Nauticus Machinery Knowledge Centre Help library Tools and Calculations Torsional Vibration Tool
Module Description
The Nauticus Torsional Vibration (TVC) tool provides comprehensive analysis capabilities for propulsion system torsional vibrations. This module helps engineers predict and mitigate harmful vibrations that could damage rotational components or shafting elements.
The tool covers two modules:
- Steady state (frequency domain) calculation module – Analyzes torsional vibration responses in frequency domain by computing free vibration and forced vibrations due to steady state excitation sources.
- Transient (time domain) calculation module – Calculate the dynamic response of torsional systems in time domain due to transient excitation such as ice impacts or electrical short circuits.
Both frequency domain calculation and time domain calculation are based on the same mass-elastic model. This chapter focuses the frequency domain calculation module.
Key Features
- One mass-elastic model supports various operating modes and load cases.
- Calculates free and forced vibrations for all types of marine propulsion plants.
- Integrate three methods (Harmonic, Theoretical and Empirical) to calculate the diesel engine gas excitation.
- Integrate various propeller damping models.
- Support dual-fuel engine in different excitation mode (Diesel mode and Gas mode).
- Efficiently identify the worst misfiring cylinder for the diesel engine propulsion system.
- Find recommended barred speed range for diesel engine system.
- Support custom load curve to handle the case like CPP system working at combinatory propeller curve.
- Handles ice impact on propeller by steady-state approach according to ice class rules.
- Compliance verification according to rule requirements and manufactor specifications.
- Advanced report and print features, integration with MS Office applications.
Workflow
- Model mass-elastic system with mass, stiffness, and damping properties.
- Define operating modes and load cases.
- Define excitation sources, including engine excitation and propeller excitation.
- Perform calculations, including both free vibration and forced vibration analysis.
- Evaluate forced vibration responses against allowable limits.
- Determine and introduce barred speed range if applicable.
- Generate compliance report.
Page Description
The TVC tool organises its input and output into the following tab pages:
Mass elastic data | Operating modes | Results | Script | Log
Mass Elastic Data
The Mass elastic data page is the first tab page of the TVC tool. It defines the torsional mass-elastic model used for vibration analysis. The page contains two data grids: Mass elements and Stiffness elements.
Mass Elements
The Mass elements grid defines the lumped masses (inertias) of the torsional system. Each row represents one mass station.
| Column | Description |
|---|---|
| Index | Sequential index number of the mass element. |
| Name | Short identifier for the mass element. |
| Description | Descriptive text for the mass element (e.g. component type or location). |
| MomentOfInertia | Mass moment of inertia. |
| DynamicMagnifier | Dynamic magnifier for the mass element. |
| AbsDamping | Absolute (external) damping coefficient. |
Stiffness Elements
The Stiffness elements grid defines the torsional connections between adjacent mass elements. Each row represents one stiffness segment connecting two consecutive mass stations.
| Column | Description |
|---|---|
| Index | Sequential index number of the stiffness element. |
| Name | Short identifier for the stiffness element. |
| Description | Descriptive text for the stiffness element. |
| TorsionalStiffness | Torsional stiffness. |
| TorsionalFlexibility | Torsional flexibility (reciprocal of stiffness). |
| DiamOuter | Outer diameter of the shaft section. |
| DiamInner | Inner diameter of the shaft section. |
| DynamicMagnifier | Dynamic magnifier for the stiffness element. |
| RelDamping | Relative (internal) damping coefficient. |
Note: The number of stiffness elements is always one less than the number of mass elements, since each stiffness element connects two adjacent mass stations.