4 - Memorial University of Newfoundland DAI

8.2 Experimental Results
8.2.1 Transient Decay Tests to Compute Damping
In-Air Tests. Averqcglobai x and y direction damping ratio variations (us-
ing lhc logarithznie decrement method) were shown in Figure 7.45. In both
twos, thc damping variation is more steady after eight cycles. Therefore, this
mgion war uscd to determine the transienl decay damping. For comparison,
con>putcd damping oatimstes using the above method and the average damp-
ing obtained fmm tho curvc fitting method (i.e., the LarenbereMarquardt
and Pinilc difference Jneobian) are shown here:
Damping Estimates from In-Air Testa
lagnrithmic Decmment Curve Pitting
In-Water Tests. Like the in-air tests, average global r: and y direction
dnrnpi~~g ratio variations (using the logsrithmie decrement method) were
depicted in Pigum 7.18. After six cycles, the variation in damping is more
rtcdy. Thc following am the damping estimates:
Damping Estimates from In-Water Tests
Logarithmic Decmmcnt Curve Pitting
, 3.5755 i 0.15% 3.6576 i 0.04%
( , 1.7033 i 0.04% 1.7221 i 0.02%
These damping rwlors are assoei~ted with the lalgiobal flexural modes in
Lhc global x and y direclions. The values oblained from the in-air tesls corre-