TYPE E double-actuated wavemakers

Abstract

The Ploeg and Funke TYPE E double-actuated wavemaker has been calibrated at the CEPYC-CEDEX Laboratory in Madrid, Spain. TYPE E double-actuated wavemakers are capable of operating as piston-only, hinged-only, or simultaneously as both piston and hinged wavemakers. An eigenfunction expansion for the fluid motion generated by a generic planar wavemaker of variable-draft is used to describe the motion of double-actuated wavemakers. This generic solution appears to be more robust and easier to apply in numerical codes than the ones that require the amplitude of the wavemaker stroke be specified at the still-water-level and that require the draft of the hinge to be forced to minus infinity in order to recover a piston wavemaker. The dimensionless transfer functions for the ratio of the wavemaker stroke to the wave amplitude are derived by equating the total average power generated by both actuators to the energy flux in the propagating wave. The solution is not unique because both the ratio of the amplitude of the piston actuator to the amplitude of the hinge actuator and the relative phase angle between the motion of the two actuators are arbitrary. Experimental verifications of the theory are given for each actuator operating independently as well as for three ratios of the piston amplitude to hinge amplitude when the relative phase angle is zero. These calibrations indicate that TYPE E double-actuated wavemakers are perhaps the optimum wavemakers for simulating double-peaked spectra such as the six parameter Ochi-Hubble spectra where the hinge actuator is optimum for generating the higher frequency components.