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SPAÇAR: A Finite Element Approach in Flexible Multibody Dynamics

SPAÇAR: A Finite Element Approach in Flexible Multibody Dynamics. UIC Seminar. Arend L. Schwab Google: Arend Schwab [I’m Feeling Lucky]. September 27, 2004 University of Illinois at Chicago. Laboratory for Engineering Mechanics Faculty of Mechanical Engineering. Acknowledgement. UTwente:

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SPAÇAR: A Finite Element Approach in Flexible Multibody Dynamics

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  1. SPAÇAR: A Finite Element Approach inFlexible Multibody Dynamics UIC Seminar Arend L. Schwab Google: Arend Schwab [I’m Feeling Lucky] September 27, 2004 University of Illinois at Chicago Laboratory for Engineering MechanicsFaculty of Mechanical Engineering

  2. Acknowledgement UTwente: Ben Jonker Ronald Aarts … MSc students TUdelft: Hans Besseling Klaas Van der Werff Helmut Rankers Ton Klein Breteler Jaap Meijaard … MSc students

  3. Contents • Roots • Modelling • Some Finite Elements • Eqn’s of Motion • Examples • Discussion

  4. Engineering Mechanics at Delft From Analytical Mechanics in 50’s: Warner T. Koiter On the Stability of Elastic Equilibrium, 1945 To Numercial Methods in Applied Mechanics in 70’s: Hans Besseling The complete analogy between the matrix equations and the continuous field equations of structural analysis, 1963

  5. Mechanism and Machine Theory Application of Numerical Methods to: • Kinematic Analysis • Type and Dimension Synthesis • Dynamic Analysis CADOM project: Computer Aided Design of Mechanisms, 1972Rankers, Van der Werff, Klein Breteler, Schwab, et al.

  6. Mechanism and Machine Theory, Kinematics Denavit & Hartenberg, 1955 • Rigid Bodies • Relative Coordinates (few) • Kinematic Constraints (few)

  7. Mechanism and Machine Theory, Kinematics Klaas Van der Werff, 1975 Finite Element Approach • Flexible Bodies • Absolute Coordinates and Large Rotations (many) • Kinematic Constraints = Rigidity of Bodies (many) Note: Decoupling of the positional nodes and the orientational nodes.

  8. Multibody System DynamicsFinite Element Approach Key Idea:Specification of Independent Deformation Modes of the Finite Elements Coordinates: (xp, p , xq , q) total 6 Deformation Modes: total 6-3=3

  9. Multibody System DynamicsFinite Element Approach Pro’s: • Easy FEM assembly of the system equations • Easy mix of partly Rigid and/or Flexible elements • Small set of elements for Large class of Multibody Systems • Absolute Coordinates and Large Rotations • Gen. Deformation can act as Relative Coordinates Con’s: • Many coordinates, many constraints • Non-Constant Mass Matrix

  10. Multibody System DynamicsFinite Element Approach Generalized Deformation can act as Relative Coordinates Ex. Hydraulic Cylinder

  11. Multibody System Dynamics Compare to Rigid Bodies with Constraints Milton Chace & Nicky Orlandea, DRAM, ADAMS, 1970 Rigid Bodies with Constraints FEM approach Constraints are at the Joints Constraints are in the Bodies

  12. 3D Beam Element Coordinates: (xp, p , xq , q) total 14 Deformation Modes: total 14 – 6 = 8 – 2 = 6 = 0 = 0 Cartesian Coordinates xp= (x, y, z)p and Euler Parameters p=(0, 1, 2, 3)p

  13. 3D Hinge Element Coordinates: (p, q) total 8 Deformation Modes: total 8 – 3 = 5 – 2 = 3 = 0 = 0

  14. 3D Truss Element Coordinates: (xp, xq ) total 6 Deformation Modes: total 6 – 5 = 1

  15. 3D Wheel Element Coordinates: (xw, p,xc ) total 10 Some Counting: Pure rolling Rigid body has3 degrees of freedom (velocities). We need 10-3=7 Constraints on the Velocities. Pure rolling is 2 Velocity Constraints, Lateral and Longitudinal. Leaves 7-2=5 Deformation Modes

  16. 3D Wheel Element Coordinates: (xw, p,xc ) total 10 Deformation Modes: Generalized Slips:

  17. Ex. Universal or Cardan Joint Physical Model Two FEModels: (a) with 4 Rigid Hinges, and (b) with 2 Flexible Hinges

  18. Ex. Universal or Cardan Joint Two FEModels: (a) with 4 Rigid Hinges, and (b) with 2 Flexible Hinges

  19. Dynamic Analysis In the spirit of d’Alembert and Lagrange we transform the DAE in terms of generalized independent coordinates qj with xi=Fi(qj) resulting in From which we solve and Numerically Integrate as an ODE. Note: the Elastic Forces are according to and

  20. Ex. ILTIS Road Vehicle Benchmark - Rigid Cabin - 4 Independently Suspended Wheels - CALSAP Tire Model The ILTIS Vehicle 85 Elements 239 Gen. Def. 70 Nodes 226 Gen. Coord. 10 DOF’s Suspension FEM Model

  21. Ex. ILTIS Road Vehicle Benchmark Static Equilibrium Results

  22. Ex. ILTIS Road Vehicle Benchmark Handling Performance Test: Ramp-to-Step Steer Manoeuvre at v = 30 m/s. CALSPAN tire model Zero Lateral Slip

  23. Ex. Slider-Crank Mechanism Slider-Crank Mechanism from Song & Haug, 1980 Rigid Crank,Flexible Connecting Rod =150 rad/s, 2% damping Transient Solution Periodic Solution First Eigenfrequency of pinned joint connecting rod 0= 832 rad/s

  24. Linearized Equations of Motion Equations of Motion can be Analytically Linearized at a Nominal Motion Even for Systems having Non-Holonomic Constraints! with: M: reduced Mass Matrix C: Tangent Velocity dependant Matrix K: Tangent Stiffness Matrix qk: Kinematic Coordinates variations A: Non-Holonomic Constraints B: Tangent Reonomic Constraints Matrix

  25. Ex. Slider-Crank Mechanism Nominal Periodic Motion and small Vibrations described by the Linearized Equations of Motion Slider-Crank Mechanism from Song & Haug, 1980 Rigid Crank,Flexible Connecting Rod =150 rad/s, 2% damping Transient Solution Periodic Solution

  26. Linearized Equations of Motion at Nominal Periodic Motion Periodic Solutions for small Vibrations superimposed on a Nominal Periodic Motion Linearized Equations of Motion at Nominal Motion: The Coefficients in the Matrices are Periodic with Period T=2/ Transform these Matrices into Fourier Series: and assume a periodic solution of the form:

  27. Linearized Equations of Motion at Nominal Periodic Motion Periodic Solutions for small Vibrations superimposed on a Nominal Periodic Motion Substitution into the Linearized Equations of motion and balance of every individual Harmonic leads to: These are (2k+1)*dof linear equations from which we can solve the2k+1 harmonics: Which form the solution of the small Vibration problem:

  28. Ex. Slider-Crank Mechanism Slider-Crank Mechanism from Song & Haug, 1980 FEModel: 2 Beam Elements for the Flexible Connecting Rod Rigid Crank,Flexible Connecting Rod =150 rad/s, 2% damping Transient Solution Periodic Solution

  29. Ex. Slider-Crank Mechanism Maximal Midpoint Deflection/l for a range of ’s Damping 1% and 2% First Eigenfrequency of pinned joint connecting rod 0= 832 rad/s Resonace at 1/5, 1/4, and 1/3 of 0 Linearized Results Full Non-Linear Results

  30. Ex. Slider-Crank Mechanism Individual Harmonics of the Midpoint Deflection/l for a range of ’s First Eigenfrequency of pinned joint connecting rod 0= 832 rad/s Resonace at 1/5, 1/4, and 1/3 of 0 Quasi Static Solution

  31. Ex. Dynamics of an Uncontrolled Bicycle Cornell University, Ithaca, NY, 1987: Yellow Bike in the Car Park

  32. Ex. Dynamics of an Uncontrolled Bicycle Cornell University, Ithaca, NY, 1987: Yellow Bike in the Car Park

  33. Ex. Dynamics of an Uncontrolled Bicycle • Modelling Assumptions: • rigid bodies- fixed rigid rider- hands-free - symmetric about vertical plane - point contact, no side slip- flat level road- no friction or propulsion Note: This model is energy conservative

  34. Ex. Dynamics of an Uncontrolled Bicycle FEModel: 2 Wheels, 2 Beams, 6 Hinges 3 Degrees of Freedom: 4 Kinematic Coordinates:

  35. Ex. Dynamics of an Uncontrolled Bicycle Forward Full Non-Linear Dynamic Analysis with an initial small side-kick Forward Speed: v = 3.5 m/s v = 4.5 m/s

  36. Ex. Dynamics of an Uncontrolled Bicycle Investigate the Stability of the Steady Forward Upright Motion by means of the Linearized Equations of Motion at this Steady Motion Linearized Equations of Motion for Systems having Non-Holonomic Constraints in State-Space form: Assume an exponential motion for the small variations:

  37. Ex. Dynamics of an Uncontrolled Bicycle Rootloci of  from the Linearized Equations of Motion with as a Parameter the Forward Speed v Asymptotically Stable in the Speed Range: 4.1 < v < 5.7 m/s

  38. Ex. Dynamics of an Uncontrolled Bicycle What happens for v>5.7 m/s? Forward Speed: v = 6.3 m/s

  39. Conclusions • SPAÇAR is a versatile FEM based Dynamic Modeling System for Flexible and/or Rigid Multibody Systems . • The System is capable of modeling idealized Rolling Contact (Non-Holonomic Constraints). • The System uses a set of minimal independent state variables, which avoid the use of differential-algebraic equations. • The Equations of Motion can be Linearized Analytically at any given state.

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