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NCE uses Finite Element Analysis (FEA) software to model ship
structures ranging from localized ship sections such as masts and
machinery spaces to full ship models. FEA models are used to assist
with the identification of potential low frequency (< 100 Hz) vibration
problems as well as identifying optimal solutions. NCE uses FEA to
understand and solve vibration issues on new designs as well as on
existing vessels.
NCE typically uses modal and forced response techniques for vibration
problems. Modal analyses are used to identify natural frequencies that
may coincide with known forcing frequencies from machinery or propeller
sources. Forced response analyses are used to predict the actual
vibration levels of ship structures to ensure compliance with vessel
specifications. NCE uses standard guidelines (IMO, DNV, SNAME, ABS) for
model creation and vibration assessment, particularly when the vessel
specification only calls for "low vibration".
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Example model of the engine room on U.S. Navy's Fast Sea Frame (FSF-1)
or X-Craft. |
NCE also uses FEA to predict and analyze acoustic phenomena,
including structural-acoustic interaction, such as the underwater
radiated noise created by an underwater diesel exhaust, the insertion
loss of novel underwater noise treatments, and the effectiveness of
specialized silencers used in gas turbine exhausts. NCE has also
performed stress analyses on specialized structures ranging from
composite deck plating to tow bitts.
First Bending Mode for a Patrol Vessel.
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Analysis results for machinery foundation
and surrounding structures (cutaway).
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Lastly, when diesel engines are resiliently mounted it is necessary
to also isolation mount the exhaust piping. The design of the mounting
system can be complicated, and care needs to be taken to account for
thermal growth and motion of the piping while maintaining high
transmission loss. Improper design of these systems can lead to noise
problems. NCE uses specialized piping based, finite element software
(CAEPipe) to investigate appropriate resilient mounts and mounting
locations to allow for a robust system that will keep vibration induced
nose from diesel engines low.
NCE primarily uses NEi Nastran Finite Element Analysis Software for
ship vibration and stress analysis. NCE also uses COMSOL Multiphysics
for acoustics and structural-acoustic interaction modeling. Other FEA
software used at NCE includes CAEPipe and MAESTRO.
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