Stereoscopic measurement of a fluctuating free surface with discontinuities

Ryota Tsubaki1 and Ichiro Fujita2

1 Graduate School of Science and Technology, Kobe University, Rokkodai, Nada-Ku,

Kobe 657-8501, Japan

2 Department of Architecture and Civil Engineering, Kobe University, Rokkodai, Nada-Ku,

Kobe 657-8501, Japan

E-mail: ifujita@kobe-u.ac.jp

Received 21 December 2004, in final form 16 March 2005

Published DD MMM 2005

Online at stacks.iop.org/MST/16/1

Abstract

This paper presents a new innovative method for measuring two-dimensional

water surface configurations. This method uses a pair of sequential images

captured by two high-resolution CCD cameras arranged in a stereo position.

The idea of the method is to make the water colour white so that the

instantaneous water surface appears like a solid surface with a clear pattern

when an irregular pattern of light is projected onto it. It should be noted that

this method is suitable to measure waves with small amplitude accurately

and at the same time discontinuous surface robustly. First, we explain the

measurement principle and the experimental procedure for obtaining stereo

images. Secondly, we examine the measurement accuracy by applying our

technique to still water surface and calibrated wavy plates. Finally, we

represent applications of the technique applied to the actual flow field such

as surface waves and ripples generated in a shallow water box. The result

shows that we can trace the propagation of small waves as small as 1 mm. In

another application, we measure periodic surface fluctuation generated at an

asymmetric cavity installed in an open-channel flow, demonstrating

robustness of the technique applicable even when a discontinuous surface

with wave breaking occurs in the course of the measurement.

Keywords: water waves measurements