Variation of
maximum capacity factor for
changes in d 0

0.6

0.5

0.4

0.3

d min = 0.10 m
d min = 0.14 m
d min = 0.17 m
FEA of orignal tower

0.2

0.1

0

0 5 10 15 20

Distance from top of tower (m)