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Vehicle Dynamics & Safety: Multibody System

Vehicle Dynamics & Safety: Multibody System. Simulation tools based on MultiBody approach are widespread in vehicle design and testing. F. M. Vehicle Dynamics & Safety : Multibody System. What is a Multibody System?

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Vehicle Dynamics & Safety: Multibody System

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  1. Vehicle Dynamics & Safety: Multibody System Simulationtoolsbased on MultiBodyapproach are widespread in vehicle design and testing

  2. F M Vehicle Dynamics & Safety: Multibody System • Whatis a Multibody System? • System consistingofrigid or flexiblepartsconnectedbyjoints and undergoinglargedisplacements: mechanisms, vehicles, trains ….

  3. Multibody Approach • Whatis • the MB approach? • The MultiBodyapproachis a set oftoolsthatallow the (automatic) writingof the equationsofmotionof a MB system, startingfrom a “description” of the system itself. • Differentsystems can beanalyzedby the same software, asopposedto a dedicatedapproach.

  4. Multibody System • MB System ofdifferenttopologiesmustbeanalyzed • Constraintsmustbereproduced • System Forcesmustbemodelled • Rigidaswellasdeformablebodiesmustbeavailable

  5. Topology of MB System A MB system can have an open chain (left, robot PUMA Programmable Universal Machine for Assembly) or a closed chain (right, slider-crank mechanism) structure

  6. Constraints Constraintmustbemodelled Constraints reduce the system d.o.f: Gruebler Formula: dof=6*n_body-n_constr

  7. Constraints • Incastro: fixed joint • Cerniera: revolute /pin /hinge joint • Manicotto: collar • Carrello: roller/rocker • Pattino: slider • C. sferica: spherical joint • G. cardanico: Hookean/Universal joint

  8. System forces Bodiesexchangeforcesalsothroughsprings, dampers or more sophisticated elements (liketyres….)

  9. Deformable bodies FEM discretization, followedbymodalanalysis and choiceofrelevantmodes

  10. MultiBody System coordinates • To define the position of a MB system a reduced set of indipendent coordinates (joint) can be used or an extended/full set (body coordinates) of dependent coordinates

  11. Joint coordinates Four bar linkage: 3 coordinates and 1 dof Two scalar constraintequations

  12. Body coordinates Four bar linkage: 9 coordinates and 1 dof Eight scalar constraintequations

  13. Body coordinates • Body position in 3D is described by position of one point ( 3 dof , centre of mass) and by orientation (3 angles). Euler or Cardan conventions are used (zxz). In vehicle dynamics Roll(x)-Pitch(y)-Yaw(z)

  14. Body orientation

  15. Multibodysimulation: classesofproblems • Kinematic analysis: position, velocity acceleration when no dof exists (forces have no influence on motion….) • Dynamic analysis: nonlinear, linear (small oscillations, frequency response) • Sensitivity/parametric analysis • Optimization

  16. Multibody simulation: kinematic analysis of a suspension

  17. Geometric modelling

  18. Constraints, Loads, Forces

  19. Assembly

  20. Kinematic analysis Position, velocity and acc. analysis. Range of motion, workspace, collisions …

  21. Dynamicanalysis and Post-processing

  22. MSC ADAMS • -MD Adams (Mech. Dynamics, later Multi-Domain…), now MSC Adams is a commercial software developed from a research software by Orlandea (1973…University of Michigan, Ann Arbor). • -It’s an acronym of Automatic Dynamic Analysis of Multibody Systems.

  23. MSC ADAMS • It consists of three main modules and several “vertical” application: • Adams Pre for data input, modelling • Adams Post for results analysis (graphs, animations ..) • Adams Solver for equations assembly and solution (static, kinematic, dynamic sim.) • All these modules are integrated in ADAMS-View

  24. MSC ADAMS • Customized version for special purpose applications: • ADAMS Car, Chassis, Driveline • Solver modules (plugins): Linear (eigenmodes, eigenfrequency), Vibration (frequency response), Flex (flexible Bodies), Durability (computation of stresses in def. Bodies).

  25. MSC ADAMS • Adams Control allows the introduction of simple control systems in simulation. • With Mechatronics ADAMS can be used for co-simulation with Matlab Simulink (or Easy5) Mechanical system Control system

  26. MSC Adams • The Adams/View Modeling database is a hierarchical (binary) database. Each object in the database has an object that owns it, called its parent, and many objects own other objects, called their children. The top level objects in the database are models, views, plots, and libraries containing such things as dialog boxes.

  27. MSC Adams

  28. Testi di consultazione: • A. Shabana, Dynamics of Multibody Systems, Wiley. • G. Legnani, Robotica industriale, Casa Editrice Ambrosiana.

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