  We study the direction-dependent drag acting on a cylindrical solid intruder
with length $L$ and diameter $D$ as it moves in water-saturated granular beds
at constant depth. Polysterene and hydrogel grains with diameter $d$ are used
to investigate materials which have high contact friction and those which are
nearly frictionless, respectively. The drag on the intruder is measured while
oriented perpendicular $F_\perp$ and parallel $F_\parallel$ to its axis as a
function of speed $U$ from the quasi-static to the rate-dependent regime. We
find that the drag anisotropy $\xi = F_\perp/F_\parallel$ is not constant, and
increases significantly with driving rate and $L/D$ in both mediums. In
particular for $L/D = 40$, $\xi$ increases from 2.6 to 4.5, and from 7.0 to 8.2
in the high and low friction beds, respectively, as the nondimensional Froude
number $Fr =U/\sqrt{g(D+d)}$ is varied between $10^{-4}$ and $2 \times
10^{-2}$. On average, $\xi$ is observed to increase logarithmically with $L/D$
for $L/D \gg 1$. Exploiting the index-matched nature of hydrogel grains in
water, we further show that the sediment flow around the cylinder in the two
orientations is consistent with skin friction dominated drag. The relative
contributions of the cylindrical side and the circular flat-ends on $\xi$ are
estimated with thin disks to understand the observed variation of drag with
aspect ratio and surface friction.
