Abstract
In this paper, the analytical derivatives of flexible multibody dynamics with the floating frame of reference formulation are derived in a new way using the invariants and their sensitivities. This enables the decoupling of the sensitivity analysis of flexible multibody dynamics from the finite-element solver and guarantees high accuracy and efficiency of the sensitivity computations. The invariants are shown with both consistent and lumped mass approaches. The latter allows generality towards the formulation of a finite-element type, including beams, shells, and solids. The expressions are fully derived with lumped masses, showing for the first time the compensation term of inertia due to the non-consideration of the mass distribution with this approach. It is then shown that the expressions of the system parameters in the lumped case with the newly introduced inertia compensation term correspond to the general case, and, therefore, the derived approach and equations are of general nature. Crucial for the decoupling of the sensitivity analysis are the analytical derivatives of the system parameters that contain the derivatives of the invariants and whose analytical expressions are derived and provided here for the first time. The partial derivatives arise in the sensitivity analysis with both the direct differentiation method and the adjoint variable method, and the former is shown here. In addition, the partial derivatives arise in the Jacobian matrix of the nonlinear solver for the transient solution of flexible multibody systems.
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Abbreviations
-
:
-
zeroth-order tensor or scalar
-
:
-
first-order tensor or vector
-
:
-
second-order tensor or matrix
-
:
-
third-order tensor or 3D matrix
-
:
-
fourth-order tensor or 4D matrix
-
:
-
first time derivative
-
:
-
second time derivative
-
:
-
expressed in floating coordinates
-
:
-
skew symmetric matrix
-
:
-
total derivative of
w.r.t. \(\underline{\mathsf{x}}\)
-
:
-
partial derivative of
w.r.t. \(\underline{\mathsf{x}}\)
-
:
-
partial derivative of
w.r.t.
-
:
-
Jacobian of
w.r.t.
- \(\underline{\underline{d}}\) :
-
dam** matrix
- \(\underline{e}\) :
-
unit vector
- \(\underline{\underline{e}}\) :
-
unit matrix (identity matrix)
- \(\underline{\underline{k}}\) :
-
stiffness matrix
- \(m\) :
-
mass
- \(\underline{\underline{m}}\) :
-
mass matrix
- \(\underline{q}\) :
-
generalized position vector
- \(\underline{\dot{q}}\) :
-
generalized velocity vector
- \(\underline{\ddot{q}}\) :
-
generalized acceleration vector
- \(\underline{r}\) :
-
position vector to inertial frame expressed in intertial coordinates
- \(t\) :
-
time
- \(\underline{\overline{u}}\) :
-
position vector to floating frame expressed in floating coordinates
- \(\underline{u}\) :
-
position vector to floating frame expressed in inertial coordinates
- \(\underline{\mathsf{x}}\) :
-
vector of design variables
- \(\underline{\underline{A}}\) :
-
rotation matrix
- \(\underline{\underline{B}}\) :
-
Boolean matrix
-
:
-
function of
- \(\underline{\underline{G}}\) :
-
angular velocity matrix that relates \(\underline{\omega}\) and \(\underline{\dot{\theta}}\)
- \(\underline{\underline{\mathcal{I}}}\) :
-
invariant (inertia shape integral)
- \(K\) :
-
kinetic energy
- \(\underline{Q}{}_{\mathrm{e}}\) :
-
generalized external force vector
- \(\underline{Q}{}_{\mathrm{v}}\) :
-
quadratic velocity force vector
- \(\underline{\underline{\overline{S}}}\) :
-
matrix of shape functions expressed in floating coordinates
- \(V\) :
-
volume
- \(\underline{\zeta}\) :
-
vector of modal coordinates
- \(\underline{\theta }\) :
-
vector of orientation coordinates
- \(\underline{\lambda }\) :
-
vector of Lagrange multipliers
- \(\rho \) :
-
density
- \(\underline{\tau }\) :
-
position vector of floating frame
- \(\underline{\chi}{}_{\mathrm{o}}\) :
-
center of mass of undeformed body
- \(\underline{\omega }\) :
-
angular velocity vector
- \(\underline{\underline{\Theta}}{}_{\mathrm{o}}\) :
-
inertia tensor of undeformed body
- \(\underline{\Phi }\) :
-
vector of kinematic constraints
- \(\underline{\underline{^{q}\hspace {-2pt}\mathtt{J}\Phi }}\) :
-
Jacobian matrix of kinematic constraints
- \(\underline{\underline{\overline{\Psi}}}\) :
-
modal matrix expressed in floating coordinates
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Acknowledgements
This work is supported by the project CRC 2017 – TN2091 doloMULTI \(\underline{D}\)esign \(\underline{o}\)f \(\underline{L}\)ightweight \(\underline{O}\)ptimized structures and systems under \(\underline{MULTI}\)disciplinary considerations through integration of \(\underline{MULTI}\)body dynamics in a \(\underline{MULTI}\)physics framework funded by the Free University of Bozen-Bolzano.
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V.G.: conceptualization, data curation, formal analysis, investigation, methodology, resources, software, validation, visualization, writing – original draft, writing – review & editing. A.Z.: conceptualization, formal analysis, investigation, methodology, supervision, validation, writing – original draft, writing – review & editing. E.W.: conceptualization, funding acquisition, methodology, project administration, supervision, writing – original draft, writing – review & editing.
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Gufler, V., Zwölfer, A. & Wehrle, E. Analytical derivatives of flexible multibody dynamics with the floating frame of reference formulation. Multibody Syst Dyn 60, 257–288 (2024). https://doi.org/10.1007/s11044-022-09858-5
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DOI: https://doi.org/10.1007/s11044-022-09858-5