Guest lectures by the THREAD PIs Prof. Sigrid Leyendecker and Prof. Martin Arnold

DATE: Thursday February 4, 2021.


Speaker: Martin Arnold

Time:10:15-12

Title: Lie group methods for industrial multibody system simulation

Abstract: Industrial multibody system simulation relies on robust and efficient time integration methods for constrained mechanical systems with structural damping and embedded control structures. The methods of choice are second order methods of Newmark type with user defined algorithmic damping (HHT method, generalized-$\alpha$ method) and higher order multistep methods of BDF type with sophisticated algorithms for step size and order control.

Multibody system models in Lie groups are attractive from the viewpoint of modelling since they allow the representation of large rotations without singularities. But nonlinear configuration spaces are beyond the range of applicability of classical solvers in multibody system dynamics. Standard Newmark type methods and BDF may, however, be generalized to the Lie group setting exploiting the linear structure of the corresponding Lie algebra. We discuss theoretical and practical aspects of a Lie group generalized-$\alpha$ and a BLieDF multistep Lie group method for constrained mechanical systems and show that the novel Lie group methods have the same order as their classical counterparts and may be implemented by minor modifications of well approved generalized-$\alpha$ or BDF solvers.

References

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Speaker: Sigrid Leyendecker

Time:13:15-15

Title: Lagrangian mechanics and variational integrators

Abstract: This lecture will address the derivation of the Euler-Lagrange equations from Hamilton's variational principle and discuss geometric structural properties like the conservation of momentum maps due to invariants of the Lagrangian (Noether's theorem) and symplecticity. Then, similar steps are preformed in the temporal discrete setting to derive the discrete Euler-Lagrange equations via a discrete variational principle. This leads to a time integration scheme which preserves the geometric structure of the underlying dynamical system in the sense that it is symplectic and there exists a discrete Noether theorem.

Presentation

2021-02-14, Elena Celledoni