Introduction

With the WS AWACS Reflection Analysis Module it is possible to determine wave reflection and evaluate wavemaker performance. The module requires that the feedback from DHI's digital wavemaker controller (AWACS²) is stored. Depending on the mode of operation of the wavemaker the following time series data will be available for analysis:

Position mode: desired paddle position, actual paddle position and surface elevation at the wavemaker paddle (requires that wave gauge on the paddle front are calibrated)

Absorption mode: actual paddle position, desired elevation and actual sur­face elevation at the wavemaker paddle.

Depending on the input time series the module will return parameters as:

1.       Reflection coefficient

2.       Servo delay

3.       Incident and reflected wave spectra

4.       Spectrum parameters, e.g. spectral peak-to-peak and period estimates

5.       Reflection function (amplitude and phase)

6.       Re-reflection function (amplitude and phase)

7.       Generation function ((amplitude and phase)

8.       Coherence spectrum

The module uses the theory of the active absorption technique (see Schäffer & Hyllested (1999)) to extract both the incident and reflected surface eleva­tion, accounting for the influence of evanescent modes present in the surface elevation measured at the wavemaker paddle.

Figure 8.1           The figure shows wavemaker performance in terms of actual and theo­retical re-reflection function and wavemaker phase delay calculated from wavemaker feedback.

Figure 8.2           The figure shows the reflection function calculated from wavemaker feedback.