Despite considerable progress in the theoretical and experimental treatment of ship
vibrations, questions about the accuracy of analysis methods for predicting the vibration
behaviour as well as for solving vibration problems on completed ships are as topical as ever.
The aim of this article is to describe the “state of the art” in computational and measurement
techniques. Here, the main emphasis is placed on the description of general
approaches. Theoretical backgrounds are explained only if this is necessary for an
understanding of physical situations. This paper is, therefore, aimed in particular at
engineers and inspectors of shipyards, shipping companies and consulting offices, in the
expectation that improved communication will be achieved between vibration specialists
and engineers responsible for design and operation of ships.
In this context, “ship vibrations” consist exclusively of elastic vibrations of the ship’s
hull and/or its parts. These vibrations can impair well-being, efficiency and the health of
people on board, can cause damage to the ship and its cargo, and – in especially serious
cases – can endanger the safety of the vessel.
The paper is structured as follows: after a discussion of questions concerning the building
specification and standards for assessment of ship vibrations, analysis methods for calculation
of free vibrations are dealt with. Here, various aspects of the determination of
natural frequencies for simple components, large subsystems and entire ships are described.
After that, aspects of the calculation and assessment of the forced vibration level are
dealt with, since in many cases a final evaluation of vibration questions in the design
stage cannot be made with adequate certainty solely by comparing natural frequencies
with main excitation frequencies.
Finally, this is followed by general remarks about the state of the art for experimental investigations
and by a description of some vibration problems experienced on completed
ships. The measurement procedure for diagnosis and actions taken to solve these problems
are described in detail.
Here, it must also be pointed out that the subject of ship vibrations certainly cannot be
dealt with completely and conclusively. It is our opinion that highly specialised questions
– concerning, for example, elastic mounting of engines, sloshing phenomena in tanks or
torsional vibrations of shafts – nevertheless lie outside the scope of this article, important
as such questions undoubtedly are.