Y.M. Desai

Finite element modelling of transmission line galloping

A computationally efficient, finite element idealization is presented to analyse galloping, which is characterized by large amplitude vibrations of iced, multi-span, electrical transmission lines. A three-node, isoparametric cable element having three translational and a torsional degree-of-freedom at each node is developed to model a conductor. Support insulator strings and remote conductor spans are represented by linear static springs. A transmission lines interactions with a support tower are modelled through the towers equivalent stiffness at the conductors suspension point. An expedient time marching scheme is developed to obtain the envelope of galloping. The scheme can be utilized to integrate dynamic equilibrium equations involving not only geometric and material nonlinearities but also nonlinear damping. Time integration is performed in the sub-space to minimize computational effort. The finite element model has been employed to successfully simulate field galloping records. It is shown that it is necessary to consider a multi rather than a single span for a conservative estimate of the galloping amplitudes to enable sufficient clearances to be designed between adjacent conductors.

Elastic guided waves in a layered plate with rectangular cross section

Guided waves in a layered elastic plate of rectangular cross section (finite width and thickness) has been studied in this paper. A semianalytical finite element method in which the deformation of the cross section is modeled by two-dimensional finite elements and analytical representation of propagating waves along the length of the plate has been used. The method is applicable to arbitrary number of layers and general anisotropic material properties of each layer, and is similar to the stiffness method used earlier to study guided waves in a laminated composite plate of infinite width. Numerical results showing the effect of varying the width of the plate on the dispersion of guided waves are presented and are compared with those for an infinite plate. In addition, effect of thin anisotropic coating or interface layers on the guided waves is investigated.

Application of a three-dimensional mixed finite element model to the flexure of sandwich plate

Abstract The bending analysis of sandwich plates consisting of very stiff face sheets and a comparatively flexible core material offers challenge due to large variation in the magnitude of stress and strain components in the face and in the core regions of the plate. Similarly, the displacement fields do vary in zigzag manner at the layer interface of stiff face sheet and the soft core, thereby making the transverse strains highly discontinuous at such layer interfaces. All these behavioural aspects indicate that only an individual layerwise model can appropriately analyze sandwich plates. A layerwise (three-dimensional), mixed, 18-node finite element (FE) model developed by Ramtekkar et al. [Mech. Adv. Mater. Struct. 9 (2002) 133] has been employed for the accurate evaluation of transverse stresses in sandwich laminates. The FE model consists of six degrees-of-freedom (three displacement components and three transverse stress components τ xz , τ yz , σ z , where z is the thickness direction) per node which ensures the through thickness continuity of transverse stress and displacement fields. Results obtained by using the FE model have shown excellent agreement with the available elasticity solutions for sandwich plates. Additional results on the variation of transverse strains have also been presented to highlight the magnitude of discontinuity in these quantities due to difference in properties of the face and the core materials of sandwich plates.

GEOMETRIC NONLINEAR STATIC ANALYSIS OF CABLE SUPPORTED STRUCTURES

Abstract A numerically efficient procedure is presented for generating the stiffness of a parabolic, three-node finite element for the static, nonlinear analysis of three-dimensional cable-supported structures. Numerical computations are minimized by explicitly evaluating the large deformation stiffness matrix with respect to global coordinates while avoiding incompatibilities with existing, displacement-based elements. Representative improvements are illustrated by using three typical geometrically nonlinear, cable supported structures. Also, an efficient method is presented to evaluate the self weight profile of a pretensioned inclined cable.

Simple model for dynamic analysis of cable supported structures

A simple, nine degrees-of-freedom model has been presented to describe vibrations of an inclined cable by using a generalised finite element approach. All three translations of a vibrating cable and of the support points have been included in the model for its use over a wide range of cable supported structures. The model has been validated for free as well as forced responses of inclined cables by comparing the results with analytical solutions. Some illustrative examples are considered to demonstrate the applicability of the model for analysing vibrating cables and guyed towers subjected to gusty wind. It has been demonstrated that the model can be utilised to expeditiously predict the dynamic response of cable supported structures.