Hull Water Waves experiments Wave Energy Cascade in a Rectangular Tank P Denissenko 1, S Lukaschuk 1, S Nazarenko 2 1 Fluid Dynamics Laboratory, University of Hull 2 Mathematics Institute, University of Warwick The work is supported by Hull Environmental Research Institute (L Frostic, S McLelland, B Murphy)

Total Environmental Simulator, The Deep water tank 6 x 12 x 1.6 m wave generator 8 panels current generator 1 m 3 /s rain generator PIV & LDV systems

We study the energy cascade from long to short wave lengths to test the effects of wave-wave interaction and the finite size of the domain. Isotropic wave field is generated through excitation in the band 0.4 to 1.2 Hz (maximum wavelength is of the order of water depth). The water depth is recorded at two points continuously (400 Hz) using capacity probes, and along the line with the time separation 0.5s. Dependence of spectrum on the excitation amplitude is studied. Effect of rainfall on the spectrum is detected.

6 metres 12 metres 90 cm 8 Panel Wave Generator Laser Capacity Probes Rain Generator

Wire probes,  - space Laser sheet + floaters + camera, k - space Isolated 80 cm copper wires Generators 59 kHz and 55 kHz Lock-in amplifiers ADC sampling rate 400Hz min records MATLAB signal processing 30  m floating glass spheres,  = 0.9 Nd YAG pulse laser Underwater laser sheet optics Camera 2048x2048 pixels, 12 bit MATLAB image processing + FFT 2000 images

Power spectra of surface waves. Wire probes,  - space Elevation std = 5.0 Fit slope = Elevation std = 6.6 Fit slope = Elevation std = 4.1 Fit slope = Elevation std = 6.1 Fit slope = -5.52

Slope of Spectra, std of water depth, excitation amplitude

Power spectra of surface waves. Image analysis, k - space

Power spectra of surface waves with and without rain. Wire probes,  - space Rain ONLYRain OFF Rain ON

Probability density functions for surface elevation is NOT symmetric for large wave amplitude (wire probes)

Probability density functions of squared surface elevation at 6 ± 1 Hz, wire probes Low amplitude, smooth wavesHigh amplitude, splashing

Squared amplitude of surface elevation at 6 ± 1 Hz, wire probes Probe 1 Probe 2

Time evolution of spectra. Difference between the time dependent and the mean spectral density