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The Deposit surface and the Deposit Layered surface were then modeled using the ellipsoidal-blockage-element drag function. There are two options available to employ the ellipsoidal-blockage-element drag function in the discrete-element model: 1) use an average eccentricity at each height or 2) build an input file that contains the eccentricity for every blockage element at each height. Figure 11 shows the mean eccentricity and the maximum-transverse-width weighted eccentricity for the Deposit surface. The maximum-transverse-width weighted eccentricity weighs the eccentricity of the eccentricities of the larger blockage elements more. The maximum-transverse-width weighted eccentricity is important because the larger blockage elements contribute more drag. The maximum-transverse-width weighted eccentricity was calculated using equation (19).

Height Above Surface Mean Line (m)

Figure 11. Deposit Surface Blockage Eccentricity versus Height

Height Above Surface Mean Line (m)

Figure 11. Deposit Surface Blockage Eccentricity versus Height

Based on Figure 11, an eccentricity of 0.8 was used for the average eccentricity model. The discrete-element model was also run taking in the eccentricity for each blockage element at a given height. The results of the ellipsoidal-blockage-element model are presented in Table 3 and compared to experimental results and the results of the circular-blockage-element model. Table 3 shows that the results of the models with the average eccentricity and with the eccentricity for each blockage are comparable and are much closer to the measured results than the circular blockage model. The prediction for the Deposit surface is 21% high, and the prediction for the Deposit Layered surface is 12% high. Without uncertainty information, this suggests other factors influencing the drag on the rough surfaces may not have been considered.

Table 3. Computer Results Incorporating Ellipsoidal-Blockage-Element Eccentricity
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