Nonlinear Analysis of Cables with Identification of Flexural-Torsional Stiffness.

Introduction: Electrical transmission lines are normally composed of large spans that have large displacements and are subject to complex three-dimensional motions. The dynamic behavior can be analyzed through non-linear mathematical models obtained by the finite element method that can be validated by experimental data. Materials and Methods: The analyses consisted of obtaining experimental data for two different tests, bending and torsion, using accelerometers placed along samples of three different cables and with varying mechanical tension. The experimental data were compared with numerical data obtained by computer simulation of mathematical models obtained by the finite element method and using 3d frame elements. For the bending tests, the natural frequencies of the first five modes of vibration were compared and for the torsion tests, the torque angle was compared. Data were adjusted using the particle swarm optimization method (PSO). Results: For all situations analyzed (different cables, tensile loads and positioning of sensors and excitation) an excellent agreement between numerical and experimental values was noted. For bending tests, numerical and experimental values of the first five natural frequencies were compared using PSO method. Differences lower than 0.5% were noted for low loading values where the nonlinear behavior of the first modes is evident. The torsional behavior was analyzed using a bench containing a lever manually excited. By minimizing a function taking into account the difference between numerical and experimental values of the twist angle, the shear modulus is adjusted using PSO method. For all situations, it was possible to obtain good agreement between numerical and experimental values of the twist angle with deviation lower than 1%. Conclusions: It was evident that the non-linear mathematical model presented good results for both the bending and torsion tests. The differences between numerical and experimental values were small with rapid convergence using the PSO method. The proposed methodology for torsion tests using a manually operated lever proved to be efficient for adjusting torsional stiffness. It was noted that the shear modulus is influenced by the position of the lever and direction of the torsion. [ABSTRACT FROM AUTHOR]