Wave Forces on an Oscillating Water Column Device

Abstract

The Oscillating Water Column (OWC) is one of the wave energy device working on the principle of rise and fall of free surface water oscillation due to continuous impingement of waves that penetrates into a semi submerged chamber. It is one of the successful device that has been proved up to pilot stage in the field. There have been many studies on optimizing various parameters of the OWC device through laboratory modeling. In order to quantify the horizontal and vertical wave forces on a 1:12 OWC model, a series of experiments has been conducted in a wave flume, 72.5m long, 2m wide and 2.5m deep. The chamber with dimensions of 1910mm wide(w) (parallel to the wave crest) and 300mm length (b) (along the wave direction) was made of 20mm thick acrylic sheet. The total height of the chamber is 900mm and the water depth (d) in front of the chamber is 500mm. The bottom opening (o) in the front lip wall is 300mm. An air vent of 0.68% of the plan area of the device was maintained. Custom made strain gauge based force transducer has been mounted to measure two force components namely vertical and horizontal. The test set-up was located at a distance of 45m from the wave maker. The strain gauges in the load cell were placed in such a manner to nullify the effect due to moment in the measurement. The experiments were conducted for regular waves with the wave characteristics defined by Froude model scale law. The wave frequencies range between 0.42Hz and 1.25Hz with the wave steepness, H/L in the range of 0.0107 to 0.0524 and relative water depth, d/L in the range of 0.09 to 0.30 have been considered in the present study. It is observed that at natural frequency of system, the force on the structure is less dueto high-energy absorption by the OWC.