Page 303 - Introduction to Naval Architecture
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288 VIBRATION, NOISE AND SHOCK
B
M,, = M 1.2 + —
3T
The Todd formula gives consistendy lower values than Burrill, ranging
from 93 to 86 per cent for B/T values ranging from 2.0 to 3.5
respectively.
8
Lewis made a detailed study of added virtual mass of near ship shape
sections. He arrived at an added virtual mass per unit length ofnpBPC/
2. He plotted C for various beam to draught ratios and for sections of
differing fullness, Figure 11.5.
Figure 11.5 Lewis C values
The application of these results to ship shapes involves two
interpolations, for Cand B/T values between those specifically used for
the curves. A more convenient presentation is to plot Cy> that is the
coefficient for vertical oscillations, against a cross-sectional area
9
coefficient for a range of beam/draught ratios as in Figure 11.6. Values
9
of Qj are shown in Figure 11.7 for horizontal oscillations . Using
these:
added virtual mass for vertical oscillation =
added virtual mass for horizontal oscillation =
