Structural design of a wooden wind tower structure

Abstract

A modular design of a wooden wind turbine support structure is developed by Modvion. The distinction between the commonly used steel towers are the tall height of 120 m and that it is made out of wood, which enlarges the dimensions of the structure in order to endure the loading. The thesis work primarily covers the initial structural design of the support structure adopting an analytical method. Important parts for the understanding of the project includes wind characteristics and interference with the turbine; building standards and codes; load and resistance factor design and also the materials / wood products that are to be used. Relevant global dimensioning loads are identified and considered in the structural strength capacity verification. An analytical initial scantling tool is established based on a cantilever beam model and implemented in MATLAB, thereafter verified with a shell model of the tower using the general purpose finite element software ANSYS. Sufficient dimensions of the tower cross sectional elements are derived for given circumstances of a future location of the tower. The strength calculations are made in ultimate limit state and the deformation analysis in serviceability limit state. Furthermore the first natural frequencies of the tower are verified to not coincide with the rotor frequency and the blade passing frequency of the turbine during operation, as well as the risk of vortex shedding. The dynamic analysis is carried out in FAST, simulating a turbulent and an uniform wind field. The thesis work shows that the simple beam model is a good candidate for conceptual design of wind turbine wooden towers.