Application to Vehicles Dynamics. Taking into account local non linearity in MBS models. This document is the property of SAMTECH S.A.

Transcription

1 Application to Vehicles Dynamics Taking into account local non linearity in MBS models This document is the property of SAMTECH S.A. Page 1

2 Tables of contents Introduction SAMTECH Expertise SAMTECH Methodology Application to Vehicle Dynamics Optimisation Conclusions This document is the property of SAMTECH S.A. Page 2

3 Introduction This document is the property of SAMTECH S.A. Page 3

4 References in the automotive industry WIA KATECH This document is the property of SAMTECH S.A. Page 4

5 SAMTECH experiences in Automotive Suspension Cam shaft Chassis Machining Differential Gears Brakes Vehicle Dynamics Pipe Engine This document is the property of SAMTECH S.A. Page 5

6 Challenges for simulation Non linearity Handling Misuse FEA Secondary Ride Durability Primary Ride Control systems MBS NVH Frequency This document is the property of SAMTECH S.A. Page 6

7 Simulation in the design process beginning of design process Prototyping: Replace real ones by virtual ones Consequences on final product minimisation of time-to-market & costs Project definition Vehicle targets Requirements definition Global analysis Detailed design NUMERICAL SIMULATION Local analysis System Integration System Test and verification System Validation Project test and integration Need of reliable CAE solution integrated in the design process This document is the property of SAMTECH S.A. Page 7

8 Modelling chronology Suspension geometry FEA Body in White Lateral Steady state manoeuvre Jturn (step steer) Lateral Transient sine sweep corner entry Braking manoeuvre Combined manoeuvre braking in curve gas release Lane change Ride and durability Complexity This document is the property of SAMTECH S.A. Page 8

9 Global analysis System level model for time response static, kinematic (suspension), dynamic (manoeuvres, durability, ) Necessary to accurately describe the dynamic loads acting on the vehicle or on vehicle components: Driving conditions Ride and comfort Misuse (kerb hitting), This document is the property of SAMTECH S.A. Page 9

10 Local analysis Classical Linear & non-linear Structural Analyses Need of loads and boundary conditions from Global Analysis Global-Local coupling Static stresses evaluation Vibration modes computation Non-Linear Structure Analysis with contact/friction Fatigue Analysis This document is the property of SAMTECH S.A. Page 10

11 Classical methodology FEA (local analysis) CAD data MBS (Global analysis) FEA model Rigid bodies model Super Elements export Replace rigid bodies with SE Run simulation Calculate detailed stress export Fatigue Prediction Superposition of stress Cycle counts Damage sum Export node forces time history This document is the property of SAMTECH S.A. Page 11

12 Classical methodology Several different models (local, global) Several different software (linear FEA, non linear FEA, MBS, ) Probably several different users/teams A lot of data transfer Hypotheses made: - Flexibility in MBS model - Local non linearity not taken into account - Transient loads transformed in static loads for FEA model This document is the property of SAMTECH S.A. Page 12

13 SAMTECH evolution FEA=Finite Element Analysis MBS=Multi-Body Simulation KBE= Knowledge Based Engineering GUI= Graphical User Interface Linear FEA in standalone GUI 1980 FEA and MBS in standalone GUI 1990 Integration Level 1 through Interfaces FEA and MBS in unified GUI 2000 Integration Level 2 with CAD Based Pre- and Post- Processor Non-Linear FEA&MBS in KBE 2010 Integration Level 3 within the Engineering Process MultiPhysics in KBE 2020 This document is the property of SAMTECH S.A. Page 13

14 SAMCEF Field Every SAMCEF solver is driven from one common GUI: SAMCEF Field (FIELD = FInite ELement Desktop) Need of only one model CAD Model (IGES, STEP, Catia, Brep ) Changes Modeler to create your CAD geometries Analysis data Mesh / Import mesh Solvers Post-processing HTML Report This document is the property of SAMTECH S.A. Page 14

15 SAMCEF Capabilities as linear FEM solver Linear FEM capabilities include: static composites Fracture Modal analysis Dynamic response Contact Linear analysis Flexible/flexible Solid/flexible Buckling Meshed part #1 Meshed part #2 This document is the property of SAMTECH S.A. Page 15

16 MECANO capabilities as non linear FEM solver Non linear FEM capabilities include: Geometric non linearity: Large strain Large deflection Material laws (viscoelastic, hyperelastic, ) Temperature dependency Rubber bushing example Large displacement This document is the property of SAMTECH S.A. Page 16

17 MECANO capabilities as Rigid MBS solver Library contains over 150 kinematic joints: Spring Spherical Prismatic Tyre Gear and pinion Bushing Hinge This document is the property of SAMTECH S.A. Page 17

18 MECANO link with control system 3 ways to handle digital control with our tools: A SAMCEF Mecano model is linearized and transformed into space state matrices to be used by Matlab Simulink Matlab Simulink controller is exported to a Fortran/C subroutine linked to SAMCEF Mecano Matlab Simulink is launching Mecano computations to update its structural model This document is the property of SAMTECH S.A. Page 18

19 SAMCEF MECANO unique approach Linear Non Linear Kinematic Joints Digital Controller This document is the property of SAMTECH S.A. Page 19

20 Original methodology of Samcef MECANO Finite element approach Implicit solver Cartesian coordinates (6 dof by nodes) Rotation vector theory Joints defined by kinematical constraints Augmented Lagrangian method Φ: constraint λ: Lagrangian multiplier p: penalty factor k: scaling factor This document is the property of SAMTECH S.A. Page 20

21 Implicit Explicit : what to use? Explicit conditionally stable Solution at t+δt entirely based on solution at t, meaning that the initial errors are accumulating into further time steps Time step has to be smaller than L min : smallest element dimension C d :characteristc speed If the time step is greater than Δt cr, non physical oscillations appear in the results As CPU time is inversely proportional to time step size, calculation can be very long Or a compromise needs to be found between CPU time and accuracy Explicit Schemes are well suited for very fast dynamic phenomena (crash) This document is the property of SAMTECH S.A. Page 21

22 Implicit Explicit : what to use? Implicit unconditionally stable Use equilibrium at t, t+δt to solve solution at t+δt Time step only depends on the frequencies you want to represent (curves must be properly described) Results are more stable and simulation is faster for longer runs (no simulation time limit) Several schemes exist with different behaviour regarding numerical damping Implicit schemes are well suited for dynamic analysis with longer phenomena (vehicle dynamics, engine dynamics ) This document is the property of SAMTECH S.A. Page 22

23 SAMCEF MECANO solvers Implicit time integration Newmark HHT Chung-Hulbert Resolution of potentially large problems Sparse solver Mumps solver Parallel solver 4 sections of fuselage 18,580,217 dof's 2,521,568 shells elem. 3,092,810 elem. In total 28 h 30' on a cluster of 10 nodes. 7 time steps, 5 rejected, 57 iterations up to 91% of the load Intel(R) Core(TM) 2.67 GHz 12 Gb per node This document is the property of SAMTECH S.A. Page 23

24 SAMCEF MECANO advantages Generalised non-linear mechanical tool box Non-Linear FEA & S.E. Rigid/Flexible kinematical joints Contact/Friction Integration of design & verification engineering in a common environment Strong coupling between FEM & MBS MECANO = MBS features inside a FEM code NOT flexibility inside MBS code This document is the property of SAMTECH S.A. Page 24

25 Application to Vehicle Dynamics This document is the property of SAMTECH S.A. Page 25

26 Vehicle dynamics context Nowadays virtual prototyping plays greater role in vehicle design Better accuracy needed to predict the vehicle performances based on CAE estimations and results Simulation Challenges faced for vehicle dynamics: Local non linearity Frequency domain coverage Multi disciplinary Data exchange between platforms MBS FEA Control systems Fatigue program Virtual Real This document is the property of SAMTECH S.A. Page 26

27 Vehicle dynamics context Durability Handling Control systems Kinematics Ride and comfort Misuse This document is the property of SAMTECH S.A. Page 27 NVH

28 Model complexity Results accuracy 100% MBS model with FEA MBS model with FEA and meshed tyres Bicycle model 4 wheels model MBS model MBS model with SE Number of parameters This document is the property of SAMTECH S.A. Page MBS Test Mecano

29 Possible sources of non linearity in a vehicle Pre-stress Aerodynamic forces Friction Local plasticity Damper Bushing Brakes (contact, friction and temperature) Free play Tyre Bump or rebound stop Antiroll bar Power steering Spring Chassis flexibility This document is the property of SAMTECH S.A. Page 29

30 Rigid body or Flexible Possibility to import mesh from external sources - Created in another model by SAMCEF - NASTRAN - ANSYS When objects are defined as rigid, SAMCEF Field automatically creates: One node at the Centre of Gravity One node at each interface with other objects or the ground Mass and inertia of the object are assigned to the CoG Extra masses and inertias can be manually assigned This document is the property of SAMTECH S.A. Page 30

31 Large modelling capabilities Different types of Elements for different levels of models Lumped mass and Inertias Rigid body elements Super elements (elastic bodies) Joint elements Real Flexible Finite Elements Easy switch from one model type to another Choice must be done following the requested level of precision CAD model Motion (rigid) model Super Element model FEA model Mixed model First rigid approach can be done improving model in following analyses This document is the property of SAMTECH S.A. Page 31

32 Use of parts Model Substructure Parameters Data front suspension rear suspension Chassis Steering system Powertrain... Attachment points Material Tyre Spring Damper Substructures (parts): - are easily tuneable - can be stored in libraries and reused later This document is the property of SAMTECH S.A. Page 32

33 Super Elements Super- Elements: Craig and Bampton Component Mode Synthesis Elastic bodies represented by static deformations and vibration modes (Mecano large rotations submodelling formulation) Real part Reduction of the number of d.o.f. -> calculation time reduction by generation of the reduced stiffness matrix, the related load vectors and/or the mass and damping matrices. Finite Elements dof Super Elements 2000 dof This document is the property of SAMTECH S.A. Page 33

34 Linearity: Chassis flexibility Carbon : MTM49-3/CF1103 (hot parts) VTM264FRB/CF1103 Aluminium honeycomb (Nomex) First torsion mode for 36.2 Hz Reinforcement to introduce (for suspensions) This document is the property of SAMTECH S.A. Page 34

35 Wheel stroke(mm) Non linearity: the coil spring Coil springs have a non-linear behaviour due to large displacements Transmitted forces display an hysteretic behaviour Body transmitted force A classical MBS like spring element cannot represent this effect SAMCEF MBD solver Test Body transmitted force (Upper Support Moment (Nm)) This document is the property of SAMTECH S.A. Page 35

36 Non linearity: the tyre TNO Tyre model (Pacejka Magic Formula and SWIFT) is currently being implemented Contacts have been initiated with COSIN (FTIRE) CDTIRE RMOD-K Road models will be available with Projects with meshed tyres are on going This document is the property of SAMTECH S.A. Page 36

37 Vehicle dynamics example The Imperia GP ( This document is the property of SAMTECH S.A. Page 37

38 Motion in FEA Rigid vehicle MBS approach: Front and rear double wishbone suspensions Front and rear antiroll bar Joints: hinges bushing non linear springs non linear dampers Non linear tyre model (Pacejka Magic Formula) Rigid Multi Body Simulation allows: Short calculation time Investigation of an important number of designs covering several input variables and their full range of interest This document is the property of SAMTECH S.A. Page 38

39 Motion in FEA Flexible vehicle Flexible approach: Meshed wishbones Possibly meshed spring Enables optimization of: - Ride and Comfort performance - Handling performance Compromise between the two!! This document is the property of SAMTECH S.A. Page 39

40 Modeling of misuse Car body and suspension modeling Car riding (30Km/h) over an obstacle (25cm height) Super-Element for large car body model (shell) Flexible mechanisms for suspension Wheels, beams, springs, sliders, spherical joints This document is the property of SAMTECH S.A. Page 40

41 Welding Spots Optimization Welding spots idealized with small beam elements Sizing optimization on a car body Design variables: discrete beam properties Objective:minimize number of welding spots Constraints on given displacements 5000 variables This document is the property of SAMTECH S.A. Page 41

42 Motion in FEA Rigid vs Flexible vehicle with MECANO Flexible approach Physical suspension compliance definitions: FEA parts non linear 3D bushings elastomer Greater details improve the accuracy of the results: Higher frequency contents Higher number of cycles for fatigue performance assessment No need to re-measure the suspension if geometry changes (attachment point) part redesigned (new FEA model) fatigue can be integrated early in the design process Rigid MBS Better modularity This document is the property of SAMTECH S.A. Page 42

43 Test rig modelling Any test rig can be defined and used - Kinematics and Compliance - 4 post rig - Durability Modelling Rig helps model validation Camber Angle Toe Angle This document is the property of SAMTECH S.A. Page 43

44 CYCLES ALTERNATING STRESS [MPa] Durability Step 1: Import Loads for FEM computation from aeroelastic behaviour Step 2: Stress computation by FEM Step 3: Stress transients in hot spots 1.E+07 STEEL EN-S355 S-N CURVE 1.E Step 6: Input in S-N material data 1.E+07 8.E+06 6.E+06 4.E+06 2.E+06 0.E+00 E Step 5: 100 Computation of fatigue damage: Sfl(74); 5.00E+06; 74 Sfl(160); 5.00E+06; E+04 ni 1.E+05 E P T p(s i) 1.E+06 ds 1.E+07 1.E+08 ( D) b CYCLES i Ni i ksi Step 4: RFC of stress cycles EQUIVALENT STRESS [MPa] This document is the property of SAMTECH S.A. Page 44

45 Virtual Proving Ground capabilities Possibility to use different level complexity Rigid body Super elements Meshed parts with non linear behaviour Possibility to use advanced tyre models Commercial models Meshed tyres Possibility to use advanced road models (From This document is the property of SAMTECH S.A. Page 45

46 Other example of vehicle dynamics A few thousands of contacts static contact wheel - track dynamic contact wheel - track This document is the property of SAMTECH S.A. Page 46

47 Solver capabilities: chaining Chaining enables you to "chain" or "link" two calculations together, using the results of the first calculations as an input for the second. Modal Vibro acoustic Thermal Linear transient and harmonic response Response to random forces This document is the property of SAMTECH S.A. Page 47

48 Conclusions SAMCEF Mecano enables you to increase: Your simulation non linearity range Your simulation frequency range Pushing the limits of virtual prototyping Increasing confidence you have in simulation results This document is the property of SAMTECH S.A. Page 48