Solution to Multi-axial Fatigue Life of Heterogenic Parts & Components Based on Ansys

Abstract

It is very difficult to utilize traditional method for strength analysis and life calculation of heterogenic parts & components in mechanical products. In this paper, finite element analysis software Ansys is used to analyze hub of core parts and components in wind power generator unit. Addition of external load is subject to finite element calculation, so as to work out “stress hotspot” of unit load on the hub, namely “high load area”. Moreover, rain-flow counting method is used to calculate the number of times of stress circulation. According to the life curve of material, accumulative damage is calculated, and the life is determined. Introduction In this paper, ANSYS 11.0 finite element analysis procedure of American ANSYS Company is adopted for mechanical analysis on the hub. ANSYS software is large-scale universal finite element analysis software integrated with structure, fluid, electric field, magnetic field and sound field analysis. This software was developed by American ANSYS Company, one of the largest finite element analysis software companies in the world. It can be interfaced with most CAD software, so as to realize data sharing and exchange. It is one of advanced CAE tools among modern products. Wind power generator unit experiences various bad weather and complicated wind alternating loads in wild for a long period of time. Its design and production involves complicated multi-disciplinary system integration technologies including mechanical manufacturing, motor, electric control, air dynamics, high molecular material and hydraulic pressure. It requires solid theoretical foundation and rich practice experience. Hub is the most key component and one of the most complicated components in wind power generator unit. Its good design, reliable quality and supreme performance are key factors guaranteeing normal and stable operation of wind generator unit as well as key and difficult points for structural design of wind generator unit. Requirements for hub: light specific gravity, good mechanical performance and fatigue strength, convenience for manufacturing and assembly, and enduring windstorm and other bad conditions and random load. Establishment of hub model Geometric model Hub of a modern wind generator unit is usually casted part or component (QT400-18). Advanced casting technique can be used to produce hub featured by complicated shape, high fatigue strength and light quality. Hub is served as the connecting part of blade and spindle. Its geometrical shape and dimension are decided by blade and axis, especially for the size of hub directly decided by diameter of blade flange side and diameter of blade variable pitch bearing. If the connecting dimension is given, the shape of hub is basically determined. The shape of hub can be roughly divided into spherical and star structure. Due to complexity of shape, finite element method is usually used for optimization design. The optimization function of finite element software is utilized to design the wall thickness and reasonably allocate the structure according to stress distribution rules of the model. Fig. 1 shows the finite element model of a company’s 1.5MW hub. 5th International Conference on Information Engineering for Mechanics and Materials (ICIMM 2015) © 2015. The authors Published by Atlantis Press 51 Fig. 1. Three-dimensional Hub Model of A Company’s 1.5MW Wind Power Generator Unit Coordinate system Fixed hub center coordinate system is adopted as global coordinate system. Local coordinate system of load adding point is converted into blade coordinate system respectively. Global Coordinate System Local Coordinate System Fig. 2. Hub Coordinate System of A Company’s 1.5MW Wind Generator Unit Mesh generation For better control over the shape of mesh, the hub simplification model is guided into ANSYS11.0SP1 Workbench for mesh generation. The hub model is divided by hexahedral element solid186 and tetrahedron element solid187, with the result shown in Fig. 3. Fig. 3. Hub Finite Element Model of A Company’s 1.5MW Wind Generator Unit