dc.description.abstract |
The origin of shipboard vibrations is dominantly determined by vessels propulsion system, main
machinery, auxiliary systems, pumps, breaking of the waves at the ship hull, etc. All of these
peripherals and systems origin the static and dynamic induction of vibration onboard a ship while
various analytical and statistical methods may be declared to assess the levels of vibration in order
to declare a combined safe operational criteria for ships depending on the spectrums. Few similar
researches had been completed on identification and quantified estimation of the noise or the
multiple vibrations resulted from ship and machinery during passage.
However, those researches were addressed mainly towards developing a relationship for a single
new ship or category particularly prior to commissioning. This research was focused on studying
the shipboard transferred vibration (of the vessel's structure and to sea) and vibration spectra
generated by shipboard machinery / structures using portable vibration analysers for in-service
ships. Data was recorded onboard classes of ships/ craft (new and old) through a series of sea trials
to establish a common relationship for ships and to comprehend use this methodology as a tool in
understanding complex patterns of ship vibration spectra to predict possible defects.
The study commenced on 05th May 2014 under the patronage and guidance of the Department of
Mechanical Engineering, University of Moratuwa to identify the unique patterns of shipboard
vibration signatures generated whilst vessels are on sail, paying attention to the external forces and
to develop a data base with existing vibration levels after being identified as safe operational limits
(depending on the observations based on datum readings). The research data was collected using
two modern vibration analysers (Make: Areva, Model: Oneprod MVP -2C, Country of Origin:
France, Frequency Range: 0 – 40,000 Hz) integrated with Areva XPR 300 software system
uploaded computers for the spectrum analysing task. Sea trials at following conditions had been
carried out.
a. Sea State : 3 and below;
b. Ship Loading Condition : Full Load, Half Load;
c. Wind Condition : Moderate < 15 knots;
d. Sea Direction : Ahead, Astern
Numerical relationships and probabilities were established using practical outcomes of the sea
trials. Data analysis and Spectrum datum comparison were used to identify and quantify the safe
operational vibration limits with respect to individual classes of ships being the primary outcome.
The similar defect patterns and respective statistics were averaged to find out a common
relationship to identify a figure named “Shipboard Machinery Vibration Safety Index (Sv)”, which was the secondary outcome of the study. |
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