Aerodynamic and Mechanical System Modelling

This thesis deals with mechanical multibody-systems applied to the drivetrain of a 500 kW wind turbine. Particular focus has been on gearbox modelling of wind turbines. The main part of the present project involved programming multibody systems to investigate the connection between forces, moments, positions, velocities and accelerations of rigid bodies.
A 500 kW wind turbine model has been used together with experimental data for validating a model in FLEX 5, which is a recognised aero-elastic tool also used by the wind turbine industry. Among other things, multibody modelling of a planetary gearbox, both including and without constraints using flexibility, is an area that has been investigated. A rigid and computationally fast together with a flexible more correct multibody-model, has been developed. The flexible multibody-model specifically excels from distributing the internal loads physically more correct. A substantial problem which a proper model description has been accomplished for, is when alternating one or two teeth is in mesh at once. This causes a momentary and almost immediate change in tooth stiffness, which is implemented in the flexible model. The stiffnesses involved have been found using separate calculations using the Finite Element Method. The effect of this discontinuity is evaluated in simulations where damping is also included. A detailed investigation and calculation of e.g. tooth normal forces, stresses and fatigue problems in the tooth surface of gears have been conducted. In the fatigue calculations, considerations of turbulence from the wind are also included in order to investigate the fatigue effects from the latter, on or below the tooth surface.