Abstract
The failure of the traditional grouted connections of offshore wind turbines has led to the investigation of alternatives that provide a connection between the foundation pile and the turbine tower. An alternative to the traditional joint is a steel-to-steel connection also called a slip joint. To ensure a proper fit of the slip joint a dynamic installation of the joint is proposed. In this contribution, the effectiveness of harmonic excitation as an installation procedure is experimentally investigated using a 1:10 scaled model of the joint. During the dynamic installation test the applied static load, settlements and dynamic response of the joint are monitored using respectively load cells, taut wires and strain gauges placed both inside and outside the conical surfaces. The results show that settlement occurs only when applying a harmonic load at specific forcing frequencies. The settlement stabilizes to a certain level for each of the specific frequencies, indicating that a controlled way of installation is possible. The results show that it is essential to vibrate at specific frequencies and that a larger amplitude of the harmonic force does not automatically lead to additional settlement.
Highlights
At the end of 2012 more than 70% of the offshore wind turbines (OWT) were standing on a monopile (MP) foundation [1]
To simulate the dynamic installation under self weight, the following requirements were set to the test setup:
A dynamic installation procedure of a transition piece with a slip joint connection under self weight has been investigated on a 1:10 scale
Summary
At the end of 2012 more than 70% of the offshore wind turbines (OWT) were standing on a monopile (MP) foundation [1]. It was assumed that the cone angle of the top piece is slightly smaller than that of the bottom piece, to ensure a more durable fit To install such a joint offshore ,after the monopile has been installed, an additional forcing mechanism is needed. Introduction To simulate the dynamic installation under self weight, the following requirements were set to the test setup: For this purpose a design of a space frame has been made, actuators for the static and dynamic load are selected and bearings that allow movements in the vibration direction are chosen. Two eccentric masses rotating in opposite direction with the same angular velocity will result in an effective linear harmonic force in either vertical or horizontal direction In this experiment a vertical direction of the vibration is used.
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