Determining the Service Life of a Steel Wire Under a Working Load in the Wave Energy Converter (WEC)

Abstract

There are different types of energy in nature. Kinetic energy of natural movements like ocean waves is one of them. It is advantageous to convert this energy into a form suitable for use. Ocean waves can play important role in tomorrow’s energy production. At the Swedish Center for Renewable Electric Energy Conversion at Uppsala University, the Wave Energy Converter (WEC) was launched offshore outside the Swedish west coast in March 2006. The WEC consists of the linear generator placed on the sea bed and connected to the buoy via the rope, see Fig.2. Different rope solutions were tested. In May 2008, the steel wire Powerplast (28mm) was connected to the WEC. The steel wire has a shorter service life than other parts of the WEC. The steel wire connects the translator and the buoy. Therefore, the steel wire’s lifetime appears to be very important characteristic for the WEC. It is necessarily to determine the service life of the wire. Aggressive environments reduce the calculated service life which results in corrosion of an ordinary steel wire. A high wave climate and the contact loads can drastically affect wear of the wire. In order to prevent metal-to-metal contact between a steel wire and a funnel, the steel wire was impregnated in a black high density (HD) jacketing compound, that had a good abrasion, scratch resistance and a very good heat deformation resistance. The pulsating nature of waves can cause dramatic transition of the wire from the ductile to brittle fatigue fracture appearance. The residual stresses was also the causes of failures in the wire. The research results and the result from a full-scale experiment of dynamic behavior of a steel wire under a working load in the WEC are considered in this work. The measurements of the dynamic force along the steel wire under a water line were conducted offshore at Lysekil off the Swedish west coast.