Developement of a numeric tool for fatigue life evaluation of the regulating mechanism in Kaplan runners

Sammanfattning: Kaplan turbines are a type of hydropower turbine with adjustable runner blades. This allows the turbine to alter its power output while maintaining a relatively high efficiency over a wide range of power levels. But these frequent blade angel adjustments exposes the turbines internal mechanism to wear and the possibility of fatigue failure. A Kaplan turbine, and the regulating mechanism inside it, usually has an expected service life, but depending on how the turbine is operated its actual lifespan could potentially either exceed or fall short of this expected service life. The objective of this thesis was to create a tool to evaluate the fatigue damage and fatigue life of the components in the Kaplan runner's regulating mechanism. This thesis was mainly focused on two components that are found in practically all Kaplan runner regulating mechanism. One of these components is the "crank", which is the part that rotates with the runner blades, and on which the runner blades are often directly attached. The other component is the link, that attaches the cranks to the crosshead, which is the part that is moved with hydraulics axially inside the runner. The reason for this is that these components have been found to be among the most susceptible to fatigue damage in the regulating mechanism. The tool was realized in the form of a program with a graphical user interface. It was programmed in Matlab's AppDesigner, and has a direct connection to the OSIsoft PI database. This program lets the user enter dimensions of the mechanism's components manually, and reads data such as load and runner blade angle directly from PI. The program also features different options the user can select depending on the design of the mechanism's components. Load and angular data is retrieved from a selected time period. The program evaluates the fatigue life of the components using stress based fatigue evaluation. The stresses and stress concentrations in the components are calculated using mathematical formulas. Most of these formulas were gathered from literature, but a formula describing the stress concentration in the crank was experimentally developed during the thesis. This formula was developed based on FEM-simulations carried out in the program Ansys. The finished product is a program that relatively quickly lets the user evaluate the fatigue lifespan of the link and crank in a given turbine, based on measurement data and dimensions entered by the user. The program is computationally fast as it utilizes mathematical expressions to numerically calculate the maximum stresses in the components, instead of FEM-analysis. The program can be run on any computer a standalone program as it has been compiled to an executable file for ease of use.