The mobilities of the engine base of a RO-RO ship were
calculated with two FE models in frequency ranges 0 - 100
Hz and 100 - 200 Hz. The mobilities of the same engine
base with the engines mounted have been measured on the
ship and the diesel engine has been measured alone.
Also the suitability of FE programs and the traditional
calculation method was of interest in this study. In
principle the mode superposition method should have
worked well and with minimum manual work. However, at
every step during the calculation starting from the
modelling of the geometry the automatic functions failed
due to the large size of the model causing much more
manual work than expected. This makes it in practice
impossible to use FE programs with the kind of
limitations as
I-Deas to calculate the mobilities up to required high
frequencies.
On the other hand the high natural mode density at high
frequencies makes the use of the traditional mode
superposition method questionable. It can be estimated
that in the CPU time, which was used to calculate the
natural modes, about 100 direct solutions could have been
calculated. Thus for this kind of calculations the
feasibility of the direct solution method should be
studied.

Series | VTT Manufacturing Technology. Research Report |
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Number | BVAL35-011179 |
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