• Journal of Ocean Engineering and Technology
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• v.26 no.3
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• pp.61-65
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• 2012

Air-water flow measurements are of importance for the coastal and ocean engineering fields. Although kinematic investigations of the multi-phase flows have been conducted for long time, velocity measurements still are concerned with many researchers and engineers in coastal and ocean areas. In the present study, an imaging technique using shadowgraphy and fiber optic probe for velocity measurements of air bubbles is introduced. The shadow graphy image technique is modified from the typical image velocimetry methods, and optical fibers are used for the well-known intrusive coupled phase-detection probe system. Since the imaging technique is a non-intrusive optical method from the air, it is usually applied for 2D flows. On the other hand, the double fiber optic probes touch flows regardless of flow patterns. The results of the flow measurements by both methods are compared and discussed. The methods are also applied to the measurements of overtopping flows by a breaking wave over the structure fixed on the free surface.

• Journal of computational fluids engineering
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• v.20 no.2
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• pp.96-102
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• 2015

In this study, the green water phenomena on rectangular shaped structure is numerically simulated by STAR-CCM+ to investigate the flow pattern including the velocity profiles in bubbly water flow. 5 phases of the formation of green water in front of and over the rectangular shaped structure is simulated at the design condition which is scaled down by 1:125 from FPSO operating in GOM. All numerical results are compared with the experimental results performed in a two dimensional wave flume. The water deformation due to the green water are obtained by the high speed CCD camera with employing the shadow graphy technique, which is allowed to take the bubbly water flow into images. A series of image taken by shadow graphy technique is analyzed with MQD method to calculate the velocity in bubbly water flow.

• Journal of Ocean Engineering and Technology
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• v.30 no.1
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• pp.44-50
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• 2016

An experimental study was performed to investigate the behavior of green water on a structure with a rectangular cross section under wave conditions, along with the flow characteristics in bubbly water flow. An experiment was conducted in a two-dimensional wave flume using an acrylic model (1/125) of FPSO BW Pioneer operating in the Gulf of Mexico under its design wave condition. The occurrence of green water, including its development, in front of the model was captured using a high-speed Charge Coupled Device (CCD) camera with the shadowgraph technique. Using consecutive images, the generation procedure for green water on the model was divided into five phases: flip through, air entrapment, wave run-up, wave overturning, and water shipping. In addition, the distinct water elevations of the green water were defined as the height of flip through, height of splashing jet, and height of freeboard exceedance, and showed a linear relationship with the incoming wave height.