Vogel Number

The efficiency of passive reconfiguration processes of individual seaweeds was characterized by the Vogel number. All tested individuals exhibited an increase in drag with increasing velocity that was less than could be expected from Equation 3.1. Vogel numbers ranged from a maximum of B = -0.25 to a minimum of B = -1.21, with an average of B = -0.86 ± 0.31 (mean ± 1 SD). Grouped by morphology, the wave-exposed individuals averaged a lower Vogel number than the intermediate/wave-sheltered individuals (B = -1.08 ± 0.15 and B = -0.65 ± 0.28, respectively), i.e., the wave-exposed individuals performed with a significantly more efficient mode of streamlining (Welch's t-test, p <0.05).

FIGURE 3.10 Correlation of the Vogel number, B, with the mass of the tested seaweeds. The black oblique line indicates the regression, while the dashed black lines are the 95% CI for the linear regression. The gray horizontal line indicates the mean at B = 0.86 for all tested individuals, while the dashed gray horizontal lines represent the 95% CI.

FIGURE 3.10 Correlation of the Vogel number, B, with the mass of the tested seaweeds. The black oblique line indicates the regression, while the dashed black lines are the 95% CI for the linear regression. The gray horizontal line indicates the mean at B = 0.86 for all tested individuals, while the dashed gray horizontal lines represent the 95% CI.

The Vogel number could be correlated best with the mass of an individual (R2mass = 0.84) (Figure 3.10). The other tested morphometrical parameters — volume, length, and planform area — yielded lower correlation coefficients (R2volume = 0.56, R2length = 0.32, and R2area = 0.77). The correlation could be improved by considering the overall morphology as an additional independent variable (e.g., R2mass + wave exposm-e = 0.97).

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