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Page 48: of Maritime Reporter Magazine (April 1998)
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PROPULSION UPDATE tion gear vibration requirements will be met.
The design phase of low noise gearing focus- es on the five areas noted below. In all cases, the basic design objective is to minimize vibra- tion stimuli. • Rotating Elements - maximize balance, roundness, concentricity; • Gear Casing - ensure rotating element support and parallelism; • Bearings - optimize stability; • Couplings - optimize arrangement and shafting system dynamics; and • Mesh Design - maximize uniformity of load transfer.
The benefits of these low noise gearing design features are realized through manufac-
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Mounting System Design and
Performance
The ultimate objective of the mounting sys- tem design is to minimize the overboard radi- ated noise attributable to the reduction gear- ing. This is achieved by isolating the reduction gear from the ship foundation. Consider three typical mounting system configurations - hard mounted, metallic isolation and elastomeric isolation. Each of these configurations is shown schematically in Table 2, along with some of their performance comparisons.
The mounting system selection must consid- er the following:
Ship mission requirements; Performance comparison trade-offs; and level of isolation needed to satisfy the system noise performance (determined from noise performance evalua- tions).
System noise performance evaluations should be conducted throughout the reduction gear design phase to ensure that noise perfor- mance requirements are satisfied. (Continued on page 54)
Table 1
Table 1
Typical Propulsion System Noise Sources and Control Approaches
Prime Movers Reduction Gears System Resonance
Sources
Rotationals &
Harmonics • Blade Passing, Fluid
Stream
Crank-Effort
Pulsations
Electrical Tones,
Power Converter,
Pole/Slot Passing
Sources • Shaft Rotationals &
Harmonics • Mesh Tones • Undulation Tones
Sources • Casing & Support
Structures • Shafting System • Isolation System
Control • Dynamic Balance • Rotor / Stator /
Casing Design • Couplings / Bearings • Isolation System - Ship Foundation
Control - Dynamic Balance
Roundness &
Concentricity • Couplings / Bearings • Mesh Design
Manufacturing
Accuracy • Isolation System • Ship Foundation
Control
Resonance
Frequency Tuning • Stimulus Frequency
Avoidance
Component &
System Damping • Isolation System • Ship Foundation
Table 2
Table 2
Mounting System Comparisons
Hard-Mounted Compound Metallic Single Stagtomeric
System Complexity
Low Complexity • Gear Casing Bolted
Directly to Ship
Foundation • No Shock Snubbers ////////
Moderate
Complexity
Several Isolators
Required
Shock
Required
Snubbers
Noise Performance - Foundation Vibration
Higher Complexity
Numerous Mounts
Required
Shock Snubbers
Required
Periodic Mount
Replacement
Higher Overall
Vibration
No Gear-to-
Foundation Isolation • Non-Tunable Design for Given Ship
Foundation
Lower Overall
Vibration • Tunable Design —
Can Optimize to
Foundation and Ship
Mission
Significant
Attenuation Above
Isolator Resonances (Limited by High
Frequency Modes)
Lowest Overall
Vibration • Non-Tunable Design - Standard Application
Mounting Frequency
Significant
Attenuation Above
Mounting Frequency (Limited by High
Frequency Wave
Modes)
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