The droplet sizes and velocities contained in vessel generated spray are difficult to quantify. This paper describes three different methods to quantify velocity and size distributions from high speed video of spray from a planing boat. These methods include feature tracking, displacement tracking and video inversion. For the feature tracking method, the images were preprocessed using contrast limited adaptive histogram equalization, and then converted to binary images with a specific intensity cutoff level. Image statistics were then generated from this image, including droplet area and effective diameter. These images were processed using commercial PIV software to obtain velocities. For the displacement tracking method, the images were also converted to binary images with a specific intensity cutoff level. Image statistics were again compiled from this binary image. A droplet filter was then applied using a binary erosion image processing technique, where large droplets were removed because the entire droplet may not be in frame, and small droplets were removed because they might not overlap between frames. Droplets were then tracked by comparing the bounding boxes of two droplets between time frames. The video inversion method consisted of the manipulating the original high speed videos from spatial x-y frames in time space to time-y frames in x-space, where the x-axis is longitudinally along the ship and the y axis is vertical to the ship. From this orientation, the speed of the general spray mass could be determined by summing the pixels in time columns for each × frame. Comparisons of droplet size distribution between the feature and displacement tracking method yield qualitatively similar results, with some disagreement likely due to the different threshold levels. The trend of the distribution curve suggests that both methods are unable to resolve the smallest droplet sizes, due to the processing filters applied as well as the field of view of the camera. The three analysis methods compare well in their spray velocity computation, and are also similar to spray speed predictions found in the literature for a given geometry and vessel speed.

This content is only available via PDF.
You do not currently have access to this content.