The document describes an experiment to study the extraction dynamics of rigid cylinders pulled horizontally through a granular material. Cylinders of varying diameters were tested at different initial depths. The force required to extract the cylinders was measured. Larger cylinders experienced a greater peak force and exhibited an upward lifting motion not seen with smaller cylinders. As cylinder diameter increased from 1/2" to 2", the peak force saturated, likely due to confinement effects. Further testing will vary additional parameters to better understand the extraction dynamics and inform anchor design.

1. Extraction Dynamics of Rigid Bodies in Granular Materials
Ryan KUBIK1, Emilie DRESSAIRE1
1Dept. of Mechanical and Aerospace Engineering, NYU Tandon School of Engineering, USA
Abstract
Abstract
Abstract
Introduction
Abstract
Experimental set-up
The need for anchoring systems in granular materials is
specifically present in the marine transportation industry,
e.g. to layout moorings, keep vessels and docks fixed in
bodies of water, build oil rigs, etc. The holding power of
an anchor is associated with the drag and lift forces
exerted by the granular media. Empirical evidence
indicates that the holding power depends on the size and
shape of the anchoring structure. In this study, we start by
investigating the relationship between the size of a
cylinder and the extraction dynamics.
Using a two-dimensional geometry in which a rigid body
is pulled through a granular media at constant speed, we
determine the drag force exerted by a granular medium
on a moving object. The method allows measuring the
drag force and recording the trajectory of the rigid object
through the sand. We systematically vary geometry of the
rigid body, the properties of the granular medium, and the
extraction speed. For different initial positions of a
cylindrical object pulled horizontally through the medium,
we record large variations in magnitude of the drag and a
significant lift force that pulls the object out of the sand.
Using this data, we aim to provide a theoretical model
that can aid the design/analysis/selection of marine
anchors.
Abstract
Observations
Abstract
Extraction Dynamics
Abstract
Conclusion
Abstract
References
Abstract
Contact Info
R.Kubik - rk1941@nyu.edu
Prof. E.Dressaire – emd13@nyu.edu
PIF Lab at NYU Tandon SOE -
http://engineering.nyu.edu/piflab/
CCBY-SA3.0byTosaka
www.Hbanchors.com
[1] Ding, Y., Gravish, N. and Goldman, D.I., 2011. Drag induced lift in
granular media. Physical Review Letters, 106 (2)
[2] Neubecker, S.R. and Randolph, M.F., 1996. The performance of
drag anchor and chain systems in cohesive soil. Marine
georesources & geotechnology 14 (2)
[3] Savage, S.B. and Hutter, K., 1989. The motion of a finite mass of
granular material down a rough incline. Journal of fluid
mechanics, 199
[4] Gravish, N., Umbanhowar, P.B. and Goldman, D.I., 2010. Force
and flow transition in plowed granular media. Physical review
letters, 105 (12)
• Tested cylinders are not behaving like anchors, and are experiencing a lift force. Since the cylinders are symmetrical,
this result is not intuitive
• The peak force required to extract the cylinders seems to start saturating after the two inch diameter, may be due to
the boundary conditions/confinement of the sand in the tank
• The trajectory of the anchor depends on the amount of sand displaced.
• Force required to keep the anchor moving at constant velocity decreases the size of anchor decreases.
• Further testing will continue to determine how the weight, pull angle, velocity and shape of the rigid body effect the
dynamics of the system (Force and Trajectory)
• Peak force increases with diameter
of cylinder and initial depth
• Comparing the increase from ½” to
2” diameter, we see saturation of
the Peak Force value from 2” to
3.5” Diameter cylinder
• Typical force propagation trend is
seen to the top right. Data is from
½” diameter anchor initially at 3”
depth.
• Bottom right shows how increasing
the diameter leads to an upward
motion and a larger overshoot value
for depth. Difference in steady
vertical position value is due to
different radii.
Time
• As the cylinder is pulled horizontally, it pushes forward a pile of sand whose shape and size vary over time
• Even though the cylinder is pulled horizontally, it moves up toward the surface of the sand
• Force increases until the cylinder starts moving, then decays over time
• Steady/Final vertical value does not seem to depend on initial depth, only diameter. May also be affected by weight
Set up:
• 2D system
• 250μm glass beads
Experimental Protocol:
• Varying pull angle, pull speed, initial depth,
anchor diameter, anchor weight are fixed
• The force, anchor position and sand
dynamics are recorded
Analysis
• Anchor depth and sand dynamics are tracked
using video analysis and MATLAB.
• Force data is provided by the force gauge
Depth Indicator
Cylindrical Anchor 250µm glass beads
𝑣
𝑣
1
22
43
64
85
106
127
148
169
190
211
232
253
274
295
316
337
358
379
400
421
Force(N)
Time(s)
1
0
10
20
30
40
50
60
0 0.5 1 1.5
PEAKFORCE(N)
INITIAL DEPTH (CM)
1/2"
Diameter
2"
Diamater
3.5"
Diameter
60
String