4 - Memorial University of Newfoundland DAI

7.1.1 Free Vibration Results
Computed natural frequency comparisons of the maicl nud protntylre (ob-
tained from the frec vibration nnnlyscr 01 the 3-0 and stick nlodcl) mw ~prc-
sented i n Table 1.1 and 1.2, respectively. Table 7.1 ahows thc rtmr c.zncoal,-
tered when aurling up tho prolotype vnl~tes from the modcl vnlaw. l'wrlv,?
frequencies were mmputcd for lhe idealized 3-D cam, but only the ~ntaicv
associated with lhe ten lroquender were used in the dynamic n~91,ons and-
yses. Beesuse, it wss eonsidcled lhnl it might nol have ba:n pmvil~le to
excite more resonant frequencies, e~~crimentaily, is lllu wnvc tank facility
st Memorial University. Wr tllo idcalhcd slick rnwlcls, it was only i,ouailrle
to extract seven frequencies, bmnuso the strucl!tre WNI idcnliv*.~i irs a xcvc.~
lumped mass system-i.e., one mass at each ievcl.
To ascertain tho typcaf models) (i.c., global benrlisg, twislittg, ctc.) NI~O-
ciated with a particular resonant freqt!oncy, mode shapes wmre llrw,rcl.ic.dly
computed. Figures 1.1-7.10 show five lypicnl modes far llte iklc!dizml :I-I1
hydmeiwtie and pmtotypc~ it wM from lllc conlpltpr g,!~~~~.lht(.t~
mode shapes that tho typc ofmodo asnocialed with n pnctictmlar 1ruqa~ts:y
shown i n Tsbies 1.1 and 1.2-was labelled. Tilo modl:d~nl,ts were nlu, ~ ~wui
to identify the typeof models) assoei~lcd with tlac xaonalll peaks Llt8:ax-
perimentally mensured spectral density functions from thc wnvc: and irnlurt
tests.
As has already been stated, various rnemlrcrs werc male ihalin: to ninl-
ulale dmlgc, and to aolect the most suitahlc mcmher(s) lilat would opti-
mize the structural integrity mclltod in thc oxpcrimenld plmw: of tlnix xt~aly.
'NB: The mrrcapandin8 rrquency roresrl~ mode 1% "la, nltovn will> earl tu~alcnlmfn.