Torsional Vibration Analysis
Standard marine TVA: mass-elastic modelling, natural frequencies, mode shapes, harmonic excitation and forced response across the operating speed range — in normal firing and with one cylinder misfiring.
Torsional vibration analysis · TVA
Torsional dynamics for marine propulsion
Simulation and class-review-ready torsional vibration analysis for conventional, electric and hybrid propulsion systems.
- Calculations for DNV and Lloyd's Register review
- Frequency- & time-domain simulation
- No expiring licences
- Developers of OpenTorsion
The core question
Are torsional vibrations within acceptable limits throughout the operating range?
Engines, motors, couplings, gearboxes, shafts and propellers form one torsional system with inertia, stiffness and damping. Excitation from engines, electric machines, propellers, waterjets or ice can drive it into resonance. We find out where, and what to change.
01Where are the torsional natural frequencies, and are there resonances in the operating range?
02What vibratory torques and shaft stresses occur?
03What happens with one cylinder misfiring?
04Is a barred speed range required, and where are its limits?
05Is the selected flexible coupling suitable?
06Does the design satisfy the classification requirements?
Services
We simulate torsional vibration in marine propulsion systems.
You design the vessel and propulsion system. We handle the torsional dynamics — from the first mass-elastic model to the report that goes to class. If you would rather hold the capability in-house, we also build the calculation software your own team runs.
Class Calculations
Class-review-ready TVA calculations and documentation for DNV and Lloyd's Register, with shaft stresses and barred speed ranges assessed against IACS UR M68. Class-review support within the agreed scope.
Design & Optimisation
Parameter sweeps and sensitivity studies to compare propulsion configurations and assess how coupling stiffness, inertia and gear ratio affect resonances and torsional loads.
Transient Analysis
Time-domain simulation of non-steady operation: start-up and shutdown, clutch engagement, generator connection, motor torque transients and fault conditions.
Ice-Class Analysis
Propeller–ice interaction and the resulting transient shaft torque, component loads and vibratory stress — ice load cases per the Finnish–Swedish Ice Class Rules and IACS Polar Class requirements.
Special Drivetrain Studies
Electric, hybrid, PTO/PTI, waterjet and unusual propulsion architectures — multi-engine and branched drivetrains, dual-fuel engines in both diesel and gas mode, and nonlinear systems.
Propulsion arrangements
Vendor-independent, which matters most in the gap between suppliers: the engine maker, the gearbox maker and the propeller maker each see only their own component. Missing engine harmonic excitation data is not a blocker — we derive it.
Acceptance criteria
- Permissible continuous torsional stress per IACS UR M68
- Transient limit for passing a barred speed range
- Barred speed range limits, including tachometer tolerance
- Normal firing and one-cylinder misfiring
- Coupling vibratory torque and heat dissipation
- Component torque limits from the equipment makers
Beyond pass / fail
Design changes to reduce torsional vibration
Analysis is most valuable while components can still change. We evaluate coupling stiffness, component inertias, shaft dimensions, gear ratio and operating speed to identify suitable design alternatives before hardware is ordered.
- Coupling stiffness & inertia
- Flywheel, motor and generator inertia
- Shaft diameter, length & material
- Gearbox ratio & operating rpm
- Propeller inertia & control strategy
Initial configuration
A resonance occurs at 720 rpm, inside the continuous operating speed range.
Modified configuration
In this model, reducing coupling stiffness moves the resonance below the continuous operating speed range.
Illustrative example
Ice-going vessels
Ice-class torsional analysis
We analyse loads from propeller–ice interaction using time-domain simulation and frequency-domain methods, with the ice load cases of the Finnish–Swedish Ice Class Rules and the Polar Class machinery requirements of IACS UR I3.
- Ice-induced transient shaft torque
- All four UR I3 excitation cases, at MCR, bollard and above resonance speeds
- Drivetrain response to blade impact and milling sequences
- Maximum shaft and component torque
- Vibratory stress & fatigue-related load assessment
- Drivetrain alternatives compared under ice loading
When to call us
Even a small change can shift a natural frequency.
- New vessel
- New propulsion design
- Class requesting TVA
- Class comments on a TVA
- New engine or electric motor
- Engine replacement and repowering
- Gearbox replacement
- Coupling selection and replacement
- Propeller replacement
- Waterjet propulsion
- Dual-fuel or gas engine
- Shaftline modification
- Power increase
- Hybridisation and electrification
- PTO/PTI installation
- Alternative-fuel conversion
- Ice-class vessel
- Unusual drivetrain architecture
- Resonance problem
- Component failure
- Ageing in-house TVA program
- Calculations stuck in spreadsheets
Process
How a project works
Send us a short description of the project. We review the requirements, agree the scope and provide a proposal. Our work is simulation-based and delivered remotely.
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01
Tell us about the project
A short description of the vessel, propulsion system or problem. No documents needed at this stage.
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02
Technical discussion
We confirm the calculation scope, applicable class rules, available input data and schedule by email or in a short online meeting.
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03
Proposal
Simulation scope, applicable rules, required input data, deliverables, design alternatives, included revisions, schedule and price.
A Simulation model
Mass-elastic representation of the full drivetrain: engine, crankshaft, flywheel, coupling, gearbox, shafts, motors, generators, PTO/PTI, propeller or waterjet. Single or multi-branched.
B Calculation results
Natural frequencies, mode shapes, Campbell diagrams, vibratory torque, torsional stress, critical speeds, barred speed ranges, misfiring cases, time histories and sensitivity results.
C Engineering assessment
Identification of the relevant modes and excitation sources, assessment against applicable limits, and evaluation of potential design changes.
D Report for class review
A technical report documenting the applicable requirements, methodology, assumptions, component data, results, limits, barred speed assessment and conclusions.
Standard TVA
Quoted per project
Each project is quoted according to the agreed scope. A standard analysis includes:
- Model construction
- Natural frequency analysis
- Frequency-domain forced response
- Engineering assessment
- Report for class review
Priced separately when needed
Framework agreements available for recurring work — shipyards, integrators, engineering offices and component manufacturers.
No licence to buy, no renewal to budget for, no tool to learn. You send the drivetrain data and receive the analysis — and if you later want the capability in-house, the software we build for you is yours to keep.
Send the shaftline and the question you need answered. We will tell you what the analysis involves.
Discuss your projectIn-house capability
Or we build the tool your team uses
Some teams would rather own the capability than buy the analysis. We take on software development projects for exactly that: a torsional calculation environment your own engineers run, built on the same methods we use ourselves. Typically because an internal program has aged past the engineer who wrote it, or because the workflow still lives in spreadsheets.
Legacy tool modernisation
An existing in-house TVA program that is undocumented, unmaintained or tied to obsolete dependencies — rebuilt with its engineering logic preserved and verified against its own historical cases.
Calculation workflow automation
Model build from your component data, standard load cases, batch parameter sweeps and report generation — so a recurring calculation stops being a manual afternoon in a spreadsheet.
Custom analysis tooling
A calculation tool around your own component libraries, engine excitation data, class templates and acceptance criteria — built on the OpenTorsion core, delivered with source code.
What you own afterwards
The tool, the source and the right to keep using it.
Built on an open-source core and delivered with the source code. It keeps running whether or not you work with us again.
What you never get
An expiring licence.
No annual renewal, no seat count, no licence server, no calculation that stops working because a subscription lapsed or a vendor changed its terms.
Open source
We develop OpenTorsion.
OpenTorsion is an open-source Python library for torsional vibration modelling and analysis. It supports finite element shaftline models, natural frequency and mode-shape analysis, forced response and time-domain simulation.
import opentorsion as ot
# Engine, coupling hub and propeller as lumped inertias
disks = [
ot.Disk(0, I=1.2e3),
ot.Disk(1, I=85.0),
ot.Disk(2, I=2.4e3),
]
shafts = [
ot.Shaft(0, 1, None, None, k=4.1e6, I=0),
ot.Shaft(1, 2, None, None, k=9.8e6, I=0),
]
assembly = ot.Assembly(shaft_elements=shafts, disk_elements=disks)
lam, modes = assembly.undamped_modal_analysis()
ot.Plots(assembly).plot_eigenmodes(modes=2)Who we work with
Torsional analysis without an in-house specialist
Specialist torsional vibration analysis for ship designers, shipyards, propulsion suppliers and vessel operators, and calculation software for teams that do the analysis themselves.
Ship design offices & naval architects
You design the vessel and shaftline. We perform the TVA and prepare the class calculation.
Shipyards
Newbuild and retrofit yards needing class TVA once engine, gearbox, coupling, shaftline and propeller are selected.
Propulsion system integrators
We provide torsional analysis for your propulsion package.
Engine & motor manufacturers
Application engineering, unusual installations, hybrid and electric arrangements, independent analysis.
Gearbox & coupling manufacturers
Coupling selection, stiffness optimisation, gearbox integration and component load calculation.
Waterjet manufacturers
Complete engine–gearbox–shaft–waterjet drivetrain dynamics, including transients.
Engineering consultancies
We act as the specialist subcontractor for the torsional part of your design project.
Shipowners & fleet operators
Repowering, retrofits, drivetrain failures, operating restrictions and independent assessments.
We do
Model and simulate the drivetrain — and build the software that does it.
Delivered remotely. Where measurement data already exist, we can use them as input or for comparison against simulation.
We don't
Perform mechanical or measurement work onboard.
No shaft installation, alignment or vibration measurements, condition monitoring, balancing, repair, commissioning or inspection.
The engineers
Founders
Marine Engineering Dynamics is a specialist simulation company based in Finland. You work directly with the founders throughout the project, from defining the scope to modelling, analysis and reporting.
Dr. Sampo Laine
Co-founder · D.Sc. (Tech.), rotordynamics
Doctorate in rotordynamics, lateral and torsional, covering bearing, support and foundation modelling and fluid–rotor interaction. Lead contributor to OpenTorsion, the open-source torsional finite element library from Aalto University's Arotor group. His work includes finite element modelling, spectral analysis in Python, and simulation of electric drives and power electronics.
LinkedIn
Dr. Tuomas Tiainen
Co-founder · D.Sc. (Tech.), mechanical engineering
Mechanical engineer with a strong background in software engineering, and a contributor to OpenTorsion. Develops tools for model assembly, parameter studies and report generation, and works on drivetrain modelling for conventional, electric and hybrid propulsion.
LinkedInContact
Request a quote
Send us a short description of the propulsion system or calculation you need, or the analysis tool your team needs built. We will review the information and contact you about the scope, required data and quotation.