Respect of contractual specification limits
Minimization of machinery structural borne noise and vibration
Reduction of risk of resonance phenomena and cracks
No risk of penalty payment
Increased comfort on board
Vibration
Assessment
The aim of the activity is to assess the vibration behaviour of the vessel during the yacht design phase.
All the described activities are fundamental in order to respect the contractual vibration specifications, to minimize the risk of structural cracks and damages, and to reduce the structural borne-noise source.
VIBRATION PREDICTION CALCULATION
The first step in order to achieve this goal is to create a whole vessel 3D finite element model in accordance to the received structural drawings.
The generated model helps determine both global and local structural natural frequencies and mode shapes. The aim of this study is to avoid the risk of resonance phenomena with the main exciting frequencies and, where natural frequencies and excitation sources match, structural alterations have to be proposed.
In the second calculation step, the dynamic forced frequency response analysis determines the velocity vibration levels for the entire vessel, which have to be compared to the vibration contractual levels. In case these limit values are exceeded, it becomes necessary to study adequate structural solutions in order to respect them.
ADDITIONAL VIBRATION ANALYSIS
A full vibration assessment has to be completed with the following activities:
⦁ FOUNDATION MOBILITY The foundation mobility has to be calculated to verify the dynamic stiffness of the foundations and of the basements, and the values have to be compared to Cergol’s internal target.
⦁ SHAFT WHIRLING ANALYSIS The main target of this activity is to prevent any resonance phenomena of the shaft with the operative conditions.
⦁ 6 DOF and TVC
The 6 Degrees of Freedom calculation helps evaluate the natural frequencies of machinery installed on resilient mounts, as well as DDGG and Main Engine.
The TVC Torsional Vibration Control consists in calculating the shaft torsional vibration modes and allows the reduction of the structural borne noise transmitted to the machinery foundation.
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