FINITE ELEMENT ANALYSIS IN OFFSHORE GEOTECHNICS ELEMENT ANALYSIS IN OFFSHORE GEOTECHNICS –A...

FINITE ELEMENT ANALYSIS

IN OFFSHORE GEOTECHNICS– A 30-YEAR RETROSPECTIVE

J. S. Templeton, III

SAGE USA, Inc.

SIMULIA Community Conference

Providence, Rhode Island

May 15-17, 2012.

1

2

FINITE ELEMENT ANALYSIS

IN OFFSHORE GEOTECHNICS

Outline

•Milestones

•Piles and Well Conductors

- Performance under lateral loading

- Suction Foundations, total stress analysis

- Suction Foundations, long term holding

•Jack-up Rigs

- Performance in Severe Storms

- Performance in Earthquakes

•Conclusions

•Further Developments

•Acknowledgements

3

MILESTONES

(global)

• 1962, First published foundation FEA (Clough and Wilson)

(the second published paper to have “Finite Element” in the title)

• 1968, Roscoe and Burland modified Cam Clay theory of Critical

State Soil Mechanics (Schofield and Wroth).

• 1970, Hibbitt, Marcal and Rice (1970) established rigorous basis

for large strain FEA. McMeeking and Rice (1975) further elucidated.

• 1974, Nagtegaal, Parks and Rice (1974), resolved the problem of

shear locking of finite elements under large deformations.

• 1978-9, Miller, Murff and Kraft, as well as Carter, Randolph and Wroth

applied Modified Cam Clay to the problem of pile setup.

• 1980, Nystrom proposed incorporation of soil mechanics

capabilities into Abaqus.

• 1981, Abaqus soil mechanics capabilities released.

4

MILESTONES

(personal)

• 1967, Dynamic FEA of Saturn-Apollo vehicles in pre-NASTRAN era

• 1974, Studied Critical State Soil Mechanics,

via Tulane/Cambridge collaboration.

• 1981, Early Abaqus foundation analyses

• 1985, Analysis of geologic history of Mississippi Canyon soils

• 1986, First Abaqus analysis of offshore GBS foundation consolidation

• 1991, First Abaqus analysis of offshore subsidence effects.

• 1992, First FEA analysis to explain observed pile skin friction in sand

• 1996, Abaqus continuum dynamic FEA of wave propagation in soils

• 2002, Defined role of FEA in suction pile design.

• 2003, First FEA for offshore foundation under vortex-induced vibration

• 2004, First FEA of long term holding uplift capacity for suction caissons

• 2006, Standard setting publication on use of Abaqus for jack-up rigs

• 2008, First published FEA of continuum soil and structure EQ response

• 2009, Abaqus analysis plus centrifuge tests changed lateral pile practice.

• 2011, First dynamic FEA to match jack-up hurricane wave response

including foundation hysteretic damping effects

PILE FOUNDATIONS

More recent work has concentrated on lateral

performance issues and on suction piles

(aspect ratios typically 7 : 1 or less).

Early Abaqus offshore foundation analyses concentrated

on issues related to axial capacity of slender

driven piles (aspect ratios ~ 50 : 1 or > 100 : 1)

New issues:

• different installation problems

• more complex soil/pile interaction

• axial and lateral capacities interact

• reverse end bearing

• long term uplift holding capacity

LATERAL PERFORMANCE OF

SLENDER PILES AND WELL CONDUCTORS IN CLAY

0 0.1 0.20

2

4

6

8

10

12

14

16

API WSD 21st

API WSD 21st Errata

FEA

Centrifuge

test 1 - 24ft - FEA @ 23.3ft and 25ft

Lateral Displacement / Diameter, Y/D

Res

ista

nce

/ S

hear

Str

en

gth

, P

/Su

DOUBLE-BLIND Abaqus analysis and centrifuge test results

agreed extremely well, but both indicated substantially

greater capacity than current recommended practice.

SUCTION FOUNDATIONS

SUCTION CAISSONSSUCTION PILES

Installation by suction gets progressively more

effective as water depth increases, while driving

becomes more problematic and more expensive.

0

5000

10000

15000

20000

25000

0.0 0.2 0.4 0.6 0.8 1.0 1.2

Vertical (pullout) displacement at anchor point, m

Lo

ad

, kN

Anchor pointpenetration = 6.4 m




Abaqus results with pile loaded

above midpoint and low water depth

resulted in little separation and

negligible effect on performance.

With a high attachment

point, and an inclined load,

soil can separate from pile

here - even in clay, if water

is not too deep.

10

0 0.1 0.2 0.3 0.4 0.5

0

5

10

15

20

25

Fig. 6. ABAQUS Results Compared to

Inclined Load Test Data

Vertical Displacement, m

Incl

ined

Lo

ad

, M

N

Legend

Tub 7

Tub 8

Tub 9

Tub 10 ABAQUS

0 0.1 0.2 0.3 0.4 0.5

0

5

10

15

20

25

Fig. 6. ABAQUS Results Compared to

Inclined Load Test Data

Vertical Displacement, m

Incl

ined

Loa

d, M

N

Legend

Tub 7

Tub 8

Tub 9

Tub 10 ABAQUS

Suction pile performance for low attachment & inclined load (left)Abaqus results and centrifuge test data (right), after Raines et al. (2005)© 2005 Taylor & Francis Group plc, London, UK. Used by permission.

Finite Element Results for OTRC Workshop Straw Problem

Load elevation angle = 26 degrees

0

1000

2000

3000

4000

5000

0 1 2 3 4 5 6 7 8 9 10

Vertical displacement, ft

Lo

ad

re

su

ltan

t, K

ips

Program C, small deformation theory

Program A, small deformation theory

Program A, large deformation theory

Program C, large deformation theory

Workshop solution, ax. cap. limiting, unfactored, e. b. cap. fac.= 9, excl. weights

Results from Abaqus (A) and comparison

program (C) for pullout performance of

suction pile with 5 : 1 aspect ratio, 26-degree

inclined load and low (3/4) attachment point

Pore Pressure Dissipation with time near tip of pile

during long term hold of uplift load

At start of hold After 11,000 days

13

0.60

0.65

0.70

0.75

0.80

0.85

0.90

0.95

1.00

1 10 100 1000 10000 100000

Hold time, t (days)

Q/Q

ult

FEA parametric study , NC GOM clay, L/D = 5.3

UWA centrifuge test, kaolin, L/D=3.9

C-Core centrifuge test, Alw hite kaolin, L/D=4.8

FEA design case, GOM site 1, L/D=5



FEA par. study adjusted for alpha = 0.8

FEA par. study, adjusted for Cv/2 and L/D=7

FEA par. study, adjusted for alpha = 0.8, Cv*2 and L/D = 4

displacement = 5% D

displacement = 10% D

displacement = 5% D

10%

7%

7%

6%

6%

Results for Uplift Holding Capacity vs. Hold Time

JACK-UP RIGS(Bottom Founded Mobile Offshore Drilling Units)

Independent Leg Mat Supported

EPJoints

MODELS FOR

JACK-UP RIG

ANALYSIS

Finite Element Penetration Analysis

ML 116 C, initially embedded at 55 ft

preloaded to 62 ft, debalasted and reloaded

-80

-70

-60

-50

-40

-30

-20

-10

0

0 5000 10000 15000 20000 25000

Vertical Load, kips

Pe

ne

tra

tio

n,

Ft

PenetrationCurve, Example,GOM Clay

F. E. Analysis

Load, Kips




-80

-70

-60

-50

-40

-30

-20

-10

0

0 5000 10000 15000 20000 25000

Vertical Load, kips

Pe

ne

tra

tio

n,

Ft


F. E. Analysis

SINGLE SPUD CAN PENETRATION ANALYSIS

CEL

Standard

SINGLE SPUD CAN PERFORMANCEForce and Moment Capacity Interaction

FEA Results Compared to Interpolation from Parabola to Ellipse

0

0.2

0.4

0.6

0.8

1

0.5 0.6 0.7 0.8 0.9 1 1.1

Verticalal Force Capacity, Relative to Maximum

Mom

ent

Cap

acity

, R

elat

ive

to M

axim

um

FEA Results, D/B = 1.7



b = 1, Ellipse

b = 0.8

b = 0.6

b = 0.4

b = 0.2

b = 0, Bulletin 5-5 Parabola

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1n = -1.25 (N/A)

n = -1.0 (maximum sharpness), hyperbolic tangent

-0.75

-0.5

-0.25

n = 0, sand per original Bulletin 5-5, exponential

function

0.25

0.5

0.75

n = 1.0, clay per orig. Bul. 5-5 (min. sharpness),

hyperbola

n = 1.25 (N/A)

SAGE FEA, work hardening GOM clay, with vertical

load and preload


load but no preload

SAGE FEA, work hardening GOM clay, with no

preload or vertical load

n =




-80

-70

-60

-50

-40

-30

-20

-10

0

0 5000 10000 15000 20000 25000

Vertical Load, kips

Pe

ne

tra

tio

n,

Ft


F. E. Analysis

vertical

horizontal

V - H

interaction

stiffness

reduction

-1.5

-1

-0.5

0

0.5

1

1.5

-3 -2 -1 0 1 2 3

Mo

me

nt

/ M

ax M

om

en

t

Rotation / Refence Rotation

Cyclic FEA Analysis Results

Complete Cyclic Reversal:Low Stiffness, High Damping

Partial Cyclic Reversal: HighStiffness, Low Damping

rotational hysteresis

SINGLE SPUD CAN PERFORMANCE

INTO SIMPLIFIED SPUD CAN FOUNDATION MODEL

Force and Moment Capacity Interaction

FEA Results Compared to Interpolation from Parabola to Ellipse

0

0.2

0.4

0.6

0.8

1

0.5 0.6 0.7 0.8 0.9 1 1.1

Verticalal Force Capacity, Relative to Maximum

Mom

ent

Cap

acity

, R

elat

ive

to M

axim

um




b = 1, Ellipse

b = 0.8

b = 0.6

b = 0.4

b = 0.2

b = 0, Bulletin 5-5 Parabola

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1n = -1.25 (N/A)

n = -1.0 (maximum sharpness), hyperbolic tangent

-0.75

-0.5

-0.25

n = 0, sand per original Bulletin 5-5, exponential

function

0.25

0.5

0.75

n = 1.0, clay per orig. Bul. 5-5 (min. sharpness),

hyperbola

n = 1.25 (N/A)


load and preload


load but no preload

SAGE FEA, work hardening GOM clay, with no

preload or vertical load

n =




-80

-70

-60

-50

-40

-30

-20

-10

0

0 5000 10000 15000 20000 25000

Vertical Load, kips

Pe

ne

tra

tio

n,

Ft


F. E. Analysis

vertical

horizontal

V - H

interaction

stiffness

reduction

-1.5

-1

-0.5

0

0.5

1

1.5

-3 -2 -1 0 1 2 3

Mo

me

nt

/ M

ax M

om

en

t

Rotation / Refence Rotation

Cyclic FEA Analysis Results

Complete Cyclic Reversal:Low Stiffness, High Damping

Partial Cyclic Reversal: HighStiffness, Low Damping

rotational hysteresis

NEW

STANDARD

ISO 19905

19

Adriatic III ( ) on Hurricane Rita

path ( ). Map, courtesy of

Transocean and Ken Schaudt

Adriatic III Adriatic VII

86889092949698

GSF Rigs

Hurricane Rita track

Adriatic III during Hurricane Rita

(map courtesy of Transocean and Ken Schaudt)

+

LeTourneau 116-C rig,

Adriatic class

Photo, courtesy of Transocean

Deck accelerations were recorded on independent

leg jack-up rig, Adriatic III, during it’s exposure to

severe storm conditions in Hurricane Rita

20

Adriatic III in Hurricane Rita

Abaqus Results from time domain random wave

dynamic analysis compared to field observation

surge displacement time history, 2 min. incl. max response

-4.4

-3.3

-2.2

-1.1

0

1.1

2.2

3.3

4.4

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Dis

pla

cem

en

t, f

t

Time (min)

Surge displacement

Abaqus results Measured displacement

Time Domain Earthquake Analysis of Mat

Supported Jack-Up Structure on Soft Clay

Maleo Producer, a Bethlehem 250

Mat supported jack-up,offshore,

Indonesia, photo courtesy of

Stewart Technology and Global

Process Systems

“Soil Island” model for 3-D time domain

nonlinear analysis of unified site soil

response, soil-structure interaction and

structural dynamic response

3-D Response to two times DLE 1 motions, Maleo Producer, Final Soils

Contours of plastic strain on deformed mesh with 40x magnification

Burgundy = 0.5% strain or greater; Navy Blue = .01% or less

Maleo Producer Acceleration Response Spectra

Sway direction motions for DLE2 (based on El Centro)

3-D FEA results

0.01

0.1

1

0.001 0.01 0.1 1 10

Period, seconds

Sp

ectr

al re

sp

on

se

acce

lera

tio

n (

5 %

da

mp

ing

), g

Deck, center of mass

Mat, center of mass

Mudline, far f ield

Maleo Producer Acceleration Response Spectra

Sway direction motions for Ductility Level Event

3-D FEA results

24

CONCLUSION

After over 30 years, Abaqus is still the leading program for

high-end finite element geotechnical work

Top 10 reasons:

1. General quality.

2. History of successful use.

3. Extensive material behavior library.

4. Selection of element types and features..

5. Worldwide leadership in nonlinear FE analysis.

6. Rigorous large strain capabilities.

7. Unlimited 3-D feature applicability.

8. No program-imposed problem size limitations.

9. Level of program documentation, verification and

technical support.

25

CONCLUSIONAfter over 30 years, Abaqus is still the leading program for

high-end finite element geotechnical work.

Number one top reason:

1. Substantial continuous improvement since 1981,

e.g.:

- Extensions to the Modified Cam Clay

- Implementation of NLGEOM for soil models

- Extended Drucker Prager

- Contact surfaces

- Drucker Prager Cap

- Explicit dynamics

- Mohr Coulomb yield

- Combined hardening

- Multiple exponential kinematic hardening

- ALE adaptive meshing

- Extended finite element method (XFEM)

- Combined Eulerian-Lagrangian (CEL)

26

FURTHER IMPROVEMENTS

NEEDED

• First order (Nagtegaal) elements in Explicit (and CEL)

• Pore pressure-enabled elements in Explicit (and CEL)

• Creep in combination with the parabolic yield surface in Drucker Prager

• Creep in combination with K values other than 1.0 in Drucker Prager

• Creep in combination with the extended finite element method (XFEM)

• Sub-yield kinematic hardening, in Drucker Prager and clay plasticity ls

• Update of Pi plane shape function in Drucker Prager and Clay Plasticity

• Update of the formulations in the Spud Can option of Elastic-Plastic

Joint elements to conform with the new ISO 19905-1.

With developments like these, Abaqus seems likely

to maintain its leadership position in geotechnical

FEA well into the future.

The American Petroleum Institute, The International

Association of Drilling Contractors, ExxonMobil, BP Americas,

Freeport McMoRan, The French Institute for Marine Research,

Global Process Systems, Lewis Engineering, Matthews-

Daniel, Stewart Technology, Transocean and SAGE USA

Former colleagues at Exxon Production Research and

McClelland Engineers

Present and former SAGE colleagues, M. K. Hossain, PhD.,

P.E., F. B. Biegler, Z. M. Oden Duffy, PhD., E. L. Templeton-

Barrett, PhD., M. J. Barrett, A. A. Rahim, PhD., P.E. and X.

Long, PhD., P.E. (on loan from GEMS)

Principals and staff of HK&S and Dassault Systèmes,

particularly H. D. Hibbitt, E. P. Sorensen, J. C. Nagtegaal, and

D. Datye

ACKNOWLEDGEMENTS

Abaqus Effective Stress Analysis of long term uplift capacity for suction piles/caissons

Soil modeled as

elastic-plastic

porous material with

Modified Cam Clay

constitutive theory.

Pile / Caisson modeled

as elastic material

with Young’s modulus

and Poisson’s ratio

representative of steel.

FINITE ELEMENT ANALYSIS IN OFFSHORE GEOTECHNICS ELEMENT ANALYSIS IN OFFSHORE GEOTECHNICS –A...

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