NoVibTech

Applications

Where contact and friction govern the vibration.

Wherever components touch, stick, slip or lift off, the dynamics become nonlinear. We compute them with OrAgL in the frequency and the time domain and evaluate them in ARGUS: in turbomachinery, gearboxes and bolted joints.

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01 · Turbomachinery

Blades, friction dampers and the full wheel.

The most important application of OrAgL: bladed structures in aero engines, gas and steam turbines and compressors. Contacts at the platform, shroud and blade root damp vibration and shift resonances. How reliably they do so decides design and service life.

Contacts

01

Friction dampers

Below the platform between neighbouring blades. Normal load, friction coefficient and contact stiffness decide how far the resonance drops.

*SURFACE INTERACTION
02

Shrouds & interlocks

Contacts at the blade tip couple the wheel. Gap, preload and creep change their behaviour over the service life.

03

Blade roots

Dovetail and fir-tree joints: micro-slip in the interface adds damping and stiffness that depend on the amplitude.

04

Flutter with friction

Self-excited vibration that only friction limits: limit cycles with aerodynamic coupling.

*LCO · *AEROCOUPLING

Nonlinear frequency responses

A friction damper only works within a window of normal load. Too low, and it slips almost freely. Too high, and it sticks and stops damping. In between lies the tuning with the lowest resonance amplitude. OrAgL traces these responses across the frequency range and varies the parameters systematically.

Frequency →Amplitude (log)freestuckwell tuned
Frequency responses for several normal loads, between free and stuck (dashed).
Normal load (log) →Resonance amplitude (log)optimumslips almost freelysticks
Resonance amplitude over normal load: the optimum lies between sticking and slipping.

Schematic, not solver output: harmonic balance of a blade as a single-degree-of-freedom oscillator with frictional contact.

ND 3
Schematic: travelling wave with nodal diameters (ND) on a disk with 30 blades. Red and blue: deflection in opposite directions, dashed: nodal lines. In ARGUS you animate the computed mode shapes on the FE model.

Animations: from a sector to the full wheel

With cyclic symmetry, OrAgL computes a single sector and assembles the wheel through nodal diameters. ARGUS shows the computed mode shapes as an animation on the FE model, as a sector or as the full wheel, and makes the contact state at the interfaces visible.

*CYCLIC SYMMETRY MODEL*MISTUNING*ANIMATE SYSTEM*ANIMATE INTERFACE

ARGUS MESH: sector model of a bladed disk, expanded to 30 sectors through cyclic symmetry

ARGUS MESH: a sector model, expanded through cyclic symmetry to a wheel with 30 sectors.

Published

02 · Gearboxes

Tooth contact with backlash.

In the gear mesh, the contact is preloaded. Once the vibration exceeds the static deflection, the teeth lift off and strike again. The stiffness drops, the resonance bends towards lower frequencies, and during run-up and run-down the response jumps between different branches.

  • Lift-off and impacts

    Loss of contact and re-contact in the model, with contact stiffness or as a rigid contact.

  • Jumps and hysteresis

    Which branch the system follows depends on its history. Continuation reveals every branch, frequency sweeps in the time domain show the actual path.

    *CONTINUATION CONTROLS*FSWEEP

  • Impacts in the time domain

    Transient simulation with rigid contact when impacts and their consequences are the focus.

    *NOSTIA

contact closedcontact lifts offunstable branchFrequency →Amplitudejumpjump
Schematic, not solver output: harmonic balance of a preloaded tooth contact that lifts off above a certain amplitude. The branch overhangs to the left; between the turning points the solution is unstable and the response jumps.

03 · Bolted joints

Micro-slip in the interface.

Bolted structures are usually analysed as linear, yet behave nonlinearly: even at small amplitudes the interface starts to slip at its edges. The natural frequency drops and the damping rises. Often the joint is the most important source of damping in the whole assembly.

  • Stiffness and damping from the interface

    Amplitude-dependent behaviour from the contact model of the joint interface, instead of blanket damping assumptions.

  • Preload and geometry

    How bolt load and interface design shift frequency and damping, systematically across variants.

  • Large jointed models

    Model reduction and substructuring for thin-walled, frictionally clamped structures.

    *ROM*SUBSTRUCTURE ROM

Vibration amplitude (log) →natural frequencydampingstuckmacro-slip
Schematic: as the amplitude grows, the natural frequency drops while micro-slip damping rises to a maximum and falls again in macro-slip. Harmonic balance with an Iwan contact model.

Methods

Frequency domain and time domain.

Both views belong together. Harmonic balance delivers periodic responses quickly and with every branch. Time integration shows transients, sweeps and impacts as they actually unfold.

Frequency domain

Harmonic balance

Periodic and quasi-periodic responses, continuation across the frequency range including unstable branches, nonlinear modal analysis.

*HBM · *FRF · *NMA · *CONTINUATION CONTROLS
Time domain

Time integration

Transient responses to periodic excitation and frequency sweeps, limit cycles and tori, impacts at rigid contacts. Stored states serve as starting points for continued runs.

*NOSTIA · *HARMONIC · *FSWEEP · *MWF
ARGUS: time history of a transient run with stored states from which the analysis continues
ARGUS: time history of a transient run (*HARMONIC). Stored states are starting points for a continued run or an animation.

Next step

Your application is not listed?

Contact and friction are part of many assemblies. Describe your structure briefly and we will tell you what can be computed.

Discuss your application