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SAFER, SMARTER, GREENER

NAUTICUS™ MACHINERYTorsional Vibration

With Nauticus Machinery – Torsional Vibration you can identifycritical components by analysing the torsional vibration levels in all types of marine propulsion systems from direct coupled systems to more advanced systems with multiple engines and gears. Control of vibration levels is essential in order to have machinery that operates safely and reliably.

DNV GL’s wide contact with different marine component manufacturers provides the best insight into diesel engines, gas turbines, electric motors, dampers, couplings, clutches, gear transmissions, shafts, bearings, propellers and water jets. All this experience is the foundation for development of DNV GL’s Torsional Vibration tool.

Nauticus Machinery – Torsional Vibration is a state-of-the-art software tool using the latest available technology both for graphical modelling of the propulsion system and solution of the equation systems.

Two calculations on same modelThe Torsional Vibration tool contains two calculation modules: the Frequency-domain module and Time-domain module, which are controlled by different licences. The user interface and modelling are exactly the same for both modules. Both frequency-domain calculation and time-domain calculation can be performed on the same mass-elastic model. The Frequency-domain module is used to perform the steady-state torsional vibration, while the Time-domain module is tailored to handle shaft line transient dynamic analysis regarding the propeller ice torque excitation for the ship with ice class notation.

Benefits ■ Easy-to-use graphical user interface with flexible modelling options

■ Integrated scripting language for efficient modelling and analysis

■ Supports all types of systems (diesel, electric, gas, single or multiple branches)

■ Supports multiple engine systems ■ Engine library for excitation- and mass-elastic data ■ Be able to handle ice impact on propeller by both time-do-main approach and steady-state approach

■ Import and conversion functions for datasets from engine suppliers

■ No limitations with respect to number of mass- or stiffness elements

■ No limitations with respect to number of operating modes or load cases

■ Acceptance criteria check for all components (IACS M68, DNV Rules and custom curves)

■ Support for SI and US unit systems ■ Advanced charting/reporting utilities and support for dual screens

■ Flexible reporting features and integration with MS Office

Easy, reliable and effective software for evaluating torsional vibration on shafting systems.

DIGITAL SOLUTIONS

DNV GL AS, digital@dnvgl.com, www.dnvgl.com/digital April 2018

Calculation scope ■ Free vibrations, natural frequencies, mode shapes and vector sums

■ Forced vibrations in frequency-domain - Angular deflection, velocity and acceleration for masses - Vibratory torque and stress amplitudes - Power loss and dissipated heat - Propeller curve - Fixed and controllable pitch results- Combinatory propeller curve mode calculation for controllable pitch propeller system - Consider ice impacting in forced vibration calculation by steady-state approach

■ Forced vibration in time-domain- Shaft line transient dynamic analysis regarding the propeller ice torque excitation- Find the least favourable phase angle for ice versus engine excitation- Find the least favourable free water running speed before entering into ice impacting.- Ice impacting torque on the propeller - Rotational speed of the masses in time domain- Shaft torque/stress in time domain- Peak torque due to ice impacting

Modelling elements ■ Diesel engines, gas turbines and electric motors ■ Lump mass ■ Steel shaft ■ Elastic couplings (linear/progressive) ■ Vibration dampers ■ Reduction gears ■ Propellers, water jets and generators

Modelling interfaceThe user works in a graphical modelling environment where various components are selected from a menu and dropped into a mass-elastic modeller. The modeller supports zooming and panning, so it is easy to work with relatively complex systems consisting of several mass- and stiffness elements. Each user interface action is recorded in a script journal (using Java-script syntax).

Scripts can be written in dedicated text editors and executed inside the application. Thus, building parametric models is done efficiently – users can quickly create them inside the application. There is also a powerful property grid for input of the various parameters. The application includes a report generator where it is possible to preview and send reports directly to a printer or export them to Microsoft Office applications.

Acceptance criteriaFor all masses (e.g. flywheel) the maximum limits for angular acceleration, velocity and displacement can be specified. For

stiffness elements (e.g. crankshaft or propeller shaft) the maxi-mum torque and stress limits can be specified. For coupling and damper the maximum heat-dissipate can be specified. Custom acceptance curves by imported text files are also supported. The calculation methods in IACS UR M68 for intermediate and propeller shafts are also fully integrated in the software. In ad-dition, DNV GL - Software offers alternative methods by means of Nauticus Machinery – Shaft Fatigue (DNV GL Class Guidelines 0038) and Nauticus Machinery – Crankshaft Fatigue (DNV GL Class Guidelines 0037 and IACS UR M53).

Special support for 2-stroke systemsThe application can automatically import mass-elastic data files from the major 2-stroke engine manufacturers. In addition the excitation data, data files can be imported by means of gas harmonics. The application also provides an internal format to represent the gas force harmonics in cases where the engine manufacturer does not have any standardized format. The mass-elastic and excitation data can be saved in an engine database and shared with other users.

Special support for ice class vesselFor the ice class vessels, special calculation is required for the propulsion system to ensure safe operation. Torsional vibration calculation regarding to the ice torque impacting on the propel-ler is one of the main challenges when designing the propulsion machinery. According to the latest ice class rules, both steady-state approach and time-domain approach can be used for the ice impacting calculation. Nauticus Machinery – Torsional Vibration provides both approaches in accordance with the latest ice class rules. DNV GL’s extensive expertise on this area has been highly integrated in the tool. The steady-state approach has been embedded in the frequency-domain module and the calculation results by this approach are considered more conservative than those in the time-domain approach. The Time-domain module is tailored for transient dynamic analysis on the shafting regarding ice impacting. It allows you to efficiently perform the time domain approach and optimize the design.

The workflow to evaluate the ice class strength on the propul-sion shaft can be described by the following chart. Use Nauticus TVC to calculate the torsional vibration with ice impacting by either the time-domain approach or steady-state approach. Use Shaft Fatigue in Nauticus Machinery to evaluate the shaft strength according to ice class requirements.

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