Application of dam-break flow to green water prediction

The present study investigates, through analysis of laboratory measurements, the practice of applying Ritter’s dam-break flow solution to the prediction of overtopping green water on an offshore structure. The flow field of green water has been very difficult to obtain from either numerical computation or laboratory measurement. The dam-break flow model has been used in design to approximate the effect of green water due to the possible resemblance of the two flows, the simplicity of the dam-break flow, and the availability of analytical solutions of dam-break flow. In this study, the velocity of green water on a two-dimensional simplified model structure was measured using a newly developed technique called bubble image velocimetry (BIV). The profiles of horizontal green water velocity along the model deck are presented herein. Ritter’s analytical solution for the dam-break flow problem is examined and compared with the measurements. Two alternative approaches for quantifying the initial water depth, a parameter required in the analytical dam-break flow model, are investigated. The solution with the initial water depth estimated using the front velocity of green water is found to be in good agreement with the green water measurements. In addition, the influence of the deck length on green water velocity is examined.