top of page

Depth from Defocus Technique For High Number Density Particle Images

Rixin Xu (1), Zuojie Huang (1), Wenchao Gong (1), Wu Zhou (1), Cameron Tropea (2)

1. University of Shanghai for Science and Technology, Shanghai, China
2. Technical University of Darmstadt, Darmstadt, Germany


A method for tracking position and orientation of regular and irregular particles is developed. The method uses two perpendicular cameras and the computer vision library OpenCV. It allows for simultaneous tracking of 3 translational and 3 rotational degrees of freedom and for multiple particles trailing each other. The method requires a model of the geometric shape of the particle to measure orientation. The model is projected to both cameras and compared to shadow images of the real particle. The method is validated by using synthetic data. Three regular particles are used, a cube, a short rod and a flat plate. Irregular particles are obtained from a plastic granulation process. A total of 10 irregular particles are used. The fluid medium is room temperature water and the particle densities are approximately $1030\,\mathrm{kg/m^3}$ and $1420\, \mathrm{kg/m^3}$ for the regular and irregular particles respectively. The Reynolds number for the irregular particles vary between $550 < Re_p < 850$ for the regular particles it is $Re_p \approx 250$. The particle drag coefficients and their change in rotation is discussed. The variation in orientation is observed to be linked to the aspect ratio however with notable outliers. Irregular particles falling in distinct modes are observed and four are selected and further analyzed showing the close link between instantaneous velocity and orientation.

bottom of page