Advances in Transient Multibody Simulation SKF BEAST. Presented to MODPROD 2014 Presented by Dag Fritzson,

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2 Advances in Transient Multibody Simulation SKF BEAST Presented to MODPROD 2014 Presented by Dag Fritzson,

3 Outline Is dynamic analysis needed? Some aspects of transient MBS simulation methology. Application example touchdown bearings for magnetic spindles Ongoing research SKF Group Slide 2 7 February, 2014

4 Motivation

5 Radial loaded spherical roller bearing SKF Group Slide 4 7 February, 2014

6 Dynamic application - wind turbine Wind mill: very dynamic system, from wind to electric grid, stop/start Very large bearings: structural weak, and more dynamic effects. More dynamic, i.e., - Inertia forces m^3 - Contact forces m^2 SKF Group Slide 5 7 February, 2014

7 Dynamic applications Gear transmissions Vehicle suspensions Rough roads for cars & trucks Wheel flats for trains Touchdown bearings for magnetic spindles. (more later) SKF Group Slide 6 7 February, 2014

8 Simulation techniques

9 Modelling Desired: High quality of models: Strict model description language 3D editor Support for model verification/debuging Re-use of components and models: Object-oriented model language (with deep connectors) Library of components and models CAD import SKF Group Slide 8 7 February, 2014

10 Detailed geometry description Very high accuracy (10^-7 m). Allow arbitrary geometry, details matter. Computation performance paramount: Parametric and inverse description. CAD import Replace contact surfaces Measured surface import. Material removal. Challenges: CAD quality is not fitting for the purpose. SKF Group Slide 9 7 February, 2014

11 Multibody simulation (3D) MBS and not transient FEM due to performance. Flexibility (CMS) through reduction of FEM Utilize geometry description directly. Compute mode shapes with FEM Structural deformation and stresses. Separation of scales Local contact deformation not included in structural deformation. Thermal and thermo-mechanical also with CMS. Challenges: Make reduction procedure more easy to use. Improved performance & accuracy. SKF Group Slide 10 7 February, 2014

12 Efficient contact computation Requirements: Separation, pressure, shear, power density, heat flow, (material removal) Arbitrary geometry Performance paramount (>90% of computation time) Standard techniques like MLMI, FFT, FEM, etc., are too slow. Technique: High order elastic contact elements + approximate local EHL formulas for film and pressure moment. Utilize fast parametric and inverse geometric representation. Verified with FEM, experiments, and Hertz (when valid). Snapshot computations with MLMI (interactive post-processing) Challenges: Even higher performance & accuracy SKF Group Slide 11 7 February, 2014

13 Parallel computation the way forward Serial execution time Can be split into independent jobs Not possible to split Parallel execution time Speed up Serial execution time Parallel execution time Parallel part Serial part Additional overhead (due to the parallel execution) Efficiency Efficiency Speed up Number Speed of processes up Number of parallel processes SKF Group Slide 12 7 February, 2014

14 Parallel computation, cont. Techniques: Master/slave Two-level dynamic scheduling Message passing interface (MPI) Master Slave 1 Slave 2 Slave 3 Slave 4 Slave 5 Slave 6 SKF Group Slide 13 7 February, 2014

15 Solving techniques Main solver is CVODE (modified) Variable order, variable step BDF method Improved step control (G. Söderlind). Extended interfaces for better integration in MBS/BEAST. Utilize the structure of the model, i.e., use symbolic expanded Jacobians. Sub-Jacobians computed analytical when possible. Embedded solvers for thermal, material removal, etc. Important to ensure total system numerical stability. Way forward: exploit structure/characteristics even more. SKF Group Slide 14 7 February, 2014

16 Service life Service life is determined by many damage mechanisms: sub-surface fatigue, wear, smearing, fretting, etc. Most are transient, accumulating phenomena. Future: More will come. SKF Group Slide 15 7 February, 2014

17 Application touchdown bearings for magnetic spindle

18 Active magnetic bearings operating principle Components of a magnetic bearings 1. Electro-magnets 2. Rotor 3. Position Sensors 4. Power Amplifiers 5. Control Operating principle of the control loop SKF Group Slide 17 7 February, 2014

19 Magnetic bearings: Touchdown bearings Part of any MB supported system Touchdown bearings are not in contact during MB operation Prevent contact between rotor and stator parts Emergency system in case of magnetic bearing failure Rotor support at standstill Backup system for MB overload situation SKF Group Slide 18 7 February, 2014

20 Touchdown event characteristics High acceleration rates of the ball bearings Shaft whirl (shaft motion in the clearance) Centrifugal forces Marginal lubrication due to application requirements. Differential temperature increase SKF Group Slide 19 7 February, 2014

21 7-Axes Rig Rotor model W24 W57 Thrust bearing K3 W13 Force generation V57 K2 V24 K1 Motor (330Hz) V13 Model features Three sets of paired full complement angular contact ball bearings Flexible shaft Thermal calculation of the bearings SKF Group Slide 20 7 February, 2014

22 7-Axes-Rig Agreement of whirl behavior Whirl frequency Whirl onset time Simulation Whirl at 110Hz Synchronous speed 0.05 sec Drop Test Whirl at 110Hz Synchronous speed 0.1 sec SKF Group Slide 21 7 February, 2014

23 7-Axes Rig Ball to race contacts Friction power intensity 0 W/m² W/m² W/m² W/m² W/m² W/m² Friction power intensity normalized -1 K1 K2 W/m² K3 Preload Brg W/m² K3 Load Brg SKF Group Slide 22 7 February, 2014

24 7-Axes Rig Evidence from bearings inspection (after 20 drops) Outer rings Inner rings Fax SKF Group Slide 23 7 February, 2014

25 Ongoing research

26 Some ongoing research activities Parametric optimization for heavy goal functions. Few function evaluations important Wall clock time matters ->extensive use of parallelism PhD thesis Per-Magnus Olsson March 2014, EDOp project (LiTH, SKF) Reduction techniques FE model have states -> states in reduced model Moving contacts, large contacting surfaces, viscoelastic materials SKF project at Umea University, Dept. of Mathematics Robust reduction for CAD bodies CAD geometry is often corrupt, or often have to many features Use of OctTree based FEM in the reduction computations Simovate project (Enmesh, SKF) Co-simulation Itea 2 MODRIO project (LiTH, SicsEast, SKF) SKF Group Slide 25 7 February, 2014

27 7 Slide February, The SKF co-simulation framework Operational since 2007 SKF Group Transmission Line Modelling (TLM) Physical motivated time delays Conditional stable simulation (T<time delay) No Jacobians are needed Asynchron communication (world-wide) Inherit parallel computation An OO meta-model description language provides: A strict notation and grammar Model abstraction Hierarchical modelling A generic way to connect tools Model editor (3D), Building meta model (pre-processing) Animation (post-processing) Plotting tool (2D)

28 Coupled simulation? MSC.ADAMS SKF BEAST Modelica Simulink MATLAB Facts: Large investment in specialized tools/models No universal tool solves everything Questions on the Way: How to couple different simulation models? How to model coupled simulations? How organize models of coupled simulation models? How to simulate on a company wide scale? SKF Group

29 Application Example - Car with Hub unit BEAST hub-unit model BEAST allows for detailed contact analysis in the wheel Bearings. MSC.ADAMS car model MSC.ADAMS allows for analysis of chassis and body dynamics. Hub-unit placed in front wheel SKF Group

30 A car and SKF hub unit SKF Group

31 The Complete Modelling Process Modelling in specialized environments Define interface points and encapsulate models Meta-modelling Sim. tool specialists Sim. tool specialists and/or meta-model designers Meta-model designers SKF Group

32 Application example - Medical Scanner General structure in MSC.Adams Control system in Simulink C-archs and trolley with 24 guiding wheels in BEAST SKF Group

33 Toy example: Pendelum with 10 bar segements SKF Group Slide 32 7 February, 2014

34 With BEAST only, NO co-simulation SKF Group Slide 33 7 February, 2014

35 New ongoing activities in MODRIO SKF donate the SKF co-simulation framework to OSMC Further developments, maintenace, under OSMC management To be generally available from OSMC Decoupled from SKF inhouse tools (Done) Replace model editor, plotting tool, etc. FMI extension proposal Extensions; more physics, etc. SKF Group

36 Conclusions

37 Conclusion Rolling bearings are dynamic machine elements, and many applications as well. Transient MBS/BRG simulation techniques has been reviewed. For the application touchdown bearings for magnetic spindles: Good agreement of motion patterns between simulations and drop experiment. Evidence found on inspected bearings matches with simulation results. Transient simulations creates knowledge of the behavior of complex, dynamic, machinery The SKF co-simulation framework will be generally available through OSMC. SKF Group Slide 36 7 February, 2014

38 Thank you!