Page 310 - Introduction to Naval Architecture

VIBRATION, NOISE .AND SHOCK 295

positions in the ship it can be activated and the stuctural response to
known forces measured.

Reducing vibration
Ideally vibration would be eliminated completely but this is not a
realistic goal. In practice a designer aims to:

(1) Balance all forces in reciprocating and rotary machinery and in
the propeller.
(2) Provide good flow into the propeller and site it clear of the
hull
(3) Avoid resonance by changing the stiffness of components or
varying the exciting frequencies.
(4) Use special mounts to shield sensitive equipment from the
vibration.
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3
(5) Fit a form of vibration damper , either active or passive .
The two main sources of vibration are the machinery and
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propellers ' .

Table 11.3 Vibration response and endurance test levels for surface warships

Ship type Region Standard test level Endurance tests
Peak values and
frequency range

Minesweeper Masthead 1.25mm, 5 to 14 Hz 1.25 mm, 14 Hz
size and above 0.3 mm, 14 to 23 Hz 0.3 mm, 23 Hz
0.125 mm, 23 to 33 Hz 0.125 mm, 33 Hz
Each 1 hour

Main 0.125 mm, 5 to 33 Hz 0.125 mm, 33 Hz
For 3 hours

Smaller than Masthead and 0.2 mm or a velocity of 0.2 mm, 50 Hz
minesweeper main 63 mm/s whichever is less.
7 to 300 Hz For 3 hours

Aftermost | of 0.4 mm or a velocity of 0.4 mm, 24 Hz
ship length 60 mm/s whichever is less.
7 to 300 Hz For 3 hours