Drag and Added-Mass Coefficients of Large Sandbags

Abstract

Experimental investigations to understand the mechanics of motion of large sandbags and to simulate their settling behaviors are reported in this paper along with the details of experimental setup and procedures. Two high-definition charge-coupled device (CCD) cameras recorded the motion of the sandbags from the side of a glass water tank and a digital particle tracking velocimetry (DPTV) technique was used to determine the settling velocity of the bags. The drag and added-mass coefficients are estimated for the sandbags and the values of the added-mass coefficient are compared to those for solid spheres. The unit weight adjustment and the drag coefficient adjustment approaches are investigated for simulating the settling behavior of permeable sandbags. The results show that the unit weight adjustment approach gives better results than the drag coefficient adjustment approach, if the reduction in the drag coefficient because of porosity is taken into consideration and the effect of permeability of the sandbag on the drag coefficient is small and neglected. An exponential equation to estimate the percentage increase of the unit weight for the permeable sandbags is presented.