IIHR Towing-Tank Wavemaker

A description is provided of the acqms1tton and calibration of a plunger wavemaker for the Iowa Institute of Hydraulic Research 100x3.048x3.048 m towing tank. The collaboration procedure determines the wavemaker response function, i.e., nature of generated waves over range of single (regular waves) or multiple (irregular waves) input plunger frequencies, strokes, and phase angles. Capacitance wires are used to measure wave time. histories, which are analyzed (using average wave crests and troughs, Fast Fourier Transforms, and Fourier series) for evaluation of wave amplitudes and frequencies. Only regular waves are investigated for input frequencies and strokes corresponding to wavelengths 0.5-6.0 m and steepnesses 0.025-0.3. The uncertainty assessment methodology follows the AIAA Standard S--071-1995. The results indicate that the primary frequency wave frequency response is equal to the input wavemaker frequency within the uncertainty in the data and analysis, i.e., 1-3% for low-high frequency, whereas the primary frequency wave amplitude significantly exceeds the wavemaker stroke for most wavelengths and steepnesses. The wavemaker meets the design requirements and limits. The response function is less than the theoretical prediction used in its design. The certainty in the wave-elevation measurement is small compared to the magnitude and trends of the primary frequency amplitude response such that the magnitudes and trends exhibited are much larger than the noise. The sub-frequency amplitudes are small, except for small wavelength and steepness. The super-frequency amplitudes are also small. but do show the trend of increasing with wave steepness and correlate with second-order Stokes wave theory.