Free Vibration of Flexible Cables

2015 ◽  
Author(s):  
Andrea Arena
Keyword(s):  
Free Vibration ◽  
Nonlinear Equations ◽  
Equations Of Motion ◽  
Torsional Stiffness ◽  
Axial Stiffness ◽  
Geometric Nonlinearities ◽  
Nonlinear Equations Of Motion ◽  
Extensible Cables ◽  
Flexible Cables ◽  
Elastic Cables

The free undamped vibrations of cables undergoing stretching, bending and twisting are investigated. To this end, a geometrically exact model of elastic cables accounting for bending and torsional stiffness is employed. The cable kinematics retain the full geometric nonlinearities. Starting from a prestressed catenary configuration, the nonlinear equations of motion are linearized about the initial equilibrium. In particular, two initial equilibrium states (shallow and taut) are considered while varying the cable elastic axial stiffness. The influence of the bending flexibility on the cable frequencies is assessed by direct comparisons with the frequencies predicted by classical cable theories of purely extensible cables.

Direct Linearization of Continuous and Hybrid Dynamical Systems

2009 ◽  
Vol 4 (3) ◽  
Author(s):  
Julie J. Parish ◽  
John E. Hurtado ◽  
Andrew J. Sinclair
Keyword(s):  
Dynamical Systems ◽  
Nonlinear Equations ◽  
Equilibrium Configuration ◽  
Equations Of Motion ◽  
Hybrid Dynamical Systems ◽  
Linearized Equations ◽  
Direct Linearization ◽  
Taylor Series Expansions ◽  
Nonlinear Equations Of Motion ◽  
And Control

Nonlinear equations of motion are often linearized, especially for stability analysis and control design applications. Traditionally, the full nonlinear equations are formed and then linearized about the desired equilibrium configuration using methods such as Taylor series expansions. However, it has been shown that the quadratic form of the Lagrangian function can be used to directly linearize the equations of motion for discrete dynamical systems. This procedure is extended to directly generate linearized equations of motion for both continuous and hybrid dynamical systems. The results presented require only velocity-level kinematics to form the Lagrangian and find equilibrium configuration(s) for the system. A set of selected partial derivatives of the Lagrangian are then computed and used to directly construct the linearized equations of motion about the equilibrium configuration of interest, without first generating the entire nonlinear equations of motion. Given an equilibrium configuration of interest, the directly constructed linearized equations of motion allow one to bypass first forming the full nonlinear governing equations for the system. Examples are presented to illustrate the method for both continuous and hybrid systems.

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