A Negative Stiffness Double-Helical Torsional Magnetic Spring for a Wave Energy Converter

This paper presents the design of a new type of double-helical torsional magnetic spring for use in a wave energy converter (WEC). The integration of a negative stiffness spring within a WEC lowers the WECs natural resonant frequency. This improves impedance matching and therefore allows significantly more power to be generated for the same WEC structural mass. The double-helical torsional magnetic spring is made up of a right-handed magnetic helical spring in series with a left-handed helical magnetic spring. The helical design increases the stroke length and the energy density relative to other magnetic spring designs. The use of a double-torsion spring is shown to be beneficial because the off-axis torque is fully cancelled out. Thereby eliminating non-uniform torque oscillations that would otherwise be imparted on the bearings. This paper presents the magnetic spring parameter design using finite element analysis as well as the mechanical design drawings.