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Numerical Simulation on the Dynamic Installation of the OMNI-Max Anchors in
Clay Using a Fluid Dynamic Approach
Conference Paper · June 2017
DOI: 10.1115/OMAE2017-61570
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Proceedings of the ASME 2017 36th International Conference on Ocean, Offshore and Arctic Engineering
OMAE2017
June 25-30, 2017, Trondheim, Norway
OMAE2017-61570
NUMERICAL SIMULATION ON THE DYNAMIC INSTALLATION OF THE OMNI-MAX
ANCHORS IN CLAY USING A FLUID DYNAMIC APPROACH
Yuqin Zhang
State Key Laboratory of Coastal and Offshore
Engineering, Dalian University of Technology
Dalian, Liaoning, China
Jun Liu
State Key Laboratory of Coastal and Offshore
Engineering, Dalian University of Technology
Dalian, Liaoning, China
K
LA
LB
LF
LPE
LTF
Ltip
Ltail
n
sum
su,ref
tf
v
v0
WB
WD
wf
z
ߛሶ
ߛሶ ୰ୣ୤
τ
τ0
η
β
ABSTRACT
The OMNI-Max anchors, which are used as foundations
for mooring deep-water offshore facilities, are raised recent
years for their dynamically installation. ANSYS CFX 17.0 is a
computational fluid dynamic (CFD) program, capable of
simulating the dynamically installation process of the OMNIMax anchor. In the simulation, soft clay with linearly increasing
shear strength is modeled as Eulerian fluid material. The clay is
subjected to high shear strain rate during the dynamical
installation procedure, hence the H-B model is proposed as it is
applicable to a wide range of shear strain rate. Different anchor
impact velocity levels are modeled to investigate their effects
on the anchor final penetration depths. To improve the anchor
impact velocity and final penetration depth, a booster, which is
retrievable and renewable, is attached to the tail of the anchor.
The results demonstrate that the anchor would achieve deeper
penetration depth with the increase in impact velocity. Also the
anchor with a booster could reach a deeper penetration depth
than that of the single anchor owing to the increase of the
anchor total energy.
Keywords: dynamical installation; anchor; booster; numerical
modeling; CFD
NOMENCLATURE
Cd
drag coefficient
DB
booster diameter
Dinner diameter of the subdomain
DL
diameter of the loading arm
Dout
diameter of the outer domain
Dp
anchor frontal projected area equivalent diameter
de,t
anchor tip embedment (final penetration) depth
dt
anchor tip penetration depth
HP
padeye height
Hair
initial height of the air domain
Hinner height of the subdomain
Hsoil
initial height of the soil domain
k
shear strength gradient with depth
viscosity consistency in the H-B model
total anchor length
booster length
head fin length
padeye length
tail fin length
booster tip length
booster tail length
power law index in the H-B model
undrained shear strength at mudline
reference undrained shear strength
fin thickness
anchor velocity
anchor impact velocity
booster dry weight
anchor dry weight
fin width
depth below soil surface
shear strain rate
reference shear strain rate
shear stress in the H-B model
yield shear stress
viscous property
shear-thinning index
INTRODUCTION
The development of offshore oil and gas exploration
industry from shallow to deep-water brings an associated
requirement of new mooring systems. Suction caissons, suction
embedded plate anchors (SEPLAs) [1] and dynamically
installed anchors (DIAs) are available choices. Two kinds of
DIAs have evolved recent years. Torpedo anchors are rocketshaped anchors with elliptical or conical tips and usually with
zero to four fins towards the rear. The anchor is usually 12-17
m in length, 0.8-1.2 m in diameter and 230-1150 kN in dry
weight [2]. The OMNI-Max anchor consists of three
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Copyright © 2017 ASME
computational efficiency [24]. This approach was also used to
investigate the stability and anchor final embedment depth of
torpedo anchors [26,27]. The CFD model is capable of
modeling the installation from the release point to the final
embedment depth and the transition from water to soil.
Considering the features of the CFD approach, this study is
intended to set up a model of the OMNI-Max anchor using
ANSYS CFX, a commercial CFD software, to investigate the
installation procedure in soil. As mentioned in the previous
part, the centrifuge tests [19] and numerical simulation results
[20] indicated a limited penetration depth in strong soil
conditions and the anchor impact velocity was also limited. To
improve the practicality of the anchor, different boosters are
designed and attached at the rear of the anchor. The booster
geometry is similar to the torpedo anchor owing to its relatively
low drag coefficient, meaning less resistance during the
installation. The assembly anchors (refer to OMNI-Max
anchors with attached boosters) are also simulated in the
present study to investigate the improvement of the penetration
depth. In the simulation, soil is modeled as non-Newtonian
Eulerian fluid material considering the shear strain rate effect.
Different impact velocities of the anchor and assemblies are
modeled and compared. Two different interface conditions
between anchor and soil (fully rough and smooth) are selected
to assess the effect of the friction applied during the
penetration.
intermittently discontinuous planes and a loading arm located
near the front end. The OMNI-Max anchor has a relative small
size, which is approximately 9.7 m in length, 3.0 m in width
and height and weighs about 38 t [3]. Two stages are mainly
involved in the dynamical installation procedure of DIAs: (a)
free fall through water; and (b) dynamical penetration within
seabed. The anchor impact velocity is one of the key factors in
predicting the anchor final penetration depth which is directly
related to the capacity of the anchor system. For a torpedo
anchor the impact velocity could reach 35 m/s from a drop
height of 50-100 m above the seabed [4]. While field
installation of OMNI-Max anchor in the Gulf of Mexico (GoM)
recorded the terminal velocity of 19 m/s corresponding to a fall
distance of 30 m [5]. As for model tests [6], the free fall tests
with a 1/15 scale anchor indicated the anchor terminal velocity
was about 4.45 m/s. Numerical investigations conducted by Liu
and Zhang [7] indicated the OMNI-Max anchor terminal
velocity of 28 m/s and the impact velocity could reach 25 m/s
with a drop height of 60-70 m. Shelton [3] recorded a terminal
velocity of 23 m/s with an estimated drag coefficient of 0.65. It
is obvious that the terminal velocity of OMNI-Max anchor is
lower compared with torpedo anchor due to its large drag force,
which may directly result in low penetration depth and capacity.
Previous studies on the torpedo anchors including
experiments, field tests and numerical simulations, are
relatively mature. Centrifuge tests [8-12] were carried out to
investigate the anchor dynamically installation procedure in
normally consolidated (NC) clay and calcareous silt. Kim et al.
[13, 14] and Liu et al. [15] simulated the anchor installation
procedure using the Coupled Eulerial-Lagrangian (CEL)
approach and considered both the soil shear strain dependency
and the strain softening behavior. Investigations and
experiences on OMNI-Max anchor are limited compared with
the torpedo anchor. Experimental and numerical tests were
carried out to study the anchor capacity and keying behavior [3,
16, 17], but studies on the penetration procedures are rare.
Shelton et al. [3,18] and Zimmerman et al. [5] reported the
field data of the dynamically installation of OMNI-Max
anchors in the GoM, and the penetration depth ratio ranged
1.16-2.20 in normally consolidated (NC) clay [5]. A serial of
1/24 scale model penetration tests indicated the anchor final
embedment depth ratio of approximately 1.5 [7, 18]. Centrifuge
tests [19] in 1/200 scale indicated that the embedment depth
ratio ranged 1.18-2.0 in kaolin clay with su=3+1.1z kPa and
ranged 1.14-1.46LA in calcareous silt with su=3.3z kPa. Owing
to the limitation in field and experiment tests, numerical
simulation methods were developed. Kim et al. [20] and Liu et
al. [15] applied CEL approach to investigate the effects of
impact velocity, anchor weight, and soil strength on anchor
final penetration depth. The simulation results showed that with
an impact velocity of 20 m/s, the anchor final embedment was
merely 1.13LA in the NC soil with su=10+3z kPa.
The computational fluid dynamics (CFD) approach was
initially used to simulate the submarine landslide [21, 22] and
riser-seabed-water interaction [23-25]. CFD approach offers
advantages over CEL by providing much improved
NUMERICAL DETAILS
CFX Model details
The commercial software ANSYS 17.0 is used in the
present study to simulate multiphase flow and fluid-structure
interaction. In the CFX procedure, soil and air are modeled as
Eulerian fluid materials. To improve computational efficiency,
the installation procedure was modeled from the soil surface,
with different impact velocities.
The anchor simulated in the present study was
simplified and its dimensions are shown in Figure 1 and
listed in Table 1. Three different boosters were designed
with almost the same shape but different weights and lengths
(see Figure 2). The booster diameter, DB, is the same as the
loading arm diameter, DL, and the mass of the three boosters
are 0.5, 1.0 and 1.5 times the anchor weight, respectively.
The booster is attached to the tail of the OMNI-Max anchor
and retrieved after installation. Thus in practical engineering,
the booster is an installation tool and can be reused. The
kinetic energy and potential energy of the assembly anchor
would be much improved and the anchor is expected to
penetrate a deeper depth. Three fins may be attached at the
tail of the booster to sustain the directional stability, but in
this simulation no fin is simulated for simplification as
presented in Figure 2(b). The streamline shaped boosters are
designed trying to reduce the resistance during free-falling
and penetration. Details of the boosters are presented in
Figure 2 and Table 2.
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Copyright © 2017 ASME
set to 1 and the volume of air is 0, while it is opposite in the
elements above the mudline.
Figure 1. Schematic diagram of the OMNI-Max anchor and
soil strength profile
Table 1. OMNI-Max anchor details
Description
Padeye height
Total anchor length
Symbol
HP
LA
Value
4.35m
9.05 m
Head fin length
Padeye length
Tail fin length
Fin width
Fin thickness
Anchor dry weight
Anchor frontal projected area
equivalent diameter
LHF
LPE
LTF
wF
tF
Wd
2.45 m
1.26 m
5.21 m
1.95 m
0.2 m
390 kN
Dp
1.23 m
Diameter of the loading arm
DL
1.1 m
Figure 2. Booster used in the simulation: (a) with three
fins; (b) assembly anchor with finless booster
Table 2. Booster dimensions
Description
Booster diameter, m
Booster length, m
Booster tip length, m
Booster tail length, m
Dry weight, kN
Only half model was simulated due to the symmetry of the
problem. A half cylinder is used to form the numerical domain
with a diameter of 100 m (about 50wf , wf is the fin width) as
shown in Figure 3. An inner subdomain, the shadow part in
Figure 3(a), is created outside the anchor with a smaller half
cylinder of 16 m in diameter. This subdomain method was used
in simulating the riser-seabed interaction to improve
computational efficiency and precision [23-25]. The size and
shape of the mesh in the subdomain does not change with the
anchor motion but those outside this domain might get distorted
as the anchor moving downwards. The domain and subdomain
heights are related to the heights of the assembly anchors (see
Table 3). Anchor and boosters are defined as rigid body with
their masses, initial velocities and other conditions predefined.
The lower 90 m of the domain is filled with soil while the upper
part is air. The water component could not be considered in
CEL [15, 20] for dynamically installation problems. To
compromise the CEL simulating results, the effect of water,
therefore, was ignored in the present study. But this part may be
considered in the forthcoming work. The anchor tip is located
at the mudline initially, which is formed by defining the volume
fraction of the materials using CFX Expression Language. In
the elements below the mudline, the volume fraction of soil is
Symbol
DB
LB
Ltip
Ltail
WB
Booster
A
1.1
5.03
0.75
1.5
0.5Wd
Booster
B
1.1
8.92
0.75
1.5
1.0Wd
Booster
C
1.1
12.88
0.75
1.5
1.5Wd
The mesh is formed using the pre-processing software
ICEM CFD. Figure 3 depicts the unstructured tetrahedral mesh
used in this simulation. By analyzing the mesh sensitivity, a
very fine mesh size of 10 mm (tF/20, tF is the anchor fin
thickness) for the anchor thickness direction and 20 mm (tF/10)
for the lateral part is used for the simulation, considering the
computational efficiency and precision. For the booster part, the
minimum mesh size of 50 mm (DB/20) is used. The mesh size
is increased with the distance from the rigid body.
All the anchors′ and boosters′ surfaces are defined as walls,
which are impermeable boundaries to Eulerian fluid materials.
Symmetry boundaries are applied to all the symmetry surfaces
of the anchor and domains with unspecified mesh motion
option selected. The bottom and lateral surfaces of the outer
domain are also defined as walls. No-slip boundary is applied
to the bottom while free-slip boundary is applied to the lateral
surface. An opening boundary is used for the top surface to
allow air flow in and out alone.
Different impact velocities of the OMNI-Max anchors
were simulated. Owing to the field data [3, 5] and free-falling
numerical simulation results [6], three different velocities of 15,
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Copyright © 2017 ASME
20 and 25 m/s were selected. While for the assemblies, three
velocities of 20, 25 and 30 m/s were simulated, considering the
possible improvement of the impact velocity by adding
boosters.
Modeling of soil
The anchor dynamical installation procedure is short thus
the soil is under undrained condition. NC soil is modeled in the
present simulation. As reported by Hossain et al. [9], the soil
undrained strengths in the Campos Basin, Gjøa field and GoM
are typically in range of 2-7 kPa at the mudline and the strength
gradient of 1-3 kPa/m. A relatively strong soil strength profile is
selected in the present simulation, with strength of 2.4 kPa (sum)
at the surface and gradient (k) of 3 kPa/m, as shown in Figure 1.
The Eulerian fluid material used to simulate soil is defined with
a typical destiny of 1600 kg/m3. In CFX, the dynamic property
of soil is modeled using H-B model (Herschel-Bulkley model).
The H-B model in CFX is expressed in equation (1) as:
  0
, for    0

(1)

n
    0  K  , for    0
where τ0 is the yield shear stress, K is viscosity consistency, n is
the power law index and τ is the shear stress. The shear strain
rate effect reflecting the strength increase owing to the high
strain rate of soil is also considered in the simulation. Kim et al.
[13, 14] studied the dynamic installation of OMNI-Max anchor
considering both strain rate and strain softening effects using
CEL. The results demonstrated that the soil strain softening
behavior had quite limited effect on anchor final penetration
depth. Therefore, only strain rate effect is involved in the
present study. And the strain rate effect is expressed in equation
(2), as following:


    su,ref
(2)
su  1   
 

 ref   1  
where su,ref is the shear strength at the reference shear strain rate
of ref . In this simulation, su,ref = 2.4+3z kPa. The parameter η
is a viscous property factor and β is the rate parameter. Values
of these parameters have significant effects on the calculation
results as discussed by Liu et al. [28]. Kim et al. [20]
summarized these parameters used in previous studies. By
back-figuring reported field data and centrifuge test data in
clay, together with previous data, the values of η=1, ref =0.1 s-1
and β=0.1 were adopted in their simulation. Parameter analysis
is not main point in the present study, so the same values are
used to simulate the shear strain rate effect. Discussion on these
parameter analysis may be conducted in the following works.
Owing to the limitation in CFX, different value of τ0
cannot be defined. To best fit the expression in equation (2), the
parameters in equation (1) were taken as τ0=979.94 Pa,
K=1925.74+3427.07z Pa·s and n=0.0575, by back-figuring
using equation (2) and parameters from Kim et al. [20]. The
property of normally consolidated clay was simulated by
setting the parameter K as a function of the depth (z).
(a)
(b)
Figure 3. Typical mesh used in CFD analysis:(a) typical 3D
domain and mesh; (b) mesh in the subdomain
Table 3. Details of the domain dimensions (m)
cases
OMNI-Max anchor
OMNI-Max anchor
with booster A
OMNI-Max anchor
with booster B
OMNI-Max anchor
with booster C
Dout
100
Hsoil
90
Dinner
16
Hair
54.05
Hinner
25.05
58.58
29.58
62.47
33.47
66.43
37.43
RUSULTS AND DISCUSSION
Different cases were simulated to investigate the effects of
impact velocity and booster on anchor final penetration depth.
Two different boundary conditions (no-slip and free-slip
conditions) were considered to show the effect of frictional
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Copyright © 2017 ASME
to the soil strength increasing linearly with depth as well as the
shear strain rate effect.
The results indicate that the anchor final penetration depth
is limited in strong soil. For the impact velocity of 20 m/s, the
OMNI-Max anchor could constrainedly get immerged in soil
with the penetration depth of 9.01 m (0.996LA). But it could
hardly get fully penetrated into the soil with a smaller impact
velocity (15 m/s), considering a lower drop height through
water. Kim et al. [20] also investigated the anchor performance
in strong soil using CEL. For the soil strength of su=10+3z kPa,
the final penetration depth was merely 1.13LA with an initial
impact velocity of 20 m/s. But in the CEL simulation, frictional
interface and strain-softening effect were considered and the
embedment depth would be deeper compared with the present
results.
force acting on the anchor during the dynamically installation
procedure.
Mesh deformation
During the anchor dynamically installation procedure,
meshes outside the subdomain might get distorted as previously
mentioned. Figure 4 presents the mesh deformation at the end
of the installation. Compared with the initial condition (Figure
4 (a)), the finial mesh deformation mainly appears in the upper
and lower part outside the subdomain. Meshes in the upper part
would get stretched while the lower part get compressed due to
the mesh motion. But meshes in the subdomain would not get
changed and those around the subdomain get distorted slightly
(see Figure 5). As mentioned by Howlader et al.[25], strains
outside this subdomain are not very significant, therefore the
mesh deformation would not significantly affect the simulation.
0
5
Anchor velocity, v: m/s
10
15
20
25
30
Tip penetration deption, dt : m
‐1
(a)
(b)
Figure 4. Mesh deformation in the simulation: (a) initial
condition; (b) final condition
‐3
‐5
‐7
‐9
no-slip condition
15m/s
20m/s
25m/s
‐11
Figure 6. Velocity-depth for OMNI-Max anchor with
no-slip condition
Compared with the anchor, the assembly anchor could
achieve a deeper penetration depth because of the increase in
total energy. Figure 7 shows the results of the assembly anchors
with the same impact velocity of 20 m/s. The results suggest
that the anchor final penetration depth exhibits an increase of
23.09%, 36.58% and 55.3% for the assembly anchors with
three different boosters compared with that of the OMNI-Max
anchor only. Figure 7 also indicates a longer acceleration
procedure for the assembly anchor with a larger booster. Table
4 concludes the results of all the calculated cases. And a
comparison is made between the anchor final penetration
depths with different impact velocities and different boosters,
with that of the base case (the final penetration depth of OMNIMax anchor with an impact velocity of 20 m/s).
As it can be seen from Table 4 that the anchor final
penetration depth of the assembly anchors could be much
improved. The maximum improvement could reach 84.24% for
the case of OMNI-Max anchor with booster C of 1.5 times
anchor weight and an impact velocity of 30 m/s. But the no-slip
boundary conditions used in this simulation would overestimate
(a)
(b)
Figure 5. Mesh deformation in and around the subdomain:
(a) initial condition; (b) final condition
No-slip interface condition
In this part, all the wall boundary conditions of OMNIMax anchor and boosters are no-slip. The material around
would be attached to the anchor/booster surfaces and move
together with the rigid body. In this simulation, three different
impact velocities of 15, 20 and 25 m/s are simulated. The
anchor velocity-final penetration depth curves for the anchors
are shown in Figure 6. The anchor velocity would not decrease
immediately due to the lower top soil resistance. But the
acceleration trend is weakened for higher impact velocity. The
velocity decreases rapidly as the anchor penetrates deeper due
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Copyright © 2017 ASME
Figure 8 presents the soil shear strain rate around the
anchor with instantaneous velocity of 9.05 m/s and penetration
depth of 9.17 m (with anchor initial impact velocity of 25m/s).
The soil shear strain rate values at the anchor tip and corners of
the loading arm are relatively high owing to complex changes
of the configuration. For the lateral parts with smooth geometry
(no tips or corners), the shear strain rate is relative low.
the frictional force and result in a shallower penetration depth.
Thus the benefits of the boosters could also be underestimated.
0
5
Anchor velocity, v: m/s
10
15
20
25
Tip penetration deption, dt : m
0
‐5
Free-slip interface condition
Cases of free-slip wall boundary of the anchor and
boosters are studied to investigate the effect of the soil
frictional force acting on anchor. As the anchor and booster
surfaces are set as free-slip boundary, the material around the
anchor could flow freely with no friction acting on the anchor
surfaces. The assembly anchors and OMNI-Max anchor with an
impact velocity of 20m/s were simulated and the results are
also presented in Figure 7 and are listed in Table 5. The anchor
final penetration depth experiences an increase of about 30%
for the free-slip conditions compared with the on-slip ones,
indicating that frictional force is a significant component during
the anchor dynamically installation procedure. When the
frictional force is not considered, the acceleration procedure
after impacting the seabed would be more obvious, especially
as a larger booster is applied.
‐10
anchor(free-slip)
anchor with Booster A(free-slip)
anchor with Booster B(free-slip)
anchor with Booster C(free-slip)
anchor(no-slip)
anchor with Booster A(no-slip)
anchor with Booster B(no-slip)
anchor with Booster C(no-slip)
‐15
‐20
Figure 7. Velocity-depth for OMNI-Max anchor and
assemblies with impact velocity of 20 m/s
Table 4. Conclusion of the penetration depth for no-slip wall
boundary condition
cases
OMNI-Max anchor
OMNI-Max anchor
with booster A
OMNI-Max anchor
with booster B
OMNI-Max anchor
with booster C
Impact velocity,
v0 : m/s
de,t/LA
comparison
15
0.870
-12.65%
20
25
20
0.995
1.091
1.225
Base case
9.54%
23.08%
25
30
20
1.371
1.510
1.362
37.73%
51.72%
36.85%
OMNI-Max anchor
25
30
20
1.509
1.682
1.546
51.61%
68.92%
55.27%
OMNI-Max anchor
25
30
1.715
1.834
72.25%
84.24%
Table 5. Results of the free-slip boundary condition
cases
OMNI-Max anchor
with booster A
with booster B
OMNI-Max anchor
with booster C
de,t/LA
de,t/LA
(no-slip)
(free-slip)
0.995
1.210
21.53%
1.225
1.566
27.77%
1.362
1.814
33.17%
1.546
2.051
32.67%
comparison
Anchor impact velocity, v0: m/s
10
20
30
40
0.5
de,t/LA
1
anchor (no-slip)
anchor with booster A (no-slip)
1.5
anchor with booster B (no-slip)
anchor with booster C (no-slip)
anchor (free-slip)
2
anchor with booster A (free-slip)
anchor with booster B (free-slip)
anchor with booster C (free-slip)
2.5
Figure 8. Soil shear strain rate for the OMNI-Max anchor
with instantaneous velocity of 9.05 m/s
Figure 9. Final embedment depth of different
assemblies and velocities
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Copyright © 2017 ASME
penetration depth increased with the increase in the impact
velocity and the booster mass. The maximum increase of
anchor penetration depth could reach 84.24% compared with
the OMNI-Max anchor with an impact velocity of 20 m/s.
Effect of soil strain rate was considered, however only noslip and free-slip boundary conditions were available. The noslip condition overestimated the frictional force and resulted in
a shallower anchor penetration depth, while the free-slip
condition neglected all this part of force. These two kinds of
boundary conditions were simulated and compared. Results of
free-slip cases suggest an increase of 21.53%-32.67% in anchor
penetration depth compared with that of no-slip conditions.
Despite the overestimate of friction, the benefit of the booster
was still obvious. In the following study, the influence of
friction should be taken into account and simulated exactly.
Figure 9 summarizes the anchor final penetration depths of
all the cases in the present study. The results show a slight
increase in the final penetration depth with the velocity but
more obvious trend with the booster mass. This indicates that
for both kinds of boundary conditions, the boosters could
significantly increase the anchor penetration depth. Figure 10
shows the soil velocity vector at different embedment depths
for the two boundary conditions with the same initial impact
velocity of 20 m/s. For the no-slip condition, most of the soils
around the anchor flow downwards, while the flow direction is
perpendicular to the anchor surface for the free-slip condition
owing to the ignorance of the frictional force.
CONCLUSIONS
The dynamical installation procedure of OMNI-Max
anchor was investigated using CFX method in the present
study. Owing to the limited anchor penetration depth in strong
soil, three boosters with different weights were designed to
increase the anchor penetration depth. The effects of impact
velocity and booster on the anchor final penetration depth were
investigated and the efficiency of booster was highlighted. The
ACKNOWLEDGMENTS
This research was supported by the National Natural
Science Foundation of China (51479027, 51539008).
(a)
(b)
Figure 10. Instantaneous soil velocity vectors with anchor embedment: (a) free-slip condition; (b) no-slip condition
[3] Shelton, J.T., 2007, "OMNI-Max Anchor Development and
Technology," Proceedings of the 2007 Oceans Conference,
Vancouver, B.C, Canada, pp. 1990-1999.
[4] Hossain, M.S., O'Loughlin, C.D., and Kim, Y., 2015,
"Dynamic Installation and Monotonic Pullout of A Torpedo
Anchor in Calcareous Silt," Géotechnique, 65(2), pp.1-14.
[5] Zimmerman, E.H., Smith, M.W., and Shelton, J.T., 2009,
"Efficient Gravity Installed Anchor for Deepwater
Mooring," Proceedings of the 41st Annual Offshore
Technology Conference, Houston, Texas, Paper No.
OTC20117.
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