Research On The Galloping Of Iced Conductors Based On Finite Element Method And Isogeometric Collocation Method

Galloping of iced conductors is characterized by large amplitude,low frequency and self-excited vibration,which is caused by unbalanced aerodynamic loads due to the asymmetric surface of the iced conductor.The galloping is a multi-degree-of-freedom coupled vibration of the flexible structure,which usually involves the geometry dependent nonlinear aerodynamic loads and geometric nonlinearity caused by the large amplitude motion of iced conductors.The galloping problem is an internationally recognized scientific issue due to its complexity and perniciousness.In order to prevent the destruction on transmission lines by the galloping and to ensure the security and steady operation of power systems,an in-depth study on the galloping problems of transmission lines has great significance on theoretical and engineering practice.The cable model of iced conductors with large amplitude movement has been established in this thesis and a systematic research on the galloping problems has been carried out through the finite element method and isogeometric collocation method.Specific contents as follows:(1)The Pai and Nayfeh's conventional nonlinear cable theory is generalized and the four-degree-of-freedom dynamic model of iced conductors,which involved torsional motion and eccentric ice accretion,is developed by employing the Hamilton's principle.It is revealed that the third-order nonlinear equations of motion are accurate enough to describe the large amplitude galloping problems of transmission lines.(2)Aiming at resolving the limitation of the traditional catenary theory in solving the static configuration of iced conductors under concentrated loads,a static numerical method with higher applicability and accuracy for continuous three-span iced conductors is proposed by integrating the precise static governing equations of conductors successively.(3)With the conductor segments between two adjacent spacers considered as a sub-structure,a dynamic sub-structure method for bundle conductors is proposed,which can consider the relative movement of each sub-conductor,the difference of aerodynamic load and the vibration of subspan.Through the modal analysis and nonlinear dynamic response analysis under time-dependent distributed loads,the accuracy of the dynamic sub-structure method in solving the dynamic problems of bundle conductors is verified by the ANSYS finite element software.The galloping problems of iced bundle conductors can be further studied with the consideration of aerodynamic forces.(4)Numerical simulations of the galloping of an iced single conductor and continuous three-span bundle conductors are carried out based on the finite element method.Both the amplitudes,frequencies and the galloping trace of the single iced conductor obtained from the present simulation coincide quite well with the measured results and the computational accuracy of twist angle is improved dramatically compared with the existing galloping numerical simulation methods.The dynamic sub-structure method is applied to study the phenomena of asynchronous motions of bundle conductors.The vibration characteristics of bundle conductors and the galloping amplitudes,dynamic tensions and galloping traces at each typical span position are studied emphatically and the influences of wind speed and anti-galloping hammer on the galloping of iced conductors are analyzed(5)Aiming at resolving the huge computation of galloping time-history analysis based on the finite element method,the isogeometric collocation(IGA-C)method is extended to solve the nonlinear dynamic problems of iced conductors for the first time.The typical convergence characteristic and high efficiency of the IGA-C method are studied and the influences of different numbers of basic functions p and control points n are analyzed to obtain a sufficiently accurate stable galloping solution with minimum computational cost.Further,the superiority of the IGA-C method in solving the galloping problems of larger-span iced transmission lines is considered.A four-degree-of-freedom dynamic model of iced conductors is developed in this dissertation and the related nonlinear static and dynamic problems are studied in depth.The proposed galloping analysis method is accurate and effective to study the galloping problems of the single conductor and bundle conductors,which is an important complement and refinement of the existing galloping analysis methods,and can provide an effective theoretical basis for the galloping prediction and anti-galloping control research of the actual transmission lines.