Juraj Hrabovský

Numerical Calculation of Overhead Power Lines Dynamics

Abstract This paper contains results of transient analysis of airflow around the ACSR power line cross-section in unsymmetric multi-span. The forces applied to the power line are obtained from CFD simulations, where the wind induced vibration is studied. Effect of these forces to the maximal displacement of the power line and the maximal mechanical forces in the points of attachment are studied and evaluated.

Dynamic Analysis of Overhead Power Lines after Ice–Shedding Using Finite Element Method

Abstract In this paper, the analysis of ice-shedding from ACSR conductors to its swing up height and vibration using Finite Element Method (FEM) is presented. For the numerical simulations the effective material properties of the ACSR conductor are calculated using the homogenisation method. Numerical analysis concerning vibration of one and triple-bundle conductors with icing for a whole range or on their certain parts are performed. The impact of ice-shedding to the mechanical tension in the conductors at the points of attachment is investigated and evaluated. Identification of the impact of ice-shedding from the ACSR conductors on its mechanical state may contribute to increasing the safety and quality of an electrical transmission system.

Effect of Non-Uniform Torsion on Elastostatics of a Frame of Hollow Rectangular Cross-Section

Abstract In this paper, results of numerical simulations and measurements are presented concerning the non-uniform torsion and bending of an angled members of hollow cross-section. In numerical simulation, our linear-elastic 3D Timoshenko warping beam finite element is used, which allows consideration of non-uniform torsion. The finite element is suitable for analysis of spatial structures consisting of beams with constant open and closed cross-sections. The effect of the secondary torsional moment and of the shear forces on the deformation is included in the local finite beam element stiffness matrix. The warping part of the first derivative of the twist angle due to bimoment is considered as an additional degree of freedom at the nodes of the finite elements. Standard beam, shell and solid finite elements are also used in the comparative stress and deformation simulations. Results of the numerical experiments are discussed, compared, and evaluated. Measurements are performed for confirmation of the calculated results.

Modeling of Ice-Shedding from ACSR Power Line

Abstract In this contribution, the analysis of ice-shedding from Aluminium Conductor Steel Reinforced (ACSR) power lines is presented. The impact of the icing position on the overhead power lines, the resulting jump height, and impact on attachment tension points after ice-shedding is examined. In the numerical simulations the effective material properties of the ACSR conductor is calculated using the homogenisation method. Numerical analysis of one power line and double-bundle power lines with icing over the whole range or only on certain sections of single and double-bundle power lines are performed

Numerical Analysis and Experimental Verification of Eigenfrequencies of Overhead ACSR Conductor

This contribution deals with the modal analysis of ACSR conductor using the finite element method (FEM) and experimental measurements of eigenfrequencies. In numerical experiments for the modelling of the conductor the material properties of the chosen conductor crosssection are homogenized by the Representative Volume Element (RVE) method. The spatial modal analysis of the power line is carried out by means of our new 3D FGM beam finite element and by standard beam finite element of the commercial software ANSYS. Experimental measurements are also carried out for verification of the numerical calculation accuracy.

NUMERICAL SOLUTION OF DIFFERENTIAL EQUATIONS WITH NON-CONSTANT COEFFICIENTS

Abstract. Nowadays, new materials like Functionally Graded Material (FGM) are necessary for sophisticated structures like MEMS systems, advanced electronic devices, etc. Computer modelling of such complex systems, like structures with spatial variation of material properties (e.g. FGM) are, using commercial FEM code with classic elements, needs remarkable effort during preparation phase and sufficient computer equipment for solution phase because of necessity the numbers of elements and material models. Therefore new methods for modeling and simulation of FGM beams with spatial variation of material properties are developed. In the proposed contribution, semi-analytical method (based on calculation of transfer functions and transfer constants) for solution of differential equation with non-constant polynomial coefficients, is presented. This method is used in derivation process (for setting up the transfer matrix) of our new beam finite elements for modeling and simulation of Functionally Graded Material (FGM) beam structures (e.g. new 3D FGM beam finite element for modal and structural analysis, new FGM beam finite elements for coupled electro-thermo-mechanical analysis). Numerical experiments are made to show the accuracy and effectiveness of this method.

FINITE BEAM ELEMENT WITH PIEZOELECTRIC LAYERS AND FUNCTIONALLY GRADED MATERIAL OF CORE

Abstract. New smart materials have been developed in material science, that are suitable for mechatronic applications. Modern mechatronic systems are focusing on minimizing size, active control and low energy consumption. All this attributes can be incorporated into term Micro Electro Mechanical Systems (MEMS). To improve performance of MEMS system, new materials and technologies are developed one of them, which found broad application usage is Functionally graded material (FGM). MEMS application usually contains multilayer structure and in some application class MEMS systems contain piezoelectric layers. Piezoelectric structures offer facilities to make motions. Piezoelectric layers can be also used to damp vibrations as an active damping or as an active sensor. For better understanding these multiphysical problems new mathematical models are developed. The paper deals with finite beam element with piezoelectric layers and functionally graded material of core. In the paper homogenization of FGM material properties and homogenization of core and piezoelectric layers is presented. In the process of homogenization direct integration method and multilayer method is used. There is also presented the derivation of individual submatrices of local stiffness and mass matrix, where concept of transfer constants is used. Functionality of new FGM finite beam with piezoelectric layers is presented by numerical experiments.

MODELLING OF WARPING EIGENVIBRATION BY NON-UNIFORM TORSION

This contribution contains a novel investigation of the influence of warping of the cross-section of twisted beams on their eigenvibrations. The investigation is based on the analogy of the bending beam theory and the non-uniform torsion theory of thin-walled open and closed cross-sections. Based on them, the differential equations for dynamic loads, considered as equivalent static loads, are presented. The effect of the secondary torsion moment deformation is taken into account. A part of the first derivative of the twist angle is taken as a warping degree of freedom. The solution of this differential equation is then used for setting up the transfer matrix. The numerical investigation contains the analysis of the natural frequencies and mode shapes of straight cantilever beams with and without consideration of the influence of warping of the cross-section. Beams with open and closed cross-sections are considered. Obtained results are compared with the ones calculated by standard solid and warping beam finite elements.