Torsional Vibrations

Torsional Vibrations in Rotating Machinery, Cars + Trucks, Ships

Drive of a Cement Mill with Planetary Gear / (c) Laschet Consulting

 

Basics

The engineering jobs contain calcu­lations and simula­tions of TOR­SIONAL VIBRA­TIONS of straight, branched, and inter­mesh­ed drive sys­tems (drive­lines, power­trains) also con­sider­ing non­linear cha­rac­teristics (e.g. rubber coup­lings, gear stages with back­lash, shift and en­gage effects in clutches, etc.) in the time or fre­quen­cy do­main. We can follow steady-­state condi­tions or time-­tran­sient effects in the si­mu­lation en­viron­ment. Further­more, con­trol effects may be part of an ex­panded tor­sional vibra­tion mo­del.

The CAE results show the natural fre­quencies (critical speeds) usual­ly pre­sented in so-called “Campbell” dia­grams (inter­ference dia­grams, water­fall dia­grams), as well as the gra­phi­cal inter­pre­tation of the vibra­tion modes (modular forms, mode shapes). We also get simu­la­tion re­sults showing the ex­pected ampli­tudes and magni­tudes (usually taken from torque signals, velo­cities and speeds, accelera­tions) depend­ing on the exist­ing excita­tions (i.e. excita­tion torques of the motor, the engine, the work­ing process, and the operat­ing con­ditions).

 

Procedure

A typical torsional vibration analysis (TVA) is structured as follows:

  • MODEL GENERATION
    creating the computer model according to the task
  • ANALYSIS OF EXCITABILITY
    calcu­la­tion and inter­pretation of the natu­ral be­havior in­cluding reso­nance ana­ly­sis depend­ing on the sys­tem exci­ta­tion (studying inter­ference dia­grams), first mo­del vali­da­tion
  • SIMULATION
    determination of the system response like torques in the shafts, couplings, gear stages, etc. – either time dependent or speed dependent
  • POSTPROCESSING + INTERPRETATION
    analysis of the results compared to measure­ments and expe­riences, final mo­del vali­da­tion and model refine­ment (if necessary)
  • OPTION: FURTHER CASE STUDIES, SYSTEM OPTIMIZATION
    specification of a technically and economically reasonable “best” drive system configuration

 

Simulation Methods

We distin­guish between two different simu­la­tion methods for our CAE analysis:

a) the “STEADY-STATE SIMULATION” (i.e. the simu­lation of the steady-­state operat­ing con­dition with con­stant operat­ing speed also known as “simulation in the frequency domain”)

b) the “TIME-TRANSIENT SIMULATION” (i.e. the “simu­la­tion in the time domain” to deter­mine the time-­transient response of the drive system depend­ing on time-variable operat­ing con­ditions also consider­ing non­linear effects like gear back­lash)

Simulation of a Compressor Drive System / (c) RBTS

 

Possible resonances can be pre­destinat­ed (“simu­lat­ed”) – simi­lar to a “wea­ther fore­cast” of the dyna­mic beha­viour of the com­plete drive sys­tem (drive­line, power­train).

 

 

 

Source: RBTS, Inc. / USA (Software: ARMD)

 

 

Special Analysis, NVH Studies

Measurements compared with CAE Analyses

Even dynamic-­acoustic effects can be pre­dict­ed as part of so-called NVH studies (NVH = “Noise, Vibra­tion, Harsh­ness”) which are im­por­tant when opti­miz­ing auto­motive drive­lines and com­plete power­trains (cars, trucks, any other vehicles). Spe­cial re­ferences and ex­tend­ed in­for­ma­tion par­ticular­ly on this sub­ject are available on re­quest.

 

 

Applying CAE Tools: Simulation Models of Complete Drive SystemsSource: ESI-ITI, Dresden / Germany (Software: SimulationX)

 

More detailed infor­ma­tion concern­ing all the other sub­jects are available as well.

Please contact us.

 

Further Information on Special Sites

Please visit our special sites for more detailed information:

Rotordynamics, Lateral + Flexural Vibrations

Analysis especially of lateral and flexural vibrations including a stability analysis of rotor bearing systems in rotating machinery supported by the software ARMD. Learn more …


Virtual Engineering, Development, Simulation

The virtual development process requires suitable R&D software tools, simulation environment, measurements, field tests, experiences. Learn more …


Technical Papers, Publications, Conferences

Publications by Dr. Andreas Laschet: technical papers in journals, conference papers, book contributions. Learn more …

 

Further Information as Downloads

Further information are also summed up in the following documents (PDF):